A lucky escape

2019-03-08 08:18:01

By Charles Seife in Washington DC A LARGE piece of space junk hurtled towards the International Space Station last week, threatening to obliterate it. But when ground control ordered the station to move out of the way, it refused to budge. Although the debris eventually passed by harmlessly, NASA and its international partners are embarrassed by the failure of their emergency procedures. On 11 June, the US Air Force’s Space Command, which tracks orbital debris, told NASA that a spent Russian rocket stage would come close to the space station. By late evening, Space Command believed that the debris would pass within one kilometre—with just under a 1 per cent chance of a collision with the station. “We decided to take a conservative approach and attempt a manoeuvre,” says NASA spokesman James Hartsfield. By the following afternoon, flight controllers had figured out how the station’s thrusters should fire, and they radioed a command as it passed over communications stations in Russia. But this meant that the Russian module, Zarya, would have to fire one of its thrusters longer than its onboard computers allowed. So the computers refused to obey the command and instead shut down the station’s attitude control system, setting it adrift. By the time flight engineers regained control, there was no longer enough time to complete the safety manoeuvre. Luckily, the debris missed the station by around seven kilometres. If there had been a crew on board the station, they could have initiated the manoeuvre themselves. But NASA officials are not taking much comfort from this. “There were procedural errors, and we learned a lot from the experience,” says Hartsfield. “We’re going to ensure that this situation never,