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Associated Press
In this image made from video provided by NASA, astronaut Christopher Cassidy, foreground, holds a power wrench as he stows away a suspect coolant pump on the International Space Station on Saturday, May 11, 2013. Thomas Marshburn is at left. The two astronauts made the spacewalk to replace the pump after flakes of frozen ammonia coolant were spotted outside the station on Thursday. (AP Photo/NASA)

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