Mission Atlantis: Astronauts Gear Up For Last Spacewalk

This story was updated at 9:56 a.m. EDT

HOUSTON -- A pair of astronauts will venture outside the International Space Station (ISS) one last time Sunday to prime the orbital laboratory?s newest solar wings to rotate and track the Sun.

Atlantis shuttle astronauts Patrick Forrester and Steven Swanson are due to begin the final spacewalk of NASA?s STS-117 mission at 12:33 p.m. EDT (1633) and spend more than six hours working on the station?s new starboard trusses and other areas.

?There?s nothing on this EVA that I think is challenging,? NASA ISS program manager Mike Suffredini said Saturday of the extravehicular activity (EVA). ?But they all will take time, so how much of this we get done is to be determined.?

Forrester and Swanson are expected to perform a series of tasks carried over from previous STS-117 spacewalks, including engaging a cross-wired gear on the station?s starboard side and coaxing a stubborn vent heat shield into place.

The spacewalk is the fourth for Atlantis? STS-117 crew and an added bonus after mission managers extended the mission by two extra docked days last week. The extension allowed the repair of a torn heat-resistant blanket on the orbiters left engine pod.

Inside the space station, six Russian control and navigation computers remain operational after being fully activated Saturday after a major shutdown last week. Aside from the station?s Russian-built Elektron oxygen generator, which engineers are holding off on restarting pending final checks, most of the systems affected by the glitch are back online, mission managers said.

?We can report that things are still improving,? ISS flight director Holly Ridings said early Sunday. ?We?re back to almost nominal in terms of all the systems.?

On Monday, ISS flight controllers plan to activate the station?s Russian attitude control system for about 45 minutes as a final check on the health of the computers, Ridings added.

Clean up crew

The primary tasks for Forrester and Swanson revolve around the station?s new starboard Solar Alpha Rotary Joint (SARJ) that bridges the recently delivered Starboard 3 (S3) and Starboard 4 (S4) truss segments installed during the STS-117 mission.

During their Wednesday spacewalk, Forrester and Swanson were unable to completely remove a series of launch restraints that secured the SARJ inside Atlantis? payload bay for its June 8 launch. They also discovered that the two gear motors designed to drive the SARJ?s rotation were cross-wired, with command for one affecting the other, but were unable to verify that both were engaged at the time.

The two spacewalkers are expected to pick up where they left off on their last EVA to prime the SARJ which, once freed, will be able to rotate its new starboard solar arrays like a Ferris wheel to track the Sun. They will also clear the S3/S4 segments of obstructions on rails for the station?s railcar-like Mobile Transporter, which serves as a base for the outpost?s robotic arm, so it can aid in ISS assembly tasks on the new truss.

?Those are the two big things we need to accomplish tomorrow,? Swanson said Saturday. ?Those are big keystones in building the space station.?

If time allows, the spacewalkers may also revisit a recalcitrant hydrogen vent heat shield on the station?s Destiny module. Fellow STS-117 spacewalkers James Reilly and Danny Olivas were unable to reattach it Friday after installing the new vent, NASA said. They are also expected to route a computer cable along the exterior of the station's Unity node, the agency said.

Suffredini has said that he hopes the spacewalkers will have time to install a video camera stanchion - to free up hardware to be discarded on a future spacewalk - and engage locks on a broken antenna so it can be returned to Earth for repair.

NASA is broadcasting the space shuttle Atlantis' STS-117 mission live on NASA TV. Click here for mission updates and SPACE.com's video feed.

• SPACE.com Video Interplayer: Space Station Power Up with STS-117
• STS-117 Power Play: Atlantis Shuttle Crew to Deliver ISS Solar Wings
• Complete Shuttle Mission Coverage