CAPE CANAVERAL, Fla. (AP) – Space shuttle Discovery and its crew of six returned to Earth through thick clouds Monday, ending an impressive mission that put NASA’s space program back on a solid, safer course.

“It was a great mission, a really great mission,” Commander Steven Lindsey declared at touchdown, at 9:14 a.m. at Kennedy Space Center. It was only the second shuttle flight since the 2003 Columbia disaster killed seven astronauts.

Later, Lindsey noted that he and his crew accomplished both major objectives: completing the post-Columbia testing of the shuttle and its redesigned fuel tank, and readying NASA to resume building the international space station.

“We’re ready to go assemble station,” Lindsey said after climbing out of Discovery, “and we’re ready to start flying shuttles on a more regular basis.”

The smooth landing left NASA officials jubilant, after conquering the chronic threat of foam chunks that break off the external fuel tank during launch _ still a problem, but not a serious one in this mission.

“This is as good a mission as we’ve ever flown,” NASA Administrator Michael Griffin said. “But we’re not going to get overconfident.”

The shuttle came in from the south, swooping over the Pacific, Yucatan Peninsula, Gulf of Mexico and across Florida to cap a 5.3 million-mile journey that began on the Fourth of July.

A last-minute buildup of clouds led NASA to switch the shuttle’s direction for landing. By the time Discovery approached, it was so cloudy, Lindsey couldn’t spot the runway until about a minute before landing.

A couple of minutes out, NASA made a racket to keep birds out of the way of the approaching spacecraft. Car horns blared, and the sound of gunshots and firecrackers erupted.

At touchdown, shouts and whistles came from the few hundred astronauts’ relatives and space center workers at the runway. “It’s exciting to see the shuttle back,” said astronaut Scott Kelly, the identical twin brother of Discovery’s co-pilot, Mark Kelly. “We’re back on track with maybe flying the shuttle regularly here starting again in August.”

Atlantis is up next with a crew poised to carry out assembly of the international space station, a task put on the back burner after Columbia.

Congratulations poured in from afar. “A proud nation congratulates the brave shuttle Discovery crew on the completion of their successful return to flight mission,” said Sen. Kay Bailey Hutchison, R-Texas.

NASA officials had been certain going into Monday’s landing that Discovery’s heat shield was intact and capable of protecting the spaceship during the fiery re-entry.

Repeated inspections of the ship’s thermal skin in orbit had given everyone confidence. Unlike Discovery’s flight a year ago, the external fuel tank shed little foam insulation during liftoff. That flight was the shuttle’s first after a chunk of falling foam doomed Columbia and its crew.

Officials acknowledged re-entry into Earth’s atmosphere was, along with the launch, the most dangerous phase of the mission and nothing could be taken for granted until Discovery was safely back from its 13-day trip to the space station. Discovery’s astronauts and flight controllers kept close watch on a slightly leaking power unit.

NASA did not know whether harmless nitrogen gas or flammable hydrazine was dripping from the auxiliary power unit, one of three needed to drive Discovery’s hydraulic landing systems. The leak was small and didn’t grow during descent, and the unit operated properly. One of two probes for measuring air flow around the shuttle, however, was sticky and took longer to deploy than usual.

Discovery sported a new, tougher type of landing gear tire for improving safety. In another shuttle first, an on-board GPS receiver helped guide the shuttle down to the 3-mile-long landing strip.

It was the first shuttle landing at Kennedy in nearly four years. Columbia never made it back in February 2003 _ shattering over Texas _ and Discovery had to take a weather detour to California last summer.

“Welcome back, Discovery, and congratulations on a great mission,” Mission Control radioed at touchdown.

“It was beautiful,” Lindsey told controllers. “We could see the bright orange glow above and I could see the Earth moving below and it was just spectacular. We actually also saw the moon through the plasma (scorching gases), so it was a great entry and a great landing.”

A preliminary look showed Discovery to be in outstanding condition with hardly any dings. “This is the cleanest orbiter anybody remembers seeing,” Griffin said.

Some at NASA, including the chief engineer and NASA’s top safety officer, wanted to put off the latest mission until further repairs could be made to a sensitive area of the fuel tank. Griffin pressed ahead with what turned out to be the space agency’s first Independence Day launch.

“We are playing the odds,” Griffin said at the time. The astronauts said they were confident in the decision.

The shuttle carried up seven astronauts, but departed the space station on Saturday with six _ Lindsey, co-pilot Kelly, Michael Fossum, Piers Sellers, Lisa Nowak and Stephanie Wilson. German astronaut Thomas Reiter of the European Space Agency was left behind for a half-year stay, joining two other men there and boosting the station’s crew size to three.

The Discovery crew conducted three spacewalks, one of them to test shuttle patching techniques, and used a 100-foot inspection crane to check the shuttle’s entire thermal armor for any damage from launch or orbital debris. The rocketship turned out to be the cleanest seen in orbit from a thermal perspective, officials said.

The astronauts also demonstrated that the boom could function as a work platform for spacewalkers and delivered several thousand pounds of supplies to the space station, still in need of restocking because of the 2 1/2-year grounding of the shuttle fleet after Columbia’s demise.

By fixing a broken rail car on the outside of the space station, the astronauts paved the way for space station construction to resume in earnest with the next shuttle flight.

Atlantis is scheduled to blast off as early as Aug. 27. Unlike Discovery’s missions, which focused primarily on the flight test aspects, the Atlantis crew will haul up a major space station piece _ a building-block beam _ and attach it to the orbiting outpost.

The station is just half finished, eight years after the first piece went up. NASA wants it completed by the time the three remaining shuttles are retired in 2010 to make way for a new spaceship capable of carrying astronauts to the moon.

“We’ve got 16 flights to go to assemble the station, hopefully do a Hubble (space telescope) repair,” Griffin said. “But we’ve got to take that one flight at a time.”

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