This story was updated at 12:47 p.m. ET.
The space shuttle Atlantis has begun the trip home from orbit. The shuttle's six astronauts bid farewell to the International Space Station early Sunday after a week of orbital construction for their mission ? one slated to be the final flight of Atlantis.
Atlantis undocked from the space station at about 11:22 a.m. EDT (1522 GMT) while both spacecraft flew 220 miles (354 km) above the Indian Ocean southwest of Australia. The 25-year-old shuttle is due to land in Florida on Wednesday and be retired later this year.
Shuttle commander Ken Ham said the two crews, which added up to 12 people on the linked Atlantis and station ? had great fun working together, but it was time to head home. The two crews shared hearty hugs and handshakes before going their separate ways.
"Of course, it will be a little bit sad," Ham told the station crew. "But we'll see you all on the surface of planet Earth soon."
Station astronaut Tracy Caldwell Dyson, of NASA, rang the ship's bell on the orbiting lab ? a tradition for departing spacecraft.
"Have a safe trip back and Godspeed to you," radioed station commander Oleg Kotov, a Russian cosmonaut, to the shuttle crew as Atlantis headed home. "And thank you again."
Farewell to space station
Shuttle pilot Dominic "Tony" Antonelli flew the orbiter on a victory lap around the station so his Atlantis crewmates could see the fruits of their labor at the orbiting lab. The shuttle launched on its 12-day mission on May 14.
During their flight, the Atlantis crew attached a new Russian research module to the station, replaced six solar array batteries and delivered a spare antenna and other cargo.
The $100 billion space station is about 98 percent complete in terms of habitable volume and weighs more than 816,000 pounds (370,131 kg).
"This place is now a palace. It's huge and I've had a great fun exploring it," said Atlantis astronaut Piers Sellers, adding that it's been fun exploring the outpost. "We're seeing the station pretty much in its final form and it's really magnificent."
Construction began on the station in 1998 by 16 different countries. Today, it is the largest human-built structure in space, home to six people from three different countries and can easily be seen in the sky on clear nights with the unaided eye.
Station's new Russian room
The $200 million Rassvet module is a 19.7-foot (6-meter) cylindrical room that doubles as a docking port on an Earth-facing spot on the station's Russian-built Zarya control module. Its arrival boosted the station to 13 rooms, counting its small seven-window lookout dome.
Metal shavings were found floating inside the Rassvet module, but the module's fans and air filters should clean up the debris, station managers said.
"The new module Rassvet looks really, really good," Kotov told reporters early Sunday. It will be used primarily for research, he added.
More than a ton of supplies is also packed away in the new Russian chamber, which is called Rassvet (Russian for "Dawn"). Three spacewalks were performed by the crew of Atlantis to upgrade the station.
The space station crew still has a busy few weeks ahead. Kotov and two other members of the station's six-person crew plan to return to Earth on June 2 aboard their Russian Soyuz spacecraft. A new trio of spaceflyers will launch soon after to replace them.
Remaining shuttle flights
NASA will launch one more new room, a storage closet, to the space station with shuttle Discovery in September. Russia also plans to deliver one more, larger compartment in the next year or so.
Only two more shuttle flights remain after this one (on Discovery and Endeavour) before NASA's shuttle fleet is retired.
While this mission is Atlantis' 32nd and final scheduled mission, NASA and some lawmakers are lobbying to fly the shuttle one more time in June 2011. NASA already plans to prepare Atlantis for flight as a precaution. The orbiter must be ready to serve as a rescue ship for NASA's final shuttle mission on Endeavour in late November.
NASA currently does not have approval for an extra shuttle mission in 2011. President Barack Obama's administration would have to order the flight and sign off on extra funding for it by the end of next month to make it happen, NASA officials have said.
Antonelli said he wasn't sure what would happen with Atlantis after its final flight (museums across the United States are vying for the three orbiters) but he knew where the shuttle would go if he could pick: His own backyard.
"I get plenty of letters from my homeowners' association about leaving my garbage can out and not keeping my grass trimmed," Antonelli told reporters before leaving the station. "But if I got Atlantis parked in my backyard, it would make all those letters just kind of disappear,
But first, the crew of Atlantis has to return home.
On Monday, the astronauts plan to inspect their spacecraft's heat shield for any new dings caused by space debris or micrometeorites. The shuttle has already received a clean bill of health with respect to any launch debris. Shuttle inspections have been standard since wing damage from debris led to the tragic 2003 loss of shuttle Columbia and its crew.
On Tuesday, the Atlantis crew will ready the shuttle to once again fly in Earth's atmosphere. Landing is set for Wednesday at 8:48 a.m. EDT (1248 GMT) at NASA's Kennedy Space Center in Florida.
- POLL: Should NASA Retire the Space Shuttles?
- Gallery - Photos From the Last Launch of Atlantis
- Wow! Shuttle, Space Station Photographed Crossing the Sun
SPACE.com is providing complete coverage of Atlantis' STS-132 mission to the International Space Station with Senior Writer Clara Moskowitz and Managing Editor Tariq Malik based in New York. Click here for shuttle mission updates and a link to NASA TV.