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Engineers aim to sweep up junk in space: Jason Forshaw, aerospace engineer at the University of Surrey, speaks to Joseph Flaig about the RemoveDebris mission to capture orbital rubbish.

You might know that there's about 7,000 tonnes of junk up there in space. It presents a hazard for launching things in future, and everyday things that humans do rely ever more on satellites. Observation, weather monitoring, communications, your TV, phones, GPS: most things you can imagine go through satellites. So a lot of orbits become full of satellite space junk and it's a threat.

What we are aiming to do is launch the RemoveDebris mission either later this year or in early 2018. We aim to test a net and a harpoon system in space to capture some of this junk. The real aim in the future is, once you've captured this junk, you can pull it down to Earth and it will burn up in the atmosphere.

The object of this mission is to start maturing and developing the technologies, so in future we can use them for this important application.

What we are launching is a 100kg satellite, like a lm cube, and it will contain the net and harpoon on one of its faces. 'Cube-sats,' very small satellites about the size of a shoebox, will get ejected from the main satellite and we will use these as artificial targets. We are launching with SpaceX to the International Space Station. It goes up as cargo and gets ejected from the space station when it starts its mission. All the experiments are automated sequences, so once we want to run the experiment we say 'Go' and it will begin.

The harpoon is made by Airbus in Stevenage, Hertfordshire, and the net is made by Airbus in Bremen, Germany. It is just as you imagine a harpoon, based on original whaling techniques. We looked at Moby-Dick and things like that to see how harpoons were designed and what kind of projectile heads you need to hit things.

The plate it will hit is representative of real satellites, which is normally some kind of a metal honeycomb lattice. As the harpoon goes through, it releases barbs which stop it pulling backwards.

We have got the net as well--when it gets fired at the cube-sat it engulfs the target. There are weights at the edge of the net and little motors which pull the net inwards, so you have got a sort of drawstring bag that encapsulates the target.

For the harpoon we have a gas generator, a type of solid fuel which combusts quickly and produces a propulsive force to fire the harpoon. We have had to design these systems based on going to the International Space Station, which has restrictions on things like compressed gas, so the firing mechanism isn't necessarily what we would use in future.

The net is fired by a series of springs. They are heavily compressed and, once you release a lockdown mechanism, they open up and the springs fire out the net. That's it really.

It is mostly built. We are in the final testing stages, and it will get shipped to the launch site in the next few months. Nobody has ever tested a net or a harpoon in space before for these purposes, so we'll be the first.

This is a 15.2 million [euro] European Union-funded project. In space terms that is quite low budget because of the huge costs of launching things up there. Still, we aim to get the best possible outcome.

We have tested the net and the harpoon to death, but you can't get the real environment on the ground.

Caption: Keep space tidy: harpoon and net set off to catch junk

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Author:Flaig, Joseph
Publication:Professional Engineering Magazine
Date:Jun 1, 2017
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