Astronauts including Columbia native Terry Virts returned to the U.S.-operated section of the International Space Station on Wednesday afternoon, hours after evacuating over fears of an ammonia leak.
Virts, fellow NASA astronaut Barry Wilmore and European Space Agency astronaut Samantha Cristoforetti donned protective masks and re-entered the American side of the space station about 3 p.m. and found no indications of any ammonia inside the cabin.
Space station engineers had been on alert since about 4 a.m., when sensors suggested that ammonia from a cooling system on the outside of the space station was leaking into a water loop that flows inside the satellite, Michael Suffredini, manager of NASA's space station program, said in an interview on NASA TV.
The astronauts immediately evacuated to the Russian half of the space station, closing a hatch behind them to contain any leak. NASA officials said the crew mates were in good condition and were never in any danger.
An alarm indicated that ammonia could have been present in the space station cabin, and a rise in cabin pressure appeared to possibly confirm that, NASA officials said. A space station cooling system transfers heat inside the station from the water loop to an ammonia system on the outside of the station.
An ammonia leak is among the chief risks crew members train for, Suffredini said.
But no ammonia leak was found, and NASA flight controllers were working to analyze data and determine what triggered the alarm.
"You don't want to have hazardous chemicals flowing through water loops," he said. "You could potentially leak ammonia into the water loop, and then there's a path through which it can find its way into the cabin."
The incident was not expected to have a major impact on space station activity and research. The NASA astronauts were preparing to begin an experiment using fruit flies to study the effects of space flight on response to infection.
The alarm rang two days after a resupply mission reached the space station. In the hours before the suspected leak was reported, Virts tweeted pictures of the opening of the hatch to a Dragon spacecraft flown by NASA contractor SpaceX, and of some mandarin oranges it presumably brought from earth.
Virts launched to the space station in November, replacing Cockeysville native Reid Wiseman, who was on board the station from May to November.
Virts spent two weeks in space in 2010 as a pilot of the space shuttle Endeavour, on a mission to deliver one of the segments of the American section of the station — known as Tranquility, which includes a treadmill and the Cupola observation area.
His stay on the space station as part of the 42nd and 43rd expeditions is scheduled to last until March.
Along with Virts, Wilmore and Cristoforetti, there are three Russian cosmonauts aboard the space station.
The station spans the area of a football field and takes up about the same space as a six-bedroom house. It is divided in half into a Russian segment and a U.S. segment, which also houses Japanese and European space agency labs.
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