Live in Orbit: Crews Grapple Girder

Blogger update, 12:08 p.m.: Movement of the "S6" truss has begun.

Astronauts steering a robotic arm from inside the International Space Station have grabbed hold of a 31,000-pound girder packed inside shuttle Discovery's payload bay at 11:45 a.m. EDT.

It's the first in a series of moves that will position the 45-foot aluminum truss segment called "S6", or Starboard 6, for installation during a spacewalk Thursday.

Discovery crew members John Phillips and Sandra Magnus are controlling the station's robotic arm, shown at left.

Next, latches fastening the truss into the payload bay must be released.

Later, a little after 2 p.m., they'll hand the truss off to the shuttle's robotic arm and slide the station arm to the far starboard end of the outpost.

Around 6 p.m., the shuttle's arm, operated by Discovery pilot Tony Antonelli and mission specialist Joe Acaba, will hand the truss back to the station arm.

It will remain "parked" overnight, ready to be installed Thursday.

The relocation of the truss is done very slowly to ensure that momentum generated by the move doesn't cause space station gyroscopes to lose control and push the station off course.

"Some people think lose control means you're going to go spinning wildly through space, and that's not the true," Paul Dye, lead shuttle flight director, said during a briefing Tuesday. "It just means that you can't hold the attitude that you wanted, and you're going to slowly drift out of attitude. Well, we don't want that to happen.

The truss holds a final pair of solar array wings that will complete the station's power supply when deployed.

That will double the amount of electricity available for science experiments, and support a planned doubling of station crews from three to six people this summer.

Mission specialists Steve Swanson and Ricky Arnold today are preparing for Thursday's spacewalk to install the S6 truss, checking out their suits and tools and reviewing procedures.

It's the first of three spacewalks planned during the 13-day mission.

IMAGES: Click to enlarge the images grabbed from NASA TV. Above, the station's robotic arm prepares to grapple the Starboard 6 truss from shuttle Discovery's payload bay. Astronauts John Phillips and Sandra Magnus operated the arm.