Spacewalk to repair International Space Station cooling system complete

STS-51D mission specialists Jeffrey Hoffman and David Griggs work outside the space shuttle Discovery during NASA's first unplanned spacewalk in April 1985. (NASA)

Repairs to the International Space Station have hopefully been completed today after members of the crew suited up and headed outside to track down the source of the ammonia leak discovered on Thursday.

Crew members Chris Cassidy and Tom Marshburn exited the ISS just before 9 a.m. EDT and headed for the suspected site of the leak, in what was scheduled to be a six-hour long spacewalk (or EVA — extra-vehicular activity — in technical terms).

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Unfortunately for the astronauts, the source of the leak wasn't so easy to find as hoped. According to a CTV News update, NASA reported at 10:27 a.m. that "Cassidy and Marshburn are working 'like two CSI investigators' in their attempts to locate the ammonia leak."

NASA commentary on their live stream of the spacewalk reported that Cassidy and Marshburn were unable to spot any flakes of leaking ammonia despite tests to find the source. However, just in case the problem was similar to what happened back in August 2010, they swapped the coolant pump with a spare unit, refilled the system with ammonia to test the 'new' pump, and it seemed to be working.

Cassidy and Marshburn have since returned to the station's airlock, waited for any residual ammonia to burn off their space suits, and then closed the thermal hatch and repressurized, completing the work on schedule.

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Along with the NASA commentary, Canadian ISS Commander Chris Hadfield had also been providing his own commentary on aspects of the walk via Twitter.

Ammonia is used as a coolant in the station's power system, venting waste heat from the station's electronic systems into space. NASA had stated that the leak posed no threat to the safety of the station or the astronauts on board. Since the specific leak was not found, it's unclear whether this repair will fix the problem, but things are looking good for Hadfield and the rest of Expedition 35 to return home on Monday.

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