MOSCOW, November 1 (RIA Novosti). US astronaut Sunita Williams and her Japanese colleague Akihiko Hoshide ventured outside the International Space Station (ISS) on Thursday to isolate and repair a persistent ammonia leak.
The spacewalk officially began at 16:29 Moscow time (12:29 GMT) and is expected to last six and a half hours.
Ammonia is used to cool down power units associated with eight solar arrays installed on the ISS.
Space station partners have known about the ammonia leak in one of the solar arrays since 2007, but it was not considered a major concern due to its very low leakage rate. Astronauts aboard the space shuttle Endeavour recharged the coolant system with 8 pounds (3.6 kilograms) of ammonia last year.
However, in June 2012 ISS flight controllers noted a sharp increase in the leakage rate, and it was decided that the problem should be solved so as to avoid an automatic shutdown of the power unit affected.
Williams and Hoshide are making their way over to the port side of the station's truss. They will attempt to detect the source of the leak, reconfigure some of the lines in the coolant system experiencing problems, and install jumpers to bypass it with a spare radiator already on the truss.
This is the third spacewalk for Williams and Hoshide during their mission at the ISS. Their first spacewalk lasted 8 hours and 17 minutes and was the third longest in history of space exploration.
The current ISS crew, apart from Williams and Hoshide, comprises US astronaut Kevin Ford and three Russian cosmonauts - Yuri Malenchenko, Oleg Novitskiy and Evgeny Tarelkin.
