NASA managers said several pieces of foam fell off the external fuel tank during launch but by then the shuttle was beyond the point in its flight where they could be a hazard to the spacecraft.

"This isn't too abnormal," said Bill Gerstenmaier, associate administrator for spaceflight. "We fully expected to lose some foam."

Any flyaway foam was expected to be small and of no consequence to the shuttle. Work remains on one area of the tank foam and the agency's top engineer and chief of safety had wanted to postpone Discovery's launch until after the work was done.

NASA Administrator Michael Griffin, however, decided to proceed with launch, knowing that the shuttle crew could be housed aboard the space station if their ship was hit by debris and sustained damage too severe to return home safely.

Delaying Discovery's launch, Griffin said, would put too much pressure on the shuttle program, which needs to fly 16 missions to the station to complete construction before 2010.

On Wednesday, the Discovery crew will begin detailed examinations of their ship's heat shield for signs of damage from debris impacts. The astronauts will use a sensor-laden boom to scan the shuttle's wings and nose-cap, areas that are particularly vulnerable to damage.

The space station crew also will photograph and videotape the heat-resistant tiles on the shuttle's belly as Discovery approaches the space station for docking on Thursday.

NASA already has spent about $1.3 billion fixing the shuttle's fuel tank and developing other safety upgrades since the Columbia accident. The agency has no more time or money to spend on major refurbishments if additional problems are discovered.

Shuttle commander Steve Lindsey, 45, pilot Mark Kelly, 42, and mission specialists Mike Fossum, 48, Lisa Nowak, 43, Stephanie Wilson, 39, and British-born American Piers Sellers, 51, waved small American flags as they headed from their quarters to the launch pad, marking the U.S. Independence Day.

Thomas Reiter, 48, of Germany, waved a German flag. He will be the first European to live on the space station and is scheduled to return home with another shuttle crew in December.