Christmas Eve spacewalk aims to finish crucial space station repairs

Cosmic Log

Alan Boyle, Science Editor NBC News

37 minutes ago

Nearly two weeks after a faulty coolant valve crippled the International Space Station, two NASA astronauts went on a Christmas Eve spacewalk to get things back to normal.

Spacewalkers Rick Mastracchio and Mike Hopkins opened the air lock and set the clock running at 6:53 a.m. ET for what's expected to be a six-hour-plus outing. They're due to install a refrigerator-sized coolant pump module with an assist from Japanese astronaut Koichi Wakata, who's operating the station's 58-foot-long (18-meter-long) robotic arm.

Mastracchio was in the holiday spirit as he unpacked his tools for the job. "It's like Christmas morning, opening up a little present here," he joked.

Tuesday's spacewalk follows up on Saturday's successful operation to remove the faulty pump module. A valve inside that apparatus failed on Dec. 11, forcing one of the station's two ammonia coolant loops to go offline.

The cooling system plays an essential role in keeping the onboard electronics from overheating. When the first loop failed, NASA had to shut down non-essential systems and switch other systems over to the second loop, reducing the station's safety margin in the process. If the other loop were to fail, that would spark an emergency that could have forced the six-man crew to abandon the station.

A similar situation required three difficult spacewalks in 2010, but this time around, the repairs have gone more quickly than expected. Aided by the robotic arm, Mastracchio and Hopkins are scheduled to pull a spare pump module out of storage, set it in place and get it hooked up on Tuesday.

"If the reconnections go as smoothly as the disconnections did, we should be able to do everything we need to do in less than the six and a half hours that's planned," NASA spokesman Kelly Humphries told NBC News.

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Christmas Eve spacewalk aims to finish crucial space station repairs