America's manned space program roared back to life Tuesday with the launch of Space Shuttle Discovery (search), and engineers immediately began analyzing video of falling debris in hopes of ruling out a problem like the one that doomed Columbia 2 1/2 years ago.

National pride and the future of space exploration itself hung in the balance as Discovery and its crew of seven rose from the launch pad at 10:39 a.m. into a hazy blue sky and headed out over the ocean in the most scrutinized launch in NASA history and the first shuttle flight since the Columbia disaster.

NASA Administrator Michael Griffin (search) urged everyone "to take note of what you saw here today: the power and the majesty of the launch, of course, but also the competence and the professionalism, the sheer gall, the pluckiness, the grittiness of this team that pulled this program out of the depths of despair 2 1/2 years ago and made it fly."

Nevertheless, Griffin and other NASA officials said they will not celebrate until Discovery comes home safely. Columbia, after all, seemed to be home free until it fell to pieces on its return to Earth.

Two chase planes and more than 100 cameras documented Discovery's ascent from every possible angle to capture any sign of flying debris, and hours after the shuttle had settled into orbit, NASA officials said an object that may have been a 1 1/2-inch piece of thermal tile appeared to break off from the Discovery's belly during liftoff. It came off from around a particularly vulnerable spot, near the doors to the compartment containing the nose landing gear.

Also, a large object — perhaps a piece of foam insulation — seemed to fly off from the giant external fuel tank but did not hit the shuttle itself, NASA flight operations manager John Shannon said.

"The big question is, what is that?" Shannon said.

He said it is too early to say whether the two incidents pose any danger to the shuttle. Among other things, it is not yet known how deep the gouge in the tile is.

Shannon said the cameras have provided the space agency with more detailed images than it has ever seen before, and it not clear whether the debris represents anything out of the ordinary. Also, the tiles on NASA's shuttle fleet have sustained thousands of dings over the years.

Shannon disclosed that the nose cone of the fuel tank hit a bird just seconds after liftoff.

NASA promptly notified Discovery commander Eileen Collins of the debris sightings and said the agency's image-analysis experts were looking at the pictures frame by frame and would have more information Wednesday morning.

In addition, the astronauts will use a new 50-foot boom to inspect their ship on Wednesday, and the crew of the international space station will photograph all sides of Discovery before Thursday's linkup between the two.

The baffling fuel gauge problem that thwarted a launch attempt two weeks ago did not recur this time, and the countdown was remarkably smooth. If the sensor had acted up during the countdown, NASA had been prepared to bend its safety rules to get the shuttle flying.

Space program employees and relatives of both the Discovery and Columbia crews looked on nervously as the shuttle lifted off.

"On behalf of the many millions of people who believe so deeply in what we do, good luck, Godspeed — and have a little fun up there," launch director Mike Leinbach told Collins and her crew just before liftoff.

Across the country, Americans watched the liftoff, cheering and applauding in New York's Times Square as the Discovery roared away from the launch pad. In the hometown of Japanese astronaut Soichi Noguchi, the pop of firecrackers and congratulatory cheers of "Banzai!" rang out.

At the Kennedy Space Center, nearly 2,500 guests of NASA, including first lady Laura Bush and brother-in-law Gov. Jeb Bush, cheered, whistled and clapped as the shuttle lifted off, watching through sunglasses as it soared out over the Atlantic. The spectators included members of Congress, as well as relatives of the 14 fallen Columbia and Challenger astronauts.

From Washington, the president wished the crew a safe and successful mission.

"Our space program is a source of great national pride," he said in a statement, "and this flight is an essential step toward our goal of continuing to lead the world in space science, human spaceflight and space exploration."

Hours after Discovery had settled into orbit, Collins saluted "the great ship Columbia and her inspiring crew" and said of the fallen astronauts: "We miss them and we are continuing their mission. God bless them tonight and God bless their families."

During the 12-day mission, Collins and her crew will deliver supplies to the space station and test new techniques for inspecting and patching the shuttle in orbit.

The 114th shuttle liftoff came after a humbling self-examination on NASA's part, extensive safety modifications to the spacecraft and many months of hurdles and setbacks.

Columbia was brought down by a suitcase-size piece of foam insulation that broke off the big external fuel tank during liftoff and caused a gash that allowed hot gases into the wing during the return to Earth 16 days later on Feb. 1, 2003. But NASA could barely make out the blow in the photographs of the launch because the few available images were poor.

This time, the space agency added more and better surveillance cameras for Discovery's launch and sent up a pair of camera-equipped planes to chase the flight. As soon as the shuttle reached orbit, the astronauts took digital pictures of the tank falling away. Spy satellites will also photograph the shuttle in coming days.

If any serious damage is found, NASA will have to choose between attempting repairs or, more likely, moving the shuttle crew into the space station for at least a month to await rescue by the shuttle Atlantis, which is already being readied for liftoff. Both scenarios are extremely risky.

NASA's chief acknowledged a lot is riding on the flight: the shuttle program, the space station, the president's plan to send astronauts back to the moon and on to Mars — and seven lives.

"It's about hope, it's about imagination, it's about the future, and when you take away a great space program, you take away a lot of people's future," Griffin said in an interview with The Associated Press on the eve of launch. "What's riding on this flight is people's hope for the future."

In all, nearly 50 safety improvements were made to the shuttle in the wake of Columbia tragedy. The fuel tank was extensively redesigned, with less foam insulation than before but extra heaters to prevent a dangerous buildup of ice once it is filled with super-cold liquid propellant. NASA feared falling ice could be as lethal as chunks of foam.

Also, dozens of motion and temperature sensors were embedded in the wings to detect any blows from debris.

At the same time, the space agency revamped the way it makes decisions and listens to dissenting views, especially from lower-level employees. Columbia accident investigators blamed the catastrophe in part on a broken safety culture, or a tendency to downplay risks and discourage engineers from speaking up.

While in orbit, the astronauts will try out repair kits on deliberately broken samples of thermal tiles and panels. They will practice working with goo and other patching materials and different types of brushes, putty knives and a caulking gun.

The liftoff was a relatively solemn affair. NASA did not hold the usual post-launch party.

"The first thing you learn as a student pilot is that the flight's not over until the engine is shut off and the airplane's tied down," said Griffin, NASA's chief. "Twelve more days, plus, before we achieve that state, and that's when we'll know that this was a safe flight."

In addition to Collins and Noguchi, the crew members are pilot James Kelly; Stephen Robinson; Andrew Thomas; Wendy Lawrence; and Charles Camarda.