A US-Japanese team has returned to the to the Quest airlock module of the International Space Station (ISS) late on Thursday after completing a spacewalk to fix the station’s cooling system.

The space station commander, NASA astronaut Sunita Williams and her Japanese colleague Akihiko Hoshide spent six hours and 38 minutes on the exterior of the ISS.

The objective of the spacewalk, which began at 16:19 Moscow time [12:19 GMT] and ended at 23:07 Moscow time [19:07 GMT], was to isolate and repair a persistent ammonia leak.

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.

In a bid to locate the malfunction, Williams and Akihiko isolated the radiator in question in order to determine whether it was the source of the leak. They also rerouted coolant lines to a spare radiator to take over cooling.

It will take several weeks to find out whether the fix works. If the leak ultimately goes away, it will be known that the problem radiator was indeed the source of the problem, most likely caused by a collision with space junk.

But if ammonia continues to escape, engineers will know that the problem was in some other part of the system. In this case, another spacewalk might be required.

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. Thursday’s spacewalk brought the overall time that Williams spent outside the station to 50 hours and 40 minutes, making her number five on the list of most experienced spacewalkers

Hoshide now has three spacewalks, totaling 21 hours and 23 minutes, on his record.

Source and photo: NASA