THERE is an awful lot of junk in space. The latest data from the European Space Agency suggest some 7,500 tonnes of it now orbits Earth. It ranges from defunct satellites and rocket parts to nuts, bolts, shards of metal and even flecks of paint. But something as small as a paint fleck can still do serious damage if it hits a working satellite at a speed of several thousand kilometres an hour. There have already been more than 290 collisions, break-ups and explosions in space. Given the likelihood that thousands of small satellites, some only a few centimetres across, will be launched over the next decade, many worry that large volumes of space near Earth will soon be rendered risky places for satellites (especially big, expensive ones) to be.
What is needed, then, is a clean-up. Various ideas about how to do this have been proposed, and some are about to be put to the test. In February a resupply mission to the International Space Station will also carry a satellite, about the size of a domestic washing machine, called RemoveDEBRIS. Once this has been unpacked and prepared by the station’s crew, they will use a robotic manipulator to send it on its way into orbit around Earth.
RemoveDEBRIS has been designed and built by Surrey Satellite Technology, a British manufacturer of small satellites spun out of the University of Surrey in 1985, which is now majority-owned by Airbus. Mission Control for the RemoveDEBRIS project is the Surrey Space Centre at the university. The plan is for RemoveDEBRIS to carry out four experiments. The first two will involve launching from it a pair of CubeSats (mini-satellites 10cm across). These will play the role of space junk.
Once launched, the first CubeSat will inflate a balloonlike structure a metre across, to which it will remain attached, in order to create a bigger target. The mother ship will then approach to a distance of seven metres and fire a net at the balloon. This net is designed to unfurl and warp itself around the target. Once the target is entangled, a cable connecting the net to the mother ship will be tightened, closing the neck of the net. It will then be hauled in, like catching fish.
The second CubeSat will test the sensors of RemoveDEBRIS. This trial will use cameras and a lidar (an optical version of radar) aboard the mother ship to build up a detailed three-dimensional image of the object. If that works it will permit future clean-up vehicles to recognise what they are dealing with, and react appropriately.
In the third experiment, RemoveDEBRIS will extend a 1.5-metre-long arm that holds a 10cm-square target. It will then fire a harpoon at the target. The idea is that harpoons could be used to pierce some items of space debris and, like the net in the first experiment, then haul them in. The final experiment is intended to ensure that RemoveDEBRIS and its captured items do not themselves become space junk. The mother ship will deploy a ten square-metre plastic membrane, supported by four carbon-fibre booms, to act as a “dragsail” that will employ the limited atmosphere at this altitude to pull the craft downward to the fiery death of re-entry.
If space-debris capture systems like this succeed, then future missions could start to go after some of the most worrying bits of junk. Such ventures could be commercial, according to Guglielmo Aglietti, director of the Surrey Space Centre, if governments (probably acting collectively) were willing to pay to keep space clean so as not to damage their own activities and those of their citizens. There are already guidelines to try to limit the accumulation of space junk. Defunct satellites should be disposed of within 25 years, either by being tipped into re-entry or parked in an out-of-the way “graveyard” orbit. But the rules are not always followed and a lot of older debris remains in orbit. A bounty on removing the most threatening hulks might even see the launch of a new space business.
This article appeared in the Science and technology section of the print edition under the headline “Junk hunting”