Space shuttle Atlantis' astronauts thanked the international space station residents for their warm hospitality and then began their journey home to Earth, ending a weeklong visit.

"Godspeed and happy landings," space station astronaut Carl Walz called out to the shuttle crew.

"You've been outstanding hosts," commander Michael Bloomfield replied following Wednesday's undocking. "Thanks so much for taking care of us the last week. We'll keep you in our thoughts and prayers, and we'll see you on the ground in a couple of months."

The shuttle is due to land Friday.

Atlantis' crew of seven installed a $790 million girder and railcar on the space station and also dropped off fresh food, clean clothes and mail for the three station men, who have two months remaining in their six-month mission.

Before closing the hatches between the spacecraft, the two crews shook hands and embraced. The shuttle undocked as the spacecraft sped 250 miles above the Atlantic just west of Ireland, with the station's bell chiming. "Atlantis, departing," announced station astronaut Daniel Bursch, a Navy captain.

The shuttle astronauts left space station Alpha 27,000 pounds heavier with the addition of the 44-foot girder.

They conducted four spacewalks, lasting a total of 28 hours, to hook up the aluminum beam. They also tested the railcar mounted to tracks on the girder. The railcar will be used later this year to transport the station's robot arm and more girders.

By 2004, this framework should extend 356 feet. Solar wings and radiators will be bolted to it.

"When we get all done with the huge truss ... we will actually have enough power where we can add two more laboratories" from other countries, Bloomfield said in a TV interview Thursday. "So by adding this first segment, we've opened the road and, with the railroad car, to make sure that we can continue to build the station."

Walz, Bursch and their Russian commander, Yuri Onufrienko, are expecting more guests in another week. A Russian spacecraft carrying a Russian cosmonaut, an Italian astronaut and a South African millionaire tourist is due to lift off April 25 and arrive at the station two days later.

Before Atlantis left, Bursch proudly showed off some of his young sons' artwork, which was hand-delivered by the shuttle crew.

"The separation's been tough," the father of four said earlier this week. "Four down, two to go," he said, counting down the months.

Bursch and his crewmates are due to return to Earth in June.