Spacewalking astronauts have replaced a broken computer outside the International Space Station.
The two Americans on board, Rick Mastracchio and Steven Swanson, hustled through the repair job, swapping out the computers well within an hour.
The removed computer, a critical backup, failed nearly two weeks ago. The prime computer has been working, but Nasa wanted to instal a fresh spare.
Mission Control waited until after the arrival of a capsule full of fresh supplies on Sunday.
Replacing the computer – a compact 50lb box – involved just three bolts, hardly anything for a spacewalking chore.
Engineers do not know why the original failed. Mission Control asked the spacewalkers to keep an eye out for any damage that might explain the breakdown.
Flight controllers were trying to load software into the spare computer on April 11, but it failed to activate. That set off a frenzy of ground meetings and tests to fix the problem.
Nasa feared that if the primary computer went down as well, the entire space station would be in jeopardy. These two computers – the primary and backup – control the pointing of the solar wings and radiators, as well as the movement of the robot-arm rail cart.
It was the first failure of one of dozens of so-called MDMs, or multiplexer-demultiplexers, in and outside the space station.
All routine spacewalks by US station crew had been on hold since last summer’s near-drowning by a spacewalking astronaut. His helmet filled with water from the cooling system of the suit, and Nasa is continuing to investigate the problem.