Nasa orders three emergency spacewalks to repair the ISS

A failure in the coolant system last Wednesday led to the shutting down of all nonessential systems, though Nasa reports the astronauts are safe and comfortable

Russian cosmonaut Alexander Misurkin participates in a session of extravehicular activity (EVA) in AUgust 2013 at the ISS. (Nasa)

Nasa has announced that astronauts on board the International Space Station (ISS) will undertake a series of urgent spacewalks to fix a broken cooling system.

The cooling system is powered by ammonia and is critical for dispelling heat generated by equipment on the space station. It malfunctioned last Wednesday after a valve overloaded and the ISS’s six-man crew was forced to turn off all nonessential equipment.

The astronauts are in no danger or discomfort, but Nasa wants to restore the station to its full capacity in case of any further equipment failures.

Two American astronauts will undertake the spacewalks this Saturday, next Monday and possibly next Wednesday – Christmas Day – as well.  Nasa hopes that the third spacewalk will not be necessary, but if so, it would be the first such mission on 25 December since 1973.

"The next week will be busy with space walks so not much tweeting from here," said Nasa astronaut Rick Mastracchio via Twitter after the decision was announced.

US-led spacewalks have been on hold since this July, when an Italian astronaut nearly drowned after water leaked inside his helmet.

The missions on Saturday and Monday will be to replace a valve for the coolant system. Flight controllers had tried to fix the problem remotely, but Nasa opted to avoid a short-term solution.

Mastracchio – an experienced spacewalker – will undertake the mission alongside Michael Hopkins, a first timer. The pair will have to manoeouvre the replacement valve (a package weighing 350kg) in zero gravity whilst wearing bulky space suits.

An identical repair job was undertaken on the station in 2010 and will provide a template for Mastracchio and Hopkins. Nevertheless, the pair have been busy preparing themselves all week, in case of just such a decision.

"Have not looked out the window in 4 days. Too busy building space suits," Mastracchio tweeted on Tuesday. "Where did I put my gloves?"