Along with John Glenn, who flew three months before him, Carpenter was one of the last two surviving original Mercury 7 astronauts for the fledgling U.S. space program.
His wife, Patty Barrett, said he died in a Denver hospice of complications from a September stroke. He lived in Vail, Colo.
"We're going to miss him," she said.
At a time when astronauts achieved fame on par with rock stars, people across the country sat glued to their TV screens, anxiously awaiting the outcome of Carpenter's 1962 ride. He overshot his landing by 288 miles, giving NASA and the nation an hourlong scare that he might not have made it back alive.
The fallout from that missed landing was a factor that kept NASA from launching Carpenter into space again. So he went from astronaut to "aquanaut" and lived at length on the seafloor — the only man to ever formally explore the two frontiers.
The launch into space was nerve-racking for the Navy pilot on the morning of May 24, 1962.
"You're looking out at a totally black sky, seeing an altimeter reading of 90,000 feet and realize you are going straight up," Carpenter said 49 years later in a joint lecture with Glenn at the Smithsonian Institution. "And the thought crossed my mind: What am I doing?"
For Carpenter, the momentary fear was worth it, he said in 2011: "The view of Mother Earth and the weightlessness is an addictive combination of senses."
For the veteran Navy officer, flying in space or diving to the ocean floor was more than a career. In 1959, soon after being chosen as one of NASA's pioneering seven astronauts, Carpenter wrote about his hopes, concluding, "This is something I would willingly give my life for."
"Curiosity is a thread that goes through all of my activity," he told a NASA historian in 1999. "Satisfying curiosity ranks No. 2 in my book behind conquering a fear."
Even before Carpenter ventured into space he made history, also with Glenn. On Feb. 20, 1962, he gave the historic sendoff to his predecessor in orbit: "Godspeed, John Glenn." It was a spur-of-the-moment phrase, he later said.
"In those days, speed was magic because that's all that was required ... and nobody had gone that fast," he explained. "If you can get that speed, you're home free, and it just occurred to me at the time that I hope you get your speed. Because once that happens, the flight's a success."
Three months later, Carpenter was launched into space from Cape Canaveral, Fla., and completed three orbits around Earth in his space capsule, the Aurora 7, which he named after the celestial event. It was just a coincidence, he said, that in his homeotwn of Boulder, Colo., he grew up on the corner of Aurora Avenue and Seventh Street.
His four hours, 39 minutes and 32 seconds of weightlessness were "the nicest thing that ever happened to me," he told the NASA historian. "The zero-g sensation and the visual sensation of spaceflight are transcending experiences, and I wish everybody could have them."
Carpenter's trip led to many discoveries about spacecraft navigation and space itself, such as that space offers almost no resistance, which he learned by trailing a balloon. He said astronauts in the Mercury program found most of their motivation from the space race with the Russians. When he completed his orbit of the Earth, he said he thought: "Hooray, we're tied with the Soviets," who had completed two manned orbits at that time.
But things started to go wrong on re-entry. He was low on fuel, and a key instrument that tells the pilot which way the capsule is pointing malfunctioned, forcing Carpenter to take manual control of the landing.
NASA's Mission Control then announced that he would overshoot his landing zone by more than 200 miles and, worse, that it had lost contact with him.
Talking to a suddenly solemn nation, CBS newsman Walter Cronkite told his audience, "We may have ... lost an astronaut."
But Carpenter survived the landing that day.
Always cool under pressure — his heart rate never went above 105 during the flight — he oriented himself by simply peering out the capsule's window. The Navy found him in the Caribbean, floating in his life raft with his feet propped up. He offered up some of his space rations.
Carpenter's perceived nonchalance didn't sit well with some NASA officials, particularly flight director Chris Kraft. The two feuded about it from then on.
Kraft accused Carpenter of being distracted and behind schedule, as well as of making poor decisions. He blamed the astronaut for the low fuel.
On his website, Carpenter acknowledged that he hadn't shut off a switch at the right time, doubling fuel loss. Still, he said in his 2003 memoir, "I think the data shows that the machine failed."
In the 1962 book "We Seven," written by the first seven astronauts, Carpenter described his thoughts while he was waiting to be picked up after splashing down.
"I sat for a long time just thinking about what I'd been through. I couldn't believe it had all happened. It had been a tremendous experience, and though I could not ever really share it with anyone, I looked forward to telling others as much about it as I could. I had made mistakes and some things had gone wrong. But I hoped that other men could learn from my experiences. I felt that the flight was a success, and I was proud of that."
One of 110 candidates to be the nation's first astronauts, Carpenter became an instant celebrity in 1958 when he was chosen as one of the original Mercury team. Like his colleagues, he basked in lavish attention and public rewards, but it wasn't exactly easy. The astronauts were subjected to grueling medical tests — keeping their feet in cold water, rapid spinning and tumbling, open-ended psychological quizzes. He had to endure forces of 16 times gravity in his tests, far more than in space, something he said he managed with "great difficulty."
"It was the most exciting period of my life," he said.
Carpenter never did go back into space, but his explorations continued. In 1965 he spent 30 days under the ocean off the coast of California as part of the Navy's SeaLab II program.
Once again, the motivation was both fear and curiosity.
"I wanted, No. 1, to learn about it (the ocean), but No. 2, I wanted to get rid of what was an unreasoned fear of the deep water," he told the NASA historian.
Inspired by Jacques Cousteau, Carpenter worked with the Navy to bring some of NASA's training and technology to the seafloor. A broken arm kept him out of the first SeaLab, but he made the second in 1965. The 57-by-12-foot habitat was lowered to a depth of 205 feet off San Diego. A bottlenose dolphin named Tuffy ferried supplies from the surface to the aquanauts below.
"SeaLab was an apartment, but it was very crowded. Ten men lived inside. We worked very hard. We slept very little," he recalled in a 1969 interview. Years later, he said he actually preferred his experience on the ocean floor to his time in space.
"In the overall scheme of things, it's the underdog in terms of funding and public interest," he said. "They're both very important explorations. One is much more glorious than the other. Both have tremendous potential."
After another stint at NASA in the mid-1960s, helping develop the Apollo lunar lander, Carpenter returned to the SeaLab program as director of aquanaut operations for SeaLab III.
He retired from the Navy in 1969, founded the company Sea Sciences, worked closely with Cousteau and dove in most of the world's oceans, including under the ice in the Arctic.
When the 77-year-old Glenn returned to orbit in 1998 aboard the space shuttle Discovery, Carpenter radioed, "Good luck, have a safe flight and ... once again, godspeed, John Glenn."
Malcolm Scott Carpenter was born May 1, 1925, in Boulder, Colo. (He hated his first name and didn't use it.) He was raised by his maternal grandparents after his mother became ill with tuberculosis.
He attended the University of Colorado for one semester, joined the Navy during World War II and returned to school but didn't graduate because he flunked out of a class on heat transfer his senior year. The school eventually awarded him a bachelor's degree in aeronautical engineering after he orbited the Earth.
He rejoined the Navy in 1949 and was a fighter and test pilot in the Pacific and served as an intelligence officer.
He married four times and had seven children; a daughter helped him write his memoir, "For Spacious Skies: The Uncommon Journey of a Mercury Astronaut." He also wrote two novels: "The Steel Albatross" and "Deep Flight." In addition to his children, he is survived by his wife.
He earned numerous awards and honorary degrees. Carpenter said he joined the Mercury program for many reasons: "One of them, quite frankly, is that it is a chance for immortality. Most men never have a chance for immortality."