NASA’s Perseverance rover is set to touch down on Mars this week, and we had the opportunity to talk to one of the people who had a hand in bringing this mission to fruition. Adam Steltzner is the chief engineer of the Mars 2020 project at NASA’s Jet Propulsion Laboratory (JPL), and he designed the rover’s ambitious sample return system. He’s featured heavily in the upcoming Nat Geo documentary Built for Mars, which follows the twists and turns of getting this robot to the red planet. Our conversation below was lightly edited for clarity and length.
wfoojjaec: When preparing for Mars 2020, was the plan always to build on the Curiosity chassis?
Adam Steltzner: Yes. From the very, very beginning, our currently deputy project manager, who was previously the flight system manager on Curiosity, after Curiosity was off from Earth and on the way to Mars, he sat down and blue sky said, “How much spare equipment do I have?” At Curiosity’s launch, there was no plan for any follow-on missions. So Matt Wallace sat down and said, “How much equipment do we have? Could one put that together and defer the costs of a build and get a mission to Mars building essentially on the investment that we’ve made with Curiosity?” From its very first–the idea was to build off of Curiosity’s foundation.
wfoojjaec: Were there any ideas pitched for Perseverance that you just couldn’t make happen because of time or expense?
Adam: Not really!
wfoojjaec: You got everything you wanted?
Adam: I’m just making sure that–it’s rare that somebody says, “Did you get everything you wanted?” That’s why it takes me a while to say yes because I’m like, “I guess I did.” I’m not used to that, but yes.
wfoojjaec: What’s the specific geological significance of Jezero Crater where Perseverance is going to touch down?
Adam: The scientists want to go to Jezero crater, they tell me, because it was once a lake back in that wet time for Mars, and right where we’re landing was the delta. I am being educated that deltas are deltaic deposits. That’s to say, the sediment that creates the fan-like structure of a delta.
The fan-like structure of a delta comes from when a river runs into a bigger body of water, the water slows down. When it was moving quickly, it was able to carry particles and sediments with it in suspension, in Stokes flow. But when it slows down, mean velocity in the flow is reduced, and it can no longer carry those particles in Stokes flow.
When they settle out, they are incredibly good at preserving evidence of life that was carried with those stream beds or living there, as they add on a protective layer of geological material. Deltaic deposits are the best places we find here on Earth to look for signs of ancient life. The Jezero Crater, where it is on the globe of Mars, and the fact that it’s wet, the fact that we’ve got a very clear delta are the reasons that we wanted to go to Jezero.
wfoojjaec: The Ingenuity Helicopter is just a technology demonstration with no important instruments, but if it flies and works beautifully, is there any way that it could be used to help Perseverance complete its mission?
Adam: A helicopter or an aerial asset such as Ingenuity could be very, very useful to a surface mission. Ingenuity herself, because she’s a ride-along and a late addition, is sized such that she doesn’t have much of a life expectancy on the surface of Mars.
Seasonally, we will get to a place where the temperatures drop and there’s not enough sunlight for her to maintain battery temperature overnight to keep the battery cells good. She’s got a limit to her life expectancy, and therefore, we don’t have a plan. We don’t believe there’s an opportunity for a windfall use of Ingenuity. Now, if we’re wrong about all that, she survives, there may be, but we think that we’re really taking her there proving that we can fly on the surface of Mars in less than one percent of the atmosphere we have on earth. It’s very, very low density. That’s a very high altitude here on earth, way higher than helicopters ever fly.
We had to totally redesign the relationship between the elastic flexible modes of the rotor system and the atmospheric interaction modes. It’s upside-down compared to how helicopters are designed here on earth. She’s also taking some lightweight, highly integrated avionics electronics, flight electronics, that are offshoots of commercial consumer electronics. For instance, she has a Qualcomm Snapdragon chip, which is a cellphone chip that is the size of my thumbnail and does an amazing job doing pretty much what our visual compute element, which is the size of a lunchbox, does.
wfoojjaec: Let’s talk about the sample return system. Why go to the trouble of bringing the samples back to Earth? What can you do with a Martian core sample here on Earth that you can’t do with a rover on Mars?
Adam: The answer to that is pretty easy. Anything you want. The problem with the other way, that is to say, doing the science investigation, what we call in situ at Mars, is you have to conceive of the measurements, you have to conceive of a hypothesis. You conceive of your scientific hypothesis, that there are, let’s say, organic materials trapped in the clays found here. Then you need to say, “what science instrument could take measurements to determine if there are organic compounds there? Can I miniaturize that science instrument?” Most of the time, the answer is, “No, you can’t,” but for some science, the answer is, “Yes, I can.”
So, you take something that would be the size of a room, a big piece of equipment, and make a miniature version of it that’s hardened for space flight, stick it on a rover, put it on Mars. You make the measurements and it’s like, “Yes, it does look like there’s organics. Are they biogenic? Gee, it’s hard to tell. Boy, I would like this other measurement.” Now I hypothesize an instrument to do that. That could be miniaturized and ruggedized and I do another expedition to Mars.
The problem is, as is always the case when we’re learning or understanding, each question we answer opens another question, and each of those question cycles is about 10 years for you to figure out how to build it, shrink it, build it, put it on Mars, take that measurement, get a new question, and do it again. If you bring the samples back from Mars to Earth, you have all of Earth’s equipment, all of Earth’s scientists, all of the ingenuity that is across this globe that can be brought to bear on the investigation.
wfoojjaec: It seems like if you’re bringing all these samples back and you’re going to do all these tests, you want to make very certain that you don’t accidentally analyze any bits of Earth.
wfoojjaec: How do you make sure? You’re building these things in the Earth’s atmosphere. There’s Earth all around you. How do you make sure none of it gets into the sample containers?
Adam: It’s a humungous pain in the ass. We’ve built the cleanest hardware that has ever been put in space. I designed the sampling system and invented the cleaning protocols. It was a huge effort. The way you do it is you carefully choose your materials. For instance, the sample tubes are made out of titanium, but they have a titanium nitride surface. The titanium sample tube is exposed to a low-pressure plasma of nitrogen gas in a high-energy environment. That high-energy nitrogen plasma penetrates the surface of the titanium and creates titanium nitride, which is a refractory material and is incredibly inert. It’s more passive than gold. That passivity means that things don’t like to stick to it. It’s like super Teflon in some sense.
Then we take that super clean passive system sample tube and we put it behind a fluid mechanical particle barrier. This is a specially designed barrier that does not allow any particles greater than 0.3 microns in size to make it into the volume in which the sample tubes are sealed. Then once they’re in that, we put them in an oven, and we bake that oven for hundreds of hours and clean everything out of the inside of that tube. Then we have something that looks a little bit like, in some sense, functionally, it’s a little bit like a Band-Aid. That is to say, it’s sterile, individually wrapped.
wfoojjaec: Did making the “cleanest hardware ever” cause any unforeseen issues?
Adam: Yes! Here’s a fun fact. Every friction measurement that an engineer has ever known is a friction measurement that’s conducted with a very, very thin film of hydrocarbons present on the surface of the material. If I take a piece of aluminum foil and I bake it, let’s say, at 500°C in an oxygen environment, that will combust all of the hydrocarbons on that piece of aluminum. Then I bring it outside of the chamber in a clean room, and I put it on a desk with a HEPA-filtered flow bench, with absolutely sterile, particle-free air blowing over it. Within hours, it will have accumulated a monolayer of hydrocarbons that just get sucked out of the atmosphere.
Your breakfast, my lunch, the decomposition of fall leaves — Earth is a soup. We think we’re walking around, but we’re really swimming in a soup of life and the byproducts of life. Those show up on every single piece of stuff you’ve ever touched. Some stuff has lots less of it. For instance, if you have a piece of titanium nitride, it doesn’t have as much. It accumulates more slowly, and it accumulates less, and it accumulates slightly different, in a molecular weight sense, than if I have a piece of aluminum. Aluminum’s very hungry. It has a reactive surface.
If you go to a testing laboratory that’s testing the friction coefficient between 440 stainless steel and nitronic 60, and they say, “Oh, yes, the friction coefficient between these two is X.” Well, what they were really doing is they were testing it with that thin film of hydrocarbons present on it. When you bake those away like we did, it’s much stickier. Everything is much stickier. We struggled a lot with that. In fact, we had to change, on the fly, our cleaning protocols. We had originally envisioned baking at 350°C for about 10 minutes, and we had to back down to 200°C, essentially to leave a little bit of hydrocarbons present on parts. When you go into this unworldly clean domain, you find yourself fighting against challenges that were hard to anticipate because they are challenges very different than any faced with all of human activity to date.
wfoojjaec: You need, I think, two more missions to get these samples back to Earth. Correct?
Adam: That’s correct.
wfoojjaec: Ballpark, when do you think you can have them back on Earth?
Adam: About 10 years, 10 to 12 years from now.
wfoojjaec: If Perseverance discovers life on Mars, when you get those samples back and you’re looking at them, what’s the piece of data that convinces scientists something was alive in Jezero crater three billion years ago?
Adam: Signs of ancient life can come in different forms. To make a convincing argument, you are likely to have several of those forms of evidence aligned. For instance, you would look at morphological shapes that look like microstructures or microfossils. Then you would look to see if those shapes were made out of what I think the scientists called carrageenan, which is essentially the carbon residue of life. You would use multiple lines of evidence.
You would look at the location in the geological deposit that these things were in and see that it was associated with, for instance, a lake shore in the past. You would use sets of evidence that were aligned and corroborated the position that ancient life in the form that you see. Just as we do today. You find things called stromatolites. Stromatolites are algae mats. They make this special form. That form, although not uniquely biotic — there are abiotic processes that can make similar forms and shapes in geology — but when you find the stromatolite-like forms and you are in a place where it’s an ancient lake bed, and the mineralogy of the elemental makeup of the stromatolite demonstrates the presence of these carbon-rich compounds associated with life, then all of those things together say that is a biotic stromatolite. That was an ancient lake bed, and that microfossil was the algae that was forming at the edge of the lake.
wfoojjaec: What does Mars smell like? Obviously, you haven’t been there to smell, but if you were to guess?
Adam: Mars smells like your grandparent’s clothing trunk that hasn’t been opened in decades.
wfoojjaec: I like that. Why?
Adam: There’s that kind of like empty, there’s a hint of something… it’s dry, it’s old, it’s dusty.
wfoojjaec: Kind of musty?
Adam: Yes. That’s what it is for me.
wfoojjaec: How far away do you think we are from being able to colonize Mars? And would you ever go?
Adam: I hope infinitely far away from being able to colonize Mars.
wfoojjaec: You don’t think that Mars is someplace we should live?
Adam: No. In the evolution of Earth, the Earth’s environment has gotten pretty bad at times. Most notably, about 65 million years ago, when an asteroid smashed into what’s now a region of the Yucatán Peninsula and killed all the dinosaurs with a dusted atmosphere. It killed a lot of the plants and 90 percent of the species. In the middle of that moment, the environment on Earth was still infinitely more habitable for life than I think we could ever make Mars.
We evolved to have one Earth gravity that keeps my spinal fluid in the right pressures as I stand, and if I don’t stand frequently, my body doesn’t like it, I age poorly. People who are bedridden die very rapidly because their bodies are made to move and they’re made to move in one G. The fibers of my bones grow in directions of the principal stress state of my skeleton as defined by the way it interacts with Earth’s gravity. I am so much of Earth that me away from Earth isn’t really me, and so that’s true for you.
wfoojjaec: What do you think is the next game-changing technology for planetary exploration?
Adam: I think the next game-changing technology for planetary exploration, which may not sound too whiz-bang, is the utilization of commercial, off-the-shelf consumer electronics. Here is an illustrative example although a preposterous one. Imagine 10 iPhones sitting in a box. They are not radiation-hardened, but they vote. A processor asks them all the same question and takes a voted result. The ones that have gotten gorked by a cosmic ray running through the neighborhood or a little local radiation as we approach Jupiter are just counted in the voting scheme. We do this all the time with certain things like, for instance, a Boeing 777 has got three computers and they do triple loading arrangements so that if one computer has a hiccup, it doesn’t bring the plane down.
Imagine a set of iPhones in a voting scheme somehow being utilized to overcome the radiation environment. The processor that we have running Perseverance is the same one that ran Curiosity. It’s the same one that was in my Beige box G4 Macintosh in 1999 when I got my Ph.D. When we build the [Perseverance] computer, we do it with a person hand-soldering wires to wires. It’s heavy, it’s expensive, and 25-years-ago technology. There’s 10 times the power, 100 times. I haven’t done the math lately on my current iPhone to how much more processing power it has. [Ed note: We checked, and the current iPhone is about 15-20 times faster than the CPU in Perseverance.]
An interplanetary spacecraft’s about a billion bucks. When launch services come down to the order of $100 million, the launch is no longer the big price, the price is the building of the thing. Now you say, if I really wanted to reach out and do a lot more exploration, how do I bring the price of the spacecraft down? Well, you can look across the whole gamut, but one of the big places that could be is in the way we control, the way we program, the kinds of ways in which we operate the vehicle. Taking cues from modern technology and applying it to space exploration may allow us to drive down the cost and further increase the value proposition of our robotic exploration of space.
If you want to learn more about NASA’s Perseverance rover, the documentary airs on Nat Geo on Thursday, February 18, at 8 PM ET. That’s the same day Perseverance will touch down in Jezero Crater, which NASA has scheduled for about 4 PM ET.