Glenn's Friendship 7 capsule circled Earth three times on Feb. 20, 1962. Carpenter followed aboard Aurora 7 on May 24, 1962.
They were the third and fourth Americans to rocket into space. Alan Shepard and Gus Grissom flew short suborbital missions in 1961, the same year the Soviet Union launched two cosmonauts into orbit on separate shots.
The Cold War was raging, and America was desperate to even the score. Glenn could have died trying if the heat shield on his capsule was loose as flight controllers feared. But the protective shield was tight, and Glenn splashed down safely.
"Flying in space at age 77, you've given me hope. I've got a few good years left, and I'm ready," Kennedy Space Center director Robert Cabana, a former shuttle commander, told Glenn.
Another retired shuttle commander, NASA Administrator Charles Bolden Jr., shared how the Mercury astronauts "really lit up the world for me in terms of probability or possibility of things that we could do."
Glenn recalled how the Mercury astronauts traveled during their training to Cape Canaveral to watch a missile blast off. It was a night launch, and the rocket blew apart over their heads.