Home  /  Interviews  /  Matt Wallace

# Matt Wallace

### Deputy Director for Planetary Science, JPL

##### March 1, March 8, March 22, April 11, April 25, May 9, June 6, July 6, and August 5, 2022

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Tuesday, March 1, 2022. I am delighted to be here with Matthew Wallace of the Jet Propulsion Laboratory. Matt, it's great to be with you. Thank you for joining me today.

MATTHEW WALLACE: Thanks for having me.

ZIERLER: To start, would you tell me your affiliation and title at JPL?

WALLACE: I am the Deputy Director for Planetary Sciences at JPL. I've been in that role now for about eight months or so.

ZIERLER: To give a broader sense of where Planetary Science fits in administratively at JPL, what's the overall structure, and where is Planetary Science within that?

WALLACE: There are a number of different directorates essentially that the Laboratory is organized into, including Heliophysics, Engineering and Sciences, Mission Assurance. There are a number of different sort of stovepipe directorates. Planetary Sciences is the directorate that's responsible for essentially for running the missions to go to the different solar system bodies, the different planets, as well as things like asteroids and that sort of thing. We're probably about 60% of the Laboratory's business. That's what JPL is kind of known for, its planetary missions. Of course, part of that is the Mars program, which I spent a lot of time in.

ZIERLER: In the org structure, obviously you would report to the Director for Planetary Science. What are the steps between the director and the Director of JPL as a whole?

WALLACE: The Director of Planetary Sciences reports directly to the Laboratory Director.

ZIERLER: On that point, what do you think it means for the Lab that Laurie Leshin is coming in? What new directions do you think it might take under her leadership?

WALLACE: I think it's terrific. I'm really excited. It's always good to see some turnover, new ideas and approaches. Mike Watkins represented that when he came in after Charles's stint, and I think Laurie will do the same. I do think we have a very strong leadership team at the Laboratory right now. It's a team with a lot of experience in running these programs and these missions. I think Laurie coming in out of academia, from a science background, is a perfect complementary addition to the leadership at the management level. I'm excited. I had known her a bit here and there because of my time in the Mars program, and I had a chance to speak with her for a while last week. I think it's really exciting. She did a town hall for the Laboratory a couple weeks ago, and I happened to be in the car listening to it with my 18-year-old daughter. [Laugh] It was pretty inspirational. I told my daughter, "This is the first female Laboratory director that we've ever had." We've never even had a deputy Laboratory director that's a female. My daughter turned to me and said, "You do know that it's 2022, right, Dad?" [Laugh] I think it's terrific. I think she's going to be great, and I'm looking forward to it.

ZIERLER: What are some of the most exciting things happening at JPL that are really going to give a boost to Laurie's leadership right from the beginning, things for her to build on that already have real momentum?

WALLACE: There are some fantastic upcoming missions in the Planetary Sciences area where I work. For instance, we're getting ready to launch a mission called Psyche to an asteroid, which will help us understand the history of that particular body. We're about two and a half years away from launching a big flagship mission to Europa, which is a moon of Jupiter. That's going to really unlock a lot of information about these ocean worlds that we've been waiting to understand. We're just getting started over the last year or so more seriously on the Mars Sample Return campaign. It's a series of different missions, a follow-on to the Perseverance Rover, which is collecting samples on Mars as we speak. The Sample Return campaign is a technologically challenging set of missions that will ultimately bring these samples back to the Earth. This has been an agency objective for us for a long time, decades and decades. There were Mars Sample Return studies in the 1980s. With the launch, successful landing, and surface operations of Perseverance, we're finally getting that started. Then, there's a host of other missions we're supporting that are going to the moon. It's an exciting time at JPL.

ZIERLER: On the flip side of that, for the new incoming director, what are some of the key challenges at the strategic level? Relations with NASA, relations with Caltech and campus. What are some challenges you see in the future?

WALLACE: I think there's always an opportunity to improve our relationships with our sponsors. Laurie is clearly well-suited to that. She's spent time in VC and understands how that relationship can operate efficiently, I think. We're coming out of a global pandemic, and we have things like supply chain challenges that we need to be aware of and will need to deal with logistically. We have a whole new way of working, all of us. Right now, we're talking in a way that we wouldn't have a couple years ago if we were doing an interview. I think that presents a challenge for the Laboratory relative to its workforce and how it wants to interact with especially the next generation of laboratory engineers, scientists, and leaders.

I think those are some of the big challenges that are still coming. I think, also, one of the things we found is that the Laboratory is very, very busy. It has a certain set of capabilities that are hard to find anywhere else, so we get more than enough work. [Laugh] We try to do what we can when we're asked to do particular jobs, but there will always be a challenge. There's going to be a challenge in the near and medium terms, I think, in dealing with the volume of work, making sure that we can maintain our standards and commitments to our stakeholders. Plenty of challenges.

ZIERLER: A few questions about your own path and background. First, with your background in systems engineering and electrical engineering, do you see your role as an engineer as affecting your managerial and administrative responsibilities? In other words, is your work different than if you were a planetary scientist, for example, in terms of your overall responsibilities currently?

WALLACE: I think so. I think the fact that I have an engineering background that I have used in this business for 30 years or so makes me more suited for certain types of leadership roles and less suited for certain types of leadership roles. But certainly, I think that the technical strength of the people, whether it's in the sciences, electrical engineering, propulsion engineering, that Laboratory leaders can bring to the table is one of the things that makes JPL very unique. I've worked in industry, I was in the military, and one of the things that really is a powerful capability we bring to the table is the ability to integrate that technical depth, strength, and understanding with our leadership positions. It's interesting because I occasionally hear people talk about how managers need to manage, technical people need to make the technical decisions, and there will always be people bent in one direction or the other, but I find that the most effective people, and I encourage this in all of the leadership I've ever worked with, I think the most effective folks are people who aren't afraid to marry those two things together. I think that's what allows us to do things at JPL that other organizations can't do. I think it's a critical piece of who we are and what we do.

ZIERLER: And in your current position, are you able to act as an engineer in the day-to-day, or are your responsibilities at this point more administrative, managerial?

WALLACE: It's surprisingly some of both. There's certainly part of my job that is not technically oriented, where it's a lot more about communication, and interactions with people, and strategic planning, and things like that. But an enormous fraction of what I do is still about dealing with technical challenges. I've expected my whole career to elevate to a point where those skills are not as important, and I've never hit that point. [Laugh] I was looking through a mass equipment list yesterday, which is not something I do very often, but occasionally I still have to do it. Surprisingly, I think, I still get to exercise those muscles.

ZIERLER: Within JPL, if there's such a thing as a normal day to you, what are the meetings like with your direct reports, the key people who are most important for you executing your mission?

WALLACE: It's changed over time. In my current role, a typical day would be a couple meetings, standard meetings, periodic meetings, weekly meetings, if you will, that I have with the project management leadership for our key projects. Then, there are always the up-and-out reporting opportunities to both our headquarters sponsors and to the Laboratory leadership. Not unusual to have some of those meetings scheduled. I do find that I need to step back and look occasionally more strategically at, for instance, the directorate budget or the technology tasks that we have going on. Again, not all that unusual for me to be getting briefed or providing some feedback on that portfolio that we have in the directorate. Then, there's always a part of the week that seems to be geared toward future work, where we're looking at proposals coming down the pike. That's a good fraction of what I do. Here and there, I'll have one-on-one meetings, which I like, with a junior engineer or a young manager looking for advice. I had one of those yesterday. Somebody looking for their next job who wants to understand a good career path and what kinds of opportunities might be coming down the pike. I try to always make time for those as well.

ZIERLER: I'm curious in what ways the proximity and relationship to Caltech is an asset for your work, either from students, professors, PIs. Just having that intellectual connection, what does the Caltech relationship mean to you specifically on a day-to-day level?

WALLACE: I think there are some very specific things that have happened as a result of that relationship, then I think there are some things that are a little bit more intangible that are nonetheless as or more impactful than the specifics. The specifics are that we can draw from a talent pool for future employees. I came out of Caltech to work at JPL. That's a great connection to bring in talent, whether it's engineers or scientists. Many of our project scientists and co-Is and things like that are Caltech professors. There's an enormous opportunity for us to talk across that interface, and really, we gain a lot of strength in our missions because of that relationship. Obviously, the fact that we're an FFRDC is a very important and critical characteristic for JPL. All those things I mentioned before that we do well, all that interest we have in various types of work, a lot of that comes because of the flexibility we have being an FFRDC.

The way Caltech runs JPL, I think they're both very engaged and knowledgeable, yet understand that JPL is a different organization than an academic institution like Caltech. I think because the relationship is so long, I think it works very well. Those are all very specific things. There's definitely an intangible aspect to this where you can walk around JPL and it feels more like a campus than anything else. I think that's part of it, and the mindset for the people in Laboratory is much more associated with an academic mindset, a level of curiosity, a level of independence, a level of individualism, a level of collaboration. People at JPL don't care if they're collaborating with Europeans, Canadians, or high school students. If the collaboration is valuable to the job that they're doing, or the questions that they're asking, or the technology they're developing, they're ready to do it. I think that's very much influenced by our connection to the academic aspects of Caltech. It's a very powerful, very important connection. I think it's a model that a lot of government organizations would be well-suited to follow.

ZIERLER: Beyond Caltech, NASA in general, either at headquarters, other NASA research centers, or other FFRDCs, are there counterparts or peers that are really important for you that you're in touch with on some regular basis?

WALLACE: Relative to headquarters, for instance, there certainly are. Our structure at JPL with the different directorates is actually kind of mirrored, or maybe we mirror headquarters in many ways. We have counterpoints in the headquarters organization that we're constantly in communication with. In our case, it's the Planetary Sciences Division of the Science Mission Directorate. That is certainly the most important external relationship that we have in what I'm doing. There are other types of work. There's what we call reimbursable government work that we do at the Laboratory, where there are ties into other government organizations, for instance, and those are critical relationships, again, for other parts of the Lab. But for Planetary, the most important, really, are the ones into the Science Mission Directorate at NASA Headquarters. Then, there's a host of other science organizations out there that we're connected into. Because 90% of our missions are science missions, so we need to stay connected into the science organizations that support planetary sciences, whether it's outer planets, Mars exploration, Venus. We try to stay tightly coupled with those organizations.

ZIERLER: A very in-the-headlines news kind of question. With the crisis in Ukraine right now, from anything ranging from space diplomacy, to supply chain issues, to national security, is JPL affected? Do you see, in the long term, JPL or even your work being affected by what's unfolding in Ukraine right now?

WALLACE: It is, and it's going to be, moving into the future. I don't work in the sort of defense support domains of the Laboratory, but you could obviously imagine there being longer-term implications on those programs and technologies. But for me, in the present tense, we're already seeing some ramifications of what's been happening in Ukraine. We do a lot of collaborative work with the European Space Agency and with different European countries' space agencies. They, for instance, have and continue to collaborate with Russia, just as our space agency has relative to access to the Space Station, launches, things like that. As a matter of fact, one of the programs we're involved in in Europe is a program called ExoMars. There's a ExoMars rover, the name of which is Rosalind Franklin, and it was scheduled to be launched this year.

We were providing some science instruments and some other engineering components, and we have also helped them with certain technologies and things like that. But in general, that was a collaboration between the European Space Agency and Russia. As you can imagine, that collaboration is transitioning, to say the least, and that will have implications on that program. And that program, then, could domino into other collaborations that we have with ESA, including the Mars Sample Return. They're a big player in our sample return activities. They're providing an orbiter that's going to rendezvous with the samples in orbit around Mars and bring it back to the Earth. They're also providing what's called a fetch rover, which goes out, picks up the samples, and brings them back to the lander, where we have the Mars Ascent Vehicle. We're already seeing and hearing about these potential implications, and we'll have to react to them.

ZIERLER: Another current question, although this one is a little more broadened out. Commercial spaceflight and space exploration seems to be becoming a bigger deal by the day. For planetary science at JPL and NASA in general, for companies like SpaceX, Blue Origin, and Virgin Galactic, where do you see collaboration, cooperation, and simply a divergence of missions where there really isn't much shared space?

WALLACE: That's a big question. Probably the most impactful area so far for us has just been the cost of space access. The launch vehicle competition that's happened over the last decade has obviously had very positive impacts on total mission and lifecycle costs by reducing the cost of getting those kilograms up and off the Earth. But they've also started to change the way we think about some of our systems. Before, we'd spend a lot of money saving every kilogram, or gram, in some cases. With the costs dropping due to the competition that's out there, we have more flexibility in the way we go about building and designing systems. That's one immediate that's happening now across the board. The agency clearly wants to leverage that commercial interest and capability beyond just the launch vehicle side of this. Crew access, obviously, has been one great example of that.

We're starting to see that with lunar exploration. There's a series of commercial lunar landers that have been essentially lined up. We're part of that in that some of the science packages going on those landers, for instance, would be developed at JPL. There's an opportunity, I think, in the lunar domain for that type of collaboration in leveraging up the different strengths between industry and what we do in the agency. I think there's no question that over some period of time, like just the Dutch East India Company, eventually, the engine of commercialization will create opportunities for outer planets, solar system body concepts, and missions. Those are coming. They're still hard missions that require a lot of infrastructure and investment. There's a natural progression to get there. But I do believe that's all part of the future for us. I think it's a terrific thing. I think it allows us to leverage the marketplace and all those marketplace forces into doing a better job of exploring, for science and other reasons.

ZIERLER: On that point specifically, what does the commercial sector do now, or what is it projected to do in the future, simply better or more economically that frees up JPL to play on its strengths?

WALLACE: Depending on how the commercial organization gets structured, funded, and things like that, one of the things that I think is easier for them to do is to fail. That may sound like a weird thing to say, but failure is what creates success, ultimately. It's the innovation and the learning process. We're the best in the world when it comes to organizing and managing big, complex, multi-organizational strategic campaigns and efforts. The United States and our industrial base is unparalleled. Nobody else can do it. And JPL's part of that. We do some of the most complex missions, and we do them the first time, and we do them right. We're really, really good at that. But not every activity and every objective is well-matched to that model. And I think that there's a lot of value in having a construct that allows for the opportunity to fail without devastating consequences, without the world watching or something really unrecoverable happening. Again, you can't do that when you're launching Mars Perseverance. You can't do that when you're launching James Webb Space Telescope. These things are too big, too complex. There's no trial and error here. They're too expensive. But there are plenty of places where that model works and works very well, and I think that's one of the places industry has a leg up.

ZIERLER: It's probably as much a philosophical as a science and engineering approach, but if you listen to the founding mission of, say, SpaceX versus Blue Origin, where Blue Origin very much looks at space exploration as enhancing life on planet Earth, and SpaceX seems to be more about, "We need a plan B for humanity," speaking just for yourself and not JPL, given your deep experience working on and thinking about Mars so much, where do you fall on that spectrum?

WALLACE: Typically, when they talk about exploration, they're talking about human exploration, I think, so I'll answer in that context. I've primarily done robotic exploration my whole career, but I get asked this question a lot because every time I go and talk somewhere, people ask the question. And it just goes to show, I think, that no matter how capable our robotic systems are, there will always be this fundamental interest in human space exploration. I think they're very synergistic, and I think one needs the other. As a context for this question, I'll say that. And I think both types of exploration enhance our lives here on Earth in many, many ways. Obviously, just the technological advances that are created by the need to do these missions that can then be applied commercially, whether it's GPS, materials, or what have you, that's one advantage.

I think there's also obviously an advantage just in stimulating and inspiring people in these technological areas, STEM and all of that, and that's very hard to put a price tag on, but it's enormously important for our country and us as a society to continue to advance. I think exploration of all kinds brings those advantages. I'll also say that very often, the question is asked in the context of, "How can we justify spending all this money?" independent of whether it's to help build these technologies for space or ultimately to provide a pathway for humans to leave the Earth if they need to for a second habitat, if you will. Independent of that, people often ask the question, "Why are we spending money to do these things when we have so many problems here?" We were just talking about Ukraine, COVID, cancer. Very often, the question's asked in that context. And I've always had the list of advantages that it provides, but I have really come to the conclusion that the answer to the question isn't all that important, strangely enough. [Laugh] Because we're going to do it anyway. It's just what we do. It's in our DNA.

ZIERLER: As humans, you mean.

WALLACE: As humans. We're going to explore, go to places we haven't been, answer questions that are fundamental and that we don't understand. In that sense, I think, you can argue the SpaceX model is a little more fundamental than our nature, which is that it's going to happen, and it's going to happen because it's just what we do, whether or not we fund it this way or that way, or whether the objective is to help people here or create an outpost for humans in the event that we mess this one up. [Laugh] After all this time, I've kind of come around to feeling like the motivation and the benefit part of it is–we could have that conversation for a very long time, but in the end, it's just going to happen. We're going to go to Mars. There are going to be people on Mars. It's just going to happen. It's a question of when.

ZIERLER: On that point, given all that you've learned with your focus on exploring Mars on robotic missions, where is the hype and where's the reality when people talk about terraforming Mars, establishing colonies on Mars? What does all of that look like to you?

WALLACE: I'm not an expert in this area, but from everything I've read, terraforming is a very long-term sort of objective. I don't think it's out of the realm of possibilities. There are resources we know exist. There's water, subsurface water, water ice at the poles. You can envision different ways of that. But these things happen on a very long timescale. It's interesting on a 1,000-year timescale to have that conversation. And I'm sure there are experts out there who might tell me I'm wrong, but to my mind, that's where that exists. I think other types of outposts on Mars, though, are definitely near-term things that can be talked about. The agency, to the first order, would like to see human exploration of Mars in the 2030s. That's a very aggressive timescale based on my experience of putting robots on Mars. It's not an easy planet to put things down on the surface of. It's big enough that it has a lot of gravity like the Earth.

Unlike the moon, where you can come down nice and slow, it's going to pull down, and if you don't do something to stop yourself, you're going to crash and crater. That makes it hard, but unlike the Earth, there's not enough atmosphere to slow yourself down with things like parachutes, heat shields, and things like that. While you see Apollo capsules returning to the Earth with parachutes, you can't do that on Mars. The bigger the system, the harder it gets. You need propulsion or some other means of really slowing yourself down in a pretty big way. It's a hard planet to land on. The biggest payload we've put down is a one-metric-ton rover. Human exploration's going to require probably 40 to 60 metric tons minimum at a time. It's difficult. That's, of course, before you get to the physiological challenges of being in space over long periods of time, not to mention the psychological challenges of these long-duration spaceflights. But technology-wise, we can do it, whether it's surface or subsurface habitats. It might be subsurface for reasons of radiation and things like that. That's on a timescale that at least my daughter can think about. [Laugh]

ZIERLER: It's intangible, but I wonder where you would rank the search for life. As you say, it's in our DNA. We're going to search, we're going to discover. Of all the motivating factors that pull us into space, Mars in particular, where do you rank this question, which remains a big question mark, of course, about whether there's life outside of planet Earth? Where do you rank that among all the reasons to go to a place like Mars?

WALLACE: Well, we're looking for ancient life on Mars, and we're looking for the possibility of even extant life in other places around the solar system. There are exoplanet technologies coming down the road that will help us understand habitability of planets outside our own solar system. Those are all aspects of searching for life. I think they're fundamental, transformative questions for us as a species, as humans. You think about the impact of Copernicus, for instance. As we began to understand that the universe didn't revolve around the Earth, but we orbited the sun, it decentralized our perspective of ourselves, and it did have philosophical, religious, and other implications on us in a societal way. I think the question of whether life exists or existed somewhere other than the Earth is in the same category. I think it's a transformative type of shift in the ways we think about ourselves and the universe. And I think it's something that fascinates not just people like me who are in the business, and not just astrobiologists.

ZIERLER: Everyone wonders.

WALLACE: Yeah. People want to hear about the geology of Mars and things like that, but what they really want to know is, is there life there, and was there life there? That's part of that motivation, that drive that's part of our DNA. I think it's a critically important thing. And I've changed my perspective, I have to say, over time on the possibility. When I was in school, taking biology, 40 years ago, we didn't have anywhere near the kind of understanding of the molecular processes and evolutionary processes that we do now. Genetics has really changed, in many ways, what we understand about how life forms, how evolution happens, and everything else. When you step back and look now at how evolution works, I've kind of gone from, "It's unlikely Mars ever had life. It's a barren, arid place with radiation environments and no magnetic field to protect it," to really believing that because the environment existed on Mars billions of years ago, it would've been very hard to stop life from happening. I am fascinated by it, personally, and I think it's a really important question. I think we'll be able to answer it.

ZIERLER: To clarify your phrasing, in Mars, you're looking for ancient life, and elsewhere in the solar system, we're looking for extant life. Is that to say that the search for current life, even in its microbial form, on Mars is sort of on pause right now?

WALLACE: I think when you talk to the science community, in general, the conditions that would've supported the evolution of life really existed primarily three, four billion years ago on Mars. That was a point where the Martian core was active, so there was a magnetic field protecting from galactic radiation, the surface of the planet was wet and warm, it had an atmosphere. It looked a lot like the Earth does three and a half billion years ago. It really, really did. When you're on the surface, there's an energy source. The sun provides that energy source. You had many of the components that you need for life under that scenario. That's really the focus for Mars, the ancient environment. And that's a tough thing to tease apart because all the planetary processes that happen over billions of years tend to destroy these long chain organics, what we call bio-signatures of life. You're looking for these really faint traces, these tell-tale signals. And it's very, very hard to do. You need extremely sensitive equipment. We've kind of concluded that we can't take sensitive enough equipment to Mars. We need to bring Mars back to the Earth to do that. That's really the motivation for sample return. You're looking for parts per billion, or maybe even lower, trace organic signatures, and those are tough things to find. That's really the focus for Mars.

ZIERLER: Just to give a sense of scale, in the way that we've barely scratched the depths, if you will, of our own planet, given how difficult it is to go down to the ocean floor, can you give a sense of the uncharted territory that we haven't even begun to look at on Mars? We've had amazing success getting rovers to Mars, but what have they been able to probe relative to the sheer size of the planet, not to mention the fact that they're literally just scratching the surface?

WALLACE: I think there are probably a couple different domains, if you will, of thought with respect to that question. One is that we have found seven or so sites on Mars where, despite what Mars looks like in pictures, it's very heterogeneous. Much more so than you might think. You go to one place, and all you see are igneous rocks, rocks formed by volcanic activity. You go to another place, and all you see are sedimentary rocks. You see different chemical compositions depending on the history of the water, the volcanic history, the geological context of all these things. I think diversity-wise, one of the things we have to recognize is that we may or may not go to the best place to search for life. I think one of the most overlooked and most powerful collaborative events that have happened in Mars exploration is between the orbiter systems that are mapping the entire globe from orbit at a certain resolution, with certain types of spectrometry, imagery, instruments, and then the ground truth.

By tying together these orbital datasets, which are global, to various specific ground truth from rover systems or lander systems, we've gotten quite good at interpreting our orbital data. That's one of the reasons why Perseverance went to Jezero, because we looked at what we saw at Gale, what we saw at Gusev, what we saw at Meridiani, and we tied those back into the orbiter science datasets, and we were then able to extrapolate forward and say, "If we're looking for life, and we think we need these characteristics, Jezero is the best place to go that we can get to." I think we've made a lot of progress there. Although we're actually on a tiny surface area of the planet, I think we've gotten pretty good actually at selecting sites that are valuable scientifically, that have high promise for the types of signatures we're looking for. That's one area we've made good progress in. I would say the subsurface domain is a place we have not yet. We know there's subsurface water, but it's deep and only in certain locations.

Those may be places that we want to ultimately get to. There's also an aspect of the subsurface that makes it more valuable, in some ways, which is that it has not been bombarded by UV radiation for tens of millions of years, which does have a tendency to break down some of these chemical systems. If you go deep enough, you can potentially find chemicals with a molecular signature you wouldn't find on the surface. That's probably an area that's still open for improving our access to. We do try to take account of that by coring. For instance, Perseverance is not just taking a surface sample, it's actually coring into rocks to get below that surface. We do try to account for that. We also look at the context of the stratigraphy of where we land, and we try to go to places that have not been exposed for 50 million years, that have been uncovered within a reasonable geological timeframe so that it was protected from radiation, and trying to understand that. We do try to compensate for that, but I do think the subsurface domain, with deep enough drills and whatnot, is still a rich area to look.

Then, the poles. We've managed to get towards the poles, but it's a difficult place to operate, as you might imagine, just like it is on the Earth. Those are probably some of the opportunities that are still open for new exploration and finding new things. One of the other things I'll just mention briefly is that Perseverance carried an Ingenuity helicopter. We carried it as a technology demonstration. It was supposed to fly five times to show it would fly, but it's still flying. We just finished our 20th flight. We're going out into places in Jezero Crater where we can't send rovers because it's too rugged, and it is providing the science team with valuable data that we wouldn't otherwise have. There are mission concepts that provide aerial reconnaissance into deep ravines, large crater walls, or mountains we can't get rovers into. There's an opportunity to explore those places, too.

ZIERLER: What depths are our current drills capable of going to on Mars? How deep into the ground can we get right now?

WALLACE: The drill that Perseverance carries will core down to about eight centimeters, so about two and a half, three inches. That's as deep as we go. Insight and Phoenix did do some trenching, and we can trench with the wheels, so maybe six inches or so. But that's not very deep. You want to get many meters down. I mentioned earlier the ExoMars rover the Europeans have built. They have actually built a subsurface drill, and I don't know exactly how deep it goes, but I think it's on the order of about a meter or so. That's one of the science objectives of that rover.

ZIERLER: Where I'm going with this of course, at least anecdotally, on Earth, you really have to dig pretty far down to get to some interesting stuff. It's a relatively recent development that human civilization even became aware of dinosaurs from being able to dig. Just theoretically, is it naive to think that if we ever get serious drilling equipment on Mars, that there might be a whole world of life well below the surface beyond what we're capable of getting to now?

WALLACE: I think if you're looking for extant life, life that's there now, then no, I don't think it's naive to think that. I think that's where you want to look at the subsurface water and ice regions. I think that probably is a game-changer for extant life.

ZIERLER: Beyond Mars, where are you focused right now in terms of searching for extant life in our solar system? Where are most of the resources based on the theory and assumptions that we might have life now in our solar system beyond Earth?

WALLACE: I think the next target is the ocean worlds. These tend to be the moons on the bigger gas giant planets. I mentioned Europa. That's really the next target for us as a laboratory, that area. We know there are oceans on the planet, we know there are ice caps, we know there are occasional plumes and things like that. We've had some fly-by information, but we really need to better understand those systems, and we need to send systems that are tailored to specifically go to those places with the right instrumentation and can repeatedly observe them, like Europa, which is going to do on the order of 50 or so fly-bys on Europa as part of a prime mission. That's the next place to look inside the solar system.

ZIERLER: To clarify, Europa is a fly-by mission, it's not going to actually land on the satellite.

WALLACE: That's right. We use the term fly-by if it just goes by once. We'll use the term orbiter when we talk about orbiting a planet. In this case, there are going to be multiple passes over Europa at different heights to get that data.

ZIERLER: Thinking about Europa, all of the PIs, all of the instruments that need to be coordinated on this one large piece of equipment, for you and your administrative roles, what kind of quarterbacking do you need to do to make sure that all of the different PIs, all of the technologies, everything's working in concert?

WALLACE: I'll start by saying that we have a tremendously experienced and capable set of project leadership and project scientists on Europa. Certainly comparable to my experience level. They do 98% of the work themselves. [Laugh] At this stage of the development, my primary function is to see where they're struggling and see if there are resources, institutional priorities, or organizational relationships that need attention. It's a mission with ten complex science instruments, a mission that tends to try to operate all those science instruments concurrently, which makes it even harder. It's operating in a very aggressive radiation environment, it's a long-duration mission, so there are lifetime challenges and qualifications that have to get dealt with. It's got a lot of organizational contributors. We have a big partnership with the applied physics lab for Europa. I see my job on Europa at this stage of the development as looking for the places where they need some help, just trying to help plug the holes, find out where they need some additional resources or priority calls. They do and need to do a lot of coordination among the different organizations, instruments, experiments, all of that. It's complicated. As we get closer to launch, and certainly after launch, as we get closer to the encounter and all of that, it'll ramp up in a big, big way.

ZIERLER: Just to conceptualize ten highly complex scientific instruments hurtling through space on a fly-by mission that doesn't even land, what do we expect to learn about Europa that we don't currently know?

WALLACE: Again, this is a little outside my domain of expertise, but what we're hoping to understand is the constituency of the oceans. I think they want to understand the thickness of the ice cap. I think they want to understand the nature of the surface features and the dynamics of the ocean, the surface aspects of the ocean. There are science objectives associated with understanding the constituencies of plumes. All of those things are targets here for Europa.

ZIERLER: Do you see it in historical terms as essentially a reconnaissance mission for an eventual rover mission to Europa or other ocean world satellites?

WALLACE: I think it is a standalone mission in and of itself. I think the hope here is that the amount of science we get back justifies the mission without any follow-up mission. Having said that, there are Europa lander concepts that the Laboratory has been working on for quite a while. It's difficult landing on something that far away, but that technology work is still ongoing. Hopefully, there's an opportunity to do that.

ZIERLER: To go back to the question about searching for extant life in the solar system, is there any chance that the Europa mission will get us that much closer to a sense of whether there's life on Europa?

WALLACE: I think so, yeah. I think we should think of Europa in that way. The instruments are very much designed to help us understand the system and the moon in that sense. I think it was Carl Sagan that said extraordinary claims require extraordinary proof. Exactly how far down that extraordinary proof domain we get is something I'm not sure I can speak to necessarily. But I think it will give us strong indications of whether or not we're looking at something that could be habitable for life.

ZIERLER: The idea that there are concept missions that visualize or envision a rover mission on Europa, with your expertise in Mars, what are some of the obvious technical challenges, new ways of doing things where Mars rovers might not necessarily provide a game plan?

WALLACE: I think the Europa landers have a number of technologies that don't exist. One good example is autonomy. We can communicate with things on Mars. It may sound like it takes a long time, but it's a ten minute light-time. We can provide daily updates or multiple updates over the course of a day as far as mission objectives, sequencing, commanding sets, and things like that. But on Europa, that's a lot tougher, given the distance. Autonomy is a big technological challenge for systems trying to operate that far away from the Earth. That's one example of a technology that needs to be matured for Europa. The radiation environment, obviously, as well as is fundamentally different from Mars.

ZIERLER: What about temperatures? I presume it's extraordinarily cold there.

WALLACE: I do not know the surface temperature profile on Europa. I just haven't been engaged on the lander systems and concepts at a level where I know. Mars gets very cold because of the diurnal cycle. It'll get down to -200 degrees Fahrenheit at night. The Martian systems have to deal with very cold environments. Because of the gravitational interactions between Jupiter and Europa, there's an energy, if you will, there are certain actors that, for instance, keep the ocean from freezing all the way through and things like that. I don't know exactly what the surface conditions are relative to Mars.

ZIERLER: Even farther in our solar system, talking about things the public was really engaged about, was Planetary Sciences involved in the question about whether Pluto is really a planet? Does it have an institutional response to that, given the fact that so much of this decision-making went on at Caltech?

WALLACE: That was a little before my time. I don't think I'm qualified to answer, and even if I were, I'm not sure I would, given the emotion surrounding the question. [Laugh] I'm perfectly happy to call it a planet.

ZIERLER: What about beyond our solar system? Is your directorate involved in exoplanet research?

WALLACE: No, that comes from a different part of the Laboratory. We stay inside the solar system.

ZIERLER: From both an administrative and a scientific perspective, what would mandate that distinction for exoplanets, which obviously are planets?

WALLACE: I think the fundamental reason is the technologies needed to do that are very different from what we do. To the first order, obviously, spectroscopy, you need systems that'll operate in space and all that. But a lot of what is done in that domain is done with these cryogenic systems that are looking at very sensitive UV, IR, and other things with big, big telescopes or interferometry. Those are things that are somewhat outside the field of technologies that we typically use for planetary exploration. There's a logical distinction there.

ZIERLER: Do you see technologies that have developed within your directorate as providing a boost, given how essentially young exoplanet research is as a field?

WALLACE: I think so. I haven't given it too much thought. Almost every telescope system has mechanisms in it, and we all care about long-life mechanisms in space and how to create and manage those. We all have a lot of deployment systems. These big telescopes and things like that we put in space have large sunshades, aperture doors, things like that. To the first order, we care about understanding how to engineer those types of things. The sensitivity of imaging focal planes is going to help no matter what you're trying to do with that focal plane. The processing power is important no matter whether you're using it to autonomously drive a rover on Mars or to do onboard data compression of science information. I think generally speaking, there are plenty of crossover technologies. But the way in which they get packaged and applied–it's kind of a different set of science objectives to the first order, which is why they get separated.

ZIERLER: Last topic we'll touch on for today. One planet we haven't discussed in our solar system is Earth. As you well know, JPL, over the past 20 or 30 years, has increasingly become a more important player in turning those satellites toward us to learn more about our own planet. Where does the Directorate for Planetary Sciences fit in that overall mission at JPL to better understand planet Earth?

WALLACE: That's a great question. The Earth Sciences Directorate is a separate directorate. Again, in part because of the science objective. The science communities are very different as well, so we're interacting with different science groups. But we have a lot of cross-talk, collaboration, and movement of people across the border between these two areas because in both cases, we're dealing with deep space spacecraft, satellites. They have many of the same functions and do many of the same things. An orbiter around the Earth has a lot of similarity, in some ways, to an orbiter around Mars or Europa, for instance. We're working in many of the same domain areas, I would say, and we're talking to many of the same technology groups. Radars are becoming increasingly important. Every time I turn around, we're finding a new radar application for sciences, and the same is very true for planetary sciences. A host of spacecraft actually are heading towards Venus in the next decade. One is Veritas, which we're the lead on, which has a radar on it. Another is Da Vinci, which Goddard is leading, which has radar on it. The third is a European spacecraft, which has a radar that we're building on it. I think there's a lot of applicable crossover there in technology.

ZIERLER: If we can turn out all of the administrative and Zoom meetings, just as a snapshot in time circa March 2022, what's most interesting to you? What are you working on right now where you're really moving the ball forward for your directorate?

WALLACE: So many different places. I mentioned Venus. We haven't been there in quite a while, and it's just reenergizing that entire science community. I think that's going to be exciting for everybody. Sample Return is a very engaging program. It's one that we're not doing on our own. This is a complex, multi-organizational programmatic endeavor. It really is a pretty epic space campaign. I think that's very challenging and very engaging for us. I'm excited by all the interests we continue to get in the planetary sciences. I think there's a stronger motivation now to do more of the types of things we did in the 60s with human precursor-type work. When we went to the moon with Surveyor and things like that as a precursor in the Apollo regime. I think some of the work we're doing on Mars, for instance, very much has that flavor. We carried an oxygen-generation technology experience on Perseverance, where we were ingesting the carbon dioxide atmosphere and creating purer oxygen for both life support and for fuel to get back from the planet. That's a forward-looking human exploration-type thing. We are engaged more and more on these lunar systems, which again, I think is really a precursor for the Artemis campaign of sending humans back to the moon. That's an exciting part of what we're doing in the directorate. There are so many. Every time you look in one direction, there's something new and interesting.

ZIERLER: That's a good thing.

WALLACE: Yeah, it is.

ZIERLER: On that note, we'll pick up for next time.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Tuesday, March 8, 2022. I'm delighted to be back with Matt Wallace of JPL. Matt, it's good to be with you again.

WALLACE: Thank you. It's nice to be talking with you again, David.

ZIERLER: We had a great conversation last time and took a sort of wide-angle view of your approach to the research and administrative responsibilities at JPL. Let's go back all the way to the beginning and start with your parents. Tell me a little bit about them?

WALLACE: [Laugh] My dad grew up in New York City, Brooklyn. He was in the Air Force for a little while, then he got involved in the aerospace community at what used to be the old RCA facility, which is now Lockheed Martin in Northern New Jersey. He was mostly in the contracting side, he wasn't an engineer, but one of the groups he got to work with were the people contributing to the Lunar Module for Apollo. He would tell me stories about how amazing these folks were, how he'd sit in meetings and just be overwhelmed with the talent and brilliance, things like that. I think that had an impact on me.

ZIERLER: That planted a seed.

WALLACE: [Laugh] I think it did. Of course, being a bit of a space aficionado, when it came time to land on the moon, I remember him coming in, waking us up, and sitting us in front of the old black-and-white TV, messing with the antennas, just like you see in the TV programs.

ZIERLER: So you remember that?

WALLACE: I do, yeah. And I remember, interestingly, the thing that was most impactful to me was watching how impactful it was on my dad. My dad just understood how profound a moment it was. I was 6 or 7, something like that. But watching my father and what it meant to him helped me understand ultimately what that moment was.

ZIERLER: What exactly was his work where he was interfacing with these people?

WALLACE: He was a contracts manager. He'd work on various defense systems. But for instance, if they were buying a radio or something like that, he would get involved in radio for contracts, help them support the contract oversight and technical management, that sort of thing. He was not on the engineering side or the technical side. And we have a whole group of people at JPL who do acquisition and that sort of thing, and that's what he did. He went on to do a lot of other things. He got involved in the government, he worked at OMB, he worked at HUD, then became a senior executive at a large energy company. He had a very successful career. But that part of it was important.

WALLACE: My mom's from New Jersey. They actually met at RCA. She and her three brothers grew up with a single mom, no dad, through the Depression, through the War. I think she graduated first in her high school class, but at the time, it was tough for girls to get an opportunity to go to college. Her mom needed money, so she went out and worked as a secretary, basically. I think she was smarter than all of us. [Laugh]

ZIERLER: Didn't have the opportunities.

WALLACE: Didn't have the opportunities. But later in life, it was interesting, she also got involved in working in the government, and she ended up working as a personal assistant to Elizabeth Dole, who was Secretary of Transportation, then Secretary of Labor. She ended up being part of some government history. She often tells the story about how she was asked at transportation to do all the research on seatbelts.

ZIERLER: I remember, Ralph Nader, "Unsafe at any speed." [Laugh]

WALLACE: Exactly right. We would get in the car, and there would be no seatbelts for the kids, much less any other safety devices. She was working in transportation, and Detroit was very adamantly opposing it as an additional cost. She did a bunch of research and found out that where they were implemented in other countries, in fact, the cars sold better than the cars without the seatbelts. Detroit finally clicked over that consumers, especially parents, are willing to pay for those extra safety devices. She's very proud of that. She presented it to the Secretary, and the Secretary then worked with her husband, Bob Dole, who was in the senate at the time. They got legislation passed, and she's very proud of that. And she should be, of course. It's part of her story. But she's a remarkable woman. My dad passed away, but my mom's still with us.

ZIERLER: Did you spend your whole childhood in New Jersey?

WALLACE: No, I lived there until I was 6, then, we moved to the DC area when my dad got a job in the government, I think at OMB at the time. Then, when I was 9, we moved back to New Jersey, and I stayed there until I was 13. Then, we moved back to Northern Virginia. We kind of ping-ponged back and forth from the DC area to New Jersey.

ZIERLER: Did you have a sense through your father of NASA and the larger space exploration, aerospace world in DC?

WALLACE: Oh, yeah, absolutely. As I said, my dad was just fascinated by space, fascinated by exploration. Although he wasn't a technical person, he was a very intelligent and curious person. There was almost nothing my dad couldn't talk about, including space. He took us to 2001: A Space Odyssey, he was a Star Wars and Star Trek fan. Anything to do with space, he certainly was plugged in. In the government at OMB, he did have an opportunity to do some budget work with NASA. But other than that, he didn't have any official capacity with government space.

ZIERLER: I'm curious, after Apollo, as a kid, if JPL registered with you at all in the 70s.

WALLACE: It really didn't. I was, of course, aware of things like Voyager and the Viking landings, as we all were. And I knew I wanted to do engineering work. But when I graduated high school in 1980, I had been thinking for several years about being in the Navy, joining the military. I was a little more focused there at the end of the 70s, I think, than on civil space.

ZIERLER: Where did your interest in the Navy come from?

ZIERLER: When you graduated high school, were the options Naval Academy or regular college? Or were you so committed to the Navy, you would have gone into some other education or beginning a Naval career?

WALLACE: I was going to high school in the Washington DC area, and to get into an academy, you first have to be nominated by a congressman. Once you get nominated, you go through an acceptance process, and the Naval Academy decides if they want to offer you a place. The back half of that is a little more like a college application, but the front half of getting a nomination by a congressman, in the Washington DC area, with all the military families and things there, it's very difficult. Congressmen are given, like, two nominations a year. As you can imagine, there's so much competition in the DC area that I actually didn't think I was going to get a nomination. I was exploring other colleges. And in fact, I didn't get a nomination, interestingly enough. Apparently, the Naval Academy holds back a couple nominations for people they're interested in for whatever reason, and the Academy decided, "Hey, this Wallace character might work." They offered my congressman another nomination, I think contingent on the fact that I get it, so I did get through the nomination process and did go to it. But as part of that delay, I applied to a bunch of normal colleges as well. If I couldn't get into the Naval Academy, I was hoping for MIT. I applied to Georgia Tech, Carnegie Mellon, things like that. I applied to other schools, and that's what I would've done had I not gotten in.

ZIERLER: I'm curious, as a high school graduate, an 18-year-old, the late 70s, early 80s, pretty significant international tensions at this point. China, Taiwan, Soviet Union is on the march and has invaded Afghanistan, obviously the Iran crisis. Did these things appear on your radar when you were thinking about military service, being at the Naval Academy?

WALLACE: Yeah, we were right in the middle of the Cold War, and our military was very much focused on that aspect of the military challenge. It was something we thought about all the time as midshipmen at the Naval Academy, then once we were in the fleet. You had to take it very seriously. There were conflicts, as you mentioned, in different places. When we got into the 80s and the Reagan Administration, there was a real re-emphasis on the military budget, strengthening and expanding the military. I was coming out of the Naval Academy right into all that.

ZIERLER: What was it like when you got to the Naval Academy? What were your initial impressions?

WALLACE: A little bit of fear. [Laugh] And pride. A fair amount of uncertainty. You get to the Naval Academy, and the first thing they tell you is, "One out of every three of you won't be here in six months." The first thing you go through is something called Plebe Summer, which is a cycle of indoctrination. By the time I got there, it was a little more controlled than it used to have been. But there was still a lot of rigor and a lot of testing of your mettle, a lot of knowledge, especially for those of us who didn't come out of career military families and things like that. We had a lot to learn. The summer was tough, but I had been a runner in high school, so I came into the Naval Academy physically in great shape.

I'd never had any trouble with physical aspects of the Plebe Summer, which can be pretty daunting and difficult if you hadn't been an athlete or exercising regularly. That part, I dealt with pretty well. I was pretty smart, so I did OK with the academics and that part of it. The part that challenged me the most probably was managing under pressure. You get four or five guys yelling in your face, you're an 18-year-old, and that's never happened to you before, you've got to learn how to deal with that. But that's part of what the Naval Academy was trying to do, teach you those skills. And it did. But some of it can go a little too far at times. All in all, it was OK. I got through the summer. When the school year started, I was running, back in my element with the academics. I did OK. I never really felt like I was in jeopardy of wanting to leave or being asked to leave. I think I was OK.

ZIERLER: Do you declare the focus in engineering in the beginning, or that comes after a more general education?

WALLACE: It comes pretty quick. I think it was after the first semester, we had to identify our major. We may have had some flexibility beyond that. But I knew I wanted to do systems engineering pretty much going in.

ZIERLER: Systems engineering, is that a study through a specifically military context? Or would it be like systems engineering at a regular four-year school?

WALLACE: The term systems engineering means different things in different places. At JPL, it has a certain meaning. But at the time, it was still a relatively new-ish discipline, although again, it's been used in the aerospace industry for quite a while. But there usually weren't degrees in it. There weren't degrees in systems engineering. If you were a systems engineer in the industry or civil space, you were an aerospace engineer, you might be an electrical engineer, or something else. By the time I got to school, there was this desire to start marrying the different disciplines, especially given the rise in computer technology and capabilities. Being able to, for instance, simulate different types of systems, whether they were electrical, mechanical, hydraulic, whatever, there were certain principles that crossed over all of these systems.

For instance, there was a big emphasis and a lot of focus on being able to do digital simulations, digital problem-solving rather than analog problem-solving, being able to do control work, both classical, which is a little more under the theoretical side, as well as aspects of digital control. Some of this was relatively new and was being influenced pretty heavily by computers becoming more powerful and accessible. That's what the systems engineer program was at the Naval Academy. Not a lot of schools had it. MIT, Carnegie Mellon, some of the real heavy engineering schools certainly had systems engineering programs. I liked it because first, it married the new technology with the old theory, because it allowed me to look across all different kinds of systems, which I found very interesting and challenging, and it's a perfect thing to study if you're interested in robotics. Back then, there weren't high school robotics teams. There weren't even robotics degrees in college. It was as close as I could get to robotics, which was something I was very interested in. I did my senior project in robotics and robotics systems. Those are the things I liked about it.

ZIERLER: What do summers look like at the Naval Academy? Do you get to go home like a regular college kid? Do you stay there, do you deploy? What does it look like?

WALLACE: You get to maybe go home for a week or so, [Laugh] but the training doesn't end. My first summer, I was detailed to Honolulu. Pearl Harbor. I was detailed to a submarine, actually, as a midshipman. It's a six- or seven-week sort of thing. I got to Pearl, we got a week or so in port, then we transited to the Philippines, Subic Bay, which is quite a sight.

ZIERLER: What does it look like there?

WALLACE: At the time, it was just short of a den of iniquity. It was the wild West. Every vice you could think of existed in Subic Bay at the time. It was a little eye-opening for a kid from New Jersey or Virginia. [Laugh] Then, we spent a week in port at Subic Bay. It's a big port of call, a little messy, but we had some fun there. Then, I flew back. That was my first summer. Most summers at the Naval Academy, they try to do some sort of training. One summer, I was an exchange midshipman with the Norwegian Navy. I got to go to Northern Norway, where the Norwegians at the time had a set of patrol boats, which would patrol the fjords. I showed up, didn't speak any Norwegian, but thankfully, Norwegians speak exceptional English. And I spent four or five weeks learning how they operate. It was really fascinating. This is a group of folks that was basically trying to protect their country from Russian submarines coming into the fjords with 20- or 30-year-old technology. The fishermen had better equipment, I think, than some of the patrol boats. [Laugh] It was a lot of fun. The Norwegians are a remarkable group of people. They can drink a lot, I'll say that. I really struggled, even at 20 years old or so, to keep up. I got a chance to see and experience that. Those were summers at the Naval Academy. You don't come home for too long.

ZIERLER: In what ways did the broader Cold War register while you were at the Naval Academy? I'm thinking Able Archer in 1983. Was that on your radar? Would you be aware of things like that?

WALLACE: Yeah, we were. At the Naval Academy, we certainly were. We were about to enter into that environment. I think it was something we would track and be aware of. The Naval Academy would spend a fair amount of time trying to prepare you, both from a military technology perspective, as you might imagine, but also from an ethics and leadership perspective as well. We spent a lot of time trying to understand. It was also close enough still that the Vietnam War was still very influential in the military, so that was a big influence. But the Cold War, the Communist and Soviet systems, the history of the country, their current capabilities and geopolitical interests, all of those things were part of the education.

ZIERLER: Is there a separate line of education or preparation for students who intend to make a career in the Navy as opposed to it being your education, you'll do your service, but you have other interests beyond that? Is there any bifurcation in the academy for people with different ambitions?

WALLACE: There's a very small number of people that graduates from the Naval Academy or one of the military academies that do something other than what we call line. Almost everybody is Marines, Surface, Submarines, Air, one of those four things. But there's a very small number that might go into the JAG Corps, law, logistics, that sort of thing. Sometimes, it's because of medical constraints, sometimes other reasons. But almost everybody that comes out has been trained for and is going to join some form of what we call the line. And everybody gets trained the same way. There's no difference. Eventually, as you go through your career, you get to a point where you're offered post-graduate opportunities and things like that, and if you don't intend to make it a 20- or 30-year career, you might decide against that kind of path. When I left the Naval Academy, I didn't know if I'd be in the Navy for 5 years or 25 years. I really hadn't decided at the time.

ZIERLER: When you graduate, how many options do you have based on your interests and aspirations?

WALLACE: There are four basic options. Maybe things have changed now, and there are some others, but at the time, you had to go onto a surface ship, or you had to go submarines. If you were going submarines, you'd also leave the Naval Academy and immediately start nuclear power training because all of our submarines were nuclear-powered. And that took about a year. That's what I did. You can go air, and if you leave the Naval Academy to go air, you go down to Pensacola and start training as a pilot or NFO, something like that. Or you can go Marines, where you go to Quantico and get some post-graduate training there. Those were kind of the big options. Part of me wanted to fly, but at the time, there were no real safe eye surgery options, and I did not have good eyes. That wasn't an option. I chose submarines.

ZIERLER: Were you specifically interested in nuclear engineering? Was that part of it?

WALLACE: Nuclear engineering was just something that came with the submarine choice. I liked the idea of getting a broader engineering experience with nuclear engineering. You finish the training preparing for submarines, and you really have the equivalent of a master's in nuclear engineering. I appreciated the fact that I had an opportunity to do more academic work in that area, and we operated a nuclear power plant on a submarine. From an engineering perspective, as a pure engineer, there are a lot of fascinating aspects to that. I enjoyed that, too. But I chose submarines not because of the nuclear power training opportunity, but because I felt that they were really a very impactful part of our Navy at the time and still are. Whether you were on a fast-attack boat or a strategic-missile boat, they both had very critical roles. I felt like I could contribute the most there.

ZIERLER: Once you make the decision to go submarines, within that decision branch, what are your options at that point? Do you get to choose the kind of submarine you want to be on?

WALLACE: You do, actually. There are two basic kinds of submarine. One is a fast-attack submarine. These are the submarines that escort carrier groups. They'll carry intelligence officers, they'll do insertion extractions, they'll go out and hunt down enemy submarines. They're the boats that get up close to the coast and fire tactical missiles, for instance, at targets and things like that. That's the fast-attack side of things. The other part is what's called a strategic-missile or ballistic-missile submarines. We call them boomers because they carried the big ICBMs. Their job was to go out into the middle of the ocean, dive deep, go as quiet as humanly possible, and not let anybody find you. And they had a very unique cadence. They had two crews on the ballistic missile side, blue and gold. Basically, you'd crew for two months, be off for a month, come back and train for a month, then crew for two months. They'd go out for long durations and just try not to be found because they were strategic weapon assets. They were a deterrent. Perhaps, not surprisingly, I chose the fast-attack path. It just sounded a lot more interesting to me. You don't always get your choice, but I got mine. That's what I decided to do. I got stationed on a submarine in Connecticut.

ZIERLER: What is life like on a submarine?

WALLACE: It's kind of weird. [Laugh] Looking back on it, it's definitely not normal. The fast-attack boats unfortunately only had one crew, so if you were on a relatively new ship that didn't need repairs and things like that very often, you'd spend a lot of time at sea. I was on a Los Angeles class new submarine, so we had what was called a 70% op tempo. That means 70% of the time, we were at sea doing something. The other 30%, we were working five days a week in port, usually 12 hours-plus a day. One out of every three days, you would have duty, so you'd be on the sub for 24 hours that whole time. I just never left the submarine. For three and a half years, I was stationed on the Albuquerque, which was the submarine I was on. For junior officers on a ship with a high op tempo like that, it was very, very consuming, to say the least. That's part of it. When you're at sea, it's an unusual feeling.

You'd typically go out for maybe three, four, five weeks at a time, but sometimes we'd deploy for much longer periods of time. I went 117 days at sea with, I think, one day in port to come in and fix a periscope that had broken. You can spend a lot of continuous time at sea. When you're at sea, as a junior officer, you have 18-hour days, which has got to be the most messed up concept ever invented. Your body just does not work on 18-hour cycles. You're just constantly tired. But there had been some kind of study, I guess, that said after six hours on watch, you start to lose focus. They said, "OK, we won't make an eight-hour watch cycle, we'll make a six-hour watch cycle." You had six hours on watch, then you had six hours of training and administrative work because you had a whole department you were responsible for as an officer in addition to being on watch, then you got six hours to supposedly sleep, but you never got six hours.

Your body's on this crazy Circadian thing that doesn't make any sense, and you're always exhausted and behind, there's something you're always supposed to be doing. It was very demanding. [Laugh] Fortunately, I was young and capable of doing that. But as I peered into my future and thought about families and things like that, I had to wonder if I could actually keep doing that kind of thing. But life at sea is exciting. It's just super, super interesting. That's the adrenaline part. That's what keeps you going through all of it. I talked about the missions of a fast-attack submarine. We did all those things. We were able to really engage in a way that made you feel like you were doing something contributing and certainly kept your interest. Some things, I can't talk about, but some things, I can. There were some interesting times.

ZIERLER: Including any close calls with Soviet subs?

WALLACE: Well, that's the stuff you don't talk about. One of the stories I like to tell, just to kind of give you a sense, we were going into the Mediterranean to spend a few months on a tour, which was good duty because every once in a while, you pulled into Italy, Spain, or something like that, which was nice. But during the transit in, you have to go through the Straits of Gibraltar, which are the heaviest shipping channels in the world. Constant freighters, ocean liners, and everything else. At the time, before you went through the Straits of Gibraltar, you had to know exactly where you were because you were going through submerged, and if you were too far south or north, you were in a lot of trouble. The channel was not that wide. Before you went in through the Straits, you don't have to come up to periscope depth and get what's called a navigation fix.

You had to understand where we were before we tried to make the transit submerged into the Med. And I was an under-instruction officer of the watch. One of my first watches. Officer of the watch is the guy driving the ship, basically. They want to get to periscope depth, get this nav fixed. I'm looking at the sonar signals, and it's ship, after ship, after ship. Going up to periscope depth is one of the most dangerous things you do in a submarine because you can easily get run over. I'm just looking at these traces, and I see no way to get to periscope depth. The captain comes out and looks, and he says, "Come left to 330." I did it. "Come right to 120," or whatever. I did. He said, "Go to periscope depth, Mr. Wallace." I'm like, "What?" To me, it looks like we're going to get run over three or four different ways, but he was so experienced, he knew exactly what he was looking at, and he knew how to read the charts and things.

I went to periscope depth. When you go to periscope depth, you put the periscope up. You see it in the movies. They're circling, looking for shapes and shadows. As the periscope breaches the surface, you're looking for close contacts. We were coming up in the middle of the night. I'm looking, and the periscope breaches the surface. I look up, and at 30 or 40 degrees, I see a row of lights. I'm thinking, "Oh my God, we're about to get run over by an ocean liner or a freighter." I'm about to call emergency deep, and I realize it's the lights up on the Rock of Gibraltar shining down. It was terrible. It was the most terrifying moment in my entire life. But submarine work on a fast-attack boat can be pretty exciting.

ZIERLER: When did you start to think about leaving the Navy and pursuing new opportunities?

ZIERLER: What kinds of programs were you looking at for graduate school?

WALLACE: I applied to all the same schools I applied to for undergraduate with one additional one, which was Caltech. When I applied to MIT for undergraduate, they waitlisted me. While I was waiting to get an answer, I got accepted into the Naval Academy. I accepted the offer, and later on, they told me, "We've got a spot for you." When I applied to graduate school, I applied to MIT, of course. And I got accepted. But something about my undergraduate waitlisting still was sticking in my craw, so I decided to go to Caltech, and I'm glad I did. Of course, I knew Caltech was connected to JPL also.

ZIERLER: You did, you made that connection at the time?

WALLACE: I did. I didn't realize exactly what the relationship was or whether or not it would necessarily give me an opportunity to work at JPL. But as I got partly through my master's degree at Caltech, I realized there was probably an option to go up the hill and work at JPL. That was pretty appealing.

ZIERLER: In terms of your career ambitions at that point, was the idea that the degree in electrical engineering was the course of study that would be most effective for what you wanted to pursue?

WALLACE: It was, yeah. There wasn't a systems degree. I probably could've done something like aerospace, but I felt like the electrical engineering degree, in addition to giving me a set of skills I knew I could use in aerospace, when I looked at the Caltech course constituency, there were all kinds of really fascinating things. Deep space communications protocols and things like that. It wasn't just circuits, resistors, transistors. The other thing that fascinated me was neural networks, artificial intelligence. My robotics background really gave me some real interest there. I knew that I could get exposed to that at Caltech in the electrical engineering department, although I probably could've still gotten some of that from other places. When I looked at the curriculum, it just seemed like a good fit for the things I wanted to understand. I really hadn't been doing engineering. I had been doing operational things. I felt like I really had to recharge that skillset. I had also never used a personal computer. [Laugh] I literally had these big mainframes and things like that, but I was way behind the kids. When I got to Caltech, I had to learn how to use a PC in addition to all the other academics. I needed something that gave me some breadth and exposure to the technologies that were going to influence the industry I was interested in.

ZIERLER: Beyond the learning curve with PCs, coming into graduate school, most of your fellow students were probably straight out of undergraduate. Just in terms of the muscle memory, getting back in a classroom, what were some of the challenges versus obviously the maturity and experience you had relative to your fellow students? What were some of the opportunities and challenges there?

WALLACE: I think, for the most part, I hadn't lost most of those muscles, and it was mostly just getting the experience and the exposure. I managed to keep up in the classes. Part of it, as you said, is that I was five years older, I'd had a lot of leadership experience. I knew exactly what I wanted to do. I was certainly more mature and more focused, I guess, but most Caltech grad students are pretty mature and focused. I did OK, I managed to keep up just fine, I think, for most of my classes. There was one advanced math class–I had done well in math in high school and at the Naval Academy. I fancied myself as reasonably competent mathematically, so I was like, "Bring it on, Caltech. Give me one of your more advanced math classes." I took one, and after a week, I changed it to pass/fail immediately because I was lost. I was so lost. I eventually started to understand maybe a third of it or whatever, but that's the one place that just blew me away. The theory was so far beyond anything I had a chance to see, understand, or do before. Really impressive. But beyond that, I kept up OK.

ZIERLER: Now, in EE, is there a terminal master's program? Or are you admitted on the basis that you'll stay on for the PhD?

WALLACE: No, it was a one-year master's program. A lot of master's programs are two years. I was 29 by the time I got to Caltech. I was ready to get out in the workforce. I didn't want to spend two years, much less another four, five, six years getting a PhD. I wanted to just resharpen the skills, get some exposure. I wanted to be able to go to a place like JPL, Goddard, or Lockheed Martin and say, "I'm a real engineer." There's a tendency for people coming out of the military to get slotted into programmatic positions, partly because they have the military background, partly because they have leadership, communications skills, other things you don't get with engineers coming straight out of school. But I didn't want that. I wanted to do the engineering. I wanted to make sure I had that opportunity. I don't know if I really had to do it or not to get that opportunity, but that's what I wanted to do.

ZIERLER: Now, in graduate school, did you meet Charles Elachi? Did you know about the remote sensing class he had taught?

WALLACE: I didn't meet Charles or take that class. I wish I had. I didn't meet Charles until much later at JPL.

ZIERLER: Who were some of the professors who were formative in your education at Caltech?

WALLACE: There was a comms professor named Professor Posner. He was old school. He was a fascinating guy to me because he was easily in his late 50s when I was taking his class. He had been trained maybe concurrent at best with the technological/computer revolution, but he had embraced it so wholeheartedly. He was responsible for a lot of the encoding, for instance, that our spacecraft still use today. He spearheaded it. He taught a communications course that really was eye-opening to me because it was everything from these coding schemes to traffic theory. And the thing I liked about it was, he'd bring these very theoretical concepts and have very hard, concrete applications he would apply them to. He had a pretty big impact on me, just helping me understand how to translate theory into practice, I would say. And I took a class with Carver Mead, which blew my mind. There was a mechanical engineering professor, Burdick, whose class I loved. Most college professors think on a certain plane, and it's very hard for them to come down and explain things to people who aren't yet at that plane.

And he did that so exceptionally well. It was an interesting crossover course to me in the mechanical engineering domain, very robotics-oriented. It really helped me prepare for a lot of the things I would eventually have to manage down the road. But that was a great course. I took a Shakespeare course. One thing about Naval Academy is, you don't take electives. You take war history or something. If you've got a spot, there's no room to sort of play around. I love Shakespeare, and it was the first time I'd had a chance to take a Shakespeare course. That was kind of fun. I took an econ course. I'd never taken any economics before. That was eye-opening for me. It was fun. The engineers always got blamed for busting the curve in the econ course. My daughter has an econ course now as a senior in high school, and I've forgotten a lot of it, but that's the full basis of what I know about econ. It was a great opportunity to take a range of different things and prepare for what I was going to do.

ZIERLER: Get that humanities education.

WALLACE: That was it. That was my full humanities education, one semester of Shakespeare.

ZIERLER: Last question for today, which will set the stage for our next discussion. What was that initial point of contact or opportunity that opened the door at JPL for you?

WALLACE: They came down to recruit at Caltech, and I talked to a guy by the name of Dave Lehman, who, interestingly enough, had been a submarine officer. He was recruiting for systems engineering positions. But I submitted by résumé for some positions in the power systems area as well. The power guys offered me something first, primarily because a number of our spacecraft, then and now, were and are powered by radio isotope thermoelectric generators. They're basically plutonium decay systems. I had nuclear experience. The Cassini folks wanted me to come in and help them with some of their power systems work because of my nuclear background, which was a weird way in, but it got me in.

ZIERLER: On that note, we'll pick up next time for when you begin your career at JPL.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Tuesday, March 22, 2022. I'm delighted to be back with Matt Wallace of JPL. Matt, nice to be with you again. Thanks for joining me.

WALLACE: Nice to be here.

ZIERLER: Just a point of clarification, when JPL recruits, as in your case, is it mission-specific? In other words, are you hired on the basis that they've identified a match between your area of expertise and specifically what they need, in this case, the energy propulsion issue as it related to Cassini?

WALLACE: I think sometimes, it is. Sometimes, it's driven by a mission-unique skillset that's required. In my case, that was true. Other times, and most of the time, I would say, it's really discipline-driven. We have a series of different jobs that are drawing on our mechanisms engineers, and we need more mechanisms engineers, or we need more propulsion engineers because we have a number of different missions that are propulsion-heavy, or we have new technologies that we want to develop in this particular area. It's very often discipline-driven. In my case, the discipline was unusual. You don't go out in the aerospace industry very often to find people who do space nuclear power, for instance. For me, it was driven primarily by the Cassini need for that particular skillset.

ZIERLER: What was the state of play with Cassini at that point?

WALLACE: Cassini was about six years from launch. They were still finishing off their critical design activities, they were a couple years away from really getting heavily into the plate hardware fabrication. In the area I was working, they were building essentially a new radioisotope generator. There had been ones that had been built before for other missions, but this was a new design with higher efficiencies, and they were essentially partnering through headquarters with the Department of Energy and a division of Martin Marietta, which became Lockheed Martin, to develop this new generator, which was getting built at the Lockheed plant in Valley Forge. My job was to help make sure all those interfaces were well-understood, to help track the progress the Department of Energy was making on it.

They had to make new plutonium fuel for it, there were new launch safety analyses and tests that had to be done. Then, we were particularly interested in the radiation environment. That actually fell on me. I became the RTG radiation expert at JPL, and I used a lot of Monte Carlo code that came from Los Alamos used for weapons and other stuff. [Laugh] It was an interesting phase of my career, but I got to do a lot of radiation analysis and simulation work with some advanced code. It was a big community code that was used in a lot of different places, and Los Alamos would give you $5 if you found a software bug. Every once in a while, I'd send in a note that I found a bug, and they'd literally send me a$5 bill in the mail. [Laugh]

ZIERLER: What were some of the biggest learning curves when you joined JPL, even from a cultural perspective?

WALLACE: It's different, obviously, than the military. It's a much flatter organization, and that wasn't something I was used to. I think that was something I had to kind of acclimate to a little bit. I think there were parts of it that, for me, kind of came naturally. Engineering is a data-driven sort of activity. The focus for engineers is making sure you get it right. That's what it's about. It's not about how many people you know, how many contacts you have, what your LinkedIn page looks like. [Laugh] It's about getting the right answer, and I think that meshed in well with my history, my interests, and the military experience. But I think the flatness of the organization took a little bit of getting used to for me, culturally. Technically, I had a lot to learn. I really had not done any hands-on engineering.

I had managed people who were running engineering plants, I had done a lot of obviously theoretical work in classrooms, I had done some hands-on work in projects and things like that in undergraduate, but I had never done any real engineering. I wanted to get those skills, I wanted to get a foundation. I wanted to run these Monte Carlo codes, I wanted to go into the laboratory and learn how to use oscilloscopes, and do design work on circuits, and things like that. Technically, I had a lot of those things to learn. Then, I had to learn a lot about the cultural approach to different types of missions. Cassini was a class A mission all the way. It was a very reliability process-driven system, and the next mission I worked on was Pathfinder, which was almost exactly the opposite. There were some cultural adjustments depending on what type of environment and project we were doing.

ZIERLER: On a technical level, what was unique about Cassini that required this unique approach to its propulsion?

WALLACE: It was the power system rather than propulsion. But Cassini was going to Saturn, which is an outer planet. It's just too far away to use solar arrays, or at least to do the type of mission that Cassini wanted to do, a flagship mission with a lot of instruments, a long-life mission. You couldn't do it with solar power. It's tough to do a solar power mission even to Jupiter. We've done it, and we're doing another one here with Clipper, but the size of the arrays is just enormous. It needed a radioisotope generator. Every watt mattered. They were counting tens of milliwatts, I think. [Laugh] The efficiency of the generator mattered quite a bit. For what I was working on, that's what was unique, that was the driver.

ZIERLER: How big was the team, both in your immediate environs, then overall?

WALLACE: I was working at a pretty low level, so I'm not sure I have a good handle on the total number. A typical flagship at JPL might be 700, 800 people. Full-time equivalents, it might peak there. I suspect Cassini was in that range or maybe a little more, but I don't know with certainty. The number of people working on this radioisotope system at JPL was really just three, two guys who were approaching retirement, and me. It was really just us who were sort of focused on this part of the system.

ZIERLER: What was the timeframe between when you joined and launch date?

WALLACE: I joined in summer of '91, and Cassini launched in '96, '97. A good five years or so. I only worked on the project until '94, I think about two and a half years. Then, they fired me. [Laugh] They didn't really, but they didn't need me at that point. We'd gotten through most of the development. They felt they could go without all three of us.

ZIERLER: Between '91 and '94, what exposure did you have more generally at JPL? Were there other projects you were involved in?

WALLACE: Not really. I was really working entirely on the Cassini project. I may have done one lunar study. I remember getting involved in one mission, just for a little bit of experience. One small, quick return, low-cost lunar mission, I remember working on. But for the most part, it was all Cassini.

ZIERLER: What was next for you in '94?

WALLACE: They decided that they needed somebody to come in and help manage the power system on this little thing called a Microrover. The Microrover was targeted to be part of, potentially still, this new technology lander system, which at the time was called MEaSURE. The power system on the rover was small. The whole rover effort, I think, ended up at $25 million or something like that, and the power system was probably a couple million dollars. It was really just some solar arrays and commercial battery cells, commercial power converters, things like that. It was all low-cost, a lot of commercial hardware. They really kind of brought me in mostly to help manage it, to keep an eye on the budget and the schedule. But I of course got engaged on the technical side, and I started to learn more about power systems in general. As I did that, I got shanghaied into the spacecraft. There was a rover, which was part of the payload, but then there was larger spacecraft, which ultimately became Mars Pathfinder. I got dragged into the spacecraft power system and was doing systems engineering on that side. Eventually, I rolled into the Assembly Test and Launch Activities for the spacecraft, the whole time maintaining my job on the rover. I was one of the few people, actually, maybe the only one, who had a job both on the rover and on lander. There was this tension between the two. I was always in the middle. [Laugh] ZIERLER: Maybe this is a dumb question, but the concept of a Microrover, is it always about going to Mars? That's the conception from the beginning? WALLACE: No, there were and have been other miniature rover ideas, everything from asteroids to other moons, our own moon, obviously. There have been other miniature rover concepts and targets. But by the time I got onto this, it was trying to take a technology development program associated with rovers, some of which were actually targeted towards military utilization, and apply it to this planetary activity. ZIERLER: During your early years at JPL, how connected were you intellectually and physically with campus? Would you go down to campus? Was that a resource for you? Or not so much? WALLACE: I guess I would say not so much at that point. Obviously, I had just come up from campus, so I still knew people there and things like that, but from a work perspective, it was pretty consolidated in the JPL regime for what I was doing. ZIERLER: In the early years, is there anybody who stands out in your memory as a real mentor to you? WALLACE: Yeah, there are several people. When I got to JPL, one of the older gentlemen who was working on the radio generators was a guy by the name of Bob Campbell, and he was this southern gentleman kind of guy, something of a character, and he really took me under his wing, and helped me understand how the laboratory worked and how to interface with our partners at the Department of Energy. He was a PhD in nuclear physics, so he was a good second check on a lot of the radiation work I was doing. He became a good friend to me and to my family. Bob was probably the first person who had stepped up and gave me a hand, I think. Once we got to the rover side of things, there were a couple people. The rover team was full of young guns who didn't know any better. [Laugh] And I was definitely one. Literally, they were giving me this subsystem lead, and I had never done a project, much less led a subsystem. And that was the same kind of across the board, all of us were just kids. Certainly, not very experienced. Exactly how it all happened, I don't know, but there were a couple strategic insertions of graybeards. Probably the one who had the biggest impact on me was a guy by the name of Bill Layman. Bill was the chief mechanical engineer for the Voyager spacecraft. He's a bit of a legend at JPL. He came out of division 35, which was a mechanical area, and I was obviously in electronics, power systems, and things like that. But he became the chief engineer for the rover. He just is this kind of tall, lanky, Midwestern guy who always was calm, always understood what was going on, always had the right perspective. He worked 8 o'clock to 4:30, and the amount of work he got done between 8 o'clock and 4:30 is closer to what I would get done in four days. He was remarkable. At that point, we were all starting to get pretty computer-savvy, and a lot of the problems we were solving were done with computer tools and skills. Bill would always take out a pad of paper, and he would do it in first principles because he fundamentally understood the physics of the problem all the way down to the closed-loop equations. It was impressive to watch. It's not like he was afraid of technology or whatever, but he wanted to just imbibe it. He wanted to absorb it via osmosis. He wanted it to be part of him, he wanted to have a feel for the numbers, what they meant, and not just that they were numbers. He was remarkable in that sense. I've never seen anybody–I wouldn't call it intuition because that's not really something you work for. He had this sense that had come from decades of doing problems this way that I've never seen before, or since, probably. It was remarkable. He had a big impression on me and everybody on that project team. He taught us some things that we all still use every day. He taught us test. Test, test, test. No matter what you do, when you design something, do the testing. He taught us the importance of margins. We have a tendency to sharpen the pencils, we're engineers. If we don't need that extra kilogram, we're going to get rid of it. He really helped us understand why it's important to always build in large margins when you're doing design work, and he fundamentally influenced the way JPL handles its margin management, frankly, and still does. His thinking is still part of that. After Pathfinder was successful, people said, "How did this happen? It's crazy, it's a tenth the cost of other missions that have gone to Mars," and I always remember him saying, "If you just let us fail every once in a while, we can do remarkable things." He was unique. [Laugh] He had a big influence. ZIERLER: When you were forcibly retired from Cassini in '94, is it incumbent on you to find your next opportunity, or is there an internal placement program at JPL that puts that together for you? WALLACE: I was still pretty new, and so for somebody in that position, I didn't have a network of folks who were going to call me up and say, "Hey, come work on my next project." Which does happen a lot of times with people transitioning on projects. But at that point, I didn't have that. My group supervisor said, "He worked this for a while, let's broaden him out. Let's put him over here, they need some help." I was placed. ZIERLER: In terms of broadening it out, what was new about this work for you? WALLACE: The RTG work was very unique. It was very nontraditional aerospace work. As I said before, you're not going to go to Lockheed Martin or Northrop Grumman and find somebody who does RTG work. The next step for me was to do work that was more broadly applicable, and I was working inside the power systems department. I learned a lot about batteries, solar arrays, contract management, the way we do power management. I learned a lot about the environments we put these things through. I actually did a lot of ground support equipment, which doesn't sound too exciting, but basically, it's the electronic test equipment we use to test the hardware before we deliver it to our system-level integration and test activities. I learned a lot about that. And like I said, I'd go in the lab, and I'd stay there until 8:30 or 9 o'clock at night, just trying to understand how to do basic hands-on electrical engineering because I hadn't done that in college or in the Navy. It was a little weird because I was doing stuff that typically you're doing when you're 20 and 22, and I was 30 and 32, and I felt like the old guy. And I guess I was. But I just had this sense, and this has just always been part of how I deal with things, that I can't skip that step. I have to learn that, or else I won't be comfortable. I'm never comfortable going and doing the next thing unless I understand this part of it. It was a great opportunity to get that foundation. ZIERLER: This initial work in 1994, how much of it was ultimately funneled into Pathfinder? WALLACE: It was all Pathfinder. I was working on the Pathfinder project. I was working on Sojourner. Microrover was the name of the rover before we went through the naming process of calling it Sojourner. It was the flight vehicle that ultimately flew on Mars Pathfinder. Everything I was doing was part of that mission at that point, it wasn't precursor work. They were in the middle of the mission. We launched in '96, so we were deep into the mission at that point. ZIERLER: Obviously, these conversations would've preceded your time at JPL, but do you have a sense how far back the idea of sending a wheeled rover to another planet goes at JPL? How new a concept is that where it transfers from science fiction to, "We really think we might be able to do this one day"? WALLACE: There had been lunar rovers for the astronauts, and the Russians as well had built lunar rovers, so the concept of using rovers on other celestial bodies was not particularly new. I think trying to do it on Mars where there are new humans to joystick it, there really is a level of autonomy that's required, that part of it was certainly new and challenging. We had to figure out how to balance the management we were doing from the Earth with the autonomy that the vehicle needed to have to keep itself safe and execute things in an efficient way. When we're doing Mars missions, and this is still true, we generally can't really send commands to the vehicle more than once a day, otherwise it becomes very inefficient and hard to do. There's a 24-hour cycle with a set of commands to execute, and that was new for us on Sojourner. This concept of waking up, getting its instructions, going to work for six or seven hours, shutting down and taking a siesta because it needed more energy, then at the end of the day, getting your data back to the lander, then going to sleep and safely surviving the very cold night on Mars, and making sure it woke up again the next morning, independent of whether we were trying to wake it up, or we forgot to wake it up, or we couldn't wake it up, and it had to wake up itself, set its own alarm, all those things, all the fault protection and failsafe that went along with it, all the things that could go wrong, that was certainly new. I think, also, the hazard avoidance aspect of it. There was some small amount of hazard detection and avoidance capability in some robotics systems terrestrially, but very little. There are no self-driving cars. ZIERLER: It's still far in the future. WALLACE: It's got a ways to go. But we were making up all those control systems ourselves. We were having to come up with concepts and understand the sensors, the algorithms, the approach to making that safely work. There's a balance between being aggressive enough to actually get the thing done and not get yourself in trouble. We were figuring all that out. That was all very, very new. ZIERLER: To go back to the increasing importance of computation, in the 1990s, there were tremendous strides in computation across the board. Looking back, though, it's orders of magnitude how much better computers are now. What stands out in your memory as working on computers in a way that was remarkably cutting-edge at the time, and where might you look back and say, "I can't believe we were able to accomplish what we did with the computers we had at the time"? WALLACE: One of the things in our business we always have to deal with is whether or not the technology is capable of dealing with the environments. Even though many of the computers and processors that were available back then were still rudimentary, what we had to fly was even more rudimentary because it had to be low-power, it had to deal with these crazy thermal cycles and be pretty robust from that perspective. You'd start worrying about pins and things like that you have. It had to be robust to radiation at some level, although we took some liberties there. One of the things we find, and this was true for Sojourner as well as the missions we're doing now, is that we have a tendency to need to be ten years or so behind the technology. As a result, Sojourner flew with an 8086 processor. It was Atari-level stuff. [Laugh] There's only so much you can do with that processing capability. A lot of the fault-protection and hazard-point algorithms really had to be tuned and optimized to account for the limited memory and processing power. I was this guy working with solar arrays, batteries, and things like that, and I remember when we got into testing and getting ready for surface operations, we started to see some behaviors that didn't make sense. I literally went and grabbed the C code. I'm not even a flight software guy, and I'm looking through the code because at that point, it was 10,000 lines or something, not two-million lines. I'm looking for the logical error, and I think I found it. It was still understandable to the common engineer at that point. But like you said, we were able to really push the boundary, despite the limitations in computers and computing power. ZIERLER: In the mid-1990s, was there already the sense that Pathfinder would be the first of many landed missions to Mars? WALLACE: No, not at all. We had gone with Viking 20 years before. There was a long gap. There was some sense that Viking had done a kind of fundamental analytical experiment that was somewhat insightful with respect to the lack of extant life on Mars. I think looking at it now, we realize all the different ways that particular experiment was flawed, just looking for extant life, not to mention, obviously, ancient life, which has been the focus of our program for a couple decades. But there was not a strong push to get back to Mars. It looked kind of barren and lifeless, and there were other places in the solar system that we hadn't been to. Pathfinder, I think, was constructed very much because of that perspective. It needed to be low-cost, it needed to be relatively short development durations, it needed to not interfere with the big flagship mission at JPL, which was Cassini. It was constructed very much to fit into that sort of thinking at the time. There was no conversation that I was aware of, though I was working at a lower level at that point, this leading into decades of Mars surface exploration at all. This looked like a one-off technology experiment, trying to see if we could get to the surface of Mars in a relatively cheap landing system. And the project was started without any rovers. The rover technologist folks managed to convince the management on the lander to put the rover on. As a matter of fact, every other week, Brian Muirhead, who was the flight system manager for Pathfinder, would threaten to throw us off. "You guys are going to be late. We're going to throw you off. That's not going to work. We're going to throw you off." We were like, "No, no, no, we'll figure it out." "You weight too much." "OK, we'll get it." It always felt like we were scrambling to hold on by our fingernails just to get a ride to Mars. There was no perspective on this opening a door to something much, much bigger. ZIERLER: I think the public perception is that Sojourner is the mission, it's synonymous. To flip that around, what is Mars Pathfinder absent Sojourner? WALLACE: It was going to do, and did do, fixed lander science. It had a meteorological station, it had imagers, a radiation experiment, a dust experiment, things like that. It was going to do some surface science, but it was primarily a technology demonstration mission to try to see if we could come up with a way of doing a low-cost landing on Mars. It didn't start out that way. It originally began as a series of different landers that were going to land at different parts of the planet, and it was going to do seismology, basically. But the funding wasn't there, so that fell by the wayside, and it eventually became really a technology demonstration mission more than anything else. ZIERLER: This is such an important historical point. Given the fact that Opportunity and Spirit are not too far off, not decades like it was from Viking, that must mean that it's only the success of Sojourner that allows for this compressed period of excitement that makes Opportunity and Spirit possible. WALLACE: That's exactly right. They were not on the books at the time we landed. I think a couple characteristics of the mission really spawned that next phase. One was Sojourner, of course. The internet was in its infancy, and Sojourner became the unexpected darling of the internet for a while. My daughter's a big Taylor Swift fan, and she likes to tell me, "Every time Taylor Swift drops an album, she breaks the internet." And I'm like, "Hey, your dad was the first guy to break the internet." Because when Sojourner went down, we had to mirror all this stuff in these different servers, and we were still dropping stuff down. But it just caught people's imagination, that was a big part of it. This kind of ran under the radar, but scientifically, we found that even Sojourner, with its very limited science capability–it had an Alpha Proton X-ray Spectrometer on the back, which was pretty low-resolution–was enough to intrigue people. And of course, we had imagers. We found as we crawled off the lander that just the rocks in the very close vicinity to the lander itself were different. They had different geological histories and characteristics. The science community recognized almost immediately that just this small amount of mobility was very, very powerful, and they wanted more. They wanted more capability, more mobility. That was the second thing that, I think, became a big driver for the following missions. And of course, lastly, it successfully landed inside of airbags and did it all for$175 million or something like that, which is an absurdly small number for a good planetary science mission. If you can put all those things together, it becomes clear that we need to extend this modality into the future.

ZIERLER: What were some of the key science questions that affected your work at a day-to-day level for Pathfinder?

WALLACE: There was a limited amount of science. It was very much a tech demo project. The science that went on went on however we could fit it in. There was true on the lander, and that was true that the first order on Sojourner. I guess you could call Sojourner a science technology demonstration at some level. We always thought of it more as a rover technology demonstration, but it became something we learned from from a science perspective. I think because the fundamentals of the mission were driven by cost, and schedule, and tech demo, we didn't do a lot of first-principle mapping of science objectives to mission hardware. But once we had some of the science instruments, for instance, the Alpha Proton X-ray Spectrometer, APXS, on the rover did consume a fair amount of our thinking, time, and efforts. It was an instrument being contributed from a German science institute called Max Planck, which still exists, and it had a PI by the name of Tom Akanamou, and by the way, versions of this instrument flew on future rovers as well.

It became quite an important workhorse part of our science going forward. But we had never seen anything like it before, and we were just busy trying to get this six-wheeled thing to actually work under this really intense schedule and cost pressure. And we were learning on the job because this was our first project for most of us. The instrument came in, we put it on the vehicle, and we went to do a functional test, and the spectrum was just this big, ugly mess of noise. It was useless. And somehow, Bill Layman, the mentor I mentioned before, the chief engineer, said, "Hey, Matt, why don't you go figure out why this thing is noisy?" I'd never debugged an instrument noise problem before, but in we went, and it became quite a struggle. Typically, when you have a sensitive instrument, you have a sensor, then you have electronics. The sensor is taking the measurement, looking for low-level signals and things like that. Then, you digitize that signal, and you bring it back to the electronics.

Once you digitize it, you don't have to worry about noise. Well, this was low-cost. They brought the analog signal back, these very small, tiny, little signals, from the sensor to the electronics inside the rover. It was picking up all this noise from the rover vehicle, all these chopping power converters, motors that were driving, things like that, and it was totally hopeless. We were telling the PI, "You've got a terrible design that's never going to work," and the PI was telling us, "There's something wrong with your rover, it's too noisy. It works in our lab." It just went on, and on, and on. We eventually shielded the cable, rerouted it, did some additional filtering, and we eventually got it to work somehow. But that was maybe the most intense science in development.

ZIERLER: Was there a period during the Pathfinder work where you sensed you were on a leadership track already at that point in terms of increasing responsibility, promotions? Did that happen that early on for you?

WALLACE: I think on Sojourner, one of my jobs was to manage. On Cassini, I was doing technical and interface work. But on Sojourner, on the power system area, I was kind of the adult supervision. It just came naturally because of my military background and things like that. I knew how to lead groups of people. I had a sense that I could do that there. It was five or six people I was managing, not a lot. But I think where I started to transition was, as we got closer to operations, the integrated spacecraft and rover needed somebody to manage the interface between the rover and the lander. Because I had worked on both sides of the interface, I was given that interface leadership role. Now, I was semi-managing the entire rover operations and test team, interfacing back into the lander management and systems engineering organization. I think that was my first real leadership role, I would say. Then, after we landed, we got some opportunities to kind of be out in front. And with the press, for instance, to do that kind of work. I started to feel like I was moving, I guess, in that direction, coming off of Mars Pathfinder.

ZIERLER: Did you feel the faster, better, cheaper mantra for Sojourner at all? Did that mantra filter down to your level?

WALLACE: Yeah, I think it did. The message at the working level is faster, better, cheaper. Pick two. It's defying the laws of physics to actually do all three at the same time. Of course, you can change the laws of physics if you change the efficiency factors and things like that. If you do things differently, you can do all three, I think. And that's what we were trying to do. We believed it could be done, and it was a little bit of a David and Goliath thing with Cassini out there. Cassini was the big monster, had all the experienced people, got 10 or 20 times more money, whatever it was. We were flying under the radar, doing things differently. There were laboratory practices that we looked at and said, "That's a lot of money and time. How important is it?" There were obviously technical conversations and other things, but we'd say, "We're not going to do that analysis, we're going to do extra testing on the back end instead." We were running open loop on a lot of things, and I think that mantra was part of how we felt about the project.

ZIERLER: As a tech demonstration, as you call it, what exactly was that stake? In other words, if it doesn't work, what does that mean, and if it does work, what can happen as a result?

WALLACE: It's kind of an alternate reality. You can predict what could've or might've happened. There were parts of the agency leadership that told the Pathfinder management team, I heard later, that, "If all you did was get to the pad, it would be a success. You're blazing a new trail and doing something we haven't tried to do. If you can just get launched, we're going to say, 'This was a partial success.'" Because it was so low-cost, and we were running so fast. Then, after we launched, it'd be like, "If you can just get to Mars, whether you land successfully or not, you arrive at Mars and start entry, that's a success." Of course, we get through all of that and land, and it's like, "OK, you're safely on the surface. If you don't ever get the rover off the pad," and we almost didn't, "we're going to call this a success." It seemed like maybe the goalpost moved a little bit as we went, so it's hard to really know. But I think to be successful, you have to exercise the technology, otherwise, from a tech demo perspective, yeah, there's a development process you can point to and say, "We learned how to build a rover. We learned how to do airbag testing in a chamber. We learned how to open petals and things like that." But I think, really, in a tech demo sense, if you're a flight tech demo, you really have to exercise the technology. To be successful, with this new entry, descent, and landing system, we had to at least get some of the way down to the surface and get telemetry back, if it had failed, to understand where it failed.

ZIERLER: Did you have an opportunity to interact with Tony Spear at all and get a sense of his management style?

WALLACE: Yeah. Tony was a crazy, crazy man. Of course. We all had a chance to work with Tony and sometimes see him outside of work. I was several layers down, so there were other people who had a lot more insight into Tony, but again, another real character. A believer in this when I'm not sure there was a good reason to believe in it. He did teach me that, don't give up on motivated people. No matter how illogical the future may look, if you've got a group of motivated people, something good may come out of that. And he trusted his people. He trusted the people he put in charge. He didn't constantly second-guess them, he empowered them very much, in my opinion. He was a very strong communicator and advocate. Nobody was more excited about the mission than Tony. Tony was all-in every time. Again, that taught me something about what you have to do when you're leading these types of things.

ZIERLER: You have to be a cheerleader.

WALLACE: You have to be a cheerleader, and hopefully it's very genuine. And in Tony's case, it was. It was like it was the greatest thing on the face of the Earth. Maybe whatever he was doing at the time was for Tony, but certainly when I saw him on Pathfinder, it was the most exciting thing in his life.

ZIERLER: Where were you for launch day, and what was it like?

WALLACE: Oh, there's a story there. I was on the power system team. They don't do this anymore because of what I'm about to tell you now, but back then, the deltas had a launch tower, obviously, and nearby, they had something they called the bunker. Because at least back then, you couldn't run a lot of the ground -support equipment lines a long, long way. You couldn't get safely out of the way of the launch. You had to go down to this underground bunker to operate the ground-support equipment, like the power supplies that were turning the vehicle on and off, or the communications, or the arming switches for the pyrotechnics, things like that. There were two Mars Pathfinder people in the bunker, then another maybe 10 or 15 launch vehicle people. Maybe less. But there were only two of us from the project, and I was one of the people in the bunker because of my role on the lander side.

I was in there with a communications guy who ran the com interface. I was literally in the bunker 100 yards away from the rocket when it went up. By the time they let you out of the bunker, it was gone, so I didn't even really get a chance to see it. [Laugh] But I could feel it, and it was an exciting place to be. The very next delta launch, the rocket blew up on the pad, essentially right after liftoff. All of the stuff fell down, including big chunks of fuel and things like that, onto the bunker, and the people in there had to emergency evacuate. It was a mess. The launch site was a wreck. The bunker basically caught on fire, and everybody was smoked out. I was one launch ahead of that. [Laugh]

ZIERLER: Last question for today. To go back to the alternate reality, what would have happened. It did work, you demonstrated the technology. Was it immediately apparent at that point that it opened up a new era for Mars exploration?

WALLACE: I think there was a sense that rovers were in our future, that more of the faster, better, cheaper sort of approach was coming. I think there was a reinvigorated interest in Mars, in part because of Allan Hills 84001. There are Martian meteorites that have landed on the Earth and been here for a long time. Most of them, we can't ever find because of terrestrial processes and things like that. But some landed in the Antarctic. Planetary scientists would make treks down there and occasionally find a Martian meteorite or one that they thought was a Martian meteorite. There was one found in 1984, and I guess it was the first one found in 1984, which is how it got its name, in the Allan Hills. In the 1990s, they started to do more detailed analysis of that meteorite, and they found certain features and mineralogical deposits that looked like they could've been biotic in nature. It was a big deal. President Clinton did a press conference. This happened in, I want to say, 1996.

As a matter of fact, our new laboratory director, Laurie Leshin, was part of all this. She was doing planetary science at the time. That really stimulated a lot of interest in Mars, which had already been re-stimulated by the Mars Pathfinder activity. There was a series of missions, a lander and an orbiter, part of the faster, better, cheaper, that were launched to get to Mars in 1999. Unfortunately, both of those missions failed. There was a resetting of the program to rethink what we needed to do. But clearly, the success on Pathfinder was going to be part of the future, if there was a future for the Mars program. And it turned out there was.

ZIERLER: On that note, we'll pick up post-Pathfinder for next time.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Monday, April 11, 2022. I'm delighted to be back with Matt Wallace of JPL. Matt, it's great to be with you again. Thank you for joining me.

WALLACE: It's nice to be back talking to you again, David.

ZIERLER: We're going to pick up right after Mars Pathfinder. I want to ask, it's an interesting historical perspective. Nowadays, because of Mars Climate Orbiter and the Mars Polar Lander, there's a black mark over the NASA faster, better, cheaper approach. We inevitably orient that endeavor with these two failed missions. But right after Mars Pathfinder, as a proof of concept, was the feeling for you and JPL that faster, better, cheaper really was a successful mission coming from Washington?

WALLACE: We certainly felt like we had done a successful faster, better, cheaper mission with Mars Pathfinder and that if implemented the right way, it was a concept that had merit. For certain mission classes. I think that was one of the keys, to make sure that we understood the risk tolerance when we were going in. I also think that there were some fundamental tenets of that approach that have to be respected and fully implemented for it to be successful, and the margin is not high. There's not safety net after safety net. If you don't do those things, you can have failures. That's how I think the Pathfinder veterans felt about it.

ZIERLER: What was it about Pathfinder that worked so well within the faster, better, cheaper framework?

WALLACE: I think there were a couple advantages that Pathfinder had. One was, while there were a lot of young, somewhat inexperienced but energetic engineers like myself on the mission, we had a good mixture of experienced people as well, and we talked about some of those folks last time. I think that's just fundamentally important when you're trying to do this kind of mission. We've tried to carry to philosophy now into what we call our type-2, class-C and class-D projects at JPL. And I think we do a better job of making sure we have that mixture of graybeards and young guns. I think that's one thing. I think Pathfinder benefitted also from being done concurrently with the flagship mission at JPL. There were certain hardware systems and processes that existed to make these big, complex missions reliable and successful, and we could pick and choose. It was a smorgasbord, and we picked our favorite menu pieces that fitted into our particular mission and the unique aspects of the mission.

And I think without that, it's very hard. You see some of these startups that have never done a big, complex mission, a high-risk mission, and they struggle a lot more because they don't have a starting point from which to filter and neck down. I think that was a big advantage for us. I think there was perhaps a misperception about what faster, better, cheaper meant in terms of Mars Pathfinder for some of those follow-on missions that did fail. I think one of the tenets, the importance of which was not fully recognized was this test, test, test philosophy. If you don't have the money to do these detailed analyses upfront, or you don't have the money to make redundant systems, if you've got single-string, and you've got systems that you're pulling off the shelf, test them. Test them, test them, test them. It's pennies on the dollar. Spend the time, spend the money.

Every way you can think of to aggressively test these systems, you've got to do it. Then, you've got to test them with high fidelity. The one place Pathfinder not only didn't short-change the development but I think actually accentuated the philosophy for bigger missions was in what we call test as you fly, where we really created these environments where the spacecraft thought it was really in space, the spacecraft thought it was landing on Mars. We surrounded it with these complex, real-time simulations, and we ran those in an integrated sense. It's done at some level for GNC and other things, but since Pathfinder, that's become a big part of how we do business at JPL. And I think we were still learning that coming out of Mars Pathfinder. Those are some of the things I think work well to make Pathfinder successful.

ZIERLER: As a proof-of-concept, because Pathfinder worked so well on the science and engineering side, what pathways or portals did that open up for subsequent projects, where there was a boost of confidence that, "We did it with Pathfinder, we can go bigger and even better next time around"? What sticks out in your memory?

WALLACE: Obviously, the Rover. The Rover was really just an afterthought, an add-on onto a technology project. It was an embedded technology, technology squared. I think the confidence that we had to grow this vehicle from 12 or 13 kilograms to 175 kilograms is the fundamental place where we really took a part of that mission and amplified it in a major way. It's not unusual to double or triple in size, but to increase it by more than a factor of ten, that's pretty tough to do. And yet, we did it and successfully on Spirit and Opportunity. And I think part of it was that the principles were fundamentally the same. You need a mobility system, you need a communication system, you need a computer and hazard-avoidance. We were still within the realm of the types of developments we would do on missions like this. I think that was probably the key place.

ZIERLER: In terms of how successful Pathfinder was for you, for your recognition as a contributor to the mission, what did it mean for your career prospects at that point? What new opportunities did that open up for you?

WALLACE: Well, it meant everything to me. It was my first real mission that I took to the launchpad. And not only did I get to stay on the mission through launch but all the way through operations and the first four or five months on the surface. It was really beneficial to me because I was working from the ground up. I was doing everything from hands-on electronics and test work to running a small team of operators and interfacing with senior laboratory management. I got my first taste of interacting with the press. [Laugh] I remember right after we landed, we were all I a little bit of shock and of course ecstatic. Brian Muirhead, who was the flight system manager on Pathfinder, grabbed me and said, "Hey, you're going to go do a press conference." I was like, "What?" Nowadays, you go through media training, you practice. Back then, they just grabbed you and put you in front of the camera. It was a big boost of confidence for me that I was able to see this thing from end to end and be a substantive contributor. I think it helped me in many ways. I made the decision after Pathfinder to leave the Laboratory. I left for about three years or so to go work in industry for various reasons, some of which were personal. And I got a lot of tremendous experience that I eventually brought back to the laboratory. But I think it helped me believe I could do a good job in industry as well.

ZIERLER: What opportunities were you exploring in industry?

WALLACE: I had an opportunity to move back to the Washington DC area, where my parents, who were getting older, were. I had other family living in the area who had just moved away. I'd spent my whole career not living anywhere close to home, either under an ocean somewhere or out here in California. I kind of felt like it was an opportunity to geographically relocate back to where my parents were. It was a good thing at that point. And I also got an opportunity to work on a remote sensing satellite at a company called Orbital Sciences, which was a relatively new aerospace company. But it was getting established, so it was a great opportunity to get more breadth of experience working on that program.

ZIERLER: Being in private industry, what did you learn about the pace of engineering projects outside of a direct NASA budgetary framework? Did things move faster? Was the approval process quicker? What were some of the big distinctions as you got comfortable in this new position?

WALLACE: I think it varies a little bit with respect to what company you're in and what kind of job you're doing. If you're in one of the big, established aerospace companies, and you're working on a big defense project, for instance, it's going to be pretty similar to working on a flagship here at JPL. In that sense, it could be like that. It turned out the project I was on, though, was a relatively low-cost spacecraft bus. We were trying to adapt a previous commercial bus for a high-resolution commercial imager. There was less infrastructure, I guess, is what I'd say. You were doing more yourself, making more decisions with less oversight. And of course, the bottom line matters when you're in commercial industry. Those were all things to adapt to, but not significantly in my mind. Engineers are engineers in many ways, no matter where they're working. They want to get the right answer, the best answer. Managing engineers isn't all that different, I don't think, in industry as it is at JPL. The programmatics get different, when you're reporting to the CEO or a business development officer of some sort. And customer relations are obviously a little different. But the day-to-day getting the thing done doesn't change that much.

ZIERLER: In terms of your trajectory in management, what did it mean to go to private industry in terms of your oversight? Were you directing more people, fewer people, about the same? What was that change like?

WALLACE: I was hired in as a systems engineer in the program, but I very quickly became the program manager, which is equivalent to a project manager here at JPL. The project value was roughly half of the entire Mars Pathfinder value. Scope-wise, I was very quickly managing a lot more people and a much bigger budget. I felt like I was ready to do it, even though I really hadn't been in the industry all that long, but I had obviously a lot of management and leadership experience coming out of the Navy that other people maybe didn't. I think I was able to step in, and we got the job done, we got the bus built. We ended up waiting for the instrument, which was being delivered by a different organization. As the spacecraft went into storage, there was an opportunity to come back, and that's when I came back.

ZIERLER: Leaving JPL, did you have the perspective that you wanted to go and explore the private industry world, and see if that was worth staying in, and ultimately maybe not come back? Or did you always know you wanted to come back to JPL?

WALLACE: I didn't know. I wasn't sure. Things were pretty uncertain after Pathfinder. At that time, there was no continuous Mars program, there was no flagship mission on the books. The two failures made things even a little less certain. I wasn't sure what the future held at JPL. I think that was part of it. I enjoy a challenge, so I saw the commercial side as just a different type of challenge, a challenge where the budget, the finances, and making it commercially successful were just as important as the other things. And I think I enjoyed that part of it. And I was ready to stay, I'd gotten accepted into an executive MBA program at Wharton, and I was kind of gearing myself up for that path when the Spirit opportunity arrived. It's hard to predict these forks in the road in life. I can't say I had some big strategic plan. As I went along, I looked at what the options were and tried to make the best decision.

ZIERLER: Just so I understand the chronology correctly, for Mars Climate Orbiter and Mars Polar Lander, you were away from JPL?

WALLACE: Yes, I was.

ZIERLER: Did that register with you? Did that reverberate throughout the industry? What was that like from your perspective?

WALLACE: I certainly remember watching Polar Lander in particularly, the television coverage. I was at Orbital, and a friend of mine I've worked with for years who also came back to JPL, Dave Gruel, had gone to Orbital, and he and I had worked on Pathfinder together. We were sitting in a conference room at Orbital Sciences, and we were watching as we weren't getting the signal back from the Lander, and we knew it was going to have a very transformative effect on the future for Mars exploration. We didn't know what was going to come of it, but we knew all the people we were watching on TV, personally knew them, and it was tough to watch. It was really hard to watch somebody have to go up in front of a set of cameras, get asked hard questions, and basically talk about what looked like a failure. It was a painful, difficult thing to watch. Your friends are up there suffering through it.

ZIERLER: What about the succession of Charles Elachi after Ed Stone's leadership? Did that register with you as well? Did that sort of influence, ultimately, your thinking about perhaps returning to JPL?

WALLACE: It did, actually. I didn't know Charles, but I'd had a chance to get to know Ed a little bit, and I knew a lot of people who knew Charles. I realized it was going to be a very dynamic environment going forward. That's what Charles brings to the table, that energy, that excitement, pushing the envelope, wanting to do more, believing you can do more. That was definitely a factor. I had loved Ed Stone, too, don't get me wrong. Ed was a tremendous intellect and a really steady hand. And he believed in Pathfinder when a lot of people didn't. Hats off. What a tremendously influential part of our history. But you could tell Charles was bringing the future to the table, and that was exciting.

ZIERLER: What was the point of contact for returning? Did you reach out? Did they ask you to come back? Was it just too exciting and irresistible to you?

ZIERLER: What were some of the key values that you brought back with you from private industry, both in terms of budgets, to the bottom line, to just being in a more lean environment? What was beneficial as you came back to JPL?

WALLACE: I would say some of the experience I had in industry was actually geared more towards understanding how JPL is different and stronger. I think I was able to accentuate those strengths in some of the things I did after I came back. Different industry players do it differently, but we do things a certain way at JPL that's a little different, and until I left and saw the other model, I don't think I appreciated how powerful some of those things were. For instance, we take developers, and we go what's called cradle to grave. We start them in the formulation, we bring them all the way through development, they're part of our integration and test teams, and they operate the vehicle. They go all the way from the beginning to the end.

That provides people with very powerful insight into the important things in a mission and a design. I think that's one of the things, a recognition of that. When I staffed up the ATLO team on MER, I didn't go looking for people who had just done tests their whole lives, I looked for people coming out of the project who understood unique parts of the spacecraft or coming out of subsystem developments. I think that was one thing I could point to. Also, JPL has a tremendous amount of infrastructure that doesn't exist in industry, and I think being able to leverage more of that, understanding that type of thing, was helpful for me when I came back.

ZIERLER: It's the counterfactual question, you can't know what would've happened had you stayed, but is your sense that when you came back to JPL, you were at a higher level as a result of being in private industry, that you had leapfrogged one or two rungs on the ladder, to some extent?

WALLACE: Oh, definitely. No question. People stay at JPL their entire careers, typically. It's unusual to do anything else, so there's plenty of time to move through the ranks. I came to JPL, as I mentioned, eight years behind a lot of other people. I started a little late. To be able to go out into industry and get the kind of budgetary and project management experience that I immediately jumped to was really helpful. I'm pretty certain that had I stayed, I would not have had an opportunity to become the ATLO manager, then eventually lead from that to other bigger jobs very quickly. I think it checked a lot of boxes for me and was helpful in that sense. It wasn't something I had premeditatedly done, but it did work out from a career perspective.

ZIERLER: Coming back, what were your responsibilities in that first position?

WALLACE: My job was to put a plan together that got the two Rovers ready for the 2003 launch windows. It really didn't look possible. It just was so compressed. Nobody had ever seen anything like it. Still, to this day, there's this curve that somebody created of spacecraft complexity on one axis and development duration on the other. You can draw a line, then you put the dots for all the different spacecraft. There were, I don't know, 30 dots on there. And the mission that were failed were red. And you could draw a line through that data, and everything that fell below the line was red. Everything that was above was successful, which implies that for a certain level of complexity, you need a certain amount of development time, which makes sense. Spirit and Opportunity were way, way below the line. It would've defied the laws of the universe to get these things launched and successfully. But one of the things I realized was, we had something that other missions didn't have. Maybe a couple things. One, we had a team that had done a faster, better, cheaper mission. I think that was instrumental. But more importantly, we had two vehicles. That was a factor that was not accounted for on that craft.

ZIERLER: The positions chief technologist and chief scientist at JPL, where so much of the work is forecasting out 10, 15 years into the future, was there a backstory going 10, 15 years into the past that you were building on that provided some guidance that made this actually possible when, in fact, it seemed impossible at the time?

WALLACE: I don't think the previous five or ten years of technology were a major factor. I think landing Pathfinder inside of airbags was obviously a big part of why we were able to do MER in the shorter duration, although we ended up changing airbags, changing landers, changing a lot of things we hoped we wouldn't have to change. But architecturally, it had what we call heritage from Mars Pathfinder. And I think that was a factor. I think the biggest factor, at least with respect to the part I was responsible for, was the previous dual missions we had done, Viking and Voyager. I ended up going back and really doing a lot of research on those two missions to try to understand how they had processed these two identical spacecraft concurrently and what that meant. One of the things I found is that it was a multiplier. It didn't take twice as long to do two spacecraft. It didn't even take the same amount of time to do one spacecraft. It took a shorter period of time because you had two spacecraft, if you did it right, if you were able to diversify. There's kind of a total scope of tests that you have to do to validate or verify a design.

If you have two test vehicles, in theory, you could do half of them on one and half of them on the other. That's not perfectly true, but if you're able to break down all of that work and understand which work is associated with the design as opposed to which testing is really there to validate things like workmanship, which can be different from vehicle to vehicle, you can construct a test program that greatly accelerates what would otherwise be possible. And that's the lightbulb that went off for me after looking back over the history of the dual spacecraft missions. I note to people that all of our dual spacecraft missions were very aggressive. Voyager, unheard of. Viking landing on another planet, it was remarkable what they were doing with the technology they had on it. In both cases, and now MER, too, the missions were successful. Many times, they did two hoping to just get one. And in each case, we got two. That, I think, is a reflection of the power of having dual vehicles when you're doing these things.

ZIERLER: If you could square the circle for me, in the way that there really wasn't a solid game plan going back five, ten years, if you were just extrapolating this forward, the engineering didn't work, well, why did it? How did it work? What were the key factors?

WALLACE: Again, we had a team that was moderately seasoned from Pathfinder, that was still young enough to believe they could do things that maybe didn't look like they'd work in a traditional sense. People were willing to try. Everybody on the project thought we should try. That was part one, I think. Part two was, we were able to leverage what was done on Pathfinder from a heritage perspective. While we had to change a number of things, I think we understood the fundamentals. One of the big challenges on these missions is that they're really three, maybe four different missions all piled into one. There's the launch mission, there's the cruise, there's the entry descent and landing, then there's the surface mission. The systems we built are not super decoupled. For instance, the computer on the Rover is used for all four of those mission phases, those submissions inside the primary mission.

The systems get super interconnected and super coupled. Understanding how this thing over here is going to knock on and affect this thing over there is a big systems engineering challenge. But if you can maintain the architectural heritage, which we did from Pathfinder into MER–we had a pretty good understanding of those dependencies and those coupling factors. I think that was a big help going into MER. Then, as I said, I think the last major factor was that we built two. I came up with this idea where I would start the first vehicle, and then three months or so later, I would start the assembly and tests on the second vehicle.

Well, things were so late that the first vehicle started three months late or something like that, then the second vehicle started almost six months after the first vehicle. But then, I leapfrogged the second vehicle in front of the first one, and it became the first launch. On the second vehicle, we were shipping to the Cape within three and a half or four months of when we really started assembling the vehicle, which is crazy. Normally, it's 16 or 18 months. But we were able to do that because we had the other unit here that we could continue testing while we started processing the vehicle down at Kennedy Space Center. On that first launch, we probably cut out 10, 11 months, which is a third of the development time on the project. And that was an enormously important factor, getting it to the pad on time.

ZIERLER: To get a sense of the hierarchy, the organizational structure at this point, who are your peers? Who are the people at the same level but in different directorates than you are who are important to the mission?

WALLACE: I was the ATLO manager, so my peers were really the subsystem managers. For instance, the person who managed the telecommunications subsystem development, or the person who would develop the mechanical aspects, or the person who did the power subsystem, or the avionics. They were my peers. I worked for the flight system manager, sometimes called the spacecraft manager. Then, he, in this case, worked for the project manager. I was coordinating and getting visibility into all of the other discipline development cycles, schedules, challenges, technical problems, and everything else from my peer group, if you will, then coordinating schedules, delivery cycles, budgets, things like that, through the flight system manager.

ZIERLER: Who do you report to? Who's your direct report?

WALLACE: I reported directly to the flight system manager. It was Richard Cook.

ZIERLER: The people who were under you, what are they doing? What does the day-to-day look like for them?

ZIERLER: Do you have a specific memory of the initial reaction of, "How the heck are we going to get this done?" to, "We're actually on the path to making this happen?" Is there a moment, a month, a year when that changes, or you start to feel like this is actually all going to work out? Or is it only after the fact that you can look back and make that assessment?

WALLACE: I think the way it went was, there was this sort of initial, "It's not going to ever happen. We can't launch in 2003. We're going to push to 2005." There was a whole bunch of problems with that, but nonetheless. It was kind of this chaotic quest. Then, when we started to put together the details, and I started to look at the ways of structuring the assembly and tests, given that we had two vehicles, I remember we gathered at Rob Manning's house with a group of the senior managers and my leads. We sat down, we had some pizza and beer, and I said, "We have to find six to eight months, or else we're not going to make it." They all said, "You don't need six to eight months." I said, "No, we need six to eight months. I've been looking back at these dual-spacecraft missions, and I've been thinking about what tests we have to do on one versus both vehicles. And I've come up with these things."

And we walked away from that three- or four-hour conversation, I remember, feeling like, "Hey, wait a second, this might actually work." I think as my leadership team started to really absorb the plan, and look at the flexibility in the plan, and understand how much margin we could build for late deliveries, because we needed a lot of margin, they started to believe it could get done. Then, of course, you run into trouble along the way, and you have doubts again. [Laugh] But nobody stopped running hard. I would say when we got the first vehicle ready to ship to the Cape, which was not long before launch, maybe four and a half months, that was really when we said, "Hey, it looks like we're going to make this thing."

ZIERLER: It's such an intangible, but Charles Elachi and the axiom, "Dare mighty things," how does that ethos, which works so well in speeches and in the media, translate to the day-to-day, where you can actually see or feel that this is JPL's mission, they do things that no one else does, and it actually gets you to launch day, it actually gets you on the pathway to success?

WALLACE: I'm not sure it's something that you consciously think about every day. I think there are moments that you experience in your career, obviously things like landing day, or the first time you see a spacecraft fully assembled, or you put a really forward-thinking proposal or instrument opportunity together, and it gets selected, I think you go through those moments in time where it's just in your face. You just know you're part of it. And I think that sustains you through the day-to-day, which is work. There are people unhappy with you, there are milestones you're missing, there are things you're worried about making a mistake on, there's money you don't have. You don't come to JPL, and everything's a bed of roses, and the angels are singing every day behind you. That's just not how it is. It's very hard work.

But I think at the end of the day when you go home, a lot of times, or when your mom calls you up and says, "Hey, I saw something about your mission," or you come home, and your kid brings their science book home from 7th grade, and on the cover is a picture of the Rover you helped build, there are those events, and they just kind of become part of an understanding that you have subconsciously or whatever of the importance of what you're doing and how lucky you are to be able to do it. And I think the, "Dare mighty things"–there are certain times when you're really challenged with something big and unexpected, and it might be just putting this really technically challenging proposal together, where it comes into play very, very directly, or you may be facing something like we did on Perseverance, where you're just shipping to the Cape, and you have a global pandemic hit you in the face. And you know that's one of those moments in your life where you can't just work hard, you can't just be diligent, you can't just keep your nose to the grindstone, you can't be good. You have to really elevate your game to great. You've got to be great. And that's when those words really, I think, make a difference.

ZIERLER: For both good and bad, how does the legacy of the failures in the late 1990s loom for MER?

WALLACE: There was a lot of suspicion that we were going to make the same mistake, that the philosophy was fundamentally flawed. We honestly stopped using the words just because they kind of came with a certain stigma, maybe, at some level. But I do think MER was done very much in the faster, better, cheaper mentality. I think there was a lot of concern at the agency. I think there was even more concern among Laboratory leadership. Laboratory leadership was primarily the old hands, the people who had worked Cassini and Galileo. They were flagship-mentality leaders. Some of them never thought Pathfinder was going to work, and they thought we got lucky, and honestly, I think some believed that the failures were inevitable, that they were going to come because that particular model just wasn't going to work. I think we got more oversight. One of the challenges on Spirit and Opportunity was to satisfy that group of individuals. Some were on our review boards, some were part of our sponsors and headquarters management structure, and frankly, a lot of them were just part of the JPL infrastructure.

I think we had to explain what we were doing, why we were doing it, and why it was OK a lot more. And I think, in many ways, it was useful because I think there were parts of what we did on Pathfinder that could be improved. There were things we didn't do that maybe we should've. And certainly, MER was not $175 million, it was$800 million, and it was the beginning of a longer-term program. There was more verticality in making sure it was successful. I think the downside was, the development schedule was so compressed and short. There was just no way we were going to do a flagship-type of development cycle. We had to balance all of that. I feel like we did. The thing I ended up telling a lot of the lab management was, "We're not skipping many steps, we're just doing them a lot faster." I think that was true, and I think that was part of the key to the success.

ZIERLER: You mentioned faster. What about the cheaper part? What was the budgetary environment for MER?

WALLACE: It was nowhere near as constrained as Pathfinder. We had more flexibility. We still, primarily because of the development schedule, had to use some commercial components, we still had to push certain sets of tests we would normally do at a lower level to a higher level of assembly and aggregate tests together. But most of that was done for schedule. And honestly, the schedule was so fast, we couldn't spend a lot of money. That really constrained it. I would get questions about overrunning, but first of all, I didn't overrun, and second of all, it was really more about the schedule. And people had recognized that if we hit the '03 launch date, there was only so much money we were going to spend.

ZIERLER: Where were you on launch day?

WALLACE: On Spirit and Opportunity, I was down at Kennedy Space Center, and I was in the control room with the Assembly, Tests, and Launch Operations Team. I was there with my systems, electrical, and mechanical leadership. Our job was to control the spacecraft right up until the launch vehicle was ignited. Then, after that, there was really no communications with the spacecraft. Eventually, we separated from the launch vehicle and turned on the radio. That's when the JPL operations team took over. I was busy right up until launch.

ZIERLER: In terms of your responsibilities, your overall management, what can be gleaned from the fact that you're at the Cape and not at JPL? What's the significance there?

WALLACE: My job was really to get it to a point where it could be launched and make sure we didn't make any mistakes. If there was an anomaly, I had to interact with the team at Kennedy. They were operating the spacecraft at that point. My job was to step in and provide the senior leadership in the case of an anomaly. Once you get into the last couple days, it's primarily a launch vehicle process and a Kennedy process until the last few hours. Then, you're turning on systems, doing final checkouts. You inevitably get something you don't expect on one of the telemetry channels, and you have to caucus and decide if it's OK to launch. You make that recommendation to the project manager, flight system manager, things like that. That was my job.

ZIERLER: Any real dramatic, hold-your-breath moments at the moment of launch?

WALLACE: There usually are, but I can't remember any right now on Spirit and Opportunity. There were some difficult things that happened at the Cape in the months running up to launch. We found a damaged board that we had to take out of the spacecraft, ship it back, get that cycled and back in. We had a blown fuse in the middle of the spacecraft, and we had to go through almost a month worth of analysis to determine whether it was OK to launch with that fuse having blown. It would've been very tough to take the thing apart, get it back together. It did delay us into that first launch window, trying to deal with that particular anomaly, so the first launch window was a little late in opening. You always worry about storms and things like that, but we got through that. I do not remember a problem on the pad.

ZIERLER: At that point, you almost let go, it's a Zen kind of moment?

WALLACE: Well, I have to pay attention, and I have to give my go for launch, and that's an exciting thing to do. That's something you remember. Then, the launch vehicle ignites. We all ran outside to try to catch a glimpse of the launch vehicle going up above the trees. The operations facility is actually, I don't know, six or seven miles away maybe. Then, you're holding your breath, hoping that the spacecraft survives the launch, turns on the radio, and starts talking to you. That's called initial acquisition, and that's always exciting. Spirit and Opportunity were pretty well-behaved. Curiosity was good, too. Perseverance was a nightmare on the pad, and that's a whole different story.

ZIERLER: We'll get there. [Laugh] Just in terms of conveying to an audience that doesn't understand how these things work, when you give the go, what are you looking for? What are all of the checks you have to make sure are working before you give that command?

WALLACE: At that point, the team has validated and verified thousands of telemetry channels are all what they should be or acceptable, and there's a hierarchy of, "OK, guidance, navigation, and control is ready," and they report to the test conductor, then the test conductor will report to the systems lead, and the systems lead will report to me. There are multiple chains all coming up to me, as far as ATLO goes, and then there are other chains reporting up to the project manager as well. I was sort of at the top of one of those chains. Really, what I'm looking for is that my team thinks the vehicle is ready. If they're giving me the go, and I haven't seen anything that gives me pause, I'm going to vote go.

ZIERLER: The hold-your-breath moment, as soon as the launch happens, and you're making sure that it was successful, when is the next dramatic moment? Is it at landing? Is it when it leaves the Earth's gravitational pull? What are the other dramatic moments before actually landing on Mars?

WALLACE: There's the initial acquisition that happens within half an hour or so after launch. That's a big, big event. We do trajectory correction maneuvers on our way to Mars. We have to adjust where the spacecraft is so that we arrive at exactly the right place on Mars. That first trajectory correction maneuver where we're firing up the propulsion system, exercising all those algorithms, that's a pretty big deal. Then, there's a whole sequence of entry descent and landing events that happen that starts days beforehand, where you're starting to check out the systems you need to land, your radars, your IMUs, your landing systems, all of that, to make sure they work. Those are all pretty big events. But really, the heart-stopping event is entry descent and landing, and that starts when you separate the pre-cage, really, and get ready to enter the outer atmosphere. That's all happening autonomously. All you can do is sit there and watch the telemetry come back. It's terrifying. [Laugh]

ZIERLER: Last question for today. In what ways were the scientific objectives of MER different obviously than Pathfinder, and from the engineering perspective, how did the new challenges and opportunities for new scientific missions and objectives for MER change your mission?

WALLACE: Pathfinder, as I said before, was really a technology demonstration mission. We got some decent science, but it was very minor. Spirit and Opportunity were designed to be scientific robots, and they carried a suite of instruments. I think that was a new experience for me. It turns out that there had been a plan after the '99 missions, which as you noted, both failed, to try to land an '01 mission. That mission was scrapped after the failures, but the instrument suite still existed. It was called the Athena Science Instrument Suite. Our job was to adapt that science instrument suite, which was on a fixed-legged lander, for a rover, then to get it integrated, tested, and make sure it was going to work the way we wanted it to work. I think, for me personally, once we got to operations, it changed the complexion of operations. MER was meant to just be a three-month mission.

That's all we thought we were going to get. We thought the solar arrays were going to be covered with dust, so maybe we'd get four months, five if we were really lucky. Everything we did on the surface was geared toward getting the science and super fast. It wasn't until later that were realized that the arrays were getting cleaned by these swirling dust devils. And as you know, Spirit lasted six years, and Opportunity lasted 14 years. Ultimately, we had to very much change how we were thinking about the surface mission and how to do it. The change in the mission lifetime affected us. I was on operations for a while, I was the Opportunity operations lead, so I remember crawling up to the edge of the Endurance Crater, and the Rover was basically looking over the edge. It was very steep. The project scientist, Steve Squyres, who I'd gotten to know very well, and I had a good relationship with, said, "We need to go down in there. That's just too exciting." I was like, "We're not going down in there, Steve. We're never going to get out."

I think part of that thinking was understanding that this could be a long-life science mission now, not just something we were going to cycle through very quickly. Steve just kept saying, "We've got to go in there. The stratigraphy you could get by looking at the layering as you go down"–his mouth was watering at the science. I said, "OK." We want up to the Mars yard, we sent scientists out to try to get rocks that mimicked the Mars rocks, and we'd dust them lightly. We tried every different combination to try to figure out the best way to climb back up, and we figured out we could crab our way back out if we really needed to. Eventually, we drove down into the crater. Those were the kinds of science decisions we were trading off once we got to the surface. But the mission was really geared towards understanding the history of water on the surface and confirming the fact that there was liquid water on the surface, which it did in spectacular ways, particularly at Meridiani, and that was particularly exciting to watch, the science team looking at all these new things and explaining to us what they meant from a geological history perspective.

ZIERLER: On that note, we'll pick up next time from the MER landing, and we'll go from there.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Monday, April 25, 2022. I'm delighted to be back with Matt Wallace of JPL. Matt, it's good to be with you again.

WALLACE: Thank you. It's good to continue this discussion.

ZIERLER: We're going to pick up right where we left off last time. We had a great detailed discussion about what it was like at the launch, some of the dramatic moments. Now, we have landed on Mars. Right at that moment, what's that like for you and your team? What's happening right now?

WALLACE: Landing on Mars is a unique experience. It's terrifying. No matter what anybody tells you, the most immediate reaction when you land on Mars is immense relief. You know that you've put a lot of effort into the project, you know that you've done everything you could to make sure it was going to work, you know you've got a strong team, you know that you've tried to follow the processes, best practices, and guidelines that have built up over the decades at JPL, but there are still a lot of unknowns when you're going through that cycle. Mars still has aspects of it that we don't fully understand, and the complexity of the mission, all of these missions, is such that it really is impossible to get above a certain probability of success, in my opinion. There's a ceiling you can't get above. Despite all the confidence you have in the team and work you've done, it's just relief. In the case of Spirit and Opportunity, just landing was not enough.

We had to get the airbags deflated, then we had to pull them in, then we had to open up the petals, which the rovers were mounted on, then the rovers themselves had to open up some panels to get solar power. They were all folded up into a pyramid-shaped thing to fit inside this pyramidal lander. There was a series of things that had to happen autonomously on the surface, and it had to go right to be able to continue safely on the surface. That's all happening pretty much autonomously. The vehicle was downlinking its status at the end of the day. We landed late in the day. Right before it goes it sleep, it says, "Hey, I'm power-positive. I've got enough energy. Nothing seems broken. Things are warm enough."

And it enters into the night, we lose contact with it, and we wait until the next morning to start the mission. Really, the whole first couple weeks were designed just to get the vehicle commissioned. We had to essentially break the mobility system and crush it down to fit inside this lander, so we had to essentially un-crush it. We had to stand it up and put things in their right positions for the surface mission. We had to look around, make sure there was a safe place to egress off the lander and onto the surface, then we had to go through that entire cycle. And that's a pretty complex cycle. For Spirit, it took quite a while. Opportunity, it went a little quicker. Less than a week for Opportunity to get off the platform.

ZIERLER: At the moment of landing, I wonder if you can convey the chain of command. Who's transmitting information to you, what are you doing with it, and what are you kicking up the ladder to however high it goes, the director of JPL or below him?

WALLACE: On Opportunity, I was the mission manager, so I was conveying what we knew about the health of the vehicle as it came in. During landing itself, for those two missions, we only got a limited amount of data on the vehicle. Once we got onto the surface, and stopped bouncing and rolling inside the airbags, and deflated the airbags, we were able to get more data off one of the antennas on the lander. But still, the data's very limited. It's really just basic health information. We know if the lander's on its side or right side up, we know if the airbags have been retracted, we know if the petals have opened or not. It's basic health and safety data. And the management is really sitting there with us. We're talking to them, at least pre-COVID days, Perseverance was a little different, but during Spirit, Opportunity, and Curiosity, we were face-to-face telling them what we were hearing so they were aware of it in real time.

ZIERLER: What are the stakes for JPL? Once the landing is a success, what does that mean for your group immediately, JPL, the Caltech-JPL relationship, and ultimately, NASA? What does the success mean in those concentric circles, moving out, just what a success this was and what it might mean for future Mars exploration?

WALLACE: For the group that designed, built, and tested the vehicle, it's just immensely gratifying and relieving to know that the system you developed and tested worked the way it was supposed to work. It's unlike any feeling I've ever had. I think it's one of the reasons I kept doing it and stayed in the business. That moment stays with you pretty much your entire career because it's the ultimate validation of a lot of hard work. As engineers, we tend to do our work in a fairly insular way with our peers or organizations. To some degree, we get some visibility with our sponsors. But when you land, you get visibility everywhere. Your family's watching, the country's watching, the press is watching. It's gratifying in that sense, too, that there's that much interest in what you do, that people think it's that valuable and exciting. But it's just very gratifying from a professional perspective to get that feedback.

To the program, it's critical. These missions were designed as stepping stones. To get to the next level, the more advanced set of science questions you want to answer, you have to take this step. To get to the next one, you have to take the next step. And if you miss a step, there's a very high probability that the program will collapse in upon itself, and you can't just cycle back and recover. We did try to architect the program in a way that made it more likely to be successful. We didn't try to overreach, either scientifically or from an engineering perspective, and I think that's a good thing. But it's an existential event for the program itself. Then, I think, at the agency and broader construct government level, it's a demonstration that we're capable of doing these things, we can do things other countries and organizations can't do.

In that sense, it's very meaningful as a vote of confidence and in the country's ability to do really challenging, technical work of all sorts. It's just representative of that. Then, interestingly, there's an excitement factor when you go out into the public. And there are people very interested in science as well. But I think the most meaningful impact in the broader public is really what it means for the kids who are interested in science, technology, engineering, and math, which later became STEM. I think it's very impactful in that sense, building a base of capability to not only do space missions, but other technical work.

ZIERLER: We talked a lot about the interface between the scientists and engineers prior to launch. During launch, with the landing, what are some of the changes in that relationship? What do the scientists need from the engineers, and what do the engineers need from the scientists once the rover is operational?

WALLACE: In many ways, the leadership flips a little bit once you get into the operational mission. There's a commissioning period, where you've got to take care of getting everything up and running and evaluated, make sure the system's healthy. But you get past that, and it's really about where the scientists want to go with the rover mission. You do remote sensing, mostly with cameras, but sometimes remote sensing spectrometers and things like that. They look for features in the area we landed, sometimes in the orbital imagery, sometimes in the imagery that comes back from the rover itself. And they look for the most interesting place to go. They start really calling the shots on the high-level set of plans you're executing against. I think it's something the scientists have been waiting a long time for sometimes, but it's also good for the engineering team. A lot of the engineering team, at that point, have a chance to take a little bit of a breather, and that's certainly true for the management, and really start to learn more about the details of the science mission. And I enjoy that. A lot of the engineers enjoy doing that before they cycle back and start the development on the next one.

ZIERLER: How did your day-to-day change following the landing?

WALLACE: For one thing, you're on Mars time. Unfortunately, it's remarkable that Mars is as similar to the Earth as it is in many ways. It's not that different in size, it's got a tilt to its axis, much like we do, which gives it seasons, and it rotates, just like the Earth does. It's very close to a 24-hour rotation, but it's, like, 24 hours and 37 minutes, and that's just enough of a difference that you start walking around the Earth clock. Daytime on Mars may start out as being the daytime on the Earth, but 12 or 16 days later, daytime on Mars is in the middle of the night on Earth. You have to follow the Martian clock. People actually got watches that ran 37 minutes slower and things like that, but fundamentally, it just means that you're walking your daily schedule around the Mars clock. Which is pretty painful. Humans are not designed to have that kind of variable circadian rhythm. That's one difference.

You have to get used to getting up at 11 o'clock at night and going to work, and coming home at 10 am. I was on submarines, so I did that kind of stuff a lot. But it's still tough when you have families and stuff. That's one sort of fundamental way it's different. I think, also, when you're about to enter Mars, you have no choice. You're going to enter Mars. You're going to hit the outer atmosphere, and one way or another, you're going to go to the surface. Hopefully, successfully. Post-launch, that's pretty much true. For launch, you're going to do trajectory direction maneuvers. There aren't a lot of judgment calls. But once you're on the surface, there's more of that. We have to decide, "Are we ready to bring this capability online? Is it really ready? Or do we need to test it some more?"

Or, "Are we going to go down into that crater? Are we going to try to go over the crest of this hill? If we go over here, what kind of tilt will we have on our solar array, and how much power will we get? What if we get stuck in that sand dune?" From a management and leadership perspective, there are a lot of those things you have to start thinking about. You have to weigh the science versus the safety of the vehicle. It was an interesting trade on Spirit and Opportunity in particular because we only thought we had 90 days. When we landed Perseverance with the radioisotope generator, we knew we were going to have a long mission. But when we landed Spirit and Opportunity, we thought the dust would cover the solar arrays, and we really felt like we had to be aggressive to get the mission done. There were a lot of those kinds of conversations.

ZIERLER: How long did you stay on Mars time? What was that process like?

WALLACE: I believe on Spirit and Opportunity, we stayed the full 90 days. Because the mission was so short, we'd designed it for maximum efficiency, which you get by following the Mars clock. We had planned to stay on Mars time for 90 days, and we did. At that point, we came off and went to more block-y sort of coverage. It's a little less efficient, but it's a lot easier in terms of time management.

ZIERLER: What came next for you?

WALLACE: I stayed on Opportunity, leading it for most of the prime mission.

ZIERLER: What's the timeframe for that?

WALLACE: The 90 Martian days. We landed in February of 2004, so through most of the spring, I guess, I was running Opportunity. Then, I moved over to start helping on this big new rover we were conceptualizing. At the time, it was called the Mars Smart Lander. It ultimately became Curiosity.

ZIERLER: The sequencing of this, the Smart Lander that would ultimately become Curiosity, how much of it is contingent on what's happening with Spirit and Opportunity? In other words, you don't really think deeply about this until we see how MER plays out? Or is there a backstory that happened regardless of what happens in 2004?

WALLACE: It was concept work that was based on the something that at least one of Spirit and Opportunity would be successful and that the mission objective, which was to demonstrate with confidence that there had been liquid surface water on Mars at one point in its geological history. That was the key question those missions were attempting to prove. There was concept work, assuming that the mission would be successful and that scientifically, we'd be able to demonstrate that. And people were starting to think, "What's the next science question we want to answer?" Before we solicited the payload for Curiosity, we actually had time to get some results back from the two smaller vehicles, and that helped inform the instruments we ultimately took on Curiosity. There's a dependency, an actual progression. They dovetail in a number of different ways.

ZIERLER: What did that mean for you? Did you volunteer for Curiosity? Was it obvious this would be the next stage for you? How did that work out?

WALLACE: I was pretty convinced I wanted to do another Mars mission. There was a mission spinning up at Lockheed Martin called Phoenix, which was a legged lander, and they were looking for some help as well. I was talking to that team. Then, I was talking to the Curiosity team, the MSL team, but MSL was a much more aggressive and challenging mission, and it was going to be done what we call in-house. We were going to do a lot of the design work, and a fair amount of the build, and all the integration testing at JPL. That made it more interesting to me. That's the way I went.

ZIERLER: What were the initial discussions around what would become Curiosity? How did it get started? Is it the drawing board? Are you going to the scientists first to see what they want? How does it all get started?

WALLACE: Basically, because Mars had an overarching program, which is not true for a lot of targets, that program was able to start some of the technology work we needed to do a more aggressive and capable mission that would take the next step in the science question. The question was, fundamentally, "Was Mars ever habitable?" We know there was liquid surface water. Great. But do you need more than just that to support the formation of life? The question on the table next was, "Was it ever habitable? Are there potentially even some signs of bio-signatures from a long time ago?" And to answer those questions, we needed much more sophisticated instruments. The instruments on Spirit and Opportunity were under five kilograms. The instrument suite on Curiosity was, I want to say, 90- or 100-plus kilograms. Almost 20 times more by mass of a capable science platform.

And to carry that much science, we needed a much bigger and more expensive rover. As the size and complexity of the rover grows, the risk tolerance starts to drop a little bit. When you're spending billions of dollars instead of hundreds of millions, you want to make sure it's going to work as much as you can. Not only do you have these more complex instrument suites and a bigger overall rover, but you also add in things like redundancy. You bring two radios or computers in case one fails, and that grows it even more. When I got to MSL in the formulation phase, it was going through this growth period. And we were trying to figure out as a group how we were going to land it because we knew at some point, the airbags just were not going to scale for something the size we were talking about.

ZIERLER: What was so interesting to you personally about Curiosity? How was it new work and not MER part two?

WALLACE: It was a generational change in capabilities from an engineering perspective. Instead of having a few months on the surface, we were talking about two years, one Mars year, on the surface. Instead of just going to an equatorial region, where you know it's going to reasonably warm, we were talking about going to higher latitudes, significantly higher latitudes, initially. Instead of carrying these small instrument suites, we were going to carry much more capable analytical instruments. Then, like I said, trying to figure out how to land something of this size on the surface of Mars was a big engineering challenge. Engineers love challenges, and I may love them even more than most engineers. When somebody says, "You can't do it," I'm like, "Yeah, I want to try that." And there's no better place to do that than JPL because there's a whole group of people ready to go along with you and give it a shot. I think, also, I was very attracted to the position I was offered. I was offered the flight system manager job. The flight system manager is responsible for basically everything that flies except for the payload, the science instrument suite. It's 65% of the project by budget, so it was a big management challenge. Just another challenge. [Laugh]

ZIERLER: When you say bigger, let's put some stats to that. How much bigger is it, both by weight and size?

WALLACE: Spirit and Opportunity were about 170 kilograms, I think 350 or 380 pounds. Curiosity was one metric ton or so, like, 2,200 pounds. A factor of six probably larger in mass. Whereas Spirit and Opportunity are, at best, small go-kart-sized vehicles, Curiosity was much bigger, the size of a small car. When Curiosity put its mast all the way up, the top of the mast would've been eye-to-eye with Shaquille O'Neal. And the budget grew by about the same amount. It's a much larger vehicle. The motors on Spirit and Opportunity were maybe on the order of an amp. The big motors on Curiosity were pulling, like, 10 amps. It's a big vehicle.

ZIERLER: Obviously, a bigger vehicle is a bigger engineering challenge, but in what ways? Why is it a bigger engineering challenge?

WALLACE: The size became part of the challenge. Not all of it. But let's say you're building a gearbox. When that gearbox only has to pull a small vehicle along, it's a much easier set of gears to design. You don't need as many stages, you don't have to deal with as much pressure on the faces of the gear face. I'm just picking one example here. But when you're pulling a one-metric-ton vehicle around, it's a much more complex gearbox, for instance. You need a lot more gearing, you need to design for higher loads, and also, in the case of Curiosity, that gearbox had to operate at much lower temperatures. We weren't just going for the three summer months that Spirit and Opportunity were designed for.

We were going for a year-round mission and higher latitudes. It'd be like going to Greenland instead of Florida. And that was true not just for mechanical systems, but electrical systems as well. We were going to see big temperature swings. And those temperature swings put stress in the solder joints, create problems for batteries, etc. The environment was more challenging, the size was more challenging, the amount of hardware that had to be supported. We had many more instruments, so you need more interface electronics. They had different flavors because this instrument's different from that instrument. Then, you need the right software that controls those instruments. By having five times as many instruments, you've got five times the complexity in your software. Then, just getting the system onto the surface of Mars–both Pathfinder and Spirit and Opportunity were primarily mechanical delivery systems.

They had parachutes, they had aeroshells, they had airbags, and they had petals that were protecting the rover that had to open up. Those were all mechanical systems driven by timers and things like that. It was very mechanically oriented. Curiosity was too big to do the mechanical system. We needed rockets, we needed guidance and control, we needed a real-time control loop controlling our engines, we needed a much bigger, more complex parachute. We needed to guide the vehicle to where we wanted to go this time because it didn't have the capability to land anywhere. It was just, in every aspect you can imagine, 5 to 10 times more complicated.

ZIERLER: Was the increased size simply a function of the expanded science objectives of Curiosity? In other words, was it also an engineering challenge in and of itself to demonstrate that we could get a larger rover on the planet?

WALLACE: I think it was driven by the science. In the end, the capability to deliver that much payload was a great thing to develop, and we reused it, as it probably went on Perseverance. But really, it was driven by the science. I think we were more confident than we should've been that we knew how to scale up that much. We didn't realize how much of a challenge it would be and how much more complex the vehicle was going to be when we were in formulation. In retrospect, we had never seen anything like that. It was unquestionably at that point the most complex thing JPL had ever done. It was very hard, when we were in the initial stages of the conceptual frame workout, to understand how difficult those details were going to become from an implementation perspective. But it was driven almost entirely by the science. Not just the science to carry more instrumentation, but to go to a very specific place. We had to guide the vehicle to that place. And to go to a wider latitude, where the temperature ranges were much more severe. Then, to last for a much longer time on the surface. But those fundamentally were all science-driven.

ZIERLER: Nowadays, you hear people like Elon Musk talking about establishing a settlement on Mars. From 2004 and MER, we've already established we're capable of putting a rover on Mars. Was part of it with Curiosity just seeing how big the payload could be in and of itself, independent of the science?

WALLACE: It was not. At least, that's not what I was thinking of. We were responding to the science. I think you could argue there's a little interaction there. We could've turned around to the scientists and said, "I'm sorry, it's too big a step. We can't go that far." And they would've broken down the science objectives into smaller chunks. But we thought we could make that leap. We didn't think we needed an intervening point. In that sense, maybe there was some interaction there. But fundamentally, we wanted to put an analytical instrument on the surface of Mars, and we wanted it to be there for a long time, and we wanted it to go to a very specific place that we chose. And that's what drove it.

ZIERLER: Are the science objectives an internal JPL effort? In other words, when we're putting together the science objectives, and you have to translate this into the engineering success that actually makes it happen, how far and wide are those science objectives coming from?

WALLACE: It is partly JPL-driven in that we have a lot of scientists who work here who are part of the Mars community. But there are a lot more scientists who are part of the Mars community who don't work here. The science choices and objectives are driven by that community, really, and that's done with a couple different mechanisms. Once every 10 years, there's a planetary science decadal survey, where they bring representatives of the planetary science community together, and over a pretty long period of time, they look at the state of knowledge for the solar system, and they assess the highest priority science for the solar system, and they lay out prioritized objectives. And the mission set we do over the next 10 years, to a large degree, is directed by that guidance we get. It's interpreted along the way by different science groups. In the case of Mars, there's a Mars Exploration Program Analysis Group called MEPAG that meets a couple times a year. In the Mars community, there's the NASA Academy of Sciences, there are different science organizations that influence the NASA mission objectives, selection, and budget. It's not something where we get together and say, "This looks like a mission we can do from an engineering perspective. Who wants to do science?" It works in the other way.

ZIERLER: What were some of the obvious engineering challenges, not just as a result of the rover being as big as it was, but all of the different enhanced science objectives for Curiosity?

WALLACE: I've talked about some of the engineering challenges, the size it grew to because of the instruments and how that created a challenge in the landing system. Probably the most definitive new challenge we had in that realm was the need to sample. The analytical instrument on the rover in particular wanted powdered samples of rocks. We could dump in regolith or soil samples, but really, the most interesting samples came from the rocks themselves for various reasons. We had to figure out a way to collect powdered samples, then transfer them into the science instruments on the body of the vehicle, and that resulted in a big rotary percussive drill and this powder sample transfer system, which doesn't sound as hard as it really is. Very hard to do autonomously. That was a big mechanism challenge. The arm was big, the drill was big, managing the powder was challenging. I would say that was one of the big challenges.

ZIERLER: What were some of the options for power systems for curiosity?

WALLACE: There are really only two on Mars. One is to go solar, and the other is to use radioisotopes. In the US, radioisotopes is a plutonium dioxide powder that is pressed and encased inside an iridium clad. Then, you have several of these pellets, we call them, and you put them together inside these big graphite blocks. They create heat by decay. A lot of people get confused. "It's nuclear power like the nuclear power plant down the coast. Could there be a release? Or is it like a bomb?" Those are different things. Weapons are fission and fusion, and the reactors we have are fission processes. This is just decay. It's a very stable way to create heat. It doesn't create anywhere near as much heat as a reactor system or as much energy as a weapon, obviously, but it creates low-level heat.

We then use a conversion technology called thermoelectrics, which basically puts two dissimilar materials close to one another, and if one material is cold and one material is next to the hot heat source, you get a potential across it, and you get current. It's called a Peltier effect. We use that heat from the radioisotope and the thermoelectrics to generate a very small amount of electrical power for the vehicle. And the whole thing together, we shorten it to RTG, which stands for radioisotope thermoelectric generator, and that's what we used on Curiosity, primarily because we knew we were going to have to go to a higher latitude, where the solar panels in the wintertime would not produce enough heat to keep us warm. It would've basically frozen to death, so we went with the radioisotope generator. This type of generator has been used on many other planetary missions, Cassini, Galileo, Pluto Express. We've been using them since the 1960s.

ZIERLER: Looking ahead to what hopefully Mars Sample Return will ultimately do, were any of those ideas considered as early as when Curiosity started, and it was just too far afield at that point?

WALLACE: We knew, even when we were building Curiosity, that ultimately, the next rover would kick off the sample return campaign potentially. We were waiting for the next decadal survey to see if that was what the science community wanted to do. There was some thought along those lines. Although we weren't designing or building Curiosity to do that job, I had a pretty good sense, as we got into the development of Curiosity, that it was going to be a good candidate to do those future missions as well. But the missions are hard enough just trying to do the specific objective you have on the table, so we didn't take on any additional objectives.

ZIERLER: The science wasn't there to do Mars Sample Return prior to 2012, but what about the engineering? Whatever engineering magic is going to happen for 2028, would that have been feasible 20, 25 years ago?

WALLACE: I don't think so.

WALLACE: For one thing, the Perseverance sampling system is much more complicated even than the Curiosity sampling system. When we started Perseverance, we didn't even know how we were going to do that sampling activity. It was fundamentally different, in part because of the cleanliness requirements. We really had to bring back a pristine sample from Mars, which meant we couldn't contaminate it with anything we took to Mars, and at levels of parts per billion. That was certainly a technology we needed for Perseverance, or else that wasn't going to happen. Then, precision landing as well. Not only did we need to go to a more specific area, but we needed to avoid hazards, and for sample return, we have to land very close to where the samples are. It's a much more capable system than we had on Curiosity. That didn't exist. I would say the Mars ascent part, when you take the samples, and put them into an ascent vehicle, and launch it, trying to build a rocket that launches from another planet, that didn't exist. The rendezvous in orbit with that sample, we didn't know how we were going to do that 15 years ago. Sample Return had a lot of new technology development.

ZIERLER: The point about cleanliness, the idea is that you need a place to safely isolate the sample from everything else on the rover so that it's not contaminated?

WALLACE: Basically. You build a car at a shop, and whatever dirt's in the shop, some of it ends up on the car. You build a spacecraft in a clean room, but the term clean room is relative. It's a lot cleaner than the shop, but it's nowhere near the level of sterility you might want in an operating room, for instance, or in this case, the level of sterility and cleanliness you'd want for a sample coming back from Mars. The fundamental science for sample return is to take a sample that was formed billions of years ago and look for trace chemical signatures, again, parts per billion or trillion, very, very faint. First of all, there's not a lot of them to begin with, and second of all, over time, they break down, decay, degrade, things like that. To find those signatures–and they might be biological in nature, organic in nature.

We're surrounded by biological and organic trash. Every time you breathe, you are breathing out millions of biological organisms, cells. And we're trying to collect a sample that doesn't have a single one of those terrestrial contaminate organisms in it. Everything we have is organic. Our whole world is organic. There are organics in the air. If you clean a surface and put it in the cleanest clean room you can find, you still build up organic layers, monolayers and things like that, that would create levels of contamination there are too high for the science that we're trying to do on our sample. Figuring out how to architect a system that, one, you can clean, and two, you can keep clean enough, isolated from the rest of the vehicle, which is going to be dirty no matter what you do, then collect a sample into it and seal it, that was a big, big challenge on Perseverance.

ZIERLER: It sounds like all of the concern about contamination is avoiding a false positive. We've collected a sample, and we're all excited, but what we've done is, we've detected live we've brought to Mars and not back from Mars.

WALLACE: That's exactly right. The science is all about making sure there's no false positive. However, there's a school of thought that says there might be existing life on Mars. We don't think so. We think the life that existed on Mars was billions of years ago, and that's the focus of our science. But it's not entirely out of the question that there's a living organism on Mars. The other part of all of this is, when you bring the sample back, you have to be able to find that Martian organism, and you don't want a false negative, where you release a Martian organism into a terrestrial environment, and it's harmful in some way. Interestingly enough, we had to keep the system clean enough to both avoid false positives and false negatives.

ZIERLER: What about even bouncing it one step further, back on Mars, we contaminate life on Mars, and we killed something inadvertently? Is that a concern as well?

WALLACE: It is. The description I gave you about bringing an organism back and potentially having it released is called back-planetary protection, but we have always practiced something called forward-planetary protection, which is to make sure our spacecraft are clean enough such that when we go to Mars or another planet that's potentially habitable, another place like Europa, which we have a mission to. We don't want to take so many biological organisms with us that we could initiate a colony. That's an easier thing for us to manage than this other problem, the cleanliness of the return sample. We've gotten pretty good about cleaning the spacecraft to a point that we don't have to worry about the biological, partly because chemical contamination to Mars is not a problem, it's just biological contamination, where it could multiply or aggregate. That's the only thing you really have to worry about, which makes it a little easier.

ZIERLER: And of course, the kicker with all of this is, to this day, we still don't know if any of these concerns are justified because we don't know if there's life now or has ever been on Mars. It's a big question mark that we're protecting, essentially.

WALLACE: It is. And the science has changed a lot. The discipline grew up in the time of Viking in the 1970s, when we didn't know a lot about Mars, and our science capabilities were more rudimentary. With all the genetic capabilities and sensitivity of the analysis tools we have now, there is an argument that has been made that we don't have to worry about taking Earth microbes to Mars anymore because we can tell them apart. We're not going to contaminate the planet in some way that would be harmful from a science perspective, and by the way, as soon as a human goes to Mars, it's inevitable. We are going to bring our own living organisms with us unquestionably. We can't control it at that point anyway, so we might as well learn to distinguish the two.

ZIERLER: Last question for today, simply a timing question, maybe even before the name Curiosity was adopted. For you, when did the project go from Smart Rover, we're not sure where this is headed, to the next flagship mission for JPL? What's the timing of that?

WALLACE: It happened in about late 2005. We went through a key decision point, a delta MCR, I believe.

ZIERLER: What's MCR?

WALLACE: Mission concept review. It's basically the review that kicks off the life cycle for a project. It takes you out of pre-project and into the project. But we were actually at the next stage, I think PMSR. Anyway, late 2005, we went through a pretty major review, and we were essentially authorized to start soliciting for our instruments, and we knew at that point that the agency was serious about moving forward with the mission. At that point, we had renamed it to Mars Science Laboratory, MSL.

ZIERLER: On that point, we'll pick up for next time, when you can actually start to get building.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Monday, May 9, 2022. It's great to be back with Matt Wallace of JPL. Matt, thanks for joining me again.

WALLACE: Happy to be here. Thank you.

ZIERLER: Today, we're going to start right at the beginning of when it became MSL, the Mars Science Laboratory. At that moment, what was your title?

WALLACE: I was the Deputy Flight System Manager.

ZIERLER: And this is a theme we've touched on before, and I'm curious to what extent it changed with MSL. The interplay between the science objectives and the engineering capabilities. What aspects were driving one over the other in terms of building the rover, in terms of what the science objectives were for this portion of Mars research?

WALLACE: I think the science objectives were really driving the engineering requirements to the first order. We really wanted to take a step forward on Curiosity in the science capability, which meant a big analytical wet laboratory, if you will, and we knew that wasn't going to fit on a vehicle of the class we had built so far. In addition to that, there was interest in a much longer mission lifetime. Although Spirit and Opportunity were lasting, it was a bit of serendipity and providence that we happened to get these dust devils that would come by and clean the solar panels. To really have a long-duration mission, we needed a nuclear source, and that required a bigger vehicle. And then, there was interest in getting to a larger range of latitudes, which also required more capability, driving farther, driving over more hazardous terrain, landing in more scientifically interesting locations. That changed the entry, descent, and landing system. All those things drove the engineering requirements.

ZIERLER: Let's take a look at the MSL key missions, and first, habitability. How does the word habitability fit in within the context of discovering the possibility of current or previous life on Mars, then the question of habitability in terms of humans establishing a presence on Mars at some point in the future? How was that discussed from an engineering perspective for MSL?

WALLACE: Habitability really is referring to whether or not the planet in its past could have supported the initiation of life and sustained it through its early evolution. It was not necessarily referring to the notion of current viability of living organisms or habitability of the planet today for humans. There are certain feet-forward aspects of the Mars program that do support that, but the science on Curiosity was really geared toward the habitability of the planet previously, a long time ago.

ZIERLER: Is that to say that circa 2008, 2009, the consensus was, "There is no current life on the planet"?

WALLACE: I think the consensus among the science community is, what we call extant life, current life on the planet, would have a much more difficult time. The surface of the planet is very arid, very dry. We know water is one of the key elements of carbon-based life as we understand it. Also, Mars no longer has an active core, or at least it's not very active, so it doesn't have a magnetic field around it. It's not shielded from external radiation. The surface of the planet gets a heavy dose of radiation and has for a very long time. And that's a hazardous environment obviously for life. Any extant life on the planet, based on our previous measurements and missions, was perceived to be a much more difficult proposition and would probably have to exist deep under the surface or in some very unique circumstance that might still exist on the planet, but finding it would be very unexpected. Really, the focus for the science community was understanding the ancient habitability of the planet.

ZIERLER: What could you build on from the previous rover missions to further shed light on past habitability on Mars for Curiosity?

WALLACE: I think one of the keys, really, was from Spirit and Opportunity. We knew from those locations we landed in and with the instrumentation that we had that those areas had once had liquid surface water. I think that was one of the most important previous mission discoveries relative to taking the next step towards habitability and looking for life. That was really the key stepping stone for those missions. Of course, we had orbiters prior to those two rovers, and we had the Viking data from 20 years earlier, and Pathfinder had gotten to the surface and taken images. We could see indications of what we thought were sedimentary-type things, which could've been the byproduct of a wet environment, a lake, stream, or something like that. But really, we needed to get to the surface with a mobile capability and enough instrumentation to understand the chemical and mineralogical aspects of what we were saying that the surface of Mars had definitely been wet at one point.

ZIERLER: What did Curiosity offer from the instruments that verified what was previously thought to be the case in terms of the existence of water?

WALLACE: Curiosity landed in Gale Crater, and there was really no question from the time we landed that we were seeing chemical compositions of materials and surfaces that were consistent with a crater lake. And at various points where Curiosity went to, we could see indications of flowing water as well. Rounded rocks, for instance, instead of sharp angles, things that were smoothed out by this flowing liquid. There were a number of indications right off the bat that we had landed in a place that had once definitely been a lake. And the nice thing about Curiosity is, it kind of went beyond that with the chemistry capability it carried to look at the more subtle chemical signatures to see that there were indications of residual chemical compounds, organic signatures that would've indicated that the ancient conditions in that lake would've been conducive to life. Relatively neutral pH, for instance. It wasn't too acidic or basic. I think our project scientist at the time said, "If you had a cup of that water, you could drink it." [Laugh] Really, Curiosity brought not just the reinforcement of what we had seen at Gusev and Meridiani, but at Gale, we could also take the next step with the chemical analysis capability the mission had.

ZIERLER: What was the decision-making process? Of all places to land, why Gale? What were previous missions or findings that said that was the spot for landing?

WALLACE: There's a very long process for selecting a landing site for these things, and it's a combination of scientifically interesting characteristics, primarily determined by our orbiting spacecraft sensors, and then safety. Doesn't help to pick an interesting spot if you can't land safely at it. Gale had certain signatures from orbit, bulk signatures, biosilicates, which are clay-like signatures, which are formed in water. Those types of things were interesting. Also, you could see evidence of a flow down into the crater from an external area, so features that would indicate that water had once flowed down into the crater. Another interesting thing about Gale is that it's a crater, but in the middle, it has this mountain called Mount Sharp. And one of the things the science community loves, geologists, geochemists, is stratigraphy. If you go to the Grand Canyon, you can see the different layers of history that were deposited.

You can look back tens of thousands or millions of years, and scientists love that. Having a mountain right in the middle of a lakebed was like heaven. It had everything they wanted. Gale was very attractive from that perspective. They had the vertical stratigraphy, the history, opportunity to go up Mount Sharp, the crater lakebed, all these interesting chemical signatures. From an engineering perspective, it was a little hairy in that we were trying to hit a nice flat spot at the base of the mountain, but it's not that big a crater. If you go a little right, you could hit a crater bed. If you go a little left, you could hit the mountain. Trying to land in a nice flat spot was more challenging. For the first time ever, we had to use something called guided entry to actually safely land in Gale Crater.

ZIERLER: What is guided entry?

WALLACE: Our previous missions were what we called ballistic entries. You hit the outer atmosphere of Mars, which slows you down, the heat shield slows you down, and wherever you hit determines ultimately where you land. You slow down, you curve over, gravity takes over, open parachutes, you might get a little wind to blow you around or whatever, but you're going to go wherever your velocity and position take you from where you reached Mars to begin with. It's what we call the entry deplane, which determines exactly where you're going to land. But we can't control the spacecraft, and there's a lot of uncertainty first in where you hit Mars, and in the atmospheric conditions, the density, how fast you're going to slow down and turn over, and also the wind and things like that. What we call our landing ellipse, the uncertainty in where we land, had a very large error bar, 60 or 80 kilometers along.

You had to pick a spot that had a lot of flat surfaces and not many hazards on Mars. And that was not Gale Crater. Gale Crater was very constrained. We were hitting a postage stamp right at the base of the crater. After we entered the outer atmosphere on Curiosity, we had to guide the capsule. And that's what's called guided entry. It's a little hard to explain, but the capsule is mass-offset, so it's sort of tilted up a little bit, it's lifting. We would roll the capsule to the left, and it would fly to the left, then we'd roll it back to the right, and it'd fly to the right. We would essentially bank the entry vehicle into the landing target.

We knew where it was, we just couldn't control the vehicle in the previous missions. We knew where we wanted to go and where we were, we just couldn't control the vehicle. This is what guided entry gave us. And you're executing these things in a hypersonic condition. You're moving very, very fast. All of these things are extremely complicated. The flow problem, for instance, the computational flow dynamics that you have to do to model this correctly is really very demanding, and we had never done anything like this on Mars. Curiosity took a giant leap forward in our ability to get to these interesting sites on Mars by having this guided entry.

ZIERLER: This idea that Mars had flowing water at some point in its ancient past, how was MSL equipped to study the time scale of that process? In other words, how far back in Martian history do we go when we know there was water on the surface?

WALLACE: I think the best guess is that Mars was wet billions of years ago. We're talking two, three billion years ago. It was a long time ago, really in the early periods of the planet's formation. The ability to kind of understand that timeline, I think, comes–and keep in mind I'm not a scientist–from the ability to visually observe the stratigraphy, where those layers are relative to the different features in those layers. But there's also kind of a rudimentary age analysis capability in the analytical instrument that we have as well. But I'm probably not the right person to answer that question.

ZIERLER: But from an engineering perspective, what instruments were included on MSL to help answer that question?

WALLACE: We had an instrument called SAM, which was Sample Analysis at Mars, which was the most capable system. It gave us chemical compound analysis capabilities, different types of compounds we would look at. That was one of the capabilities we had. We had a standoff elemental spectrometer at the top of the mast, which was called ChemCam, which is a contributed element partly from the French and US. It used a laser essentially to fire at a rock, and that would create a bit of a plasma cloud from the dust and the surface material on the rock, then it could image that with the spectrometer, essentially, and get basic elemental or composition information from that. We have a neutron analysis capability. There's an instrument on the back of the vehicle that produces essentially neutrons, which penetrate the surface, which would then reflect back up and be read by the sensor, so we could get a sense of what kind of material, particularly what kind of hydraulic material might be subsurface on the vehicle. Those were some of the bigger ones.

ZIERLER: What about the climate of Mars? How was MSL built so that we'd learn new things about the Martian climate?

WALLACE: We did have an atmospheric environmental monitoring station, which was a contributed element from the Spanish, called META. It was basically a weather station, and so it had everything from dust-collection analysis, to wind speed, to pressure sensors, to temperature sensors, a radiation monitor, and that sort of thing. That would tell us more about the environment and weather on Mars.

ZIERLER: The idea that MSL could study soil, what does that mean in the current context of Mars? Past soil? Or there's actual soil on the Martian surface today?

WALLACE: There's what's called regolith on the surface of Mars, which is basically the soil. And being able to collect some of that, for instance, put it into the spectrometers on the vehicle, such as the SAM instrument, that tells you something about the composition of the soil. The soil is very often composed of the same elements the rocks are in that area, but it also has a different signature as well. Being able to collect the soil was part of the Curiosity capability.

ZIERLER: Were there advances in radar or telecommunications that made MSL a more interactive experience than previous rover missions?

WALLACE: We had a new set of UHF radios with much higher bandwidth capabilities, which would talk to the orbiters, which would then relay the data back to the Earth. That was one technology advancement for Curiosity. Curiosity had much more data volume capability than Spirit and Opportunity from that perspective. We built a new radar to land on Mars, and it was a Ka-band pulse-Doppler radar. And it was really part of what we needed to land this new delivery system, to exercise this new sky crane capability. Sky crane is carrying the rover basically down below the descent stage, and when the rover touches down, it's touching down on its wheels. And it's very important for us to understand the velocity with which we're controlling the system, not just the vertical velocity but also the horizontal velocity. This new Ka-band radar was critically important to making sure we could safely get the vehicle down onto the surface, and that was one of the key new technologies on Curiosity.

ZIERLER: Given the size of MSL, how much bigger was it than previous missions that you had to throw out the drawing board and start brand new?

WALLACE: Yeah, it's a lot bigger. We're talking about one metric ton, basically 1,000 kilograms. The previous missions, we were landing rovers that were 170 kilograms or so. It was on the order of six times larger of a surface system.

ZIERLER: Does that negate the airbag system right off the bat?

WALLACE: Yeah, the airbags for Spirit and Opportunity were about two stories high, just to give you a sense. That's to land a rover inside a lander, and that rover's only about 170 kilograms. If you could imagine scaling two airbags, which are already two stories high, by a factor of five or six for Curiosity, you understand the challenge. It was just too big a payload to land inside airbags. The other problem we had was that Curiosity was carrying a nuclear power source, which is a fundamental heat source, and packaging airbags around this thing that's quite hot was difficult from a thermoengineering perspective as well. We didn't have a good solution for that. But really, it was the fundamental size of the surface mission that just didn't allow us to scale the airbags up to the size we would've needed.

ZIERLER: What are the ways that JPL works with the DOE in handling radioactive material? Does any radioactive material come onsite to JPL? Where does that happen?

WALLACE: The Department of Energy is responsible for building the radioisotope units. They produce the fuel, they package the fuel inside a set of graphitics, basically, then they take those graphitic blocks, stack them up, and surround them with hundreds and hundreds of thermal couples, which convert the heat to small amounts of electrical energy. When you aggregate those small amounts of electrical energy, you have around 100 watts of material. The Department of Energy is responsible for producing that entire unit. Then, when it's time to integrate that unit, it goes straight to Kennedy Space Center. We never bring it to JPL. We use mass models, we use thermal simulators, and those sorts of things, but we never bring the actual RTG to JPL.

We take it straight to the Cape. And in the case of Curiosity, and Perseverance, for that matter, the RTG is really integrated up on the top of the launch vehicle. We take the rover, assemble it inside the spacecraft, which then gets mounted on top of the upper stage. The upper stage goes out to the launch site and is lifted onto the top of the launch vehicle, the booster, at what's called the vertical integration facility. Then, at the top of that integration facility, there's a platform, and we bring the RTG in on that platform and install it through the outer aeroshell and onto the rover pretty much at the pad at the integration facility for the launch vehicle. It comes in very late, and the Department of Energy's responsible for doing the build and transportation.

ZIERLER: The fact that there's no radioactive material on site at JPL, is that a security issue? Is that an administrative decision? Why not have it so that they're together at the spot where the rover is actually built?

WALLACE: I think it's a couple things. One, they do produce certain amounts of radiation. You do have to wear dosimetry and take precautions. You have to minimize the time you're working around the unit. All of that is relatively untenable when you're trying to build and test a spacecraft. It's just not very practical to integrate the RTGs or bring them here to JPL. In addition to that, we don't really need them. They're very simple interfaces. They've got four bolt holes and a power connecter. And it's pretty straightforward to simulate them in a dynamic sense, a mass sense, or a thermal sense. We can build things that look just like them and test the spacecraft without them. It's just a lot easier, when you're handling that much material, to take it straight to the launch site.

ZIERLER: On the administrative side, between cost overruns, delays, when it was actually going to be launched, was MSL more or less on track going all the way back to its conception? What were some of the significant bumps in the road?

WALLACE: MSL did not hit its original launch date. We had hoped to launch it in the 2009 opportunity, but we had a number of systems that were just not ready. It was really an enormous step forward, as I mentioned before, in capability, technology, size, and payload. The development cycle for the vehicle just took us longer than we anticipated. We moved the launch date from 2009 to 2011. You can only launch to Mars every two years because of the orbital mechanics. Unfortunately, you've got to wait 26 months for the next window, which is not very fun if you miss the first one. But that was the situation for MSL, and that was certainly the biggest bump in the road. Then, just costs associated with that as well. That slip was something we had to do to make sure the vehicle was going to work and work the way we wanted it to. It was a brand new entry, descent, and landing system, and it had much bigger, more capable, more complex mechanisms, gearboxes, motors, the power system was bigger. All the instruments were more complex. We had to make sure it was going to work, and we needed an extra two years to do that.

ZIERLER: Given these challenges, from where you sat at the time, what credit do you give Charles Elachi for just keeping everything going?

WALLACE: Charles was a steady hand through all of this. We could see that we were struggling before we even decided to move the launch window, and Charles could see it, too. He was terrific about supporting the team, talking to the stakeholders in DC, giving them the information they needed to understand the situation. He was critical during that period of time in keeping the project moving forward. You always want good, strong leaders, but you want them the most when you have trouble. [Laugh] And that was a point in time when we had technical and programmatic struggles, things to get through. Charles never lost faith in the team and our ability to get it done. I'll always appreciate that about his leadership at that time.

ZIERLER: Given the size of MSL, was the Atlas V the only game in town? Were there other options to choose from when thinking about the best launch vehicle for this mission?

WALLACE: It was a competed launch vehicle, but there are very few. In theory, I guess we could've gone on a Delta Heavy, I think, but at the time, there were very few US launch vehicle options. We needed the V, we needed at least three or four of the solids on it as well. And the Atlas V had a good track record, which is important when you have a nuclear launch. You want to understand your launch vehicle. Practically speaking, it was perhaps the obvious choice. But it was a competed assignment.

ZIERLER: Given the size, let's talk about the EDL system, entry, descent, and landing. What are some of the challenges in figuring out how to get this thing safely on the planet?

WALLACE: They never ended, really. The sky crane system was conceived of as a system that was sort of inherently robust. It architecturally gave you a lot of advantages and made you not impervious, but more capable of absorbing uncertainties, whether it was touchdown, uncertainties in the Martian conditions, surface hazards. It was a very elegant architectural option, which is why it's used for heavy lifts, cargo and things like that. It really has a lot of advantages. It separates your delivery system to the first order from the thing you're trying to deliver, your package, and that has advantages. Having said that, it was not an easy system to build. Whenever you have a new architecture, you're going to learn a lot. And we really did learn a lot building Curiosity. We had to, for the first time, understand the multi-body system during touchdown. That was something we had never tried to do before.

We had to understand everything from the separation of the power systems, for instance. When you're providing power to different instruments, sensors, and things like that, you want that power to be pretty solid and not too noisy, otherwise you can induce noise into your measurements. If you've got a radar, IMU, camera, or whatever that you're trying to use, and that power system is noisy, that's a problem. We basically created two spacecraft. We created a different noise structure, a different grounding system, between the two. And every time we turned around, there was something relatively new to learn about the sky crane system. It was a big challenge. And just the size. A 21-meter supersonic parachute was a big challenge. It was the biggest aeroshell that had ever entered any planet at 4.5 meters. The guided entry, which I mentioned before, and all the hypersonic aspects of that. The entry, descent, and landing system was a big challenge for Curiosity.

ZIERLER: How did the sky crane actually work? What was the method of propulsion that kept it above the surface of Mars itself?

WALLACE: The difference between the sky crane and a propulsive legged lander is that the propulsive legged lander comes out of the entry capsule, and it's just one monolithic unit. It's got engines and legs, and it just flies itself down to the ground. For a sky crane system, it comes out as one unit, the rover, but it's basically two systems. There's the rover, which repels down a tether, then there's the descent stage, which has all the propulsion elements, guidance, navigation, radar, and all the systems you need to kind of fly the rover down to the surface. It's the descent stage that has all the propulsion elements that provide the thrust to slow you down during the last terminal descent period of the vehicle.

It's what we call a monoprop. In other words, instead of having an oxidizer and a fuel, it just has one liquid called hydrazine, which you flow down through catalyst beds, it heats up the fluid, then it vaporizes, and that provides the thrust. It gives you the force to slow down the system. That's what we used, a monoprop hydrazine system, and we used eight big main engines to slow us down. These engines were much bigger than the previous engines we had flown on propulsive landers, and they were modeled off some of the main engines used on Viking, but we used more of them, and we had to change the design, and we had to add something called a throttle-able control valve. But that's the fundamental system that slows you down.

ZIERLER: I have this image that it's levitating above the surface. The rover lands safely, but you still have the sky crane on top. What's the method to ensure that the sky crane doesn't just fall on the rover itself? Does the rover scoot out of the way? Does the sky crane move to the side? How is that figured out?

WALLACE: Basically, the rover's on a tether, and it's about 20 feet below the descent stage. When you touch down, the descent stage can very quickly recognize that the mass of the rover has been offloaded from the system. It can see that the thrust levels needed to maintain this downward velocity have gone way down. We're throttling way back on the engines because the mass of the rover no longer needs to be supported. That triggers logic in the system that says, "Hey, I've touched down." And we're moving slowly. We have all kinds of time to recognize that signal. Propulsive landers have to recognize it very, very fast, otherwise they start bouncing and things like that.

That's one of the challenges with a propulsive monolithic lander, that you have to touch down very, very quickly. When you have this compliant tether between the two, you have basically all the time in the world. Seconds, which is a lot for a GNC system. Instead of tenths of seconds, you've got all the time in the world to see that signal. Then, we cut the tether, and the descent stage knows that the tether's been cut down at the rover, and it uses up all its remaining fuel to get as far away from the rover as it can. I think with Curiosity, it flew over a kilometer, and it eventually just impacts the surface.

ZIERLER: Then, that's just where the sky crane will live in perpetuity?

WALLACE: It's still there. [Laugh]

ZIERLER: What were some of the considerations in terms of best case scenario, how long Curiosity would be operational? What were the furthest reaches in terms of envisioning how long it would keep going?

WALLACE: We designed the system for one Mars year, which is basically two Earth years. And then, we expected it to last at least that long, but obviously, there was nothing on the vehicle that was necessarily a near-term consumable, as we say. We had tested a lot of the mechanisms to much longer periods of time, we had thermal-cycled the systems to make sure they were robust. Based on our Spirit and Opportunity experience, if it stayed healthy, we expected it to go much longer than one Mars year. And of course, we're ten years down the road, and Curiosity's still on the surface doing good science. It's got some wear and tear. The treads on the wheels got torn up earlier than expected, and that was primarily because Gale Crater, we saw a set of rocks we'd never really seen before with very sharp edges. They're like can openers, and when you torque a big wheel over the can opener, you're pressing that point of the rock into the tread, so we did start tearing holes in the treads of the wheels. Fortunately, we recognized it relatively early, before the wheels were damaged too badly, and we were able to put a number of mitigations in place to minimize that. And there have been other mechanisms that have started to wear after ten years. But all in all, Curiosity's doing pretty well.

ZIERLER: We have to take our car in every year for service. [Laugh] It's amazing what can happen in ten years. What were the treads made of? And if you had to do it over, knowing what you know now about these sharp rocks, what material would've been better?

WALLACE: They're made out of aluminum, and aluminum's perfectly fine. The problem was, with spacecraft, we're always minimizing the mass, so the thickness of the tread mattered. It's a big wheel. We don't want to make that tread any thicker than it has to be because of mass. Really, the change we made after Curiosity when we started designing Perseverance was, ultimately, we had to thicken up the tread. There are chevrons for traction, and there are points, and all of these have sharp edges. Those are what we call stress concentrations. Basically, they're places where the wheel is more vulnerable to failure because of those sharp edges we designed in. If you look at the wheels we have on Perseverance, they're all very wavy treads designed differently to avoid those places where you're concentrating pressure and force. Those were the two fundamental changes we needed to make. But we didn't have to change the material. The aluminum was fine.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Monday, June 6, 2022. I am so happy to be back with Matt Wallace of JPL. Matt, once again, it's great to be with you. Thank you for joining me.

WALLACE: Thanks for having me.

ZIERLER: If we take a look in historical perspective, just how incredible it is that Curiosity is still running strong, what do you see, now that we're sort of removed from the drama of the moment, as the engineering triumph that has allowed Curiosity to keep going after all these years?

WALLACE: I think there are probably a couple flavors of answer to that question. One is that we have built this set of standards, guidelines, and best practices here at JPL since the 1960s. The first six probes we tried to land on the moon failed. [Laugh] We've learned, through hard knocks, what we need to do to make things work. And one of the things that we think very hard about, and talk about, and measure as best we can is margin. And I think we have learned over time that you can have a lot of robustness, you can recover from a lot of sins and mistakes if you build in a system that is not inherently, for instance, limited by consumables. If you think you're going to drive 20 kilometers, we test to 60 kilometers. We put margin on top of the things that we do. If we are concerned about a certain communication system, let's say we're worried about our X-band system, we add a UHF system.

We have a fallback, what we call graceful degradation. If you can build in those kinds of margins, and our practices, design principles, and things like that encourage us to do that during the development period, then I think that adds tremendously to the robustness of the system and its ability to go far beyond what we had designed it for. I think that's part of it. I think the other part of it that's often overlooked is the ingenuity of the operations team in figuring out ways around problems we face. Curiosity is a great example of that. We got to Gale Crater, we started driving, we noticed we were putting holes in the wheels. We were driving over these types of rocks we'd never seen before, and the team understood that ultimately, if we kept going without changing something, we were going to severely limit the mission.

They came up with ways of identifying those things as hazards and driving around them as well as driving with different torque limits on the wheels so that if we were driving over these things, we wouldn't sort of can-opener those holes. And to a large extent, Curiosity figured out that if we drove backwards, it was actually much easier on the wheels. All those things got put together, developed, and implemented in operations after landing, and I think those are the types of things,, the engineering solutions, that make really make it viable for us to do these extended missions.

ZIERLER: Either officially or unofficially, what was the benchmark by which Curiosity, after it crossed that time threshold, for you and the team where Curiosity defied expectations?

WALLACE: The surface mission was defined as one Mars year, which is about 660 Mars days, which we call sols. And each Mars day is pretty close to an Earth day. It's on the order of two Earth years. That was the prime mission. That was what all the design requirements were anchored to. Once we got past that, I think we were into an extended mission, and that's officially, I guess, when you would say the mission exceeded its warranty. [Laugh] Having said that, I think the people who worked on the mission and previous rovers weren't too surprised that we got there. Like I said, we had some issues to deal with, like the wheels, but we got there with most of the redundant systems still fully functional, so I think we knew it was going to go quite a while.

ZIERLER: In terms of your day-to-day involvement, how do you compare engineering management pre-launch to keeping tabs of what's happening while Curiosity is roving around Mars?

WALLACE: On Curiosity specifically, I left the project a little after launch, just before landing. But on Perseverance and many of the other missions, I continued into operations, so I have seen both sides of the equation. It's very different. The pre-launch work and management is extremely strategic, at least at the level I'm working at now. You really have to look ahead and think a lot about where the shoal water is, what's coming up. The time scale of the management challenges is very different, whereas on the surface, you're reacting to often something new that just happened the day before, so you're turning around plans on a much shorter time scale. I think that's one thing that's fundamentally different. It's a different family of engineers as well.

Our operators are not down in the weeds of reliability analysis or circuit analysis, they tend to be folks who are very tuned into the toolset we use to build commands, and to understand the telemetry that comes back, and analyze this operational spacecraft as opposed to the group of people that's trying to finish a design, hit a delivery milestone, assemble something, fix a problem that just came up. It's different. I think for me it was a lot more stressful pre-launch. Once you're on the surface, you can make mistakes, but it's usually the shooting yourself in the foot kind. You're a little more in control of your own destiny. Pre-launch, the systems are so complicated. You're constantly fighting some new issue and problem, and you don't have long to get it done, fix it, and move forward. Once we got to the surface, I was able to go home, sleep, and turn off a little bit, but pre-launch, I never stopped thinking about the project. [Laugh]

ZIERLER: Do you have a sense of how Curiosity's science objectives have changed, given how long it's been able to run? In other words, how do we ensure that it's not doing redundant scientific work simply because it's still there and still going?

WALLACE: I think the fundamental reason we want mobility on the surface of Mars is that Mars is heterogeneous. Having the ability to go from one place, where we landed, at the base of Mount Sharp, up the slope, up towards the top of the mountain, looking at the changes, look at the areas with different chemical signatures that we've been able to observe in the orbiter, we're basically seeing new geological records by moving around at the landing site, and that's fundamentally why the vehicles are very powerful and why, a lot of times–and this was true, I would say, on probably all the science rovers I've worked on–the biggest science breakthroughs come in the extended mission. You hope that you can get sufficiently justifiable return on your investment for the primary mission, but very often–and this is true for orbiters as well because they're looking at different parts of the planet, how things change over time and over seasons–you very often get the biggest bang for your buck in the extended mission.

ZIERLER: Was being named project manager for Mars 2020 predicated on the success of the Curiosity mission? In other words, did you only get pulled into that once you didn't need to stay on Curiosity?

WALLACE: Partly, yes. I was the flight system manager on Curiosity, and the flight system had been assembled, tested, launched, and at that point, either I needed a new job on Curiosity, or I had to get another job somewhere else. And it just so happened that they needed some help formulating the next mission. I was extremely motivated to take the lessons learned from Curiosity and apply them to the next project. I asked to be part of that early study work. We were trading a lot of different options, including this big Mars 2020 rover. I got involved in the formulation at that point. Matter of fact, the entire Mars program up to Curiosity, we took a step back and looked at reformulating the entire thing, so there were a bunch of different paths we could've gone down. Ultimately, we headed down the path we were already on, which was to continue towards a sample return mission. But I really got involved early on 2020 for that reason. For better or worse, I was one of the most knowledgeable people about these systems because of my history, and I think that just made it a natural option for me to step into the project manager role.

ZIERLER: Just to give a sense of the hierarchy, when you say that you asked to go into this new position, who do you take that ask to? Does that go right to the laboratory director? Once step down, two steps down? How high up does that decision go?

WALLACE: I went up to talk to Fuk Li, who was the Mars Program Manager at JPL. All the Mars projects were under him, including Curiosity, all the formulation work, all the technology work. I basically went to Fuk and said, "Hey, I think I can help here." I don't think he had any doubt about that, so he was fine with me jumping in. That's how I started in the formulation pre-project work. Once there was a decision to actually stand up a formulation project office, Charles Elachi was the person who assigned me as the deputy project manager. I doubt it was a unanimous choice. Charles has always had a lot of, somewhat ill-founded at times, faith in me. And I'm extremely appreciative of the fact that he did that and that he had enough confidence in me to ultimately give me that chance. I wanted to land Perseverance ultimately for a lot of different people, but Charles was one of them. But he made the call. And like I said, I'm an aggressive implementation manager. I'm not everybody's cup of tea. [Laugh] It was a little bit of a leap of faith on Charles's part to give me the opportunity, but we pulled it off.

ZIERLER: You said you wanted to apply the lessons learned from Curiosity to Mars 2020. What were those key lessons learned?

WALLACE: They kind of came in two flavors, although they're somewhat related. One, Curiosity was a one-metric-ton vehicle. It was a generational change in our capabilities, in roving, in surface in situ science capability, in mechanisms, in processor capability. We had more redundancy in Curiosity than all the rest of the previous missions. It was a painful and very, very difficult process to get Curiosity built and to the launchpad. Part of what I wanted to do was to make sure that we leveraged that investment into the next mission. And there were concepts going back to these smaller rovers and doing other things, and I spent a lot of time convincing management and other independent analysis teams that by far, the most robust and least expensive thing we could do was to take those systems we'd just built, and to the degree that we can, replicate the basic systems so that we had the capacity in volume, mass, and intellectual capability, enough free neurons across the team, to really do the super-hard stuff that was part of Perseverance.

That was a big part of the lesson-learned process. I really wanted to inherit as much of that as we could. I think the other thing was, generically, I respect how hard these big rovers, big systems, and EDL systems are. Trying to land a car on the surface of Mars is just hard, and we underestimated it. We ultimately recovered and got there, but I didn't want Mars 2020 to go through that. I wanted to set up the system so that it was achievable and executable, that the team believed it was executable, and a lot of that required me to solicit feedback from the team on their experience on Curiosity. I had to listen to a lot of people tell me about bad decisions I made and things like that, but I needed to hear it. I wanted to do it right. And I built a tremendous amount of flexibility and margin into the schedule. I directed the team, and I set a policy that would really respect the challenge of this thing we were about to do. I think that was the other part of the lesson learned.

ZIERLER: Maybe it's as much a management question as an engineering question, but at the end of the day, if the mission was a success, why do you need to hear all of the little decisions you made that subordinates might have disagreed with? What's the value there, looking forward?

WALLACE: Curiosity was a success, but it was costly. Especially the part that I was managing certainly grew in cost more than I would've liked. And we didn't hit our original launch date. We hoped to launch in 2009. It became pretty clear relatively early on that that was going to be beyond us. But I don't like to set a goal, personally. And when those things happen, they create ripples in the program. If you need more money on this project, that means there's no more money over here to do this other thing, and whatever stakeholders there are for that other thing start to look at your project and say, "Is it really worth it?" And it delays these other strategic mission objectives and things like that. It's a hard thing to plan against when you don't have a deterministic schedule and budget. And this is very much from the eyes of our sponsor at headquarters, but also at JPL. Certainly, the mission was successful, but I didn't feel like I was fully successful as a manager on Curiosity, and I wanted to fix that. I wanted to do better on Perseverance.

ZIERLER: When I hear about cost overruns, time delays, and things like that, what about just having a knee-jerk reaction against the faster, better, cheaper ethos that got JPL into trouble in the late 1990s? In other words, maybe I'm acting like your cheerleader here, but maybe one of the reasons Curiosity landed successfully is because you pushed back against doing it faster.

WALLACE: I think you're right. Really, the first faster, better, cheaper mission was Mars Pathfinder and Sojourner, and that was my first flight project. I believed and still believe there's value in that development model, but it's a tricky thing to use. You have to apply it in the right places, and you really have to know what you're doing to decide what it's okay not to do, for instance. That's much harder than deciding to do something. Deciding not to do something is the hard part. MSL got $2.5 billion. Mars Pathfinder was$175 million. The investment and risk tolerance has to match up with the implementation philosophy. If you're going to use faster, better, cheaper, you better do it in the right setting and with people who understand what it means, what risks you're taking, and how to mitigate those risks.

And you have to make sure that the system is applicable and simple enough sometimes to really be able to use that. We got into Curiosity, I think, having inherited some of those faster, better, cheaper–although, we'd grown a bit beyond Mars Pathfinder, but we went into Curiosity with a little more of that mentality, and we recognized as we got deeper into the project that it wasn't appropriate. The risk tolerance was not there, the system was too complex to really do it that way. I think we did the right thing. I don't want to give you the wrong impression, I think we did the right thing in delaying it and making that additional investment. Mission success is what we're known for around here. And I think it was the right thing to do. But ultimately, you want to be able to predict those things no matter what. You want to be able to predict the schedule and costs, even if it's a higher cost or longer schedule. And we didn't do that as well as I wanted to on MSL, and I wanted to fix that.

ZIERLER: But of course, it's a counterfactual to wonder, "If I didn't dig in on this issue here, maybe the mission would've crashed and failed," or something like that. Looking back, what were those lessons where you could say with as much confidence as possible, "I might've been able to do this a little more efficiently. I might've been able to scale back costs," and have that same level as confidence that Curiosity would succeed? When you made those distinctions, what did you bring with you to Mars 2020?

WALLACE: I think once we had architected and done the basic conceptual design on Curiosity, there weren't those things. There weren't things I looked back on and said, "That was a waste of money." What I looked back and said was, "I should've recognized the implications of that complexity and those decisions and been able to predict it and plan for it." You're right, it's a hard question to ask no matter what. You're basically asking to prove a negative. I listened to a theologian recently who said, "That's an unfalsifiable assertion," which is a great way to say it. Those are very hard questions to ask, and even harder to answer. But I don't actually feel like we did that on Curiosity. I don't feel like we wasted money or time, but I feel we architected too much complexity into it at the beginning, then we failed to appreciate how much we'd architected in. Not in some horrific way, but more than I would've wanted. We got it launched, and it was a very successful mission. But I think we could've done better.

ZIERLER: What do you mean by the assertion that at you architected too much complexity? Do you mean over engineered? Redundancy?

WALLACE: For instance, there were some reasons for this, but early on Curiosity, we had planned to go single-string, which is a much simpler design. And through a myriad of different events, we transitioned to a redundant system. The problem was, we had sort of laid out some of the skeleton as single strength. As we tried to add in the redundancy, it became a more complex arrangement to fit it in after the fact. That's one example. Another example is, we had endeavored to be as discovery-responsive as possible on MSL. The idea was, the orbiters could potentially find something at a very high latitude, for instance, on Mars, and we would need to go to those high latitudes. When you go there, you have to deal with very cold temperatures, and so you need a lot of heater power. We tried to build components that didn't need heat.

Gearboxes generally have grease in them. Grease freezes somewhere around -70 or -65, so we tried to build gearboxes without grease, for instance, and we tried to build them out of titanium instead of steel to optimize the mass, ultimately, so we could fit more instrumentation on the vehicle. Both of those things, by the way, we abandoned because we couldn't get them done. But we were trying to take a step too far. That's part of the cycle, but again, we were doing something that was outside our experience base.

We were really taking an enormous step forward in capability, and once we had done that on Curiosity, I knew we could learn those lessons on Perseverance. And we structured the system on 2020 such that there were things we could do and knew how to do that did not represent a lot of risk and gave us a foundation of stability so that we could layer on even more complexity. The sampling system on Mars 2020 was far more complicated than anything we'd ever built on MSL. Same with some of the instruments. We were only able to do that by making sure we had diversified the complexity of the mission. That was a lesson we'd learned from Curiosity because we just didn't do enough of it.

ZIERLER: Another potentially unfalsifiable question. Let's say, heaven forbid, Curiosity was a failure and had crashed. Would Mars 2020 move forward at that point?

WALLACE: No. First of all, 2020 was a follow-on scientifically, but more importantly, the engineering systems on 2020, the big aeroshell, the sky crane, the hydrazine-propulsion engines, the computers, most of the power systems, the radar–it's possible that if we understood exactly what caused the failure, and we thought it was a one-off, we could go back, fix it, and build 2020 with a similar system, but it would've been a tough sell. It was really predicated on the success of Curiosity.

ZIERLER: Just to give a sense of the backstory to Mars 2020, how much planning took place prior to the launch and successful landing of Curiosity? In other words, are there things that are being prototyped where you can hit the ground running so long as Curiosity is successful? Or is everything just an idea, and you really can't get started in any substantive way until you can declare success with Curiosity?

WALLACE: The 2020 was one branch of a set of options for the program, and that branch was clearly predicated on the success of Curiosity. There was some study work before me, which would've been maybe mid-2011 or so, where they'd done a little bit of work on that particular branch. But I joined the team in January of 2012, and that's when they really expanded it out, grew it, and understood that option. And ultimately, I think Curiosity landed in August, and we got the project start in December of 2012. There were other paths. Had there been a failure, I think one of those other paths might've been viable. But frankly, at $2.5 billion, if Curiosity had failed, the Mars program as we know it may not have survived, so there was a lot riding on it. ZIERLER: Meaning that potentially, in an alternate scenario, JPL would no longer be in the Mars rover business. WALLACE: Yeah. I think so. ZIERLER: At this point, how much more are you involved with headquarters? Do you have a clearer sense of their decision-making, the JPL-NASA decision-making process, when you joined Mars 2020? WALLACE: For Curiosity, even though I was managing a lot of scope, I was still mostly down and in. I would report up and out somewhat, but I wasn't doing a lot of the programmatic work. For Mars 2020, I immediately jumped into the programmatic work, so I was learning as I went. [Laugh] I had pretty good insight. I was talking to headquarters a lot during the early phases of the study and the project. There was also something called MPG that was headed by a couple more-senior experienced managers. Their task was to look holistically at the program and see what made sense. I was interacting with them significantly as well because they were essentially advising headquarters on the path forward. I was getting pretty good insight into the criteria, thought process, and things like that. We were not sure, after Curiosity landed successfully, exactly how it was going to play out. I think most people did not believe we were going to get a start that year at all. And it was kind of critical to hitting the 2020 target. But because the program was in a little bit of disarray, in part because of the Curiosity launch delay, there was no funding wedge early on to get the project going. John Grunsfeld was the science mission director and associate administrator at the time, and he made a fairly bold decision in December of 2012, after having watched Curiosity successfully land, to start this Mars 2020 mission. It was a little bit of a surprise, but he was right. He basically established the project and the mission before the funding existed, which doesn't usually happen. ZIERLER: Is that what the term funding wedge means, to make up that gap? WALLACE: Basically, projects start out needing a little bit of money, and as they go through, they need more money. The wedge of money on a chart over time grows, and that wedge is what gets projects started and moving into implementation. It was not at a level that was sufficient for this project, but he started it anyway. We were making every penny a prisoner in those early years. We were very heavily constrained to keep Mars 2020 going in the early years. Basically, we get funded on fiscal-year boundaries. Roughly, on October 1, you get your next year's funding, or a large chunk of it. The trick, if you're limited in funding, is to make it through the end of September, and every year, I was down to my last dime. I was spending every cent I had to try to keep the technology work and project work going so we could hit the 2020 milestone. But ultimately, usually in August or so, headquarters would come to the rescue and find us a little extra money that somebody wasn't using. It was a little hairy there for a while. [Laugh] ZIERLER: This would be obviously above your pay grade, but by 2011, 2012, the United States was just coming out of the '08 financial crisis. Do you have a sense that that was important and was a consideration that allowed you, as tight as the budget was, to even have as much as you did to work with? WALLACE: I think so, yeah. Had everything been shifted three or four years earlier… ZIERLER: The money might not have been there. WALLACE: Yeah. A flagship new start like that probably would've been delayed. I think it probably was a factor. ZIERLER: Who do you credit at headquarters with making that case? Does that go all the way up to the administrator? Is it Congress? Who are the cheerleaders who are really making sure that Mars 2020 happens during a time when the economy is really just starting to get back on its feet? WALLACE: There's a series of people. And by the way, the JPL director's office is immensely influential in this kind of conversation, and Charles and Larry James were obviously strong advocates. This could not have happened without their belief that we could do the mission, that the science was valuable, and all those sorts of things. It really starts here. Fuk Li was the program manager, and he reported to a guy named Doug McCuistion, who was the program manager for the Mars Program at headquarters at the time. And he was an advocate. But the person with enough of the purse strings was the associate administrator, John Grunsfeld, as I mentioned before. I'm not privy to all the inner-workings of those budgetary things, but he and Jim Green, who worked for him, were big believers in what we were doing. And they took some risk in making that call. ZIERLER: Maybe it's an ironic question, but given how successful Curiosity was, we talked earlier about how it could expand its scientific objectives, was try any concern or pushback like, "Curiosity is doing great stuff. Do we really need the next rover mission so fast while it seems like Curiosity is going to have plenty of time to do good science?" How much more expansive was the scientific objective that made the decision-makers pull the lever to make this a go? WALLACE: I think the best way to answer that is just to talk in thumbnail form about sample return. People started to dream about bringing a sample back from Mars ever since Viking landed. And you can go back and find the first concepts in the JPL archives and libraries. I know people who worked on the first studies in the 1980s. We went through a big study cycle in the 2001, 2002 timeframe and another cycle later that decade. There's an enormous belief in the science community that to find these ancient trace signatures of early life on Mars, if they're there, you need extremely sensitive instrumentation. Not only that, but you need to do one test, see the result of it, then react to it and decide what the next instrument you need is. You can't, a priori, take and know everything you need to get an answer to this question. For that reason, the planetary decadal survey, which is the document generated by the entire planetary science community once a decade, the number-one priority was Mars sample return, and we couldn't bring anything back with Curiosity. We could look at the data, we could understand that the planet was once habitable, which is a major step forward, but we couldn't show the rigor that would obviously be required to make a statement along the lines of life having evolved on another planet. We had to do it. Sample return was the consensus. I don't think in the science community, there was ever any sense we could've stopped at that point. We were and still are going for that holy grail, that one fundamental question of whether life evolved somewhere other than Earth, and we needed Perseverance. ZIERLER: Just to clarify, Mars 2020 was initially conceptualized as a return mission? In other words, now, we talk about Mars 2028. But was the original plan that Mars 2020 would be able to bring back samples? WALLACE: The guidelines we got were to be responsive to the objective of advancing toward sample return. It was a little broader when we began the project. We interpreted that as, "Collect returnable samples." ZIERLER: On this mission or the next mission? WALLACE: Well, to collect the returnable samples on Mars 2020 so the next mission could bring them back. And there were other folks who didn't quite interpret it that way. At the beginning of a project, you have to go through what's called a science step mission team cycle, where the science community comes in and says, "You've started up this project. Do you have a general sense of the objectives? Let's get a little bit more focused and converge specifically on what the requirements are going to be, what kind of instrumentation we need, what you're really going to do from a science perspective." And coming out of that science step mission team process, it was very clear that what 2020 at the time was supposed to collect returnable samples. There was some concern that with Curiosity having cost$2.5 billion that a mission to collect pristine samples might cost $5 or$6 billion, so there was a little reluctance early on to fully commit to that science concept. But I believed that by leveraging off of Curiosity, we could do it in the price range and on the schedule duration that the community was looking for. And 2020 didn't ultimately cost $5 or$6 billion. We kept it in about the \$2.5-billion range. But there was uncertainty early on that we could do it.

ZIERLER: Last question for today. To what extent was Curiosity, which was roving around and doing things, defying expectations, and its ability to rove around Mars part of the equation in conceptualizing this sequence of events? In other words, the next mission is going to collect samples, and a subsequent mission is going to return them. Was Curiosity doing the scouting work to figure out what samples were worth collecting?

WALLACE: I think Curiosity did a couple things. One, it demonstrated our ability to land a system of this size and complexity necessary to do the mission that 2020 needed to do. From an engineering perspective, it was definitely a proof-of-concept for that part of it. I think on the science side, had Curiosity not identified the kind of chemical and mineralogical signatures it did at Gale, I think there would've been a no-gate. I just don't think it would've been compelling enough to believe that it's worth the investment to bring samples back. I think Curiosity was instrumental. And of course, when Curiosity landed, it was a big success and got a lot of attention. All those budget overruns and schedule delays were forgotten, by some people at least. And I think it generated excitement about sky cranes, seven minutes of terror, all of that. I think it generated a groundswell of excitement to keep exploring Mars in these daring ways. I think it was useful from that perspective.

ZIERLER: On that note, we'll pick up next time in the design phase, 2013, 2014, going forward.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Wednesday, July 6, 2022. I am delighted to be back with Matt Wallace of JPL. Once again, it's great to be with you. Thank you for joining me.

WALLACE: Happy to do it, thanks.

ZIERLER: I want to go back to a really important point you made in our last discussion about the fundamental importance of curiosity's engineering as a proof of concept to even think about Perseverance as a possibility. My question there is, as we get to the design phase, 2013, 2014, how do you take all of the good things that were demonstrated with Curiosity but at the same time, begin a design phase that obviously needs to be bigger and better, more reliable, have better research capabilities? This is as much an engineering/R&D 101 question as it is germane to the Mars Rover mission. How do you take all of the assurances of the success and engineering of Curiosity while not simply replicating it for Perseverance?

WALLACE: That was one of the first, most fundamental challenges that we faced on Mars 2020, as we called it then. We had never, strange as it may sound, really tried to rebuild a significant spacecraft mission at JPL before. Our systems wouldn't even let us reuse the engineering documentation from the previous development on a current development, just because it was never done. You had to start from scratch. We had to change some of the institutional processes to allow us to do that. And then, the very first thing I did, recognizing that it was a fundamental challenge for the mission, was to form what we called a heritage working group, and we decided we needed–first thing you always do, engineering/problem-solving 101–was to go get more information.

We actually went out to different projects and even into industry, different NASA centers, read all the lessons learned we could about inheriting technologies, designs, and systems from previous efforts into new efforts. We went and talked with Northrop Grumman, who was building a new fleet of communication relay satellites that were–this new fleet was separated from the previous one by about six or seven years, as I recall, so they were trying to do something that we wanted to do, and we needed the lessons learned from them. One of the things we found was, almost every time the agency has tried to rebuild portions of the previous mission, it hasn't worked out well. Something broke. We ended up analyzing all of those case studies and coming up with a set of risk factors, of which there were seven or eight, then we started to put mitigations against each one of those risk factors to make sure we wouldn't run into those problems.

For instance, one example is trying to build the same system with a different organization or different people. You realize quickly that a lot of what you're inheriting is not on an engineering drawing or in a document, it's the knowledge and experience that people have, having developed, built, and tested that system. That was one of the risk factors. Changing the environmental testing requirements, for instance. Every component we build, we have to shake it, bake it, and whatnot to simulate the space environment. And our standards had changed at JPL. In other words, if we were expecting it to get to -40 degrees Celsius, we needed a certain amount of margin, and the standard that says how much margin you need had changed. We grandfathered ourselves into all the previous standards relative to environmental testing, and there was just a whole bunch of those types of lessons learned relative to interfaces, to not dropping a component into the middle of a new system, things like that.

That was the first thing we did, try to figure out how to preserve the heritage successfully for the places we could do that. We were fortunate. We had about six or eight months to go through that cycle, study it, come up with risk factors, and develop all the mitigations to do that. Then, as we progressed into the project, I was very careful to make sure that the mission objectives and payloads that were selected were compatible with the systems that we needed, the delivery systems, for instance, the SkyCrane system we had built on MSL. It was a challenge. We actually put the entire spacecraft under configuration control, which is something you normally don't do until four years into the mission. We put it into configuration control, like, the first year of development, so if somebody wanted to change or add something that would cause a ripple effect into the system, they had to come get permission from project management, and that put enough change in the system to make sure we were looking at all those implications carefully. It was a real challenge. I think we learned a lot about how to do that successfully.

ZIERLER: At the beginning of the design phase, what is the interface with the scientists? What are the things they're communicating to you that are really setting the agenda for what you need to do on the engineering side?

WALLACE: All of our projects are driven by something called the Planetary Decadal Survey. Once every ten years, roughly, the science community gets together, and as a matter of fact, they just released one a couple months ago for the next decade. But in 2012, we were dealing with the decadal that had just been released, and the number-one objective for solar system science was to prepare for sample return from Mars and to advance the progress toward sample return from Mars, so we already had a foundational objective for the mission. We knew that was where we needed to go to the first order. That helped.

Then, we formed what's called a science definition team, where we take people from the science community, bring them, and pair them with team members on the project, and they lay out a much more detailed set of science. In this case, also technology objectives. Mars 2020 actually had two fundamental agency-level thrusts. One was to do the decadal science, and the other was to advance the technology and preparation for human exploration of Mars. We were really given the task of being the first human precursor mission to Mars. We took those two things and merged them together in something called a science definition team, and they created the foundation we needed to go out and solicit for science and technology instruments, which is what we did in 2014.

ZIERLER: An administrative question. Who are your peers at the design phase? Who are the people you're working with at your level?

WALLACE: That's a hard question. I have sponsors at headquarters, and I need to understand what they want. I have office managers, who are the next layer down of people I look to for flight systems, science instruments, systems engineering support, mission operations, those kinds of things. We have a matrix system here at JPL, so I interface into our line organization, primarily at the division manager level. Each division is roughly a discipline. For instance, we have a mechanical division, which is propulsion systems, mechanical structures, thermal systems, harnessing, and stuff like that. Then, we have an avionics system, which is power systems, computers, guidance and navigation, control. We have a telecom division, which does telecom, radar, all the RF, things like that. Each of those divisions has a division manager, so we spend a fair amount of time talking to those organizations at that level.

ZIERLER: Another way of getting to that question is, how many layers are between you at this point and Charles Elachi as director?

WALLACE: Some of that depends on what Charles wants. [Laugh] My direct report was Fuk Li, who was the Mars program manager at the time, and he reported directly to Charles and Larry. But it was not at all unusual for Charles to want to get together with project and hear directly from us. He was very hands-on, particularly when he had a sense that we were struggling with something. I knew that if Charles heard about it, he was going to do what he could to help us. He was certainly part of the initial staffing, the key staff. We kept him informed on who we were putting in these key positions. He was part of the initial budget estimates early on in the formulation phase. You have to kind of make some rough guesses at what those are going to be. We had some particularly unique challenges. We really, really struggled with something called planetary protection.

We were trying to do something that had never been done before relative to the cleanliness of the system that was collecting the samples. And we were paving new ground. Honestly, there were parts of the agency that were still layering requirements on us based on what had happened with Viking four years prior, so we were really having a hard time with planetary protection. Charles stepped in and really fundamentally enabled the mission, I think, by setting the tone in that particular area. And I've told him probably 100 times since then how much I appreciated that. Charles is a hands-on manager, even though his scope of responsibility is enormous, and he always has to be working the sponsorships, Congress, headquarters, and everything else. He's instrumental.

ZIERLER: On a specific point of planetary protection, but more generally, what had everybody learned about the Martian environment from previous rover missions that really influenced the design for Mars 2020 early on?

WALLACE: Reaching way back a decade or more to MER and Pathfinder, the orbiters and landers we had put on the ground, it was clear there really was no substantial amount of surface or near-surface water in most regions of the planet. And that's extremely important because where those things exist, there's a potential for creating your own colony, if you will, of organisms. There are particularly stringent cleanliness requirements if you're going to go to what we call a special region on Mars. Understanding where those special regions were and were not was a key factor in designing the mission so that it was implementable.

Certainly, from the science perspective, being able to correlate what we're getting from the orbiters to what we're seeing on the ground from the landers and the rovers was instrumental in selecting the landing site of Mars 2020. We really have learned a lot about how to interpret our global datasets, how much we get a certain thermal image profile for a certain area, and we can translate that to rock abundances and things like that at some level. that helps with understanding what the surface looks like, and then, of course, the safety of landing in that particular area. Learning those kinds of things about the planet was incredibly important. I think we learned that the dust environment was significant early on, and we had to think about how we were handling dust and the debris that gets kicked up during landing. For instance, we had to think about whether or not our radar was going to lose lock because the dust starts to swirl from the plumes from our engines.

Those are the types of environmental factors that we learned more about. We learned, interestingly enough, that there are very specific gravity gradients in different parts of Mars depending on the topography, and while it's very slight, it does, in fact, affect our touchdown closed-loop control processes, and it can spook the spacecraft, and it did change our touchdown on Curiosity. We ended up touching down a little bit slower than we expected because of the local gravity gradient from the mountain in the middle of Gale Crater.

And certainly, Curiosity taught us that for a rover vehicle, there were certain rock structures that could be very damaging to wheels, so we had to redesign the wheels on Mars 2020 and Perseverance so they were a lot more robust. I call them can openers, these very sharp rocks we hadn't seen before we landed at Gale. And there are more. But across the board, every time we land, we learn something about Mars that feeds into the probability of success. Same is true for wind distribution. I can go on and on. It affects every part of the mission.

ZIERLER: To go back to the decadal survey and what the science community was hoping for, were there any asks that were simply beyond the capabilities from an engineering perspective circa 2013, 2014?

WALLACE: There was a sort of fundamental science option space that was on the table. One was whether to carry what we call an analytical laboratory with us that does wet chemistry and that sort of thing. In order to feed that kind of instrument, you have to be able to provide powdered samples, powder process sifted samples, and then portioned into that analytical laboratory. They tend to be very large, and they take up a lot of space, and they need to be in the front of the vehicle where the robot arm is because they're fed by the robot. The alternative to that was to develop a suite of much more sophisticated and capable spectrometers.

Spectrometers are not things that you put a sample into, but you take the sensor head out to the rock or to the soil, and you use various types of spectroscopy, like fluorescence, Raman spectroscopy, and other things, and you essentially get a signal back from the surface you're interrogating that allows you to differentiate it either from an elemental perspective, chemical compound perspective, or whatever. And part of the advantage potentially of these sophisticated spectrometers is that they can give you very, very small spot sizes, down to, like, 100 microns, so you can raster across, say, the face of a rock, and you can see all the veins and all the embedded minerals. You can essentially spectroscopically see how the chemicals are structured in the rock. That's an advantage of a spectrometer, but they're sophisticated and difficult.

The problem with the other option, the analytical chemistry option, is that it needed to be right in the front of the vehicle, where we needed the core handling system to be. If we were going to take a sample and store it in a tube to return it to Earth, we needed that whole sample handling system to be right up there in the front of the vehicle where this analytical instrument wanted to be. The other problem was, it required a lot of powdering, sifting, and filtering capability out on the end of the robot arm, where we also needed a very big rotary percussive drill. I basically told the science community, "You're not going to have an analytical instrument. You've got to figure out how to do this with spectrometers." Long story short, they defined, they solicited, we selected, we built, and we are operating some remarkable spectrometers on Mars that are giving us new types of information that we've never seen. But that was an early fundamental instrument issue.

ZIERLER: It's a narrow question, but you know as well as anybody, it's the small stuff that matters. In going to an aluminum-based wheel, obviously there are some traction issues to deal with. How did you overcome that?

WALLACE: They had been aluminum on the previous rovers as well. There were two things we needed to do. One, we needed to thicken the tread because of this vulnerability that we had found on Curiosity from these sharp rocks. The other thing we had to do was to change the shape of the tread. On all the previous missions, there were a lot of sharp-angle–if you're looking to grab something when you're turning a wheel over a rock, you want sharp angles. As a matter of fact, way back on Sojourner, we basically created these super-sharp teeth on the wheel, and I swear, every time I picked up the test vehicle, those wheels puffed up, and I still have scars on my hands from those teeth. [Laugh] But we were used to designing those types of traction patterns on the tread, and we had to move away from them on Perseverance because all these sharp angles created what's called a stress concentration.

If you can imagine, every time you have something that comes to a point, when you put pressure on that point, it creates a very high-pressure opportunity to puncture the wheel, so we had to go to these kind of wavy treads. Then, we had to go up and do all the testing associated with making sure that tread gave us the traction and traverse-ability we needed. We did make the wheels bigger so we had a little more surface area on the ground as we were turning. We had to make them more narrow because we couldn't fit them in the vehicle. There was a process we went through on the wheels, but we managed to make it all work.

ZIERLER: What was the back and forth, best-case scenario of how deep the scientists wanted Perseverance to core, its drilling capabilities, versus what you were actually able to achieve at the time?

WALLACE: Very early on, the very initial concept days, we talked about the possibility of what we call a deep drill several meters down. In fact, the Europeans had built a rover, Rosalind Franklin, that was carrying a deep drill. The theory there is that you want to get far enough below the surface where the radiation has not damaged these long-chain organics. You have to drill down far enough such that you have essentially pristine material. Because we're looking at chemical signatures from billions of years ago. If you're looking close to the surface when you sample, a lot of these chemicals can be damaged, broken down, and you lose that history just because of the radiation environment of Mars over hundreds of millions or billions of years.

But the science community on our side figured out that there are parts of Mars that–this goes back to understanding what we're looking at by orbital imagery by having correlated what we've seen on the ground and things like that–have been more recently excavated. And by more recently, I mean millions or tens of millions of years instead of billions of years. If you go to a place like that, you don't have to drill as deep because the area close to the surface of the rock just has not seem that much cumulative dose and flux from the radiation environment. That's what we chose to do, to go with a relatively shallow coring capability based on our understanding of coring in places where we believe we'd see preservation of those chemical signatures.

Different rocks preserve these signatures better, and there are other ways to pick places where you see better-preserved samples. We really focused on making sure we had the capability to do that rather than drill very deep. That also allows us to interrogate the places we're drilling with these spectrometers I mentioned before. We grind off the surface of a rock, put the spectrometer just below that rind, and we can understand what we're coring and what we're sampling. We can core from six to eight centimeters. We never look beyond probably 10 or 12 centimeters.

ZIERLER: How much of the research or effort to get as deep down as possible is really about seeing evidence of past life on Mars?

WALLACE: A lot of it. It's not the only motivation; there's a lot of geological context, environmental information, and all of that we're learning about Mars. But a lot of the motivation for the fundamental decadal science is about looking back billions of years and understanding whether or not life evolved at the same time life was evolving on the Earth. Because we know from our previous missions that the Martian environment was very, very similar to what the Earth looked like billions of years ago. It's a fundamental objective of what we're trying to do.

ZIERLER: This is as much a PR question as anything else. It's about managing expectations. 8 centimeters, 10 centimeters, 12 centimeters, realistically, if Perseverance gets that far, how much closer does that get us to not proving or proving a negative about whether there was ever life on Mars?

WALLACE: The signatures we're looking for are in the parts-per-billion in many cases. They're faint, subtle. Even if you go deep, you're dealing with those sorts of things. The reason we're doing what we're doing from a campaign perspective is that to really convince yourself you're seeing signs of ancient life, you have to bring the samples back to the Earth. You just can't carry enough science instrumentation to conclusively decide you're seeing signs of ancient life. 2020, we were trying to come up with the high-level moniker or tag line for the mission for a while. For Curiosity, it was, "Understanding habitability," looking at whether or not ancient Mars had an environment that could've supported life, and it concluded that it could. It was a big step forward in our understanding of the possibility of ancient life. Our tag line I suggested that I think pretty much has stuck is, "Seeking the signs of life." Not necessarily proving there's life. But we're going to go and look, and maybe we'll see something in situ, but really, we're gathering samples we believe could answer that question so that they can be returned to the Earth and analyzed in that way.

ZIERLER: If there are the naysayers, who say, "Obviously, Perseverance isn't going to find anything at 10 centimeters. We need to go down to three meters," or whatever it is, the obvious counter to that or way of getting away from a situation where you're chasing your tail in a never-ending pursuit of going deeper, we could say, at least theoretically at this point, that Perseverance has already collected samples that indicate signs of ancient life. We just won't know until we get those samples back here on Earth.

WALLACE: That's exactly right. And we're going to get a couple more in the next few days, I think. I think that's the right way to look at it. We're seeing some remarkable stuff at Jezero Crater. Based on what we saw on Curiosity, we know if we do our job right, and they're doing a great job on the project, scientifically and otherwise, we're going to have some really exciting samples to analyze when we get back. We're just seeing the telltales of things that tell us that we went to the right place. We're in a place that was wet a long time, it was warm. It's got a lot of exciting potential. I think we've already kind of demonstrated that the fundamental philosophy we had relative to the mission, and the sampling techniques, and depth, and all that stuff were valid based on what we're seeing.

ZIERLER: I don't know if you ever interacted with Professor Don Burnett, the PI for the Genesis mission, but he's still searching through the samples Genesis brought back, and this is decades after. From your perspective, I know it's a little outside of your field of expertise, but for the general population that might wonder, what's the big difference between analytical capabilities on the rover itself versus bringing those samples back here on Earth? What can we do here in terms of analyzing those samples that's simply not possible with the rover on Mars?

WALLACE: It's an order of magnitude. The science community at this point has tremendous capability on the Earth to look at very detailed and very faint signatures of systems and separate them from the noise. Not just chemically or spectroscopically, but in a lot of other ways. Just being able to look, for instance, at the gradient of certain chemical signatures from the outside of the core to the inside of the core. We're looking for signatures that are so faint, one of the primary concerns is whether or not we could've contaminated the sample. By looking at the gradient from the exposed part on the surface down to the center of the core, which these instruments are more than capable of doing, you can really differentiate anything that might be contamination from what is inherent in the sample itself. There's so much more capability here than we can take with us.

One of the other things one of our project scientists once told me we can do with a sample here that you can't do elsewhere, even if you could take 5 or 10 times the mass of instruments to Mars, the odds of you finding something in your first pass looking at the sample and knowing a priori, before you do that first pass, what the next test you want to do is can be very hard. When you have it here on the Earth, you say, "Look at that. I know this lab in France that has instrumentation that can do this type of analysis." Being able to predict what you want to do scientifically with the samples and what you're finding ahead of time is hard. We do our best to take the right things with us to Mars, but we're limited in what we can take, and we don't have perfect knowledge. We always find new things. We have already find things we didn't expect to find at Jezero. I think that's another powerful aspect of having the samples here.

ZIERLER: These things were all known at the beginning of Mars 2020. Now, looking ahead, where sample turn is really feasible conceptually, from an engineering perspective, technologically, what has changed? Why could we not simply leapfrog Mars 2020 and go right to a sample return mission circa 2013, 2014? What was lacking at that point that we now have, at least conceptually?

WALLACE: There are a number of technologies I think we would've struggled with in 2013. But even besides that, we just did not and probably still do not have the engineering experience to take that much on a single mission to Mars. We're reacquiring the capability to put a lot of mass into space with SLS and with some of these bigger commercial launch vehicles, but that did not exist 10 years ago. Trying to take not only a system that would go and collect samples but also return those samples all on one mission would've been extremely difficult. We just didn't know how to do it. We had to break it up into steps. There were concepts, though, for instance what's called a grab-and-go sample. You don't take a rover or instruments. You just land somewhere, grab the nearest rock, throw it into a rocket, and try to get it back to Earth. One thing we've found is, that's a bad model.

We landed in Jezero Crater, just as an example, which was an ancient lakebed. We thought we'd see a lot of sedimentary rocks, rocks that were formed at the bottom of a lake with water processes as opposed to the salts or igneous rocks that are born volcanically. When we landed, all we saw were igneous rocks. [Laugh] Until recently, when we traversed 12 kilometers or so and are really getting to the base of the delta, where we're seeing sedimentary rocks. You just don't know. It's a very, very geologically heterogeneous environment. It's hard to imagine because you see the pictures, and it's all a bunch of red rocks. But there are a lot of really fundamental differences in different parts of Mars.

If you want to collect a sample worth of spending billions of dollars to bring it back to Earth, you should collect a good sample. And not only do you want the sample from the right location, but you want to understand the context of the sample, how that rock was formed, what the things are around it. It's critically important to have that. There just wasn't a good way to do a well-considered single mission to bring the sample return back. And we didn't have a return sample ascent vehicle, we had to do technology development on that, we didn't have a precision-landing capability, a hazard-avoidance capability. 2020 proved out those technologies. We had work to do technologically.

ZIERLER: If we step back and look at all of the rover missions as a narrative chronology where advances in the proceeding one make the next one possible, with sample return in mind, what aspects of Mars 2020, ultimately Perseverance, were specifically with that next mission? What was the proof of concept in sample return that was baked into planning for Perseverance?

WALLACE: One of the biggest ones was the Terrain Relative Navigation capability. This is where, as we come down, when we drop the heat shield away, we take a picture of where we're at, and we compare it to an onboard orbiter image of the landing site, match up features, and figure out where exactly we are. Then, we guide the spacecraft to a safe landing spot. Jezero Crater, if you look sort of generically across where Perseverance landed, was too dangerous to land in without some type of hazard-avoidance capability. That gave us the ability to go to a place that was safe to land in the local area of Jezero Crater. That has been adapted not only for hazard avoidance but what's called precision landing for sample return. The sample return mission wants to land as close as possible either to the cache, the group of samples that 2020 puts down on the ground, or as close as possible to Perseverance so that Perseverance can bring the samples on board over to the return rocket.

That was a big part of what we were doing. We also built a much bigger air shell. Curiosity actually used a similarly sized air shell as 2020. I think the sample handling technologies we put together and the planetary protection, what we call break the chain, making sure we don't bring back certain elements of Mars when we bring a sample back, a lot of that was rooted in the contamination control work we did on 2020, how to maintain a certain level of cleanliness, which is critically important when you're bringing samples back. That technology has fed into the way in which they're doing sample-handling and making sure that the samples remain clean and valid.

Those things also fed into the next mission. And while we were building Perseverance, there was technology work ongoing to support some of the rendezvous requirements in orbit on Mars for sample return as well as the Mars ascent vehicle. There was ongoing technology. The bigger parachute was another one. We put a much bigger parachute on 2020, and we figured out how to qualify that parachute on the Earth, which is very hard to do because the Earth is not like Mars from an atmospheric perspective. It's very hard to qualify a supersonic planetary parachute. We successfully did that, and sample return is going to use that same technique.

ZIERLER: If we look at the seven years between design phase and launch, when in that chronology would you say, looking back, "This is a go," that everything was working to plan, and there's a high level of confidence things were going to happen how and when you wanted?

WALLACE: My philosophy is, you never say that. [Laugh] The second you do, you'll be wrong. I think even if I wanted to say it, I couldn't bring myself to. Maybe it's just how I work, I don't know. But I spend most of my time thinking about ways it's not going to work and trying to mitigate those. There are so many ways for missions to fail. These systems are so complex. The second you start thinking, "I got it. We're going to get this done in time," or, "I'm not going to make a bad decision and embed some kind of failure that's going to come to light during the mission," I think you're in trouble. [Laugh] There are certain big milestones. When we get the basic funding commitment–that doesn't happen right away. It didn't happen in 2012, 2013, 2014. It didn't happen until 2015.

When the review boards, and your sponsors, and all the independent auditors, and everybody else think you're on the right track and doing the right things, we go through a commitment review, and that's an enormous milestone. It's when you feel like you've got the support to get the job done. I think when you start assembling the flight spacecraft in the high bay down here, that's the point when you feel like things are getting real. "Maybe we'll get there." [Laugh] But a day really does not go by where somebody doesn't walk in your office and say, "I'm sorry to have to tell you this but X, Y, or Z just happened."

ZIERLER: Administratively for you, did your role change significantly in those seven years?

WALLACE: No. I was assigned the deputy project manager right away. The nature of the mission work changes over time, but my fundamental role, managing the team and communicating to the outside world what we were doing, interacting with the various organizations, where we need support from–not really. As you get closer to operations, your role as a project manager team moves. As we got close to landing, the things I was worried about and the things the project was focused on changed. When COVID hit, I became, like, the chief medical officer of the project. You morph into whatever challenge it is you face. But I'm still pretty much dealing with the same group of key leadership.

ZIERLER: To give a sense of the administrative situation beyond your own immediate role, there's a lot of significant transition that happens in these seven years. Of course, there's a new JPL director in 2017, Mike Watkins succeeds Charles Elachi. There's a new president at Caltech, Tom Rosenbaum succeeds Jean-Lou Chameau in 2014, and there's a new President of the United States, in 2017, Donald Trump succeeds Barack Obama. How did these things register with you, and did anything affect your day-to-day in getting Perseverance to where it needed to go?

WALLACE: When there's an administration change, as there was 2016, 2017, there's always a little bit of nervousness. The good news is, our planetary missions really have very strong bipartisan support. And by then, we were mature and really moving along. I wasn't overly worried about that. But there's a little transition there. I think whenever there's a laboratory leadership change–it wasn't just Charles to Mike, but Mike changed the structure of the laboratory below him as well, so there was a new group of people to get up to speed. The good news was, I'd been at JPL a long time, and a lot of those people were ex-Mars people and people I'd worked with, so that wasn't too significant a change. The Caltech change on campus kind of gets buffered through the laboratory management to the first order.

I think if the system is working the way it's supposed to work, the people on the project don't get jostled by a lot of those external factors, if possible. And I think to the first order, that was true for Mars 2020. Certainly, when the laboratory leadership changed over, there were a whole bunch of new things people were worried about, and they were different from the ones people were worried about before, so there was that cycle to go through. But we all kind of know each other, so we all know what questions are going to get asked. It wasn't too difficult for the project.

ZIERLER: From the NASA HQ side, did the change in presidential administrations change anything?

WALLACE: Not directly. There was a change in the SMV associate administrator from John Grunsfeld to Thomas Zurbuchen. That was a pretty fundamental change for us. They have very different styles. As we went through different challenges on the project, we had to learn how to communicate in a different way with Thomas. But once the project is rolling and funded, we control a lot of our own destiny. It's kind of like a ship at sea. It's not like people don't come on board a lot. Every time you hit port, you get somebody else who comes on board to take a look around or whatever. But you have to be able to deal with your own issues and kind of keep making progress, independent of what's causing noise around you. I think 2020 did a pretty good job of that. We had a lot of continuity with our leadership. People came on board and stayed. It was an exciting mission, we had a great team, very cohesive. While other projects sometimes have to deal with turnovers and changes, we didn't see a lot of that. We were very fortunate.

ZIERLER: Last question for today. Going all the way back to our earlier conversations, all of the mentorship that you were a beneficiary of earlier in your career, at this senior stage in your career, did you have the bandwidth in the years leading up to the launch to serve in a mentor capacity to younger scientists, visiting graduate students, post-docs, things like that?

WALLACE: I hope so. It was hard with interns who came and went over a summer's period. I tried to stop in, talk with them, tell them about JPL and what we were doing. They often want to hear about your own career trajectory, how you ended up where you are, "What do you think of this? What do you think of that?" A few of the interns, I'm still in contact with. The science team tends to go to the science leaders, engineering team to engineering leadership. I think one of the places I feel good about that aspect of what I did on 2020 was, in some of the key leadership roles, for instance, our flight system manager had never been a flight system manager before, never worked on a Mars mission, which is pretty unusual. I picked him out because I saw something in him that I just thought would work. The flight system manager is one of the hardest jobs on the project. He or she is responsible for 60 or 70% of the scope of the project. I felt like I was able to successfully mentor that new flight system manager. He wanted to learn and to listen. But I hope I was able to teach some of the key team members in the way I was taught.

ZIERLER: On that note, we'll pick up next time. Finally, we'll get to launch date and hopefully bring the story right up to the present.

[End of Recording]

ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Friday, August 5, 2022. I'm delighted to be back with Matt Wallace of JPL. Matt, as always, great to be with you. Thank you for joining me again.

WALLACE: Happy to be here. Thanks, David.

ZIERLER: We're going to pick up right where we left off last time, the launch of Mars 2020. We talked about all of the engineering and science considerations up to that day. At this point in your career, relative all of your involvement in Mars exploration rovers before, what was different about that day? What felt brand new, despite all of your history going back?

WALLACE: In some ways, it was similar. I was down at the Cape for a lot of–maybe all the previous launches I had done. It was in the middle of COVID. I think that was the biggest change. The pandemic had forced a lot of modifications to our flow, it had really existentially threatened the launch, and we were still socially distancing, still wearing our face masks.

ZIERLER: This is pre-vaccines, we should remember. This is early days of the pandemic, when things are real dangerous still.

WALLACE: It was pre-vaccines. We had just really come out of three or four months of trying to figure out how to operate in this environment. There's always a sense of relief of getting to the point where you're ready to launch the vehicle, but I would say it was a tenfold increase in that feeling on Perseverance just because of what we had to push through with the pandemic. It was very satisfying to know that the team had gotten it done, gotten ready to launch it.

ZIERLER: Just in terms of the size of the rover, the mechanics of the launch, what was different, and what was the same about Mars 2020, looking back at March 2012?

WALLACE: The vehicle is maybe 10% bigger than Curiosity, so in physical size, it didn't look that much different, and the spacecraft was only a little bit larger overall. But we were able to put all of that additional capability into the instruments and technology payloads. We had 50% more science and technology payloads than Curiosity had been able to fly to the surface. Not only did we utilize that extra space and mass capability, but we knew where all our margins were relative to entry descent and landing functionality, fuel utilization, and everything else because we had flown a similar system before. We could really leverage all the nooks and crannies, all the margin we had. In that sense, it was very different. And of course, Perseverance was the start of the campaign. It was much more so connected to the next set of missions to bring samples back. I think that was obviously a fundamental difference between that and the previous missions we had done.

ZIERLER: What were your responsibilities in the in-between time during flight, from launch to landing? What are the day-to-day responsibilities and any concerns you have during that period?

WALLACE: One of the things I worried a lot about, we had done a lot of practicing and had put a lot of effort into understanding how to fly the vehicle safely with the pandemic implications, but I was still concerned. It's hard to gauge the intangibles associated with being able to talk to people face-to-face every day, sit next to them, walk into their offices. I was worried about the network connection that you need to safely fly and operate a vehicle, especially when we started to hit anomalies. And we hit anomalies, like, on the day of launch. [Laugh] We had an exciting launch. And the team was able to work through that.

Then, we had follow-on anomalies a month or two later that we had to work through, and we had other concerns, especially as you approach entry, descent, and landing. It was something that was on my mind a lot. I brought the team together a lot to talk about making sure the communication paths were open, making sure we were robust to any sort of surge in the virus. We had to split teams out, we had to have backup plans. There was a lot of that going on between launch and landing. A lot of my time was spent doing that. And then, just kind of staying up at night, worrying about getting it to the surface. I think that was one of the things that kind of consumed me during those seven months.

ZIERLER: Let's fast forward to February 2021, landing day. What was that day like for you?

WALLACE: It's always a little surreal. It's an odd thing because you basically spend every day of the development cycle thinking about it. You know that's the most dangerous part of the mission. It's just constantly on your mind. By the time you get there, there's really nothing you can do. You have done all the preparation, we've uploaded all of the final parameter sets, we'd done the final vehicle health checks, we had looked at all the configuration data that had come from the vehicle. We'd done everything we could think of. Early in the morning, there's this gathering of the technical leadership team where we have to look at the navigation information to make sure the last check on navigation looks good, that we're going to hit Mars at exactly where we want to hit it, and so there's always kind of a nervousness as to whether we're going to have to make last-minute trajectory correction maneuver or some kind of adjustment.

We're always on guard that some piece of telemetry's going to come in that we didn't expect, and we'll have to jump into a contingency procedure of some sort. But typically, none of those things happen. On Perseverance, none of those things happened. We were just getting ready for the event. There's some press you've got to do, you've got to talk about–it's a little hard to focus because your mind is on what's about to happen, and you end up talking about the mission, the development. There's a lot to talk about, the science, what you're hoping for, all those things. But really, you're kind of consumed, emotionally and mentally, on the things that are about to happen. I found myself, interestingly enough, thinking about my job on landing day, my only real job other than going and talking to people, was to be prepared in the event that there was something unexpected, an anomaly.

I found myself making call lists, text message lists, pre-writing emails with terrible connotations of awful things that could've happened. I think, in some ways, it was good because it kind of took my mind off of things. But right up until 20 minutes before landing, I was looking at an old video of the control room. I was there, head down. And I know exactly what I was doing, I was making a text list of all the senior management up and down the chain at headquarters and JPL that I would have to text in the event we had some kind of anomaly or something went wrong. That's what I was doing that final day. [Laugh]

ZIERLER: The sequence, entry, descent, and landing. I wonder if you could rank them in terms of your own stress levels. Which of the three is most harrowing as it's happening?

WALLACE: Entry is a little nerve-wracking because it's the front end of the process, but the number of things that have to happen for entry is not that significant. Normally, a spacecraft's slowly rotating for stability purposes, so we have to stop that rotation, and we have to release the crew stage, which is that ring on the top of the vehicle that gets us to Mars but is not part of the entry capsule, so that has to happen. When that happens, we drop comms for just a moment as it plots the antenna, then we pick it up again. That first sequence of things, it feels good to see them happening, but you know those aren't the most demanding parts of the mission. Entry, the capsule is inherently stable going into the atmosphere, and we're good at creating entry capsules, so we don't worry too much about that.

We do have to do something called hypersonic guidance, where we rotate the vehicle, and it has a slight lifting aspect to it, so it'll fly left or right, and based on where we think we are relative to the ground, it has to steer us. And that's a little tricky, so we worry about that a little bit. But I think the first real nerve-wracking moment–not that there aren't other things that are nerve-wracking, but the first time you're really sitting there going, "Okay, did it happen?"–was the parachute deployment. Parachutes are soft fabric goods. Engineers like to work in metal and electronics. We literally are dependent on seamstresses to do this right. They're not run-of-the-mill seamstresses, of course. These are experts in their field who have been sewing parachutes for a long time and know what they're doing. But it's a very different feel for us, and it's opening at essentially mach two. Parachutes don't like to open at mach two, and when they do, they often shred themselves, and something bad can and many times has happened in our testing.

Parachute deployment is just an enormously frightening moment. You're watching the doppler from the radio signal. You very often don't have comms, but you can see the carrier. Comms are lost as you create this plasma cloud as you're entering. But you can usually see the carrier, and you can see the doppler, which is basically measuring the change in the speed. As the capsule is going through the atmosphere, it's absorbing energy and slowing down. But it's when that parachute hits, and you see that big step function change. If you look at the video, you'll see us all glued to that doppler signal up on the monitor, looking for that step function change. It's exhilarating when you see it. That's a big deal. That's entry. Descent, you have to drop the heat shield, and the radar has to acquire the ground.

That's tricky, but that radar system is the same one we'd used on Curiosity, and I had pretty high confidence that was all going to work the way we expected it to. Then, the vehicle has to drop out of the entry capsule, and the engines have to fire. And that first firing of those big hydrazine engines is also very nerve-wracking because the propulsion system is much bigger than the ones we typically use on our spacecraft for orbital and cruise operations. These are big, throttle-able hydrazine engines, and there are eight of them, and every single one has to work. We're flowing a lot of fuel through them all at once. There are pyrotechnics going off, so there are shock events shaking the spacecraft. That's very dynamic, and it keeps your attention. Interestingly, on 2020, right when that was supposed to have, we got a pressure and tank low pressure alarm.

The pressure and tank provides the gas to pressurize the fuel to push it through the engines, so if we'd lost pressure in that tank, the propulsion system would not have worked. And I remember turning to my chief engineer, who was also an Entry, Descent, Landing expert, and I said, "Hey, what about this alarm?" He turned to me and said, "That's expected." My heart stopped racing for just a moment. I found out later that he misheard my question and thought I was talking about something entirely different, and that was not expected. [Laugh] That propulsion alarm was created by that pyrotechnic shock, which knocked out a pressure sensor in the tank. But thankfully, the tank never depressurized, and the descent worked well.

ZIERLER: Would that have been catastrophic if it had depressurized?

WALLACE: Yep, that would've been it. When that red alarm came up, I was very worried. He said, "It's expected." I thought, "Maybe we mask that, I don't know." I couldn't figure out why it would be expected, but I trusted him. [Laugh] He hadn't even seen it, he thought I was talking about something else. Anyway, we got through that. The rover has to separate from the descent stage into the SkyCrane activity, and that's something we expect to run smoothly. Really, the next thing we worry a lot about is the rover touchdown event. There's always the possible you'll come down on a big slope, land on a soft dune, hit a rock in high center and tilt, or the system is not going to slow down enough, and you'll hit too hard and damage the rover.

Or the system won't recognize that you've touched down, and it'll just keep coming, and the descent stage will crush the rover. There are a thousand things that can be catastrophic and mission-ending on touchdown. When we see the rover touch down, see that it's got a stable tilt, and that we have fired the pyros to cut the tethers, and there's no indication that the descent stage has landed on top of us, we still have communications and all those things, that's when they call out, "Tango delta nominal," which means touchdown nominal, and that's when we all start jumping up and down.

ZIERLER: We've talked before that there's a narrative flow to these rovers, that one builds on the next to help plan for one in the future. With that in mind, so much of the EDL was based on Curiosity, which was such a great success. What about ways that the mechanics of entry and landing for Mars 2020 were looking ahead to sample return? What were some of the improvements or ways we could use this to think about an even bigger or more expansive mission in the future?

WALLACE: We made a couple of specific changes, but the biggest fundamental change was that we sued something called Terrain Relative Navigation. Essentially, we added a camera and a dedicated computer to process the imagery from that camera. Once the heat shield fell off and the radar came on, we started taking pictures of the surface, which were then compared to maps from orbiters of that area. We feature-mapped and matched to figure out exactly where we were in Jezero Crater. By doing that and knowing where the specific hazards were, craters, escarpments, rock fields, we were then able to essentially divert away from those hazards and land in a safe location. Had we not had Terrain Relative Navigation, we could not have landed in Jezero Crater. It was too dangerous a place to go.

ZIERLER: What was so dangerous about the crater?

WALLACE: There are just too many hazards. If you look at Jezero, the delta comes in, and there's a big wall we could've hit, there are a lot of rock fields, there are a lot of dunes that are problematic. Just the sides of the crater, we could've hit. There are some high slope areas we couldn't have landed safely on. There were just too many hazards. Jezero was a candidate even for Curiosity, but it was filtered out very early on in the process because it was too dangerous. But it was a fantastic science site. By having Terrain Relative Navigation, we enabled ourselves to go to this very high-value science target on Mars, but number two, as you alluded to, it's a system that fed forward into Mars Sample Return, which has to not only land in Jezero, which is a dangerous place, but has to land very close to Perseverance to get the samples.

The next mission has to actually drive to what we call precision landing, recognize where it is on the map, and not just divert away from hazards, but go to a place that's close to the Perseverance mission or the cache that's on the ground, so it's enabling for future missions. It's also, by the way, a capability that we and other organizations are looking at for lunar robotic landers as well. And other commercial companies have actually utilized a lot of the algorithms and systems for their systems. It's something we've been talking about for more than a decade, and to be able to implement it and see it operate successfully is a huge plus.

The other thing we did, which was also a little bit feet-forward, is that we added a bunch of commercial, off-the-shelf cameras all over the spacecraft. For the first time, we could actually watch ourselves land on the surface of another planet. It was a very historic thing to watch. And that allowed us to better understand a lot of the engineering systems that we couldn't really understand from previous missions because we didn't have the imagery and high-definition videos. Of course, it was incredibly exciting for everybody to see that as well, and that's also a capability that will feed into the next launch.

ZIERLER: I want to make sure I understand correctly. Mars Sample Return will rely on Perseverance for actually collecting the samples. Is that to say that the rover for Mars Sample Return will not be doing any collection itself?

WALLACE: Very recently, Mars Sample Return has changed its architecture a bit. It had been a series of several pieces, actually three different missions. It was going to be a mission to launch a lander that would carry a Mars ascent vehicle to get the samples up into orbit. It was a separate mission that was going to bring something called a fetch rover to go out, get the samples, and bring them back to the Mars ascent vehicle on the first lander, in the event that Perseverance was no longer operational. The alternative is, Perseverance could've brought those samples directly to the Mars ascent vehicle, but the concern was that we didn't know how healthy the vehicle was.

Then, there's a third mission, which is an orbiter, which essentially rendezvouses with the samples in orbit around Mars, brings them back, and gets them down onto the surface of the Earth using an Earth return vehicle. It was really three different projects. Very recently, one of those missions, we decided to essentially not do. It was the fetch rover mission. The one that was going to take an additional rover to go collect samples, we decided that number one, Perseverance is very healthy at this point, and once we get down and last a year and a half on the surface, and it's still healthy, that's a very good sign.

We did a reliability analysis, which told us that the probability of Perseverance being healthy enough to bring samples to the ascent vehicle was very, very high. Then, we decided as well to build off the Ingenuity helicopter, which we flew on Perseverance, and add a couple fetch helicopters to that Mars ascent vehicle lander. In the event, which I consider unlikely, that Perseverance is no longer healthy enough to bring the samples to the Mars ascent vehicle, the helicopters can go out and bring the samples back. That's a change. There's actually not a follow-on rover in the next mission.

ZIERLER: Tell me about the timing considerations for the deployment of Ingenuity a few months after the landing of the rover. Why the delay?

WALLACE: There were several reasons. One, whenever you get onto the surface of a planet, you have to kind of look around and figure out what's going on. We had a lot of work to do to get through our initial commissioning activities. For instance, we have to jump from our entry, descent, and landing software to our surface software, and to do that, we've got to go through a cycle of uploading a lot of code, checking that everything is working properly, and then jumping to that code. That takes a while. Then, in order to deploy Ingenuity, we have to find a nice, flat space where it'll be safe to actually drop the helicopter.

And to do that, we have to be able to actually manipulate the robot arm, we have to have our communications systems, our UHF, our X-band all working properly. We have to make sure our power and thermal systems are all working well. The combination of just making sure that the vehicle got through commissioning and is working well, then finding a good location to actually do the deployment was–we expected that it could take actually quite a bit longer than it did. Perseverance was so healthy, and it turns out where we landed was actually a pretty good place to deploy the helicopter, so we didn't have to drive very far. It actually happened pretty fast relative to the timeline we expected.

ZIERLER: This might be more of a conceptual than engineering question, but do you tend to think of Ingenuity as a satellite support instrument of Perseverance, or is it its own mission that got there thanks to the rover?

WALLACE: Probably some of both. Clearly, it got there because we got it there, then it uses a lot of the infrastructure on Perseverance to be able to do its job. Everything from imaging for safe places to land, at least initially, to communication relays that go through us. We have wind sensors to give them environmental information, flight data. The rover is definitely a base asset without which this particular helicopter that operate. But the original concept for the helicopter was really just to use it as a technology demo, just to go see if we could make it fly. And that was challenging enough. We basically had defined mission success as getting up in the air one time and seeing it stably fly. Our original mission concept for the helicopter was really all about technology demonstration, and five flights was about as far as we thought we would get.

What happened was very different. We got through the five flights, the helicopter itself, although it's single-string, and there are a lot of commercial parts, has turned out to be very robust, and reliable, and has lasted a very long time in some very aggressive environments. We've now flown close to 30 times on the surface. And beyond that, the navigation systems and the self-sufficiency of the helicopter has allowed it to keep up with the vehicle. We didn't think it was going to be able to keep up with Perseverance. We're traveling 200, 300 meters a day sometimes, and we thought the helicopter was going to take several days to go through a cycle of flight and things like that. But everything just worked extremely well on this helicopter, to the point that the imaging it was taking itself during its flights was good enough to identify future landing pads for itself. It would fly out, do recon, find a good landing pad, come back, and then on the next flight, it could fly to that landing pad.

We thought we were going to have to survey every single landing site for the helicopter. The science team originally considered Ingenuity a distraction and worried it would detract from the fundamental science of the mission, to the point where we had to come up with what we called farewell flights, where we had to fly it over the horizon, just so it'd stop interfering with the primary science mission operations. But it was starting to fly out to places the rover had not gone yet and get imagery we didn't have yet, which informed the science community relative to where we wanted to go. It became a scout in the true sense of the word and really informed a lot of the early science activities, particularly on Perseverance, and it became a real science tool, part of the science mission. And that was very exciting for the Ingenuity team, very good for the science team, and quite a relief for the management, who were trying to keep the two camps from going at each other a little.

ZIERLER: It's really the surprising robustness of Ingenuity that allowed it to sort of gain a science mission in real time because nobody thought it would do as well as it did.

WALLACE: That's exactly right. There's a lot of commercial hardware, which generally doesn't like to operate at very cold temperatures. A lot of the very limited amount of energy that Ingenuity can collect during the day from its solar panels gets stored in the battery to keep things nominally warm overnight. But as we got into the Mars winter, it was not getting enough energy, and the nights were getting colder, and it couldn't keep its heaters on all night. Eventually, it got to the point where the bus didn't have enough energy to stay powered, and it would die. Voltage would go to very low levels, the heaters would turn off, and everything would get cold, and we thought it'd just freeze and never wake up again. These are commercial parts, stuff coming out of iPhones and things like that. And it's getting down to -150, -160 degrees Fahrenheit at night. But to everybody's surprise, it would rise from the dead the next morning. We called it Lazarus mode. There it would be, talking to us by noon or so. And this has gone on for months now. It looks like it's going to survive the winter, and we'll be able to fly it again here very soon.

ZIERLER: Given that the proof of concept for Ingenuity has been such a success, how might that inform future helicopter missions on Mars? What's been demonstrated, and what can now be envisioned as a result?

WALLACE: I think it's just like Sojourner, which was almost exactly like the helicopter. We had a seven-day mission, and we didn't think we were going to last beyond that. We had batteries that couldn't be recharged, so as soon as they were dead, we couldn't keep ourselves warm. We had a whole bunch of commercial parts, just like Ingenuity. We got to a point where we would die overnight, and the next morning, sure enough, we would rise from the dead. And Sojourner was really just supposed to be a technology demonstration. We put a little spectrometer on the back, thinking, "We'll show that we can carry a spectrometer." But we got out there, and we were doing real science. We were reaching rocks with contact instrumentation that the lander couldn't do. Exact same thing is true here on Ingenuity. It's a remarkable analog, to be honest with you. Just like we've had a decade's worth of rovers, we have a future that clearly involves helicopters. Right off the bat, the very next mission to the surface of Mars, we're now carrying fetch helicopters, fundamentally because Ingenuity worked so well. And there are more concepts with bigger helicopters, quad copters. It's really exciting, really great stuff.

ZIERLER: What have been some of the surprises in learning about Martian weather as a result of the Mars Environmental Dynamics Analyzer?

WALLACE: That's a good question for that team. I'm trying to think of what really jumped out at us from MEDA. I think the repeatability and the dynamic range of the wind speeds. First of all, it's been very helpful to understanding the risk and when we should fly the helicopter during the day, things like that. That's a more sophisticated capability that we did not have before. I think that's been beneficial.

ZIERLER: In terms of forecasting, obviously, it would be a great value for future missions, landing, and things like that. What about in addressing fundamental questions about life on Mars? Is there a connection between Martian weather and understanding what past life on Mars might look like?

WALLACE: There's a connection between understanding Martian weather and how to look for life, I would say. For instance, there's a radiation detector capability in the system, which helps inform us relative to that environment and what effect it might have on the chemical composition on the surface of Mars and what sort of chemicals might be affected and broken down by long-term exposure, things like that. I would say that's a true statement. There's not a lot of it, but there's some humidity and moisture in the atmosphere, which probably feeds back into some of the models that the science community uses. In that way, yes, I think there's a connection.

ZIERLER: Moving to June 2021, when Perseverance first starts doing science, what are the thresholds that the rover needs to pass in order to fully embrace its science objectives on Mars?

WALLACE: Our fundamental science objective is to collect samples. We have auxiliary science and technology objectives, like Ingenuity, producing oxygen with the oxygen-generation system, but our fundamental objective is really to collect samples. To do that, we had to make sure that the rest of our instruments and mechanisms were working. Obviously, we've got to be able to drive to find the targets we want. The mast has to be working. The remote-sensing capabilities up on the mast, the stereo camera sets, the laser-ablation capability that comes from the super cam instrument that's a standoff analysis capability has to be working. The big robot arm has to be operating properly. We have to be able to get our spectrometers out on the end of the robot arm down onto the surface so that we can interrogate these rocks we're potentially going to sample from and understand whether they're the rocks we want or not.

All that has to be working pretty flawlessly. Then, of course, the sampling system itself. We've got this big rotary percussive drill out on the end of the vehicle. For the first time ever, we were having to do these free-space docking maneuvers, where we'd engage different bits, take those bits off, then transfer tubes down into the belly of the vehicle, into the sample caching system. We have to be able to extract those tubes, we have to look to make sure they actually have a sample in them, we have to make sure we can then seal them and store them, then eventually drop them on the surface. That whole complex sampling system was by far the most complex mechanism we have ever taken to Mars. Being able to check all of that out and make sure that was working properly, all those things had to be working.

ZIERLER: Back on planet Earth, for you specifically, when are you named deputy director for planetary science?

WALLACE: The announcement was in March, but shortly after landing. First, I became the deputy project manager, then in mid-June, I formally transitioned off the project into the deputy director position.

ZIERLER: I assume the timing is not coincidental, that when Perseverance is in a good place, it was a good time for you to make this transition.

WALLACE: Yeah, there was always an unwritten assumption that if there were problems, I didn't need to transition. But we had a really strong team, I had a great deputy project manager in Jennifer Trosper. She's worked every mission I've worked since Pathfinder, and she knew exactly what she was doing. One of her many strengths is operations. She had been a longtime project manager on Curiosity on the surface. I had every confidence that unless there was some really gnarly hardware issue that had to be dealt with, I'd be able to confidently move into my new job. The mission still reported up through a couple channels to me, so I still got to talk to them.

ZIERLER: Between your predecessors and the mark you want to make on this new position, how expansive is the purview as deputy director of planetary science? Are you now sort of responsible for the entire solar system? How much of it is still about Mars just because of your own expertise? How big is your vista in this new role?

WALLACE: This particular directorate is about 60% of the laboratory base. There's a lot going on in the planetary sciences directorate. Not only do we have the operational Mars missions like Perseverance and Curiosity, and the orbiters like MRO and Odyssey, but we also have the Mars Sample Return campaign. There are the Mars program and all the Mars Sample Return activities inside the directorate, so I have plenty of opportunities to not have withdrawal symptoms from Mars. But it's much more than that. We have missions to Europa, a big mission called Europa Clipper, which is going to the moon of Jupiter, and it's a massive, complex flagship mission that's going to launch in 2024. They're right in the heart of the place in the mission where you've got to fight through a lot of challenges. We're actually doing more lunar work. We have Lunar Trailblazer, Lunar Flashlight.

We have three different lunar technology and science packages we're responsible for, so we're doing a lot of that work as well. We're always looking ahead. We just got the next decadal survey, which is the planetary decadal survey, so there are a number of exciting missions there. We're planning that formulation activity. We've got a number of functions and activities associated with Venus. We've got a discovery-class mission called Veritas, which is going to go to Venus. Then, we're building a big radar for the Europeans called VenSAR, which is going to go on one of their Venus missions. That's another plan that I've learned a lot about, and there are new concepts all the time for the new frontier- and discovery-class missions.

And then, there's one other mission called Psyche, which is going to an asteroid called Psyche, and it's a great discovery-class mission. We shipped it to the Cape and were scheduled to launch it this summer, but we were unable to complete the verification/validation of the software to a level where we felt comfortable we could launch it with confidence in the system. That's a planetary launch window we've missed, and we're looking at opportunities for next year. We've got to go through a cycle with headquarters to programmatically get all of that settled. But as a result of all that, I have been asked to become the Psyche project manager. As of about a week and a half ago, I've been reassigned to do that, so that's what I'm doing full-time for the time being.

ZIERLER: What are some of the big science objectives and engineering challenges for the Psyche mission?

WALLACE: Psyche's a great science target. It's a big asteroid in the outer parts of the asteroid belt. What's unique about it is that it's a metal asteroid, not a rocky asteroid. The going assumption is that it may have been the core of a planet that never fully formed. By going there, we'll hopefully confirm some of these theories, but also get a good look at something that has survived from the early days of planetary formation in our solar system. It's going to be a great encounter, and there are several orbital phases where we're getting closer and closer, and the imagery and science that will come back will be terrific and exciting. We're really motivated to get the rest of the work done on the project to enable the opportunity for launch, get it on its way.

ZIERLER: From Venus to the satellites of Jupiter, what are you most personally excited about, both in terms of new things to learn about our solar system and engineering challenges to overcome to get there?

WALLACE: Of course, Mars Sample Return is always going to be close to my heart, with all the Mars work I've done. And these planetary missions that are doing remarkable fundamental science. The spacecraft we're going to be sending to these big ice giants and ocean worlds are going to be searching for life as well. There's an opportunity to find evidence of the same types of things we're going to be looking for in these core samples we're bringing from Mars. To me, scientifically, that might be the most exciting part of the job. I would love to see some evidence that life has evolved somewhere other than the Earth. Even if we find that it hasn't in these environments that are conducive to life, that would also be fascinating. But I've kind of gotten to the point where I've heard enough that I feel like it's going to happen, that we're going to find something in one of these habitable environments, and for me, that's incredibly exciting on the science side.

On the engineering side, all these missions come with great engineering challenges. But we also have some lunar programs coming up. In particular, in the decadal survey, there was something called Endurance A, which is a big robotic lunar rover, and the idea is to take it to the South Pole and collect samples, like 2020, only big rocks, think a big truck-like thing, and to bring these samples to a place where an astronaut could actually view the samples, decide which ones they want, and bring them back. And in fact, we're talking about ways of modifying this big rover vehicle so that we can change its mission, take different payloads, and things like that. It's a really cool mission concept, and it was very highly rated in the planetary decadal survey. A lot of these missions will take 5, 6, 7, 10, 12 years to get to their targets. That's the nature of it. The moon's right there.

We have an opportunity to do something that's challenging for our roboticists and that's a little less formal than a flagship mission, so we can bring a lot of new technology to bear, which is engineeringly very exciting. We could do this even kind of in a skunkworks mode, much like Mars Pathfinder was done. I would like to see us exercise those muscles we used to use, and we do use them in certain places, but I'd like to see us redevelop that fast turnaround, not afraid of failure kind of mentality a bit, and I think there's an opportunity from an engineering perspective to do that. It's the kind of thing where people are coming out of college, seeing these commercial space organizations really pushing the envelope, and it's an opportunity for us to do the same thing at JPL.

ZIERLER: For the last part of our talk, a few forward-looking questions. First, we're really waiting for Mars Sample Return to truly understand the evidence for past life on Mars. When we talk about the ocean worlds and the outer solar system, are we going to need sample return missions to have that same level of confidence? Or will the engineering get to the point where the analysis of those ocean worlds might not require waiting another 10, 20, 30 years for a sample return?

WALLACE: There are some sample return concepts from comets and other outer bodies, but to the first order, the idea is to get orbiters with the capability to carry the instrumentation they need to find those signatures in situ, by flying through a plume, by using remote spectroscopy. And there's also a number of lander concepts where you can put a lander down on these icy oceans and either go through the outer ice sheet or use what's at the surface of the ice sheet to really get a sense of whether or not there's a habitable environment or potentially even some form of extant life there. Interestingly enough, it's almost easier sometimes to find extant life, because extant life responds to certain things, than what we're doing on Mars, looking for extinct life. That's all chemically based, trace organics, and things like that. It's a different type of analysis, although there's a lot of crossover. But the idea is to be able to do those missions primarily in situ.

ZIERLER: Given what you've accomplished so far in your remarkable career trajectory, are you ever concerned at JPL that you'll rise to a level where you'll be removed to an uncomfortable degree from the science and engineering, or is JPL simply not like that?

WALLACE: Yes, I worry about it. The truth is, you do get to a point where you're not as familiar with the technologies and tools as the engineers who either stay entirely technical–we have a lot of those people at JPL. They're called fellows, principals, things like that. They just have no interest in managing anything. They just want to do a technical job and be the best in the world at it. Then, of course, folks coming out of school, people in mid-career, the technical capabilities they have are remarkable. I'm not even going to pretend I have those skillsets anymore. But I find, and this is true of pretty much everybody at JPL, is that nearly all of us got promoted because we were good technically. We developed that base understanding of core fundamental physics, chemistry, electrical engineering, then we built on it and exercised it enough that we understood how to take that skillset and make or do something with it.

Just about every manager I've ever worked with at JPL is still capable of understanding very difficult technical problems. I like to think I am, too. [Laugh] I feel I am. The key, in my mind, and this is what makes JPL unique, is to make sure your managers never forget that they can do it, to encourage them to do it. I often hear people say, "You're the manager, you worry about cost and schedule. You're the technical person, you worry about making the circuit that works and doing this analysis." I always tell the leadership on 2020, and particularly on Perseverance, "I don't accept that. If you work for me, I expect you to feel just as responsible for the technical work in this mission. Don't ever come and tell me that it didn't work because so-and-so didn't do it. You have the ability to understand this technically. Yes, you have schedule, cost, and other implementation responsibilities. But you are not relieved of that responsibility." And I'd tell my chief engineer the same thing. "Don't bring me a technical solution that doesn't get me to the launchpad in 2020. You understand this. You've built hardware."

I never let people separate into those camps on 2020. I think it's a fundamental difference between us and a lot of other organizations out there. You don't see it in the military-industrial relationship at all. There's a clear separation. And in many businesses, where the bottom line is so important, they'll hire people because the bottom line is important, and it's about profit. They're very focused on that part of it that may or may not have those technical skills. I think the reason we do hard stuff and do it well is because the people here can do both. I don't think I'll ever have to completely give up that part of my interests. Because I don't think it'd be a good thing for me to do. And it was not unusual for me, even as a project manager, to go down to pretty low levels to understand something because I believed I could, and I think it's important.

ZIERLER: Maybe that culture that you're describing is really central to the magic of JPL, what makes it all possible.

WALLACE: I think it is, 100 percent. And I think it was modeled by so many people before me, including Charles Elachi. A preeminent world expert in radar science and systems becomes the manager of this massive, 7,000-person organization with all kinds of programmatic and administrative responsibilities. And we constantly bring scientists, and in some cases, engineers, into that role. I think it's 100 percent the fundamental driver for the magic that JPL can create.

ZIERLER: Matt, this has been an incredible series of discussions, a treasure for Caltech history, for JPL history, for space history. I want to thank you so much for taking time out of your busy schedule to do this with me. Thank you so much.

WALLACE: I was happy to do it, David. I want to thank you for asking really good questions. You obviously did your homework. I have given a lot of interviews, none at this level of detail, and this was just really enjoyable to do, so thank you.

[END]