The US space shuttle Atlantis returned safely to its Florida home on Thursday, capping a successful mission to resume International Space Station construction 3-1/2 years after the 2003 Columbia disaster.
After 12 days in space, including six at the half-built $100 billion space station, Atlantis returned to Earth's atmosphere, soaring through predawn skies over the Pacific Ocean, Yucatan Peninsula and Gulf of Mexico before reaching Florida's west coast.
Commander Brent Jett circled Atlantis high over the Kennedy Space Center, then ended its nearly 5-million-mile (8-million-km) voyage with a smooth touchdown on a three-mile (4.8-km) long runway at 6:21 a.m. (1021 GMT)
Double sonic booms rang out over central Florida as the shuttle slipped below the speed of sound for the first time since it blasted off on Sept. 9 after two weeks of delays.
The mission marked NASA's re-entry into the space-station construction business -- a task put on hold for nearly four years for safety upgrades after Columbia exploded -- and boosted confidence the massive construction project can be completed by 2010, when the shuttle fleet is to be retired.
"The space station's half built. We have half to go," NASA administrator Michael Griffin said. "When we're all done it will weigh nearly a million pounds, for humanity's first really long-term outpost in space. We're halfway there but I think we're going to make it."
Jett and his five crewmates - pilot Chris Ferguson, flight engineer Dan Burbank, Canada's Steve MacLean, Joe Tanner and Heidemarie Stefanyshyn-Piper - delivered and installed a $372 million solar power system during a complex series of robotic maneuvers and three spacewalks.
FINISHING THE OUTPOST
NASA needs to fly at least 14 more station assembly missions to finish the space station. The shuttle is the only spacecraft able to carry the station's components.
A series of problems had troubled Atlantis' mission, including a lightning strike, a hurricane and technical problems with a power generator and a fuel sensor that delayed launch for nearly two weeks, as well as unidentified objects flying outside the shuttle that postponed landing for a day.
"This is just routine life in the space business," Griffin said.
NASA had planned to land Atlantis on Wednesday, but wanted the crew to make additional inspections of the ship's heat shield after the objects were spotted. The sightings prompted concern that the shuttle had been hit by something and possibly damaged.
But the mystery space junk caused no worry on board, Jett said.
"Actually we were not very concerned," he said. "In my experience on shuttle flights, a lot of things float out of the payload bay ... We just assumed that whatever objects we saw had come from the payload bay."
NASA has been particularly cautious about damage to the shuttle since Columbia disintegrated while returning to Earth on Feb. 1, 2003, due to heat shield damage from the impact of debris that flew off the shuttle as it was launched. The seven astronauts on board were killed.
Engineers believe the floating object that caused the most concern was a spacer, a piece of rigid plastic inadvertently left between pieces of ceramic tile on the shuttle's belly.
NASA's next shuttle launch is targeted for Dec. 14, when Discovery is scheduled to head on another space station construction mission. Space agency managers are discussing the possibility of flying a week earlier.