NASA’s Mission Control focused Christmas Day activities on restoring thermal control systems aboard the six person International Space Station to normal operations.
Those efforts were to be followed by a return of powered equipment throughout the six person orbiting research lab to action, including science experiments that were suspended when a flow control valve in an external cooling system pump faltered on Dec. 11.
U. S.astronauts Rick Mastracchio and Mike Hopkins responded with emergency spacewalks on Dec. 21 and Dec. 24 to remove and replace the degraded pump module with a spare that included an active flow control valve. Mastracchio and Hopkins were so successful a third spacewalk, originally penciled in for Christmas Day, was unnecessary.
“Everything looks good, Houston,” Mastracchio alerted Mission Control in Houston, Tex., as the Christmas Eve spacewalk activities 260 miles above the Earth came to a close.
A pump module failure is among what NASA’s Mission Operation team considers a member of the “Big 14,” a list of high priority equipment failures that could jeopardize station operations, even the ability to keep astronauts aboard.
The station depends on two cooling circuits, Loops A and B, to circulate ammonia coolant through radiator panels attached to the long left and right side solar power trusses. The cooling system dissipates heat generated by internal and external electronics, including life support systems and science experiments, to space through the circulation of ammonia, a toxic substance.
The Dec. 11 failure degraded Loop A, prompting the shutdown of non essential hardware, including equipment in the European Space Agency’s Columbus and Japan’s Kibo science modules as well as the U. S. Harmony module. The failed flow control valve allowed ultra cold ammonia to reach heat exchangers in theU. S.segment that circulate water for the thermal control of habitable modules. Too much ammonia exposure could freeze the water loops, causing damage to the plumbing and the possible escape of unwanted ammonia into the station’s living volume.
The two spacewalkers and spacewalk planners were aided by the experiences of astronauts Doug Wheelock and Tracy Caldwell Dyson, who contended with a similar pump module failure in 2010. Their repair campaign required three spacewalks.
However, Mastracchio and Hopkins were the first to attempt spacewalks in NASA space suits since a July 16 incident in which Italian astronaut Luca Parmitano’s NASA space suit helmet leaked water. The leak source was traced to a plugged fan pump separator in the personal life support system backpack of his NASA space suit. In the failed state, the fan pump diverted cooling system water into a helmet air flow vent.
Hopkinswore Parmitano’s suit but with a new fan pump separator. NASA ground controllers also had the spacewalkers place absorbent pads in the back of their helmets and install makeshift snorkels in their space suits for the Dec. 21 and 24 repair activities.
Neither Mastracchio nor Hopkins reported a similar leak. They did contend with small leaks of frozen ammonia as they removed and replaced coolant lines during the repairs. The exposures, however, were minor.
Japanese astronaut Koichi Wakata served as the station’s robot arm operator during the repairs, moving Mastracchio and Hopkins around the outside of the station with the 58-foot-long robot arm.