 Good afternoon, everyone. Hi. Welcome, everyone, to the very first Purdue Engineering Distinguished Lecture of this 2019-2020 academic year. We have nine outstanding distinguished lecturers and panels planned for the entire academic year for your enjoyment, intellectual satisfaction, and pleasure. My name is Arvind Raman. I'm the Senior Associate Dean of the Faculty of Engineering, and my staff work very closely with the school staff in arranging some of these amazing visits. So the Purdue Engineering Distinguished Lecture Series started in 2018. And really, what it aims to do is to bring leaders in engineering, both in academia and in professional life, be it in the government, be it in the private sector, to come to Purdue, spend some time with our students or faculty, and really engage in very thought-provoking discussions on what are the grand challenges in their field and where are the opportunities, what's the next thing in their field. And so that's the scope of the Purdue Engineering Distinguished Lecture Series. I encourage all of you to try and attend as many of those as possible. Now to introduce our distinguished lecture for today, I'd like to invite Kathleen Howell, the Sulu Distinguished Professor of Aeronautics and Astronautics. OK, I have to stand on my toes. OK, this afternoon, we're here to welcome Professor Daniel Shears. And the panel earlier today actually had a very interesting discussion and reflected on Dr. Shears' range of interest. His research work spans the areas of space science, astrodynamics, and celestial mechanics. And it's really focused at the intersection of those areas. Professor Shears was awarded a PhD degree in aerospace engineering from the University of Michigan in 1992. He immediately went and spent five years as a member of the technical staff at JPL in the navigation systems section. From there, he went on to faculty positions in aerospace engineering, first at Iowa State University, then at the University of Michigan, before joining the University of Colorado in 2008. So he's currently a University of Colorado Distinguished Professor, and the A. Richard Seabass Endowed Chair Professor in the Ann and H. Day-Schmeed Department of Aerospace Engineering Sciences at the University of Colorado at Boulder. So Dr. Shears has contributed extensively to the fields of astrodynamics and orbit determination with a specific interest in asteroids. His general areas of expertise include celestial mechanics, dynamical astronomy, astrodynamics and optimal control, areas of applications within these fields include the motion of natural and artificial bodies in space environments, the physical evolution of small solar system bodies, navigation of spacecraft, orbit determination and parameter estimation of dynamically evolving space objects, space situational awareness, guidance for space trajectories and optimal design of space trajectories. Dr. Shears has also been well recognized for many of his contributions. He's a fellow of the American Astronautical Society and a fellow of the American Institute of Aeronautics and Astronautics. He's the past chair of the American Astronomical Society's Division of Dynamical Astronomy, President of the Celestial Mechanics Institute, a member of AAS to the Division of Planetary Sciences and a member of the International Astronomical Union as well as the International Astronautical Federation. He received the Dirk Brower Award from the American Astronautical Society in 2013 and gave the John Bracwell Lecture at the IAC International Astronautical Congress in 2011. Asteroid 8887 is named Shears in recognition of his contribution to the scientific understanding of the dynamical environment about asteroids. Professor Shears was elected to the National Academy of Engineering in 2017, the election citation read, for pioneering work on the motion of bodies in strongly perturbed environments such as near asteroids and comets. Today, please welcome Professor Daniel Shears. Thanks very much, Professor Howell. It's a pleasure to be here to talk with you about my passion, one of my passions, which is exploring, studying, and trying to understand some of the small bodies of the solar system. And it's a great honor to be here as, you know, for this distinguished lecture series. And I've really enjoyed my stay so far. And I think a lot has changed since the last time I was here, which was 20 years ago, almost to the day, so. So with that, let's start off on the talk. So I'm gonna talk a little bit today about asteroid exploration, why we do it, why we're interested, what some of the current things that are going on right now as we speak in terms of asteroids, and then talk a bit about what's coming up in the near future. So I should really start with, you know, with the basic question, what are asteroids? I mean, sitting here today, all you hear is asteroid, asteroid, asteroid. Okay, what are they? Why are we interested in them? And first of all, just what are they? Essentially, we could consider them to be small solar system bodies that orbit the sun. They range in size from Ceres, which is the largest, although it's now a dwarf planet, so it's not quite an asteroid anymore. All the way down to, you know, the smallest speck of dust, technically you could think of as an asteroid if you wanted to. Ultimately what these are, it's a diverse collection of bodies that have very different compositions, physical morphologies, histories, locations in the solar system, et cetera, et cetera. So it's a very, very broad term that we use. This is, to give you a picture of where they are on the solar system, this is a snapshot of locations of asteroids. At some epic, you see all these yellow dots, those are all the asteroids. But that's not very, that's not necessarily the best way of thinking of them because asteroids, of course, like the Earth and the planets, travel in orbits around the sun. It's a little more instructive if instead you just overlay on there, here these are just showing the near-Earth asteroids. So these are all the asteroids' orbits that actually come close to the Earth's orbit at 1AU. And these are the ones that become meteors that hit the Earth eventually. They're also the easiest ones for us to go investigate and to go visit. So they're naturally of interest to us. Another way to introduce asteroids is to sort of walk through the size scale that we're interested in. And here, let's start large, where we have the Earth, the Moon, and you get to see Ceres and respect to that. Ceres is the largest asteroid, even if it's not an asteroid anymore. And you see, okay, well, it's quite a bit smaller than the Moon. So then let's take another step and let's look at the four largest asteroids and you start to see, okay, well, they're getting smaller and smaller. We've investigated Vesta in great detail and Ceres is like. And we can keep on going down, and this is now going from 1,000 kilometers to 500 kilometers and even smaller. Here's Vesta, compared with all these other main belt asteroids that we've seen in the past. And you see some of the ones that are of interest to us. I don't have a good way of, modern technology has taken the laser pointer from us with all these LCDs. So, but if you look down at the bottom, we see the asteroid Itacaua and it's barely visible because it's so small compared to Vesta that it appears as a speck on this graphic. If you look at the second largest one, Lutitia, which was visited by the Rosetta spacecraft, here we're starting to get down to the shapes and sizes of asteroids that we've actually visited and had rendezvous with. And you realize that there's a huge scale difference over which we've looked, going from 1,000 kilometers down to really less than, much less than one kilometer in size. And then of course the masses of these are also scaling by an order of magnitude easily across that realm. So this is another way of thinking about asteroids, just in terms of what they look like, their shapes, their sizes and the like. So again, you can look at this and say, okay, that's sort of interesting, but why exactly should we be interested in studying and understanding these objects? And that's a perfectly valid question. So there are really four reasons that I've identified. I think there are many more, but I'll just walk you through those very briefly. First is science and a little joke, nature as well, because as a scientist, these are high profile publications. Why are they so interesting? Why would they put pictures of rocks on their covers and the like? And it's really because when we study asteroids, we're answering and studying some very fundamental scientific questions. These small bodies are really remnants in some sense of the formation of the early solar system, leftovers from the formation of the solar system. And they retain material that if it doesn't go all the way back to the very earliest stages has at least been minimally processed potentially for billions of years. So when we go and we study these small bodies, it's really doing archeology of the solar system. We get to see them sort of in this natural state where they don't have a whole lot of degradation and we get to study them and we get to use them to understand how the solar system as an entire system has actually evolved over billions of years. Some innovative, recent uses actually use these asteroids in their orbit sort of as tracer particles in order to put constraints on how the major planets of the solar system have migrated over time. That's just another example. And there's many more. From a human perspective, they've shaped life on Earth, delivered minerals, water and the like to the early Earth. Occasionally have wiped out species that were maybe in our way, opening things up for us. They're also a unique form of matter. When you have these small bodies, they're held together by gravity, but the gravitational pull that you have with such a small body is tiny. And other forces become very important such as solar radiation pressure, Van der Waals forces between the different grains and the like. So it's really, it's almost like a new form of matter. And by studying this matter with these exploration missions and scientific missions, we actually get insight into other processes that happen in the solar system. So from a scientific perspective, the case is very clear, but there are other perspectives too. From a human exploration perspective, it's also interesting to think about visiting asteroids. And in some people have considered them a natural destination for human, future human exploration. They are the most easily accessible bodies outside of the Earth-Moon system. And NASA has seriously considered them for human exploration in the past. The little picture, the blue picture actually shows the project NEMO where astronauts were actually simulating working in the low gravity environment of an asteroid by actually carrying out scuba underwater operations somewhere off the coast of Florida, I believe, in order to plan for future missions to asteroids to understand how they would want to synchronize and carry out their activities. Okay, we had this panel, resource exploitation of asteroids. They have a lot of valuable materials. And it's really been considered as sci-fi for many years, but there have actually been companies that have been formed to study and try to implement or think about how you would implement asteroid mining techniques. There's also been a continuous interest in NASA in terms of using resources that we can find in these natural systems in order to support additional research activities. And here we have this beautiful chart on the right showing the space economy of modern-day gold rush, showing all the vast benefits of mining stuff in space. However, there's a word of caution. The company that made this plot is now actually out of business. So we do have to be a little careful in making these plans and the like. So those are three. Maybe the most compelling reason why we're interested in asteroids is really from a human society perspective. So we know that small bodies continually impact the Earth. Just think of shooting stars you see at night, more dramatically the Chelyabinsk media right that occurred a few years ago in Russia. And we know that these have caused large-scale extinctions in the past, the dinosaurs. And in fact, there's just been this year many interesting additional articles that have explored the aspects of that big impact that essentially wiped out the dinosaurs. And it's a practical question to ask if we detect a asteroid that's a bit larger on a collision course, could we stop it? And this is a topic that's actually considered very seriously across the nation and certainly at NASA as well. And in fact, we have planetary defense conferences that we hold every few years where we actually explore the consequences, the systems that we need in order to detect hazardous asteroids, what we would do if we detected one. And it's a very interesting meeting that combines engineers, scientists, policy makers, and insurance and FEMA and the like. So these are the reasons why we're interested in asteroids and what drive a lot of the research that we do. So it's also relevant to ask which asteroids have we explored? And it turns out we've actually explored quite a lot, okay? And I could gladly go through and talk about each one of these in detail, but I think that would be beside the point. But one of the things is is when I started in this field, back in the early 90s, we had seen no asteroids up close, okay? And now, just 25 years or so later, we've actually explored very many of these bodies. And what we find with each new body that we explore is a larger range of diversity, new questions that get posed, new understandings that really drive our future explorations, of which there are many in the planning works. So the easiest way to visit an asteroid is just to do a flyby. And I use the analogy at the panel, this is a great way of getting information, but it's sort of like visiting a city by driving down the freeway that goes through the city and taking a couple of pictures. And it's important, in fact I'm involved with the mission that this is all we're gonna do. So it can be very important, but it's a little bit, it's not as exciting as actually stopping and going and getting out of the car, if you will, and visiting the asteroid. So the two most important missions that sort of laid the groundwork for a lot of the current rendezvous missions that are going on are the Near Earth Asteroid Rendezvous Mission, the Near Mission, and I was privileged to work on this when I first got to JPL. And is the movie going? Yeah, okay, it doesn't go on here. And this was launched in 96, got the Aeros, the asteroid Aeros, you see that movie of it spinning around in 2001, landed actually in 2002. So it was the first landing on a small body as well. And this was a great mission. It told us a lot about asteroids. It had a lot of challenges because of the shape and size of the body. And it achieved great science and came up with a lot of very pretty pictures. We only seem to show the picture sometimes. But they really are a stand-in if you will for the great science and the breakthroughs and scientific understanding that we actually achieve by visiting these bodies. Now, with this picture, I just want you to look for a second. You see the scale. We see the sort of oblique view of Aeros. If you look at the very tip of the rim, you actually see some huge boulders, probably hundreds of meters in size, distributed across the surface. And then for scale, we have the Empire State Building and sort of remember this size scale. And this is in fact, is one of the challenges that we deal with in asteroids. So this was the near mission. There also was the Hayabusa mission, which is a Japanese sample return mission to the asteroid Itakawa. I was also privileged to be involved with this mission as well to some extent and got to spend some excellent time in Japan working with them and trying to understand and direct how that mission was carried out. So this was launched in 2003, got to the asteroid in 2005, and returned to Earth in 2010. I think it was like two years late. So if you know anything about orbit mechanics, that's sort of a shocking statement. If you don't show up, if you're not on time in orbit mechanics, generally you're just out to launch and you can't do anything. But there's actually a great story behind this whole mission that lost two of its three reaction wheels. It had no attitude control propellant. It had degraded solar panels and missed its original return opportunity. Yet it still limped literally all the way back home and brought its valuable sample. So here we visited the asteroid Itakawa, which looks in some sense similar to the asteroid Aros that I showed before, sort of elongated shape. Here we see some big boulders across the surface, some very smooth areas. This to the upper left is just an image of one of the sample, about 100 microns across that it actually brought back to Earth. But here we can pop in the Empire State Building and you realize that this asteroid is just a tiny, tiny fraction the size of the other asteroid that we visited, Aros. So in fact, this is one of the challenges for doing exploration of asteroids is coming up with methods and techniques for operating spacecraft about these bodies that will scale from something this small, which we can actually orbit all the way up to the size of Aros, which was much larger and even larger. I'm not even talking about the Don mission to Vesta and Ceres, and those are much more planet-like bodies. So to do these asteroid missions, we actually have to understand the physics and the dynamics across this large size scale. So I'm not gonna get very technical here, but this is maybe the most technical. We can talk a little bit about what the challenges are in order to fly spacecraft and navigate spacecraft at these bodies. And for me, it's been a fascinating field of research that me and my students have carried out because the nature keeps on throwing things at us that are much more complex, much more bizarre than what we could ever dream up. And that's sort of a field that you wanna be in because it just keeps you busy and it keeps you invigorated, really. So the challenges for spacecraft exploration of asteroids, one of them is that this small body environment that we fly the spacecraft into is really one of the most perturbed orbital environments that we can find in the solar system. It really presents an extreme exploration dynamical environments, especially in the orbital sphere of things. You can put a satellite in orbit around one of these bodies and in less than a day, it can actually impact on the surface or escape from the body just like that if you don't design that orbit just right. So it's very highly unstable. Just the sunlight can actually blow you out of orbit if you don't account for it appropriately or if you account for it appropriately, it can actually give you a very nice, stable orbit design that you can utilize. They have weird shapes, weird surface environments. As I showed, the size of them can vary in many orders of magnitude, yet we still want one or some key approaches to how we do these explorations. So let's just look at a few examples of some of the bizarre things that we see. First, this is asteroid 1994-6KW-4, and this is a very interesting binary asteroid that we have radar observations from. We would love to fly by and take a closer look at this guy. And what you see is something at face value actually looks like the Earth-Moon system, a big central body that's a little bit tipped. It's a blade spinning faster than the orbit. The secondary is spin synchronized with the orbit, just like the Moon, vibrates a little bit, we believe. Yet, even though it shares so many similarities with the Earth-Moon system, it is so different. First of all, it's only a couple kilometers between these two bodies. If you were standing on one of the bodies on the secondary, say, you could actually jump very easily to the primary. It would just take you a few hours to do that transit, depending on how fast you jumped. If you jumped too fast, you could actually escape from the system. And we note that it sort of looks like that primary is spinning fast. In this next plot, we can sort of show what this means. This is, these are what we call zero velocity curves and these little ease on here. These are actually like geosynchronous satellites. These are locations where if you put a satellite in this rotating frame with the body, it would just sit there. Just like with your Direct TV dish, you point it to one point in the sky, right? Because the satellite is just sitting there. So these are those stationary points around KW-4's primary. And if we superimpose the primary on there, you realize that the surface is almost in orbit. And if you were standing on the surface and you picked up a rock and just let it go, it would actually be in orbit and would just stay in orbit and follow you around. So if you wanna land something on this, we gotta be a little careful, right? If you wanna touch the surface even, you have to go at orbital speeds in order to touch the surface, grab something and pull it off. So something like this is a very challenging body to explore. In addition, it's also a three-body problem. We have the world's expert on the restricted three-body problem here, Professor Howell, and it's a great problem, isn't it? I know you have your students working on these things too because it's a beautiful problem. How do you design missions that can actually take advantage of this complex dynamical structure? Some of the challenges we have, I mentioned, I'm not gonna talk about it in detail, but here I've got three orbits. I'm just shifting these initial conditions a little bit. We go from an orbit, the red one that's stable, just goes in orbit around arrows for a long time, move it in a little bit and within a day or so within a couple of orbits, we've escaped. We're actually in orbit around the sun at hyperbolic speeds of centimeters per second. Or if we shifted a little bit in another direction within a couple of orbits, we've hit the surface. So you have to be very careful and we need to understand how the orbits and orbit mechanics change around these bodies. Another example, this is just a point mass and the effect of solar radiation pressure. And I'm just launching a couple different orbits here separated by just a hundred meters. One of them impacts, the other one escapes in orbit about the sun. Another example, solar radiation pressure affects again. I put myself in orbit around an asteroid. The orbit is sort of holding together, it seems stable. But the asteroid itself is on an elliptic orbit around the sun, gets close to the sun and at some point I just get ripped right out of orbit just because of the sunlight shining on the spacecraft. One more example, this one is a binary asteroid in an orbit around a binary asteroid. Everything looks fine, except it turns out that there's a resonance between the spacecraft orbit period and the orbit period of the secondary. And at some point, I don't know if it's playing, yeah. That small resonance within a few days, maybe a few weeks actually completely destabilizes this orbit. And this guy ends a sorry fate of impacting on the secondary. Is it hit? OK. OK, so how do we deal with these challenges? And the interesting thing is for every one of the challenges we've raised here and for the other dozen that I haven't even mentioned, turns out that there are always proximity operation solutions, but they can be extremely different. And even with the two missions that we have going on right now, which I'll talk a little bit about, the Hayabusa II mission and the Osiris-Rex mission, they both take extremely different philosophies to how they carry out all their operations about these bodies. So one of the takeaways is it's an exciting problem. There are a lot of challenges, but there's always solutions that we can find for how we do this. But you've got to study it, you've got to understand it, and you have to prepare appropriately. So I'll do a little plug. There's so much here. I actually wrote a book talking about many of the methods. But since I published this a few years ago, we've actually developed a lot of new methods and new situations that we can analyze. So it's a very rich topic, and it's been very good to me in terms of academic research and my students in terms of writing their PhD theses and the like. So let's shift a little bit, and let's start talking about what asteroids we're exploring right now. So here's all the asteroids that we've explored. And what we're really going to do is focus in on the Osiris-Rex mission that's gone to asteroid Benu and the Hayabusa II mission that's gone to asteroid Ryugu. Again, I'm fortunate enough to have connections to both of these missions. So we've been to Japan to work with the Hayabusa II team in order to measure the mass of the asteroid. And then for Osiris-Rex, I'm leading up the radio science team. What's radio science? Well, really, we're just measuring the mass in the gravity field of the asteroid Benu. And it's interesting to think. And something a couple of hundred meters across have a gravity field? Yeah, the answer is yes. I mean, we all have our own gravity fields that we carry with us all the time. And they're not point masses, similarly for an asteroid. So for the Hayabusa II mission, this is a very ambitious mission. And they've had huge success in the last year. About a year ago, they showed up at their asteroid Ryugu, started to map it in detail. And since that time, they've deployed three rovers on the surface, sampled the surface twice, created an impact crater, all with the mission that's, by NASA standards, quite inexpensive. And it's been a real joy to be involved with this mission. The way that they approach the close proximity operations around the asteroid is through hovering. So here, they're taking advantage of the fact that this asteroid has a very, very weak gravity field. And just by occasionally thrusting on the spacecraft, you can effectively null out the effect of that gravity field. And hence, they define these different boxes. And they're really just dead-band boxes where they put the spacecraft in this box for a while and in this box for a while. Whenever they detect that they've crossed some boundary, they just do a small maneuver. And they keep it in there. And so this is turning out to be a very effective approach. There's a couple of movies showing actual images from the spacecraft as they descend down to the surface of the asteroid. And this was early in the mission last year or a year ago. Come close, sort of measure the gravity attraction, also test out their systems, and then they back up again. And they did a number of these drops to the surface and coming back up again. When we went out there, we actually, one of these drops, they just turned off the thruster system and just let it naturally fall down so they could measure the ambient gravitational attraction. And from this, we were able to estimate the total mass of the asteroid. So this is where they started. What they did next is they actually delivered a number of rovers to the surface. And here we have really the first images ever taken from the surface of an asteroid. And in fact, the one, the movie that you see running right now is actually showing the, on the, yeah, is actually showing the daytime or a full day on the asteroid surface. I've been told that some of these rovers may still be in operation hopping around the asteroid almost a year later. They also deployed the ESA mascot rover, which was a highly instrumented small surface package. And those results are about to be published or have recently been published in high impact journals as well. Again, for the first time, measuring the surface properties of this asteroid. And looking at it, you see that there are a lot of rocks. And in fact, this is a huge challenge for this mission and a huge challenge for the Osiris-Rex mission as well. The Hayabusa-2 mission has been able to successfully carry out their operations. And the way they do this is they continue this hovering all the way down to almost within 100 meters or so of the surface, then they actually rotate themselves, do a maneuver so that they're traveling at the same rotation rate as the asteroid and they use some closed loop sensors tracking these small target markers, the shiny bits on the surface. We'll see one in a little bit. All the way down to the surface, you see the results in that movie that should be playing right now. They come down to this rocky surface, they touch, as soon as they touch, they turn on their thrusters to leave and it just blows the whole surface up. But in that second that they're touching, they're actually able to carry out a sampling and get bits of the asteroid in their sample chamber. You can also see before on the left and an after picture on the right and the before is really where this blue circle is and here you see this big dark area. That's where the spacecraft actually sampled the surface and they disturbed a lot of material when they did that. So we're still trying to understand this. Not only did they sample it, they also carried out this cratering experiment which was pretty crazy. It's like a Rube Goldberg device. They had this high explosive sort of a bazooka on their spacecraft which they kicked overboard and they gave it a little spin so it could orient itself. They also kicked overboard a little camera. They could take pictures of it and then the spacecraft itself ran around and went behind the asteroid. The bazooka went off, shot a penetrator into the surface and you see a little bit of the ejecta field in that middle box. And made a crater on the surface. They came back and you can see the before and after picture that should be flicking right now showing the surface before the cratering and after the cratering. And the reason why they did this is that they could go back and that's a little target marker that they, a little red circle that they actually navigated to that they put on the surface beforehand. Then they went back to this crater and they actually sampled again. So they're not only sampled the surface the first time but they were able to sample subsurface material the second time. And again, these are images from that second one. And there's actually a lot more to come with this mission. Within a week or so, I think they'll actually be deploying additional bodies in orbit around there, some spare target markers that they have in order to do more science. So it's very exciting. Another one is the Osiris-Rex mission which I'm more involved with. This is run out of University of Arizona with Dante Loretta as the PI. It's a NASA New Frontiers mission. And again, it's a sample return mission. Both of these are. So they have to touch the surface, grab samples and then bring them back to Earth in order to be successful. So there's a few differences between the NASA mission and the JAXA mission, Hayabusa 2. One is this is a NASA mission so the name has to be an acronym, right? So here it is, origin, spectral interpretation, resource identification, security, Regolith Explorer. The Japanese one is just a cool motorcycle, right? Hayabusa, right? So anyway, we're currently at Bennu with the Osiris-Rex. We rendezvoused in December 2018, we'll sample next year at some point and then we turn to Earth in 2023. Where did we go? We went to the asteroid Bennu. This guy is about half the size of asteroid Ryugu, about 500 meters across. It's a spherical spinning top shape, spins pretty fast, once every 4.3 hours. So that's actually a relatively rapid rotation rate. It's also similar to Ryugu made out of some of the most primitive material that we know still exists in the solar system in the asteroid belt. It's also interesting because it's the most potentially hazardous asteroid known. And what does that mean? It means that it's not hazardous right now but in about 150 years its orbit evolves such that there's a 1 in 1800 chance of it striking the Earth in 2182. So by going there we can actually determine what the precise orbit of this guy is and if this is really a threat or not. And if it is, we've got a long time to worry about it. What do we do? We arrived in late 2018, reconnaissance mapping the surface in detail, measuring mass, gravity fields, shape and spin. Right now we're to the point where we've chosen to touch and go sites and we're preparing for the TAG surface sampling next year in 2020. This movie that you're seeing is actually one of the orbits that we use in order to hang out and close proximity to the asteroid. It's called a solar terminator orbit and it actually uses solar radiation pressure to torque the orbit so that it always faces the sun. Because you can see the star background and the stars in the background actually moving. So this orbit is actually being dragged by solar radiation pressure and it always faces the sun. That has some advantages, some disadvantages as well. We can do some analysis. What's the largest orbit we could be in around this body? About two and a half kilometers. Larger than that, we actually just get stripped out of orbit and we escape. What's the closest orbit we could be in? Maybe around 700 meters. On the right here you see a 500 kilometer orbit that actually impacts relatively rapidly on the surface. So there's this zone of orbit radii that we can actually be in. And the spacecraft has spent a lot of time in these orbits sitting there taking observations of the body. What else do we wanna do? Well here, instead of using a hovering approach, we're actually using an orbiting approach. Very different than the Hayabusa II mission. At some point though, we have to come down and touch the surface in order to get that sample. And this cartoon sort of shows the different measurements and the different set of operations that we actually go through in order to descend to the surface and grab our sample. And when we descend to the surface and grab our sample, we'll use this thing developed at Lockheed Martin called the TAG SAM head that actually once it touches the surface, the regolith will actually blow gas through there and actually capture the material in the sample head so we can bring it back to Earth. So we're building up to this but it's still about a year away. So I can show you some awesome images of Bennu. Although after a while, you're really literally looking at a pile of rocks, right? About 500 meters in size. But this is sort of a map of the surface, a couple of different views. This is to make it real. So you could easily walk up and down this hill. So that would work. Some close-up images show some real challenges that we have and that we're addressing right now. The surface is kind of nasty, okay? Rocks all over the place, big boulders, not many smooth, nice areas for us to go do our sampling. Here's a couple of zoom-ins on a couple of those areas and big rocks. Other things that's doing, you may not see it but there's the little tiny white dots that's sort of in the center of this picture. So the asteroid also is spitting particles out, centimeter-sized particles. Every couple of weeks it seems to send out a spray of these guys. There's a lot of debate over what these are. One of the theories is that there's some sort of a, you know, almost an outgassing or thermal breaking that's happening. Another theory is that there's this small micrometer rights are hitting this guy, throwing up this cloud of particles. We're still trying to figure it out. Got huge boulders on the surface, huge boulders on the surface with weird white things sticking in them. Okay, who knows what that is? Here's a bunch of movies zooming in and out, showing how the surface changes its resolution and sort of gives you a scale of what it looks like at different scales. And with this next image, we'll actually show where on the surface the different sampling sites that we're currently analyzing are located. Now the shape model here is actually a shape model based on the imaging data that we've taken, but you see that it looks quite realistic and in fact it's accurate to tens of centimeters. So that's a huge other endeavor that's very interesting. And here are just some close-up snapshots of these potential sample areas that we're gonna be looking at closer in the fall and getting ready to sample one of them at least next summer. We've done a lot of other characterizations. One thing that's of interest is the bulk density. So it looks like a pile of rocks, but it really has the density of water, the density of one gram per centimeter cubed. And we actually think that inside of those rocks, about 50% of that space is just voids. So there's just a bunch of boulders resting on each other. It's also what we call a microgravity environment. The gravity at the poles is about eight microGs and at the equator it's down to three microGs. So this is a true microgravity environment and the weakness of these forces factors in very importantly when we try to understand the geophysics and the geomechanics of this body. Here we map slopes over the surface and you can see that this is looking at the south and the north pole. All of the slopes actually run down to the equator or the equatorial region of this body because it spins so fast. Sort of like if you're on a merry-go-round that's spinning fast, you get pushed out to the edge similar to that. We also see very interesting phenomena such as transitions in the slope at something that's called the Roche slope, which I'm not even gonna talk about here, but we actually see that the surface has been changing over time as it spins faster and slower due to different effects. Finally, just a quick snapshot is we even see that there's some inhomogeneity in how things are distributed inside of Bennu. And this again comes back to the fact that half of it should be empty void space and we wonder how is that void, how are those voids transferred or where are those boulders in the more dense boulders in the interior? Okay, so that's a very brief, high-level view of these two missions, Hayabusa II and a Cyprus Rex. It's exciting because they're still going on, they're still gonna be in the news in the next couple years. But not everything's gonna end then either. And in fact, there's a lot of very compelling scientific missions that are still coming in the future. So I also wanted to talk just a little bit about which asteroids we will be exploring in the near future. And NASA has a number of these. There are some future selected NASA missions, discovery missions, the Lucy mission, which is run out of Surrey and Boulder and it's gonna fly by multiple Trojan asteroids and it launches in just a few years. The Psyche mission, which is a JPL mission is gonna go to a large metallic asteroid and there's a lot of excitement about what it's gonna see there and if they'll be able to correlate that to a protoplanetary core that may have existed earlier. The Applied Physics Lab has the DART mission, which is one of the first planetary defense missions and they will actually go to a binary asteroid and essentially just run an asteroid or a spacecraft into the surface of that secondary and then detect and determine how much impulse was actually transferred to that thing. So you think that might be a solved question if you drive your car at a high rate of speed into a garbage truck you can calculate what the impulse is, except for asteroids it's actually an open question because when we hit, we create this huge ejecta field that comes off and it actually enhances that delta V that we can provide the object. So with the DART mission it's designed to help measure what that enhancement is so if we ever need to use this technique to push an asteroid out of the way we'll have a better understanding of it. And in fact going to one of these binary asteroids is a awesome challenge as we spoke about before and here's just a sampling of the different types of orbits you could actually realistically put a spacecraft in around a system such as the one that the DART mission will go to. And this is related to a proposed mission by ESA, the HERA mission, which actually wants to send the spacecraft to this DART mission asteroid to check out what happened after this impulse and they'll make a decision on this mission later on. What I'm very excited about just recently we won a simplex mission, a NASA simplex mission at the University of Colorado called Janus and here this is really a ride along or it's a ride share and when the Psyche spacecraft launches what we'll do is we'll have two satellites on there both of those satellites will go off into the solar system after an Earth flyby, flyby two very different binary asteroids and take images of them and map these binaries at a level of resolution that we haven't seen before. So we're very excited about this. There is a lot of science that goes behind this even though it's just a flyby. This is a cartoon I just lifted from the proposal showing all the different transitions that we believe rubble pile asteroids go through and some of these transitions actually end up with binary asteroids and the two binary asteroids that we're going to, 1991 VH and 1996 FG3 actually fall into very different sort of classifications and we hope that our mission will be able to untangle our understanding of these processes and we hope before we get there we'll have better names for these asteroids. So if you have any suggestions let me know. We're also doing a lot of technology development. Here I'm just showing some stuff going on at the University of Colorado, understanding how to deploy vehicles to the surface in this microgravity environment. Things are actually a bit different than they would be putting probes landers on the surface of the earth or even planets like Mars. Other work going on by Jay McMahon in our department is actually looking at ways of disaggregating an asteroid for resource utilization and here they're using some innovative approaches that combine Van der Waals forces with very pliable materials so you can sort of creep along the surface of a microgravity body and sort of expel material up into orbit where it can then be captured. There's other topics that we're looking at as well. There are other missions that are just hanging out there asking to be investigated. There is this one asteroid 2016 H03 which was recently discovered essentially to be another moon of the earth. Essentially it's in an orbit around the earth that makes it look like it's trapped. Now people that know orbital mechanics we know that this is really a closely Wilshire type of an orbit but hey, it's orbiting around the earth so that's good enough for me. Actually the Chinese have a mission that they just approved which will go to this relatively small asteroid, about 40, 50 meters across, take a sample from it and bring it back to earth. Even though this is low hanging fruit, it's always hanging out around the earth. It takes a little delta B to get there but you can solve that problem. It's already spoken for to some extent so the Chinese will be working towards a mission that will do this. So that's exciting too to see them get involved more deeply. So we're doing all this stuff and there are some big challenges out there. Not just understanding from a scientific point of view. If you think about it, understanding from a scientific point of view, at some point has an end. We understand it and we can move on to other deeper questions. Resource exploitation, well if that works, that works if it doesn't. There's lots of other resources in the universe that we can explore and exploit. But the societal challenge of these asteroids is definitely there. A large asteroid is gonna hit the earth at some point in the future. It may be in a million years, okay? But it behooves us to at least think about these things and be prepared. And here's a great example of this. So asteroid 1950 DA, it's pretty large. It's like over a kilometer in size. So Jake can attest to the fact that this would not be a nice day if it hit, right? How big was the one that made Schick's a Bloob? Is that a couple kilometers or 10? It was about 12 kilometers. 12 kilometers, so not as bad as that, okay? Which has been a lot of press about that lately, citing you, in fact. But it's still a pretty bad day. Impact probability is one in 4,000. That's pretty high. I would buy a lottery ticket, okay? If I knew a one in 4,000 chance, right? But the year is 2880. So it's way off in the future. Yet it's a risk that we can identify now and start thinking about now. This is a very interesting asteroid. It spins so fast that it's held together by weak Vanderwall's forces. I think dust bunnies. So this thing is a dust bunny. So we go up to it and if we poke it, if it cracks, it's liable to just fall into a million pieces, or just crack in half, come back together again and smash together again. It would be a very challenging mission or asteroid to deflect, but we can start thinking about it and get working on it now. And here we have one of the more elegant solutions, maybe not the most practical one, but using this thing called a gravity tractor where you just use gravitational attraction between two objects and you can very slowly tow it out of the way. There are many other innovative techniques. Professor Milosz has worked on using really concentrated sunlight to just boil the surface and make jets that push the asteroid out of the way. And there are many other concepts that have been thought of and are being developed at some level for dealing with this problem. So this is a challenge for all humanity and it's hopefully something that we can all unite around. So to summarize, I can say that, and I think this is true, we are living in a golden age of asteroid exploration, even if we haven't found gold on these asteroids yet. We have many, many missions that are really deepening our understanding of these bodies. We're coming up with new techniques and capabilities for how we explore these bodies and now we're moving from flyby to orbiting to grabbing stuff off the surface to now being on the surface and at some point in the future, hopefully digging inside of the surface and really exploring, at first hand, the geomechanics of these small bodies which will inform our understanding of many other phenomena in the solar system. Even though we have this wide range of different sizes, morphologies, spin states, et cetera, et cetera, there's always a solution to how we explore it. The fun part is figuring out which one works the best. In fact, we have this competition right now between NASA and JAXA, similar sized asteroids, two very different approaches and it'll be interesting to see which one actually works the best. So it's pure competition at that level, even though it's just science. And what's been most beneficial for me in studying this is as you go through this problem, you need to understand astronomy, planetary science, get into autonomous control, space robotics. There's a host of topics, granular mechanics that you have to develop if you really want to understand and then explore these small bodies. So it's a sort of a beautiful problem that keeps on giving. So with that, I think I'll end up. Hopefully you have some time for questions and just in case you get bored, this is one of the cross-eyed stereo ones. So if you look at it and you cross your eyes, because I can't do the other ones. I can't do the magic eye ones. But if you cross your eyes, then you'll get a stereo vision of this big boulder on the surface of Bennu. And with that, I'd be happy to take a few questions. Thank you. Thank you very much. So we have some mics, mic runners who if you raise your hand for questions, they'll be happy to bring a microphone to you. Oh, there's lots. Go ahead. Hi. Can you talk a little bit about the challenges of doing mission design? Not just for strange gravity fields like you mentioned, but for when there's a lot of uncertainty in those gravity fields before you go there. You need to go there to figure out what the field actually is. Yeah, that's a good question. And with these small bodies, you have no idea what the environment is, what the gravity field is until you actually show up. But we have ways of bounding the range that we believe the size will be. And we actually have to develop designs that will be robust across that range, which is actually another interesting topic in mission design. How do you design something when you have such large uncertainty? And so that's another fundamental problem. But, you know, you can certainly do this, but it's an interesting problem, yes. So the asteroid redirect mission planned to use a gravity tractor to deflect the asteroid. Do you know if there are any current plant missions that will use a gravity tractor? No, none right now. So you were talking about NASA arm mission, which was going to pluck a large boulder off the surface. I think I had a figure of it early on. And that was, yeah, this one in the lower left. It was a very interesting, exciting mission, but unfortunately it was canceled. So that happens a lot too. Okay, others over here? Oh, come on, you guys. There we go. Test, oh right, there we go. So once the samples are returned with our cyrus wrecks and high-boosted tube, what are the, I guess, most interesting questions that you're excited to find out the answers once those samples are in a lab? Well, I'm not a meteorist, so. My most exciting answers are happening right now when we're there measuring the mass morphology of these bodies. What the fundamental goal of these missions are, though, however, is to get these samples back into Earth laboratories, and then they can do very detailed analysis. They can measure cosmic ray rates and ages and get the detailed chemistry of it. And that gives them a direct insight into the chemistry that was going on in the protoplanetary disk and the solar system in the early stages. So I'll say that. I'm not an expert, so if I started to say more, I would say stupid things. There's another one. Hello. One of NASA's space technology areas that they outlined in their space technology plans in 2015 was to capture an asteroid and put it into cis-lunar orbit. How likely of a mission do you think that is in the near future? I don't think it's very likely. I mean, it's a very difficult mission. I had a lot of challenges, and it never had political or scientific or at some level technical support from the larger communities. And then you can also ask, and there were some good goals for what they wanted to do with this, but it never had strong buy-in. So I don't see this the arm mission essentially coming back anytime in the near future, but I could very well be mistaken. I think it would certainly be exciting to grab a large boulder and to analyze it. But from what we're seeing on Bennu, there's some real question that if we try to grab this thing, it could just crumble underneath our pinchers, because the large boulders on the surface of this asteroid are actually more porous, less dense than the surrounding materials, which is completely flipped from what people would ordinarily expect. So it would be trying to get an asteroid or pluck a boulder off the surface would be an awesome geotechnical experiment, whether you could bring it all the way back without it falling apart into bits. I'm not sure, but I would love to go there and try. Good question. Okay, there's one in front here. Hello, so I wonder how far do you think we are from landing a human on the asteroid? At this point, I'd say we're also pretty far, because when people first started talking about sending humans to asteroids, it was thought of as, oh, it should be easy, because once we get there, there's no gravity field or anything. We started doing the detailed system analysis, and you realize that you only want your total mission to last 40 days, maybe. That means you have to go off into interstellar space on a hyperbolic orbit, fly by, get to the asteroid if you want to stay there, you have to stop, you have to hang out there. At first they were talking about, oh, they can jump out and touch the surface and all that, but once they start looking at it, it's like, well, maybe we'll just look through the porthole and throw a couple of softballs on the surface to see what happens. So it's a goal, people talk about it, and I think it's certainly feasible, but it takes a huge investment, and I don't see that investment coming right now, but I'm not a very good predictor of the future either, so. We have time for one more. So how do you see some of the discoveries we make on these asteroids help develop some of our models for space situational awareness back at home? It's an interesting question, because I have a research area that focuses on space situational awareness as well, and I really started that research because I saw so many things that we were learning from studying asteroids that I knew had a counterpart in Earth orbit for debris particles or small particles in terms of their orbits and their rotational dynamics and the like. Just one quick example, there's this effect called the YORP effect, Y-O-R-P, Yarkovsky-O'Keefe-Rezvitsky-Paddock. And it basically says, if you take an asymmetric body and put it in sunlight, it'll get a torque and then it'll spin up, right? Same principle as the propeller almost, in the wind, right? And we know that this is hugely important for asteroids, and in fact it's probably why they form binary asteroids and how they change over time and the like, but it takes millions of years to operate. However, the same thing happens for defunct Earth satellites, and we have these large geobirds in orbit in geosynchronous orbit, and we've been able to show that within a few years they actually get spun up to very high spin rates, and that may actually lead them to shed material creating additional debris and the like. So right there, you have this Earth-based lab for this asteroid phenomena, and we can take all that we know about the YORP effect from asteroids and apply it to these satellites, which is part of SSA, but then we can also take what we learn from these satellites and apply it to the asteroids as well. So it's sort of a nice closure between these two, and I think there are many other examples of where SSA and asteroid research are actually pretty tightly coupled or can be tightly coupled. Good question. It sounds like we are still learning unexpected things at every asteroid that we go to, and so we still have a long way to go before you'd want to visit one yourself. Well, it would be fun. I would love to jump from the one primary to the other one. That would be great, and I think you'd pay a nickel to do that, right? Yeah. Space tourism, going to binary asteroids and just hopping around. But you might not ever arrive. Well, yeah, yeah. You have to watch out for the radiation. Minor. Minor details. Thank you. Okay, thank you. So on behalf of the School of Astronautics and the College of Engineering, I'd like to thank Dan. So Dan, thank you very much for giving us the Purdue Engineering Distinguished Lecture for this month, and what a great time for him to be here to kick off the academic year. I'm going to overlap with our Produce This Lunar Initiative. So it's great to have you here. So thank you very much. Again, everybody, please thank Professor Shears.