This story was updated at 8:06 a.m. EDT.
Two spacewalking astronauts have ventured outside the International Space Station Monday to attach a delicate communications antenna during a tricky service call.
Atlantis shuttle astronauts Garrett Reisman and Stephen Bowen floated outside the station's Quest airlock at about 8:04 a.m. EDT (1204 GMT); they plan to spend more than six hours making the space delivery.
Reisman will spend much of the spacewalk riding the station's outstretched robotic arm between a cargo pallet and the top of the orbiting laboratory as it moves like a giant, 57-foot (17-meter) windshield wiper to retrieve parts of the antenna.
Mission Control expects the views of Reisman on the robotic arm to be spectacular.
"He'll just get a God's eye view of the International Space Station and of Atlantis as he flies over with these pieces of the communications antenna," shuttle flight director Mike Sarafin said Sunday, adding that Reisman's hands should be empty on return trips to get more antenna parts. "If I were him, I'd grab a few snapshots then."
Tricky space delivery
For Reisman, however, the robotic arm ride also promises to be tricky.
The 6-foot (1.8-meter) wide antenna dish he'll be hauling is bulky and big, and will block his view when he hauls it to its destination on the Z1 truss atop the station's central Unity module. That means Bowen will have to guide him in carefully while astronauts Piers Sellers and Tracy Caldwell Dyson ? who will be operating the station's robotic arm from inside the outpost ? take great care to move Reisman into position.
The antenna dish is fragile, too.
"There's a danger of dinging that dish before we have a chance to install it," Reisman told SPACE.com before launch.
The astronauts have never rehearsed the delicate work in its entirety. NASA's spacewalk practice pool isn't big enough to simulate the actual station worksites for the job from start to finish, Reisman has said. The rehearsals had to be broken down into pieces, he added.
The antenna is a vital spare for the station's communications system and is responsible for providing backup telephone, e-mail, video and other two-way communication services between the station and its Mission Control centers on Earth.
Atlantis arrived at the space station Sunday after a two-day orbital chase that began with a Friday launch from Florida. [Atlantis shuttle launch photos.]
Today's spacewalk is the first of three planned for the shuttle's 12-day mission, which is slated to the last flight of Atlantis and also includes the delivery of a new Russian room for the station.
Other spacewalking work
Reisman and Bowen also have a few other tasks on their plate for today's spacewalk once they complete the antenna installation.
The astronauts plan to install a spare parts storage platform on the station's Canadian-built Dextre robot and loosen some bolts on the solar array batteries that will be replaced by Atlantis spacewalkers later this week. Today's spacewalk will be the second for Reisman and the fourth for Bowen.
They will not, however, try to free a snagged cable that is blocking a sensor on Atlantis' 100-foot (30-meter) inspection boom, mission managers said.
The cable is blocking a sensor from panning and tilting properly, and prevented the Atlantis crew from completing a full inspection of the shuttle's heat shield on Saturday.
Mission managers aren't sure how the snag occurred, but think it should only take 10 minutes or so for spacewalker to move it clear. That chore, because of time constraints on this mission's extremely full spacewalks, would be reserved for later excursions on either Wednesday or Friday, mission managers said.
"It will be about as simple as you can possibly imagine," said LeRoy Cain, head of Atlantis' mission management team. "All we want to do is move that cable away from the unit."
A decision on which spacewalk to add that chore to will be made early this week, Cain added.
Atlantis' mission is the shuttle's final planned spaceflight after 32 missions since it entered service in 1985. Only two more shuttle flights are scheduled (on Discovery and Endeavour, respectively), before NASA retires the orbiter fleet later this year.
However, Atlantis will not be mothballed immediately since it must also be ready to serve as a rescue ship for the final planned shuttle mission on Endeavour, which is slated to launch no earlier than Nov. 27, NASA shuttle officials have said.
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SPACE.com is providing complete coverage of Atlantis' STS-132 mission to the International Space Station with Senior Writer Clara Moskowitz and Managing Editor Tariq Malik based in New York. Click here for shuttle mission updates and a link to NASA TV. LIVE spacewalk coverage begins at 8:15 a.m. ET.