鈥淲ITHIN 50 years, enough satellites and debris could be orbiting the Earth to lead to a catastrophic train of collisions, according to a study for the West German government. The result of the collisions would be a belt of small debris which would make flight in space impossible for several centuries.鈥�
That was the stark warning contained in our issue of 21 October 1989. Awareness of the problem stretched back to 1978, when NASA astrophysicist Donald Kessler raised the alarm about a possible 鈥渁blation cascade鈥�, in which objects abandoned in low Earth orbit would repeatedly collide over time, creating an orbital cloud of deadly, fast-moving shrapnel that no future spacecraft could hope to safely get through 鈥� and would only be dissipated by gravity over centuries.
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That was a very real possibility according to the German study, Helen Gavaghan reported from a meeting of the International Astronautical Federation in Spain. The researchers responsible concluded 鈥渢hat the critical mass for a chain reaction is between two and three times the mass of junk that they assume to be in space now鈥�. (At that time, some 7000 objects, such as the upper stages of rockets or old satellites, were known to orbit Earth.) They predicted a catastrophic collision and chain reaction 鈥渢aking place anything between 20 and 50 years from now鈥�.
That hasn鈥檛 come to pass as yet, but space debris remains a huge problem. The smaller the debris, the more numerous and deadly the cloud becomes. As of January 2019, more than 128 million bits of debris smaller than 1 centimetre are estimated to be in orbit around Earth. In 1983, a paint fleck 0.2 millimetres across chipped the windscreen of the space shuttle Challenger. In 2006, another piece of debris took a chip out of a heavily reinforced window on the International Space Station. Given they were travelling faster than any bullet, if either fragment had hit an astronaut during a space walk, it would have gone straight through them.
Proposed clean-up methods involve giant magnets, harpoons, nets and an electrically charged 鈥渟pace whip鈥�. They will have to move fast: the accidental collision of two satellites in 2009, plus intentional destruction of orbiting satellites by China in 2007 and India this year have sharply increased the amount of space junk out there. Simon Ings
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