Today's space walk, scheduled to begin just before 9:30 a.m.CDT, paves the way for installation of the station's large solar arrays later this year as Chiao and McArthur install two current converter units to process power that will be generated by the arrays, and prepare the worksite where the arrays will be attached. The converter units - called DDCUs - are 129-pound power processing systems that will provide precisely regulated power output from the massive solar arrays. With assistance from robot arm operator Koichi Wakata, who will ferry the spacewalkers around the growing station, Chiao and McArthur will unfasten the DDCUs from their locations in Discovery's payload bay and install them on the Z1 Truss in a process that will take about two hours to complete.
They will then turn their attention to final power cable connections on both the Z1 Truss and newly installed docking port, PMA-3, connecting and reconfiguring cables to route power from PMA-2 to PMA-3 for the arrival of Endeavour and the STS-97 crew next month. Finally, McArthur and Chiao will attach a second tool storage box on the Z1 Truss, providing a place to hold the tools and space walking aids that will be used during upcoming assembly flights. McArthur will retrieve a bag of tools and hardware attached to the exterior of the Unity module and place it in the storage boxes. The tools were temporarily stowed on Unity during a May 1999 space walk conducted by Astronauts Tammy Jernigan and Dan Barry during STS-96, the first shuttle docking with the International Space Station.
Overnight, space station flight controllers in Houston completed commanding a series of 16 bolts to their closed position, securing PMA-3 to its new location on the Unity module, following a planned 12-hour thermal conditioning period. The docking port, installed during yesterday's space walk, will be used by the STS-97 crew when Endeavour docks with the International Space Station.