The two astronauts are scheduled to begin a planned 6½-hour space walk about 9:30 CDT this morning to install an additional docking port - Pressurized Mating Adapter 3 - and ready the Z1 Truss for installation of the large solar arrays that will be delivered by the next shuttle crew in late November. The first task for Wisoff and Lopez-Alegria will be to release the latches that hold the PMA-3 in place and to provide Koichi Wakata with visual cues as he uses the robotic arm to gently raise PMA-3 from its support platform in Discovery's payload bay.
As Wakata maneuvers PMA-3 to its new location on the Unity module, Wisoff and Lopez-Alegria will release latches at the top of the Z1 Truss and prepare the work surface of the attach point for the large solar arrays that will be delivered during the STS-97 mission in November. They will then work their way back to Unity to act as an extra set of eyes providing Wakata with guidance as he attaches the PMA-3. Once the crew sees a series of "ready to latch" indicators, Pilot Pam Melroy will use a laptop computer to command latches and bolts to secure the PMA to its new home on the Unity module, much as she did during the installation of the Z1 truss on Saturday. However, today she will command only the first of four stages of the bolting process to allow seals on both the PMA and the common berthing mechanism on Unity to reach thermal equilibrium. The final commanding will be done by the flight crew Tuesday morning, after flight controllers in Houston confirm that the temperature variances between the two seals are within acceptable limits.
In the ISS flight control room this morning, the Power, Heating, Articulation, Lighting and Control Officer - PHALCON - successfully completed work with the two Plasma Contactor Units (PCUs) mounted on the Z1 truss. The PCUs, which are designed to discharge electrical current on the station and in its immediate environment, were launched with their valves open to allow a continual discharge of xenon gas to prevent contamination of the units. This morning, the PHALCON powered on and purged the units, closed the valves and deactivated the PCUs. The units will be powered on during the STS-97 mission once the solar arrays are deployed and begin generating current.
Today's scheduled space walk will be the eighth space station assembly space walk, the 52nd EVA in the space shuttle program and the 91st by Americans in the history of the U.S. space program.