The space shuttle Discovery undocked from the international space station Saturday, preparing for the first shuttle reentry since Columbia disintegrated over Texas 21/2 years ago.

This time the reentry track will bring Discovery over Nicaragua and Honduras on a northeastern route to the Caribbean, then over the western tip of Cuba to enter U.S. air space at Fort Myers, Fla.

Discovery will then fly over Lake Okeechobee and is scheduled to touch down at the Kennedy Space Center's Shuttle Landing Facility at 4:46 a.m. Eastern time Monday, with mission commander Eileen Collins at the controls.

"There aren't a lot of emotive people around here," Wayne Hale, the deputy shuttle program manager, said at a Johnson Space Center news conference Saturday. "But there's going to be a lot of prayers and thanksgiving."

Discovery, thoroughly inspected with new safety equipment, does not appear to have any significant cracks or breaks in its heat shielding, let alone a gaping hole in its wing like the one that doomed Columbia.

Even so, NASA has grounded the shuttle fleet because several unacceptably large pieces of foam insulation broke off Discovery's external fuel tank during launch nearly two weeks ago. Hale said the "shoot-for" date of Sept. 22 for the next shuttle launch is "not serious, at this point," suggesting that the date could slip to November or beyond.

This is one reason that Mission Control is eager to bring Discovery back to Kennedy and not land at the backup site of Edwards Air Force Base in California. Having to transport the shuttle cross-country, Hale said, "would add a month to the next launch" even if the foam problem were quickly resolved. Discovery will serve as the potential rescue vehicle in case Atlantis gets in trouble in space.

Hale noted that the pre-dawn weather at Kennedy is "about as good as you can get" in central Florida in August, but if clouds, lightning or rain prevail, the orbiter will delay landing until the next orbit. If conditions are still bad, Discovery will wait until Tuesday, make two tries at Kennedy, then land at Edwards.

The seven shuttle astronauts bade goodbye to space station astronauts Sergei Krikalev and John Phillips shortly after midnight Eastern time Saturday. At 3:24 a.m. Discovery undocked, and with pilot Jim Kelly at the controls, conducted a "fly-around" of the station, taking pictures from a distance of 400 feet.

The astronauts will spend Sunday stowing gear, reviewing reentry procedures and resting up for reentry, set to begin with a "de-orbit burn" over Central America at 3:39 a.m. Monday.

Once the burn begins, Mission Control is committed to landing the shuttle. Discovery will be 224 miles above Earth, traveling upside down and backward at 25 times the speed of sound, using its thrusters as a brake.

As the preprogrammed burn progresses, the orbiter will gradually flip over until it points forward at an angle of 40 degrees above horizontal, which it will maintain throughout most of the reentry. It will also move its orbit to line up for landing.

About a half-hour after the burn ends, Discovery, now operating as a glider, will drop into Earth's atmosphere at an altitude of 400,000 feet. Temperatures on the orbiter's heat shielding will build as high as 3,000 degrees Fahrenheit. The astronauts, strapped in their seats, will see nothing out the windows but hot gas gleaming red and white.

That will be the critical phase of reentry. Columbia's crew reported excess heat in the left wing just after entering the atmosphere, and the shuttle exploded eight minutes later.

As Discovery drops, it will conduct a series of preprogrammed rolls and "s" turns to shed velocity, eventually dropping below the speed of sound with a pair of sonic booms over Florida. Collins will then take the controls for the last three minutes of the approach, circle once and land.