9 a.m. CDT Tuesday, April 13, 2010
Mission Control Center, Houston, Texas
STS-131 MCC Status Report #17
HOUSTON – Space shuttle Discovery Mission Specialists Rick Mastracchio and Clayton Anderson completed the replacement of a depleted ammonia coolant tank on the International Space Station, finishing the complex three-spacewalk process.

Today’s 6-hour, 24-minute spacewalk began at 1:14 a.m. CDT, almost an hour ahead of schedule. Mastracchio’s first task was to hook up fluid lines of the new 1,700-pound tank, a task that had been postponed from Sunday’s spacewalk after delays in bolting that tank in place.

Anderson meanwhile began retrieving some micrometeoroid shields from the Quest airlock’s exterior to put them inside. That task too had been postponed Sunday. Mastracchio helped after completing the tank’s hookup.

Mission Control said later it was having a problem activating the new tank. A stuck valve in one of the nitrogen pressurization lines was thought to be the problem. Flight controllers decided to postpone additional activation efforts in order to study the problem.

Meanwhile, Mission Specialist Stephanie Wilson and Pilot James P. Dutton Jr. used the station’s Canadarm2 to lift the depleted tank from its temporary stowage spot on the station’s Mobile Base System. The spacewalkers removed a grapple bar from the tank and the arm moved it to Discovery’s cargo bay. Mastracchio and Anderson moved to the cargo bay and helped Wilson and Dutton guide the tank for its handoff to the spacewalkers.

The spacewalkers positioned and, after some difficulty, secured the tank to the carrier in the rear of the cargo bay on which the new tank had been brought to the station. The depleted tank will be refurbished, refilled and brought back to the station as a spare.

Late in the outing, the spacewalkers bolted a grapple bar from the old ammonia tank to the new tank. Throughout the spacewalk they worked with Mission Specialist Dorothy Metcalf-Lindenburger, the in-cabin choreographer.

Because of the delay in bolting down the old ammonia tank in Discovery, the last part of the spacewalk was replanned. Retrieval of an experiment platform from the Columbus module was postponed. Mastracchio prepared cabling at the Z1 truss for installation of a communications antenna during shuttle mission STS-132 and Anderson relocated tools for use during that flight.

Today’s was the 143rd spacewalk for station construction and maintenance. It was the sixth for each astronaut bringing Mastracchio’s total spacewalking time to 38 hours, 30 minutes and Anderson’s to 38 hours and 28 minutes.

The next status report will be issued shortly after crew wakeup, which is scheduled for 10:21 p.m., or earlier if conditions warrant.

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