After space shuttle Endeavour's rollout to Launch pad 39B at NASA's Kennedy Space Center.

After space shuttle Endeavour's rollout to Launch pad 39B at NASA's Kennedy Space Center in Florida this morning, two different shuttles are poised on two different launch pads. Shuttle Atlantis (left) already was on Launch Pad 39A. With the space shuttle fleet set for retirement in 2010, this is expected to be the final time two shuttles will be on launch pads at the same time. Endeavour will stand by at pad B in the unlikely event that a rescue mission is necessary during Atlantis' upcoming mission to upgrade NASA's Hubble Space Telescope. Atlantis is targeted to launch May 12. After Endeavour is cleared from its duty as a rescue spacecraft, it will be moved to Launch Pad 39A for its STS-127 mission to the International Space Station. That flight is targeted for launch June 13. Photo credit: NASA/Dimitri Gerondidakis