Glenn did not hear him; Carpenter was not on his radio link. Instead, he felt a jolt as the rocket left the launch pad.
"Roger, liftoff, and the clock is running. We're under way."
The Atlas did not fail. Five minutes later, he was in orbit.
The nation hung on every moment of his flight -- one man, alone in the void, in a capsule so small (6 feet in diameter at the base) that he could not stretch out his arms. He reported that weightlessness was pleasant. He marveled at the "fireflies" -- later determined to be flecks of frost -- that drifted away from Friendship 7 when he rapped on the hull of the spacecraft.
Glenn was having a wonderful time. But then, trouble. As he began his second orbit, Mission Control received a signal suggesting that the heat shield, designed to prevent the capsule from burning up during reentry, had come loose. Worried controllers feared they might lose Glenn. They ordered him not to jettison the capsule's retro rockets, strapped on over the heat shield, after he fired them to descend from orbit.
The outside of the capsule heated to 3,000 degrees as the atmosphere slowed it. Glenn watched as chunks of debris flew past the window and wondered whether it was the retro pack breaking up, or the heat shield.
It held. He splashed down safely in the Atlantic Ocean. America had probably seen nothing so daring since the transatlantic flight of Charles Lindbergh.
Crowds mobbed him at a ticker-tape parade in New York. Kennedy, who saw Glenn's star power, welcomed him at the White House. Glenn returned to work at NASA and waited dutifully for another flight assignment, but the Kennedy administration had quietly let his bosses know he was too much of a national icon to risk in space again.
The Americans would gradually overtake the Soviets in space. Neil Armstrong walked on the moon in 1969. But we no longer live in the space age. And Glenn's mantle as hero has only taken him so far; a run for president in 1984 left him in debt for years.
John Glenn is 90 now, dividing his time between Washington and Ohio after a long career in the U.S. Senate. He and his wife Annie have been married for 69 years, slowed only by the inevitable maladies of age.
He did, after years of lobbying, get to fly on a space shuttle mission in 1998. He was 77 by then, arguing that some effects of weightlessness -- bone and muscle loss -- are similar to the effects of aging. While he was in orbit he said he was having such a good time that he might like another flight after that, but Annie, visibly angry, put a quick stop to that.
Glenn and Scott Carpenter, the two surviving members of the original Mercury 7 group, have been celebrated this weekend at events near Cape Canaveral, in Washington, and in Glenn's native Ohio. They have repeatedly said they hope the nation's space effort is only in a lull.
"John, thank you for your heroic effort," said Carpenter in Florida. "But we stand here waiting to be outdone."