After a tearful farewell, space shuttle Atlantis and its astronauts undocked Wednesday from the international space station, leaving it a bigger and more elaborate outpost.

Shouts of "We want to stay!" came from Atlantis just before the two spacecraft parted company 250 miles above the Russian-Ukrainian border, ending one week of joint flight.

During their mission, Atlantis' astronauts deliveree three spacewalks to install it.

The six shuttle crew members, who are due back on Earth on Friday, admired their work from afar. "It was wonderful to pull away from the station and see the visible signs of our success," said pilot Pamela Melroy.

The space station's three crew members -- an American and two Russians -- expect more guests in two weeks, but a deadly launch accident in Russia could delay the visit.

A three-man Soyuz rocket is scheduled to lift off Oct. 28 from Kazakhstan to deliver a new space station lifeboat. On Tuesday, a slightly different type of Soyuz exploded shortly after liftoff, killing a soldier on the ground and destroying the satellite on board.

Bob Castle, deputy chief flight director, said it is too soon to know whether the accident will postpone the next flight. Two Russians and a Belgian will be aboard; 'N Sync singer Lance Bass was bumped from the crew after he failed to come up with the reported $20 million fare.

NASA has its own problems, meanwhile, investigating the launch-day failure Oct. 7 of some of the explosive charges that are supposed to release the bolts holding down the space shuttle at liftoff. Each bolt has two charges, only one of which is needed for release. The other charge is there as a backup.

"Half of them fired and half of them didn't. We know that for a fact. We just don't know what caused that second command not to get through," launch director Mike Leinbach said. "We're doing a lot of tests on the ground here, obviously, and so far we haven't found any smoking gun."

NASA wants to understand what went wrong before launching shuttle Endeavour on Nov. 10.

Leinbach would not speculate on what could have happened if the second set of charges had not fired, and stressed that "redundancy created a safe liftoff."

Endeavour will deliver another girder to the space station, along with replacements for the station crew.