Astronauts replace failed cooling equipment on space station

The repairs performed on the International Space Station's cooling system during a seven-hour-and-20-minute spacewalk Monday appear to be working, NASA said. Astronauts Doug Wheelock and Tracy Caldwell Dyson installed a spare 780-pound ammonia pump module to replace a broken unit they removed last Wednesday, NASA said on its website. After Wheelock attached four bolts and Caldwell Dyson mated five electrical connectors, ground controllers confirmed the module was in healthy condition when it began receiving power. 

A pressure check and more fluid cable connections followed, and the module was filled with ammonia, NASA said. All of the fluid lines are connected and no ammonia leaks were reported, according to NASA's Twitter feed. The spare part has been in space, awaiting use if needed, since July 2006, when it was delivered aboard the space shuttle Discovery, NASA said.

Wheelock and Caldwell Dyson embarked on their third spacewalk in 10 days Monday morning -- the final stage of a three-part mission to replace the piece of equipment that helps regulate system temperatures on the International Space Station. Wheelock and Caldwell Dyson set their spacesuits to internal battery power to begin work at 6:20 a.m. ET, NASA said. They were assisted by flight engineer Shannon Walker, who remained inside the International Space Station and operated the Canadarm2, which NASA describes as a robotic arm used to help with handling large payloads. The spacewalk ended at 1:40 p.m. ET.

After the original pump module failed July 31, it was removed during an August 11 spacewalk and temporarily stored on an external platform, NASA said. Ground controllers powered down numerous station systems and readjusted them to provide maximum redundancy, NASA said. At that time, mission managers and astronauts on the ground began choreographing the spacewalks and planning repair procedures, NASA said. 

Wheelock and Caldwell Dyson made their first spacewalk related to the cooling pump on August 7. It lasted 8 hours and 3 minutes, earning distinction as the longest International Space Station-based spacewalk and the sixth longest spacewalk in history, according to NASA. The duo's August 11 spacewalk lasted 7 hours and 26 minutes. The spacewalks were planned several days apart to give crew members time to rest and managers on the ground time to review data and make necessary adjustments, NASA said. NASA said a fourth spacewalk related to this repair may be required to clean up the work site.