Space around the Earth is full of junk and one of our listeners asks “what are we doing about that?”  To answer’s this question we bring in an expert, Joshua Lurie and dive deep into ways to clean up after ourselves in space.

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Chris:

Hello and welcome to the final episode in the first series of The Astroholic Explains!

Alfredo:

Oh no!

Chris:

Yeah! So this is a very special episode. Not only for that reason but for another reason as well. So Alfredo, what is different?

Alfredo:

We’re no longer two!

Chris:

There’s someone else with us. We have a special guest today.

Alfredo:

I wanted to give the impression they have that you might be expecting or I might be expecting.

Chris:

No.

Alfredo:

Okay.

Chris:

So, special guest, introduce yourself.

Josh:

My name is Joshua Lurie. I’m a principal engineer working on spacecraft mechanisms at Airbus Defense & Space. And I think I can put a bit of info and shed some light on the topic for today.

Alfredo:

Yes. So I’m getting a lot of spoilers about what today is going to be about. And I got the spoilers the moment I saw Josh walk in the house and just like: Ah-uh, now I know! So I’m going to guess the question today.

Chris:

You can guess the question. The question comes from Elodie.

Alfredo:

Oh, hello. Hello, Elo! She’s an old friend!

Chris:

Guess away!

Alfredo:

The question is going to be about space junk!

Chris:

It is! The question is about space junk. So Elodie asks “what are the latest solutions to collect space rubbish?” Hence why we’ve got Josh on board to help you answer that.

Alfredo:

Well, he’s the expert so I’m not sure why I’m here, but okay.

Chris:

Tell us a little bit about what space junk actually is,

Alfredo:

So there is a lot of stuff around the Earth, and now I feel very self-conscious to have an expert next to me that would nod or shake his head if I say something wrong..

Chris:

Or just jump in and correct him. That’d be good.

Josh:

Ooh, I’ll give you a shot.

Alfredo:

I’m not sure if I like that. So, but anyway, well, we’ll see. Um, so pretty much since the late fifties, we’ve been sending a lot, a lot of stuff into space. And while some stuff up falls back down and burns into the atmosphere, well mostly burns into the atmosphere. A lot of stuff is still there. And when it stopped working is simply remains space junk. And it is a problem because sometimes these abandoned satellites, but there’s also a camera, I think there used to be a spatula that was lost by an astronaut… I think the spatula came back down to earth. But there is a lot of stuff and the issue is everything up there. It’s moving at roughly eight kilometers per second, five-mile per second. So even something like a speck of paint, it’s a bullet.

Josh:

Yeah. In fact, there’s quite a famous photograph from the space shuttle which shows the impact of a speck of paint on one of the front windows and it’s quite energetic.

Chris:

What does it look like?

Josh:

It’s cracked. It’s cracked.

Chris:

Ooh.

Alfredo:

Yeah.

Chris:

Wow. Okay. So they are dangerous for a good load of reasons, especially for the astronauts in space, I’m guessing. Although is that film Gravity exaggerated in terms of the damage space junk could do, or bits?

Josh:

I think it’s a nice hypothetical about the near future. I think it’s, it’s displaying something called the Kessler syndrome where it’s an exponential increase. So something that generates more debris, debris flying around and hits something else and more and more and more. So it’s a very good example both to the safety of crewed missions. So for example, the ISS does have to make collision avoidance maneuvers several times a year.

Chris:

Wow.

Josh:

And also just the general utilization of space as a resource, with endangers other satellites in orbit.

Chris:

Oh my gosh. So it would affect launches as well, I’m guessing?

Josh:

I would say the amount of time that the launch vehicles or rockets actually spend traveling through those sorts environments are quite limited. So chances are they won’t hit anything, but it might affect the type of spacecraft or the orbits those spacecraft will be in. So maybe we’ll start putting up fewer Earth-observation satellites or whatnot, just because the neighborhoods where they’re meant to be going are polluted and risky.

Alfredo:

Yeah. So there are some orbits that are getting quite crowded and so we need to think of ways to either remove stuff or we need to just use different orbits. But there are some orbits that are extremely convenient to be.

Chris:

So let’s talk a little bit about some solutions for all of this space junk. What can be done about it? How can we get rid of it? Can we get rid of it? What do we do?

Josh:

People come from quite a few avenues. So the European space agency has an initiative called Clean Space and that’s really trying to tackle the whole gamut, in a way, the whole sort of life cycle of a mission. So there are now mandatory requirements for spacecraft to consider the end of life disposal. So to make sure they vacate the orbit they’re using. And so follow up orbit satellites, that means to try and go down, back with the atmosphere and burn up. There’s of course initiatives to try and help the satellites when they’re up there. So, you know, autonomous maneuvers to avoid tracked junk. Um, of course, every time you don’t hit something, it helps you not generate more. The final section is as mentioned for active removal. So actively going up, removing large risky pieces of debris and try and remove some of that risk.

Alfredo:

Josh, what are you working on to help with the topic of a space rubbish space junk?

Josh:

Right. So at Airbus here in the UK, we’d been working over the last eight years or so on the development of a space harpoon system. We call this a ADI, which is Active Debris removal.

Alfredo:

That is very cool. Is everyone dressed up? Like Is your boss dressed up as captain Ahab and being very Moby-Dick about this?

Josh:

No, but the first project manager who was there on the project for a while did have the nickname captain Ahab.

Alfredo:

Amazing! Okay. This is what I like to hear.

Josh:

That’s what it’s all about really.

Chris:

Professional cosplay!

Josh:

Of course!

Chris:

In terms of the size of some of this debris, how big are the pieces we’re talking about? What’s the sort of range of sizes?

Alfredo:

If I’m correct the biggest piece is an old European weather satellite,

Josh:

it is indeed.

Alfredo:

That is as big as a double-decker bus.

Josh:

That’s right.

Alfredo:

Which, you know, everything that is big is always compared to a double-decker bus. But this satellite actually is.

Josh:

So, this is the Envisat satellite. It’s a ESA mission from a while back now and it in fact stopped working several years back. I think there was even a suspicion that maybe, it had actually suffered an impact from debris; but I think it wasn’t proven. So Envisat is currently flying around, I believe in a polar sun-synchronous orbit so it can make good observations of the Earth at the same locations, same time of day. It’s very large as Alf said. Because it’s very large and has quite a massive cross-section area, it’s a very high risk to other spacecraft in a similar orbit, but also it has this risk of impacting other debris. So yeah, that’s probably the largest thing out there. Of course, then scales all the way down to tools from astronauts, so the size of a fist, and then down to paint specs so kind of one millimeter of cross-sectional area. I think a lot of this debris is being tracked. Of course they can’t track below a certain size. I believe 10 centimeters in cross-section area is the threshold and there’s several years ago I think it was reported there were over 20,000 pieces of debris larger than 10 square centimeters. So that’s quite alarming, isn’t it?

Alfredo:

Yeah, it is very, very, very alarming.

Chris:

I can imagine if there’s any like data sets of this and visualizing it. It would basically look like Earth is surrounded by a swarm.

Josh:

Yeah. I think those, you know when you see those sorts of computer-generated images and they show those sorts of clouds surrounding the Earth.. It’s not too far fetched in terms of the distribution, but the sizing is exaggerated.

Chris:

Yeah.

Alfredo:

It’s not like in Wall-E when you just see, like loads of satellites just sitting there. But there are so many that there was an artist’ project a few years back at the science museum, which had this instrument that would play certain notes depending on the type and size of space junk passing over London that specific time. And it was continuously playing. And yes, London is quite big, and above it the area it covers in space is quite big, but it’s just like… There’s a lot of stuff!

Chris:

In terms of things like the satellites and the larger pieces: is anything currently being done to actively remove them?

Josh:

Yup. Um, so that’s, that’s essentially the work that we’ve been doing in the last seven or so years. We are focusing on active debris removal and in particular, we are working on a harpoon system. So there are several different approaches you could take. We can think of things like going up and using a robotic arm to grab onto something and have a net that fires and captures something.

Chris:

I think I’ve seen footage of this.

Josh:

Yeah. So the nets and harpoon concepts have actually been tested recently, over the last year or so. I’ve mentioned Clean Space already, which is where our large harpoon project is funded. We’ve also been involved in a smaller project called Remove Debris, which is European Commission funded and has involvement with UK space. And this is essentially a technology demonstrator satellite. It went up to the space station and it got shot down from an airlock, which is quite cool. It had several experiments on it. It had, in fact, the net experiment. So they ejected a small CubeSat and then the net was fired and caught it. They have a harpoon, sorry, I’ll call the mini-harpoon, where there’s a deployable sort of target panel on a boom, and then it fired and shots and capture that.

Alfredo:

How big was the mini-harpoon?

Josh:

So the mini harpoon is about 10 to 15 centimeters in length and about a hundred grams in mass.

Alfredo:

Okay. And if you’re listening and you don’t know what a CubeSat is: CubeSat are very small satellites, usually loaf of bread size. Sometimes you can stick a few of them together. So that’s why the mini-harpoon should be that small too.

Josh:

So that’s about a kilogram. Two kilograms of satellite size. And the other experiments, there was an image-based autonomous visual navigation system to help we have satellites doing their own avoidance maneuvers. And the final experiments, and apologies if I’ve left off something; the final experiments I believe was a deployable drag sail. So testing technology for end of life where you increase your cross-section area, you can degrade your orbit a lot quicker because, of course, everything does eventually make its way back down. But the higher you are, the less atmosphere there is, the less drag, and it takes an exponentially longer amount of time higher up. So if you increase your drag, you essentially get down quicker.

Alfredo:

Okay, cool! So I have a question. How do you make sure that by shooting the harpoon into something, you’re not creating tiny little debris?

Josh:

It’s actually a really good question and it’s probably the comment that we’ve gotten most back during any sort of PR exposure on the harpoon projects. We are, of course, very conscious of debris, in a project that’s trying to remove debris. So the projects involving the harpoons tend to have quite stringent requirements placed on them from our customers. And these are essential to prevent generation of new debris. So in fact, for the harpoon system, there are four different subcategories of debris generation. There’s generation from the operation of the harpoon. Generation from the impact rupturing the target and from pulling on the target we want to deorbit. Part of the testing we’ve done over the last two years has involved trying to assess and measure and characterize how much debris gets generated, and then looking at, in terms of the design of harpoon, how to minimize that. So things like the shape of the barb tip: so square with a conical tip actually generates the least amount of debris and petals out the metal skins in a way that doesn’t rupture as much.

Alfredo:

Wow. That was pretty cool.

Chris:

In terms of size of these harpoons, you mentioned the mini harpoon being around 10 centimeters long, how big would the larger versions be?

Josh:

Right, so the larger version for the Clean Space project is quite large. Actually. It’s about 1.2 meters long compared to 15 or so centimeters and it weighs 2.2 kilograms. So it’s an order of magnitude scaled up. In terms of the type of targets that we’d go for, so of course, the small harpoon would think about small sats in a 1 kilogram – 10 kilogram type of range. The large harpoon has been sized with one of the key targets is in fact EnviSat.

Alfredo:

I was about to ask if it is that going to be your white whale?

Josh:

That is indeed the white whale. We’ve sized it based on a target selection in early tradeoffs looking at the, I believe it’s a scale called the European weight and measure, which looks at a bunch of family of debris up there. Looking primarily at old dead satellites like Earth observation family called Spot and spent upper stage of rockets, so Arianne 4 upper stages. And between those two families, so the Spot platform and the Arianne 4 rockets, it covers about 70% of the top hit list from ESA, from the European community. Luckily EnviSat does share a lot of the platform with the Spot family as well, so that enabled us to really try and get as many possible targets as we could. But fair to say that’s the 2.2 Kilos harpoon has been sized mechanically for EnviSat.

Chris:

How far away can these targets be for when they get shot at and pulled back? Is there a limit to the length of whatever the harpoon is attached to?

Josh:

Yeah, I think the limit is probably determined mostly by how long the tether is. So we’re dealing here with the harpoon and we’re dealing with what we call flexible links. So essentially you capture or you create a structural link to your target. You have a tether, like sort of a rope connecting yourself to another spacecraft which will pull the target back down out of orbit compared to say a robotic arm, which is a rigid link. The flexible links are a lot more appealing for a lot of targets which might be uncooperative. So spinning, tumbling, where it might pose quite a risk to the spacecraft that you send up to to get it. So for the large harpoon, the target distance is about 30 meters. But think the models that we’ve tested so far have tethered out to about 50 meters. And that’s quite a difficult trade-off: of course the further you are away your accuracy suffers, but the closer you are, the higher risk to whatever you send up to get there.

Chris:

And, okay. So forgive me for this mental image now because… Am I completely wrong in assuming that when you use these kinds of harpoons, it would ideally be, say for example, an astronaut on the ISS grabs this harpoon, it goes out, and he’s like, tethered to the ISS with this big harpoon gun that they then shoot, or is it mounted?

Josh:

[Laughter] It would be really cool.

Alfredo:

Sweetie, it’s not like they are space pirates, with a vessel and a harpoon!

Josh:

I think you are thinking of Futurama [singing] “We are whalers on the Moon”

Chris:

It’s basically what I’m picturing!

Alfredo:

No, it’s gonna be an independent spacecraft that is designed to shoot something then and drag it down.

Chris:

Okay. Okay.

Josh:

So two answers to the question. The first being that a lot of these systems rely on powerful deployment techniques. So pressurized gas systems or gas generator systems and the possibility of essentially projectiles firing in the vicinity of human habitation. So for crewed flights, it’s quite risky. There’s a lot of stringent measures and reviews and safety assessments that are required for example, that we have to go through with NASA for use of the ISS. And the second answer is that a lot of these targets are actually really quite far away from where we have crewed flight and that we really do have to go out to specific orbits, in specific locations to try and grab and get rid of them.

Alfredo:

I think Chris was angling for an answer about how can the astronauts injure themselves in space..

Chris:

That is one way.

Alfredo:

Although I liked the idea that eventually we’re going to have astronauts equipped… There’s going to be so much debris is that they need to constantly be on the machine gun.

Josh:

I imagined explosive decompression.

Chris:

Wow. So here is where I’m going to go for the last part of this episode. If you [Alfredo] were in charge of something in this field, what would your possibly-never-before-thought-of answer to space debris be, what would you do to get rid of it?

Alfredo:

You see realistically something that I never hear about, and I’m sure there is probably very, very good explanation for it, is magnets! Because I love magnets. So I’m gonna ask the question and give myself the answer and then Josh can correct me. So you have all this debris out there and you’re worried that your nets might not work well. You’re worried about other things. Your harpoons create maybe a little bit more debris. So we’re putting the spacecraft in danger… Magnets. You just grab all of them! So the answer that I gave myself while I was thinking about it is that most of the staff is not ferromagnetic because things that are tends to be a little bit heavier. So it’s probably made of lighter materials that you can not grab with magnets.

Josh:

Yeah. I mean to be honest, magnets were of course in our original trade-off thinking, you know, just out of the box. “What could you use?” I think the main reason, probably one of the main or main reasons, that is not feasible is exactly what you said in terms of the materials you use for the spacecraft. There’s not a lot of ferromagnetic materials, and steel happens to be quite heavy. We have lots of aluminium of various alloys and grades, lots of titanium, and lots of carbon fiber, so lots of not-very-magnet-friendly materials as well as other bits. As well as that the strength of the field you’d need to generate would be extraordinary, which I would imagine we’d have some EMC or sort of electromagnetic cleanliness issues as well with other spacecraft to use the region.

Alfredo:

Okay. Well, I was literally picturing as sort of a Scrooge McDuck style of spacecraft with a giant electromagnet.

Josh:

One of those big red and silver ones?

Alfredo:

Yeah, and it is just going around and just cleaning the orbits! Well, stupid physics always ruining the fun for everyone.

Chris:

I have one thing that pops to mind and almost certainly will not work, especially because it involves some sort of futuristic AI capability. So you have this autonomous ship that would be in the vicinity of any space debris and then the AI calculates its location and trajectory and then using some sort of robotic arm, knocks it in the direction of the Sun. And it just carries on going into the Sun. Basically use the Sun to burn up everything that we don’t want.

Alfredo:

I think now it’s time for Chris answers his own question on why is that is not going to work at all

Chris:

Because you can’t really get a ship that does that. Obviously not all debris is going to be on the side of the Sun. So sometimes the Earth would be in the way, obviously. Also, it would need a hell of a lot of energy in order to knock something away…

Josh:

That’s it!

Alfredo:

Very good! It is much easier to throw stuff down into the atmosphere…

Chris:

…Than it is to throw it out of orbit.

Josh:

No spacecraft currently has the technology or has the ability to go straight towards the Sun. It’s quite a lot of energy required to do that transfer.

Chris:

Oh, okay. Well I guess it’s no that idea then.

Alfredo:

I like the idea though. The issue with catching up with all this debris is the fact that every bit is moving very fast. You need to match that speed. But let’s assume that somehow we have this AI-powered spaceship that has unlimited fuel and can move around. Now, maybe a solution would be something that can slowly catch up with them, sort of open, like it’s a mouth!

Chris:

Oh, like PAC man!

Alfredo:

Yes. A Pacman spaceship! Is there already a plan like that?

Josh:

I think it’s not too far fetched! I think it’s just a question of trying to size that spacecraft for how much they could possibly get, you know. Do you use electric propulsion so you can keep it up for a while, and just slowly like a net in a river just slowly gather things. Not a terrible idea!

Alfredo:

Thank you. Copyright Alfredo Carpineti. You never know there might be some people listening..

Chris:

Patent officers?

Alfredo:

No, not patent officers, somebody that can fund a mission, and I just want to put my idea out there!

Josh:

It’s a good point on funding though, cause that’s kind of where we are right now. Space debris is obviously, uh, it’s been known about for a while, but maybe only taken seriously in the last decade or so. And funding is really the key in terms of who has the responsibility to deal with what is a shared resource. There’s no owned airspace by any sovereign nation, but everyone uses it. Space, in terms of orbit is also not like fixed air space. So there’s no ‘I have over there, you have over there’. So it’s why I think there’s a big push at the moment to try and instill responsibility into satellite manufacturers and customers to say: “You! You need to think about this. You need to put measures in place for the end of your mission to try and keep space clean”, essentially.

Alfredo:

So if you’re making satellites, please think about the end of your mission and if you have the money to make satellites, if you want to sponsor The Astroholic…

Chris:

Nice… [laughs]

Alfredo:

What? It’s the last episode! Let me try to squeeze in something! No, that was very, very interesting and I think it’s very important that this remains a conversation every time we talk about new missions, around Earth, and new big new projects.

Josh:

Yep.

Chris:

That’s great. No, I think I learned a lot and that was a lot of fun to talk about as well. Thank you, Josh. Thank you for being our special guest.

Josh:

It’s been a pleasure and thank you for inviting me to have a chat.

Chris:

You’re welcome. Yes, it was great to have three for one episode for a change.

Alfredo:

So, and thank you again. And a hope Elodie, I answered your question too. See your next season!

Chris:

We don’t know when we’ll be back, but we’ll be back in about six months.

Alfredo:

Yes, we will be back.

Chris:

So in the meantime, keep sending in your questions and hopefully we’ll have a massive stockpile by the time the next season starts and we will get back to you with some more special guests as well. So take care and we’ll see you soon.

Alfredo:

Bye bye!

Image Credit: ESA + Chris Carpineti