Five spacewalks are planned during the eleven day flight. Old cameras will be exchanged for new improved models, and failed equipment will be replaced.
Good weather is expected at the Cape Canaveral launch site on Monday, but rain at an emergency landing strip in Spain could delay the launch. If Atlantis can't lift off by Wednesday, the mission will have be delayed until May 22nd.
The space shuttle Endeavour is poised on a nearby launch pad, ready for a rescue mission in case Atlantis suffers irreparable damage in space. If Atlantis is unable to re-enter the earth's atmosphere safely, the crew would not be able to reach the International Space Station to take shelter.
Following the Columbia disaster, the Hubble repair mission was canceled by NASA for safety reasons, but was later reinstated, thanks in part to public opinion. Hubble has captured the public's imagination with its spectacular images from deep space.
The final repair job will be the most difficult of all. It should give the telescope at least five more years of life, at the same time providing powerful new instruments with the promise of even more scientific discoveries.