CAPE CANAVERAL, Fla. - Discovery's astronauts strapped into their seats Tuesday and the hatch was sealed in preparation for NASA's first Independence Day shuttle liftoff. After two weather delays and a debate over safety when a crack appeared in the fuel tank's insulation, officials decided the launch was a go.

"Steve, happy Fourth of July!" a launch controller told Steve Lindsey, Discovery's commander.

The six U.S. astronauts waved small American flags, and European Space Agency astronaut Thomas Reiter gripped a tiny German banner, as they walked toward the launch pad to enter the shuttle. Astronaut Mike Fossum gave a thumbs up and called out: "Hi mom! I love you!"

Even though the sky was sunny at the Kennedy Space Center, NASA managers were watching the wind speed, slowly approaching the safety limit in the unlikely event of an emergency landing. But launch controllers remained optimistic.

"The weather's looking good. Welcome aboard, Lisa!" a launch controller told astronaut Lisa Nowak...

NASA 944, is one of NASA STAs (Shuttle Training Acft); it is a Gulfstream II specially modified so as to simulate the Shuttle Orbiter during landings. NASA 944 just completed some simulated landings at the Shuttle Landing Facility and is reporting how weather conditions affected his flight at various points during the simulated landing. In summary he said that conditions were acceptable for an orbiter landing. This is being done to be sure that the Orbiter will be able to land at the SLF in the event that it must return right after launch.

With a rocket's red glare, Space Shuttle Discovery lifted off from Kennedy Space Center in a spectacular display of sound and light befitting of Independence Day.

Commanded by Steven Lindsey, Discovery and its crew of seven astronauts roared from Launch Pad 39B to begin a 15,000-mph chase to rendezvous with the International Space Station.

As Discovery raced into the bright blue sky, cheers and applause erupted across Kennedy and along the nearby beaches of Florida's space Coast. Today's successful launch came on the third try after the first two attempts to launch were dashed by poor weather.

Now under way, Discovery and its crew set their sights on a mission to deliver equipment, supplies and an additional crewmember to the station. While docked, the STS-121 crew will test new equipment and procedures to improve shuttle safety, as well as make repairs to the station.