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Astronauts replace space station coolant pump

Spacewalkers replace faulty ammonia pump aboard International Space Station, allowing engineers to begin re-activating critical coolant loop.

KENNEDY SPACE CENTER, Fla.--Astronauts Douglas Wheelock and Tracy Caldwell Dyson wrapped up a successful spacewalk Monday, installing a new ammonia pump to help flight controllers recover from a failure that shut down half the International Space Station's cooling systems.

"We had an extremely successful EVA today," Kirk Shireman, deputy manager of the space station program at the Johnson Space Center, said after the spacewalk. "We're very pleased with the results. We still have some more activities this afternoon and tomorrow to fully recover from the pump module failure, but things are certainly looking positive and we're looking forward to that."

Spacewalker Douglas Wheelock's helmetcam view of a newly installed coolant pump module, showing all four ammonia lines successfully mated. NASA TV

Wheelock and Caldwell Dyson had hoped to finish the excursion by installing a long extension cord between the Quest airlock and the Unity module that is needed before attachment of a cargo module during a shuttle visit in November.

But work to pack up tools and equipment used for the pump replacement work ran a bit long and the cable installation was deferred.

"We're going to call this a victory and go ahead and drop the J612 (cable) task and ingress the airlock," Oscar Koehler called from mission control.

The seven-hour 20-minute spacewalk began at 6:20 a.m. EDT and ended at 1:40 p.m., pushing the total time for three coolant system repair EVAs to 22 hours and 49 minutes. Wheelock's total through six career spacewalks now stands at 43 hours and 30 minutes, moving him up to 10th on the list of most experienced spacewalkers. Total EVA time for station assembly and maintenance stands at 944 hours and 24 minutes--39.4 days--through 150 spacewalks.

It will take flight controllers, working with the astronauts aboard the station, until Wednesday or Thursday to restore normal operations in the wake of the July 31 failure of the ammonia pump in coolant loop A.

With half the station's cooling system out of action, the astronauts had to install jumpers to transfer loads from loop A to loop B and to route additional power to the Russian segment of the station. All of that allowed the station to continue near normal operations with three of four stabilizing gyroscopes, life support systems and critical communications gear.

But with one loop out of action, experiments in the Japanese Kibo module and the European Space Agency's Columbus module had to be powered down, along with most of the science racks in the U.S. segment of the station. And with only one coolant loop in operation, the space station had no redundancy in a critical system.

As a result, NASA managers decided to defer a spacewalk planned for August 5, opting instead to stage two complex spacewalks to remove the failed ammonia pump and install a replacement. Four spare pump modules were available, stored on the station's main power truss as a hedge against failures.