NASA Astronauts Mike Fossum, Ron Garan Dress for STS-135 Mission Spacewalk

JAXA astronaut Satoshi Furukawa, left, assits NASA astronaut Mike Fossum prepare for spacewalk
in International Space Station airlock.  Photo Credit/NASA TV


Two astronauts suited up early Tuesday for the STS-135 mission's only spacewalk, a 6 1/2 hour excursion outside the International Space Station to move hardware in and out of the payload bay of shuttle Atlantis.

Space station astronauts Mike Fossum and Ron Garan will carry out two primary tasks, then tackle a list of maintenance activities. The shuttle's crew was too small, just four astronauts, to take on the spacewalk in addition to cargo exchanges while Atlantis is parked at the orbiting science laboratory.

Once outside the station's airlock, Fossum and Garan will literally turn around to find a failed 1,400 pound thermal control system coolant pump awaiting transfer to the shuttle's payload bay so that it can be returned to Earth.

The spacewalk is scheduled to get under way at 8:44 a.m., EDT, but could begin later.

The pump sustained a sudden and yet-to-be-explained electrical failure on July 31, 2010. The breakdown halted all cooling on the station's starboard side, which in turn prompted a dramatic power down. Station astronauts Doug Wheelock and Tracy Caldwell Dyson responded with three difficult spacewalks over the next two weeks to replace the pump with a spare.

Fossum and Garan will also transfer a satellite refueling technology demonstrator from Atlantis to DEXTRE, the two-armed Canadian robot that resides on the station's exterior. Tests of robotic techniques for future satellite refueling are planned for later this year.

The spacewalkers will also attempt to remove a snagged grounding strap from a power and data grapple fixture installed on the station's Russian segment by NASA astronauts in May.

The PDGF will serve as a Russian anchor point for the long reach of the station's Canadian robot arm, which often serves as a mobile work platform for astronauts assigned to spacewalk repairs.

Atlantis lifted off Friday on the shuttle program's final mission, a 12-day re-supply flight to the space station.

The flight was extended to a 13th day by mission managers on Monday -- a day after Atlantis docked with the orbital outpost.  

Tags: os99, NASA, International Space Station, space shuttle