Two astronauts are taking a hastily planned spacewalk to find and, possibly, fix a serious leak at the International Space Station.

International Space Station (NASA via Getty Images)

Flakes of frozen ammonia coolant were spotted Thursday drifting from the long frame that holds the solar panels on the left side. Less than 48 hours later, Thomas Marshburn and Christopher Cassidy emerged from the orbiting lab Saturday to hunt for the leak. They're prepared to replace a pump, if necessary.

The two have been at this troublesome spot before, during a shuttle visit in 2009.

NASA says the leak, while significant, poses no safety threat. But managers want to deal with the trouble now.

NASA has never staged such a fast, impromptu spacewalk for a station crew. Even during the shuttle days, unplanned spacewalks were rare.


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