Leak Fears Prompt Space Station Shuffling

International Space Station crew members evacuated to the Russian side of the station twice on Wednesday because of worries of a possible ammonia leak, but less than 12 hours after a warning alarm roused them from their sleep, everything was back to normal, Nasa said.

Wearing protective masks, two astronauts - Terry Virts of Nasa and Samantha Cristoforetti of the European Space Agency - opened the hatch that separates the American and Russian segments at 3:05 p.m. Eastern Standard Time. Tests of the air showed no signs of ammonia, which is poisonous if inhaled, so the astronauts returned to the U.S. side.

The problem appeared more likely to have been caused by a faulty computer card than an actual leak.

An alarm awakened the crew around 4 a.m. EST when pressure increased in one of two water loops in the space station's cooling system. The water loops remove heat from the space station. The heat is transferred to loops of ammonia on the outside of the station and radiated into outer space.

A problem with the heat exchanger could cause ammonia to leak into the water loop and then into the American segment of the space station.

The space station consists of two essentially independent segments, one built by Russia, the other by the United States and other nations.

The astronauts put on gas masks, moved into the Russian segment and closed the hatch.

After sifting through the measurements, the managers at mission control let the astronauts return. But then air pressure in the American segment also started to rise. "If you're leaking ammonia into the water loop and it eventually finds its way to the cabin, you would expect the cabin pressure to go up," said Michael Suffredini, the manager of the space station, in an interview on Nasa Television.

The crew evacuated to the Russian segment a second time.

Nonessential systems were turned off to avoid the possibility of overheating but were later gradually restarted.

"Everything is looking pretty normal right now," James Kelly, an astronaut at mission control, told Barry Wilmore, the station commander, in an update after 8 a.m. EST. "It's a little more positive than we thought before."

The space station crew includes three Russians - Elena Serova, Alexander Samokutyaev and Anton Shkaplerov.

Suffredini said none of the science research on the space station had been compromised. Freezers preserving samples and supplies had been briefly turned off, but those are designed to remain cold for more than eight hours even if power is lost.

"We were well within that, and all the freezers are back up and running now," Suffredini said.

© 2015 New York Times News Service