FILE - 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 ... more 
FILE - 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. On Tuesday, Dec. 17, 2013, NASA decided to schedule a series of urgent spacewalks to fix a broken cooling line at the International Space Station. The first is scheduled for Saturday, Dec. 21, 2013. (AP Photo/NASA) less 
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Associated Press | Photo By NASA
Tue, Dec 17, 2013 6:32 PM EST