Friday, April 09, 2010

Spacewalkers pry coolant tank loose

Two Discovery spacewalkers hoisted a set of ammonia coolant tanks free of Discovery's payload bay, gingerly shifting it into the grasp of a waiting robotic arm.

Mission specialist Clay Anderson needed to pry one side of the bulky tank from a cargo carrier when it wouldn't come loose after four bolts were undone.

The astronauts and flight controllers cautioned each other to pry gently, so as not to lose control of the 1,700-pound box.

The Ammonia Tank Assembly, or ATA, has been compared in size to a Smart car or small VW Beetle, or to a double industrial-size refrigerator.

Though it is weightless in space, controlling such a large mass can be challenging and dangerous for spacewalkers.

Anderson and Mastracchio handed the tanks to the station's 58-foot robotic arm, which will stow it in a temporary location on a platform near the Quest airlock.

"The big arm has got the tank," radioed Discovery pilot Jim Dutton at 3:48 a.m.

The arm can't reach the part of the station's starboard truss where the tanks will be installed. So it will be moved between today's spacewalk and the next one, planned Sunday morning.

That process will run in reverse to return an old set of tanks to Discovery's payload bay for return to Earth on a third spacewalk, planned Tuesday morning.

Next up: Mastracchio will retrieve two experiments from the Japanese Kibo lab's exposed facility, known as the "porch."

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