[Read all Times reporting on the 50th anniversary of the Apollo 11 moon landing. | Sign up for the weekly Science Times email.]

First there were the test pilots — men in possession of what Tom Wolfe called “the right stuff” — who took flight in experimental aircraft. It was absurdly dangerous work with a mortality rate to match. NASA put them in capsules, presented them as Boy Scouts and called them astronauts.

Then, there were the men of Apollo who planted the American flag on the lunar surface. Astronauts were now explorers in a new way, leaving footprints in untrodden terrain.

The space shuttle program followed, and the face of the American astronaut changed. It was no longer the exclusive domain of military fighter jocks, as scientists and engineers became fused with the public’s idea of who an astronaut was. They now looked more like America — women and men of many races and vocations. They were even construction workers of a sort as they began building the International Space Station, one of the greatest engineering achievements since the Great Pyramids.