If space is going to remain useful, it needs to be tidied up every once in a while. Debris is a persistent hazard in orbit, and every new satellite might end up as further debris. People are still figuring out how to clear that debris, and this week saw an exciting new approach. It’s a harpoon!

The harpoon is just one of four experiments in the RemoveDEBRIS mission. Funded in part by the European Commission and headed by the Surrey Space Centre, the platform was deployed to ISS in 2018. Once readied for its mission, it then set out to test ways to clear debris.

The first of these methods involved launching a smaller cubesat from the RemoveDEBRIS satellite, and then catching that smaller cubesat with a special net. The cubesat is then deorbited, letting the heat of atmospheric reentry obliterate the cubesat and net. Tested in September 2018, the net appears to have been a success.

A month later, in October 2018, the RemoveDEBRIS satellite released another cubesat. This time, the cubesat was already on a predetermined path towards atmospheric reentry. That test focused on tracking the descending cubesat with a camera and LiDAR. Getting accurate images of space debris to train removal tools on is hard. When Stanford and the European Space Agency announced a competition to design an AI that can hunt space debris, they provided contestants with a library of artificially generated images of space junk to work from.

For the Harpoon demonstration, which took place on February 8, 2019, the RemoveDEBRIS satellite deployed its own target on a boom about 5 feet away from the spacecraft And then, whoosh! Harpooned the target, with the harpoon traveling at a speed of over 44 mph. In March, the satellite will conduct its 4th and final experiment, deploying a sail and dragging itself out of orbit and back down to earth.

Clearing up orbit is, first and foremost, and end unto itself. Should the reentry sail prove effective, future satellites could be designed with one on-board, a backup parachute to clear the space in, er, space.

The rest of the technologies, though, blur the line between cleaning up in orbit and antagonizing others in orbit. AI, LiDAR, and cameras that can track space debris would also be useful for in-orbit surveillance of other satellites. Nets and harpoons that can capture space junk and send it heading towards reentry are valuable as cleaning tools, and could also be adapted or misused to disable active satellites. The overall impact of these technologies will almost certainly remain peaceful and beneficial, but it’s worth keeping in mind the way such tech could become dual-use in the right moment.

With a changed calculus on the ground, an existing robotic space sanitation force could be adapted into crude orbital combatants.

In the meantime, enjoy this video of a satellite firing a harpoon. Watch below: