The space shuttle astronauts killed in Saturday's Columbia tragedy were part of an elite corps of explorers, who have been probing the frontiers of space. The members of the ill-fated Columbia crew are mourned by their families, their country and colleagues who have also experienced the dangers of space travel.
The names of many space veterans are now in history books. They know the exhilaration of leaving earth's orbit. They also know the risks.
In 1969, Buzz Aldrin was a member of the first American space mission to land on the moon. Neil Armstrong took the initial set of steps on the lunar surface. Buzz Aldrin took the second. A colleague urged the White House to have a speech ready just in case the mission failed and the astronauts were lost.
Buzz Aldrin laughs about the old story now. "Well, I think Neil and I both enjoyed being on the moon. But I don't think we would have chosen to stay there," he said.
His face turns somber when his attention turns to those who never made it home, the three Apollo astronauts killed in a 1967 launch pad fire, and the crews of two doomed space shuttles. During an appearance on NBC's Meet the Press, Buzz Aldrin said space exploration must go on.
"We owe it to the people who lost their lives in the Apollo fire, the Challenger and Columbia and all the other contributing losses that have gone in sacrifice for the future of our space program," he said.
A number of former astronauts shared their thoughts and experiences on Meet the Press Sunday. All struck a common theme when asked about the Columbia crew. It was expressed best by Rick Hauck, a veteran shuttle commander. "They died doing what they wanted to do. I think all of those who died would say, 'don't abandon the cause. Don't let our death be in vain.'"
They saluted the bravery of the Columbia seven, and offered vivid descriptions of the beauty that draws men and women to space travel, and the dangers they face. Senator Bill Nelson, a Florida Democrat, took part in a mission on board the shuttle Columbia in 1986.
"You know, on that re-entry, we were on the night side of the earth. And I remember looking out the window, and it was just like day because of the 3,000 degree heat ... and that glow of the underside is coming around the entire craft," he said.
But when asked if he would do it again, Senator Nelson responded with an emphatic "yes." So did John Glenn, perhaps the best known of all American astronauts.
In 1962, he became the first American to orbit the earth. Thirty-six years later, at the age of 77, he returned to space in a shuttle mission, taking part in experiments on the aging process.
"If NASA said 'we found something, we would like to look at on your body again in space,' would I be willing to go? I'd be down there tomorrow morning," he said.
John Glenn says scientific research is the main reason why the space program must go on. The former U.S. senator, who is now 81, points to decades of discovery. He says the Columbia crew was pushing the frontiers of knowledge.