Space is littered with debris: Old satellite parts, rocket pieces — some even the size of a double-decker bus.

On April 4, 2018, a SpaceX Dragon spacecraft arrived at International Space Station with some tools to clean up the mess.

The spacecraft's payload was a satellite platform filled with ideas: a net, a harpoon, a laser-ranging instrument, a sail, and two miniature satellites known as CubeSats.

The RemoveDEBRIS mission, which has been designed and manufactured by a consortium of leading space companies led by the UK's University of Surrey and funded by the European Commission, is one of the world’s first concrete steps to clean up the estimated 40,000 pieces of space junk currently orbiting Earth. The RemoveDebris satellite was then led into orbit, containing four ideas for taking out the trash.

Just this month, the first of two capture experiments began: A net was discharged at a deployed target CubeSat.

Next up: The second capture attempt will launch a harpoon at a deployable, in-orbit target plate.

The third experiment relies upon vision-based navigation. Using cameras and a lidar technology, a second CubeSat will navigate to an object.

Finally, the RemoveDEBRIS spacecraft is set to deploy a large drag sail to reduce speed and de-orbit, where the satellite will then ultimately burn up as it enters Earth’s atmosphere.

Richard Duke, a research officer at the University of Surrey and a member of the RemoveDEBRIS team, keeps an eye on the experiments. Duke spoke with Tech Briefs about the problem of space junk – and which ideas might be the most effective way to pick it all up.

Tech Briefs: How much space junk is out there?

Richard Duke: There's about 7,000 tons of that at the moment. There are bits of rockets and old satellites, and things we've been using in space for the last 50 years. But often we just leave them up there. And the big problem is all this space debris is moving around at about 17,000 miles an hour. So, even if a small, tiny bit of debris hits a spacecraft it's just catastrophic.

Tech Briefs: Is space debris an inevitable aspect of space missions?

Duke: Yes, there's going to be space debris up there. Whenever you have a satellite and it comes to the end of its life, it becomes no longer useful; some we won't be able to bring back. There’s always going to be times when a spacecraft malfunctions and we have to go up there and clean it up.

Tech Briefs: Why is it so important that we deal with this problem of space debris?

Duke: The biggest problem with space debris is that it could cause large amounts of damage to orbiting spacecraft; satellites that we use for our day-to-day life on Earth; and human spaceflight as well. Astronauts on board the space station are having to face this risk from this space debris hitting them every single day.

Tech Briefs: Has space debris been the kind of problem that has just been growing and ignored, or has this come to attention recently?

Duke: Over the past 50 years we've put more and more spacecraft up in space. So, the chances of the collisions from this space debris are actually going up an awful lot. If a bit of space debris hits a working satellite or another bit of space debris, the debris can break up into even more bits. Then, these extra bits can go and hit other spacecraft. We’re slightly worried that there's going to be this tipping point that could set off a chain reaction that would be very difficult to clear up. So, we really need to try and deal with the problem now before it gets to that point.

Tech Briefs: So, how did RemoveDEBRIS come about?

Duke: RemoveDEBRIS is a European Union funded project. The EU and European Space Agency put out a call for proposals, and the University of Surrey put in a joint proposal with quite a few other members of the consortium. With Airbus and several different countries, with Surrey Satellite Technology in the UK, we all got together to work out a mission to demonstrate different ways we could remove debris from space.

Tech Briefs: What was sent exactly to the International Space Station in April of this year?

Duke: RemoveDEBRIS consists of a few different elements. The first element is what we call the "mother ship," where all the experiments are housed. That's built by Surrey Satellite Technology just down the road. We have four different experiments on board with different hardware.

The first experiment is a net experiment. We actually put one of our CubeSats inside the mother spacecraft and we eject this CubeSat, and that’s to simulate some space debris. And then on the mother ship, we also have a net from Airbus, and we can fire that net at our CubeSat and actually capture it.

We’ve tested the net experiment. That worked really, really well. We actually have some really incredible footage of our target CubeSats simulating space debris, and then the net going and capturing it:

Tech Briefs: What other experiments are onboard?

Duke: The second experiment is what we call the VBN, or visual-based navigation, experiment. With this, we're trying to develop the sensors needed to detect space debris. To make sure the sensors work, we need a fixed target. So, we use one of our CubeSats built at the University of Surrey. We eject that from the mother ship, and this CubeSat can tell the mother ship where it is. Then, we can compare that to the data we're getting from the sensors, and we can make sure the two are in alignment, and that the sensors are good enough to use on future missions.

That will hopefully be happening in a few weeks. And then we'll move on to the other experiments in the next few months.

Tech Briefs: And then there’s also the harpoon...

Duke: Yes, we actually don't want a moving target for this experiment. We eject a boom from the mother ship. This has a target on it that's very representative of normal spacecraft, and we're going to fire a harpoon at it. When you're in space, you're in a vacuum. We expect the harpoon to work very differently than it would on the ground, with gravity and a lot of aerodynamics. So, we're going to fire this harpoon at the target and then see how that works.

Tech Briefs: What’s the last experiment?

Duke: Our last experiment is the drag sail. We deploy this sail, and it captures a really thin, tenuous atmosphere. That slows the spacecraft down. When you slow the spacecraft down, it then comes out of orbit and burns up. And we're doing that because we don't want our RemoveDEBRIS spacecraft to become space junk itself. This sail experiment is actually going to demonstrate that we can use this technology to bring satellites down in a safe way.

Tech Briefs: How long will it take to conduct the experiments?

Duke: Each of the experiments occur every month or so, which gives us just enough time to get all the data down linked to the ground, so we can actually get our research scientists to analyze it and work out how everything happened.

Tech Briefs: What kind of teamwork is involved in the RemoveDEBRIS mission?

Duke: In terms of the operations, that's actually done here in Guildford, in Surrey, at Surrey Satellite Technology. And so, they're the lead in developing the spacecraft and then coordinating with the engineers.

For the launch itself we actually had to work with a lot more teams. We not only had to involve the teams at SpaceX but also NASA. And, through NASA, we're working with the Japanese Space Agency. To actually deploy the satellite, we’re also using the Canadarm, the space robotic arm on the ISS, which is from Canada. In terms of the whole mission, we have engineers from several different countries. It’s a global project by the time everything comes together.

Tech Briefs: What would you say is the biggest challenge for you in addressing this kind of larger-scale problem of space debris?

Duke: The biggest problem for clearing space debris is actually figuring out who's paying for it, because obviously a lot of this debris has been up there for quite a long time now. And we know who owns it, but it's going to be up to the respective owners to pay for it to be taken down. And there's also a lot of legality in that as well, because obviously we can't just go and remove anything from orbit. It has to be a cooperative process.

Another challenge is figuring out what objects to get and where the biggest benefit is. We’re trying to go for the really big pieces of space debris. The little pieces, the CubeSats and the smaller spacecraft, are generally in lower orbit, so they'll come down naturally anyway. But it's actually the really big pieces that we're worried about. If a big piece of space debris gets hit by a smaller piece, then that could just turn into thousands of bits of debris which just makes the problem really bad. The bigger the space debris, the bigger the spacecraft going up to remove it will have to be. In the future, we're going to have to go up and get things that are double-decker-bus-sized.

Tech Briefs: Is one idea better than the others far as dealing with objects with greater mass?

Duke: Yes, exactly. For going up and getting bigger objects, we're going to need to scale up our technology. Certainly, from the net point of view, we're working on a bigger net, and actually that looks quite promising at the moment, for going and getting very large objects.

Airbus is already working on the follow-up harpoon, which is a great deal bigger than the demonstrator that we have on our spacecraft. So, we're really trying to demonstrate a technology, and then we'll be scaling it up for proper missions.

Tech Briefs: Has there been an effort in newer missions to limit the debris left behind?

Duke: Yeah, there's definitely an effort at the moment to try and limit space debris. A lot of countries now are adopting a 25-year limit: When you launch a spacecraft, it has to return to Earth or be indisposed within 25 years. Our deployable sails actually help that because it means you can go into a high orbit and then bring your spacecraft back with a sail.

But the other alternative is actually going into slightly lower orbits where it'll return back to Earth more quickly. That, however, still doesn't solve the problem of what happens when you send a spacecraft up and then it breaks. When a spacecraft breaks, you can't then deploy a sail or deploy propulsion to actually bring it back. So, that's why we need to look at how to bring spacecraft back automatically, but still have the capability to go and bring spacecraft back when they go wrong.

Tech Briefs: Is it rare to have these kinds of launches from the ISS?

Duke: Actually, this is quite rare. We were the largest spacecraft ever to be deployed off the station. The ISS has launched very small spacecraft before, but this was actually a reasonable size.

Also, for the first time here, we had to human-rate our spacecraft so it was safe enough to go on the space station. Normally, we build our satellite, and we send it up there; we don't have to worry about sharp edges or people working with it.

Tech Briefs: Are you encouraged with your technologies’ ability to solve the space debris problem?

Duke: I'm really encouraged, especially from our first test. These tests are really, really difficult, because we only get one chance at demonstrating this. And after five or ten years of working on the project, it's actually quite a risky thing just to test your theory. The fact that the first one worked really well gives a real bit of comfort that we can actually solve the problem with some of the technologies that we're demonstrating.

See more videos of the RemoveDEBRIS mission.

What do you think? Which of the four experiments are most interesting to you? Share your comments and questions below.