"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 eight children, including two that died before him. 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.
A public funeral and memorial are planned for later this month in Boulder, Barrett said. She didn't have further details.
Carpenter 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."
Borenstein reported from Washington.
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