Nasa is assessing a problem with one of two cooling systems aboard the International Space Station, a potentially serious but not life-threatening situation, officials say.
The system automatically shut itself down after detecting abnormal temperatures, said Nasa spokesman Josh Byerly at the Johnson Space Center in Houston.
The problem appears to be a faulty valve inside a pump located outside the station, a US$100 billion research complex that flies about 400km above Earth.
Repairs may require a spacewalk, Byerly said.
''If it's a software problem, they could just do a software update or do a patch. If it's a hardware issue, that's something else,'' Byerly said.
''We'll know more in the next day or so.''
The six astronauts aboard the station are not in any danger and would not need to evacuate, he added.
''Some of the news reports that I've seen out there have been like 'catastrophic shutdown.' That's not at all what this is,'' Byerly said.
Equipment aboard the station affected by the shutdown has either been powered off or switched over to the station's second cooling loop, including three freezers that hold science samples for return to Earth.
The station has three spare pumps located outside the station if engineers determine the valve cannot be repaired and managers authorise a spacewalk, Byerly said.
US spacewalks have been suspended since July after Italian astronaut Luca Parmitano's spacesuit started leaking, causing his helmet to fill with water.
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