>> From the Library of Congress in Washington, D.C. [ Silence ] >> Jennifer Harbster: So good afternoon. I'm Jennifer Harbster, a reference and research specialist with the Science, Technology and Business Division here at the Library of Congress. I'd like to welcome you to today's program: "How to Manage a Satellite Going 17,000 Miles Per Hour: The Historic Flight of Landsat 5." This program is the second in our 2013 series presented through a partnership between our division and NASA's Goddard Space Flight Center. And I'd also like to remind you that our next lecture in June will feature astrobiologist Avi Mandell talking about exotic earths and exploring planets from around other stars. I'm absolutely delighted to introduce today's speaker today, Steve Covington. He's the Flight Systems Manager for Landsat 5 and 7 for the USGS Earth Resource Observation and Science Center or EROS, in Sioux Falls, South Dakota. And he's also the systems director at the Aerospace Corporation. I've been excited about this lecture ever since we began planning it last year. I am in awe of Steve, one of the best engineers in this country and his world-class team who can manage an object that's moving tens of thousands of miles an hour through fields of space debris 440 miles above Earth? >> Steven J. Covington: 438. >> Jennifer Harbster: Okay, 438 miles above Earth, and at the same time he's able to keep the systems healthy and in check, when I have the hardest time maneuvering through traffic and potholes through the D.C. streets, so I am in awe of that. Steve started his career at EROS in the middle of a cornfield in South Dakota. He remembers watching the launch of Landsat 5 on closed circuit TV in 1984, not realizing the role it would play in his future. After several more years at EROS Steve moved east and spent time working as a production director for a French satellite company's U.S. division. Then in 1995, Steve got back to his roots, so to speak, and began working at the Aerospace Corporation on contract to the USGS, versus the liaison between the USGS and NASA during the development and launch of the Landsat 7 mission, and then as a Landsat 7 flight systems manager. In 2001, he added Landsat 5 to his portfolio and has become the longest-running flight manager in its 29-year history. Landsat 5 was launched on March 1, 1984 with the expectancy of 3 years design life and with the hope it would collect Earth observations for at least 5 more years. Twenty-nine years and a Guiness Book of World Records award later, Landsat 5 is just now ending its historic flight, after firmly establishing itself as the grand dame of remote sensing, setting a standard of productivity and discovery that future missions will be building upon for decades to come. Steve is going to share with us the remarkable story of this mission, explaining how these Earth-observing missions are operated and telling the inspirational story of how the flight operations team on ground used equal parts engineering, determination, and luck to propel Landsat 5 into the record books. So please join me in welcoming Steve Covington to the Library of Congress. [ Applause ] >> Steven J. Covington: Thank you, Jennifer. Hi, everybody. Again, Steve Covington, and I'm here today to talk to you a bit about how it is to fly a satellite around the globe and just a little way of context to this, I also teach a course called Space Systems Overview for the Aerospace Corporation, which is a course that covers many of the same topics that I'll be talking with you here today. The difference is that course I teach over a two-day period, and the biggest complaint I get from the students is that it's like being fed through a fire hose. I've got about 45 minutes to give you that same information today, so I'll be traveling fairly fast, almost as fast as Landsat 5, to try to give you an idea of what it takes to fly the Mission. And I'm going to be using Landsat 5 to do that, because that will help me illustrate the concepts. It lets me do that, but also it lets me tell you the story, the really unbelievably fantastic story, the highlight of my career, of this mission, the little satellite that could and did, and continues to this day. I'm going to give you a really quick brief aside. We're in the process right now of decommissioning that satellite. It was launched in 1984 with a certain amount of fuel; that's a consumable on board, and we can't seem to get it to run out of fuel. Yesterday was our third -- we've done 10 maneuvers, the decommissioning the satellite, and regardedly for me and my reputation with the U.S. Geological Survey, yesterday was the third time I predicted we'd run out of fuel, and yesterday for the third time, Landsat 5 proved me wrong, and now we've got another maneuver on Friday to still try to empty the tanks. So it's a remarkable satellite. It is completely in keeping with how the satellite has worked so hard to continue flying throughout its mission. So what I'm going to start with, though, is telling you, okay, what the heck is Landsat 5 and what is the Landsat program? So this is just a -- I'm going to have a little brief aside before we get into how we fly the satellites to tell you what are the satellites that we're flying? So the Landsat Mission timeline. What you're seeing here is a whole series of satellites. Landsat 5 obviously is number 5, Landsat 1 actually launched in 1972, Landsat 8, the most recent satellite, was launched in February of this year, and actually next week I'll be out in South Dakota for its grand commissioning, and it goes into operation next Friday, actually. We have reviews on Thursday, and then it goes, transitions from NASA development to U.S. Geological Survey operations next Friday. So that's a very exciting time for us. We've got a couple of reviews that will all turn out fine, and we'll be transitioning that from NASA to U.S. Geological Survey. The one point I'll make here is that all these lines, for every new satellite, the next one follows soon, before the end of the demise of the previous one. That's important, and that's a key factor in the Landsat program that everyone has to understand because I'll be talking a bit more about it as we talk about why we fly it the way we do. Continuity, observational continuity. A key factor for these missions, these are satellites that take pictures of the Earth. They don't take pictures of license plates, they don't take pictures of clouds, they take pictures of the land for resource management, for disaster monitoring responses. I'm going to show you a couple of pictures coming up here -- just a little eye candy -- but the main point here is that we have to always have the next satellite up before the previous one fails. That's critical, because if we don't, then we lose that link of observational continuity. The satellites orbiting there, 14-1/2 times a day, taking images on every single orbit, and these images, together with the images take on the previous time that piece of land was collected, back through time, and the observational continuity is key. Another piece of continuity -- and I'm just going to speak briefly on this -- is how we build the satellites. NASA has always been at the heart of building these Landsat satellites. I will give a shout out to the U.S. Geological Survey and Department of Interior, who back in 1966 actually, first came up with the concept of a Earth-orbiting resource satellite, which then Johnson Administration, I think, said, yeah, I think we'll have NASA build that, which is probably not a bad idea. So NASA built the first satellite, actually called ERTS 1, Earth Resource Technology Satellite, then apply renamed Landsat after its launch, ERTS1, 2, and 3, Landsats 1, 2, and 3 through the '70s, Landsats 4 and 5. Landsat 6, actually we'll talk about a little bit later, but did not achieve all the successes that we hope for because it never really achieved orbit, and I'll talk briefly to that later. Landsat 5, launched in '84, it's continuing actually unfortunately to this day still -- not to yesterday but till today. That's still flying, but then we launched Landsat 7 in 1999, and this is a tad out of date but we have now launched Landsat 8. It's called the Landsat Data Continuity Mission. Up until next week when it turns operational, it gets renamed from Data Continuity Mission to Landsat 8 and it's officially in operation. Another constant through this whole thing has been Department of Interior and the U.S. Geological Survey. They right from the beginning, were a part of the Landsat program. Up through '99 on 2000, they played a ground system role where they were the land remote sensing archive for the nation. They have always stored the deep archive, the Landsat data, and then created products that were distributed to the public. And to this day, if you go to their website, any image that Landsat's ever collected, back to 1972, you can go to that website today and download images at no cost. Anyone in the world can. It's another amazing fact of the Landsat program is that it's an international program, really. Its reach has been international. There isn't a corner of this world that Landsat has not played a role in. And moving on to that, let's take a little bit of the eye candy. Flooding in the Mississippi River in 2011. Landsat data was there to record the flooding of the river and the extent of that damage, and not only that, but again, because of observational continuity, not only in this image can you see where the water was, but on the -- this is where the flooding was, but if you go back in time, you can see what was underneath it. Because from an insurance standpoint, it's not only where is the water but what was underneath the water? What got flooded? What was fallow field? What was an active agricultural field? What was someone's home? So that's the type thing that you can get from Landsat data. This is actually something I cowrote a paper on back in 1986, and that is the fact that Landsat 5 was the first satellite to actually image and confirm to the world the nuclear disaster at Chernobyl. This is one that was being produced back in the '70s when it was -- this is the day, this is the first image taken, and unfortunately I didn't create a zoom-up for you, but if you look at it, there's actually a little red dot where the core of the Reactor was on fire, and then post the disaster, all these fields that were actually being used are now all fallow. They're all growing in over time because no one grows anything anymore, no one lives there anymore. Another important point of all this observational continuity is not only to see what's happening now, but any picture has value in and of itself, but it takes on enormously more value if you can tell what was happening before that. So we can look at land cover, land use today, but we're informed by knowing what the land use/land cover was before so we can deduce land cover change, land use change. And the Chesapeake Bay region, which many of you are aware of, all the reclamation going on and renewal of that whole watershed, decisions have been made over the last 30 years on how to clean up the Bay, and Landsat 5 has been there through this entire period, taking pictures back in the '70s and '80s and '90s through the Landsat program of what was wrong with it, and decisions are made, policies are made by federal, state, and local governments, and by taking continued images into the future, we can look at the cause and effect of those policies. So again, a place where Landsat has made a real difference. I put this up because this is just iconic. Deforestation around the world. Everyone's aware of deforestation and especially in the rainforests of the Amazon and Congo. well, this is in Bolivia, as it turns out, and got to move along, but let me just say, the role Landsat's played here is probably incalculable, because it brought to attention to the world through vivid pictures the forests that were there and how they were deforested and used for logging and then for agriculture. And in fact because of that, if you look over the FAO and look at their website, the deforestation, rate of deforestation in the globe around the world, has actually decreased in the 2000 decade from what it was in the previous decades. And that's because of what Landsat's been able to do to bring to the forefront of this issue and help put pressure and smarter tactics on how to view land use to all these different countries around the world. I've got Lake Chad up here from three different time periods, basically showing how it was drying up over time, how large it used to be and how small it has gotten. But that's not why I have this picture up here. I have it up here to remind me of something that I actually took part of in the '80s, and that is the humanitarian effort that Landsat 5 participated in. If you recall back in the '80s for those of us who were there, that there was literally a continent-wide drought going on in Africa, and there were many relief projects trying to bring food and water and resources to all the people in Africa that were really having problems. Well, the relief workers ran into a very unique problem. The wells are drying up in the villages so the villagers actually traveled away from their villages, in search of water so they could survive. So then when the relief workers would take the grain to these villages, no one was there, they didn't know where these villagers had gone because there wasn't that communication to really let us know that. So someone had the right idea -- not me unfortunately -- of saying, "Let's use Landsat 5 data that can cover the continent with imagery that in a 60-day period we can cover the entire continent, and use special image processing techniques to find where the water is. If we can find where the water is, we'll be able to find where the people are, because they're off looking for that water. And in fact, that's exactly what was done. They found where the water was, they vectored their C130 cargo planes with the grain to where they found water. They looked down, if they found people, they pushed grain out the plane. And that saved millions of people during that decade. So that's just one other great story that Landsat 5 was key front and center to the world history. So that's enough about the eye candy and what the Landsat program is. Now we're going to talk about the satellite itself. So again, it was launched on March 1, 1984. On that day, I was in a conference room in Sioux Falls, South Dakota at the Earth Resources Observation Data Center, the EROS Center which they love that name. [ Background noise ] I was in the conference room on that day, watching the launch of Landsat 5 via closed circuit TV. It was very exciting, mainly because I was this young engineer -- and wow, look at this rocket science -- I was there as a photographic engineer working on aerial films, and so satellites seemed like this really cool thing to me, and in fact, I had no idea back then that I'd still be talking about Landsat 5 20 years later and in fact that I would be the Mission director of the Flight Systems Manager for that mission, actually for about over a decade. So it's been a really great honor for me. But let's get to the pictures themselves and what's happening. That's a Delta II rocket is what launched Landsat 5, and a lot of power going in through there. And why is it there? Because you've got to escape Earth's gravity. And this is where we get to the 17,000 miles an hour portion of this talk. You have to escape the Earth's gravity, or not escape it completely, but you have to harness the Earth's gravity to be a satellite in orbit. If you go too slow, you'll re-enter the atmosphere; if you go too fast, you do escape Earth's gravity, and off you go and then you're on your way to Mars, which we didn't want to do with any of the Landsat missions. Well, but let's talk a little bit about that. Landsat 6, that's a mission that did not make it to full orbit. Why? Because the rocket took it up, it got up to almost 705 kilometers, our operating altitude, but we had some problems with the attitude systems of the spacecraft, and so when it came time to accelerate it to the full 17,000 miles an hour, it didn't do it. Didn't happen, and so it tumbled and it never got the critical speed necessary to balance with the Earth's gravitational pull, and so the Earth's gravitational pull pulled it back down, it went only a couple of orbits and then it was down, we believe, in the Pacific. Now it's not a land imaging system, it's a bathometric sensor. Water for those. So anyways, it ended up in the Pacific or Indian Ocean. I believe we thought it was Indian Ocean. So that was unfortunate, and we make light of it now. We can through the lens of time, but the fact is that was a critical loss because in 1993 when that happened, this 3-year design life mission was already long in the tooth at 9 years old, and so we needed that mission to ensure that we had observational continuity. Unfortunately we lost that mission and so, it's gone. Luckily Landsat 5 persevered and pushed on well to the launch of Landsat 7 and beyond, Landsat 8. So let's talk a little bit about observational continuity. [ Background noise ] What you see here is a map of the world, and you can see for the geography impaired, there's the U.S., South America, and all these red lines represent the ground track of the Landsat satellite. There are actually, if the red lines aren't on every ground track, they're every I think ten ground tracks, there are actually 233 individual ground tracks that the spacecraft rolls over in order to cover the entire globe. Each one of those ground tracks between going down the daylight side and up the dark side, have 248 scenes. That's actually almost 60,000, 57,000 some odd individual scene centers that the satellite can take pictures of, that this is called a reference system, and the reason we have that is because if I want to take a picture of Sioux Falls, South Dakota, that is not at -- you don't say, I want to take a picture of Sioux Falls, South Dakota, you said, I want path/row 3132, and that's Sioux Falls, South Dakota, and that way, and by the way, for the record, it's not 3132; I'd have to look that up. But you take that path row, and that's what you would reference, and that's why you have the World Reference System. And it's important because that carries on not just for Landsat 5, the World Reference System-2 began with Landsat 4 and continues through Landsat 8, so we will have that from 1982 to at least the demise of Landsat-8, which isn't expected for at least 10 to 15 years, so that's another long period of time where we can use this reference system to figure out where we are. Again, part of the observational continuity. We need to be able to take pictures at the same point at the same time. So observational continuity, I just mentioned both aspects of it that we're concerned with. Location, which this Worldwide Reference System handles, but then there's time. You can't take a picture of Washington, D.C. today at 10 o'clock in the morning and take another one 6 days from now at 6 o'clock in the evening and make any scientific comparison of the radiometry, the picture itself, because you've just taken that picture with 2 completely different solar environments. One was taken at 10 o'clock in the morning, the other, 6:00 p.m. in the evening, the light is completely different, it's coming from different angles. And so what we need to do for observational continuity, is always take a picture at the same time every time. So the picture -- we don't have any flying over Washington, D.C. today, but if we were taking a picture today, the one we took 16 days ago would be taken at the same exact time, and in fact, the picture with Landsat 5 that we took 16 years ago would be taken at the same exact time. That solar illumination and keeping that consistent, that's a key part of the science of observation and change detection, and so that's 2 key points that we're going to talk about when we talk about the orbit, is maintaining our mean local time, the time that we cross the equator, every single orbit, and our ground track, staying on those lines. You can't deviate from those lines, because again, if you deviate from that line, then if you move your scene center from Washington, D.C. over to Ocean City, then the illumination, the bidirectional reflectants, the illumination, the angle that the sunlight hits at, would be different, and that's a bad thing for observational continuity. Okay, so got a little video here that will help make a little easier to see. [ Background noise ] This helps put it in a little perspective, exactly how our concept of operations works for Landsat. So here you have the WRS, now you see it's laid out upon the spinning globe. So you're the sun and you're looking at the Earth, it's 10:00 a.m. and the sunlight's going to be operating by orbiting around the Earth and taking pictures. So as it's traveling over land, it's taking pictures. Now, I will mention -- this is actually Landsat 8. This is a video done for Landsat 8, the mission that just launched this year, but the concept of operations is the same -- again, observational continuity. We operate Landsat 8 the same way Landsat 7 and 5 and 4 have been operated for that observational continuity. Now, we don't actually image over the water. We only image over the land, and so 14-1/2 times a day we orbit the Earth and we collect all those pictures. So this represents the one day of imaging that we would collect. But then there's day 2, 3, 4, 5, 6, 7, 8, 9, 16 days. To cover all 233 rows of imagery, it actually takes us 16 days. And so this is showing how it covers in and we fill in the gaps so that by the end of the 16 days, we've taken an image over the entire globe. Well, we've flown over the entire globe. The spacecraft themselves don't have the capability to collect every single image, every piece of ground. There are constraints on how much data that would be, there's constraints on how much data we can actually send to the ground, and there are technical issues, such as the instruments on board can overheat, and we have to do what we call duty cycle. You can run them so long before you can let them cool off. And so we aren't able to actually collect every single image that we fly over, so we'll talk about that a little bit later, about how we decide what images we do collect. Okay, so I told you that we have to worry about the ground track, keeping that the same, and we also have to worry about the inclination, keeping the mean local time where it needs to be. So we're going to talk about ground track first. And we control the ground track with the orbit, altitude that we fly at. That's kind of odd, but it's true, because we want the satellite -- and by the way, you can ooh and ah at the graphics all you want. I did these last weekend. Thank you. So there we are, orbiting around the Earth. Not quite that way, because the satellite's actually pitching over the Earth. I wasn't that good of an animation. So we're orbiting around the Earth, and we orbit at a very particular speed, at a very particular altitude. Why? Because that makes an orbit period. It takes 98-1/2 minutes just about, for us to orbit the globe completely, so when we cross the equator, it's 98-1/2 minutes to get back to that equator again, and we maintain that time to within a second. And we have to. Why? Because for us to stay in that ground track, we're not rotating around the Earth, the Earth is rotating underneath us. The spacecraft is always flaying in the same path, and the Earth has to rotate underneath it, and we want the Earth to rotate 24.62 degrees every time we orbit. Well, guess what? It takes about 98-1/2 minutes for the Earth to rotate 24.62 degrees, and so that's what's happening. As we rotate around the Earth, the Earth rotates underneath us and goes 24.62 degrees of rotation in that 98-1/2 minute orbit period. So what happens? If we slow down, and we do slow down, and let me tell you why. Drag. The atmospheric drag, the same thing that when you stick your hand out the window of your car and it pushes you back, we actually have that at 705 kilometers, believe it or not. Not a lot of it. There are very few molecules of atmosphere up that high, but when you're traveling 17,000 miles an hour, it doesn't take a lot of molecules to add up and start pushing you back. That's removing energy from your orbit and making you go lower. And when you go lower, this button does nothing -- when you go lower, the satellite goes lower -- I'm sorry, I meant to change this -- minus Delta-V, Delta Velocity. [ Background noise ] When we go slower, there's less energy in the orbit, and the circumference in the orbit is smaller, and what that means is that we actually orbit the Earth faster. So what happens is we orbit faster so the Earth doesn't have an opportunity to go 24.62 degrees. It doesn't get to rotate as far as it needs to, and so we start going off our ground track. Likewise, if we have too much energy in the orbit, if we're too high, it's a larger circumference, it actually takes longer for the satellite to go around, and now the Earth has a chance to rotate too far. In both cases, bad-bad, because that means we're rotating, we're drifting off our path, our target path, which means we don't have the observational continuity that's a requirement of this mission. So just to give you an idea of how exact this is, we're traveling about 17,000 miles an hour, and we have to do a Delta Velocity maneuver, we have to actually speed up -- to make up for this drag that pulls us back, we have to speed up about every 3 or 4 weeks. When we do that, we are accelerating the spacecraft by a whopping 2 to 5 centimeters per second. That's about 1 mile an hour. So we're maintaining this satellite going 17,000 miles an hour with plus or minus a mile or 2 an hour to maintain our ground track. That's how exact we have to be, and consequently, that's how exact our tracking systems are that monitor this satellite so that we know where it is and can figure that out. We have a very great flight dynamics team that does that. Okay. Now we're going to talk, and again, ooh and ah about the animation choice -- now, we're going to talk about orbital procession, and mean local time. Over the course of a year, the Earth travels around the Sun. We get all four seasons, so every corner of that turn, we just went through 360 days, 365 days all the way around. That's what the Earth does, and we want to be taking images throughout that whole period. So this is actually where we are orbiting. Here's the shadow, so this is 6:00 a.m., this is 6:00 p.m., right at the Sun, that's noon, that's solar noon. And so we want to be 10 o'clock, so this is where we always want to be so that we maintain our imaging continuity, we want to always be at this orientation to the Sun. Well, the problem is after about 3 months, we're actually imaging something closer to 3:00 a.m. in the morning. Why? Because the Earth is going around the Sun, but the orbit doesn't have any inkling to do that; it doesn't know any better, so if we were actually traveling pole to pole, the satellite would do just that. Well, we don't want that. We need satellite orbit to process around the Sun just the same way the Earth processes around the Sun, so that over a 365-day period of time, we rotate our orbit by 360 degrees so that we stay in synchronization with the Earth. If we don't do that, we don't maintain our mean over time, and we don't have our observational continuity for solar illumination. So we're back to our orbit inclination, and this should have been the clue to how we actually solve this problem, because if we were just trying to do this polar sun synchronous orbit, which is what we call these orbits -- we're going over the poles, pole to pole and we're sun synchronous, meaning that we're traveling around the Sun at the same way that the Earth is so that we maintain our mean local time, our solar illumination. If we weren't trying to do that, we would go pole to pole and all these lines would be straight up and down. But we can't do that. You see these our inclination is off at an angle, so we're actually traversing the globe at an angle. Why are we doing that? Well, harking back to your high school physics, and when your physics teacher gave you a bicycle wheel, spun it around and you're holding onto it, and then when you would churn it slightly, you'd feel it in part motion and it'd try to pull you around. The force would try to bring you around. That's exactly what we do with a satellite. Instead of flying pole to pole, we actually have a very specific inclination, 98.21 actually, that we fly at and that is just the right angle at a 705 kilometer altitude, to make the orbit process about 1 degree a day so that in 365 days we've rotated all the say around the Sun, just the way the Earth has, and we maintain our mean local time where it should be. This is always changing, just like our altitude is being pulled down and we're always having to do maintenance, we also have to do maintenance for our inclination, because gravitational forces, third body forces from gravity from the Sun and from the moon, all play havoc with our inclination, and so we on an annual basis, will do an inclination maneuver that maintains our orbit. we actually maintain our inclination to about a few hundredths of a degree. 98.21 degrees is our target and we never vary by that by more than a 100th of a degree. So we just talked about the orbit. Now let's talk about my favorite subject, Landsat 5 itself. And what we're going to do is talk about all the spacecraft subsystems because all the Landsat systems and most spacecraft themselves share a lot of the same subsystems, the same support systems that help the spacecraft operate. And so we're going to talk about the first two, power and thermal. And I'm bringing these two up together, because they are the closest example of the autonomic nervous system that we have in our bodies on a spacecraft. There are lots of things on the spacecraft that you have to do commanding with to make it happen, turning on instruments, turning on relays, switching relays, turning on transmitters. Power and thermal are two things you don't want to have to be thinking about. You want the spacecraft to do that itself. So we have these systems on board that work fairly autonomously. The solar ray. You always want that pointing at the Sun, collecting energy. You don't want the spacecraft to think about it, you don't want your flight operations team not to think about it, you want that thing to always be collecting power. And when it's collecting power, it's doing two things. It's creating energy, electricity that runs all the systems on board, but it's also charging these batteries. Because you saw the spacecraft, it's in the daylight, you're in the light and you're able to operate things. At night, there's no sunlight, there's no electricity being generated, so the batteries are what carry you through the night. And you want that all to happen autonomously. You don't want that to have to think about it at all. Likewise, thermal, same thing. When things get too hot, you want it to cool off automatically. So these louvers -- this happens to be the power module where these batteries are sitting, right here in this module, and when they get too hot, these louvers will automatically open up and radiate the heat out to deep space, cooling and allow the cooling of the batteries. Likewise, in areas like on the instrument, where you have to have a very specific temperature you don't want it getting too cold, so you have heaters in there that turn on till you maintain the temperature as well. There are actually thermostats and they turn on the heat when they need to and they turn it off when it gets warm enough. So these are things that are happening all autonomously within the spacecraft. Whenever we have an anomaly -- and take my word, we've had a few -- the first thing you want to have happen is to ensure that the spacecraft is thermally balanced and power positive. Because if you don't have enough power, you lose the mission. If you don't have good thermal balance, you'll lose the mission because your fuel lines will rupture, all sorts of things can happen. That's why you make these systems autonomous. You want them to operate and save the mission when you can't. Okay, communications. Talking back and forth to the spacecraft. Okay, first of all, this happens to be the transponder that's on Landsat 5. There are two types of communication that we have in the spacecraft. There's the engineering data, what we call health and safety data, that's all the bits of information, what's this voltage, what's this temperature, what's this current, what's the state of this component. That's all the engineering data that we need to get a hold of, and likewise, we need to be able to send commands to it. That's all that we call TT&C. It's the tracking data telemetry & commanding, and that's what we use at our Mission Control Center to talk to the satellite and to hear back from it to make sure everything's okay. The second part, and that's what this does -- this transponder is what does that, and it goes through a couple of different antennas here, here and the big one -- both can handle that data. Then we have the image data, the reason we're all there, the payload pictures that are being taken, and they go through an entirely different system. Why? Because it takes very little room, data flow to send down all the health and safety, but it takes a lot of bandwidth to send down all this image data. So we have special transmitters for that, and this happens to be what we call a Traveling Wave Tube Amplifier -- we refer to as a TWTA. And the reason I have that picture is because we're going to come back to that TwTA a little bit later. But that just kind of gives you an idea of what some of the components are. Command and data handling. This is the CPU of the spacecraft. This is the brains. This is where the motherboard is, where the onboard computer resides, where all the memory management is occurring, and it's where all the command interpretation happens. So when we send a command to the spacecraft, it goes through that transponder that you saw in the last picture, and then it's sent to the OBC, the onboard computer, where it interprets that command and acts on it. That command could be turn on a receiver, it could be turn on an instrument, it could be rotate the spacecraft or follow the thrusters. Whatever those commands are, they go through the onboard computer and the onboard computer then sends those commands somewhere else, and acts on those commands. Now, I got this picture here, too, because one of the other things we have in Landsat 5 is the ability -- we don't have the ability to record image data but we can record the engineering data. Why? Because we don't see the spacecraft very often, and I'll talk about that later, but we always want to know what was happening when we weren't looking at the spacecraft. So we need to record that data, and that's what this is. This is actually a tape recorder. Let me make sure it's clear how important that is and how remarkable it is. A tape recorder that was built in 1970 that has recorded and played back more than 50,000 times. You've got 2 of them, both have recorded and played back probably more than 50,000 times. My lead engineer on the Mission considers this to be one of the most amazing parts of the spacecraft actually, because this was built when 8-Track tapes were king, and it still operates and is recording data and we play back every day. I guarantee you -- it's a little after noon; we probably just had a pass at the primary ground station, and one of these recorders just played back its contents from the previous order. And that happens every day, every time we have contact with it. So it's really quite amazing. >> Is it recording just sound. >> No, it doesn't record sound. What it records is what we refer to as telemetry, engineering data, voltages, temperatures, configurations of different components -- anything that has to do with the spacecraft. there are actually 3,600 different types of information that get down-linked every 16 seconds. In fact, there are different data rates. We only need to see a temperature once every 16 seconds, because things change slowly. Our gyro data on the other hand, that's what we use -- and actually we're about to talk about gyros -- gyros are what tell us the altitude of the spacecraft and the motion of the spacecraft. That we actually get 10 times a second, or 8 times a second, 8 hertz. So just changes by that, but that's the kind of data that's coming down to us. It's being recorded all the time. We receive it real-time when we're seeing the spacecraft, and we also then play back the recorded data that was recorded while we weren't looking at the spacecraft. And we'll talk about that actually coming up. So the energy control system. One of my favorite parts, because this is where the diving catchers are made. When a problem happens on the spacecraft, typically it's an altitude issue that's got to be resolved, and so they're a lot of fun to work with. So let's get right to some of these components. First one I'm going to show you here -- I'm not going to talk about everything, but one thing I'm going to talk about is the star tracker. And the reason I like this is because if you want to really see that the more things change, the more things stay the same, we use celestial navigation to know where the spacecraft's pointing, so much like the ancient mariners of Greece, looking up into the stars and said, "North star, I know where I am," we look at stars to figure out where we are -- not necessarily where we are in the orbit, but how we're pointing it. We use it for attitude control. So what that star tracker does, is it looks -- and actually, we have two of them, one here and one here -- these are looking out to deep space -- they're looking for stars that they can recognize. When they see a star, they say, ah, I see that star and I see exactly where it is in relation to me, and then through some mathematical gyrations, will figure out, this is where I'm pointing. That becomes truth for the spacecraft. The spacecraft doesn't know where it is; it's got to figure this out from external sources, and the external source for attitude are the stars. And so we see a star, we shoot it, we know where it is -- don't shoot it literally -- we know where that star is and then we know where we're pointing. That becomes truth. That's where we're pointing. And then the star goes away. Well, what do we do then? That's where these gyros come into play. We have three of them on board, and what they do is they don't know where we are, but they know what the spacecraft's doing in body rates. It takes three axes and it will say -- it will know if we're moving on any of those axes. It's what we call body rates. And so if the spacecraft moves at all, those gyros will sense it, they'll tell that OBC and say, hey, we're turning where we shouldn't be turning; the OBC will say, well, that's not good, let's call our reaction control wheels, which are these spinning masses, and command those to offset whatever that motion is that we don't want and stabilize the spacecraft. So then we have magnetic torquer rods and fine Earth-Sun sensors that we're not going to talk about, because what we're going to talk about now is just how accurate this system actually is that was designed and built in the '70s. I'm only using two hands and I'm holding this pointer as still as I can after having two cups of coffee. That right there is probably 1,000 times -- no lie -- 1,000 times or maybe more, less accurate than that 4,500 pound spacecraft has to be pointing going 17,000 miles an hour 705 kilometers up in space. We measure the pointing air of that spacecraft in hundredths of degrees, and that what you're seeing right there is probably a couple of degrees at least. And so it's really mind boggling that you can take this 4,500 pounds spacecraft with moving parts on it with rays are spinning and looking and tracking the Earth, with stars coming and going, and it takes all that and figures out exactly where it needs to point and points in that direction. There's a lot behind this that I'm not going into in terms of [inaudible] and all these good things, but the fact is it's truly one of the remarkable technology feats I think, for these missions is just how accurate you have to be, and if you want to put that in real world perspective, think of the last time you took a picture with your camera phone and it was blurry. And you're holding onto it. This is flying at 17,000 miles an hour way up in space, and it was built in the '70s. So it's really pretty remarkable. I'm thrilled about it. You can't tell I'm excited about this mission. Propulsion. Okay. This is the reason we're here still. We could have everything work perfectly throughout the entire mission, but as I mentioned earlier in the talk, fuel is a consumable on board. We only launch with so much of it, and when it's gone, it's gone, or in this case, not. But what we have in the back of the spacecraft, you'll see in this picture, this is where the business end of the jets are, what we call REMS, Rocket Engine Modules, and they are what that spit out the fuel back this way, propel us forward so that we can replace that energy that got lost due to drag. Well, Landsat 5 is what we called a multi-mission spacecraft bus, and so it was designed with these 3 tanks in mind, 1, 2, 3. These are small tanks, hold about 167 kilograms of fuel between them, and they are what you'd normally launch a spacecraft with. Landsat 4 and 5, though, were very unique, because they were launched with this auxiliary fuel tank. why? Because back then in the late '70s early '80s when this concept was being developed, there was planned to be a polar orbiting shuttle, a shuttle that doesn't fly out of Kennedy but flies out of Vandenberg Air Force Base in California, and instead of flying east to west, or west to east I should say -- that a way, would actually fly north to south in a polar orbit, and the idea was that when Landsat 5 got old and tired 20 years ago, it could lower itself and use that extra fuel tank to lower itself down from 705 kilometers where Landsat 5 flies every day, down to 400 kilometers, about 250 miles, where the Shuttle would be flying. The Shuttle would bring out a grapple hook, it'd grab it, and there are actually pyrotechnics on the solar ray drive and on this big boom for the antenna boom that would cut the cords and jettisoned those off once it got collected by the Shuttle. Those pyrotechnics are still on here. Interestingly enough, when we decomissioned Landsat 4, we thought, well, let's break that all apart. We can't do it. The only way that can work is you have to have an umbilical hooked up. You need an astronaut to plug in and send commands to have that happen. You can't do it from the ground. So that's a little bit of history on these missions and what might have been for a little bit different Shuttle program. But be as it may, this big fuel tank, because of the fact it wasn't used to lower our orbit by 300 kilometers, we've been able to use that over the years to continually manage our altitude and our inclination to make sure that we have good observational continuity throughout all these years. So we've talked about Landsat 5 and all the systems that go into making it operate. The power thermal communications, command and data handling, the brains of it, the propulsion and the attitude control. These are all here, they're all very important. You couldn't run the mission without it, but you wouldn't want a mission without the payloads. So let's talk a little bit about the payloads. First one we're going to talk about is the Heritage. The multispectral scanner. This is the heritage of the mission because a multispectral scanner was flown not only on Landsat 5, but on 4, 3, 2, and 1. So what that meant is that if nothing else worked on the spacecraft, you would be able to have observational continuity from Landsat 5 back to Landsat 1, which is great. That's important, but it's also the old technology, and the new kid on the block was the thematic mapper. And this has been the workhorse of this mission from day one up till 2011. It collects more bands, it collects it more accurately with higher rate metric fidelity, higher spectral resolution, really a great instrument. So you might ask, Steve, why do we have both of these on the same mission? Well, observational continuity, it's always got to be there. And Landsats, in the Multispectral Scanner, MSS, is the Heritage, the thematic mapper, is the future. You need to be able to cross-calibrate those two so that pictures that you take with the thematic mapper can be compared to pictures taken with the Multispectral Scanner back to '72. So by flying them on the same satellite, you could cross-calibrate. They're falling under the same piece of Earth looking through the same atmosphere at the same field, and measuring the same reflectants off that field, and so the radiometric scientists could take that information from both those sensors and come up with a cross-calibration. So that's why you fly them both the same time. So I want to give you a sense of scale here. That is the thematic mapper, and that's a guy -- it's kind of hard to see on the screen, but that's a guy there, pretending to work on it. This was just before it was integrated with the spacecraft. So let's put that into perspective. This right here is an Earth shield that is right here. This guy right here is standing next to this little thing right here. Multispectral Scanner, it happens to be right up here, then the whole bus. On the way home tonight, if you see a Humvee, an H2 Humvee, that's about the size of the spacecraft, not counting the boom going up or the array going out. That's just the body of it. So it's a big payload, about 4,500 pounds. Now, moving right along -- we're running low on time, so I'm going to start zooming through a few of these really quickly -- space segment, just want to tell you really quickly how we communicate with the spacecraft. Here is the Control Center for the Mission. These are actually real-time upsize. These are the engineers. Here's a looky lou. This was actually taken just a couple of weeks ago during one of our maneuvers that we're executing right at that time. That mission operation center is located in Columbia, Maryland, just about 20 miles north of here. We need the EROS data center, Earth Resources Observation Center, out in Sioux Falls, South Dakota, to actually be the ground station for us, though, so we have the spacecraft sending data to EROS that gets transmitted over to a ground network to our ground control center, who can then send commands back, and so that's a 2-way street. When we're not flying over one of our ground stations, we can do it via Tetris. Tetris is a set of satellites flying in geosynchronous orbit, 36,000 kilometers up in space, and they act as a data relay for us. They have their own ground station located in White Sands, New Mexico, and what we can do is send data from our spacecraft to their spacecraft to their ground, and over across, and that provides us with the ability to communicate anywhere around the globe with a spacecraft, which with an old mission like this, it's important that we have that communications capability. And that gives you the idea that's everything that we've got -- I'm kind of zooming through here now -- that's all the engineering data. That's how we handle the Command Control telemetry, the engineering information. But then there's all that science data, that payload data. Well, that can go directly to the ground station via what's called next van -- a direct link to the ground, but we also have international cooperators all around the globe. This happens to be a station located in Bangkok, Thailand, one of the older international cooperators we have, but we're using them as the example of the international cooperation that we've had with this mission, really since its inception. And so when we are flying not over the U.S, but when we're flying over -- and again -- on the animations -- when we're flying over Southeast Asia, stationed in Bangkok, Thailand, one near Jakarta, Indonesia, Australia, Japan, China -- they all have ground stations that receive data from Landsat 5, or have received data from Landsat 5. And then they use it for themselves in their local applications, but then they send the data back to the U.S. where EROS can store it, so we maintain a global archive of all the data collected by Landsat, which is freely available to you all. When we're not flying over a ground station somewhere, we also have the ability to use Tetris, again, to do those same links so that between all the various different ways, we're able to collect data around the world, because this is a global survey mission. This isn't a U.S. mission, this is a global service mission, and it takes a village to make it all happen. Very quickly through the ground segment: real-time ops, flight dynamics, mission planning, ops engineering. The real-time guys, these two guys right here, they're the ones actually with their hands on the keyboard, sending commands, seeing the telemetry coming down in real-time and saying, everything's okay, or things aren't right. But they're the ones doing that interaction, that interactive interaction with the spacecraft. The Flight Dynamics at Mission planning are the guys who figure out where it's been, where it's going, and what it's got to do. Ops Engineering, they're the guys that take the long view. They don't look just at what's happening today, they looked at what's happened in the past, trend it forward to figure out what's going to happen in the future, and hopefully predict good things, and when they predict bad things, start working ahead of time on mitigations to make sure that we don't lose the Mission to something we could have predicted, prevented, or mitigated. Payload operations, nothing to do with space flight, so I'm going to ignore this pretty much, other than to say, I'll put in a plug for EROS, the USGS Station out in Sioux Falls, that not only does their ground station work but does the data processing, archiving and distribution, again, free to you on the web. That's the Ground network, international cooperators. That's where all the data goes. I'm not going to spend a lot of time on Mission Planning other than to say, what we need to do, because we can't image everywhere all the time, we have to decide where the best places are to collect. There are about 850 land scenes that we go over every day, and we only really can collect about 300 or 350, depending on the orbit and the cycle day. And so we have to decide of those 350 what are the 300 or so that we want to collect. Well, first thing you can do is knock out about 200 of them, because depending on the time of year, it's dark at one of the two poles, so that's data we're not collecting. Then the next big discriminator is clouds. We're not Cloudsat, we're not Watersat, we're Landsat. And as such, we only want to get scenes that show land, and so we start knocking out cloudy scenes. Well, how do you do that? The U.S. government has a little bit of everything. They have a National Center for Environmental Prediction, where we can get the cloud cover predicts for the next 24 hours and beyond, and as importantly, what's the cloud climatology for that area? So say we have a scene that's got 30% cloud cover. Do we want to take it or don't we? Well if it's over Phoenix, Arizona -- let's take a better place -- let's take the Sahara Desert, and it's 30% cloud cover, climatology would say, that's not a good bet, because it's always going to be clear there. If you've got a scene that's predicted to be 30% cloud cover, don't waste your time with it. There will be a clear scene coming up next time. Likewise, if you're over Amazonia, and it says 30% cloud cover, well, that's typically socked in constantly. It's really hard. We bang on that all the time to get a few pixels of clear data. So if you had a scene that was predicted with 30% cloud cover, you'd throw a lot of resources at making sure you tried to collect that scene. And that's what these Mission Planners do, is they take all this various information about where the satellite's going to be, what the predictions are, what we've collected in the past, what we want for the future, and come up with an activity list that says, for this particular time, this is the work that we're going to be doing. And it creates this list that then goes to the realtime operators, who will take that, turn it into a Command load that goes up to the spacecraft, and now the spacecraft has a spinning clock. Everything on spacecraft runs on time, unlike the trains, and when it hits a certain time, a command will go off and it will just go through the activity list and when it hits the correct time, the command will fire. And it might be image here, don't image there, transmit to the ground here, don't transmit to the ground there. Ops engineering. I'm just going to say, again, these are the people who do all that work to make sure the spacecraft keeps running. On non-L5 missions you sit back and look pretty. On Landsat 5, the engineers have done yeoman's work to make the spacecraft run 28 years, and it's really a testament to their ingenuity that we still have a Mission. So this I'm going to really zoom through, but it tells the tale of what's broken. And I could spend another hour here easily, on this. But just to let you know, red means something broke permanently, white, like a 95, something broke but there was a redundancy and green means nothing happened to break that year. So I'm just going to slowly or quickly ride through this. And you'll see that during the beginning part of the mission, things ran pretty well. I will mention back down in '92 we lost the second of our two amplifiers that allow us to churn data through Tetris to the ground, the image data, so all of a sudden back starting in '92, 8 years after the Mission started, and a lot of years after its design life ended, we were no longer able to image data when we run over ground station. We couldn't send data from our antenna to Tetris up in space down to the ground. We had to be over a ground station. That's a key loss at that point. MSS, we lost that in 1995, not a big deal for us because we'd already done that cross calibration. It was a bigger deal for the international cooperators who still were using it, but actually in a way it was a gift to them because that forced the remainder, over -- the few that remained on a Multispectral Scanner, over to the thematic mapper which is a better instrument for everyone. Then we go through the good years, green, green, green, green. I'll mention 2001 because that's when the U.S. Geological Survey took over operational responsibility for Landsat 5. We'd already taken over Landsat 7, but this is when I became a Mission director, the Flight Systems manager, for Landsat 5. I already was that for Landsat 7. '02 was a bad year. We lost some capability, '03, '04 -- the point I want to make for this decade. I'm just going to kind of scroll through, because we don't have much time, but what I want you to see, this screen gets a little busier in the last decade. This was the third decade in operation for a 3-year design life mission. And it was starting to show its age. [ Background noise ] We're stopping 2012. A couple things I want to show you real quickly. Back in '05, we lost both solar ray drives. Those are the drives that keep the spacecraft pointing at the Sun so we get power. As I said, power is king. We need to have power or we've got problems. Likewise, we need to be able to get data to the ground. We've already lost through all these other little places, all the means of getting data to the ground, except for our X Band TWTA, that picture that I showed you, we lost the first one in '87 when Reagan was still president, and we lost the second in '06 we lost the second one, but through a lot of engineering fortitude, came up with a way to turn it on, and I'm going to talk briefly about both of those because those are key points. But the bottom line is, in the end of 2012, the graphic kind of went off here, and you can't read it because it's not there, but we lost a gyro. We lost three gyros. It takes two to operate the Mission. The 705 orbit regime is very popular for Earth remote sensing. We could not fail in that orbit. when we lost that gyro, we lost a key redundancy on spacecraft, that if we lost another gyro, we would go spinning out of control in place at 705 and become a hazard to the other satellites. And so in November of last year, November 4, this anomaly happened. We gave up trying to save it about two weeks later because we recognized the symptoms and knew that it was gone, and so we began the decommissioning process, which started with the final image being collected by the instruments back on the 6th of January of this year, and on the 15th of this year, we began the decommissioning process of luring the satellite out of 705 before we had another failure that we could not control the satellite. So the reason I brought up the solar ray drive and the TWTA, is that I'll just talk real briefly and I mean real briefly, about our diving catches that engineering made. So we had the solar ray drive. The solar ray is tracking the Sun and so when the spacecraft goes around the Earth, that arrow represents the spacecraft pointing at the ground at Nader to take those pictures. The array is constantly going around the Sun, or going around the spacecraft, pointing at the Sun all the time, so that when we're in daylight, we are collecting energy, all the way through because if you think of the way the shadow is, we only have about 33 minutes of time when we're not actually in the Sun. Well, when those arrays broke, we became fixed, so now, if you see that the array is no longer turning, we stuck it at spacecraft noon, at solar noon. That meant that the only time we were actually collecting full power was once in orbit when we were at the equator. So what that meant is when we were at the poles, both North and South pole, we're edge on, we're not collecting any power. That lengthened the night a long way, and we already had battery issues that I didn't show you about before, so this was a real problem for us. This is a place where we started getting enough light on the array that we were actually generating power that would help the spacecraft. That's where it used to be. So we lost a lot of time there, and likewise in the Southern Hemisphere, same thing. We lost a lot of opportunity to collect power, and at the same time, lengthen our spacecraft night, if you will, the time when we had to rely on the batteries. Really bad, the only time we were collecting full power was in the middle. So what we came up with as a unique approach, is we actually tracked the Sun and we pitched the spacecraft. We can't move the array, so we moved the spacecraft. So we point at the sun, we go to Nadir to image during the day, then we move that imaging, we twist the spacecraft again, and collect some more sun. Ingenious idea that nobody's ever done, and so we're pretty darn proud of that. So so we start collecting sun much earlier in the orbit, and actually as we had lost about 12 minutes of charge time and added 12 minutes to night on a spacecraft, we ended up only with about a 2-minute loss. By the time we did this we lost 2 minutes and we actually maintained the full functional capability of the spacecraft, even though we had a mission-ending failure. Any other mission would have said, okay, that's it, but because Landsat 8 was delayed in being built, USGS wanted to find a way to keep this spacecraft flying and we found it. Then there was the communications, and I'll just say, this was our Apollo 13 moment. In '06, this failed. It would no longer fire. When you turned it on, it blew a breaker, each and every time. You'd turn it on, blew a breaker. If you watched the Apollo 13 movie, when they're coming back from the moon, and they're trying to repower the Command module, and they were trying different ways to turn it on so they wouldn't blow the breaker, that's exactly what we did with the TWTA. We started experimenting with different ways to turn it on. Turn it on, with no modulation, turn it on with the frequency amp turned off, all these different things that we did until we found the order to turn things on, which normally everything turned on. What we did was start with everything off and turned on individual components so that it would fire without failing. We did that, and it lasted another almost 4 years after coming up with that fix. It lasted 23 years, the redundant TWTA. The first one lasted 3 years, the redundant lasted 23 years. So for that, this is hanging up in my office, actually, little plug. I can't read it here -- I'll try to read it here: "For dedicated efforts in recovering Landsat 5 from two potentially mission-ending hardware anomalies and restoring the mission to full operations." This was given to our team for recovering the satellite back in '06. This is an international award from the Space Ops group, so we're very proud of that. So getting to the end here. What makes us amazing? Keep in mind, everything I've talked about here, it was a 3-year design life for a design that was from the '70s. It lasted 29 years. In that time, we orbited the Earth 153,000 times. It was design life was 15,000 orbits. A couple of things to think about with that 150,000, over 150,000. Every orbit we charged the battery up during the daylight, and we discharged it at night and charged it back again, 14 times a day for what was 10,538 days of operation. Imagine your Schick or Lady Schick in your bathroom, which uses the same battery technology, a Nikeid battery, charging it and recharging, and you're running it down and charging it again, 150,000 times. That's what these batteries have done -- most of them. They're not all there now. We passed that pretty quickly, too, but the fact is, it's still operating to this day. Those batteries right now well they're probably at night, but daytime they're charging, at night they're discharging. So 2.6 million images, 8 billion square kilometers of the Earth, which I forgot how many times around that -- I don't know if I wrote it down, but it's imaging the entire land mass of the Earth, many, many times, 500-some times, I believe. Now, here's the thing I'm particularly proud of. Almost half the images, about 47 or 48% of all images collected by Landsat 5 in 29 years, were collected in the last decade. That's in this time when everything was coming up, everything was coming apart. That's still in the most prolific time for the spacecraft, collecting imagery. Why? Because the U.S. just made a keen effort in its international cooperation. We couldn't get data through Tetris; we had to use our international partners to collect the imagery, and USGS made strong strides with that whole community, and we ended up with a lot of different stations around the globe, collecting imagery, and we squeezed blood from that rock and collected all those images, and collected almost half the images of the entire mission in the last decade. So we're quite proud of that. And 38 different receiving stations in those 29 years in 22 different countries. It's simply remarkable. And for that -- It's official. We are the longest operating, Earth remote sensing mission ever launched by mankind, something we take extreme pride at, because it was not an easy feat to accomplish. It took dedicated effort by some really, really thank God, smarter people than me, to make this all happen, and I am so proud to be part of the team that's accomplished this, because it's been a feat not only for our country but for the world with all it's accomplished. And before we end, which I think we're going to have questions, I want to just acknowledge that we have a couple of people from our Flight Operations team, we have the Flight Systems Manager, who sat down somewhere. Stand up there, Bob? [ Applause ] Then next to him is Jeff Define, the lead engineer for the Mission. I get to stand up here and take all the glory, they get all the credit. These are the guys who actually make it happen, and they're absolutely some of my best friends. We worked together for years and years, and I thank them very much for everything they've done with this. So with that. [ Applause ] I know we went a little bit over, and if you need to leave and get back to where you need to go, feel free, but we definitely can answer some questions, and we've got one down here. >> Steve, What's the composition of the fuel you're trying to dump from 5? >> What's the kind of fuel that we've trying to dump from the spacecraft, It has hydrazine in it. It's a monopropellant, nitrogen, hydrazine, nitrogen -- I've forgotten it now but N4 -- >> N3. >> Steven J. Covington: N3, okay thanks. It's hydrazine fuel, monopropellants, so the great thing about that is it doesn't take two different fuels in a catalyst in the fuel to make it work. You don't need an oxidizer as well as a fuel, so it's easier to work with, nothing you want to touch with your hands. It's very caustic. And actually, the NASA has been working very hard on coming up with greener fuels to use in spacecraft, because that's one of the reasons why we need to empty those tanks out before it re-enters the atmosphere, because you just don't want that stuff flying around. I don't think it's a big deal, because most of it I think would burn up, but as part of the effort to maintain our -- we have very specific rules on our decomissioning and one of them is -- the three are remove chemical sources of energy, kinetic and electrical, and all these decommissioning, these decommissioning burns are to do that first one, remove the chemical energy. Any other questions? >> So the reason that the mission was so long-lived is it had this system built in to be able to drop down the Space Shuttle for servicing. You had this surplus of fuel? >> Steven J. Covington: Okay. That's a bit of a trick question. >> Okay. >> Steven J. Covington: Absolutely, it could not have survived as long as it did without the fuel to maintain the orbit so we could have the observational continuity. However, there have been numerous mission-ending failures that have occurred along the way that would have ended the mission as well had it not been for operational workarounds. And this is something NASA's actually looking at is the fact that there's a design life that spacecrafter built to, but then there's an operational workaround that's the wild card in the process of, are there errors that can occur that you can compensate for in some way? And Landsat 5, just based o the way it was built, had lots of ways to do that, that a lot of other satellites wouldn't have. And so we were just very fortunate to have the fuel and to have the means at our disposal to do those diving catches. [ Inaudible comment from participant ] >> Steven J. Covington: Oh, excellent question. No. No. >> How does that work? >> Steven J. Covington: Okay, how does that work? There's a couple of things I didn't talk about. >> Could you repeat the question? >> Steven J. Covington: Oh, I'm sorry. Let me repeat that question. >> [Inaudible]. >> Steven J. Covington: Okay, I apologize. Last question was was fuel the only indicator of getting us as long as we were -- sorry paraphrasing -- but the question just asked is explain with a little better detail the way that we maintain attitude control? Well, the satellite's going around the Earth, pitching around the Earth, it doesn't actually know the Earth is there. It just knows that there's some gravitational force keeping it from flying straight. It keeps on falling around the Earth, because we keep the speed up because so it never falls into the Earth, it only falls around it. And we track where that is by something called ephemeris, that we track the satellite every day, we take that definitive ephemeris and predict out into the future where the satellite will be. We then tell the satellite, this is where you're going to be. Then we also load up a star catalog that says, for where you're going to be, these are the stars you should be seeing. It then, it actually uses something, a Kalman filter, and it takes stars, and it has to take more than one, it takes a few stars, only one at a time, and it looks at it in an XY coordinate system, and we have very specific -- in fact, actually, I don't have the picture anymore, but we do all sorts of very fine measurements to know exactly where that star tracker's pointing in relation to the body of the spacecraft. There are different coordinate systems, there's like 3 or 4 coordinate systems on the spacecraft. You have your navigation, you have your instrument coordinate system. And so the gymnastics or the mathematics is taking that 2-dimensional location of that star and deducing what the attitude of the spacecraft is, but then over time, it takes additional stars, and that's a refining model. And so it takes -- depending on where you're starting from, if you have to reset the Kalman filter versus restart it, it would determine how long it actually takes to collect enough information that you're over time, refining, refining, refining, that solution until you have the accuracy that we need. You don't get it from the first star. That's a very good observation. You get it over time through multiple collects, star identifications and sightings, as well as from the fine Sun sensor, which actually sits on the back of the spacecraft and at the South Pole looks back at the Sun, and we actually get some positioning information from that as well. >> Is that older technology -- does Landsat 8 still do that or are they using GPS? >> Steven J. Covington: So the question is is Landsat 8 using the same technology as Landsat 5? Excellent question, and yes and no. There's a little mixture there with what you're asking, because GPS takes care of part of it, but it doesn't take care of all of it. GPS replaces the need for us to track the satellite the day before, figure out where it's been so we can predict where it's going. Ephemeris, keep in mind, what that's doing is it's describing the arc of the spacecraft around so it knows where it is in orbit, so it knows what its pitch angle needs to be to stay pointing at the center of the Earth for Nadir picture taking. That's what the GPS replaces. Landsat 8 has GPS. It uses it to replace our need to track the satellite and figure out where it is around the Earth. GPS is telling us that in realtime on Landsat 8. Landsat 5 didn't have that, well it had it but it never worked. Landsat 5 was actually launched with a GPS. The flight software didn't work on it. There wasn't really a constellation at that time anyway. It was going to built while 5 was being built, but that receiver never worked, so we never used GPS. We always just tracked the satellite, come up with this predicted ephemeris, put it on board, spacecraft looks at stars and says, based on where I am, based on this ephemeris, I know where I'm pointing. Likewise, with Landsat 8, it doesn't need that file to be set up. It uses the GPS, but it also has star trackers because you still need that truth. You need celestial truth of where it is. Even Landsat 7 doesn't use a star tracker. It uses what's called a slit sensor, but does the same thing. It looks for stars and based on finding the stars, and that helps it figure out where it's pointing based on its predicted ephemeris. >> So like how many satellites are involved with total GPS systems? >> Steven J. Covington: Now you're getting out of my comfort zone, but there are I think 24 satellites in operation for GPS and they have a few spares and on orbit. >> [Inaudible]. >> Steven J. Covington: No more than your car's doing to get you here, except for the elevation part. We're running out of time; one more question. >> Are all of your Landsat satellites the same altitude? >> Steven J. Covington: Ah, excellent question. You saw that we had the World Reference System 2. That infers that there was a 1, and there was. Landsats 1, 2, and 3, the Earth's sensors, the Earth Resource Technology Satellites, they actually flew at 933 kilometers, because there was no plan for them to come down. That's a really benign area up there. The higher you are, the less atmospheric drag, so the less impact in work to keep it flying. That flew on WRS. It's kind of like World War I/World War II. You didn't call it World War I until there was a II. Worldwide Reference System, you didn't have a 1 until you needed a 2. So the first three satellites all flew in WRS. The Landsats 4 and up fly in WRS-2. As do many NASA missions, now, that constellation, we call it the AM and PM constellation, those across the equator in the morning, those across in the afternoon, the EOS missions, they all follow that same ground track that was developed for Landsat back in the '70s. Yes, sir? [ Inaudible question ] Nope, that was the last one to use it, absolutely. The question was was MSS ever flown after Landsat 5? And the answer is no, Landsat 7 actually used what we call the enhanced thematic mapper. Basically, the same thematic mapper that was flown for 5 and 4, but with extra calibration capabilities so that we could be even better radiometry, and in fact actually -- this is one of the great stories of the program -- the higher fidelity of Landsat 7 data was used to better calibrate the Landsat 5, so Landsat 7 actually made the Landsat 5 archive, 30-year archive even more valuable by allowing the radiometric engineers to refine the product accuracy. >> Jennifer Harbster: Yeah, I hate to do this... >> Steven J. Covington: I could stand around out here, too. >> Jennifer Harbster: I was going to say, I'm sure he could entertain some questions as we're powering down. [ Applause ] >> Steven J. Covington: Thank you very much, and thank you on behalf >> This has been a presentation of the Library of Congress.