May 10, 2013 at 9:00 PM ET
By Miriam Kramer
Astronauts on the International Space Station are gearing up to perform an emergency spacewalk Saturday to hunt for an ammonia leak in the orbiting laboratory's cooling system.
NASA astronauts Tom Marshburn and Chris Cassidy are planning to spend more than six hours outside the station to find, and possibly repair, the ammonia coolant leak.
The spacewalk comes just two days after the six-man crew of the space station noticed frozen flakes from an ammonia leak on one of the eight winglike solar arrays responsible for supplying power to the station. Planning a space station spacewalk repair in such a short time frame is unprecedented, NASA officials said. [Infographic: How the Space Station's Cooling System Works]
It also comes just two days before Marshburn and two crewmates, station commander Chris Hadfield of Canada and Russian cosmonaut Roman Romanenko, are due to return home. Monday's departure will not be affected by the spacewalk, NASA officials said.
The space station crew is in no danger, and the pump has been turned off in order to slow the rate of the leak, mission managers said. The leak is on the space station's P6 truss, at the leftmost side of the outpost's football field-length main truss.
NASA's space station program manager, Mike Suffredini, said the spacewalk's "objective is to get a look at the leak."
Spacewalk repair on tap
A team of NASA officials gave the go-ahead late Friday for the spacewalk to begin at 8:15 a.m. ET Saturday. The plan calls for Cassidy and Marshburn to float outside of the station to inspect the leaking loop. Then they'll try to replace an ammonia coolant pump that station engineers suspect may be the source of the leak.
Marshburn and Cassidy have both conducted three spacewalks — two of them together — during their 2009 mission on the space shuttle Endeavour. This spacewalk is expected to take a little more than six hours. "The crew is very familiar in this area," Norm Knight, NASA chief flight director, said during a briefing on Friday. This type of repair, however, is unprecedented in the space station's history, he added.
Usually spacewalks are planned months in advance, but this is the first time a space station crew has been expected to do a spacewalk on such short notice, Knight said.
If this spacewalk doesn't correct the leak, the space station can still function using seven of its eight solar arrays, Suffredini said. However, managing the space station's power requirements over the long term would prove to be more challenging.
Cooling system history
This wouldn't be the first spacewalk undertaken to repair a coolant leak.
Last year, NASA's Sunita Williams and Japanese spaceflier Akihiko Hoshide went a spacewalk to troubleshoot a leak in a coolant loop. That leak was in the same loop as the current leak, but engineers don't yet know if the two leaks are related.
Hadfield, Marshburn and Cassidy are part of the station's Expedition 35 crew, along with Russian cosmonauts Pavel Vinogradov, Alexander Misurkin and Romanenko. On May 28, three new crew members are expected to launch from Kazakhstan to join Vinogradov, Misurkin and Cassidy on the International Space Station. The spacewalk would not affect that schedule, NASA said.
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