NASA officials on Sunday gave the astronauts the green light to prepare for the return trip, but kept a close watch on the weather around the Kennedy Space Center (KSC) in Florida, where Discovery was scheduled to land at 9:14 am (1214 GMT.)

The decision was made after final inspections of the orbiter's wings and nosecap dispelled concerns about possible damage from the impact of sand-sized micrometeorites.

The launch and the landing are the most dangerous parts of a space shuttle mission. It was during reentry into the Earth's atmosphere that Columbia burst into flames on February 1, 2003, killing the crew of seven.

NASA hopes Discovery's mission will help ease concerns over the shuttle program that have persisted since the disaster.

"It's been a very, very clean mission. We've had very few glitches," Lindsey said in an interview with the CBS television networks. "We got a clean bill of health," he said.

Like last year's first post-Columbia flight, the latest mission was largely aimed at improving safety before NASA resumes regular launches to finish the ISS by 2010, when the three-shuttle fleet is retired.

NASA says the orbiting space station is a key component in US plans to send astronauts back to the moon, and eventually to Mars.

"I hope our legacy was that we closed out the return to flight test portion of the program following the Columbia accident, Lindsey told the ABC network. "I personally believe we are back on track," he said.

Astronauts Mike Fossum and Piers Sellers successfully performed three spacewalks, spending more than 21 hours outside Discovery, to test shuttle repair techniques and fix equipment needed to continue building the ISS.

The crew aboard the shuttle delivered critical supplies and removed vast quantities of trash, discarded material and experiment results from the orbiting laboratory.

The crew also dropped off European Space Agency astronaut Thomas Reiter of Germany, who became the space station's third resident.

The mission is the second since the Columbia disaster and the first since the shuttle fleet was grounded a year ago after the shuttle's external tank shed a large chunk of foam on take-off.

A similar piece of foam insulation had peeled off on Columbia's doomed flight, piercing the shuttle's heat shield and causing the orbiter to break apart as it returned to Earth.

The tank shed some debris this time around, but NASA found no damage on Discovery's heat shield.

Weather permitting, Discovery should land at 9:14 am (1314 GMT) Monday at Kennedy Space Center's 4,572-meter (15,000-foot) runway.

Should weather be unfavorable, the crew could choose to touch down at Kennedy about 90 minutes later, and has until Wednesday to land, either at the Florida space center or at an alternate landing facilities in California or New Mexico.

"I think we have a pretty good shot at getting to Kennedy on Monday," said Steven Stich, the mission's landing director. "The weather looks fairly reasonable," he said, pointing out however that rainstorms were common at this time of year along southern Florida's Atlantic coast.

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