Eyes on Earth Episode 14 – Space Debris
Sixty years of manned and unmanned space flight have left a cosmic junkyard circling the planet. In 2017, the U.S. government reported that it logged 308,984 close calls with space junk and issued 655 emergency-reportable alerts to satellite operators. In this episode, we learn about that debris, its potential dangers, and how Landsat flight operators keep their satellites out of harm’s way.
Doug Daniels(DD): Everything on a satellite is sensitive, and the bottom line is this: Any time that you have a satellite thatís hit by space debris itís bad. The outcomeís never going to be positive.
Steve Young(SY): Welcome to another episode of Eyes on Earth. Weíre a podcast that focuses on our ever-changing planet and on the people here at EROS and across the world who use remote sensing to monitor and study the well-being of Earth. Iím your host Steve Young. Weíve brought back our buddy Doug Daniels this week to continue our conversation on satellites 101. Doug, again, is a principle systems engineer with the Aerospace Corporation here at EROS. HE also co-chairs the 2019 NASA Sustainable Land Imaging Architecture Study Team for USGS. That group has been tasked with recommending how future Landsat missions should look and what they should be able to do. We spent the last podcast talking about the basics of satellites ñ how big they are, how high they fly ñ now we want to talk about potential dangers that satellites could face when theyíre orbiting the Earth. Welcome back, Doug.
DD: Thanks, good to be back with you.
SY: Iíve read there is estimated to be over 128 million pieces of debris smaller than 1 centimeter in space as of January 2019. 900,000 pieces of debris from one to 10 centimeters, and more than 34,000 pieces that are larger than 10 centimeters. Where in the heck did all that junk come from?
DD: Yeah, you know, itís unbelievable, isnít it? And sadly, all that junk came from us. All that junk came from space-faring nations that have over the years depositing broken or used-up equipment, spent rocket stages, old satellites or other artificial man-made debris. You know, this is a tough topic for me, because Iíve spent my whole career working in space systems, and taking advantage of the kind of things we can do for space. And itís really unfortunate that the race to space and the value that weíve gotten from these capabilities over the decades has really come at the price of polluting this otherwise pristine environment. Today, the United States Air Force tracks tens of thousands of artificial objects, as you were talking about, you went through some of those numbers, and weíre talking about tens of thousands of objects that are 10 centimeters or larger. And those are the ones that we basically can detect, and thereís estimated to be a whole lot more that are smaller.
SY: So for a satellite system like Landsat, how big of a concern is space debris?
DD: Space Debris is something that the teams, the flight operations teams, the mission managers, the flight managers are worried about on a daily basis. Avoiding any type of collision with an on-orbit spacecraft or another satellite or a piece of space debris Ö itís paramount to insure that doesnít happen. Not only would a collision with another object likely be mission-ending, it would also further pollute that environment that weíre talking about. That space debris all comes from somewhere, and collisions are one of those things thatís really detrimental.
SY: Youíre able to track debris at a certain size? Again, what size is that, and how are they able to track that kind of stuff?
DD: As I mentioned, the U.S. Air Force is the one that predominantly tracks most of the debris thatís in orbit around the planet. The kind of rough order of magnitude, if you will, of the size of object, is 10 centimeters and bigger. Thereís other capabilities that are being put in place ñ whatís called the space fence, that would have the ability to detect objects that are much smaller, make us space operators aware of many numerous objects that are out there that are smaller than 10 centimeters, but to know precisely where those are, what those orbital trajectories are is important.
SY: Do satellites ever get hit by space debris and survive it? Is there any way to know that?
DD: So oddly, the answer to your question is yes. Satellites do get hit by space debris and it does happen, but when weíre talking about a satellite being hit by a piece of debris and surviving it, weíre talking about something really small, like a paint fleck. They types of closing speeds are really extraordinary. It would be like being hit by a bullet, or perhaps something even faster. One of the examples that sticks in my mind is the European Space Agency has a satellite called Sentinel-1A. That satellites solar array got impacted by a piece of space debris and it actually punched a hole through the solar array, a divot in the solar array panel. Now, how do we know that? We know that because the performance of the solar array dropped, and also, itís cool, they have a little camera that shoots down the solar array and they can actually see a before and after picture and see the damage that was done. If you consider the item that impacted the solar array was likely less than a millimeter in size, really tiny, the impact area was one hundred times that.
SY: Really? How much does it take to hurt a satellite, I mean, Iím guessing from what youíre telling me a fleck is enough to do significant damage to a satellite.
DD: You know, it depends on where the satellite is hit. bottom line is this: Any time that you have a satellite thatís hit by space debris itís bad. The outcomeís never going to be positive. So it doesnít take much. Really, in the case of the example that I just went through, weíre talking the size of a microparticle or a paint fleck. Everything on a satellite is sensitive. The electronics, the solar arrays, the thermal shieldings, the communication platforms, these are all highly susceptible to even the tiniest degree of debris impact.
SY: So where Landsatís at, are there many satellites in that orbit, and if there are, how do we keep satellites from running into each other?
DD: Where Landsat is in orbit is actually a fairly popular orbital space. As we talked about earlier, itís roughly 705 kilometers in altitude and itís a sun-synchronous polar orbit. There are numerous satellites that are in that orbit. We share that space with other NASA satellites. We share that space with European satellites. We share that space with Japanese and French platforms, Chinese as well, thereís a number of platforms that share that space. So organizations typically communicate with each other, particularly if the spacing between satellites is on the order of short minutes. And sometimes in the past there have been accidents.
SY: Accidents meaning satellites running into satellites?
DD: Believe it or not, unfortunately, yes. Satellites have collided with each other. Perhaps the most famous collision occurred in 2009. There was an Iridium 33 spacecraft that collided with a defunct Russian Cosmos satellite. They collided at roughly 12 kilometers a second, and that was at an altitude roughly 780 kilometers above the surface of the Earth, so higher than where Landsat flies. And those satellites created thousands and thousands of little piece of debris. So thereís no easy solution to keeping these kinds of things from happening other than space operators, they have to be real diligent, they have to carefully monitor, and they have to have the ability to move out of the way. We just saw an example of that where a European satellite and a SpaceX starlink platform were predicted close approach for collision, and the European satellite moved out of the way. As we populate orbits with more capabilities and more vehicles, weíre going to see more of that.
SY: A game of satellite chicken?
DD: Itís funny that you say that, but thatís really an interesting way to think about it, and itís pretty accurate. And hereís the thing about it: Thereís no traffic lights, thereís no traffic laws for space. So in that example that I just went through, thereís a starlink SpaceX platform that is newly on orbit, you have a European spacecraft thatís been there for a while. Who moves out of the way? In this case, SpaceX opted not to move, so the Europeans did. The question about responsibility and diligence is based on an owner-operator perspective. There isnít any laws or traffic cops if you will governing those outcomes.
SY: So with so much debris, are we constantly getting out of the way of debris? Do we have time to get out of the way? How do we prepare for something like that?
DD: We do a good job, we meaning USGS, and other civilian space platforms for example that are flown by NASA really do an outstanding job monitoring the orbital debris environment. We have tools that do that. Youíd like to have a week or more to say ëhey, thereís a predicted close approach.í Weíd like to understand that, weíd like to have more eyes on it, if you will, as the time of collision approaches. Sometimes we have less than a few hours. It all depends. The environment, especially the environment of low-Earth orbit like we talked about in the last podcast, is a little bit volatile. Atmospheric effects sometimes change how objects are orbiting. So the more frequently you can track something, the more precisely you know its location, the lower your uncertainties are, the better job you can do when you have to decide to move or not.
SY: So I imagine in my mind these flight operations team members sitting down at a control panel wit a joystick, moving it back and forth, moving the satellite up or down. I imagine it doesnít actually happen that way?
DD: No, I it doesnít. Itís a fun visual, though, right? But in reality, no, it doesnít happen like that. If you think about the process, we have orbital dynamics, flight dynamics teams that carefully assess what the environment is like and they really work hard to determine what the optimal maneuver or burn plan is, because weíre located where we are for a reason. We want to stay there, thatís where our mission is, thatís the type of track we want to be on, and any time I move out of the way, it means Iím positioning myself potentially in a location I donít want to be. And reorienting myself and getting back to where I was before is not easily accomplished. So thereís a lot of planning that goes into this. What will happen is a specific burn plan will be developed, those command sequences will be uploaded to the spacecraft, and they will be executed at precisely the right time, and the burn will likely be for small tenths of a second. So the image of someone maneuvering with a joystick ñ we as humans, we donít react as accurately and precisely and quickly as we need to. So itís all done by command modes and executed by flight software.
SY: And again, you mentioned the earlier podcast that the satellite has hydrazine on it. That hydrazine is there specifically to help with manuvers like this: To burn for a few tenths of a second, get out of the way, and then Ö
DD: And then basically, more often than not, that fuel will be used as a thrust vector. Weíll change our Delta velocity at the point in our orbit that itís most optimal to hopefully balance your mission specifications as well as get out of the way. And thereís always uncertainties involved, so when you maneuver you donít want to make situations worse. So again, itís carefully planned. But again, youíre right. That hydrazine is used, itís a little bit of a push, if you will, it changes the velocity, adjusts the altitude a tiny bit, and then typically weíll stay there, and weíll allow the gravitational pull of the Earth to kind of draw us back over time to where weíd like to be, assuming we can afford to do that.
SY: You know, one of things Iíve wondered. Does that debris, does the gravity eventually pull it all into the atmosphere to burn up?
DD: It does, actually. It just takes a lot of time. So thereís a lot of factors involved in how long it takes a piece of debris to reach the Earthís atmosphere and essentially burn up. The lower an object is, the more drag there is, so the quicker itís pulled down. The objectís ballistic coefficient, in other words, how itís shaped, is it really aerodynamic or is it a booster thatís kind of got a broad side to it? All are factors. But it takes years, Steve. It takes years for something to get drawn down and eventually burn up. And in a lot of cases, itís greater than our lifetimes. So weíre talking in excess of 100 to 150 years for things in low Earth orbit to naturally decay.
SY: Has there ever been a conversation about sending robotic satellites up to clean up space debris? Is that too science fiction-y, or is that Ö?
DD: Absolutely not. Itís not that far-fetched. Thereís a lot of organizations that are giving a lot of thought to how to clean up the space environment, and those would all be basically robotic in nature. Theyíre only far-fetched in that thereís no good way to go about it, in terms of a cost-effective way to collect a lot of debris. Space is still a big place. So itís not like your neighborhood garbage truck driving down the street and, you know, making ten stops in the span of a couple blocks. The types of distances weíre talking about are substantial, so itís not easily done.
SY: So I guess my last question, Doug, is will there ever be a time when the amount of space debris just gets to be too much?
DD: Some speculate that weíre already on our way to too much. Itís interesting. Thereís a well-known theory, itís called the Kessler Effect or maybe youíve heard it called the Kessler Syndrome. There was a NASA scientist, his name was Donald Kessler. In a 1978 he contrived of a scenario where the density of objects in low Earth orbit would be such that they would collide, and collisions would create more debris, and that debris would collide and create more debris, and essentially have this escalating factor debris field low Earth orbit such that it would become unusable. Think about that, where there would be so much debris that we couldnít fly satellites like Landsat, or people couldnít leave the planet because flying a human astronaut through low Earth orbit would be too dangerous. So we obviously never want to get there. So being responsible in space, understanding how debris is created, tracking space debris, responsibly operating vehicles, moving out of the way, avoiding collisions Ö your very first question was ìwhere did all this junk come from?î Well, it came from us. So we need to do some work in understanding what that means. I mentioned earlier about SpaceX and Blue Origin. One of the reasons why I like what theyíre doing, I like where theyíre pushing technology is because instead of leaving those rocket boosters in orbit, theyíre bringing them back down. Theyíre landing them and then theyíre reusing them. So just think: Over the course of a year, there might be 10 or 12 or 15 less boosters. And then in 10 years, thereís 150 or 200 less boosters, and none of them collide with anything. It seems small, but over time makes a difference. And thatís what we need to do more of.
SY: Weíve been talking to Doug Daniels. Heís the principle systems engineer for the Aerospace Corporation out here at EROS, and heís enlightened over several shows on the basics of satellites, how they work, and today, on the issues of maneuvering around space junk. Thanks, Doug.
DD: Thank you.
SY: We hope you come back for the next episode of Eyes on Earth. This podcast is a product of the U.S. Geological Survey, Department of the Interior. Thanks for joining us.