Spacewalking astronauts made their way back inside the International Space Station today after the successful removal of an ammonia pump that failed late last month, knocking out half the cooling capability on the U.S. side of the outpost.Flight engineers Doug Wheelock and Tracy Caldwell-Dyson went through some short decontamination procedures to make certain they would not carry toxic ammonia into the closed loop environment inside the station. The two worked with ammonia coolant lines and were exposed to some leakage -- a few "snowflakes" compared to the flurry seen during an initial pump removal attempt last Saturday. A jammed fluid line connector and the more serious ammonia leak prevented the astronauts from completing the pump removal on an initial spacewalk.
Today's seven-hour, 26-minute spacewalk set the stage for a third excursion on Sunday, one that will be aimed at putting a place a replacement for the failed pump module, which was temporarily stowed on the station's mobile rail cart. The replacement work should restore full cooling capability to the U.S. side of the outpost.
Wheelock and Caldwell-Dyson removed the failed pump from a slot on the starboard side of the station's central truss after successfully disconnecting the stuck fluid line. The coolant hose was one of four connected to the pump. Three were removed last Saturday. Wheelock had to violently shake the fourth line to free it from the pump.Five electrical cables that route power and data to the pump also had to be disconnected, and four bolts holding the 780-pound pump module to the truss had to be unfastened before the astronauts could extract it and then move it to the rail cart.
The spacewalk was the 149th performed since the assembly of the station began in late 1998.
It was the fifth spacewalk for Wheelock and the second for Caldwell-Dyson.
The spacewalk Sunday is tentatively slated to begin at 6:55 a.m. EDT. Live coverage here in The Flame Trench will begin at 6 a.m.
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