The two final US space shuttle missions before the shuttle program is phased out will likely be postponed, a NASA spokesperson told AFP.
"It's not official yet but it's very likely," said Allard Beutel, media services chief at the Kennedy Space Center in Florida.
"The decision will be officially announced July 1st," he said.
The US space shuttles are being retired after President Barack Obama opted not to fund a successor program, deciding instead to encourage private spacecraft development.
The final two shuttle missions are both to the orbiting International Space Station (ISS).
The shuttle Discovery's flight to the ISS, scheduled for September 16, will likely be moved to October 29 at 2144 GMT, while the final flight of the shuttle Endeavour, currently scheduled for late November, will likely be postponed to February 28, 2011, Beutel said.
The French Higher Education Minister Valerie Pecresse, who met NASA Administrator Charles Bolden on a visit to the United States this week, told AFP that she has been invited to the next shuttle launch on October 29.
The Endeavour's mission was already postponed from its original July 29 launch date to replace a part on the 1.5-billion-dollar Alpha Magnetic Spectrometer due for ISS delivery -- the device will delve into the mysterious dark matter thought to permeate the universe.
The Discovery mission will deliver replacement parts for the Italian-made Pressurized Multipurpose Module (PMM) Leonardo, which will be permanently attached to the ISS.
The postponement of Discovery's mission to October 29 put it too close to Endeavour's first rescheduled launch date in November and the sun's disadvantageous position in following weeks forced the mission to be pushed back to February, NASA said.
Endeavour's end-of-the-year launch would also have clashed with space launches by Japan and Russia during that time, the agency added.
Once the shuttle program ends, the United States will rely on Russia's Soyuz rockets to carry its astronauts to the space station until a commercial US launcher can be developed. That is scheduled for 2015.
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