In this Saturday, May 11, 2013 photo made available by NASA, astronaut 

In this Saturday, May 11, 2013 photo made available by NASA, astronaut Chris Cassidy and Tom Marshburn, not pictured, perform a space walk to inspect and replace a pump controller box on the International Space Station after an ammonia coolant leak was discovered. (AP Photo/NASA)
Associated Press
In this Saturday, May 11, 2013 photo made available by NASA, astronaut Chris Cassidy and Tom Marshburn, not pictured, perform a space walk to inspect and replace a pump controller box on the International Space Station after an ammonia coolant leak was discovered. (AP Photo/NASA)
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