Your spacecraft has reached the end of its mission. You’ve done everything you can to keep it operational, but now it’s time to say goodbye. How do space agencies deal with spacecraft to shut them down gracefully, protect future missions and life on other worlds. So, the time has come to see your mission across the Rainbow Bridge. How exactly do you say goodbye? Let’s discuss.

Show Notes Why Missions End * End-of-Life (EOL) Planning * Risks & Externalities * Tech & Policy Outlook * Underinvestment in EOL solutions—needs urgency. * Space 101 Nuggets * What’s Ahead TranscriptFraser Cain:* AstronomyCast, Episode 766 How Spacecraft End. Welcome to AstronomyCast, your weekly facts-based journey through the Cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, I’m the Publisher of Universe Today.

With me as always is Dr. Pamela Gay, a Senior Scientist for the Planetary Science Institute and the Director of CosmoQuest. Hey Pamela, how are you doing?

Dr. Pamela Gay: I am doing well. I have to point out for the audience, for those who don’t know because they only listen to the podcast, I come up with the initial graphics and name of it, and then you give it a much more SEO friendly, but this is one of those episodes where I’m super proud my title was End of Life Planning for your spacecraft. Yours more SEO friendly, mine amused me more, and I just need to share, you are the master of titles.

I am the person who writes hokey titles that amuse me.

Fraser Cain: Yeah, yeah. I mean, this is always a tension between us, and people wonder what is the core tension between Fraser and Pamela as a production duo here, is that I want the episodes to be very no-nonsense, as a standalone and different from the other stuff that we do, because both of us are doing much more whimsical, news-based, current events. That’s our bread and butter, and so this is something that is timeless, we’ll be here forever.

The episode about Mercury, it’s called Mercury, and so often what will happen is I will pitch you a whole bunch of subjects, and mine are very much gravitational lensing, spiral galaxies, and you will be on the deepness of thought regarding the- I don’t do that, I do usually plays on words. Yes, you are very punny, you are very lyrical in the way you describe these, and for me, like normally, yeah, I’m all over that, that sounds great, those are the kinds of titles that I would do, but for Astronomy Cast, it needs to be this archive of just very straightforward, easily accessible things. So this is a creative tension, and sometimes I win, sometimes you win, mostly neither of us care enough to make a big stink about it.

Your spacecraft has reached the end of its mission. You’ve done everything you can to keep it operational, but now it’s time to say goodbye. How do space agencies deal with spacecraft to shut them down gracefully, protect future missions and life on other worlds?

So what led to your thinking about this episode, because this topic came from you.

Dr. Pamela Gay: So basically, we first did, okay, so you need to get a launch license, then we looked at rockets versus the environment, and I was like, I’m out of creativity, is there anything else that naturally follows on that cycle? Well, once they’re born, they have to die, and that’s literally where this came from, was now that we’ve launched them, what do we do with them?

Fraser Cain: But there was a really dramatic mission end that happened earlier this year with the Gaia mission, and we got this sort of blow by blow explanation of what was going on, and I think a lot of people were quite puzzled by the extremes that the European Space Agency was going to, to shut down the Gaia mission. It wasn’t just, all right, we’re just going to leave it there, turn off the switches, hopefully we’ll come back in a couple of years and maybe somebody will be able to get Gaia going again, who knows?

Dr. Pamela Gay: No, no, no.

Fraser Cain: They went scorched earth on Gaia.

Dr. Pamela Gay: Yeah, they yeeted it into a heliocentric orbit.

Fraser Cain: And dismantled its memory block by block, overwriting it with garbage to make sure.

Dr. Pamela Gay: Now that I’m not sure they had to do, but.

Fraser Cain: Yeah, well, so the rationale for that was that they didn’t want this spacecraft to accidentally come back online and to interfere with any other missions that were going on. They wanted to not only be non-functional propellant-wise, power-wise, et cetera, because it still had lots of power, right? It just didn’t have the propellant.

And so they had to, it was going to, and it was built to be super redundant, really try hard to connect with earth-based satellite. It was really going to keep trying to do its mission. And so they had to go in and they had to rewrite its memory block by block, filling it with, I think the names of everybody on the team.

Imagine you just go through your memory of some software application you’ve worked on, replacing it block by block on the hard drive with the names of people. It is not going to be a functional piece of software by the time you’re done with it.

Dr. Pamela Gay: No.

Fraser Cain: Yeah.

Dr. Pamela Gay: No. No. And, and, and this really, when you think about how hardcore that is, like in my universe, sure.

You just like overwrite whatever the, the equivalent of the BIOS part of the memory is. But no, they did the whole darn thing.

Fraser Cain: Yeah. They did the whole thing. They made sure that there is no possible way that that spacecraft can lurch from the grave and interfere and that their concern about it messing up comms, providing a false signal was just so extreme that they went to this level of finality for the mission.

And, and this is the kind of thinking, like I wanted to start with this very dramatic example because this is the kind of headspace that mission planners are in. And I think that for a lot of people that is going to feel very surprising that the expectation is you’ve already spent all this money, all this time, all this expenditure to get this thing out into space. Why won’t they just leave it?

And then maybe some future generation could come along and use it and continue to bring it back operationally. So we’ll get to all of that. But let’s sort of just talk about this limited lifespan of satellites and spacecraft.

Dr. Pamela Gay: So we, we have two major things that, that bring spacecraft to a natural end, depending on how they’ve been constructed. One is you run out of propulsion, so you’re no longer able to change your orbit, lift your orbit, do whatever to your orbit. Now there are some spacecraft, they put them where they want them.

They are fine where they are. Let’s just leave them there. And even with those, you start to then run into the risk of, okay, so propulsion isn’t necessarily my problem, but they could hit something.

They could land on some buddy. They could land someplace that doesn’t currently have some buddies and put some buddies there. There, there are a whole variety of ways that your no longer fully functional mission could cause a very bad day for a planet where the earth is a planet or other spacecraft that are out there trying to live their best life.

Fraser Cain: And we see this happening about once a year where someone didn’t take the end of life for their spacecraft or their space station very seriously. And it’s going to come back down at a random location, almost certainly into the Pacific Ocean, but maybe just maybe into a populated center.

Dr. Pamela Gay: And we’ve also started to see a whole lot of near misses where they’ve had to radically move spacecraft. And at some point, as the number of spacecrafts continues to grow exponentially, it’s going to hit the point where we don’t just have near misses. We have actual collisions that create more massive debris clouds than anyone really wants to deal with.

Fraser Cain: Right. So we’ve got the situation like in low earth orbit, these things could potentially come back down to earth in random locations, even leaving them in low earth orbit. They’re going to be, it’s a very dense environment, relatively speaking, you know, still space, you know, it’s wide open, but still satellites do crash into each other and that if you leave your satellite, it’s going to potentially crash into others and you’re going to get more debris.

The debris is going to crash into more debris. You’ve got a problem. And then the issue that we mentioned with Gaia is that they can also be a, a communications hazard that they’re going to be, you know, there’s a limited amount of bandwidth.

You’ve got a guy over there screaming, give me a job. Let me give you something to do. I’m over here.

I mean, who among us? Yeah. I haven’t had to deal with that situation, but there’s one more issue with in the outer solar system.

We saw this with the Galileo mission and the Cassini mission. What’s that about?

Dr. Pamela Gay: And this is the concern of the spreading somebodies where the somebodies are microbes, bacteria, and other life forms that get carried out there from the planet earth. And we are learning more and more about worlds in the outer solar system that either in the past or continue to have sub ice oceans. And there is potentially transfer of materials through cracks, through processing from the surface down into those seas.

And we don’t want our life to potentially destroy life somewhere else or just make it so that we’re not sure if what we’re eventually finding came from us or got there on its own.

Fraser Cain: Yeah. I always use this example, right? We send the first life mission to Enceladus and they’re like, cyanobacteria, weird.

And then they, you know, they start to Europe and cyanobacteria, weird. And they were on Mars. Cyanobacteria, weird.

Cyanobacteria is everywhere. It’s all related. It’s all just from earth because cyanobacteria just loves an opportunity to take over.

All right. So we talked about sort of the reasons why spacecraft are that some level of intelligence needs to go into what you do with your spacecraft at the end. You don’t just walk away from your spacecraft.

You got to do something with it. So what do they do?

Dr. Pamela Gay: So there, there are a number of different ways to dispose of your spacecraft. And, and, uh, there’s actually international guidelines that when you have something in orbit around the earth, uh, per UN guidance, they make arrangements with different other organizations. Uh, 25 years after your mission is over, your spacecraft should be put somewhere safe.

The FAA has upgraded that now that we have so many more things out there to five years, you have five years to dispose of your spacecraft people. And so what they’re looking at is let’s put solar sails on it. Let’s put drag systems on it.

Let’s do something with those low earth orbit satellites that allow us to make sure with certainty that atmospheric drag is able to deorbit them with things that are further out. Uh, we lift them up into higher orbits or as they did with Gaia, send them on a journey round the sun. And remember it is energetically easier to remove something from the solar system than to crash it into the sun.

So don’t ever try and crash anything into the sun unless you’re trying to study the sun.

Fraser Cain: Yeah. Uh, yeah, I think, I think it’s really important to go over this because we get this question all the time, which is like, why don’t they just crash spacecraft into the sun? Um, and you, and you gotta know, like if you ever say like, why don’t they just, then you know already there’s a really good reason why they don’t just, you just, you just don’t know the why yet.

And that is because the sun is actually the most difficult place to reach in the entire solar system that the earth is orbiting around the sun at 30 kilometers per second. And the only way to make your material actually crash into the sun is to cancel out that 30 kilometers per second of orbital momentum. Thirty kilometers per second is faster than any spacecraft has ever been launched from earth.

It would require propulsion systems that are unyet dreamed of. We literally cannot make a spacecraft crash into the sun. And I defy you, play Kerbal Space Program, make a spacecraft go into the sun.

You will realize how difficult and challenging a problem this is only through multiple flybys of Mercury and Venus slingshot maneuvers. Can you finally get something into the sun that things don’t drift off into the sun in space? We’re at the bottom of a mountain and to get up to the lunar orbit, you have to climb a mountain to get from earth orbit to the sun.

You have to climb a different mountain or backwards. I don’t know. Anyway, that moving spacecraft dramatically far away from where they currently are requires expenditures of propulsion that is way beyond what it took to even just launch the spacecraft in the first place.

So you got to deal with what you got.

Dr. Pamela Gay: Yeah. Momentum is the law. It is going to be conserved.

You have to transfer it somewhere.

Fraser Cain: Yeah. So you mentioned this idea that they put it somewhere. Can you describe these sort of parking orbits or sort of what’s the term they’ve got them for the ones at?

Graveyard orbits. Yeah. Graveyard orbits.

Dr. Pamela Gay: Yeah. So with geostationary satellites, there is a set altitude where when you’re at that distance from the earth and in a circular orbit, key is circular orbit, you go around and around the world every 24 hours, which means that if you’re planted directly over the equator, you stay over the exact same place in orbit. If you are north or south tilted, you would clearly be both north and south tilted depending on where you are in the orbit.

You’re going to go up and down a single line of longitude and geostationary orbits are super useful for communication, super useful for weather satellites. And while it is a huge orbit because it’s so far away from the earth, there’s still squabbling over space. And so when something is no longer in use, they boost it to a higher orbit.

The idea being it’s in a higher orbit, it’s now, it’s going to get out of sync with staying over the same place. It’s going to actually be orbiting in more than 24 hours at that point, but atmospheric drag is not going to pull it back down to the earth because higher, safer, less stuff. And so they just stick stuff in parking orbits with the idea that maybe someday someone will go out with their junk collector, the walleys of the future in orbit, and start scooping these missions up to do whatever we decide to do with them in the future.

That works for things in geostationary orbit. Gaia was out in a Lagrange point and that is another place that has the potential to get super crowded because we really like to put things there. Now luckily the Lagrange points are only semi-stable.

It doesn’t take very much energy to get yourself out of this balancing point where the gravity of the sun, the gravity of the earth keeps you balanced so that the earth and that Lagrange point go around the sun at the same period. It’s different rates, you’re at different distances from the sun. So if you’re on the inner Lagrange point, you’re going to be going slower to keep pace with the earth.

If you’re further out, you’re going to be going faster. But it’s really easy to remove yourself from those semi-stable points. And as Gaia did, just put yourself into your own solitary orbit around the sun that allows the earth and your dead self to meet every few months, I guess.

Fraser Cain: But it’s more than that, it’s that you have to expend energy to remain at the Lagrange It’s true, yeah. So you just stop, and this works well, if you no longer have propulsion, then you’re no longer able to remain at the Lagrange point, you are going to naturally drift. And then if you do have a little bit of propulsion left, you can sort of decide where you’re going to drift.

Dr. Pamela Gay: But it’s self-cleaning. They really want you to remove yourself though. So the issue with allowing things to yeet themselves, I just love that word by the way, is you don’t know what you’re going to hit on the way out if you’re not steering.

And this is the difference between you and I both sledded as kids, and some sleds you can steer because they have little blades on them, and others you just sort of lean and hope. And a spacecraft doesn’t even have the ability to lean and hope as it allows either the atmosphere or just instability to move it over time. So the idea is you have a controlled exit from that orbit you should no longer stay in within five years of end of mission.

And while you’re still under control, we don’t want any out of control spacecraft if we can help it. They expect this to only be a 90% success rate. It’s spacecraft.

Space is hard. But the goal is 90% within five years for US spacecraft. The rest of the world is more like, we’ll give it 25.

That’s where we are.

Fraser Cain: So we’ve talked about how you sort of deal with spacecraft here around Earth. But we saw a very interesting decision made for Galileo and Cassini. So how did that operate?

Dr. Pamela Gay: So with Cassini is referred to as the grand finale. This was back in 2017. NASA made this a massive press event.

They actually asked me to delay launch of a bunch of my programs because they didn’t want my little tiny programs to potentially distract from Cassini’s attention. Cassini was a flagship mission that gathered gigabytes and gigabytes of data at a time when gigabytes were new and phenomenally large before we entered the terabyte and petabyte world of today. And the thing about this grand finale was this was a mission that had been extended such that they were able to capture the entirety of seasons of Saturn as it went around the sun.

And we didn’t know that would be something we could do. They were able to evolve the orbit to get closer and closer to the surface and study the clouds in detail. But at the Saturn system, you have Titan, which is a methane-ethane world that we know because of Cassini has lakes and deltas.

The Huygens probe was able to catch amazing imagery of this. And this is all the stuff of life. These are carbon molecules.

And with so many organics at Titan and the recognition that the chemistry of its atmosphere is out of equilibrium in ways that require either active geological processes, active biological processes, or both, both is allowed, Titan is a world we don’t want to mess with. We want to allow it to be its special little amazing self, even though we already dropped Huygens on it. So we didn’t want to crash there.

We know that Enceladus is another one of these ocean worlds with its tiger stripes. We didn’t want to mess with things there. And so that meant we had to dispose of our spacecraft somewhere where we weren’t worried about Earth life being compatible.

And the atmosphere of Saturn and plunging through it to the high density, extreme temperatures of going through that atmosphere seemed like a really good way to dispose of a spacecraft while not risking contamination. So that is exactly what they did back in 2017.

Fraser Cain: Yeah. And I think, you know, that again, seems kind of weird to people, you know, like, why are you keeping it around? And it’s just that you can’t predict the future chaotic movements of the spacecraft as they continue to orbit around the planets and their moons.

That crashing into one of those moons is kind of inevitable. If you run the math into the future, and so, you know, it may take thousands of years, tens of thousands of years, but eventually it’s probably going to crash into one of the moons or crash into Jupiter or get into weird orbits through body interactions. So as we kind of get close to closing out this episode, I think it’s important to say that these ideas about end of life, you sort of mentioned it briefly that, you know, people are looking at putting drag shoots, putting various other methods of slowing spacecraft down and that this is actually a very under-invested, like people aren’t taking this seriously yet.

And that there are committees coming together for the European Space Agency and international groups that are trying to put some kind of regulation that all spacecraft must have an end of life plan. And this is not the case today. So right now you can launch a spacecraft and people are going to say, look, what are you going to do when this thing reached the end of its operations?

You’re like, I don’t know. Who cares? Right.

And that’s perfectly no longer acceptable. Well, it is. I mean, like nobody is going to take it a task yet, but we’re probably just a couple of years away from that being the case that there are zero debris, zero remnant policies that are being put together now by especially the European Space Agency.

Dr. Pamela Gay: The Kessler syndrome is something we truly wish to avoid. The WALL-E future is not the one I want. And unless it’s only the cute robots, I’m happy to take the cute robots and leave all of the death and destruction behind.

Fraser Cain: Who can gently push away satellites as they fly out into space, as opposed to the reality where they’re moving at 28,000 kilometers per hour and are like bullets tearing things apart.

Dr. Pamela Gay: So, yeah, we want to avoid the Kessler syndrome. We want to avoid landing things on people’s houses. There is amazing statistics that if the current growth of satellites goes up, we’re going to start to see human beings getting hit on the decade scale of time.

And just like clean up after yourselves, people. Leave nothing but footprints, take nothing but pictures.

Fraser Cain: Space footprints. Yeah.

Dr. Pamela Gay: Yeah.

Fraser Cain: Yeah. I mean, it’s like, again, it’s another tragedy of the comets that we are knowingly stumbling ourselves into, that we have this resource space. It is incredibly useful for us to be able to do our operations down here on Earth.

You can be able to communicate, be able to navigate, learn about the weather, predict, see our impact on the environment. It goes on and on. Farmers to track their fields, there’s so many benefits from us having this resource of space.

And yet, like we always do, we are filling it and not thinking too deeply about how to share it as a space. And we’re already starting to experience some consequences, but they have not gotten bad yet. We are in the pre-consequence phase of this process.

And now is the time to think about how to deal with it.

Dr. Pamela Gay: And it’s going to be an amazing future. And I look forward to doing an update on this, where we talk more about the new technologies to refuel, to grab and move, to de-orbit forcefully.

Fraser Cain: Oh, that sounds great. Yeah. Yeah.

Let’s, let’s, I mean, because it’s not just like you shut off your spacecraft and call it a day, that the kinds of things that people are yelling into their devices right now, why don’t they refuel them? Why don’t they refurbish them? This is all an industry that is starting to take off.

And in fact, various spacecraft have done this. So I think you’re exactly right. Let’s, let’s come back around in the future and talk about what are the cool ideas to deal with space junk, refurbish satellites, make them operational longer, try to live that dream of a, of a reusable, repairable future.

Dr. Pamela Gay: And we’ll be five years from now talking about how ISS is getting de-orbited. That is something like, I’m going to travel to see Apophis fly by. I’m going to travel to see YR4 potentially hit the moon.

And the ISS launching is going to be absolutely amazing.

Fraser Cain: Like seeing the ISS come down.

Dr. Pamela Gay: Yeah.

Fraser Cain: Yeah. Yeah. But I mean, it’ll be happening in the middle of the Pacific ocean, hopefully.

Hopefully. But yeah. All right.

We’ll see. Thanks, Pamela.

Dr. Pamela Gay: Thank you, Fraser. And thank you everyone out there. This show is supported by you through Patreon.

If you don’t have money to throw, we’re fine with that. Just go follow for free so that you can get regular updates on everything we’re doing. And I will be reading names separately, Rich, that file’s coming to you later today.

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Fraser Cain: Thanks everyone, and we will see you next week. Bye-bye.

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