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Mission Managers Give "Go" for Saturday Spacewalk

Published by Klaus Schmidt on Sat Aug 7, 2010 9:48 am via: NASA
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The International Space Station’s mission management team this morning gave a unanimous “go” for the first of two spacewalks Saturday to replace a faulty oven-sized cooling system component in the station’s truss that failed last weekend.

Expedition 24’s Doug Wheelock and Tracy Caldwell Dyson are scheduled to begin Saturday’s planned seven-hour spacewalk at 6:55 a.m. EDT. The first spacewalk will focus on removing the ammonia pump module that failed last Saturday and putting its replacement in place. NASA Television coverage of the spacewalk will begin at 6 a.m. EDT.

Flight Engineers Tracy Caldwell Dyson (foreground) and Doug Wheelock work inside the Quest airlock preparing for Saturday morning's spacewalk. Credit: NASA TV

Flight Engineers Tracy Caldwell Dyson (foreground) and Doug Wheelock work inside the Quest airlock preparing for Saturday morning's spacewalk. Credit: NASA TV

A second spacewalk is planned Wednesday to connect fluid ammonia lines to the replacement pump. Mission managers plan a final review of that plan early next week, incorporating updated information on the station’s configuration after the first spacewalk.

The spacewalks are challenging because the crew will be handling ammonia lines at full operating pressure, which makes the lines stiff during reconnection and mating. The timeline for the spacewalk will require numerous “break-out points” to ensure adequate time to complete decontamination procedures if the crew comes in contact with ammonia.

Teams of flight controllers, engineers, and spacewalk and robotics experts took an additional day to refine plans for the spacewalk and to give the station crew a full day to review the plans.

Aboard the station, Wheelock, Caldwell Dyson and Flight Engineer Shannon Walker participated in conferences with Mission Control to review spacewalk procedures. They begin a standard “camp-out” period at 3:55 p.m. today, and sleep in the Quest airlock module overnight. The crew is scheduled to awaken at 2 a.m. Saturday to begin final preparations for their repair work.

Robotics experts have devised procedures that will be used by Expedition 24’s Shannon Walker to guide the station’s robotic arm, Canadarm2, from the robotics workstation in the Destiny Laboratory. She will move Wheelock into position to swap the failed unit with the spare unit, 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.

NASA managers have anticipated and planned for such system failures throughout the station’s lifetime by storing key spare parts on the station for just this purpose. There are four replacement pumps on storage platforms at various locations on the station’s structure, delivered during previous space shuttle missions. Both the Japan Aerospace Exploration Agency’s H-II Transfer Vehicle and future commercial resupply craft will be able to deliver additional spare parts as needed.

This will be the 15th expedition spacewalk using U.S. extravehicular mobility unit spacesuits and executed without a space shuttle present. Overall, it will be the 148th spacewalk in support of station assembly and maintenance. 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 station’s Mobile Transporter was moved 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.

On Wednesday, 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 helping to prepare for the spacewalks as well.

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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