Space station commander Sunita Williams and Japanese astronaut Akihiko Hoshide returned to the Quest airlock module and began repressurizing the compartment at 3:07 p.m. EDT on Thursday, officially ending a successful six-hour 38-minute spacewalk to bypass a suspect solar array radiator.

File photo of astronauts on a spacewalk outside the International Space Station. Credit: NASA

This was the 166th spacewalk devoted to station assembly and maintenance since construction began in 1998 and the fifth this year. One hundred and nine astronauts, cosmonauts and international partners have now logged 1,049 hours and one minute of space station EVA time, or 43.7 days.

With today's spacewalk, Williams, a former Navy helicopter pilot, moves up to No. 5 on the list of most experienced spacewalkers with 50 hours and 40 minutes of EVA time during seven excursions. Hoshide now has 21 hours and 23 minutes of spacewalk time during three EVAs.

Williams and Hoshide successfully reconfigured ammonia coolant lines to bypass a presumed leak in a radiator used to cool electrical components in one of the space station's solar array modules. A spare radiator then was successfully deployed to take over cooling.

Flight controllers plan to monitor the system for several weeks to determine if the leak is still present. If there are no signs of a leak, they will know the problem was, in fact, in the bypassed radiator. In that case, managers could elect to simply use the spare radiator indefinitely. If the leak is still there, engineers will know it's somewhere else in the system. In that case, another spacewalk likely will be required at some point to replace a pump module.

But switching to the spare radiator effectively tapped an additional reservoir of ammonia and even with a leak, the coolant system should be able to operate for nearly a year, giving engineers time to come up with a solution.