Among them: U.S. and Russian flight surgeons who will carry out a battery of post-flight medical tests on Shepherd and his colleagues, the three of whom face an arduous recovery from four-and-a-half months in weightlessness.

"What they have to look forward to is a period of several weeks to months of rest and rehabilitation," said NASA flight surgeon Terry Taddeo.

"That rehabilitation will involve some cardiovascular-type training, some strength-type training, water training, and some massage -- assisted activities that will get them back on the road to their preflight condition."

The extensive rehab, which is expected to last at least two months, is required to counteract the debilitating effects of long stays in weightlessness.

The heart, lungs and other major organs are weakened. Muscles atrophy from lack of use and the skeletal system withers away, resulting in a gradual but potentially serious bone loss.

What's more, blood and other body fluids pool in the head and upper torso, leaving homebound space travelers woozy upon their return to Earth. The reason: Pooled blood rushes back down into the lower torso once astronauts reenter gravity.

The last leg of the station crew's journey began a little later than planned. The threat of high winds, low clouds and rain prompted mission managers to forego a 12:56 a.m. EST (05:56 GMT) landing opportunity at NASA's coastal Florida spaceport.

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The weather cleared in time for Wetherbee to fire the shuttle's twin orbital maneuvering engines at 1:26 a.m. EST (06:26 GMT), a move that sent Discovery on an hour-long freefall back to KSC's three-mile (4.8-kilometer) runway.

Soaring high above the Indian Ocean at the time, Discovery flew south of Australia and then over the Pacific Ocean. Shepherd and his colleagues felt the tug of normal gravity for the first time since Oct. 31 as Discovery passed 76 miles (122 kilometers) above Mexico.

The winged spaceship then flew out over the Gulf of Mexico, skirting the western edge of Cuba before crossing over Tampa and making a beeline across central Florida.

Ultimately, Wetherbee guided Discovery on a sweeping arc out over the Atlantic Ocean as the shuttle's trademark twin sonic booms heralded the ship's arrival back on Florida's Space Coast.

"It's also nice to be back in Florida. We almost didn't get here, but I guess we were able to make it, and it was a good night to land," Wetherbee said.

Launched March 8, Discovery and its astronauts ferried a new crew -- as well as five tons of supplies and equipment -- up to the international station.

Russian commander Yuri Usachev and two American flight engineers -- Susan Helms and Jim Voss -- were busy aboard the outpost during Discovery's atmospheric reentry and landing.

The job at hand: Preparing the 118-ton complex for the delivery next month of the station's Canadian-built robot arm. Set for launch aboard shuttle Endeavour April 19, the 57-foot (17-meter) construction crane will play a key role in future assembly of the growing outpost, which eventually will weigh almost 500 tons and span an area as large as two football fields.

Shepherd and his crew boarded the complex Nov. 2 -- almost two years after the first two station building blocks were launched and linked in orbit.

Their long-awaited expedition had been postponed several times to accommodate delays in the launch of the station's Russian Zvezda module, which doubles as a command post and crew quarters at the complex.

The bus-sized Zvezda module was launched in July 2000 and then outfitted during a shuttle mission last September.

During their hectic tour on the station, Shepherd and his colleagues took the outpost on a "shakedown cruise," working overtime to activate crucial life support and other operational systems.

They also oversaw the delivery and activation of a $600 million U.S. electric power tower and the American-made Destiny science laboratory, which is the first of six research facilities that the U.S., Russia and 14 other project partners plan to launch to the station.

The end of their expedition, meanwhile, was a bittersweet one.

"I have certainly mixed emotions," Shepherd said in an interview Tuesday.

"Turning over command of the space station to Yuri Usachev was the highlight of my professional career," he said. "I'm sad to depart. I will be happy to be safely on the ground with family and friends. So it's kind of a day with very high emotions, but very different ones as well."