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“Houston We Have a Podcast” is the official podcast of the NASA Johnson Space Center from Houston, Texas, home for NASA’s astronauts and Mission Control Center. Listen to the brightest minds of America’s space agency – astronauts, engineers, scientists and program leaders – discuss exciting topics in engineering, science and technology, sharing their personal stories and expertise on every aspect of human spaceflight. Learn more about how the work being done will help send humans forward to the Moon and on to Mars in the Artemis program.
On Episode 215, Tom Statler describes a NASA planetary defense mission to test technologies and capabilities for redirecting asteroids. This episode was recorded on August 18, 2021.
Transcript
Gary Jordan (Host): Houston, we have a podcast! Welcome to the official podcast of the NASA Johnson Space Center, Episode 215, “Redirecting Asteroids.” I’m Gary Jordan, and I’ll be your host today. On this podcast, we bring in the experts, scientists, engineers, astronauts, all to let you know what’s going on in the world of human spaceflight. Chances are, you might have seen a doomsday movie in the past, where an asteroid comes crashing into the modern Earth with devastating effects. Certainly not an unfounded idea; happened to the dinosaurs. But you’ve probably wondered what can we do to protect the planet from something like this? Enter NASA’s DART mission, D-A-R-T, stands for Double Asteroid Redirection Test. It’s a planetary defense test mission, meaning we’re going to try out some technologies and capabilities on a binary asteroid system that’s not really a threat to the Earth but will act as a good proving ground to learn how to redirect potentially hazardous asteroids. So joining us is Dr. Thomas Statler, DART’s program scientist based at NASA’s Headquarters in Washington. Tom discusses more details into the overall mission and technologies, like smart navigation, rollout solar arrays, and xenon thrusters that will be used on the mission. Exciting stuff. So, let’s get right into it. Enjoy.
[ Music]
Host: Tom Statler, thanks so much for coming on Houston We Have a Podcast today.
Thomas Statler: Hey, thanks, Gary. It’s great to be here talking about DART. We’re going to make sure that a rock from space doesn’t send us back to the Stone Age.
Host: [Laughter] That’s a pretty important mission for you, Tom. I want to understand a little bit about what it takes to put a person like you in a position like this, really, you know, we can say protecting our planet, right? So, some of your earlier works is very interesting, and I think it builds very nicely to your work with asteroids that gets you to start working with DART, which is, of course, with an asteroid. So, take us through some of the things that got you to where you are today, Tom.
Thomas Statler: Oh, boy. Well, that takes me back a long way. I mean, basically, well, you know, as a little kid, there were two things that I thought were just unbelievably cool, and one was galaxies. And I looked at, you know, saw the pictures of spiral galaxies in books and I thought, how amazing that is that something that unimaginably vast can be that beautiful? And the other thing was the idea that we could actually go to other planets, because I was a kid of the Space Age, I was just old enough to understand what was going on. I remember the Apollo 11 landing distinctly. I was old enough to know that it was cool but not old enough to know how dangerous it was. And so, so I really had kind of two, two dream jobs as a kid. One was to be an astronomer and uncover the secrets of the universe. And I did that: I majored in physics and astronomy, I went through the academic ranks, and I became a professor. But now, I have this other dream job which is helping to send robot spacecraft to other planets and asteroids.
Host: Wonderful. So why don’t we get into the mission itself? We’re going to start talking about this mission, DART, Double Asteroid Redirect Mission. So, if you had to talk to someone off the street and they said, hey, Tom, what’s DART, how would you start?
Thomas Statler: Well, DART is our first full-scale attempt to demonstrate that we can change the motion of an asteroid in space, potentially as a way of defending Earth against the hazard of asteroid impacts. And to understand this, it’s good to have, you know, the right mental conceptual movie going on in your head. So, to start with, you know, the Earth goes around the Sun. Earth orbits around the sun in, in one year. The other planets also orbit the Sun, and all of the asteroids also orbit the Sun. And that means that any asteroid that is on an orbit around the Sun that never comes anywhere close to the orbit of the Earth isn’t dangerous. The only asteroids that are possibly hazardous are the ones that have orbits that intersect with the orbit of the Earth somewhere. And even then, nothing bad happens unless the Earth and the asteroid try to arrive at that intersection point at the same time. And that’s when you can have an asteroid impact on Earth. And that’s really pointing to the essence of what we call planetary defense, defending Earth against this natural hazard. The key is to be able to find the asteroids on those Earth-intersecting trajectories, find them well in advance of any collision, and to take steps years ahead of time, not to destroy the asteroid — don’t need to do that; in many cases, we wouldn’t be able to — but just to prevent that collision from happening. And that’s what we’re going to do with DART. We’re going to demonstrate one technology to cause that deflection that, someday, if we need to, we might use this technology to prevent an asteroid from hitting the Earth.
Host: So, the mission that we’re going, the mission and the asteroid that we’re going to, is not necessarily the asteroid that’s going to cause that devastating effect on Earth. It’s really a test to make sure that we have the capabilities for that asteroid in the future, if there is one, that would have such effects.
Thomas Statler: That’s exactly right. There’s no known asteroid that has any chance of impacting the Earth anytime in the next hundred years. So, the hazard is not from the asteroids we know, and the asteroid that we’re going to with DART is not a dangerous asteroid. The hazard is from the, from the asteroids that we haven’t discovered yet. And we’re searching for asteroids all the time. We certainly hope that we will never have to deploy an asteroid deflector, but we want to do the test now to make sure that we’ve got the ability and the know-how to do it if we should need to.
Host: Very good. But what are some of the assets, what are some of the things that we have in place, to watch what’s going on in the solar system around us and make sure we’re OK?
Thomas Statler: Well, the key thing for asteroids is telescopes. You need telescopes to essentially scan the skies, take a lot of pictures of the sky with a wide-field view, and look for things that are moving. The stars don’t move; they’re in the far, far distant background. But objects that are moving in the solar system, especially ones that are moving close to Earth, will move over the course of the night, and if you take a couple of pictures of the same patch of sky, you’ll see them move. And that’s, historically, that’s how asteroids have been discovered from the beginning. So, we use a variety of telescopes in various places around the world. We’ve got projects that are operated by universities, funded by NASA, some of them funded by other space agencies, other governments around the world. All work together to, as I said, scan the sky, look for objects that are moving, track those objects, send those data to the International Astronomical Union’s Minor Planet Center, which is funded by NASA, that will calculate the orbits and determine whether each of these things that are just seen moving across the sky at night, is it an asteroid, what kind of an orbit is it in, and is it in an Earth-crossing or Earth-intersecting trajectory? And that happens every night, 365 days a year.
Host: Excellent. So, what about the destination of DART then? What is special about this asteroid that is the final destination of the DART mission?
Thomas Statler: Well, DART is going to a very, very cool asteroid. In fact, it’s two asteroids. It’s the system, the binary asteroid system called Didymos. And a binary, people may have heard of binary stars, where you have one star orbiting around another; a binary asteroid is like that too. There’s a larger asteroid and then there’s a little asteroid held in orbit by the very weak gravity of the larger asteroid, and it goes around it. So Didymos is a binary asteroid. The larger one, that’s called Didymos, is about 800 meters across or so. The smaller moon is called Dimorphos. It’s about 150 meters across or so, so kind of football stadium-sized. And the two of them are about three-quarters of a mile apart, about a kilometer and a little bit.
Host: OK.
Thomas Statler: So, well, I live near Washington, D.C., so I think of things in terms of the map around here. But if you’ve been to the National Mall, where the Smithsonian museums are, if you can imagine that, those pair of asteroids, if you put them down on the National Mall, they would fit between the U.S. Capitol and the Washington Monument with room to spare. It’s a surprisingly small and compact little asteroid system. So, DART’s going to go to this asteroid system and execute a kinetic impact on the small moonlet Dimorphos. And kinetic impact is a technical term for running into the thing, because that’s what kinetic impact is. OK. So, here’s the visual for you, OK? So Dimorphos, the little asteroid moonlet, is basically a small football stadium filled with rocks. So, get your high school football stadium, fill it up with rocks, that’s your model for the asteroid. The DART spacecraft is kind of a golf cart filled with computers and cameras and stuff. About that size. It has big solar panels on it, but they don’t weigh very much. And then, basically, what we’re doing with DART is you take your golf cart full of cameras, you get it going up to 15,000 miles an hour, and you run it into the side of your football stadium full of rocks. That’s what we’re doing with, with DART. Now, go ahead and ask me why in the world are we doing that?
Host: I’m going to go ahead and do that, Tom. Why are we doing that?
Thomas Statler: Because that’s the kinetic impact and that is the deflection mechanism. We are using that collision to impart a bunch of momentum to the big asteroid. By hitting it with a small thing at high velocity, we’re delivering a lot of momentum to change its motion. And the reason we’re doing this in this binary asteroid system is that when we impact the moonlet and change its motion, that makes a change to the orbit of the moonlet Dimorphos around Didymos. That’s really key. And that’s why the binary asteroid is a perfect natural laboratory to do this experiment in. Because the part that I didn’t tell you is that the reason we know this is a binary asteroid is we can observe it from Earth. Now, even in a big telescope, you can’t see that it’s two asteroids; all you can see is the combined light of one asteroid. But if you monitor the brightness of that asteroid that’s shining by the reflected light of the Sun, you’ll see that, every so often, like clockwork, the brightness dims just a little bit and then comes back up. And what’s going on is that the moonlet is either going behind or going in front of [Didymos], and a little bit of the light gets blocked when it goes in front or behind. And because we’ve got years of those observations, we know that that moonlet is there, and we know that it goes around Didymos like clockwork every 11 hours and 55 minutes. So, we see that little dip in the light every, maybe, you might not see it every time around, maybe every half time around. At any rate, we see those dips in the light as one goes behind the other every orbit. What we’re going to do with DART, by executing the kinetic impact, we change that orbit so that what was 11 hours and 55 minutes might end up being 11 hours and maybe 50 minutes. And by measuring, by watching those eclipses happen in the weeks and months after our kinetic impact, we’re going to see the clock is running a little bit faster than it was before. And that’s the thing that’s going to enable us to measure, extremely accurately, exactly what the kinetic impact did to the asteroid. Because DART, you know, it’s called Double Asteroid Redirection Test, which I think is the coolest name ever, because we’re doing the test on a double asteroid, there’s the binary asteroid, but it’s also a double test. It’s two tests in one. We’re testing our technological ability to actually execute the kinetic impact, to actually collide with an asteroid, but we’re also testing how does a real asteroid react to that kinetic impact. Because anybody can take a couple of hundred million dollars’ worth of spacecraft and smash it to bits, but the real question is, did we move the asteroid or not and by how much?
Host: So, if I’m imagining what you just painted for me, Tom, correctly, it sounds like you are going to crash into the moonlet Dimorphos with the orbit, thus speeding up the orbit just, just a tad, right? And what that’s going to do is, what’s your hypothesis, in terms of setting it off course or something, setting the whole binary system off course?
Thomas Statler: Well, we’re not trying to set it all off course.
Host:Oh, interesting.
Thomas Statler: Let’s take it a piece at a time. So, first of all, I got to tell you a little bit about how orbits work. They, they go not the direction you expect. So, actually, what we’re intending to do, and this could change depending on the details and the circumstances exactly when we launch and exactly when we get there, but we’re intending on hitting the moonlet asteroid head-on —
Host: Oh, interesting.
Thomas Statler: — which momentarily slows it down, but what that does is it drops it into a slightly tighter orbit around the primary body, which takes less time to go around. So, the period gets less. So, it’s this counterintuitive thing. One of the great dynamicists, dynamical theoretical astrophysicists who had a lot of work on galaxies, which a lot of influence on galaxy work, which I used to do, Donald Lynden-Bell, he used to say, orbits are like donkeys, you pull them one way and they go the other way. So that’s an aspect of this. You hit the thing to slow it down and it ends up going around faster.
Host: Yeah, you’re right. It’s not, it’s not, to me, like, I would think, OK, we want to speed it up, so let’s give it a little nudge. That’s not what’s happening here. You’re essentially putting it into a lower orbit, and that’s what makes the orbit slightly faster.
Thomas Statler: Exactly.
Host: OK.
Thomas Statler: And, and people familiar, as your podcast audience is, people who are familiar with human spaceflight know this, because you know if you’re in low-Earth orbit and you want to reenter and want to come back down, you fire your retro rockets to slow down and drop to a lower orbit, where the atmosphere then grabs you.
Host: OK. OK. Now I think what’s impressive, Tom is, so you’re talking about there’s an asteroid flying somewhere in the solar system and you have to predict not only where it’s going to be, so that the DART spacecraft can impact something that’s orbiting it, but you have to estimate the orbit of the moonlet itself so you can meet your target. Is that right?
Thomas Statler: Absolutely right. We have to get there at the right moment, when not just the whole asteroid system is at the spot that we delivered the spacecraft to, but the asteroid moonlet is in the right part of its orbit that we actually succeed in executing the kinetic impact on it when we wanted to in the head-on direction. And that is the product of a lot of work with ground-based telescopes that the astronomers on the DART team have been doing for several years now to observe, as I was talking about before, these transits and eclipses, the places where the light dims just momentarily, to observe those over and over and over again. And the more observations of those events that you get, the more accurately you can pin down exactly the length of the orbit. And so there were key observations that were just done this past winter that were absolutely essential in order to be able to predict at what time the moonlet Dimorphos is going to be at the right phase of the orbit so that we can, we can strike it with the, with the spacecraft. So those observations have been going on for years, establishing the properties of that orbit now. And if you think about it, we have to do that because the whole essence of the test is comparing before versus after. And so, you’ve got to do the observations before to pin down what the “before” state is because you don’t get to go back and do it again after you’ve done the kinetic impact.
Host: I see. OK. So, so for the binary system, where is it approximately now, and where do you expect it to be with all the measurements that you’ve just talked about at the time that you want DART to make the kinetic impact?
Thomas Statler: OK. So, the system Didymos is in orbit around the Sun. It’s on an orbit that at its, it’s an elliptical orbit, and so at its closest point to the Sun it’s pretty close to the Earth, it’s about Earth’s distance from the Sun, and at its farthest point it’s just edging out into the main asteroid belt beyond Mars. But it’s probably about two and a half astronomical units from the Sun right now. When we arrive there with the DART spacecraft, and this was intentionally done this way, it’s going to be only about 0.072 astronomical units away from the Earth. I can’t do the math in my head quite that much, but an astronomical unit is the distance from the Earth to the Sun, it’s 150 million kilometers, so multiply that by 0.072, and that’s how close we’re going to be. And we’re timing the kinetic impact for that moment so that we can have really efficient communication and high bandwidth back because, of course, on this mission, so, many of our recent missions, like, for example, people are aware of New Horizons that flew by Pluto a few years ago, two years ago, gave us our first view of Arrokoth, that fantastic Kuiper Belt object. New Horizons is built to take a lot of data, acquire a lot of images really fast, and then, later on, send it back to Earth bit by bit. On DART, we don’t have the luxury to do that because after we arrive at, you know, Didymos, there’s no spacecraft left after that. So, we’re streaming back video in real-time as fast as we possibly can. And having that high bandwidth, short-distance communication is going to be really important.
Host: OK. So, you’re planning on getting imagery, or may possibly even video back at the final moments before the kinetic impact?
Thomas Statler: Not quite video.
Host: OK.
Thomas Statler: We’re expecting a frame rate of about one per second. But this is the key to the mission. We’ve got, on the spacecraft, which is about the size of a big vending machine roughly, it’s not very large, it only weighs about half a ton. And we’ve got one instrument on it, which is a great camera called DRACO (Didymos Reconnaissance and Asteroid Camera for Optical navigation). And Draco is actually modeled after the LORRI (Long Range Reconnaissance Imager) camera that is flying on New Horizons right now. So, DRACO just looks out the front at where it’s going and, and identifies Dimorphos, Didymos/Dimorphos asteroid system, picks out Dimorphos, and points the spacecraft at it using a very sophisticated autonomous navigation system we can talk about in a few minutes. And so it’s continuously taking images, once per second, for navigation but also for the purposes of understanding the target asteroid that we’re going to impact, because in order to figure out what we did, what effect we had on the asteroid, we have to understand the asteroid. We know a lot about Didymos. We don’t know a lot about the little moonlet Dimorphos. It’s never been resolved in a telescope or even in a radar image. So, we have a vague awareness that it’s longer in one dimension than the other direction. We know about how big it is. But that’s all we know. We don’t know what the shape is, and we don’t know what the volume is. We won’t know, other than by the images from the DRACO instrument on DART, what the size and shape of that asteroid is. And we also need to know where do we hit and what’s the topography of the surface at the place that we hit, to understand the dynamics of the impact.
Host: Oh OK. So that data is critical for you to understand because it sounds like DART is not over after it crashes into the moonlet because you guys are going to be analyzing, you’re analyzing the pictures that it takes to understand more about the moonlet, and you have some analysis to do afterwards to see what happens to the orbit of the moonlet, what happens to the, to the, I guess the, I don’t know if it would be not necessarily orbit but the trajectory, I guess. I don’t know what you want to call it, of Didymos and the binary system. You got a lot going forward, even after the kinetic impact.
Thomas Statler: Absolutely. Well, like I said before, DART is two tests in one. There’s the test of the technology to do the kinetic impact, and there’s the test of what happens to the asteroid. And that first test ends and the second test begins at the moment when the spacecraft itself is destroyed by the impact.
Host: Aha, OK.
Thomas Statler: It’s a fascinating thing. And so, even after impact, you know, there will be this, I’m sure a great cheer will go up when we get the last image down and we confirm loss of signal. But at that moment, in a lot of ways, the mission’s only half done because we still have a big effort of, astronomical effort, literally, using telescopes on the ground to measure the effect of what we actually did. And that’s where, you know, the real results are going to come out from that. So those observations will be focused on the, the little orbit, right, the little orbit of the moonlet Dimorphos around the big asteroid Didymos. You’re right that in a very tiny way, we’re also changing the orbit of the pair around the Sun. But we’re not planning to try to measure that because that effect is so small and so hard, so hard to measure, it may not quite be doable. After all, DART is a small spacecraft, and even though this is a full-up test, it’s not a big test.
Host: Yeah. You mentioned a golf cart crashing into a stadium. So that picture you drew was, was absolutely perfect. Bring us through the first half of the mission then. Let’s explore that one a little bit. In terms of the mission profile for those of us that want to watch the launch and see this thing through the kinetic impact, what is the timeline here?
Thomas Statler: OK. Well, the launch period opens nighttime on November 23rd, Pacific time, just in a few months. And if we’re able to launch right at the beginning of the window, we’ll launch just before midnight California time on November 23rd; it’ll be the wee hours of the morning November 24th for most of the rest of the U.S. We launch onto, and we’re launching from Vandenberg Space Force Base on a SpaceX Falcon 9; that’ll put us on a trajectory that has a big north-south component to it because we have to do a little bit of an inclination change. We have to get away from the Earth and give ourselves an orbit around the Sun that’s a little bit inclined. And that puts the spacecraft onto an orbit that will go around the Sun just about once and meet up with Didymos when it has come into near-Earth space, right at the end of September next year.
Host: OK. So about less than a year from the time of launch to actually make the kinetic impact. So that’ll be a pretty big moment for you guys. Where are you going to be throughout that whole process?
Thomas Statler: At launch time?
Host: Both launch time and the kinetic impact.
Thomas Statler: Well, at launch time, I hope to be out in California, somewhere close to Vandenberg. I’ve never been to a launch at Vandenberg. What people tell me is that the coastal fog has a tendency to come in and prevent you from seeing much of anything. But I’m hoping we get to see a launch. And if not, we’ll get to hear a launch because it does make a lot of noise. And, and of course, the launch is tremendously exciting, but it’s just the beginning, right? We’ve got a fairly short cruise for a planetary mission. It’s only a year, once around the Sun, to kinetic impact day. And at kinetic impact day, I think everybody is going to be at the Johns Hopkins Applied Physics Lab because it’s APL that is operating this mission for NASA. They were building the spacecraft. We’re almost ready to go. And it’ll be tremendously exciting to be at the mission operations center at APL on kinetic impact day. It’s going to be quite exciting watching the images come in, in almost real-time, and watching that asteroid get bigger and bigger and bigger.
Host: [Laughter] I can only imagine. So, it sounds like you’re working with Johns Hopkins, that’s one of the folks you’re working with. What is the team that comprises the entirety of the mission that is DART?
Thomas Statler: Well, every mission has a very broad team. The major components are being built by APL. Mission operations are being done by APL. But we’ve also got some additional important components on the spacecraft. One of them is an ion propulsion, solar electric ion propulsion thruster, called NEXT-C. It’s NASA’s Evolutionary Xenon Thruster-Commercial that we’re taking for its first flight on DART. It’s going to be checked out, given its first flight experience during cruise. That’s a particularly innovative piece of technology that was built by NASA Glenn Research Center and Aerojet Rocketdyne. Because it’s solar electric propulsion, we need some hefty solar panels. So, we’re flying these roll-out solar arrays or ROSAs that are innovative technology. They are lighter than standard solar arrays. These were built by Deployable Space Systems. There have been a couple of them deployed on the International Space Station that have worked well; we’re anticipating them working really well on, on DART also. One of the other interesting things about DART is, like I said, its main imager looks out the front window. And when we successfully achieve kinetic impact, we have no more spacecraft and no more imager anymore. But the Italian Space Agency, ASI, is providing a CubeSat that will ride along on DART. It’ll be deployed about ten days before the kinetic impact. It’s going to use its own propulsion system to offset so that it doesn’t run into anything. And it’s going to follow DART in, a little bit off to the side, about three minutes behind. So, this CubeSat called the LICIACube (Light Italian CubeSat for Imaging of Asteroids) has two imagers on it; they’re called Luke and Leia. Can’t imagine what those are based on.
Host: [Laughter] We can only guess.
Thomas Statler: We can only guess. But they’re going to try to get images of the impact itself. There should be, I imagine there will be some kind of a bright flash because there will be a lot of energy liberated at that moment. But we want to be able to see the ejecta plume, the material from the asteroid that’s blown off in that energetic impact, not just for the sake of seeing it but also that ejecta gives the asteroid an additional push. It’s like a little extra rocket that you attach to the asteroid at the moment of impact. The stuff blows out one way and the asteroid is pushed another way. And that’s actually one of the key measurements that we’re trying to make with DART, is what is this momentum enhancement that we get, not just because we hit the asteroid but because we also blew out this ejecta. So LICIA is going to give us images that’ll let us see, get a handle on how much material is blown out as the ejecta and what direction it went. And then, of course, LICIA will do something that DART will not be able to do, which is go around the backside. It’ll fly past, look backward, and give us a view of the backside of the asteroid that we impacted so we get a clear picture of what its size and shape is, what its volume is, and what its mass is.
Host: That is fantastic. This plume that you’re talking about, is that mostly for research into the physics or is there some that’s going to look at, because I know you said some of the imagery on the forward camera of DART is going to look at the composition of the asteroid, will some of that plume data help with understanding what Dimorphos is made of?
Thomas Statler: It could in some ways. With the, with the DRACO imager around DART we don’t really have the ability to do much about composition. It’s not a spectrograph, it’s not a multicolor camera, it’s just a monochrome camera. We’ll be able to see, you know, geological forms. We’ll be able to see craters, boulders, and get some basic information about the physical, I mean, you know, mechanical, physical properties of the asteroid, not so much about composition unless we see some, you know, we might get lucky and see some big differences in reflectivity or something like that. But more information we’ll be getting is about the texture of the asteroid. Sorry, I forgot what the question was.
Host: No, no. I think I was asking about the plume itself.
Thomas Statler: Oh, the plume.
Host: Yeah, yeah. And what — how exactly, I guess, does it help you to understand, it sounds like it’s not so much the materials but the physics of it. And I think you did a pretty good job of describing.
Thomas Statler: Well, there’s two aspects of it. One is how does the ejecta, what direction and how much is going in, and how much ejecta there is in terms of how does that, how does it play into the dynamics of this kinetic impact deflection? So, the information that we want to get out for planetary defense purposes is, how much of a push on an asteroid are we actually going to get if we hit it with a spacecraft? The other side of it, which is asteroid science, we might be able to get a handle on by looking at that ejecta plume from different angles, under different lighting conditions. We might be able to get a handle on the particle size distributions. So, how much really fine dust, how much, you know, gravel, how many golf ball size chunks, that sort of thing. And that gives us some more insight into the surface properties of the object.
Host: Got it. Now, we went through a couple of the centers involved and APL, of course. I want to make sure we didn’t miss anyone and their involvement and contribution to DART.
Thomas Statler: Oh, boy. Well, I wouldn’t even begin to try and make sure I get the whole list. I would accidentally leave somebody out and then they’d get mad at me. But, of course, I mentioned ASI, the Italian Space Agency. Argotec in Italy is the contractor that’s building LICIACube. Of course, we have the involvement of NASA Glenn [Research Center], I already mentioned, Marshall; JPL, Jet Propulsion Laboratory, is doing navigation. NASA Langley [Research Center] was doing some independent verification and validation. See, I know I’m already missing some people. We also have on the investigation team a lot of scientists from universities involved. I know the University of Maryland, College Park is involved, Auburn University is involved. I apologize to all of the co-investigators whose institutions I’m going to forget to list here.
Host: And I’m not going to put you through that, Tom. No way. So, we’ll move on to, you sort of alluded to this a little bit earlier, but there’s some pretty critical, I believe it’s navigation equipment, guidance, navigation, and control. What’s on board DART? What is this piece of equipment?
Thomas Statler: Well, this is really the key. We would not be able to do this mission at all if we didn’t have the autonomous systems that the people at APL have designed. And so, they have a system called SMART Nav (Small-body Maneuvering Autonomous Real Time Navigation). And this is what enables us to execute the dynamic impact, the kinetic impact, on the asteroid. What SMART Nav does is it uses the images from the DART camera, in effect exactly the way you would expect to, right? I mean, if you were driving a car, OK — don’t do this at home — but if you were driving a car with the intent of running into something, imagine how you would do it. You would look out the front window and you would watch the thing you were trying to run into, and you would make sure that it just gets bigger and bigger in your windshield and doesn’t go off to the side. If you see the thing you’re aiming for going off to the side, that’s an indication that you’re not going in the right direction and you have to correct your path. So, like I said, don’t do that with your car or anybody else’s car but if you’re building a kinetic impactor spacecraft that’s exactly what you want it to do. And that’s the job that’s SMART Nav has, is to look out the front window, which is the DRACO imager, to see the asteroid, to identify the right one that is being targeted, and to make sure that the DART spacecraft is heading directly toward it at all times and then to send to the guidance, navigation, and control system on board the correct commands to fire the attitude control thrusters and the offset thrusters to alter the trajectory to make sure we stay on path.
Host: Very interesting. So, sticking with the car analogy, it sounds like it is literally the opposite of autonomous driving. Autonomous driving watches the obstacles and avoids them. It sounds like the key piece of technology here that’s critical to the mission is to watch these — I don’t want to call it an obstacle because it’s more of a target — but to make sure you’re going directly for it.
Thomas Statler: That’s exactly right.
Host: [Laughter] Interesting. You mentioned the NEXT-C Thruster, xenon thrusters. Now, this is not necessarily, from the way you described it it doesn’t sound like it’s a critical propulsion technology, but it is more of a demonstration.
Thomas Statler: It is a demonstration. We’ve got two propulsion systems on the spacecraft. One is the traditional hydrazine thrusters, which have been flown many, many times before. And that’s the primary propulsion system on the spacecraft. But we also have NEXT-C. We’re going to check it out in flight during cruise; if it works well, we’ll use it for some of our trajectory correction maneuvers as we go.
Host: But it’s not critical. You’ll have the hydrazine thrusters to back up on.
Thomas Statler: Absolutely. It’s not critical. We’re looking forward to being able to use it, but if NEXT-C has a bad day and we’re not able to use it, we’re absolutely certain we can still conduct the mission on hydrazine.
Host: I see. OK. Now, you mentioned the ROSAs. And, of course, we actually just released an episode on ROSAs on the International Space Station. I understand these are a bit smaller, but you’ve already drawn the comparison of the size of the DART vehicle. You don’t need gigantic solar arrays, it sounds like, to power the instruments that are on board DART.
Thomas Statler: That’s right. If all we were doing, if we weren’t, I don’t want to say it this way because NEXT-C has been such an integral component of the mission from the beginning. I don’t want to make it seem like I’m tossing them overboard.
Host: Sure, sure.
Thomas Statler: But had the mission been designed a different way and it were only the camera, we would not need such large solar arrays. The large solar arrays are there because we are using the mission to give NEXT-C a very thorough shakedown cruise.
Host: I understand. OK. Very cool. Now, what other technologies, you know, you mentioned it’s the size of a, I think you said vending machine, the size of a vending machine. You got your cameras. You got your guidance, navigation, and control. You got your thrusters. Are we missing any other key pieces of technology that make up the shape of this spacecraft?
Thomas Statler: There are a variety of other things. The high-gain antenna for communication with the Earth is a particularly interesting one. If you look at it, you would say is that an antenna or is it a pizza pan or something? It doesn’t look like a traditional parabolic antenna. It’s a flat plate with a bunch of little slots cut in it. And it’s called a radial slot line array antenna, which uses a really interesting combination of little phased, well, for antenna geeks out there, little phased dipoles all around this circular plate, to, to play the same role that a parabolic antenna would have and give us really good gain in transmission as well as reception. So that’s one of the most conspicuous things. The other interesting bits of technology are on the inside in the computer hardware, the use of the field-programmable gate arrays that are running the SMART Nav software, and things like.
Host: Awesome. Now, we are recording this in August. I think the episode itself will release in September. Closing in on that November window, that opens up to actually meet your target and collide or crash into Dimorphos in September of next year. What is there left to do on your timeline to make sure you are ready for when that window opens?
Thomas Statler: Well, the spacecraft is on track to be shipped to the launch site. And so, that’ll be certainly the biggest thing that’s coming, but all of the main systems are installed. Everything is on. NEXT-C is on. DRACO is on. The solar arrays are on the spacecraft. It’s really just the final checkouts that are being done at APL. And then we ship to the site and get into our integration with the launch vehicle. There are still some system tests and simulations that are being done. We’re going to be fine-tuning some of the, some of the navigation parameters, to make sure that we maximize our chances of executing the kinetic impact correctly when we want to, and planning for the things that you do in cruise on a planetary mission. That is, you check out the instruments, you calibrate the cameras; all of those things are being planned.
Host: Very cool. Now, you’re in the home stretch here and, of course, all getting to that critical moment of the kinetic impact. It sounds like you got a lot that’s packed into this mission. Besides the key, I guess, goal of the mission is to make a successful kinetic impact and then measure the effect of that on the physics of the orbit of Dimorphos and around Didymos and how the binary system itself is affected, what other key areas are you planning to explore, maybe physics-wise, that maybe go beyond that, did this work or was this a successful impact?
Thomas Statler: Oh yeah, there are lots of questions. And, and, you know, the, the texture of the landscape, the scientific landscape, has actually changed a little bit in the last couple of years because, if you had asked me this two, three years ago, I probably would have said, we’re not really expecting any surprises. We think the kinetic impact is going to be exactly what you think it’s going to be. The response is going to fit in, going to be in accord with our computer simulations and so on. And yet we’ve had a couple of surprises in asteroid science in the last couple of years. The Japanese spacecraft Hayabusa2, which is now, has brought its samples back from the asteroid Ryugu, they did an experiment at the asteroid Ryugu which they had a separate thing, an explosive device, that sent a small impactor at high speed down into the surface of the asteroid. And it was a surprise because, in some ways, it did what was expected, it dug a little crater, it went bang and dug a little crater, and ejecta came out. But the surprise was the process of, well, let me back up. If you think about it, if you just imagine, what should that look like? You’re firing a projectile into the surface of an asteroid at a few thousand miles an hour. And you think about that, and it should probably go bang and stuff flies around, and then the dust settles, and it’s done. And that’s not quite what happened. That process of excavating the crater and stuff coming out of the crater went on for minutes, which was more than a bit of a surprise. And what it told us was that there was basically no strength to that material. There was no cohesion to it. There was no stickiness to it. Everything was just controlled by gravity. And so, there was nothing to slow this process down. Even though it was going in slow motion, real-time slow motion, it just took forever for it to develop. And a lot more material was excavated from the crater than people were expecting. So that was surprise number one. Surprise number two was the OSIRIS-REx (Origins Spectral Interpretation Resource Identification Security-Regolith Explorer) spacecraft at the asteroid Bennu, that is now on the way home with its sample. When it did its sampling attempt and touched down very gently on the surface with its TAG sampler to just do a touch and go, that’s what TAG stands for, it touched the surface and the surface didn’t push back. It just sort of went into the surface. It sort of paints a picture of this asteroid that if you walked up to the side of the asteroid and you poked it, your arm would just go right into it. It was amazingly delicate material. And so, because we’ve got evidence that these asteroids can be, you know, very, very delicate material and slow to respond, I’m anticipating some surprises when we actually execute the kinetic impact on Dimorphos.
Host: Wow. So in terms of what excites you about the mission, in addition to what you said about how excited you were for launch and to be at APL for the kinetic impact, it sounds like one of the things is what is going to surprise me that’s exciting you most about this mission.
Thomas Statler: Well, I mean, boy, where do I begin? [Laughter] Yeah. There’s a lot of asteroids in the solar system, but it’s becoming clear that there’s no such thing as just another asteroid. And every asteroid has something surprising and new to tell us. Every time we get a spacecraft to a different asteroid, our socks get knocked off, and then we have to put our socks back on. And then the next one knocks our socks off again. So, I’m not going to make any bets about what is going to happen at Dimorphos. I know we’re going to execute the kinetic impact. I know there’s going to be a measurable effect. I know I’m going to be really, really thrilled to see the telescopic observations following the kinetic impact that show me the period of the asteroid has changed. And, and let’s just focus on that for a second because that’s going to be an event of historical proportions, right? When we get those observations back that show that the period of this binary asteroid has been changed, that will be the first time that humanity has actually changed something in space. I mean, we’ve left footprints and tire tracks and things like that on various bodies, but this will be the first-time humanity has changed a celestial motion.
Host: Interestingly. We’ve observed, we’ve collected samples, but this, yeah, you’re right, this is the first time we’re changing something. Wow. Unbelievable. And that’s — due to the team that’s putting this mission together, the work that you’re doing, and it sounds like the work that’s being brought together from several different centers, several different teams. What’s it like working on the DART team?
Thomas Statler: Oh, the DART team is fantastic. It’s, it’s tremendously professional, dedicated people. In addition to that, there are people on the investigation team that I’ve known for years through research and, you know, I’ve been friends with them. So, working with them in this capacity has just been great. I can’t say enough about the team at APL, the team at the collaborating universities, the LICIACube team from ASI has been great. This team has really pulled together and gotten through the pandemic, and we’re still launching the spacecraft this year.
Host: That’s right. Doesn’t matter on the obstacles, you guys are still getting the mission done. So that’s amazing to hear. And honestly, I’m rooting for you. Tom, this was a fascinating discussion to have with you today. And honestly, you got me excited about the mission. I’m very much looking forward to launch, and I’m very much looking forward to just the excitement of all there is to learn, and now especially the surprises that may come along the way. I love the way you described that every asteroid is unique, and so, it’s not just another asteroid. So, what surprises does this one have to offer? I can’t wait to find out. Tom, thanks for coming on.
Thomas Statler: Thanks so much, Gary. Glad you’re excited.
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Host: Hey, thanks for sticking around! I hope you enjoyed this conversation with Dr. Thomas Statler today. He got me really excited for this upcoming DART mission. And it’s coming up very soon; launches in just a couple of months, at least the launch window opens up. So, check out the latest at NASA.gov for the DART mission. We’re one of many NASA podcasts across the entire space agency. You can go to NASA.gov/podcasts to check us all out. That’s where we are. You can check out some of our episodes and some of our collections on various topics that we have. We’re on the Johnson Space Center pages of Facebook, Twitter, and Instagram on social media. Use the hashtag #AskNASA on your favorite platform to submit an idea for the show or maybe a question. Just make sure to mention it’s for us at Houston We Have a Podcast. This episode was recorded on August 18th, 2021. Thanks to Alex Perryman, Pat Ryan, Norah Moran, Belinda Pulido, Emily Furfaro and Josh Handal. And, of course, thanks again to Tom Statler for taking the time to come on the show. Give us a rating and feedback on whatever platform you’re listening to us on and tell us what you think of our podcast. We’ll be back next week!