In this image made from video provided by NASA, astronauts Chris Cassidy, foreground, and Tom Marshburn prepare for a possible spacewalk from the International Space Station on Friday, May 10, 2013. NASA will decide later Friday if the two astronauts will step outside the station to work on a leaking coolant line. The line chills power systems but power was rerouted and is operating normally. The six-member crew is not in danger. (AP Photo/NASA)

Two astronauts will venture outside the International Space Station on Saturday to tackle an ammonia leak in the power cooling system.

The leak was discovered Thursday and the repair job was quickly planned for the weekend.

In this Monday July 27, 2009 image provided by NASA, astronauts Tom Marshburn, left, and Christopher Cassidy participate in a spacewalk for maintenance tasks. On Friday, May 10, 2013, the two astronauts are preparing for a possible impromptu spacewalk to work on a leaking ammonia coolant line. The line chills power systems but power was rerouted and is operating normally. The six-member crew is not in danger. NASA will decide Friday evening if the spacewalk is needed on Saturday. (AP Photo/NASA)

Spacewalks usually aren't done on such short notice. But wanted to try to fix the leak before all the ammonia escaped. The space agency also wanted to take advantage of a veteran spacewalker who is due to return home on Monday with two other astronauts.

The two —Americans Chris Cassidy and Tom Marshburn—will swap out a pump box on one of the eight solar panels that supply electricity to the station.

This May 23, 2011 file photo released by NASA shows the International Space Station at an altitude of approximately 220 miles above the Earth, taken by Expedition 27 crew member Paolo Nespoli from the Soyuz TMA-20 following its undocking. NASA on Thursday, May 9, 2013 said the International Space Station has a radiator leak in its power system. The outpost's commander calls the situation serious, but not life-threatening. (AP Photo/NASA, Paolo Nespoli, File)

NASA says the station has plenty of power, and the six-man crew is not in danger.

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