The shuttle Discovery and its crew of six returned safely home Monday, rejuvenating a space program that until now had been vexed by the same chronic foam problem that brought down Columbia three years ago.
Within hours of the smooth touchdown, NASA was already looking ahead to the next shuttle launch in just six weeks and, with it, the long-awaited return to construction work on the half-finished space station.
"It's a good day," NASA Administrator Michael Griffin said. "It's an awfully good day."
Discovery's commander, Steven Lindsey, who took a walk around the shuttle after landing, said he had never seen one look so clean and undamaged after a spaceflight. It was a striking achievement for a launch that was challenged by some within NASA who wanted more improvements to protect the spacecraft from flyaway foam insulation.
Lindsey noted that both of the mission's major objectives were accomplished: completing tests of the shuttle and its redesigned fuel tank, which now carries less foam, and readying NASA to resume space station construction, left hanging after the Columbia tragedy which killed seven astronauts.
"We're ready to go assemble station," Lindsey said in the shorthand typical of NASA engineers. "And we're ready to start flying shuttles on a more regular basis."
All around the Johnson Space Center in Houston, home to Mission Control, posters advertised the homecoming ceremony that was set for the astronauts on Tuesday. "We're BAAAACK!" the signs shouted in big red letters.
The smooth landing left NASA officials jubilant, after conquering the potentially deadly threat of foam chunks breaking off the external fuel tank during launch — still a problem, but not a serious one on this mission.
The largest piece of foam that came off Discovery's tank during the July 4 liftoff was barely bigger than a sheet of legal paper and weighed less than an ounce. Like all of the handful of notable foam chunks that peeled away, it came off late enough in the launch to pose no danger to the spaceship.
During the same shuttle's launch last summer, a 1-pound chunk of foam tore away at a crucial moment. Even though it missed Discovery, it stunned and embarrassed NASA, and forced a one-year grounding of the shuttle fleet, on top of what already had been a 2½-year standdown. The piece of foam that ripped Columbia's left wing weighed 1½ pounds.
Outsiders gave NASA high marks Monday.
"What's important is that they changed their approaches to spaceflight considerably; it was an organizational test," said American University public policy professor Howard McCurdy, who has written several books about NASA management. "I don't give many A's. They're clearly back to where they want to be. A B-plus."
Columbia accident investigator John Logsdon, director of George Washington University's Space Policy Institute, said Discovery's latest mission was carried out "with the kind of laser-like attention and vigilance" that was missing before the 2003 disaster.
NASA still does not know why so much foam insulation is falling off the tank late in the launch when it poses no threat, but the just-completed flight will be "tremendously important" in providing clues, said Bill Gerstenmaier, space operations chief.
An especially vulnerable area of the tank will be redesigned, hopefully by next year.
"This is as good a mission as we've ever flown," Griffin said. "But we're not going to get overconfident. We're going to keep looking at the data and we're going to make our decisions based on the data just the way that we did on this flight."
Although safe, Discovery's hourlong descent from orbit was marked by some unusual events, reminders that spaceflight always involves a multitude of risks big and small:
— One of three power units needed to power the hydraulic landing systems was leaking, but operated properly. NASA still does not know whether harmless nitrogen gas or flammable hydrazine was escaping.
— A probe for monitoring air flow around the re-entering shuttle was sticky and took longer than usual to be released.
— Storm clouds popped up at the last minute, and Discovery had to switch direction for landing on the Kennedy Space Center runway.
— The sound of gunshots and blaring car horns heralded Discovery's return; NASA made the racket to keep birds out of the shuttle's path. As it turns out, the shuttle was decorated with bird droppings before liftoff, and the residue made it all the back from orbit, albeit a bit charred.
"It was a great mission, a really great mission," Lindsey declared at touchdown, at 9:14 a.m.
The journey spanned 13 days and 5.3 million miles. The mission saw the astronauts repeatedly inspect the entire thermal skin of their ship and conduct three spacewalks to do patching tests, try out a 100-foot boom as a possible work platform, and fix a rail car outside the station.
They also dropped off several thousand pounds worth of station supplies and a new station resident: European Space Agency astronaut Thomas Reiter of Germany, who expanded the station crew to three for the first time since 2003.
Griffin noted that NASA faces 16 more shuttle flights to complete the space station and, hopefully, repair the popular Hubble Space Telescope. A decision is expected by fall on whether to send a shuttle to Hubble one final time, to extend the observatory's life.
NASA is up against a hard 2010 deadline for completing the space station. That's when the three remaining shuttles will be retired to make way for a new spaceship capable of carrying astronauts to the moon and eventually on to Mars.
"We don't have any slack. We have just enough shuttle flights left to do the job so we can't afford to mess up," Griffin said. "The team performed superbly systemwide [with Discovery] and what we have to do is exactly that same thing again from now until the end of 2010."
Complicating matters is that NASA faces a series of tremendously difficult assembly flights, beginning with Atlantis' upcoming mission to deliver and install a massive beam and set of solar wings. NASA is aiming for a liftoff as early as Aug. 27.
Shuttle program manager Wayne Hale said he wants just as much intense scrutiny — and differing opinions among engineers — for the next flight and all the ones after that.
A few weeks before Discovery's liftoff, NASA's chief engineer and top safety officer argued for putting off the mission until more design changes could be made to one area of the fuel tank. Hale was all for going ahead. Griffin cast the final, decisive vote.
After landing, Lindsey said he trusted that launch decision and noted it was an outgrowth of the management culture lessons learned from Columbia. The successful conclusion of the mission is more of a beginning to space station assembly and exploration, he said, than an end to the post-Columbia recovery era.
"I don't think we want to ever put Columbia behind us," Lindsey said.