The space shuttle Discovery has lifted off from Edwards Air Force, riding atop a jumbo jet.

The modified Boeing 747 carrying the shuttle took off just after 8:30 a.m. PDT on its return to Cape Canaveral in Florida.

It will make several stops to refuel during the trip, which is expected to cost NASA at least $1 million. A KC-135 aircraft flies in front of the dual craft to look out for bad weather that can damage the shuttle's thermal tiles and blankets.

The first leg of the flight is expected to last about three hours and end at Altus Air Force Base in Oklahoma. It could then continue to Barksdale Air Force Base in Louisiana to rest for the night.

The flight came more a week after Discovery landed in the Mojave Desert to become the first space shuttle to return to Earth since the Columbia tragedy.

The landing was diverted to California after low clouds and lightning prevented the shuttle from returning to Florida on four earlier attempts.

NASA has now said that sister ship Atlantis will not fly in 2005. The shuttles have been grounded while the agency continues to work on the problem of insulating foam shedding from the external fuel tank during launch.

Foam came off the tank during Discovery's takeoff, though it did not damage the orbiter. A chunk that smashed into Columbia in 2003 caused the destruction of the craft during re-entry.