Columbia's crew is preparing tonight for the third space walk of the mission, a complex, seven-hour excursion that will include the unprecedented step of turning off the Hubble Space Telescope to replace the heart of its power system.
Controllers at the Space Telescope Operations Control Center in Greenbelt, MD, will begin sending commands to power down the telescope's systems around 10:30 p.m. CST. The power is planned to be off until the telescope is brought back to life at 5:30 a.m. CST Wednesday with a newly installed power center.
The shuttle crew was awakened today by the song “Carmen Ohio,” performed by the Ohio State University marching band and played for Ohio State alumni Nancy Currie and Rick Linnehan aboard Columbia. Space walkers John Grunsfeld and Linnehan are scheduled to begin their work outside the shuttle about 12:30 a.m. CST Wednesday.
Grunsfeld and Linnehan will replace Hubble's power control unit, or PCU, the central power switching station that distributes electricity to all of the observatory's systems and scientific instruments. Currie will operate the shuttle’s robotic arm, moving the space walkers to and from worksites on the telescope. Linnehan will ride the arm first to a position where he will disconnect the telescope's batteries. Meanwhile, Grunsfeld will install blankets to protect components that will not be heated while the power is off.
The pair will work in tandem to replace the PCU. Linnehan will remove 30 of the 36 connectors on the old PCU and then move to the shuttle's payload bay to prepare the new unit for installation. Grunsfeld will then work at the end of the arm to unhook the remaining connectors, ease the old PCU out of the telescope and carry it to the shuttle's payload bay to be stored. There, Linnehan will hand the new unit to Grunsfeld, who will take it to the worksite, install the new box in its bay and reattach the 36 connectors.
Inside Columbia, the flight's other space walking team, Jim Newman and Mike Massimino, will assist. They will act as in-cabin choreographers guiding Grunsfeld and Linnehan through their tasks. Newman and Massimino are scheduled to perform the mission's fourth space walk on Thursday. Columbia Commander Scott Altman and Pilot Duane Carey will operate television and still cameras to document the work.
The crew is to begin its sleep period at 11:52 a.m. CST Wednesday. The next STS-109 mission status report will be issued Wednesday morning, or as events warrant.
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