From: Johnson Space Center
Posted: Monday, May 18, 2009
As Atlantis' crew begins their eighth day in space, astronauts Drew Feustel and John Grunsfeld are hours away from conducting the final spacewalk on the Hubble Space Telescope. The STS-125 crew awoke this morning to "Sound of Your Voice" performed by Barenaked Ladies. It was played for Commander Scott Altman.
There are two major focuses for today's spacewalk. The first objective for Feustel and Grunsfeld is the removal of the battery module from Bay 3 on the telescope and the installation of a fresh module. Each battery module weighs 460 pounds and contains three batteries. Each of the nickel hydrogen batteries weighs 125 pounds, and they provide power to the telescope when it passes into orbital night and the solar arrays are not exposed to the sun. All of the batteries on Hubble are original equipment, and they were only designed to operate for five years. The batteries in Bay 2 were replaced earlier in the mission.
The second task is the removal and replacement of Fine Guidance Sensor (FGS) 2. Hubble has three of these sensors, and FGS 2 has degraded over time. The three sensors are parked at 90 degree angles around the circumference of the telescope, and two are used to point and lock the telescope on its targets. The third can be used for astrometry, which is measuring the distances between different celestial objects. The refurbished FGS that will be installed today previously had been removed and returned on the third servicing mission in December 1999. It has since been enhanced and upgraded.
After these two tasks are accomplished, Feustel and Grunsfeld will turn their attention to the New Outer Blanket Layer (NOBL) on the outside of the telescope’s Bay 5. The NOBL on Bay 8 was due to be installed during yesterday's spacewalk, but the crew was unable to accomplish it during the spacewalk. If time permits, Feustel and Grunsfeld may be asked to install a partial or full set of NOBLs on Bay 8.The team in Mission Control will make the decision in real time based on the progress of the spacewalk.
The crew's sleep period will begin at 7:31 p.m. CDT, and the crew is due to wake up tomorrow at 3:31 a.m. to begin procedures to release Hubble. The next status report will be issued at the end of the crew’s day or earlier if events warrant.
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