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Space station power system restored to full operations

Posted: May 23, 2013

Convinced an emergency spacewalk fixed the problem, engineers have restored complete functionality to the International Space Station power system that sprung a coolant leak May 9, NASA officials said Wednesday.

NASA astronaut Tom Marshburn on a May 11 spacewalk. Credit: NASA
Astronauts spotted leaking ammonia flakes streaming from the vicinity of a pump May 9 and radioed mission control to report the sighting. Engineers on the ground confirmed the leak through telemetry data and shut down one of the space station's eight power cooling loops while ordering astronauts Chris Cassidy and Tom Marshburn to prepare for a spacewalk to locate and resolve the issue.

During a May 11 spacewalk, Cassidy and Marshburn replaced the suspected culprit - an ammonia pump located at the end of the space station's port-side truss. The spacewalkers observed no obvious signs of a leak when mission control powered up the fresh pump.

Ground controllers reconfigured the space station's primary system in the wake of the leak, isolating one of the lab's eight electricity channels crippled by a cooling failure and spreading the outpost's power load across the other seven solar arrays as officials planned a repair.

Mike Suffredini, NASA's space station program manager, said Wednesday the spacewalk fixed the serious leak that appeared May 9.

"A couple of weeks ago, we changed out a pump on the port outboard solar array cooling system, and that seemed to be the source of the big leak that we saw," Suffredini told reporters. "So we today finished transitioning all the [power] loads back on to that particular solar array, and everything is in a nominal fashion as we proceed forward."

The restored cooling system, which services the space station's 2B power channel, ensures the outpost's laboratories and residents continue working on scientific research at a feverish pace easily eclipsing NASA's self-imposed objective of 35 hours of hands-on experiment work per week.

The 2B channel draws power from one of two 115-foot-long wings of the space station's P6 truss lying on the far left end of the space station's structural backbone. The leaky coolant loop dissipates heat from the electronics on the power truss.

The bulk of the space station's electricity comes from four sets of solar arrays mounted on both ends of the 450-ton outpost's 357-foot-long truss. The P6 solar panels, launched on a space shuttle mission in 2000, are the oldest of the four U.S.-built power truss segments.

Suffredini it will take up to a year to determine whether the 2B power channel's coolant system is still leaking at all. Engineers first noticed a minor leak in the same coolant loop in 2007, prompting a spacewalk in 2011 to refill the system with ammonia coolant. After the leak rate increased - likely due to the development of another leak elsewhere in the system - another spacewalk in November 2012 attempted to isolate the location of the slow leak with a bypass of a suspect radiator.

The leak from 2007 until May 9 was at a much slower, more manageable rate only requiring astronauts to recharge the cooling system's ammonia supply every few years.

"It will take us some time to sort that out," Suffredini said. "But if either of those [previous leaks] are still with us, we're talking years and that's sort of in our plan to refill this every so often."