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Crew Prepares for Spacewalks

Published by Matt on Thu Aug 5, 2010 8:12 am via: NASA
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Spacewalk preparations continue to preoccupy the Expedition 24 crew aboard the International Space Station as it gets ready to conduct a pair of spacewalks aimed at replacing a failed ammonia pump module. The pump failed Saturday night after a spike in electrical current tripped a circuit breaker. When the 780-pound pump failed, it shut down half of the station’s cooling system.

Flight Engineers Doug Wheelock and Tracy Caldwell Dyson are scheduled to start the first spacewalk at 6:55 a.m. EDT Friday to unbolt and remove the failed pump module, and install the spare. NASA TV coverage will begin at 6 a.m.

Wheelock, who will be designated as EV1, or extravehicular crew member 1, wearing the spacesuit bearing the red stripes, will be making the fourth spacewalk of his career. Caldwell Dyson, designated as EV2, wearing the unmarked spacesuit, will be making her first spacewalk.

The second spacewalk to hook up a variety of electrical and fluid connections for the new pump module is targeted for Monday.

Wheelock and Caldwell Dyson originally were scheduled to perform a spacewalk to outfit the Russian Zarya module for future robotics work and prepare the station for the installation of a new U.S. permanent multipurpose module. However, because of the importance of restoring redundancy to the station’s cooling and power systems, the two new spacewalks will be dedicated to the pump module replacement.

Wednesday aboard the station, Wheelock, Caldwell Dyson and Flight Engineer Shannon Walker participated in conferences with Mission Control to review spacewalk procedures.

Meanwhile back on Earth, fellow astronauts Robert Satcher Jr. and Rick Sturckow were underwater, practicing the spacewalking tasks in the Johnson Space Center’s Neutral Buoyancy Laboratory (NBL). Astronauts Cady Coleman and Suni Williams spent Monday afternoon in the NBL to help prepare for the spacewalks as well.

Robotics experts are continuing to refine the procedures that will be used by Flight Engineer Shannon Walker to guide the station’s robotic arm, Canadarm2, as she moves Wheelock into position to swap the failed unit with a spare unit currently stored on External Stowage Platform 2. That spare parts carrier is attached to the Quest airlock that Wheelock and Caldwell Dyson will use to exit and reenter the station.

The station’s Mobile Transporter was commanded to move to the Starboard 1 truss on Tuesday. With the Mobile Transporter in position, the ground team will be able to gather additional data to confirm power resources are sufficient for Canadarm2 to support the spacewalk.

Each pump module weighs 780 pounds and is 5 ½ feet long (69 inches) by 4 feet wide (50 inches), and is 3 feet tall (36 inches). The spacewalkers will need to disconnect and reconnect five electrical connectors, four fluid quick-disconnect devices, one fixed grapple bar and four bolts. The spare pump module that will be used to replace the failed unit was delivered to the station on the STS-121/Utilization Logistics Flight-1 mission in July 2006.

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