Space Station Crew Prepare for Emergency Spacewalk

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Close-up of Christopher Cassidy’s spacesuit helmet visor during his second STS-127 spacewalk in July 2009. Seen mirrored in the visor is astronaut Tom Marshburn. Both Expedition 35 astronauts are expected to pair up again if the emergency EVA is approved to fix the ammonia leak on Saturday. Credit: NASA

After the discovery of a leak of ammonia coolant supplying one of the International Space Station solar arrays on Thursday, NASA managers have decided to plan for an unscheduled spacewalk on Saturday to repair the problem. The final decision about whether to go ahead with the extravehicular activity will be made late on Friday.

Although the crew are not in danger, the affected portion of the station’s huge football pitch-sized solar array that supplies the orbiting outpost with electricity will be inoperative and work is currently underway to reroute electricity from the other fully functioning arrays to ensure all systems remain powered up.

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The ISS crew reported seeing “white flakes” floating away from the station, emanating from the far left-side of the station’s truss structure, late on Thursday morning. It was quickly identified as the ammonia leak. It appears to be coming from the general location of where astronauts troubleshooted a leak on Nov. 1, 2012, on the P2 truss structure, but photography by the station’s astronauts can only provide so much information about the leak’s location. Video imagery from the astronauts, however, have been able to estimate the loss rate of ammonia and that rate appears to be increasing.

The ammonia supply from the impacted 2B power channel was expected to be depleted late Friday morning.

“Station’s power relies on ammonia coolant. A few hours ago, we determined that the ammonia was leaking out of the Station and into space,” Expedition 35 Commander Chris Hadfield reported via Twitter on Thursday.

This morning, as plans were underway for a potential emergency spacewalk, Hadfield was upbeat about the situation.

“Good Morning, Earth! Big change in plans, spacewalk tomorrow, Chris Cassidy and Tom Marshburn are getting suits and airlock ready. Cool!” he said. “The whole team is ticking like clockwork, readying for tomorrow. I am so proud to be Commander of this crew. Such great, capable, fun people.”

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NASA astronauts Cassidy and Marshburn are currently working in the station’s Quest airlock, checking out the U.S. spacesuits they would wear if a spacewalk is approved, according to a NASA news release. Hadfield is also preparing to assist as the “intravehicular” crew member, or spacewalk choreographer.

“Suddenly very busy! Ammonia leak on the outside of station means that Cassidy and I will be doing a spacewalk tomorrow to try and repair it,” Marshburn tweeted Friday morning.

Cassidy and Marshburn are no stranger to working on the space station’s exterior. Both astronauts have conducted three EVAs, all during the Space Shuttle mission STS-127 in 2009. They collaborated on two of those spacewalks (pictured top).