A six hour 47 minute spacewalk by astronauts from Space Shuttle Discovery today restored the International Space Station's Mobile Transporter rail car to full operation and delivered a spare pump module for the station's cooling system.
Spacewalkers Piers Sellers and Mike Fossum exited the Quest module's airlock at 7:14 a.m. and climbed down into the shuttle payload bay, where they lifted the Pump Module from its stowage platform so Mission Specialists Lisa Nowak and Stephanie Wilson could grapple it with the station's 58-foot-long robotic arm. While the arm moved the module to its destination, Sellers and Fossum moved to the S0 Truss segment to begin work on the primary task of the EVA, replacement of the nadir-side Trailing Umbilical System (TUS).
A TUS contains a power, data and video cable that serves the Mobile Transporter as it moves along the station's truss; the nadir TUS cable was inadvertently severed late last year and required replacement. As the first step in that process Sellers replaced the Interface Umbilical Assembly - the component containing the cutter - with a new IUA, one without a blade.
By that time Canadarm2 reached External Stowage Platform 2 on the forward side of Quest with the Pump Module; Sellers and Fossum moved to the platform to receive the module from the arm, secured it to the storage platform, and returned to the TUS work site.
The spacewalkers removed the damaged TUS from within the S0 Truss, and Fossum carried it to the payload bay while riding the station arm. When he arrived, Sellers removed the new TUS from the payload bay platform, and the two swapped cable reels. Sellers stowed the old TUS on the cross-bay carrier while the arm moved Fossum back to the truss work site, where Sellers rejoined his crewmate to complete installation of the TUS and properly route its power, data and video cable through the IUA.
At two points during the spacewalk Fossum paused to take care of a loose connection of the emergency jet thruster backpack on Sellers' spacesuit, securing it the first time with a safety tether.
The spacewalkers closed the hatch and began to repressurize Quest to end the spacewalk at 2:01 p.m. to conclude a six-hour, 47-minute excursion; the combined time spent spacewalking on two EVAs on this mission so far is 14 hours, 18 minutes. A third spacewalk, devoted to testing potential repair techniques and materials, is scheduled for Wednesday.
During the spacewalk Pilot Mark Kelly oversaw the timeline for the spacewalkers while Commander Steve Lindsey managed the cameras and transferred two containers of water onto ISS. Expedition 13 Commander Pavel Vinogradov and Flight Engineers Jeff Williams and Thomas Reiter continued to work on delivery and stowage of equipment and supplies from the Multipurpose Logistics Module.
The next STS-121 mission status report will be early Tuesday.
