The early morning alarm that forced U.S. astronauts to evacuate their segment of the International Space Station on Wednesday morning was a computer error, NASA reported.
At 4 a.m. Eastern time on Wednesday, an alarm indicating an ammonia leak sounded in the U.S. segment of ISS, which is carrying six astronauts – three Russians, an Italian and two Americans – 220 miles above Earth.
Ammonia is used as a coolant, pumped through pipes on the outside of the spacecraft. But it’s poisonous if inhaled, so astronauts need to be wary of leaks. The first indication of such a leak is a rise in pressure, which Wednesday morning’s alarm indicated.
Following emergency procedures, the U.S. astronauts put on oxygen masks, turned off nonessential equipment and moved to the Russian segment of the space station before sealing the door behind them. Meanwhile, flight control rushed to analyze data to determine whether toxic ammonia was flooding the U.S. astronauts’ living quarters.
It quickly became apparent that the alarm was likely a false one. NASA representatives reported their suspicions at a 7:55 a.m. news briefing but waited until later in the day to confirm their conclusions and give astronauts the green light to return.
According to an afternoon update on NASA’s blog, one of the station’s computer relay systems had an error that triggered the pressure-change alarm. After a reboot, the relay seemed to be working normally.
