Watch live: Spacewalk to repair International Space Station ammonia leak

STS-51D mission specialists Jeffrey Hoffman and David Griggs work outside the space shuttle Discovery during NASA's …
Repairs to the International Space Station are underway this morning as members of the crew suit up and head 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 is scheduled to be a six-hour long space walk (or EVA — extra-vehicular activity — in technical terms).

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Unfortunately for the astronauts, the source of the leak hasn't been as 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."

As of the most recent updates, NASA commentary on the live stream showing the walk reported that Cassidy and Marshburn have yet to spot any flakes of leaking ammonia and were continuing tests to find the source. However, they have completed work to swap the coolant pump (which may have been the source of the problem) with a spare unit, they have refilled the system with ammonia to test the 'new' pump, and it seems to be working.

Canadian ISS Commander Chris Hadfield has 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 has stated that the leak poses no threat to the safety of the station or its residents.

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You can follow Cassidy and Marshburn as they work on NASA's live stream at NASA TV or below.

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