CAPE CANAVERAL, Fla. — With the thunderous roar of 7.5 million pounds of thrust, equivalent to the power of a small nuclear device, the United States relaunched its era of spaceflight yesterday, sending seven astronauts into orbit aboard the shuttle Discovery.

The exuberance surrounding the launch was tempered, however, when National Aeronautics and Space Administration engineers discovered three events that occurred over the 8.5-minute ride into space that raised concerns about the shuttle heat shield, the critical system that was at fault in the Columbia disaster 30 months ago.

NASA officials said they would begin a detailed analysis of launch photography and a thorough in-orbit inspection of the craft using its robotic arm.

NASA cameras and radar found that a 1 1/2-inch section of heat-resistant tile sheered off from the nose landing-gear door, damage that they could not fully assess without more detailed inspection, said John Shannon, flight operations and integration manager.

The cameras also detected an object floating away from the shuttle just after the solid rocket boosters had separated two minutes after launch. The shuttle's external tank hit a bird seconds after launch, he added. So far, the experts cannot say whether the events jeopardize safety, Shannon said.

"It's way premature to say there is a serious problem," Shannon said. But he added, "I'm not going to sit in here and sugarcoat anything."

Thousands of people packed highways near the launch site and millions watched on television as Discovery's engines painted the morning sky a brilliant gold and shook Florida's eastern coastline at 10:39 a.m. EDT (4:39 a.m. Hawai'i time), the same time Columbia started its final flight.

NASA managers, emerging from one of the darkest periods in the four-decade history of the space program after the loss of Columbia, heaved sighs of relief and slapped each other on the back in celebration.

"Take note of what you saw here today," NASA Administrator Michael Griffin said in a news briefing after the launch. "The power and majesty of the launch, but also the competence and professionalism, the sheer gall and pluckiness of this team that pulled this program out of the depths of despair 2 1/2 years ago and made it fly."

First lady Laura Bush, watching from a VIP grandstand filled with 2,500 close-up observers, said it was "pretty terrific" that the first flight after Columbia was commanded by a woman, Eileen Collins.

During the 13-day mission, the seven-person crew plans to dock with the International Space Station, replace a failed gyroscope and perform three spacewalks, one of which will test shuttle repair techniques developed after Columbia. It will take three days for the shuttle to maneuver to the higher-flying station.

After another test mission, with the shuttle Atlantis in September, NASA hopes to resume assembly of the space station, a job that was put on hold after the Columbia accident. In the past two years, plans for the station have been scaled back, and now NASA hopes to end its involvement in the program not long after the agency finishes building it.

The shuttle took 8 1/2 minutes to reach orbit. After the main engines shut off, Collins took the control stick and flipped the orbiter over so the crew could photograph the external tank as it drifted away.

The photos will be downloaded to NASA engineers who will analyze whether any foam insulation fell off the tank and potentially damaged the orbiter.

Shannon said the gouge on tiles occurred in a sensitive area near a seal on the nose landing-gear door. A laser inspection tool will be used today to determine the depth of the gouge, which is critical to determining whether it is a safety hazard.

"Depth is everything," Shannon said.

Shuttle tiles have sustained 15,000 debris hits and gouges over the 24-year history of the program, most of them harmless.

The object floating away from the shuttle after the solid rocket booster separation is of concern because, so far, NASA cannot estimate its size or whether it caused any damage or even where it came from.

"I don't know what it was. We need to understand that," Shannon said.

NASA managers said they would begin scanning images of the launch overnight yesterday. It will take up to six days to analyze all the evidence and determine the condition of the orbiter. NASA had far more cameras, 107 total, watching the launch than ever before.

One early endorsement of the work done to make the shuttle safe over the past two years came from veteran astronaut Collins, who called the launch the "smoothest ascent" she had experienced.

"We couldn't ask for a better flight," Collins said from orbit.

The mood of celebration yesterday was tempered by the realization that the launch was only half the mission. "One thing (that will be) better than the launch is landing (safely) in 12 days," said Mike Leinbach, launch director.