This story was updated at 4:49 p.m. EDT.
Two spacewalking astronauts began a tricky battery swap on the space station's solar arrays Wednesday, a job that is expected to take two full spacewalks to complete.
Atlantis mission specialists Michael Good and Stephen Bowen got ahead of schedule, successfully installing more than half of the new batteries. In addition, they were able to fix a snagged cable that was plaguing a sensor camera on shuttle Atlantis and tighten the connection between a stuck antenna and its stand.
It was the second of three planned spacewalks, or extravehicular activities (EVAs) for the shuttle Atlantis' 12-day STS-132 mission, the orbiter's final planned spaceflight.
"We had a really successful EVA today," lead space station flight controller Emily Nelson said Wednesday. "We're all incredibly excited. I don't think Mission Control could be any more proud."
Overall, the spacewalkers spent a little over seven hours floating outside the space station, and ended the spacewalk at 1:47 p.m. EDT (1747 GMT).
"Seems to me you guys are cruising, like you're riding a tsunami," spacewalk coordinator Tony Antonelli said from inside the space station at one point, commenting on how quickly Good and Bowen were moving through their checklists.
The spacewalkers exited the hatch of the station's Quest airlock ahead of schedule, beginning the excursion at 6:38 a.m. EDT (1038 GMT).
Bowen swiftly dispatched with the cable task, easily finding the spot where a cable connecting to a camera on Atlantis' sensor system was stuck, restricting the camera's motion. He was able to wire-tie that cable to another cable nearby to ensure it doesn't get caught again.
"You're awesome, man," Antonelli said.
"All right, there it is," Bowen said, wrapping up the job.
The camera is a tool used to scan the orbiter's sensitive heat shield to make sure it is intact and safe for the return trip to Earth. Shuttle astronauts conducted their usual inspection of the heat shield Saturday, a day after Atlantis launched into space. They had to switch to a backup camera, though, when the primary tool couldn't move and tilt fully because of the pinched cable.
Now the camera should be in working order, and available to use if any further inspection of Atlantis' heat shield is necessary.
After fixing the sensor camera, Bowen moved out to join Good at the far-left side of the orbiting laboratory, a spot called the P6 truss. There, the astronauts began their major task of the day: swapping out a set of aging solar array batteries with brand new ones.
The location also afforded a nice perspective on the Earth below.
"Steve-O, the view's not bad from out here, huh?" Good said, calling Bowen by his nickname.
"Yeah, it's incredible," Bowen replied.
The spacewalkers got to work removing the old batteries from the station and exchanging them for new ones brought up to space by Atlantis on a cargo carrier. For each swap-out, they had to move the old battery off the station and onto a temporary stowage platform, then secure it down on the cargo carrier, after making room by lifting out the new one.
Because each battery is large and weighs a hefty 375 pounds (170 kg), the process is more complicated than it sounds. Nonetheless, the job went swiftly and smoothly. While Bowen and Good were only supposed to install three of six new batteries on this spacewalk, they managed to dispatch with four of them.
That leaves only two more batteries to be installed by Good and mission specialist Garrett Reisman on the mission's third and final spacewalk, set for Friday.
The new batteries will help outfit the space station for the coming years, especially for the era after the space shuttles are retired at the end of 2010. The batteries are designed to last 6 1/2 years, but the old ones have been functioning even longer.
NASA hopes to keep the space station running through 2010, with unmanned cargo ships, Russian Soyuz spacecraft and possibly even U.S. commercial crew vehicles traveling to and from the orbiting lab. None of these, however, can carry as much cargo as a space shuttle, so the final shuttle flights are aimed at toting up as much large hardware as possible.
The spacewalkers' final task was to try to tighten the connection between a spare space-to-ground antenna and its pedestal-like boom.
The antenna, which will serve as a backup for communications between the space station and Mission Control centers on Earth, was delivered by Atlantis and attached to the station during the mission's first spacewalk on Monday.
Those spacewalkers weren't able to complete the installation because they noticed a gap between the antenna dish and its boom that they couldn't close. But when Bowen and Good went back to the site, they were able to crank the bolts tight enough to secure the antenna.
"Today was just an incredible, incredible EVA," said STS-132 lead spacewalk officer Lisa Shore. "We accomplished more than we ever hoped going out the door."
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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.