Spacewalkers set for mission's first excursion

Two Endeavour mission specialists are suited up for the first of the last four spacewalks shuttle astronauts will perform before the shuttle program's end this year.

Lead spacewalker Drew Feustel and partner Greg Chamitoff were scheduled to float out of the International Space Station's Quest airlock around 3:15 a.m., and may be a few minutes ahead of schedule.

Over six-and-a-half hours, they plan to install and retrieve science experiments stored outside the station, install a communications antenna and link up jumper cables before Sunday's planned refilling of an ammonia coolant loop.

Fuestal, 45,  served as a Hubble Space Telescope repairman on the final mission to service the observatory in 2009. He logged nearly 21 hours on three spacewalks, but is making his first outside the station.

It's the first spacewalk for Chamitoff, 48, who in 2008 spent 183 days living and working inside the station as a flight engineer on Expeditions 17 and 18.

The mission's third spacewalker, Mike Fincke, will coordinate today's extravehicular activiy as the "intravehicular officer," or IV, inside Endeavour's flight deck.

Feustel and Chamitoff slept in the airlock at a reduced air pressure as part of standard procedures to help purge nitrogen from their systems and prevent "the bends," or decompression sickness.

A new process will be tried out before the mission's third spacewalk that would eliminate the need for the overnight "campout" in the airlock by having the spacewalkers perform light exercise.

The airlock is being depressurized before its hatch is opened and the spacewalk begins.