Next month, the Japanese space agency, JAXA, will pilot its "electrodynamic tether" for the first time. It is one of many possible solutions that have been proposed to deal with space debris space debris.
Hundreds of thousands of pieces of spacecraft, satellites and other equipment from human spaceflight zip around our planet, some travelling faster than the speed of sound. According to a report released by the US Congressional Research Service this month, running into even a small piece of junk can be disastrous. An object 10 centimetres across could "catastrophically damage a typical satellite", it says. One just 1 centimetre across could disable a spacecraft. The worst-case scenario is the Kessler syndrome, proposed by astrophysicist Donald Kessler in the 1970s. Too much trash, he warned, and the pieces would collide with each other, resulting in more and more debris.
To build its debris-catching net, JAXA brought in Nitto Seimo, a company that specialises in fishing equipment. Unlike a net you would use in the ocean, this one is a 700-metre-long mesh of aluminium and steel wires that hangs from an uncrewed spacecraft. The net is fitted with sensors that look for light reflecting from small pieces of debris and automatically aligns itself so that it can attract the material. The tether changes its orbit thanks to an electrical current flowing through the wires, which creates an electromagnetic field that attracts the debris and pushes the net away from Earth's geomagnetic field. Once the net has grabbed enough debris it is ordered to slow down and de-orbit, allowing the debris, spacecraft and net to burn up as they enter Earth's atmosphere.
JAXA thinks the net's main advantage is its simplicity – it's lightweight and doesn't require any propellant to move. If next month's test launch goes well, it plans to build a 10-kilometre-long version to capture satellites that have reached the end of their lives.
However, the test will also explore some possible drawbacks. One concern is that the net will work very slowly, taking several months or even a year to de-orbit. Then there is the risk that the net will run into operational satellites. The engineers also worry that the debris they are fighting could fight back. "There is a possibility of the tether being severed by impacts of small debris objects or micrometeoroids," says a JAXA spokesperson.