August 9, 2010

Third Spacewalk Needed To Finish ISS Repairs

The longest expedition crew spacewalk in NASA history still wasn't enough to complete repairs on a damaged cooling system at the International Space Station (ISS), and an additional extra vehicular activity (EVA) will be needed to finish the job, the space agency reported over the weekend.

Two spacewalks had already been scheduled, with the second set to take place as early as Wednesday.

According to NASA's official ISS website, Expedition 24 Flight Engineers Doug Wheelock and Tracy Caldwell Dyson--who earlier completed an 8 hour, 3 minute spacewalk on Saturday--will look to "complete the removal of a failed ammonia pump module and installation and activation of a new pump module on the International Space Station's S1 Truss."

The coolant system was shut down on July 31 after one of two cooling loops failed. Wheelock and Caldwell Dyson managed to remove the unit's hoses, but were unable to remove the pump.

"Wheelock struggled to free an unyielding quick-disconnect fitting on one ammonia line feeding the failed system, before ground controllers told him to move on to the other lines, where the astronauts made better progress," Irene Klotz of Reuters reported on Saturday. "With time running short, the pair returned to the trapped line and were able to release it, but they noted crystals of ammonia leaking out."

"Flight directors at NASA's Mission Control Center in Houston decided not to attach the line to a bypass mechanism holding the other three lines and told Wheelock to reattach the fitting while they figured out what to do next," Klotz added. "Because of the leak, the spacewalkers spent extra time in the airlock to flush out any ammonia that may have attached to their spacesuits. The decontamination procedure is routine whenever spacewalkers are exposed to free-flying ammonia, which can be a hazard if it gets into the space station's air."

During the second spacewalk, Wheelock and Caldwell Dyson will have to finish removal of the failed unit, replace it by moving a 780-pound unit some 30 feet, and then re-connect the ammonia fluid lines. The tasks originally set for the second EVA, including the reattachment of the electrical lines and other fluid tubes, would most likely now have to be delayed until a third one.

"It would take a lot of good luck and somebody coming up with a really short tweak to the EVA for us to get to the point where we can start that (new) ammonia pump" following the second spacewalk, ISS manager Michael Suffredini told AFP on Saturday. "We're going to end up being in this condition, this risk posture, a few more days than originally planned."


Image 2: Expedition 24 Flight Engineers Doug Wheelock (left) and Tracy Caldwell Dyson work to remove a failed ammonia pump module on the International Space Station's S1 Truss. Credit: NASA TV


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