Two American astronauts are heading outside the International Space Station for the last of three spacewalks planned during shuttle Discovery's stay at the orbiting outpost.Discovery mission specialists Ricky Arnold and Joe Acaba switched their spacesuits to battery power at 11:37 a.m., marking the start of the excursion about five minutes ahead of schedule.
The two stepped through a series of safety tether checks -- inspections aimed at making certain their braided steel safety lines were hooked up properly. They also checked their jet backpacks, which are equipped with small nitrogen gas jets and would be used to fly back to the station if their tethers broke and they tumbled away from the outpost.
Arnold and Acaba exited the U.S Quest airlock as the joined shuttle-station complex was flying 220 miles above central Asia.
"Take your time. Enjoy it, and do good work. We're counting on you," station skipper Mike Fincke said.
"Thanks, Mike," the spacewalkers both replied.
The astronauts now are crawling hand-over-hand to the port side of the station's central truss, where they aim to position a rail cart for future assembly and maintenance work at the outpost.
Mission specialist John Phillips will be moving the station's robot arm toward the rail cart. Acaba will be attaching a portable foot restraint to the end of the arm, and then he'll climb atop it. Once Acaba has the rail cart in hand, Phillips will move him to a new location on the starboard side of the truss and the cart will be secured at its new work site.
The second job: trying to set up an experiment platform that Acaba and crewmate Steve Swanson were failed to fully deploy during a spacewalk Saturday. Acaba and Swanson installed a latching pin backwards and were unable to fully deploy the platform as a result.
Arnold is wearing an all-white spacesuit and is answering to the radio call sign "EV-2" Acaba is wearing a spacesuit with broken red stripes and is answering to the radio call sign "EV-3."
Both are wearing helmets equipped with cameras the size of lipstick tubes. The Wireless Video System enables crewmates and engineers in Mission Control to get up-close looks at ongoing work from the spacewalkers' perspective.
A small 16 in the right hand corner of helmet-cam views indicates the live video is being beamed back from Arnold's spacesuit. A small 18 indicates the view is coming from Acaba's helmet-cam.
Crewmate Steve Swanson is directing the spacewalk from inside the joined shuttle-station complex. The excursion is expected to last 6.5 hours.
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