Final inspections of the orbiter's wings and nose dispelled concerns about possible damage from the impact of space debris or meteorites, space agency officials Sunday.

"Is the vehicle cleared for entry?" Discovery commander Steven Lindsey asked NASA ground controllers via radio.

"You are cleared for entry," a mission officer replied from Johnson Space Flight Center in Houston, after engineers analyzed the latest high-definition video footage of the shuttle. The Discovery crew took the footage after the orbiter undocked from the International Space Station on Saturday.

The landing will conclude the 13-day mission that NASA officials hope will help ease lingering concerns about the safety of the shuttle program.

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

The late check for space debris hits was a first, and Discovery has been inspected more than any previous shuttle mission.

Like Discovery's mission in July 2005 - the first since the shuttle Columbia disaster in February 2003 - this flight, dubbed STS-121, was aimed largely at improving safety before NASA resumes regular launches to finish the space station by 2010, when the three remaining spacecraft are scheduled to be retired.

NASA officials have said the space station is critical to U.S. ambitions to send astronauts back to the Moon and eventually to Mars.

Astronauts Mike Fossum and Piers Sellers successfully performed three spacewalks during the STS-121 mission, spending more than 21 hours outside Discovery, to test shuttle-repair techniques and fix equipment needed to continue building the station.

The four men and two women aboard the shuttle delivered critical supplies to the station and moved several tons of trash, discards and experiment results from the orbiting facility and into the Italian-built Leonardo multi-purpose module.

The crew also dropped off ESA astronaut Thomas Reiter of Germany, who became the space station's third crew member and will remain a part of station Expedition 13 for at least several months.

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

A similar but larger piece of foam had fallen off on Columbia's doomed flight. Traveling at more than 500 miles per hour, it punched a large hole in the leading edge of the shuttle's left wing, which allowed superheated gases to penetrate the wing's interior during atmospheric re-entry. Columbia eventually disintegrated over Texas, killing all seven of its crew members.

Although Discovery's fuel tank shed some foam this time, NASA found no damage on the shuttle's heat shield.

Weather permitting, Discovery is expected to land at 9:14 a.m. Eastern Time (13:14 GMT) Monday on the 4,572-meter (15,000-foot) runway at the Kennedy Space Center on Florida's Atlantic coast. The runway, one of the longest in the world, is also one of the few that can accommodate the shuttle, which lands at speeds in excess of 200 miles per hour.

Should weather be unfavorable, the orbiter would have another opportunity to touchdown at Kennedy about 90 minutes later. Other landing windows will be available until Wednesday, if not in Florida, then at alternative landing strips at Edwards Air Force Base in California and White Sands in 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."

Stich noted, however, that rainstorms were common at this time of year in southern Florida. NASA tests have shown that precipitation can damage the shuttle's delicate heat shield tiles.

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