But managers of the National Aeronautics and Space Administration admitted Saturday they would not rest easy until the safe landing of the first space shuttle flight since the 2003 Columbia disaster.

During the night, Discovery's crew bid farewell to their two hosts on the International Space Station (ISS,) exchanging hugs and handshakes with the Russian and US residents of the orbiting outpost.

"These are memories we'll have forever," Discovery Commander Eileen Collins said before the shuttle undocked from the ISS.

Pilot James Kelly flew the shuttle around the station to check it for any wear and tear, and then steered it away in what NASA described as "the first step on the road home to the Kennedy Space Center."

"The undocking and the flyaround went right by the book," Discovery's lead flight director, Paul Hill, said Saturday at a mission control news conference in Houston, Texas.

The crew was given the green light for its return after NASA decided that damage on the orbiter's thermal blanket should not compromise the shuttle's safety as it re-enters the atmosphere.

"We are good for landing," Wayne Hale, deputy manager for the space shuttle program, said Saturday.

"This vehicle is in extremely clean shape," he added.

Discovery is scheduled to touch down Monday at 4:46 am (0846 GMT) at the Kennedy Space Center but could try again the next day in the event of bad weather, or head to an alternate landing strip in California or New Mexico.

Forecasters were upbeat about conditions at the seashore landing strip but pointed out that weather is unpredictable in Florida at this time of year.

Hale said the landing would mark the conclusion of "an outstandingly successful mission."

But once it is back, Discovery will be grounded with the rest of the fleet until nagging problems with the shuttle's thermal insulation have been fixed, though NASA managers still hope to launch another flight on September 22.

Foam insulation fell off the shuttle's external fuel tank as the craft blasted into orbit on July 26.

The same problem doomed Columbia, as the debris hit the orbiter's left wing, causing a crack that eventually allowed superheated gases to penetrate the structure upon re-entry into the atmosphere.

A key goal of Discovery's 13-day mission was to test improvements made to the shuttle since Columbia burst into flames on February 1, 2003, killing all seven astronauts.

Discovery's crew members were "in very good spirits," said Hale, as the seven astronauts were given time to rest before they make final preparations for the nerve-racking moment when they re-enter the atmosphere.

"De-orbit is not a risk-free activity," said Hill. "We will be pretty darned happy to get to wheelstop and see this good crew step off Discovery."

The mission initially had been scheduled to last 12 days, but an extra day was added on so the crew could transfer as much material and provisions as possible to the space station, amid uncertainty over the date of the next shuttle flight.

The crew also retrieved waste and equipment to clear out space in the cramped orbiting lab.

During the mission, Japanese astronaut Soichi Noguchi and his US counterpart Stephen Robinson conducted three spacewalks.

On Wednesday, Robinson became the first astronaut ever to carry out a spacewalk beneath the shuttle during orbit, to extract two protruding pieces of fiber that risked overheating during the shuttle's re-entry.

In the other two spacewalks, Noguchi and Robinson tested repair techniques adopted after the Columbia tragedy and replaced one of the space station's four gyroscopes.

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