August 7, 2010

 Image of Expedition 24 Flight Engineers Doug Wheelock (foreground) and Tracy Caldwell Dyson working on the International Space Station’s S1 Truss during the first of two spacewalks to replace a failed ammonia pump module. Credit: NASA TV

A pair of space station astronauts ventured out on an urgent spacewalk this morning to restore a crucial cooling system - one of the most challenging repairs ever attempted at the orbiting lab. According to NASA, Expedition 24 Flight Engineers Doug Wheelock and Tracy Caldwell Dyson switched their spacesuits to battery power at 7:19 a.m. EDT, signaling the start of the first of two spacewalks that will focus on removing the ammonia pump module that failed last Saturday and putting its replacement in place.

The ammonia pump shut down last weekend and knocked out half of the space station’s cooling system. To cope with the failure, the six-person crew had to turn off all unnecessary equipment and halt science experiments. NASA engineers spent this week developing the emergency repair plan and astronauts in Houston rehearsed every step of the spacewalk while submerged in NASA’s huge training pool. The repair tasks, which include removing the failed pump module from the S1 Truss and retrieving a spare from an external stowage platform, are expected to take about 6.5 to 7 hours. They are scheduled to complete installation and activation of the new pump module during the second spacewalk planned for Wednesday at 6:55 a.m. EDT.

According to NASA, Wheelock is the designated extravehicular crew member, so he is wearing the spacesuit bearing the red stripes and conducting the fourth spacewalk of his career. Caldwell Dyson, designated as EV2, is wearing the unmarked spacesuit and making her first spacewalk. Flight Engineer Shannon Walker is operating Canadarm2, the station’s robotic arm, and assisting the spacewalkers from inside the station. Their mission is considered so difficult that two spacewalks are required. Each pump module weighs 780 pounds (353 kg) and is 5 1/2 feet long (69 inches) by 4 feet wide (50 inches). They are also about 3 feet tall (36 inches), making them very bulky and difficult to move.

There is streaming live video coverage on if you’d like to see this project in action. Thanks also to the folks at also for the diagram below, detailing the repair.


Posted by: Seymour Simon

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