From: IAN O'NEILL, Discovery News
Published May 13, 2013 06:15 AM

ISS Ammonia Leak Repaired on Spacewalk

During an unscheduled spacewalk on the space station's exterior on Saturday morning, NASA astronauts Tom Marshburn and Chris Cassidy carried out the mother of all plumbing jobs: They detached a suspect ammonia pump, replaced it with a spare and watched for any further ammonia leakage.


The emergency spacewalk was carried out in response to a troubling ammonia coolant leak that was discovered on Thursday. The coolant is used to maintain the temperature of the vast solar arrays the space station uses to generate electricity for its systems.

But after nearly four hours of extravehicular activity, Marshburn and Cassidy reported seeing "no snow" (i.e. no ammonia flakes) as a replacement Pump and Flow Control System (PFCS) box was switched on and ammonia was pumped around the solar array at full pressure. No trace of the phantom ammonia leak was spotted by the spacewalkers' cameras nor the ever watchful mission managers in Houston, Texas.

Space station commander Chris Hadfield watched events unfold from the orbiting outpost’s interior, providing support for the astronauts working outside. "Houston just sent the command to start flowing ammonia through the newly-installed pump. Gloved fingers crossed," he said as the newly replaced PFCS was switched on. Several minutes later, Marshburn reported, "we don’t see anything."

"No leaks! We're bringing Tom & Chris back inside. In two days Tom, Roman & I return to Earth in our Soyuz. This is an amazing place & time," tweeted an exhilarated Hadfield as Marshburn and Cassidy packed up their tools and underwent a "bake-out" procedure. The bake-out was required to allow sufficient time for any possible ammonia contamination on the spacewalkers' suits to sublimate and dissipate into space. Ammonia is toxic, so every precaution was taken to ensure none was inadvertently carried back into the space station.

ISS image via Shutterstock.

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