A lucky escape

26 June 1999

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

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, ever happens