International Space Station astronauts begin spacewalk to fix ammonia leak

http://www.guardian.co.uk/science/2013/may/11/international-space-station-spacewalk-ammonia

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Two astronauts aboard the International Space Station have begun a spacewalk to try to fix an ammonia leak in a cooling system on one of the station's solar arrays that provide electricity to the orbital outpost.

The crew spotted a steady stream of small, white frozen ammonia flakes floating away from a coolant line outside the station on Thursday.

Mission managers reviewed images and data before deciding to send the American astronauts Chris Cassidy and Tom Marshburn out on Saturday morning to try to stop the leak by replacing a pump on the cooling system.

"The crew is not in danger, and the station continues to operate normally otherwise," Nasa said in a statement.

Ammonia is used to cool the power systems that operate each of the station's eight solar arrays. The leak is on the far left side of the station's truss structure, in an ammonia loop that astronauts previously tried to troubleshoot during a spacewalk in November 2012.

While Cassidy and Marshburn are working outside the space station, the crew commander Chris Hadfield, from Canada, will choreograph their movements from inside the orbital outpost. Pavel Vinogradov, Alexander Misurkin and Roman Romanenko from Russia make up the rest of the crew.

The space station, a $100bn (£650m) research laboratory that orbits 250 miles (400km) above Earth, is owned by the United States and Russia in partnership with Europe, Japan and Canada.