Space shuttle Discovery and its crew of six returned to Earth through overcast skies Monday, ending a successful mission that put NASA back in the space station construction business.
Discovery glided down through an overcast sky onto the Kennedy Space Center runway at 9:14 a.m. ET, allowing NASA to declare total victory for the first time since before the 2003 Columbia disaster.
It was so cloudy, shuttle commander Steven Lindsey couldn't spot the runway until about a minute before landing.
"Welcome back Discovery and congratulations on a great mission," Mission Control told Lindsey after Discovery rolled to a stop.
"It was a great mission. A really great mission," Lindsey replied.
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 prompted NASA to switch the shuttle's direction for landing.
At touchdown, hoots and whistles came from the few hundred astronaut relatives and space center workers watching the landing.
This was the first landing at Kennedy in nearly four years. Last year's flight of Discovery, after weather delays, came down at Edwards Air Force Base in California, the backup site.
Mission Control waited until almost the last minute before notifying the astronauts that the weather was good enough to come home.
The shuttle, with Lindsey and pilot Mark Kelly at the controls, plunged out of orbit an hour before touchdown with the firing of the braking rockets, and began the hourlong descent at 8:07 a.m. ET.
NASA was certain 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 NASA confidence. Unlike on Discovery's flight a year ago, the external fuel tank shed little foam during liftoff. That flight was the shuttle's first after the Columbia disaster, when a chunk of falling hard foam doomed the shuttle in 2003.
Officials acknowledged re-entry was, along with the launch, the most dangerous phase of the mission and nothing could be taken for granted until Discovery was safely back home following its trip to the international space station.
Toward that end, Discovery's astronauts and flight controllers kept close watch on a slightly leaking power unit that tested out fine a day earlier in orbit.
NASA did not know whether harmless nitrogen gas or flammable hydrazine was dripping from the auxiliary power unit, one of three needed to drive the hydraulic landing systems. The leak was small, managers said. If it worsened during re-entry -- considered unlikely -- the unit would shut down automatically and Discovery would become the first shuttle to land with only two functioning auxiliary power units.
Discovery sported a new, tougher type of landing gear tire for improving safety. In another shuttle first, a GPS receiver was on board to help guide Discovery down to the 3-mile-long landing strip.
It would be the first shuttle landing at Kennedy in nearly four years. Columbia never made it back in February 2003 -- it shattered over Texas -- and Discovery had to take a weather detour to California last summer.
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 particularly vulnerable area of the fuel tank. But NASA Administrator Michael Griffin opted to press ahead with what turned out to be the space agency's first Independence Day launch.
The shuttle carried up seven astronauts, but departed the space station on Saturday with six -- Lindsey, Kelly, Michael Fossum, Piers Sellers, Lisa Nowak and Stephanie Wilson. German astronaut Thomas Reiter 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 August 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, as per President Bush's mandate, to make way for a new spaceship capable of carrying astronauts to the moon.