President Bush has vowed the U-S space program will continue despite the loss of the shuttle Columbia and its crew.
At a memorial service in Texas Tuesday, Mr. Bush spoke glowingly of the seven astronauts who perished Saturday when the shuttle broke apart while returning from space.
He quoted astronaut David Brown, who told his brother before the launch of the ill-fated Columbia that America's space program would go on even if he did not make it home. Mr. Bush said discovery is not an option that can be chosen, but a desire written in the human heart.
The solemn outdoor ceremony was attended by scores of dignitaries, including former astronaut Neil Armstrong -- the first man to step on the moon -- and former senator and astronaut John Glenn.
Outside the facility, thousands of ordinary Americans stood silently to mourn, while nearly 400 kilometers above the Earth, the three-man crew of the International Space Station paused to hear a radio broadcast of the service.
Millions of people around the world also saw the service, which was televised globally.
President Bush, who met with the astronauts' families before the service, said the crew members names are known and remembered on every continent they could see from their celestial perch.
The first Indian-born astronaut, Kalpana Chawla, and Israel's first astronaut, Ilan Ramon, were among the five men and two women who died when the shuttle disintegrated during atmospheric re-entry. Besides Mr. Brown, the crew members were Rick Husband, William McCool, Michael Anderson, and Laurel Clark.
Meanwhile, about 20 members of an independent board investigating Saturday's tragedy traveled to Nacagdoches, Texas, to view shuttle debris scattered over the countryside. About 12-thousand pieces of wreckage, including the shuttle's nose cone, have been retrieved from a 72-thousand-square-kilometer area of Texas and Louisiana.
Investigators are re-examining earlier evidence and the NASA determination that Columbia was not significantly damaged when it was struck by fuel tank debris on take-off. NASA says other unknown factors also could have triggered a series of failures that destroyed the spacecraft.