Kim Steadman, a systems engineer for the Perseverance Mars rover, details the how, when, what, and why behind our incredible discoveries on Mars.

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ERIC: From the Museum of Science in Boston, this is Pulsar, a podcast where we navigate towards answers to the most intriguing questions we've ever gotten from our visitors. I'm your host, Eric, and the Perseverance rover has landed in Boston. While the real spacecraft, and its helicopter buddy Ingenuity, have been exploring Mars for a year and a half, the Museum of Science is now hosting a full scale replica in our exhibit halls. And while we often hear about the amazing science results coming from the rover's explorations, sometimes our visitors ask what a typical day looks like for Perseverance. My guest today is Kim Steadman, a systems engineer for the Perseverance rover, who has been working at NASA sending spacecraft to other planets for nearly 25 years. Kim, thanks so much for joining me on Pulsar.

KIM: My pleasure.

ERIC: So part of your job is to be the operations lead for one of the many scientific instruments on board the Perseverance rover called SHERLOC. So can you give an overview of what SHERLOC is?

KIM: Sherlock is at the end of the arm. And it's a Raman spectroscopy instrument. And so what we do is we use SHERLOC to tell us what the rocks are made of. And basically, we're looking for organics with SHERLOC.

ERIC: Can you talk about what organics are and why they're so important to look for?

KIM: Well, organics are the building blocks for life. But what we really want to find with the Mars 2020 Perseverance rover is what they call biosignatures, something that was formed inside the rock that most likely came from some sort of life being there, like billions of years ago. And so that's what we're trying to do. And that's why we're taking samples. So when we approach a rock that's very interesting to the science folks, we'll do what was called an abrade patch. We abrade away the first 10 to 11 millimeters of the surface of the rock, which gives SHERLOC a nice, flat area to do their science on. If we take a sample, we take two samples. Sometime in the next few months, we're hoping to drop our first cache of samples and then keep the rest inside the rover. And eventually, more sample return will happen. And we will go and bring the samples back.

ERIC: So you can do a bunch of science on Mars with the instruments and everything that's there. But the best would be to bring all that stuff back, which we've never done before. And that's super exciting. So how does SHERLOC work? Is it a camera? I know there's lasers on the spacecraft.

KIM: It's kind of a doughnut laser, there's a hole in the middle of it. We shoot it at the rock. And then we look back at what is reflected back into the instrument. And then the scientists can look at that data and determine what the rock is made out of.

ERIC: So if you think about it, it's not that different than studying Mars from Earth. You're just looking at light, except instead of doing it from 100 million miles away, you're doing it from like, inches away and getting a better picture.

KIM: Like yeah, like millimeters away.

ERIC: What do you think it would mean to discover evidence that life had existed on another planet? If you found really great evidence in one of these spots that you stopped at, what do you think it would mean? What it would mean to you?

KIM: I mean, it would just be fascinating and just change the story of our solar system, right? Because right now, we're the only life that we know of in our solar system, and, you know, the only life that we've detected in the universe. And so it would just mean that we're not alone, because if it formed on Mars billions of years ago, but it didn't get very far because of the way that Mars lost its atmosphere, that would just change a lot of things.

ERIC: So what is your role as operations lead for that instrument? Are you deciding what it gets to do? And when it does that?

KIM: No, the scientists decide that and I just make sure that they get what they want, and that it goes up to Mars and operate successfully. So the science team will tell you: we saw this cool rock, we want to know more about it, and they give you a target.

ERIC: How do you take that and tell the rover to actually go investigate that? Is there coding involved? What does it actually look like to go from 'we want to get the sample to getting the measurements?

KIM: Well, there's a lot of people involved in that because once we've picked an outcrop or rock that we want to science, then SHERLOC is on the end of the robotic arm. So for us to do anything the arm has to be deployed and SHERLOC has to be placed by the rover planners. And so we have a whole team of people called rover planners. And they're responsible for the mobility, all the driving that the rover does, and they're responsible for all the arm activities. And then on top of that, we have a sampling and caching team that's responsible for abrading and sampling. And so the rover planners work with the sample and caching people to decide, is this a rock that we can abrade? And if they decide yes, then the science team on that rock will pick several different targets with their most favorite target first, and then the rover planners will tell us if they can abrade that target. Because the turret on the end of the arm where we have the drill, it weighs like 100 pounds and it's very big. And so we don't want to damage SHERLOC while we're doing our abrading or sampling. And so the rock has to meet all these criteria for the rover planners and the sampling and caching people. And so once the rover planners and the scientists decide on a target, then they'll go ahead and do the abrade. And then once we see the images of the abraded patch, it's like five centimeters across. And our footprint for SHERLOC is like six millimeters by six millimeters. So they'll pick a spot on that abraded patch that they want to put the instrument. And the same thing happens with the rover planners, to see if they can put our instrument there. And there's some negotiation and then we send up what are called sequences. And so we just have basic commands, you know, because there's flight software on the rover, there's flight software on the instrument. And then we just have our commands that are like, you know, spectroscopy command, and then we put all of our parameters in there on how many pulses per point, how many points, what map we want to use. And so it just looks like a very simplified, you know, computer sequence.

ERIC: Something that not a lot of people think of is the huge team, the amount of people it takes to do any little bit of science on Mars. I mean, the amount of people that you need to coordinate to make sure everything is safe. It's a lot.

KIM: Yeah, it really is a lot, and everybody has to work well together. And so one of my other jobs besides SHERLOC operations lead is as a tactical uplink lead. And so when we go into work Monday through Friday, we are planning and uplinking all the things that the rover is going to do for the next sol. The next day on Mars, we call that a sol. And so in my other capacity, I'm kind of the herder of cats to make sure that every team knows what they're supposed to do, that every team gets the information that they need to do their job. And that everybody delivers their sequences in time for us to do integrated modeling, where we run all the sequences that the rover is going to execute the next sol through some software to tell us if it's going to be safe, if we're breaking any flight rules, and stuff like that. And so my job is to make sure everything gets done gets done correctly. And we're ready to uplink to the rover when when it's time to send her the sequences so that she can have a wonderful day on Mars.

ERIC: So basically, one robot with a lot of people trying to do a lot of different things, trying to collate it and make sure that, you know, you can use every minute of the day and nothing gets wasted, but also that you're not going to run into any rocks on the way or make sure you're not going to have too many commands or anything. It sounds pretty complicated.

KIM: It is. The care and feeding of a spacecraft or rover is very complicated. And it takes a lot of people, a lot of specialized people, that know exactly what they're doing. And some systems engineers to make sure that across the whole system, what we're doing is safe for the rover, and it's going to give us what the scientists want. Because if we get bad data, you know, because somebody did something wrong, it's not very useful.

ERIC: You said Monday through Friday. And I know that Mars time and Earth time are not the same. Just because it's nine in the morning at the Jet Propulsion Lab in California does not mean that it's even daytime on Mars. So do you have to kind of work around the clock sometimes? Are you able to get far enough ahead with the commands and the planning that you don't really have to, you know, work on Mars time, which would drift wildly and kind of mess up your sleep?

KIM: Oh, yeah, yeah, we did Mars time when we first landed, I think we did it for 67 days. And yeah, the day on Mars is just a little bit longer than a day on Earth. And so it's like, perpetual jet lag because you go into work, like at 8am one day, and the next day, maybe you go in at 10:30am. And you just keep walking down to stay on the same time as the rover. And then eventually, you're going to work at 2am and 4am. And you're wondering, what day is it? Where am I? Because you always know what sol is on Mars, you always know what the rover is doing. But you really have no idea on Earth, what day or time it is. And then when you eventually come back around, and you're you're coming home from work at like 10 or 11am. And the sun's out and you're like, look, people. I haven't seen people. There's traffic, what's going on. So we only do that for a short period of time because it is so, so difficult to change your sleep schedule like that. And so because of the time difference, we hit what are called restricted sols, where the Martian day is so far ahead of us that we'll spend a day planning and then uplink. Because we always uplink about the same time, like 9:30am on Mars, and then we get the sequences ready to go. And when we're really restricted where Mars is ahead of us that sequence, that whole load won't go to the rover until the next day, like 1pm. So when we come in the next day to plan, we don't even know what happened because it hasn't even gone to the rover. And so you have to do some little tricks, and you're a little limited on what you can do.

ERIC: It sounds like constant juggling, constant contingency plans. Even though these rovers, like Curiosity has been going for 10 years now. Hopefully we'll get that much for Perseverance, but every second is still priceless to have a robot on another planet.

KIM: It is, and Mars is always throwing us curveballs, you know, we don't always get exactly what we expect with the drive. So we command the drive, and then we find out what happens. And so sometimes we'll command a really long drive, but just in the first few meters, the rover will hit too much slip or the wheels just aren't getting enough traction. And so to keep herself from embedding the wheels in dust and dirt, getting completely stuck, if we see a certain amount of slip, the rover just stops. And so she's very good at protecting herself.

ERIC: Now, the Perseverance model that's currently at the Museum of Science is within our artificial intelligence exhibit, because it has a couple of different systems on board that have some AI. So can you talk about some of the AI that Perseverance uses or will use sometime in the future?

KIM: Well, the biggest one that we use the most often is auto navigation, where you tell the rover, that's where I want to go over there. Every day, we get these maps, we get images and stuff from the post-drive imaging. And then we build that into a 3D map that the rover can drive on. And so she can do that herself too. During auto nav, you tell her where to go, because she has a map in her brain. And then as she goes along, she takes images and processes those and picks her own path. And so that really allows us to drive a lot further than we normally could, because she knows, oh, I can't drive over a rock that's higher than this. And so if she sees a rock like that, she'll go around. It ends up with some interesting drives when we're in a very complicated rocky area, where she will go this way and say, no, that's not working, she'll back up and go around this way. But it really allows us to drive a lot further. And she also has something that she makes at the end of her drive, she'll make a world map of all the stuff that she can see. And so then so she can drive two sols in a row, because she makes us a world map at the end of one day. Because we can't drive at night, we can't drive very late in the day, because she can't see. And just like when we drive at night, she doesn't have any headlights. So the next sol, she can just continue driving where she left off. And so we end up having three sols in a row where we could drive, which we couldn't and still can't do with Curiosity.

ERIC: So yeah, we heard a little bit about the advanced self driving capability in an episode with one of the mobility engineers last year, right when Perseverance landed, and it sounded like it was going to be pretty game-changing. How is it in practice? How's it working on Mars? Have you needed to make any adjustments on the fly?

KIM: It's amazing. Yeah, we have had to make some tweaks to it, but mostly with data volume, because on these long drives she takes so many images as she goes along, it was just filling up her hard drive like on your computer. And so we had to tweak that a little bit when we had really long drives back to back to back. And the best thing is that we came in one day. And we didn't have what we call our decisional data. To get data back from the rover, she sends all of her information, her engineering information and our science information, up to one of the Mars orbiters, and then they send it back to us. And so we had a delay in getting our data back. And so we had no post drive imaging, because the DSN station that the orbiter was supposed to send us the data back through was what we call red, it wasn't working. So it was down for repair. And so we just didn't get our data. But because we have this functionality on the rover where she can, you know, make her world map. And then she can drive to that, we were able to command a drive, even though we got no post-drive imaging, or no post-drive data from the previous sol. And that was just like magic, because usually we would just be stuck. And we would just do untargeted remote science because we don't have any data. But because of this new functionality we drive. It was awesome.

ERIC: Well, it sounds like that system is really helping the mission be more efficient. What's the longest you've had the rover drive on its own?

KIM: Gosh, I think the longest drive we've done is like 500 meters. But I think that was over several days.

ERIC: Well, it's still impressive. It's more than the previous rovers could do, right?

KIM: Well, every rover has had auto nav starting with I think Spirit and Opportunity when they were doing long drives, but it's just gotten better and better. And so the thing that's new for us is the multi-sol driving, because on Friday, we build a three sol plan to cover you know, Friday, Saturday, Sunday. And so if we have the power on the rover, we can drive all three sols where the other rovers have never been able to do that. So we always build on the technology and what we've learned from the previous rovers. And so this has just been a great step forward and shockingly successful.

ERIC: That's really great to hear. To finish up, the mission is a year and a half in. There have been a lot of awesome science results. What's coming up next? What will Perseverance and your team get up to in the next couple of months?

KIM: Sometime soon we're going to be dropping our first sample cache and that's going to be really exciting. So we'll actually take the sample tubes that we've been collecting and put half of them down on Mars so that Mars sample return can go and get them later. Just in case something happens to our rover. We don't want those samples to be stuck inside. And we're also going to be driving up on top of the delta. So we landed in Jezero crater and the whole reason we landed in this crater is it has this beautiful delta formation. A delta is where a river used to flow into a lake, and it leaves all these deposits of sand and dirt. Anywhere on Earth, where there's a river delta, there's a bunch of life. And that's why we want to go there. And so we've explored the crater floor, we've been exploring what we call the delta front, right in front of the delta. And so eventually in the next few months, we're going to be driving up on top of the delta, which is the whole reason we went to Jezero crater, and it's just so exciting.

ERIC: We can't wait to hear about the results of Perseverance exploring that delta. It sounds awesome. Kim, thanks so much for telling us all about a day in the life of the Perseverance rover.

KIM: Well, thank you very much. I appreciate it.

ERIC: You can see a full scale model of Perseverance at the Museum of Science in our new exhibit Exploring AI: Making the Invisible Visible. From home, you can learn about the challenges of exploring the Red Planet in our Making it to Mars video series at mos.org/planetarium. Until next time, keep asking questions.

If you liked this episode, be sure to check out:

How Do You Land a Robot on Mars?

Mars Helicopter? Really?

Who Gets to Drive the Mars Rover?

Which Mars Rocks Are Best?

How Big Were the Apollo Moon Landing Computers?

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