CAPE CANAVERAL, Fla. — The space shuttle Discovery dodged clouds to make a textbook touchdown here Monday, capping a 13-day mission that set the stage for resuming construction of the international space station.
Two bone-rattling sonic booms heralded the shuttle's arrival over Florida, and only a couple of minutes later, Discovery plunged to its landing at NASA's Kennedy Space Center at 9:14 a.m. ET.
"Welcome back, Discovery, and congratulations on a great mission," spacecraft communicator Steve Frick told the crew.
"It was a great mission, a really great mission," Discovery commander Steve Lindsey replied. "Enjoyed the entry and the landing."
The flight ranked as one of NASA's safest ever, with almost none of the worrisome fuel-tank foam loss that marked last year's flight of Discovery. In fact, NASA said Discovery's 5.3 million-mile (8.5 million-kilometer) flight was nearly flawless.
"This is as good a mission as we've ever flown," NASA Administrator Mike Griffin told reporters after the landing.
Launch manager Mike Leinbach said the successful flight also helped exorcise the demons raised by the loss of the shuttle Columbia and its crew three and a half years ago — the last time a space shuttle attempted to land in Florida.
"Columbia's landing day was a horrible day," he said. "Today was a great day."
Lindsey said he preferred not to think of the flight as the end of a tragic chapter in space history.
"I think it's more like a beginning of another phase, which is space station assembly and then on to exploration," he told reporters here. "I don't think we ever want to put Columbia behind us. I think we need to remember the lessons learned from Columbia. We obviously have learned the technical lessons of Columbia. We are still learning them, we will continue to learn them. But more importantly, we have learned the cultural, organizational lessons of Columbia — and that's the one thing that we don't ever want to forget."
Weather worries
NASA had declared Discovery safe for landing after days of agonizing over the shuttle's heat shield and a small leak in one of the onboard power units. However, the verdict on Monday's weather went to almost the last possible minute.
Forecasters were watching a band of rain clouds north of the shuttle's landing strip here at NASA's Kennedy Space Center, but concluded that the rain would stay far enough away and gave their irreversible go-ahead for the landing attempt.
Discovery slowed down from a velocity 25 times the speed of sound — in the process, heating the shuttle's protective skin to temperatures as high as 3,000 degrees Fahrenheit (1,700 degrees Celsius). The flight path took the shuttle over Mexico's Yucatan Peninsula, west of Cuba and then across Florida itself.
Lindsey said the moon could be sighted through the glow of superheated gases as Discovery passed through the atmosphere. "It was beautiful," he said later. "We could see the bright orange glow above, and I could see the earth moving below, and it was just spectacular."
The only problem on the way down was a harmless glitch involving one of the shuttle's air data probes. But a stray rain cloud cropped up within NASA exclusion zone during the descent, prompting controllers to shift Discovery's final approach from the south end of Kennedy Space Center's 15,000-foot-long (4.6-kilometer-long) runway to the north end. Lindsey also had to fly the shuttle through a cloud bank before breaking out into open sky.
In light of those circumstances, lead flight director Steve Stich gave Lindsey "a perfect 10" for the landing.
Discovery's touchdown represented the first shuttle landing in Florida since December 2002. Columbia broke up over Texas on its way to a Florida landing in February 2003, killing all seven astronauts aboard and forcing a 2½-year-long suspension of flights. Last August, Discovery's first post-Columbia flight ended in California because of unacceptable weather in Florida.
Marking a transition
After a landing-strip inspection of the shuttle, Lindsey said on NASA TV that his mission marked a transition between the Columbia tragedy and the final push to finish construction of the international space station by 2010.
"We had two major objectives on this flight," Lindsey said. "The first one was to complete the return-to-flight test objectives ... and the second one was to get us back to space station assembly. And I think we accomplished both those objectives."
He voiced praise for his "nearly perfect" crew as well as for NASA workers on the ground. "The vehicle was clean all the way through the flight," he said. "We had very, very few problems."
Administrator Griffin agreed that Discovery was "the cleanest vehicle we've ever seen" — virtually free of the "dings" to shuttle tiles that are usually seen at the end of a shuttle flight. At the same time, he warned against complacency.
"We learned a lot from this flight, and that's all to the good," he said. "But we need to not be overconfident. We need to not get ahead of ourselves. We need to stick with the numbers and see what they tell us as we get ready to go do the next flight."
Focus on safety and the station
The agenda for Discovery's 13-day flight was so full that the astronauts found it hard to stop working, even on their designated day off. "I actually ordered the crew that they were not allowed to work," Lindsey told reporters Sunday.
This was Lindsey's fourth spaceflight, and on Monday he said "this was the toughest time line I've ever had." He wondered whether some of the tasks on that time line, such as the detailed inspection conducted after Discovery left the space station, were "worth the risk for the data you get, and we're going to answer those questions."
"We couldn't have fit anything more in, I can tell you that," Lindsey said. "I wouldn't want to add anything, but I think we were successful at what we did."
Among the highlights:
- Discovery used a lower-impact flight profile for its ascent, and four rounds of in-flight inspections showed there was minimal loss of foam insulation from the shuttle's external fuel tank. Foam debris has been a key focus of NASA's safety improvements, because the damage done by such debris is thought to have caused the Columbia tragedy. Significant foam loss was also seen during Discovery's flight last summer — which led to a second redesign of the fuel tank.
- Spacewalkers tested new techniques for inspecting the shuttle and fixing damage if necessary. One technique involves standing on a 50-foot (15-meter) extension boom attached to the shuttle's 50-foot robotic arm, to get to hard-to-reach spots on the shuttle's underbelly. The astronauts also tested a puttylike sealant that could be used to patch cracks or small holes in the shuttle's reinforced carbon panels.
- Discovery's crew delivered more than two tons of supplies to the space station, ranging from food and other basics to a new lab freezer and exercise bike. They are bringing back almost as much tonnage of old equipment and trash.
- Discovery also dropped off German astronaut Thomas Reiter for a six-month stay aboard the station. Reiter is the first long-term station resident who is neither American nor Russian, and his presence brings the station's crew complement to three for the first time in three years.
- Discovery's spacewalkers made repairs to the cable reels on a space station rail car system that had to be fixed before the resumption of assembly. They also installed a spare part for the station's cooling system.
The flight featured moments of levity as well. During one of the inspections, an imager on the extension boom turned up evidence of whitish streaks on the shuttle's panels and nose cap — and mission managers determined that the streaks were actually bird droppings deposited before flight. After the landing, Discovery astronaut Mike Fossum reported that the droppings were still there. "They made it home, a bit charred," he said.
Astronaut Piers Sellers, meanwhile, had to weather some jibes over a spatula he lost during the mission's third and final spacewalk. NASA said the wayward spatula posed no threat to the shuttle, but Sellers admitted Monday that it was "a bad moment, because it was my favorite spatula ... don't tell the other spatulas."
When asked to name his most satisfying moment of the mission, Sellers said it was at the very end, when "we all looked at each other — at 'wheels stop,' frankly — and said, 'We're done. ... We did it.'"
What lies ahead
The shuttle Atlantis is already being prepared for next month's mission, which involves the installation of a truss segment and additional power-generating solar arrays on the international space station. And in the next week, NASA will start getting Discovery back in shape for its own next mission in mid-December.
"We're in a turnaround process now that we haven't been in for three and a half years, so that feels good," launch manager Mike Leinbach told reporters.
At the same time, NASA officials said the flights ahead represented the most complex phase of the station assembly process. "We can't afford to mess up," Griffin said.
A successful end to Discovery's mission not only opens the way for the resumption of space station construction, but also makes a final mission to the Hubble Space Telescope more likely. Informally, NASA already has begun planning for such a servicing mission in 2008, but Griffin said he would hold off on deciding whether or not to add the mission to the formal schedule until later — "certainly not later than this fall."
"No one wants to do a Hubble flight more than I," he said, "but we do not want to get ahead of ourselves. We want to go about things in the right way."