Awaiting word on whether one additional shuttle flight will be approved by Congress and the Obama administration, NASA managers are protectively considering June 28, 2011, for launch of shuttle Atlantis on a rescue mission if a major problem threatens the crew of the final planned shuttle flight in late February. If not, and if NASA gets the required funding, the agency would launch Atlantis on an actual space station resupply mission to close out the shuttle program.

Credit: NASA

As it now stands, only two more shuttle flights are officially planned. The shuttle Discovery is scheduled for launch Nov. 1 on mission STS-133, a flight to deliver spare parts and a cargo storage module to the International Space Station. The shuttle Endeavour is set for takeoff Feb. 26 on mission STS-134 to deliver more spares, supplies and a $1.5 billion physics experiment known as the Alpha Magnetic Spectrometer.

Endeavour will serve as the rescue vehicle for Discovery's crew and Atlantis will be on standby for the Endeavour astronauts. The launch-on-need mission, known as STS-335, had been targeted for launch in late April. But NASA managers began processing an official "change request" Friday that would move the rescue/resupply flight to June 28, 2011. If the additional flight is funded, the mission designation would change to STS-135.

By launching with a crew of four astronauts instead of six or seven, NASA would not need another shuttle on standby for rescue duty. If a major problem cropped up during Atlantis' mission, the astronauts could seek safe haven aboard the International Space Station and rotate home aboard Russian Soyuz spacecraft.