June 22, 2010 at 1:43 PM ETManagers of NASA's space shuttle program are seeking a shift in the launch schedule that would delay the fleet's final launch until February 2011 at the earliest. The schedule shift would have the shuttle Discovery to lift off on Oct. 29 instead of Sept. 16, and schedule Endeavour's flight for no earlier than Feb. 28, 2011, rather than in November as previously scheduled. Managers asked for the shift this afternoon in a "Change of Launch" request issued to all invoved in those two flights, according to Jay Barbree, NBC News' Cape Canaveral correspondent. Discovery is to deliver the Italian-built Leonardo logistics module to the International Space Station and install it as a permanent addition to the complex. Endeavour will bring up the $1.5 billion Alpha Magnetic Spectrometer, an international physics experiment. "These two flights will be the last for the space shuttle fleet unless a plan to launch space shuttle Atlantis on a full-up supply run a year from now is approved," Barbree says. NASA is already getting Atlantis ready as a backup rescue shuttle in case something goes wrong during Endeavour's mission. Assuming that Atlantis isn't needed for an unprecedented rescue, NASA has been talking about using that shuttle and a minimal crew to deliver more supplies to the station in mid-2011. Members of Congress are likely to be amenable to that plan. NASA public affairs officials said they could not comment on Barbree's report but noted that schedule changes have been under discussion for weeks. The factors that could contribute to a delay include the need to retrofit the Alpha Magnetic Spectrometer for a longer stint on the space station, the potential for a space traffic jam involving Russian or Japanese supply craft, and the limited number of opportunities for launch due to unfavorable sun angles. NASASpaceflight.com has been following the discussions over the space agency's shuttle manifest like a hawk, and we'll pass along any further information about the shuttle schedule as it becomes available. Update for 6:30 p.m. ET:Space.com quotes Mike Curie, a spokesman at NASA Headquarters in Washington, as saying that the request for the schedule shift is still being reviewed, and that a final decision will be made July 1. "They just need a little bit more time to get some of the spare hardware ready to fly" on Discovery this fall, Curie said. He said such a delay could have a domino effect on Endeavour's later mission because of the turnaround time required between launches, plus the launch limitations in the timeframe between November and February. Join the Cosmic Log corps by signing up as my Facebook friend or hooking up on Twitter. And if you really want to be friendly, ask me about "The Case for Pluto."