The primary mission will be to install new equipment and upgrades for Hubble, which was last serviced in 2002 by Space Shuttle Columbia. The crew will install the Cosmic Origins Spectrograph, a sensitive ultraviolet spectrograph and the Wide Field Camera 3, a camera that can record a large range of spectrums. Six of the gyroscopes and batteries for the satellie will also be replaced. This mission is long overdue, having originally been scheduled for May 2008, and there were further delays last fall when problems with the production of the external fuel tanks occured. In addition, an IMAX camera will be brought up, footage from which will be used for a new film about Hubble.

What makes this mission interesting is the presence of not only Atlantis, but Endeavour as well, on the launch pad. Because of Hubble's postition in orbit, the Space Shuttle will be out of range of the International Space Station, the usual standby in case of an emergency. In the instance that there is a problem this time around, Space Shuttle Endeavour can be launched to rescue the crew of the Atlantis. This mission is designated STS-400, and will carry a crew of four.

The current mission is one of the few remaining shuttle missions before the orbiter fleet is retired in 2010. Remaining missions include deliveries to the International Space Station, and will allow Atlantis to fly one final time, with Endeavour flying two more flights, with Discovery slated to fly the last mission, STS-134.

Best of luck to the crew of STS-125!

Watch launch coverage here: http://www.nasa.gov/multimedia/nasatv/index.html

On twitter? Follow astronaut Mike Massimino, Space Shuttle Atlantis and Space Shuttle Endeavour:

http://twitter.com/Astro_Mike
http://twitter.com/SSAtlantis
http://twitter.com/SSEndeavour

Graphics from NASA and MSNBC

NASA announced that Space Shuttle Endeavour was being moved to the launch pad in preperation for the Hubble repair mission. However, Space Shuttle Atlantis is the primary shuttle for this mission. According to NASA:

Endeavour will be at Launch Pad 39B in the unlikely event a rescue mission is needed during Atlantis' May flight to upgrade the Hubble Space Telescope. After Atlantis is cleared to land, Endeavour will move to Launch Pad 39A in late May for its upcoming STS-127 mission to the International Space Station.

Why the need for a backup shuttle? The threat of a dangerous collision with space junk has increased drastically in the area where Atlantis will be operating. And at this point, the International Space Station will be unable to help in case of a problem.

Picture from marshall43402