International Space Station cooling system shuts down with six astronauts aboard

Nasa said crew are safe and experts are working to troubleshoot the problem

The International Space Station is seen from space shuttle Discovery in 2009. (REUTERS/European Space Agency/Handout)

Concerns grew on Wednesday for the crew on the Nasa International Space Station when cooling systems shut down while six members of Expedition 38 were aboard.

But Nasa said the situation posed no immediate danger to the two American astronauts, three Russian cosmonauts, and one Japanese astronaut on the ISS after a valve on a pump on one of the station's two external cooling loops shut down because it reached pre-set temperature limits.

However, if the problems became more serious they could potentially require a spacewalk, according to NBC News, even after spacewalks were temporarily suspended in July. "We are cleared for a contingency spacewalk if we need to do one," NASA spokesman Kelly Humphries told NBC.

Station commander cosmonaut Oleg Kotov, Rick Mastracchio, Michael Hopkins, Mikhail Tyurin, Sergey Ryazanaskiy and Japanese astronaut Koichi Wakata are aboard.

Engineers suspect a valve inside the pump may have been faulty, leading ground controllers to move electrical power supplies to the other cooling loop. These loops circulate ammonia outside the station to keep equipment inside and outside cool.

The space agency said experts were working on the ground to troubleshoot the problem.

Nasa spokesman Bob Jacobs added that at no point were the crew at risk, but some non-critical equipment on the massive orbital outpost was powered down.

"The station wasn't ever in any danger," Jacobs told the Associated Press.

In an update on the situation, Nasa said: “The pump module on one of the space station’s two external cooling loops automatically shut down when it reached pre-set temperature limits. [...] The flight control teams worked to get the cooling loop back up and running and they suspect a flow control valve actually inside the pump module itself might not be functioning correctly.

“At no time was the crew or the station itself in any danger, but the ground teams did work to move certain electrical systems over to the second loop. […] The crew is safe and preparing to begin a normal sleep shift while experts on the ground collect more data and consider what troubleshooting activities may be necessary.”

The outpost has been in orbit more than 220 miles (354 kilometers) above Earth since 1998.