Space shuttle Atlantis began its long trek home on Tuesday after a nine-day stay at the International Space Station in which crew members installed new solar energy panels and battled balky computers.
Atlantis undocked from the station, then performed a final inspection of its heat shield before its scheduled return to Earth on Thursday.
NASA officials said they did not expect the scan using the shuttle's sensor-laden robot arm to turn up any shield damage, but the data was being studied by NASA engineers.
"We'll know more tomorrow, but I don't anticipate any problems," flight director Cathy Koerner said at Johnson Space Center.
During one of four spacewalks performed at the station, astronaut Danny Olivas repaired a torn thermal blanket near the shuttle's tail as a precaution against heat damage when Atlantis reenters the earth's atmosphere.
Heat shield damage that went undetected led to the catastrophic 2003 break-up of shuttle Columbia as it returned from space. The seven astronauts on board were killed.
Space station program manager Mike Suffredini said Tuesday's undocking was "a picture perfect departure" as Atlantis eased away from the $100 billion space complex.
Television shots showed a few unidentified objects floating through the picture, but Suffredini said they could be ice or small particles often jarred loose at undocking.
NASA experts were looking at the images, he said, but "it's not a big concern."
Atlantis completed the main task of its mission by installing a new set of solar energy panels on the station to generate more electricity for the growing complex.
European and Japanese-built modules are to be added on flights later this year and early in 2008 as NASA tries to complete the half-finished station before the shuttle fleet is retired in 2010.
The assembly work was overshadowed by a computer crash on the station that raised fears the outpost, manned continually since 2000, would have to be temporarily abandoned.
The computers keep the station properly positioned for communications and power generation from the Sun. The crash was thought to be caused by a still-undetermined electrical problem.
After skipping two nights' sleep, station commander Fyodor Yurchikhin and flight engineer Oleg Kotov rewired the computers and they were fully revived over the weekend.
Atlantis was scheduled to land at the Kennedy Space Center in Florida at 1.54 pm EDT (1754 GMT) on Thursday, but NASA officials said the shuttle has enough supplies to stay in space until Sunday if weather or other problems force a delay.
The start of the mission was put off for three months for repairs to Atlantis' fuel tank after it was battered by a freak Florida hail storm.
(Additional reporting by Irene Klotz in Cape Canaveral)