Spacewalkers Doug Wheelock, Tracy Caldwell Johnson struggle with cooling system lines outside the International Space Station Photo Credit/NASA TV
Spacewalking astronauts Doug Wheelock and Tracy Caldwell Dyson wrestled with balky fluid lines and leaking ammonia on Saturday as they began a series of excursions to replace a failed cooling system pump outside the International Space Station.
Saturday’s spacewalk exceeded eight hours and left NASA’s Mission Control in a quandary about how to deal with the toxic leaks.
The space agency plans a second and potentially a third spacewalk by the two astronauts to finish the replacement of the 780 pound pump module assembly on the station’s solar power system truss. The next spacewalk will take place no sooner than Aug. 11.
The pump experienced an internal electrical short on July 31, shutting down half of the station’s cooling system. The pump circulates ammonia through external radiator panels that jut from the truss to cool the heat generated by the station’s avionics, life support equipment and research gear.
During Saturday’s outing, Wheelock and Caldwell Dyson worked methodically in an effort to disconnect four ammonia coolant lines.
But the “quick disconnect” mechanism on the old pump assembly ammonia lines proved to be problematic. The lines were stiff and the connection mechanisms resisted efforts by Wheelock to pull them apart. As he pried, pushed and hammered, the carbon dioxide sensor inside his space suit faltered, another factor in the decision by Mission Control to delay efforts to remove the old pump module.
One of the four coolant lines could not be disconnected; and without a new strategy to separate the leaky plumbing , the old pump cannot be removed.
As a precaution, the flight control teams instructed Wheelock and Caldwell Dyson to spend some extra time in the airlock with the outer hatch open as they wrapped up Saturday’s spacewalk. The procedure was to allow any stray coolant on their spacesuits to evaporate before the astronauts re-entered the space station.
During additional spacewalks, the astronauts intend to remove the old pump module and store it on the mobile transporter, an electric rail car that moves along the station’s solar power truss.
A $3.9 million replacement pump is fastened to a storage platform on the station’s Quest airlock. Wheelock will position himself on the tip of the station’s robot arm to move the new pump module from the platform to its cooling system mount on the truss.
As she did on Saturday, station astronaut Shannon Walker will serve as the robot arm operator.