If successful, the repair mission will extend the useful life of Hubble out to to the year of 2013. If not successful or if the mission becomes impossible to complete, the Hubble will end most of its major science services around 2009 and all of its basic services by 2011.

Classified as a risky mission to complete, one of the other space shuttles (either Endeavour or Discovery) will serve as a rescue ship should a major problem develop that necessitates retrieving the STS-125 crew. The mission is deemed risky because if the astronauts cannot return home because of some problem, they will not be able to fly to the International Space Station as a safe haven.

The rescue mission is named STS-400 Launch On Need (LON). When STS-125 lifts off from launch pad 39A, the STS-400 orbiter and its crew will be prepared to liftoff from launch pad 39B within seven days—in case the need arises.

The STS-125 crew includes commander Scott D. Altman, pilot Gregory C. Johnson, and mission specialists John M. Grunsfeld, Michael J. Massimino, K. Megan McArthur, Andrew J. Feustel, and Michael T. Good.

The STS-125 mission, also called Hubble Space Telescope Servicing Mission 4 (HST-SM4) is scheduled to be the thirty-first and final flight of the Space Shuttle Atlantis.

It is the fifth servicing mission to Hubble. The Hubble Space Telescope, named after U.S. astronomer Edwin Hubble, has been previously serviced by Discovery twice, and by Columbia and Endeavour, each once.

Atlantis will carry two new instruments and one replacement instrument to Hubble. In all, five extravehicular activities (EVAs) are planned by the NASA astronauts in order to refurbish Hubble.

The two new instruments are the Cosmic Origins Spectrograph, a very sensitive ultraviolet (UV) spectrograph, which is thirty times more sensitive in the far-UV range than previously used instruments and twice as sensitive in the near-UV range, and The Wide Field Camera 3, which is a panchromatic wide-field instrument. The Wide Field Camera 3 will replace the Advanced Camera for Surveys, which stopped working earlier in 2007 on Hubble.

The replacement instrument carried by Atlantis will fix a broken Fine Guidance Sensor. In addition, six new gyroscopes will be installed to improve Hubble’s attitude control system.

The crew will also install new batteries and a new thermal blanket layer to provide Hubble with better insulation. A Soft-Capture mechanism will be newly installed so that a robotic spacecraft can be docked to Hubble in order to assist it in a safe deorbiting at the end of its life.

The crew will also boost the orbit of Hubble so that it will remain in a stable orbit for a longer period of time.

For more information on Hubble, go to NASA’s Hubble website of http://hubble.nasa.gov/index.php and the Space Telescope Science Institute’s Hubble website of http://www.stsci.edu/resources/.

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