Humans have gotten rather good at launching things into orbit, but we don’t always bother to bring them back down when we’re done with them. This has led to a problem with accumulating space junk, which can be serious hazards for future space missions. Japan has launched the Kounotori 6 spacecraft on its way to the International Space Station, but this cargo vessel has a dual purpose. It has been equipped with an electromagnetic tether designed to drag space junk out of orbit.

ESA scientists estimate there are hundreds of thousands of individual pieces of highly dangerous space debris above Earth thanks to human activity. As of a few years ago, there were around 670,000 objects between 1 and 10 cm and 29,000 objects larger than 10cm. There are also millions of small objects under 1 cm across, and these can still have enough energy to cause damage to spacecraft and satellites if they collide at high enough relative velocities.

So, space is a bit of a junk heap. So why aren’t we more careful about bringing things back into the atmosphere when we’re done with them? Money. Once an object is in a stable orbit, you need to expend energy to slow it down (i.e. burning retrograde) until it hits the atmosphere. That means you’d need to equip most satellites and probes with engines and extra fuel, which isn’t usually considered a priority. Thus, Japan is experimenting with Kounotori 6 as a way to clean up after everyone.

Kounotori 6 has a 2,300-foot electrodynamic tether (EDT), which could one day be used to send space junk back into the atmosphere where it can burn up safely. The EDT has a 44 pound weight at the end to simulate a piece of space junk that needs to be dragged out of orbit. Electrons from the ambient plasma surrounding Earth are pulled in by the tether and emitted by the vehicle. This provides a small amount of thrust that can be used to de-orbit the object (along with the vehicle) without expensive engines and fuel tanks. The Japanese Space Agency calls this a “current drive.”

The test version attached to Kounotori 6 isn’t long enough to drag the spacecraft out of orbit. It’s going to be used to test the current drive for a week before the cargo mission to the ISS continues. The tether will be jettisoned before Kounotori 6 approaches the station. There are plans for future versions of the EDT that are 16,400 and 32,800 feet long, which should produce enough thrust to drag larger objects out of orbit.