Mr. Cunningham ruefully acknowledged that in the decades since the space race, American memory of the nation’s aeronautical derring-do during those years had coalesced around Apollo 11 — the mission that, on July 20, 1969, made Neil Armstrong the first person to walk on the moon — and Apollo 13, the ill-fated spaceflight dramatized in a 1995 Hollywood film starring Tom Hanks as commander Jim Lovell.

But Apollo 7 provided critical momentum for NASA at a time when the space agency’s mission to land a man on the moon seemed in doubt. Less than two years earlier, on Jan. 27, 1967, the three crew members of Apollo 1 — Virgil I. Grissom, Edward H. White II and Roger B. Chaffee — were killed in a fire on the launchpad during a preflight test at Cape Kennedy, Fla.

Mr. Cunningham, a physicist and former Marine fighter pilot, had been the mission’s backup lunar module pilot.

NASA conducted a series of unmanned missions to perfect the safety of its craft before launching Apollo 7 on Oct. 11, 1968. With command pilot Walter M. Schirra Jr. and navigator Donn F. Eisele, Mr. Cunningham spent 11 days in space, orbiting the earth 163 times before safely splashing down in the Atlantic Ocean.

“In its day, the Apollo command module was the most complex machine ever built by man to be operated by man,” the website CollectSpace quoted Mr. Cunningham as saying. “We launched on the longest and most ambitious engineering test flight in history, testing the spacecraft systems, verifying the operating procedures, checking out the worldwide tracking network, and that’s not to mention testing our crew.”

In a sense, the astronauts also tested the resolve of the American people, cheering the public with what NASA described as “the first live television transmission of onboard crew activities” from space.

The extraordinary flight was marred by the most ordinary of inconveniences — the common cold — which first afflicted Schirra and then Eisele. Mr. Cunningham confessed to feeling a “little blah” during his time in space.

Schirra, whose congestion was aggravated by the lack of gravity in space, at times challenged the authority of mission control, stoking the frustration of NASA officials on the ground and leading the entire Apollo 7 crew to be, in Mr. Cunningham’s description, “tarred and feathered” for his conduct.

“There was some real bickering back and forth between Wally and the ground,” he later told NASA in an oral history. “I, frankly, have never felt like I had any kind of a problem with the ground, with going over the onboard tapes and air-to-ground and what have you.”

Neither Mr. Cunningham nor Schirra nor Eisele would fly in future space flights, a source of sadness for Mr. Cunningham.

“I would have given anything to go to the moon, but that was not to be,” he told CollectSpace. “Today, I take great satisfaction in the fact that Apollo 7 was a critical mission to play a central role in getting others to the moon.”

Ronnie Walter Cunningham was born in Creston, Iowa, on March 16, 1932. His father operated a cement contracting business.

When Mr. Cunningham was 8, the family moved to Los Angeles, where he described himself as the “poorest person” in his class.

“But we didn’t spend our time focusing on that,” he told the Spokesman-Review of Spokane, Wash., in an interview last year. “I was spending my time on what I could do.” What he wanted to do was fly planes as a fighter pilot. By the time he was in high school, he could identify an aircraft overhead merely by its sound.

Mr. Cunningham attended a community college in Santa Monica, Calif., working at a gas station and furniture store and delivering newspapers on the side, before he enlisted in the Navy in 1951. He served in the Marine Corps in the Korean War, flying 54 missions as a night fighter pilot, according to NASA. He remained in the Marine Corps Reserve until 1975, reaching the rank of colonel.

Mr. Cunningham studied physics at the University of California at Los Angeles, where he received a bachelor’s degree in 1960 and a master’s degree the following year. He worked at the Rand Corp. on classified defense projects while pursuing a doctoral degree, which he completed except for his dissertation.

He recalled that he was listening to the car radio as he cruised along Mulholland Drive toward Santa Monica the morning of May 5, 1961, as Alan B. Shepard Jr. prepared to become the first American to fly in space.

“As it got down to the last 4 or 5 minutes of the countdown, I was so excited … that I couldn’t drive anymore!” Mr. Cunningham said years later in a NASA oral history. “I pulled over to the side of the road and I listened. And they got to the final count: 3 — 2 — 1 — liftoff. And before that Redstone rocket had cleared the tower, I heard myself yelling out loud” in profane excitement.

That moment, he reflected, was when he set out to become an astronaut. He was hired by NASA in 1963.

After Apollo 7, Mr. Cunningham served as chief of NASA’s Skylab program, which produced the first American space station.

Mr. Cunningham left NASA in 1971. He told the New York Times that he felt a “small amount of sour grapes” over his being passed over for later space flights but cited his “comings and goings, mostly goings” — and their consequent strain on his family — as the greater factor in his decision.

Mr. Cunningham wrote a memoir of his time in the space program, “The All-American Boys,” published in 1977. After departing NASA, he pursued careers in venture capital and real estate investment. He was also a radio host and in recent years expressed doubt about the human role in climate change.

Eisele died at 57 in 1987 of a heart attack, and Schirra died at 84 in 2007.

In 2008, Mr. Cunningham — and, posthumously, Schirra and Eisele — received the NASA Distinguished Service Medal, the space agency’s highest honor. The award was an upgrade of their earlier Exceptional Service Medal, which Mr. Cunningham described in his memoir as indicating a “NASA hero, second class.”

Mr. Cunningham’s first marriage was to Lo Irby. Survivors include his second wife, Dot Cunningham; two children from his first marriage, Brian Cunningham and Kimberly Cunningham; and a sister.

For decades after leaving NASA, Mr. Cunningham championed the space program and challenged the adversity to risk that, in his view, increasingly hampered human ambition. In the days of the space race, “we shared a common dream to test the limits of man’s imagination and daring,” he remarked to the Houston Chronicle in 2018. “That attitude allowed us to overcome every obstacle.”

For his own part, he said he had never gotten his fill of flying.

“You can’t get enough of it if you really are an aviator,” he told NASA in 1999. “I have not really done hardly any flying in the last 20 years, and yet I cannot hardly stand today to look up, especially in bad weather, and hear a T-38 going through the clouds up there. It honestly hurts.”