Friday, April 09, 2010

Discovery spacewalkers near first of three excursions

The first of Discovery astronauts' three planned spacewalks is near as mission specialists Rick Mastacchio and Clay Anderson run through final preparations inside a sealed portion of the International Space Station's Quest airlock that is being depressurized.

Scheduled to begin at 1:41 a.m. but running slightly ahead of schedule, the planned six-and-a-half hour excursion will begin a three-spacewalk effort to swap out depleted ammonia coolant tanks on the right side of the outpost's central truss.

Today's work is intended to position a boxy Ammonia Tank Assembly hauled up in Discovery's payload bay for installation on the second spacewalk.

The spacewalkers will unbolt the new assembly and hand it to the station robotic arm, operated by pilot Jim Dutton and mission specialist Stephanie Wilson, for movement to a temporary stowage location.

Other tasks planned this morning: retrieving a Japanese plant seed experiment from the Kibo lab's exposed "porch," and replacing a failed Rate Gyro Assembly, a small box of sensors that help compute the spacecraft's changing position in space.

Mastracchio, the lead spacewalker, has the radio call sign of "EV-1," while Anderson is "EV-2." Mastracchio's spacesuit has red stripes on the legs and his helmet camera shows No. 18 in the bottom right corner; Anderson's suit is all white and his helmet camera shows No. 16.

Mastracchio and Anderson are veterans of three previous spacewalks, each totaling about 18 hours -- a number that should double on this mission.

They performed two of those together in August 2007, while Mastracchio was visiting the station with Endeavour's STS-118 crew and Anderson was a long-duration Expedition 15 crew member.

Mission specialist Dottie Metcalf-Lindeburger will serve as the Intra-vehicular Officer, or IV, helping to choreograph the spacewalkers' moves from inside Discovery's flight deck.

Also inside the station, mission specialist Naoko Yamazaki, the mission's "loadmaster," is overseeing the transfer of a large freezer and an exercise device from the Leonardo cargo module onto the station.

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