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Orbital Debris

Season 1Episode 221Nov 12, 2021

Mark Matney and Jim Cooney describe the science of orbital debris and the details behind the shielding and avoidance maneuvers of the International Space Station. HWHAP Episode 221.

Orbital Debris

Orbital Debris

If you’re fascinated by the idea of humans traveling through space and curious about how that all works, you’ve come to the right place.

“Houston We Have a Podcast” is the official podcast of the NASA Johnson Space Center from Houston, Texas, home for NASA’s astronauts and Mission Control Center. Listen to the brightest minds of America’s space agency – astronauts, engineers, scientists and program leaders – discuss exciting topics in engineering, science and technology, sharing their personal stories and expertise on every aspect of human spaceflight. Learn more about how the work being done will help send humans forward to the Moon and on to Mars in the Artemis program.

On Episode 221, Mark Matney and Jim Cooney describe the science of orbital debris and the details behind the shielding and avoidance maneuvers of the International Space Station. This episode was recorded on September 10, 2021.

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Transcript

Gary Jordan (Host): Houston, we have a podcast! Welcome to the official podcast of the NASA Johnson Space Center, Episode 221, “Orbital Debris.” I’m Gary Jordan, and I’ll be your host today. On this podcast we bring in the experts, scientists, engineers and astronauts, all to let you know what’s going on in the world of human spaceflight. Space is not as empty as it seems. In Earth orbit, there are more than 100 million tiny particles of space debris that exceed one millimeter in size. More than 20,000 of that debris exceeds ten centimeters. That’s a lot of stuff, and NASA gets questions all the time about how to characterize that, and more often how big of a problem that is for satellites and even astronauts in space. On this episode, we’re going to dive deep into exploring the science of orbital debris and the operations of how we monitor and sometimes dodge debris on the International Space Station. Joining us for this episode is Dr. Mark Matney, modeling lead at the NASA Orbital Debris Program Office here at the Johnson Space Center. He’s returning to the podcast after more than four years — way back on Episode 7, he helped us to understand the total solar eclipse that swept across the United States in August of 2017. Matney covers how NASA is modeling debris and gives us insight into debris from a scientific perspective. Also joining us, for the first time, is Jim Cooney. He works in mission control as a TOPO or a Trajectory Operations and Planning [Officer] flight controller. He’s embedded into space station operations and can describe how we work to monitor debris and, in infrequent scenarios, execute a debris avoidance maneuver or have the crew shelter in place. Exciting stuff, so let’s get right into it. Enjoy.

[ Music]

Host: Hey Mark and Jim, thanks so much for coming on Houston We Have a Podcast today.

Mark Matney: Yeah, good to be here.

Jim Cooney: Happy to be here. Good morning.

Host: Hey, good morning to you both. I am excited to get into this topic. We are going to explore a little bit of the science and of course the operations of orbital debris. I’m sure both of you know this is a hot topic. We get asked about it a lot. So, we’re going to really dive as deep as we possibly can. I’ll first welcome you both and have you both describe each of your roles a little bit in more detail, more than I can do so. Mark Matney, welcome back. It’s been well over four years. Last time we were together was when we talked about the eclipse over America. So, so I think you’ll be the guest with the longest gap in between visits to the podcast, so welcome.

Mark Matney: Well, we have some more eclipses come in a few years, so we may have to revisit that topic. But today we’re talking —

Host:[Laughter] I’m going to hold you to it.

Mark Matney: OK. Today of course we’re talking about orbital debris. I am actually the lead orbital debris modeler at Johnson Space Center. We have the Orbital Debris Program Office. And modeling sounds like a very amorphous thing, but in fact what we try to do is take the data and information that we get from our sensors and try to make sense out of it, turn it into a useful tool that engineers and operators can, can use. The problem is we never measure what we want to measure. We cannot see all sizes, we cannot see all regions of space, or all the characteristics of the debris we want to measure. And even if we could, we have to try to understand what the debris environment is going to do in the future. So we want to see what it’s going to look like in a year or a decade or even a century in the future. So modeling is the tool that helps us fill in the gaps and helps us project into the future and into regions we don’t fully understand.

Host: Very interesting, Mark, and we’re going to dive deep into the modeling and what that means for, for all of those elements that you just described. Now that’s one part of our conversation today. Jim, you’re covering the operations side. Welcome to the podcast.

Jim Cooney: Happy to be here. Yes, as you mentioned, I work on the operations side, in the Flight Operations Directorate; our group is the ISS Trajectory Operations and Planning group. And basically, what we’re responsible for is, you know, working with our international and domestic partners to coordinate and integrate ISS trajectory. What that means is design all the ISS altitude changes to meet the constraints of both the ISS and the visiting vehicle requirements. We also work closely with U.S. Space Command regarding orbital conjunctions between other objects in orbit and the ISS and the visiting vehicles as well. We monitor all visiting vehicles arriving and departing ISS and also look at jettison analysis for anything that’s proposed to be deployed overboard to make sure that that’s also safe to do and make sure we don’t have an object, say, come back to ISS, which would be not ideal.

Host: There you go. So that is, you guys covered perfectly what we’re going to dive into today is understanding orbital debris and modeling it to make better predictions. And then also how that works for our day to day life aboard the International Space Station, in particular, but of course, we’re going to continue our presence in low-Earth orbit, so understanding this for the long term is definitely something that’s of the best interest of, of NASA in particular. So, let’s first understand orbital debris, just what exactly is it: Mark, I’ll pass it over to you to give us a high level, just what is orbital debris?

Mark Matney: Well, that’s actually something the lawyers struggle with. But in reality, it’s any human-made object that no longer serves a useful function in space. And what I tell the students when I talk to schools is all satellites, all technology in general, is destined to become junk. Now, ideally, we’d like to, you know, recycle junk and reuse it. But if you think about it, your iPhone or your computer, it’s all destined someday, or your car, destined someday to become junk. Now there are natural debris, there are meteoroids, and they are a risk, especially to deep space missions. But in Earth orbit, especially low-Earth orbit, below about 2,000 kilometers or 1,250 miles, human debris dominates the collision risk. And I just want to say the oldest piece of space junk out there still in orbit is the U.S. satellite Vanguard I that was launched before I was born, back in 1958.

Host: So I understand there’s been stuff, there’s been orbital debris up in space for a long time. We understand that, Mark, you described that it’s mostly human made. But I think, I think one thing that’s hard to wrap our minds around is just understanding what that looks like and, you know, I think if we imagine, just without much knowledge of it, imagine what orbital debris looks like, we’re imagining clouds of trash, right? We’re imagining just a lot, thousands, millions of particles in space. Give us an idea of just how much debris is up in space right now.

Mark Matney: OK, so it really depends on what size you’re talking about. Because we’re going to talk later about what the Department of Defense tracks for us, what the Space Surveillance Network tracks for us: they track objects about ten centimeters and larger in size, and that’s about four inches. And there, I looked it up, there are roughly 23,000 objects tracked right now. And that means you can see its orbit and predict where it will be tomorrow. But there’s lots and lots of smaller debris we can’t see but can still hurt our satellites. So there are several hundred thousand one-centimeter objects. That’s about the size of a Tylenol tablet or a pearl. And if we go down to one millimeter in size, about the size of a grain of sand, we’re talking about hundreds of millions of particles. So, now the ISS has shields that can protect up to one centimeter in size, so that helps us there. But most of the debris are in LEO (low Earth orbit), but there are also debris wherever we launch satellites, including out at geosynchronous orbit, at 36,000 kilometers or 22,000 miles altitude.

Host: So, OK, understanding that there’s a lot of that debris, there’s different varying sizes of debris. What exactly makes the debris? When stuff goes into space, you’re talking about in terms of some of the smaller scale debris in space, hundreds of millions of particles, what’s happening in space that’s causing all of this material to end up in space?

Mark Matney: Well, as you know, since 1957, humans have been launching things into space. And most of the mass in space of manmade materials is from satellites: military satellites, communication satellites, science research satellites, and from the spent upper stages that put them into orbit. However, it turns out that many of the upper stages in spacecraft are left with residual fuel or other energy sources on board like certain kinds of batteries. And maybe a week, or a month or a year or even a decade later, they might explode. And after all, a rocket is a kind of controlled explosion after all, so there’s a tremendous amount of potential energy there. And these explosive events create tens of thousands of new debris. And there have been more than 200 such explosions since the start of the Space Age. But the big problem we’re worried about is that when two large objects collide and they both disintegrate, and this has happened several times, deliberately, most spectacularly when the Chinese conducted an anti-satellite test in 2007. And there’s been one very large accidental collision between the Russian Kosmos 2251 satellite and the American Iridium 33 satellite in 2009. And the debris from those two events alone, the Chinese anti-satellite test and the Kosmos-Iridium collision, themselves nearly doubled the size of the trackable catalog. That’s how big collision events, how dramatic they are in terms of the number of particles created.

Host: So, OK, relative to the debris, we’ve got a lot of debris out there. What’s, what’s happening with the debris itself? You say there’s debris in space, it’s moving, things are colliding; give us an understanding of what exactly that means. Do we have debris orbiting at thousands of miles an hour? Is it going in different directions? What’s the, what’s the environment look like out in space?

Mark Matney: OK, in order for things to stay in orbit, satellites, debris, anything, it has to travel at a very high rate of speed. And sort of the speed is of order, typically, seven to eight kilometers per second, which is about four to five miles per second, or 15,000 to 18,000 miles per hour. There’s, there’s some variations in there, but it’s very, very, very high speed. And many of these orbiting objects are in different planes, because humans launched satellites into different planes. And the relative collision speed is, you know, you add those two directions, and especially if two objects are hitting head on, it can be up to double that speed. So it’s a tremendous amount of kinetic energy. In fact, the kinetic energy of a piece, of any object in space, is much higher than the equivalent energy of an equivalent mass of explosives. If you think about rockets use a lot of fuel to put a relatively small fraction of their mass and payload into space, that’s where all that energy comes from. It’s the fuel, there’s a whole lot more fuel to put one kilogram of mass into space. So there’s a tremendous amount of kinetic energy, and that’s, so even if those kinetic energies, even a relatively innocuous thing like a marshmallow, if there were marshmallows in space, would actually do a tremendous amount of damage to a spacecraft if it struck it at those speeds.

Host: And it’s because of the speed. Now, now it seems like there’s really not a lot of interference when it comes to that orbit, right? It has that speed, there’s minimal atmosphere to slow it down; it seems like debris would be there for, and we talked about this, right, is quite a while. When we say that, when we say, when we say debris is going to be up in space for a long time, how would you, how would you characterize that? What is a long time?

Mark Matney: Well, it all depends on where you start. The atmosphere, though it’s thin, does gradually help drag things out of orbit. And the atmosphere is thicker the closer you are to the Earth. So if you fly your spacecraft higher and higher, it stays up longer. So, at an object at the ISS orbit, which is about 400 kilometers at 250 miles, it would take several months for a piece of debris, or possibly a few years, to decay out of that orbit. Where NASA typically flies its scientific satellites at about 700 kilometers or 450 miles, it would take several decades to decay out. And objects only a little bit higher, to 1,000 kilometers or about 600 miles, will take centuries. And the objects that are even higher like our GPS (Global Positioning System) satellites out at 20,000 kilometers, 12,000 miles, or at geosynchronous about 36,000 kilometers or 22,000 miles, they’re essentially there forever, that is if we don’t do something to deliberately, you know, move them from there. But just from natural forces they’re up there essentially forever. And in most regions of Earth orbit, we have a situation where we’re launching objects into space faster than they’re being removed by natural processes. So, things are getting more crowded all the time.

Host: So with that thought, Mark, if things are getting more crowded, and we’re in an era where, you know, a lot of companies are putting out more satellites, we have human missions to space, to low-Earth orbit, all the time, whether, whether it’s a cargo mission or whether it’s people in space; what is the risk as we understand the debris that currently exists and, you know, if things continue to go up, what is the risk to satellites, to things in orbit when it comes to debris?

Mark Matney: Well the biggest risk is by impact from one of these pieces of debris. But it’s very dependent on the size of the debris. So the first level of risk I think about in terms of the environment, is getting hit by a small piece of debris, small but big enough to damage something critical on your satellite, so can no longer fulfill its mission, we call that a mission-ending collision. And it depends on where the satellite is hit, because, you know, satellites have, have sensitive areas and not so sensitive areas. But typically, the minimum danger size for debris to do serious damage is somewhere between the one millimeter and one centimeter size range. And, but there’s a whole other risk, which is that the satellite gets hit by something so large that it causes a catastrophic breakup of both objects, sort of what we had with the Iridium-Kosmos collision, and that spreads lots of debris around, lots of small debris that threatens other satellites. So it is, it is a collision risk, but we can mitigate it to some extent by how we design our spacecraft. We put a little bit of protection around it, some shields on it, to make it a little bit more robust against impact.

Host: OK, so understanding, you know, that when it comes to spaceflight, having an understanding of mitigating the, the chance of a collision but understanding that there still is that risk, give us an understanding of what that risk is. When it comes to collisions, you know, I think some of us that are just, not so familiar with, we’re hearing hundreds of millions of pieces, right, so we think, oh, space is very crowded with stuff. So give us an understanding of the probability of a conjunction, of a risk, with satellites and some of these missions with all the debris in space.

Mark Matney: Well, for small debris, spacecraft are hit all the time. The ISS alone has many small, we call them dings, like something like you would get on the freeway on your window. But most debris is too small to do any damage. But you could see physical damage on the outside of the ISS. So typically, any one mission has a low probability of mission-ending impact. But of course, the environment continues to worsen, because human beings do things that make things worse. So it depends on the mission, where it’s located, because the debris is not evenly distributed in space. There are regions with much higher debris risk than others. The ISS actually flies in a relatively low, benign region of the environment. But a lot of our science satellites fly in a relatively busy region in the environment. As for the catastrophic accidental collisions where we have two satellites collide, those are actually, that actually, the probably is very small, but we expect catastrophic collisions at approximately ten-year intervals on average. And since it’s been now 12 years since we’ve had one, we’re probably due for another. And you can, you can think about it this way: if you play the lottery, the odds of you winning the lottery are very, very small, but the odds of someone winning the lottery are actually quite high. People win the lottery regularly. So you’re the spacecraft that you’re worried about getting hit, your probability may be small, but we’re going to have large collisions in the future, which will worsen the small particle environment and worsen the risk for satellite.

Host: This is awesome, Mark. Thank you. This is really good foundational knowledge to understand just orbital debris. And that’s, I think, going to help us to kick off our knowledge. So that’s from the debris perspective, to help us set a foundation for the rest of our discussion as well. I think policy is also a good thing to address very briefly in this introduction. So when it comes to policy, U.S. and with maybe agreements with international agencies, what’s in place right now to make sure everybody understands the orbital debris environment and limits the, the, you know, makes sure that their spacecraft are protected and limits their contribution to adding more debris into space? What exists right now?

Mark Matney: OK, so what we have is a series of what we call debris guidelines to limit orbital debris generation. NASA has the NASA guidelines, there are U.S. Government guidelines, and in fact, there are guidelines really being distributed around the whole world. There are a lot of moving parts. I can cover a few high points. And they basically sound like things we’ve learned in kindergarten. So you’re supposed to clean up after yourself. You want to get your rocket or, or satellite out of the environment after you’re done with it. And the standard is 25 years, called the 25-year rule, but sooner if you can. And then another one is, avoid making messes. Don’t make a lot of long-lived debris. One of the problems with the Chinese ASAT (anti-satellite) test was it was high altitude, and some of that debris is going to be up there for decades and decades. And you know, don’t deploy lots of useless debris from your mission. Some of the early missions deployed, you know, they just jettisoned camera lens covers and other things. So be mindful of your neighbors in space. And another important one is passivate your spacecraft or rocket stage once you’re done with it. Don’t leave inner, excess fuel, don’t leave energized batteries, vent the fuel in space, so it’ll make an explosion less likely to happen. And so, the key is to not be, is to be a good citizen in space. It’s to be knowledgeable, cognizant, that you have, there are other users using space. You want to preserve it for the long term.

Host: Very good. Thank you, Mark. This was awesome foundational knowledge. I’m going to toss over to Jim for a second to help us understand, now that we understand just what the environment looks like, what the orbital debris environment looks like, let’s go to the operations side. Let’s talk specifically about, we talked about the number of satellites and other assets that are in space, but I’m particularly interested in the International Space Station and I think a lot of our listeners are as well. So Jim, you’re a TOPO when it comes to the operations and working day to day in mission control, what is your role, what are you doing?

Jim Cooney: All right. Well, for a standard day, when there’s nothing really going on other than standard mission op[eration]s, we’re basically verifying ISS’s knowledge of where it thinks it is is correct, making sure the systems are working correctly, creating and sending trajectory products out to our various customers, monitoring any updates to any orbital conjunctions that we may be following, and reviewing the crew’s timeline. So, you know, for us on a day to day basis we’re basically there at the start of what we call Orbit 2, which starts at 7:30 in the morning, and we are usually going on call around, you know, noon or so, Monday through Friday. And we are on call 24/7, you know, the rest of the time. And for more dynamic phases of flight such as, you know, ISS re-boost, debris avoidance maneuvers, just any, we’re following orbital conjunctions, you know, that have a higher risk, following those more closely; rendezvous and departing of all visiting vehicles, deployments, spacewalks, then we are actually, you know, physically in mission control for those no matter what time of day those, those take place. And if you want to get more into the, what we’re doing for debris ops, we can get into that with your further questions.

Host: Perfect, yeah, and the role really, the reason it seems like the way that you’re staffing that is because, you know, during dynamic operations, people just want to make sure that if there is some significant maneuver, you know, like you mentioned debris avoidance or you mentioned some other dynamic operations, everybody wants to make sure that the things that they want, that they’re tracking are heading in the right direction. And that’s your role.

Jim Cooney: Yeah, that is correct. If we have to do a debris avoidance maneuver, we have to make sure that, one, we are doing it safely, so we have to configure ISS to make sure it’s properly configured to do the maneuver safely, hand over to the rest of the segment to do the actual maneuver, and make sure that we’re not going to inadvertently put ourselves on a path to have another orbital conjunction that’s risky even when we’re avoiding the primary one that we know about. So it’s an integrated operation between the U.S. systems and the Russian systems and working with U.S. Space Command as well.

Host: Understand. OK, so, when something happens, you’re looking at the trajectory, and it seems like you’re watching not only to make sure that the object that performed the maneuver, whether it’s a re-boost, debris avoidance, that, to understand its trajectory where it’s going, but you are also looking for stuff along the way, in that path, making sure there’s no conjunction, which is I think the term for, you know, a collision. So, what are the tools, Jim, that you’re using to understand, to monitor, that debris? Where is the information coming from to help you to make informed decisions?

Jim Cooney: OK, yeah, so we’ll start with, you know, the objects that are in space are being tracked by U.S. Space Command using the Space Surveillance Network, which is a system of sensors around the globe, primarily radar, that are used to track the objects up in space. And basically, all that information goes into a catalog that Mark was talking about where there is, you know, 20-some-odd thousand pieces of debris that are actively tracked, that are, you know, ten centimeters or larger in orbit. And then, you know, three times a day, the folks there at Space Command take all those objects and look forward in time to see if any of those objects are going to come close to anything else. And specifically, for the ISS or any of the visiting vehicles that, you know, are approaching or departing ISS, they check those trajectories specifically and, you know, and give us a call. If we’re not in mission control at the moment, you know, they page us via a pager service on your phone and, you know, we get alerted. And so, the information that we get is primarily all the trajectory information that we would need to make a decision on whether or not we need to do a debris avoidance maneuver or not. The vast majority of, you know, orbital conjunctions that come in, the risk is, you know, very low, and we don’t need to do anything. And so, we basically get information such as, you know, where the object is going to be, what it is, what orbit it’s in, what is the uncertainty in its predicted position. And so, we take all that information and generate what we call a probability of collision: what is the risk of getting hit? And then, you know, we’re looking out at, you know, three days at a time. So, you know, we’ll get the initial alert, but it doesn’t mean you necessarily need to do anything right away. We’ll keep getting updates with more updated data, and, you know, the closer you get to the time of closest approach the uncertainty, you know, starts to shrink and, you know, either one of two things will happen. Either the probability of collision just remains low or near zero, you don’t have to do anything, or the probability of collision will be high and exceed, you know, the thresholds that we have put in place in our flight rules, and basically commands us to basically take action, do a debris avoidance maneuver, to keep ISS safe. And then once we make a decision on what the best debris avoidance maneuver is to avoid the primary object, we also model that in our own software and send our predictions out to Space Command and have them check our options to make sure that those are still safe and that we, again, as I mentioned earlier, that we don’t have a chance of having a high risk collision with something else later.

Host: So it seems like you have a lot of time, Jim, when it comes to understanding and modeling debris. It seems like you’re getting data, you’re getting data often enough where you have a lot of time to model these predictions, to work across, with U.S., with Space Command, to get the data, so, you have some time, and that’s because of the assets that are put in place. It’s not like an immediate, it doesn’t sound like it’s a very immediate thing. Or does that happen sometimes?

Jim Cooney: It’s rare when something like that happens. The vast majority of time, we know where an object is, you know, well enough that we can predict it well enough so that in two or three days’ time, you know, we’re looking forward that we can get alerted early enough. And then typically what happens, we get an alert, you know, two or three days in advance, and then we keep getting regular updates several times a day. And not only are we looking at the, you know, data that comes in for a specific update, we’re also looking at the trends and the updates to see how are things trending, are things, you know, starting to look like the risk may increase later on down the line or are things behaving normally and looks like this object is going to be of no concern. There are times occasionally where we get notices, you know, fairly late in the game. That is what happened when Scott Kelly was on board, and we had to, we couldn’t do a debris avoidance maneuver, and we had to actually have the crew shelter in place inside their Soyuz instead because it was just too late from the time we got the initial notification, and there wasn’t enough time to do a debris avoidance maneuver at the time.

Host: Interesting, OK. Yeah, I definitely want to circle back on that especially, and we’ll dive into deep debris avoidance maneuvers, too. But I want to understand your role in the decisions you’re making. So, the information you’re getting, Mark described a little earlier that the space station itself is very well, well-shielded, so when it comes to your flight rules and the things that you’re tracking, what is it about the approximately size of a debris that you’d be looking at, you know, understanding that if the probability is at a certain threshold that’s where you execute the maneuver, but are there certain, you know, if you understand that there’s smaller objects that may collide but it’s not much of a concern, what’s your threshold when it comes to size?

Jim Cooney: Yeah, well, basically, anything that is trackable that’s in the catalog as, you know, Mark had mentioned earlier, you know, Space Command tracks things are ten centimeters and larger, and any of those objects would be, you know, catastrophic, you know, situation if they were to collide with the ISS. So basically, anything that we are alerted about is, you know, potentially end of mission. So, you know, we’re not following the pieces of debris that leave, you know, the dings or the scratches because those are just too small to track by the Space Surveillance Network. And so, basically, anything that we’re alerted of is, like I mentioned earlier, end of mission, end of risk; end of mission for the ISS.

Host: Understood. Understood. So, the small, the small enough, the small debris, maybe like a millimeter or something that’s just leaving the dings, that is something you don’t care about. How about that centimeter range, one centimeter to ten centimeter? Are there different assets that are tracking some of those objects? Or is the station shielded against those too?

Jim Cooney: Yeah, and as Mark mentioned earlier, the station is shielded against, to be able to take the impact of, a one-centimeter object. Now, you know, that basically means that ISS won’t depressurize, you know; if it hits a solar array, yes, a solar array could be damaged if it hits a critical component, that component could be damaged. But, you know, the main thing for the shield to do is basically protect the crew inside, you know, the pressurized modules. And so that’s where the vast majority of the shielding is on the ISS. And as I mentioned earlier, Space Command is, you know, their guaranteed tracking capability is anything ten centimeters and larger. We could possibly see something, you know, smaller, yes, and just, I think folks know radar works, you know, the brighter, you know, the shinier an object is, if it’s made out of metal versus cloth, you know, there are things that make things easier to track. So just like if you’re looking at an eye chart, you know, you might be able to see something really clearly, you know, you read down to the point that you can see clearly, you might be able to squint and maybe see, you know, some legible letters, you know, a couple lines below, but you can’t consistently see them. So yeah, that one centimeter to ten centimeter, you know, band of objects, those are the risks that we can’t really do anything about. Either we don’t see them, and if we don’t see them they’re too big to be shielded against. So, you know, that is the risk that we can’t really do anything about. But we do, we do take action for the objects that are larger. So that is something we can do about, and then the shields take care of everything that’s smaller.

Host: Understood. OK, so that’s, so we have an understanding now of just orbital debris, what is it, we understand a little bit more about the environment. And Jim, you gave us a nice description of just the day to day operations, what it’s like in mission control monitoring the debris and the environment and making decisions based on the information that you’re getting. Mark, I’m going to go over to you for a second, because one of the things you said you’re the lead on is modeling debris and having a better understanding of it. So let’s dive into that for a second. You know, when it comes to modeling debris, what assets are in space to help you to do that? What tools are you using? Give us an understanding of what that means, modeling debris.

Mark Matney: OK. So, the core of modeling is actually measurements. And so, we have teams that are specialized in radar measurements and in optical measurements and other types of measurements. And the modeling team pulls that data together and tries to synthesize it. So it’s useful to talk about our measuring instruments. Of course, we talked about the Space Surveillance Network the U.S. Department of Defense runs, and they can see those objects about ten centimeters and larger. Actually, the new Space Fence came online recently, so they’re seeing some objects smaller than that, so we’re trying to close that gap between the ten centimeters and the one centimeter. So that tells us where humans are launching things, what they’re doing in space. But when they say track, that means they can observe an object, compute its orbit, predict where it’s going to be tomorrow or the next day or the next day. But we know there are smaller objects up there; we can see them. So one of the things that NASA does is operates a series of instruments that can statistically sample the smaller objects. We can count how many there are and what orbits they’re in. We can’t track them; that would be nice if we could, but we can’t. And so we have one of our workhorses is a large radar in, in Massachusetts called the HUSIR (Haystack Ultrawideband Satellite Imaging Radar) Radar, it’s run by Lincoln Labs. It’s a 36-meter dish, which is 120 feet, and it can measure, it can detect objects smaller than one centimeter in most of low-Earth orbit. Which is an impressive thing to do if you think about it: an object the size of a pearl that you can see at 500 or 1,000 miles distance. Again, we, radar energy is reflected off the object, and we can sort of, we can measure the speed relative to the beep, and from that we can estimate an approximate orbit. And you ask, why we need approximate orbit because we can’t track, but approximate orbit tells us what region of space that object comes from, and actually helps us understand what the source of that object. Is it from this breakup or that breakup or from some previously unknown event in space? We also sometimes have some time on the big 70-meter dish at Goldstone, that’s the big Deep Space [Network] dish, and it’s often busy doing unimportant things like talking to rovers on Mars or deep space. I’m just kidding, it’s not unimportant [Host laughs]. But we kind of, we usually get the graveyard shift on the radar, on the dish, when they have time. But it can actually see objects down to a few millimeters in size in low-Earth orbit, which again is extremely impressive. For deep space objects out in geosynchronous, for instance, we operate an optical telescope on Ascension Island in the Atlantic, and it monitors that, that environment. And instead of a radar where you bounce energy off of it, we’re just looking at sunlight reflecting off the objects. And we can see objects down to about ten centimeters out in geosynchronous. But for objects that are smaller than what we can see with Goldstone and the radars, we really have to rely on return surfaces. So if you put an object in space, a spacecraft, and then return it to the surface of the Earth, you can actually count the craters, count the impact on it. You can measure their size. You can even put the crater into an electron microscope and determine what the impactor was made of. So that way we can distinguish, was this a natural meteoroid, or was it a piece of human-made debris? And actually, our most reliable source of such data was the space shuttle. After each mission, teams examined the windows for little dings in the windows, and for the radiators, which are behind the doors that opened on the payload bay. And that was actually a fantastic source of information because we found out, for instance, that there’s a non-trivial component of steel particles, which are especially damaging to spacecraft. But as you know the shuttle is no longer flying, so we no longer have that capability, and NASA is actually currently investigating the possibility of flying special sensors so that we can continue to monitor an everchanging environment. One other thing that we do is we do ground tests. We did a test a few years ago on a spacecraft mockup called DebriSat, which we hit with a high-velocity projectile and broke it into hundreds of thousands of pieces. And we actually pick up the pieces and measure them and try to understand the size, the shape, the material, to help us better understand how those pieces would damage a spacecraft. So, there’s lots of different moving parts, and it’s the modeling team’s job to bring all that data together and make sense out of it.

Host: So that’s what I want to understand, Mark, and I think you described it well but I just want to, I’m trying to digest it. And so, what I’m hearing is you don’t have necessarily the ability to track these super-small objects, but you do have an understanding that they’re there, and so the data that you’re getting is just understanding the environment that’s in space. You can, it sounds like you can have an understanding of maybe a general idea of where they are, particularly in terms of altitude, but just maybe how dense it is, and what that does is that helps you to understand the environment, which in turn helps us to understand what it would take to fly in space. Am I characterizing this correctly?

Mark Matney: Yes, but we actually know a little bit more than just where; we know the types of orbits they’re in and the different numbers and the different size. So let’s say you’re designing a spacecraft to fly in a particular region of space, and you look at our models and you say, you know, my risk for this spacecraft having a mission-ending collision is higher than I want it to be; what can I do to reduce that? And what you could do is put extra shielding on sensitive elements on your spacecraft. The ISS was actually designed using these models with the shielding in mind, because the shields actually not only shield against size, but they shield against the velocity because the high velocities are special shields that target maximum protection for certain velocities. So the models were, with the models we’re able to tell the engineers, debris coming from this direction has these velocities; therefore, you need your shields to be these parameters.

Host: Very interesting, Mark. And it sounds like that is a pretty fun job to understand how to properly model debris. It sounds like you’re making stuff explode; it sounds pretty fun.

Mark Matney: [Laughter] When my friends ask me how the space debris business is doing, I always say business is booming.

Host: [Laughing] You guys have a lot of good puns. That’s good.

Jim Cooney: I like that one.

Host: Awesome. Jim, I’m going to go over to you for a second. We talked about modeling with Mark. And we left off when we last talked with you with understanding your role about ISS operations. And we talked about debris avoidance maneuvers for a second; I want to explore that just for a minute. Understanding now, now, how Mark is modeling for the long term, let’s go back into the operations for a second. Let’s say, let’s take a scenario where you are monitoring, you know, just like you do at mission control, and you have a risk of conjunction within the probability parameters that say, OK , it’s time to execute debris avoidance maneuver. So what exactly happens when that occurs?

Jim Cooney: Sure. And as I mentioned earlier, you know, if we’re typically following, you know, conjunction updates for, you know, one, two, you know, three days, so what we’ll typically do, you know, for TOPO is, you know, if it looks like an object might potentially pose a risk, we’ll go ahead and start modeling maneuver options very early in the process so that we, when it comes time to actually make the decision to actually execute the debris avoidance maneuver, we’ve already decided which, what we’re going to do. And in the past several years we developed something what’s called the, you know, PDAM, you know, pre-determined debris avoidance maneuver. And basically it’s a, you know, a command package that is already on board the ISS, and you have, you know, several primaries that you can choose from whether or not you’re going to do the burn to push ISS uphill a little bit or go push ISS downhill a little bit. And we have discrete, you know, delta Vs (change in velocity) that we can do, so we’re talking about, we’re only talking about an increase in ISS by, you know, 0.3 to 1 meter per second. So we’re talking about only 0.7 to 2.2 miles an hour. It’s a very small nudge compared to how fast ISS is moving. And what we’re really trying to do is, basically, you know, we have two conjunctions that are basically, you know, intersecting with each other. And what we’re trying to do is basically, you know, raise the altitude, you know, of the miss [so] we have a nice clean separation. So, you know, we do that modeling early on, and as I mentioned earlier, we send those off to Space Command for them to make sure that our maneuver is not going to run into anything else. And then, you know, as we get, you know, closer to when we had to make a decision, as I said, we have flight rules that govern when we do a debris avoidance maneuver and when we don’t. And basically, it all comes down to risk. And our risk thresholds, we have them color-coded, you know, to make it easy to understand. Basically, our yellow threshold is, you know, anything that has a chance of, you know, collision that is greater than one in 100,000; red is anything bigger than one in 10,000; and then we have black that’s anything greater than one in a hundred. And our flight rules govern, you know, basically, we will always do a debris avoidance maneuver if we exceed those thresholds. There are exceptions to, you know, to all those colors, and that’s what the flight rules kind of spell out, such as, you know, if the, if we do a debris avoidance maneuver and that’s going to cause us to have, you know, let’s say a Soyuz crew that’s coming up to ISS have to abandon their approach and go home and relaunch again, well, you know, the risk of a launch is very, very risky. So, you know, you’re comparing that risk to the risk of the collision and make a decision on, you know, which way to go forward.

Host: Hmm, OK. So yeah, you would have to evaluate the situation of the moment and all the different factors.

Jim Cooney: Right.

Host: When you say raise the orbit, let’s say when you’re executing the debris avoidance maneuver, is there about like a rough average, just based on the few debris avoidance maneuver we’ve done, with how much, are you raising by a few kilometers or miles? Or is it just, is it a matter of, is it a shorter distance, longer distance? What’s a good estimate?

Jim Cooney: Yeah, it doesn’t take much to, you know, drastically reduce the risk basically to zero. And so, most of the debris avoidance maneuvers that we’re doing, you’re talking about 0.3 to a half meter per second, so you’re talking about 0.7, you know, miles per hour, going one mile per hour. So that’s all the change. And basically, you know, we’re raising, you know, one end of the orbit where that conjunction is taking place. We’re only raising about, you know, a kilometer or a kilometer and a half, a couple kilometers at most. You know, that’s all it takes to produce a very nice clean miss, and drop the probability post-maneuver to basically zero and eliminate the risk altogether. So, it doesn’t take much. Now we do have to take into account, you know, later on what that debris avoidance maneuver does to the integrated ISS trajectory that I mentioned earlier, because we’re trying to meet the constraints for the ISS: you can’t fly too high, you can’t fly too low, we have visiting vehicles that need to meet launch dates. And so sometimes after a debris avoidance maneuver is done, we’ll have to either adjust the planned re-boost that we already had or add an additional re-boost or a de-boost, in some cases, in order to kind of put us back on the right track and meet all the other constraints. But the primary decision making is reduce the risk of the collision. The mission is always protect the crew, protect the vehicle and then meet mission objectives as they come along, in that order.

Host: Understood. And there hasn’t been many in the 20-plus years that International Space Station has been in space. I think the count is 28 debris avoidance maneuvers in International Space Station history. The other factor you said earlier, Jim, in your description of just, you know, how the space station operations worked, is you referred to something called a shelter in place. So what does that look like for the astronauts on board? What exactly are they doing to stay safe?

Jim Cooney: Yeah, and basically, it’s more or less is what it sounds like. Like basically what the crew will do, they will go to the vehicle that they launched on, whether it be a Soyuz or a Dragon, or you know, eventually when Starliner comes online, and they’ll go there, and basically, what they wind up doing in, you know, the couple hours prior to the conjunction, they wind up closing the hatches between the modules. That’s to, you know, protect for, you know, if you get hit, and it hits, you know, one module only, maybe we can say, you know, the rest of the vehicle, that’s kind of the concept. We also close, you know, the ventilation ducts between, close the valves of the ventilation ducts between the individual modules as well, to help with any sort of, you know, depressurization, you know, even that would happen. And then, since the crew is in their vehicle that they came up in, you know, worse comes to worse, they can, you know, undock, depart and leave the ISS and come home. So, but and, actually, when Scott Kelly did that, I was the one that actually got called. It was about 2:45 in the morning that that call came in, and that woke me up pretty good. But went in, did the job, protected the crew, and it was all over by 7:00 a.m.

Host: Wow, yeah. And I bet you that seemed like a long couple of hours, right. You make it sound like it’s short, but yeah.

Jim Cooney: It did. It did. It did. From the time I was alerted, I mean I, you know, took the information, talked to the other person that was on call with me, we discussed it very briefly, called the flight director. It was a fairly easy decision to make, you know: I was going to be on my way in, so, you know, I got dressed and got to mission control safely, and then we just executed the procedures that we already had in place. And you know, and then we got to the point where we were just watching the clock tick down to the time of closest approach. Nothing happened, thankfully. And then we just basically undid everything that the, you know, crew had done for the past couple of hours.

Host: Very good. Yeah, and that’s why you think about these things ahead of time, right, because you can just refer to the procedures that you already had.

Jim Cooney: Exactly.

Host: And that definitely helps.

Jim Cooney: Exactly.

Host: Now, now Jim, we’re talking about, we’ve really characterized orbital debris, I think at this point very well. We’re talking about modeling, helping to understand the debris. But really, I think the goal here is we want to reduce, you know, we just don’t, we want to have space be as safe an environment for our astronauts and everybody as possible. So Mark, what are we doing to, what can we do to help to reduce debris, to help to deal with debris, to help understand debris; what can we do to make sure that space continues to be a safe place for astronauts, for satellites, for the continued operations? Because as you said, it just keeps ramping up.

Mark Matney: Well I think the first thing to realize is that space debris is an international issue. Space has no boundaries, and so all the users of space both contribute to the problem and hopefully will be contributing to the solution. I mentioned that the guidelines that ca, that we have the NASA guidelines and the U.S. Government guidelines; in the early 90s, NASA led the formation of an international group called the Inter-agency Space Debris Coordination Committee, or the IADC. It’s now composed of 12 space agencies plus the European Space Agency, well, country space agencies and the ESA. And they created their own guidelines called the IADC guidelines. And those were in turn picked up by the UN Committee on the Peaceful Uses of Outer Space. And they have they have their own guidelines. They’re all very, very similar. A lot of those countries have taken those guidelines back and have implemented those principles in their own national regulations. And it’s, again, those things I said before: not making a mess you can’t clean up, you know; be cognizant that what you do affects your neighbors, and so forth. But there’s one thing that people have talked about that’s still in the theoretical stage and that’s called active debris removal, and that’s where you go up and take things that are already there – grandfathered, if you will — in space, and physically remove them. But that turns out to be, has turned out to be a difficult thing both technologically and financially, economically. But people are looking at that as a possibility. If you think about the guidelines as the EPA, the rules about how you don’t pollute, active debris removal is like Superfund cleanup. It’s something you go to try to clean up the mess we already have. But we’re not to that point yet. So those are the kinds of things that we try to get international consensus on, and one of the things about orbital debris is everybody pretty much agrees that there’s a problem. Everybody pretty much agrees that we should be doing certain things to clean it up. But we still don’t have quite as broad a use of the guidelines as we would like. And so, we sort of tell that story to the world to be sure to try and implement the guidelines as much as possible, as quickly as possible. And we’re making progress on that front.

Host: And it seems like you, you have a lot of assets to understand the debris environment, to understand the smaller sizes. We have the U.S. Space Surveillance Network to understand some of the larger sizes. So we have the ability to monitor, we have the ability to characterize it. And Mark, you’re working hard on modeling and understanding the environment. And so, you know, a little bit of, it seems like there’s a little bit of research there that might help, and then maybe understanding how, you know, what happens to debris when it strikes things. I know hypervelocity impact research is something that has been looked into. So just understanding the environment and understanding what that environment can do to spacecraft to ultimately help. Because as you said, removing debris can be technologically and financially difficult.

Mark Matney: Yes. One of the things you mentioned there, I want to put a plug in here. We have a group at Johnson Space Center called the hypervelocity group that, hypervelocity research group, and they actually operate high velocity guns out at White Sands [Test Facility] where they can accelerate particles to, various sizes, to orbital speeds and impact shields. And that’s how they design shields, how we, as NASA designs shields for spacecraft, and find out ways in which we can understand how different shielding will, will respond to impact. So that’s a whole other branch of our field of research. And that’s how, again, the ISS shields were designed. And new and improved shields for future spacecraft, both human and unmanned spacecraft, uncrewed spacecraft, will be, will be — going forward into the future that helps survive the environment.

Host: Very good. Mark and Jim, just what a fascinating discussion. I’ve been, I’ve been really wanting to get you both together for a while now, and I’m very glad that we got to do it. And I wanted to make sure that we explored orbital debris from both the scientific and the operational perspective. And I think we did a pretty good job of characterizing just, just what this is. And I think people have a lot of questions about it, and you both did such a great job to help us to understand it in a very digestible way. So, so Mark and Jim, thank you both for your time, for coming on Houston We Have a Podcast today and describing this, this in further detail. It was, it has been an absolute pleasure, thanks to you both.

Mark Matney: Yeah, I enjoyed it, thank you.

Jim Cooney: You’re welcome. Thanks, happy to be here.

[ Music]

Host: Hey thanks for sticking around! I hope you learned something today. We really just skimmed the surface; after I was talking to, after this episode, after we recorded, I was talking to Mark Matney, and he said, “really, you know, that was just high level, right.” I thought that was pretty funny. He said we can dive into any one of the topics we covered today in way more detail. So, I’m going to hold him to that. We got some resources online, in the meantime, if you want to check out just some of the things we talked about. There’s actually, if you just search up Orbital Debris Program Office NASA, or something like that, a website will pop up, and that’s where you can find a lot of the frequently asked questions and a lot of data, some of the modeling that Mark Matney and his group are doing to understand more about orbital debris. So you can check that out until we get them back on the podcast to dive even deeper into some of the things we talked about today. We’re one of the many NASA podcasts across the entire agency. You can check out the full catalog at NASA.gov/podcasts. That’s where we are, and you can find full transcripts of each of our, I guess, more than 220 episodes at this point. You can talk to us at the NASA Johnson Space Center pages of Facebook, Twitter and Instagram. Just use the hashtag #AskNASA on your favorite platform to submit an idea for the show. And make sure to mention it’s for us at Houston We Have a Podcast. This episode was recorded on September 21st, 2021. Thanks to Alex Perryman, Pat Ryan, Norah Moran and Belinda Pulido. And of course, thanks again to Mark Matney and to Jim Cooney for taking the time to come on the show. Give us a rating and feedback on whatever platform you’re listening to us on and tell us what you think about our podcast. We’ll be back next week.