Per NASA press release:
At 9:22 a.m. EDT, Expedition 28 spacewalkers Mike Fossum and Ron Garan switched their suits to battery power, signifying the start of today's six-hour, 30-minute excursion.
This is Fossum's seventh spacewalk and Garan's fourth. Fossum and Garan collaborated on three spacewalks during the STS-124 space shuttle mission in June 2008.
Fossum, EV-1, is the lead spacewalker and is wearing a suit with red stripes, while Garan, EV-2, wears an all-white spacesuit. Fossum's helmet camera displays the number 20 and Garan's the number 18.
Atlantis Mission Specialist Rex Walheim is at the rear flight deck of Atlantis, choreographing the activities and coordinating communications between the spacewalkers and Mission Control in Houston. Shuttle Pilot Doug Hurley and Mission Specialist Sandy Magnus will operate the station's 58-foot-long robotic arm to maneuver the spacewalkers around during the spacewalk.
Once outside, the spacewalkers will retrieve a pump module (PM) from an external stowage platform and store it in Atlantis' cargo bay for return to Earth. Garan will climb aboard the station's robotic arm and grab the pump module while Fossum releases a bolt that holds the PM in place. Grasping the 1400-pound module, Garan then will ride the arm from the stowage platform near the Quest airlock to a carrier in Atlantis' cargo bay. He will place the PM into the carrier and Fossum will bolt it in place. The pump module failed in 2010, shutting down half of the space station's cooling system. Engineers will evaluate the PM to determine the cause of the failure and plan to refurbish it for use as a spare.
Next, Fossum will trade places with Garan and climb onto the station arm. He will grab the Robotic Refueling Mission (RRM) experiment from the shuttle bay and ride the arm to Dextre, the Special Purpose Dexterous Manipulator. The spacewalkers will dock the RRM to a platform on Dextre that is used to hold equipment for the robot to use. The RRM will demonstrate and test tools, technologies and techniques that could be used to robotically refuel and repair satellites in space. Data from the tests could help reduce the cost and risk of future robotic refueling missions.
Fossum and Garan will deploy the Optical Reflector Materials Experiment, a portion of the Materials International Space Station Experiment (MISSE) 8 that was installed on the External Logistics Carrier 2 during STS-134. They also will take photos of the material samples. MISSE 8 will be retrieved late next year.
Next, the pair will troubleshoot a protruding grounding wire on a Zarya module payload data grapple fixture that was installed on STS-134. The multi-layer insulation (MLI) grounding wire is stuck in a latch door, where power and data connectors mate with connectors behind the door. With the wire extending out, there is concern the door could interfere with the robotic arm. The spacewalkers will pull back the MLI, insert a hook into the latch door to free the wire, then pull it back to the outside of the grapple fixture where it belongs. They will tuck the wire under Velcro tabs and put the MLI back in place. Fossum and Garan will perform the same operation on a second latch door and check the remaining two latch doors.
The spacewalkers will install a cover on the end of pressurized mating adaptor 3, which receives a great deal of sun.
This is the 160th spacewalk supporting assembly and maintenance of the space station and the 249th excursion conducted by U.S. astronauts.