Space Shuttle Endeavour rolled out to a Florida launching pad early Friday to serve as a rescue craft for its sister spaceship Atlantis in what is expected to be the last time in history that NASA has two orbiters in launch position.

NASA is preparing to launch seven astronauts aboard Atlantis next month on the final service call to the Hubble Space Telescope, where the spacefliers plan to perform five back-to-back spacewalks to install new cameras, replace aging batteries, gyroscopes and other components, add a docking ring and make tricky repairs to equipment never designed for in-flight maintenance.

NASA mission managers and Atlantis astronauts consider the rescue plan an extremely unlikely scenario and are confident their mission will go as planned. Once Atlantis and its crew return safely to Earth, NASA will move Endeavour from Pad 38B to 39A for its planned November 12 launch to haul fresh supplies and equipment to the space station.