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Unplanned Spacewalk a 'Precedent-Setting' Move for Space Station Crew

NASA astronauts Tom Marshburn and Chris Cassidy work outside the International Space Station during a spacewalk in 2009. They were paired again for a rare unplanned spacewalk on May 11, 2013.

Spacewalk to repair ISS

Repairs to the International Space Station began on Saturday morning as

members of the crew suit up and head outside to track down the source of

the ammonia leak discovered on May 9.