Seconds away from liftoff, astronaut John Glenn monitored the instruments in his cramped Mercury capsule, listening intently as fellow astronaut Scott Carpenter called out milestones in the final moments of a tense countdown.
Earlier attempts to launch Glenn on America's first orbital spaceflight had been scrubbed by technical snags and bad weather. But this time around, the Atlas rocket, the Friendship 7 capsule, and the weather cooperated, clearing the way for the long-awaited, high-stakes attempt to reach orbit.
Millions across the nation and around the world hung on every word from mission control, gathered around black-and-white television sets and radios. Daily activity virtually ground to a halt while the drama played out in Florida.
In a blockhouse near the launchpad, legendary test conductor Thomas "T.J." O'Malley pushed a button to start the final launch sequence, saying softly "Good Lord ride all the way."
Carpenter famously added "Godspeed, John Glenn," and counted down the final 10 seconds while the nation held its collective breath.
"...five, four, three, two, one, zero," Carpenter said as the Atlas rocket, its main engine roaring and belching a brilliant plume of fiery exhaust, climbed away from Cape Canaveral.
"Roger, the clock is operating, we're under way!" Glenn called out, his heart rate climbing to a relatively modest 110 beats per minute.
It was 9:47 a.m., Feb. 20, 1962--50 years ago today--and America had a new hero.
The Soviet Union had shocked the world on Oct. 4, 1957, when it successfully launched Sputnik, the world's first satellite. The Russians followed that triumph by launching Yuri Gagarin into orbit on April 12, 1961, the first human in space.
Under enormous pressure to catch up with the Russians on the high frontier, NASA launched Alan Shepard on May 5, 1961, and Virgil "Gus" Grissom on July 21. But both of those flights aboard modest Redstone rockets were suborbital, up-and-down missions lasting about 15 minutes each.
Capitalizing on their role as the early leader in what came to be known as the "space race," the Soviets launched cosmonaut Gherman Titov just a few weeks later on a 17-orbit mission that dwarfed NASA's accomplishments to that point.
"They beat us out. They gave us a double whammy," Carpenter said, recalling Glenn's flight 50 years after the fact. "Not only did they get the honor of the first man in space, but they sent him...into orbital flight. That was a double whammy for them. Who knew that better than Al Shepard? He was very disappointed that Yuri robbed him of the first-man-in-space title.... That only inspired all of us here to do better work."
Enter John Glenn and Mercury Atlas 6.
The clean-cut Marine Corps test pilot, veteran of 59 combat missions in World War 2 and 63 during the Korean War, was selected by NASA as one of the original seven Mercury astronauts.
While many at the time believed Shepard's selection to fly the first suborbital mission put him at the top of the astronaut hierarchy, it was Glenn who ultimately became the enduring face of America's space program, riding the Atlas rocket into American history.
"We needed someone to symbolize that we weren't going to stay behind in space," said John Logsdon, a space policy analyst and an expert on the U.S. space program. "This was after a very bad '61 with the threat of war over Berlin and Kennedy's administration slow getting started and the country's mood was not great.
"Glenn, I think, radiated a sense of competence and, if you want, 'American-ness' that made him kind of ideally suited for the role of the first U.S. person to go into orbit. He carried it off with such style, a combination of humility and grace."
The Atlas rocket, a converted intercontinental ballistic missile, had its share of problems during testing, which added drama to Glenn's flight. Glenn laughed when asked recently whether he was nervous about riding it for the first time.
"I think the first 18 or 20 Atlases that fired, I think they had a 45 percent failure rate, that's the figure I remember," he said. "The first time they took us (the Mercury 7 astronauts) down there to see a booster launch, we'd never seen a launch, and they took us down for a night launch and the thing blew at high Q at 27,000 feet right over our heads. It looked like an atomic bomb going off.
"Anyway, they came back and improved the whole thing and had several straight successes and had the problems worked out before I got on the thing. But it was something we were very concerned about at the time."
As it turned out, Glenn's Atlas performed flawlessly, boosting his Friendship 7 capsule to 17,500 mph in about 5 minutes and 20 seconds. When the capsule separated from the rocket, it was programmed to immediately turn around, putting its heat shield forward, in case of a problem that might force an emergency re-entry.
"Zero G and I feel fine," Glenn, now weightless, reported from orbit. "Capsule is turning around. Oh, that view is tremendous!"
Glenn's memory of that day remains razor-sharp, telling CBS News in an interview that "it seems more like a couple of weeks ago to me, because that fight was pretty well indelibly impressed on my memory back in that time."
Despite the fire and thunder associated with rocket launches, Glenn said the Atlas was "very gentle" at first because the thrust of the booster barely exceeded its weight. But as the propellants were consumed and the rocket got lighter, it steadily accelerated, pushing Glenn into his contoured seat with nearly eight times the normal force of gravity on the way to orbit.
"When I hit orbit up there, I said, I think it was 'zero G and I feel fine.' I think the next thing I said was 'that view is tremendous!' ... It was right after detachment from the booster, from the Atlas, that I turned around and it went immediately into retro attitude, which was nose down a little bit looking back along the flight path. I could look back clear across Florida and along the Gulf of Mexico, and it was beautiful. I couldn't believe the view."
Other than a relatively minor but persistent attitude control problem that prompted Glenn to fly the capsule manually, Friendship 7 performed smoothly as it raced around the planet, giving the astronaut spectacular views of the Earth below. He even enjoyed a salute from the residents of Perth, Australia, who turned on their lights as the capsule passed over.
But at the start of his second orbit, telemetry from a sensor indicated the spacecraft's heat shield was not locked in place. If the telemetry was correct, the straps holding the capsule's braking rockets in place were all that stood between Glenn and a fiery death during re-entry.
Glenn was not immediately told about the concern, an omission he believes was a mistake.
"There was some little chatter back and forth about did I hear any bumping on the spacecraft and things like that," Glenn recalled. "I know they were concerned they were going to rattle your cage up there and lead you to do something wrong. The best safety thing I thought was to give the astronaut every bit of information at the earliest possible time."
Asked if he realized what was going on at the time, Glenn said "there was only one thing they could be talking about. And so I knew, but it was a little irksome they didn't just come out and tell me until later, just before retro fire."
After completing three orbits, Glenn headed back to Earth. He was told not to jettison the retro rockets in hopes the straps holding them in place would secure the heat shield, if it was loose, during the critical early moments of re-entry.
Approaching the West Coast of the United States, Glenn fired Friendship 7's three braking rockets one at a time and began his descent to splashdown in the Atlantic Ocean.
Flying manually to maintain stability, Glenn could see flaming debris flying past his window.
No one, Glenn included, knew whether the debris was the remnants of his retro rockets burning off or the heat shield itself.
"Seven, this is Cape," Mission Control radioed. "What's your general condition? Are you feeling pretty well?"
"My condition is good," Glenn replied to everyone's relief, "but that was a real fireball. Boy. I had great chunks of that retropack breaking off all the way through."
Glenn returned to a hero's welcome, meeting with President Kennedy at the White House and enjoying a ticker-tape parade in New York. The Mercury program ran its course and NASA transitioned to two-man Gemini spacecraft to perfect orbital rendezvous techniques before pressing ahead with the Apollo moon program.
Glenn wanted to fly again, but NASA management would not assign him to a flight. In 1965, Glenn got tired of waiting and resigned from NASA.
"I didn't know until many years later, when a biography of JFK came out, that he apparently had indicated to NASA that he'd just as soon I wasn't used again, at least not right away," Glenn told reporters at a news briefing February 17. "I don't know what his motivations were.... There had been so much national attention on us at that time that I suppose it could have been bad if something had happened on a second flight."
After a stint in private industry, Glenn went on to a distinguished career in the U.S. Senate and in the mid 1990s lobbied for a flight aboard the space shuttle. Then NASA Administrator Daniel Goldin ultimately gave his blessing and Glenn, then 77, blasted off a second time in October 1998 aboard the shuttle Discovery.
Despite the bigger windows on the shuttle, it was his first view of Earth during his four-hour 55-minute flight aboard Friendship 7 that remains the most vivid memory.
"Oh, I think, yeah, that was the one that was a shock," he said. "It wasn't so much the type of window you were looking out of, which was bigger, of course, on the shuttle, but it was the view you were looking out at. The first time you see that, it's sort of breathtaking."
Corrected at 5:30 a.m. PST:Correcting mission duration.