August 11, 2010

Astronauts Finalize Second Spacewalk, Third Planned

Astronauts completed a successful spacewalk on Wednesday to remove a broken coolant pump on the International Space Station (ISS).

Their previous spacewalk on Saturday to restore full cooling to the ISS was foiled by a large ammonia leak.

Wednesday's spacewalk succeeded with no burst of toxic ammonia from a stubborn connector.

The ISS has been operating with only half its usual cooling capability since an ammonia coolant pump failed a week and a half ago.

Just five hours into the spacewalk, the astronauts removed the broken 780-pound pump, with just barely enough time to perform a few more chores.  A third spacewalk is planned for Sunday to install a spare pump.

Astronaut Doug Wheelock had to force a jammed connector back and forth for several seconds before coming off the failed pump.  He jerked so hard that the helmet camera felt the shock, leaving bump and static filled images being viewed by Mission Control.

"We didn't tell the guys inside to hold on when you did that," Mission Control joked.

Flight controllers lowered the pressure in the disabled cooling line just before Wednesday's spacewalk.  None of the major leakage that occurred during Saturday's spacewalk occurred Wednesday.  The spacewalkers had to hammer the connector loose that caused a leak to develop around the jammed connector. 

NASA originally planned for two spacewalks to perform this operation.  However, the jammed connector and ammonia leak on the first spacewalk set everything back. 

Since the July 31 malfunction, the ISS has been using just a single cooling loop.  NASA wants the second line up and running as soon as possible incase the first one also breaks.  That would leave the space station with only a limited amount of time for emergency repairs before the crew would have to leave the orbiting lab behind.

There are three Americans and three Russians currently on board the ISS.  They live and worked 220 miles above Earth.

Engineers expect that an electrical short led to the pump shutting down.


Image Caption: Expedition 24 Flight Engineers Doug Wheelock (right) and Tracy Caldwell Dyson work to replace a failed ammonia pump module outside of the International Space Station. Credit: NASA TV


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