For Usachev and his crew, the 80-minute flyaround marked the beginning of the last leg of a journey that began 165 days ago with their launch from Kennedy Space Center.

Over the course of the next five-and-a-half months, the Expedition Two crew oversaw the start-up of scientific research aboard the outpost as well as two key construction jobs.

Both the station's $600 million Canadian robot arm and a $164 million airlock were added to the growing complex during their tenure there.

For Horowitz and the shuttle astronauts, the departure capped an eight-day visit aimed at moving Culbertson and his crewmates into -- and Usachev and his colleagues out of -- the international outpost.

To that end, some 7,400 pounds (3,330 kilograms) of food, clothing, research apparatus and science experiments were ferried to the outpost within a shuttle-borne Italian moving van.

That same shipping container then was loaded back up with 3,700 pounds (1,665 kilograms) of Expedition Two crew luggage, surplus station gear and garbage for the return trip home.

Shuttle mission specialists Daniel Barry and Patrick Forrester also performed two spacewalks to outfit the outpost with spare coolant tanks, two suitcase-sized science packages and electrical power cables.

"Another great mission," Horowitz told Culbertson as Discovery backed away from the station.

"Have a wonderful landing," Culbertson replied. "Yuri, Jim, Susan: Dosvidanya."

"Thanks Frank, and good luck," Usachev said.

Known as the Expedition Three crew, Culbertson, Dezhurov and Turin will spend the next four months conducting 50 U.S. and Russian science experiments aboard the orbital research facility.

And while no U.S. shuttle visits are planned during their stay, air traffic around the outpost will get busy again Thursday when an unmanned Russian Progress space freighter arrives with several more tons of supplies and equipment.

The next major piece of the station -- a Russian docking compartment -- is scheduled for launch to the station in mid-September, and Soyuz taxi crew is slated to deliver a fresh outpost lifeboat in mid-October.

Culbertson and his crewmates will carry out three spacewalks to outfit the docking compartment externally before another Progress space freighter arrives in mid-November.

Discovery's departure came three hours after the joined shuttle and station crews bid adieu in a poignant farewell ceremony aboard the station.

"It's a very emotional day for Yuri, Jim and Susan as they are leaving what has been their home for over five months," Culbertson said as the 10 astronauts and cosmonauts floated inside the Destiny lab.

"I know it's a tough day. I know it's hard to say goodbye. But we really, really are proud of all you have done, and we will do our best to keep up the good tradition you have started and to maintain just as high a standard of excellence if we can."

Said Usachev: "It's time to say goodbye to the station, and good luck to the (new) crew."

"We wish them a great journey as they continue in the exploration of space that will sometime take mankind out through the solar system and beyond," Horowitz added.

To mark the occasion, Culbertson and his crewmates displayed two autographed plaques commemorating the so-called "Phase 1" portion of the International Space Station program.

Staged between June 1995 and June 1998, that chapter in space history involved launching nine U.S. shuttle missions to Russia's former space station Mir as precursors to the construction of the new international outpost.

The plaques are adorned with the signatures of every Russian cosmonaut and American astronaut that either visited Mir or served tours of duty aboard the outpost during that time period.

Seven U.S. astronauts tallied 977 days in space as part of the project, also known as the shuttle-Mir program.

Culbertson said the mementoes, which flew aboard Mir, serve as a symbolic bridge between the two stations. Also significant, he said, is the fact that several astronauts and cosmonauts who took part in that program already have served aboard the new international outpost.

Dezhurov was the commander aboard Mir when Atlantis docked there for the historic first shuttle-Mir link-up in 1995. Usachev was the skipper there when NASA astronaut Shannon Lucid chalked up 188 days in space, still a world record for female space travelers.

Voss was as a backup to two of seven American astronauts who carried out research tours on Mir, and Culbertson served a long stint as NASA's deputy director and then chief of the program.

What's more, cosmonauts Sergei Krikalev and Yuri Gidzenko -- members of the new station's first full-time crew -- also flew either on the shuttle or Mir during the forerunner program.

"There's a lot of names on this plaque, and a lot of missions, and I think one of the significant things to note is that two crewmembers of each of the first three (ISS) crews were participants in Phase 1," Culbertson said.

The veteran U.S. astronaut then said "thanks, goodbye and see you later" in English, Russian and Italian, the latter of which is the language of the nation that built a $150 million moving van used to ferry supplies to the station for Culbertson and his crew.

Hatches between the station and the shuttle then swung shut for the last time about 8:30 a.m. EDT (1230 GMT) as Discovery's four astronauts and the returning station crew prepared to undock from the outpost.

The shuttle is due back at NASA's coastal Florida spaceport at 12:48 p.m. EDT (1648 GMT) Wednesday. Culbertson and his crew will remain in space until Dec. 9.