Two Spacewalkers Venture Outside Station

International Space Station astronauts Mike Fossum and Ron Garan are venturing outside the outpost on the final shuttle-era spacewalk, a planned 6.5-hour excursion to retrieve a failed coolant pump and set up science and technology experiments.

Running about 40 minutes late, Fossum and Garan switched on their spacesuits to internal battery power at 9:22 a.m. as the station and docked Atlantis flew into an orbital sunrise over the Pacific Ocean. The switch throws marked the start of the 160th spacewalk carried out in the assembly and maintenance of the international outpost.

Fossum is making his seventh spacewalk, Garan his fourth. The two paired for three spacewalks on a 2008 shuttle mission that hauled up the Japanese Kibo laboratory module.

Fossum is wearing a suit with the solid red stripes on its legs and is answering to the radio call sign "EV-1."

Garan is wearing an all-white suit and is "EV-2."

The first big job will be retrieving a failed ammonia coolant pump from a stowage platform outside the U.S. Quest airlock. Garan will anchor himself to the end of the station's 57.5-foot robot arm.

Operating the arm from inside the station's Cupola, Atlantis astronauts Sandra Magnus and Doug Hurley will move Garan to the platform so he and Fossum can unbolt the pump. Garan will grasp the 780-pound pump and the crane operators will move him toward the shuttle's cargo bay. The pump is to be installed on a cargo bay pallet for return to Earth.

The pump failed last July 31, temporarily knocking out half the cooling capability on the U.S. side of the station. Three spacewalks were staged to replace the pump and return the cooling system to normal operations. Engineers on Earth want to determine the root cause of the failure and then refurbish the pump for a future return to the outpost.