Space station evacuation ends; crew returns to work after ammonia scare

Crew members aboard the International Space Station have returned to the American segment they were forced evacuate early Wednesday due to fear of a possible ammonia leak.

NASA astronauts Barry Wilmore, commander of the current mission, and Terry Virts, a flight engineer, wore black and pink protective masks as they opened the hatch and tested the air inside the cabin.

The tests turned up no indications of any ammonia, according to NASA.

Ground crews became concerned that the deadly gas may have escaped from the heat exchange system that helps cool the space station about 1 a.m. PST. Mike Suffredini, NASAs program manager for the ISS, said the water level in one of the coolant loops was off scale which could have been a sign of an ammonia leak.

That prompted the first of two evacuations from the U.S. segment of the space station, which has the ammonia system mounted on its exterior , to the Russian segment, which includes the service module.

The astronauts returned after getting an all-clear, but then the ground crew detected a change in cabin pressure.

If youre leaking ammonia into the water loop and it eventually finds its way into the cabin, then you would expect the cabin pressure to go up, Suffredini said. The evacuation procedure was then repeated.

It now appears that the pressure rose as a result of various actions taken during the first evacuation, not because of any leak, Suffredini said.

The initial problem was traced to a faulty card inside one of the space stations computer relay systems. After rebooting the computer equipment in question, the error message cleared and the relay box returned to good operating condition, NASA said.

Mission managers at Johnson Space Center in Houston had informed the crew several hours earlier that the ammonia system was probably fine.

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Space station evacuation ends; crew returns to work after ammonia scare