EDWARDS AIR FORCE BASE, Calif. (Reuters) - The space shuttle Discovery and its seven astronauts returned to Earth safely on Tuesday, successfully completing NASA's troubled resumption of human space flight 2 1/2 years after the Columbia disaster.
NASA officials appeared visibly relieved after the problem-free landing, which may be the shuttle's last flight for some time. The fleet was grounded after the U.S. space agency's recent safety upgrades failed to prevent Discovery from shedding insulating foam at launch, the same problem that doomed Columbia.
"Discovery is home, the crew is safe and we've come full circle now," said NASA launch director Mike Leinbach.
Following a smooth and problem-free re-entry into the atmosphere, Discovery commander Eileen Collins gently settled the 100-ton ship onto a concrete runway just as the first rays of morning light were visible across the rugged landscape.
"We have had a fantastic mission," Collins, dressed in a blue jumpsuit, said later on the runway after performing a traditional walk-around to inspect the shuttle. "We are so glad to be able to come back and say it was successful."
NASA diverted the shuttle to California after skipping four chances to land at Discovery's home port, the Kennedy Space Center in Florida, because of menacing thunderstorms on Monday and Tuesday.
The manned flight was NASA's first since Columbia broke apart over Texas on Feb. 1, 2003, killing all seven astronauts on board.
"I was pretty anxious all day," said flight director LeRoy Cain, who also oversaw the flight team that directed Columbia's failed return to Earth.
NASA suspended shuttle missions after Discovery's external fuel tank shed a piece of foam during lift-off nearly as big as the chunk that smashed into Columbia's wing in 2003. That damage was blamed for bringing Columbia down 16 days later as it headed toward a landing strip in Florida.
NASA had spent more than $1 billion fixing the tank and implementing other safety upgrades, but agency managers refused to let the problems cast too dark a shadow on Discovery's mission.
"It's going to be very hard to top this mission," NASA Administrator Michael Griffin said, while adding that more work remains before NASA will declare the shuttle fleet fit to fly again.
"We're going to try as hard as we can, but we're not going to go until we're ready to go," Griffin said.
President George W. Bush applauded both NASA and the shuttle's crew.
"It was an important step for NASA as it regains the confidence of the American people and begins to transition to the new mission we've set out for NASA. So congratulations, Commander Collins. It's quite an achievement," Bush said.
The shuttles, scheduled to be retired in 2010, are key to the future of the unfinished International Space Station because they are the only spacecraft capable of carrying large components into space. NASA wants to finish construction of the station before the fleet is retired.
During the mission, Discovery's crew restocked the space station's pantries, restored its key steering system, removed tons of discarded equipment and trash and added a new stowage platform for spare parts.
But they also for the first time checked their ship's heat shield while the shuttle was in orbit and made an impromptu repair.
Astronaut Steve Robinson strapped onto a platform on the space station's robot arm for an unprecedented spacewalk to Discovery's belly, where he removed two protruding cloth strips from the smooth surface of the ceramic-tiled heat shield.
Managers were concerned the strips could disrupt air flow over the shuttle and raise temperatures dangerously on re-entry.
NASA extended the Discovery crew's visit at the outpost from eight to nine days to transfer extra supplies when it became evident the next scheduled mission to the station likely would be delayed while engineers work on the fuel tank issue.
Joining Collins and Robinson for NASA'S 114th shuttle mission was pilot Jim Kelly, Japan's Soichi Noguchi, and astronauts Wendy Lawrence, Charles Camarda and Andy Thomas.
(Additional reporting by Irene Klotz, Jim Loney and Deborah Zabarenko in Cape Canaveral)