Mr. Young flew twice in Gemini spaceships, flew on the Apollo mission that preceded Neil Armstrong and Buzz Aldrin’s landing on the lunar surface and later drove a rover vehicle through the moon’s highlands. He closed out his explorations of space by flying on two shuttle missions.

Image Mr. Young aboard Gemini 3 in March 1965 awaiting its launching. It was the first manned mission of the Gemini program. He flew with Gus Grissom, who fired rockets to carry out the first manual change of orbit in a spacecraft. Credit... NASA

Mr. Young had a mischievous side and something of a rebellious streak. He smuggled a corned beef sandwich aboard Gemini 3 to the consternation of NASA officials, who feared that crumbs could have damaged the spacecraft’s systems, though that did not happen.

On his flight to the moon, he complained graphically to his fellow crewmen about his flatulence, evidently caused by the potassium-fortified orange juice he was required to drink. He thought he was speaking on a closed radio circuit, but his microphone was open, and all the world heard it.

While brainstorming technical problems in preparation for missions, Mr. Young often displayed an easy and seemingly casual manner.

“He drawled his way through conversation and gave the impression he was still the country boy who grew up in Orlando, Florida, back when it was mostly farmland,” Andrew Chaikin wrote in “A Man on the Moon” (1994).

“Some people saw the country-boy bit as an act; it wasn’t,” Mr. Chaikin continued. “It was just John’s way of getting the people around him to think a little harder about the problem. Inside Young was an unwavering determination, an overriding sense of responsibility — to the space country, to the program, to his crew — and an almost childlike sense of wonder at the universe.”