Always cool under pressure — his heart rate never went above 105 during the flight — he oriented himself by simply peering out the space 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 some with 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 making poor decisions. He blamed Carpenter for low fuel.
On his website, Carpenter acknowledged that he didn't shut off a switch at the right time, doubling fuel loss. Still, Carpenter in his 2003 memoir said, "I think the data shows that the machine failed."
In the 1962 book "We Seven," written by the first seven astronauts, Carpenter wrote about his thoughts while 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 a Mercury astronaut. Like his colleagues, Carpenter 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 and open-ended psychological quizzes. He had to endure forces 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 in 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.
"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," Carpenter told the NASA historian.
Inspired by Jacques Cousteau, Carpenter worked with the Navy to bring some of NASA's training and technology to the sea floor. 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," Carpenter 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 his company Sea Sciences Inc., 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 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 in 1962 after he orbited the Earth.
He rejoined the Navy in 1949 and was a fighter and test pilot in the Pacific and served as 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, Patty Barrett.
He earned numerous awards and honorary degrees. Carpenter said that 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."