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Shuttle cleared for Earth return Shuttle cleared for Earth return
(20 minutes later)
The shuttle Discovery has been cleared to return to Earth, but poor weather over the Kennedy Space Center may force it to an alternative landing site.The shuttle Discovery has been cleared to return to Earth, but poor weather over the Kennedy Space Center may force it to an alternative landing site.
Nasa controllers have the Edwards Air Force Base, in California, and White Sands Space Harbor, in New Mexico, on standby to receive the vehicle. Nasa controllers have Edwards Air Force Base, in California, and White Sands Space Harbor, in New Mexico, on standby to receive the vehicle.
If the rain and clouds lift at Kennedy, Discovery's first landing opportunity is at 2056 GMT (1556 local time).If the rain and clouds lift at Kennedy, Discovery's first landing opportunity is at 2056 GMT (1556 local time).
The shuttle has been on a mission to rewire the International Space Station. Nasa is prepared to delay the return to Saturday if needs be.
"As we get closer, we'll have much more certainty on what we're really faced with," said Norman Knight, who will direct the landing.
The shuttle has been on a 13-day mission to rewire the International Space Station (ISS).
In addition, its crew fitted a connecting segment that will allow the platform's backbone to be extended further in future.
They also delivered two tonnes of supplies; and dropped off one new resident, American Sunita Williams, and picked up a returning astronaut, German Thomas Reiter.
Future flights
Discovery needs to be on the ground on Saturday or it will run low on the fuel that powers its electrical systems.
The shuttle would normally have had more time to make a landing but its astronauts made an unscheduled, extra spacewalk at the station to free a stuck solar array.
Controllers will keep the vehicle in orbit until they see a weather opening at one of the three landing strips. White Sands was looking the most favourable location on Friday with strong crosswinds forecast for Edwards.
Europe will fly the ATV supply ship in early 2007 Europe set for bigger role During the 25 years of the shuttle programme, White Sands has been used only once, in 1982 (Kennedy has seen 63 landings; Edwards has had 50).
Shuttle pilots use White Sands to practise landings in a simulator aircraft, but Nasa would prefer not to put the shuttle down there for real, if it can be avoided.
After the last landing at the New Mexico desert location, the orbiter was covered in fine sand. It would also take longer to move the shuttle back to Kennedy for future flight preparation.
The next construction mission to the ISS will be undertaken by the Atlantis shuttle in March. This will see a third set of solar arrays and batteries fitted to the station.
May should see the maiden flight of a new re-supply vessel for the station. Known as the Automated Transfer Vehicle (ATV), it will be launched on an Ariane 5 rocket from the European spaceport at Kourou in French Guiana.
Europe also has keen interest in Discovery's next mission scheduled for October. This mission will deliver the Columbus science module, Europe's biggest contribution to the ISS project.