The first spacewalk of Discovery's STS-121 mission to the International Space Station will highlight Saturday activities for crews of both docked spacecraft.
Spacewalkers Piers Sellers and Mike Fossum have two major tasks. First they will work to ensure that the second power and data cable linking the mobile transporter to the rest of the station is spared the fate of the mobile transporter's other trailing umbilical system cable. It was inadvertently severed by its safety cutter last December. The second activity is to test the capability of the shuttle's robotic arm and its 50-foot extension to act as a platform for spacewalkers making repairs.
Expedition 12 crewmembers tried to install a safety bolt to protect the remaining cable. They were unable to insert the bolt, so they removed the cable from the emergency cutter.
Sellers and Fossum will install a device to block the cutter blade. If that doesn't work, they'll install a new unit, called an interface umbilical assembly, this one without a blade. Once they reinstall the cable, the mobile transporter will again be able to move the station's robotic arm along the rails on the station's main truss. The arm is scheduled to be moved during the Monday spacewalk.
For the test of the arm as a repair platform, Sellers will work on the end of the 50- foot extension, called the orbital boom sensor system. Then both spacewalkers will simulate working motions at the end of the extension. That will be done in at least three arm positions.
Sellers will be the lead spacewalker and wear the spacesuit with red stripes. He did three spacewalks in October 2002 during the STS-112 mission of Atlantis to the station. On that mission he helped install the station's starboard one (S1) truss.
Fossum will wear the all-white spacesuit. He is making his first spaceflight. Discovery Pilot Mark Kelly will serve as the intravehicular officer, coaching and helping the spacewalkers from inside the station-shuttle complex.
Mission Specialists Lisa Nowak and Stephanie Wilson will operate the robotic arms during all three of the mission's spacewalks. They will maneuver the shuttle's Canadarm with its extension during the first, scheduled to begin at 8:13 a.m. CDT Saturday. They will use the station's Canadarm2 during the second spacewalk on Monday and the third on Wednesday.
Expedition 13 Flight Engineer and NASA Science Officer Jeff Williams and Discovery Commander Steve Lindsey also will help out during the spacewalk.
Meanwhile Thomas Reiter, the European Space Agency astronaut from Germany who became part of the Expedition 13 crew shortly after docking, will work with station commander Pavel Vinogradov to transfer cargo and equipment from the Leonardo multi-purpose logistics module.
In staggered wake ups, the shuttle crew arose at 2:08 a.m. CDT to the sound of "God of Wonders" by Marc Byrd and Steve Hindalong. The music was selected for Fossum by his family. The station crew was awakened about 30 minutes later.
The next Mission Status Report will be issued Saturday evening, or earlier if events warrant.
