A broken cooling system valve on the ISS has forced Nasa to postpone the first commercial Cygnus cargo mission

Emergency spacewalks to fix International Space Station

Astronauts aboard the International Space Station (ISS) will perform a series of spacewalks, starting on 21 December, to repair a faulty pump module of the station’s cooling system that stopped working last week.

The repairs have forced Nasa to postpone the first commercial cargo mission of Orbital Science’s vehicle Cygnus, originally scheduled for 19 December. According to Nasa’s announcement, Cygnus’ mission won’t take place before early January.

After one of the station’s two ammonia cooling systems stopped working on Wednesday, 11 December, the crew aboard the ISS had to turn off unnecessary equipment and suspend some laboratory experiments. The crew itself was not in danger, Nasa reassured.

After Nasa engineering teams concluded it was not possible to bypass the faulty valve pump located outside the station, Nasa has decided the crew’s flight engineers, astronauts Rick Mastracchio and Michael Hopkins, will have to venture in open space to replace the broken part with a spare one, located in an outside storage unit.

The operation will require three space walks, now scheduled for the 21, 23 and 25 December.

The broken module, supplied by Boeing, was installed in 2010 after its predecessor had suffered a short circuit. Back then, the replacement operation proved more complicated than expected.

Based on the 2010 experience, Nasa foresees astronauts will first have to disconnect five power and data lines, three 1.5in ammonia lines and a half-inch coolant line, attaching those as quickly as possible to a ‘jumper box’ to prevent loss of pressure.

The emergency spacewalks will be the first conducted by Nasa since the incident in July when European astronaut Luca Parmitano experienced problems with his Nasa spacesuit resulting in his helmet filling with water. The investigation launched after Parmitano’s accident has not yet been concluded.

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