Walter M. Schirra Jr., one of the original Mercury Seven astronauts and the only astronaut to fly in all three of NASA’s earliest manned space programs — Mercury, Gemini and Apollo — died yesterday in San Diego. He was 84 and lived in Rancho Santa Fe, Calif.

His death, at a hospital in La Jolla, was caused by a heart attack, said Ruth Chandler Varonfakis, a family friend and spokeswoman for the San Diego Air and Space Museum. Captain Schirra, a Navy combat pilot in the Korean War and later a test pilot, became the fifth American in space and the third American to orbit the earth when he lifted off from Cape Canaveral in the Sigma 7 Mercury craft in October 1962.

He later took part in the first rendezvous between two spacecraft, in December 1965, flying with Thomas P. Stafford, the mission pilot, when their Gemini 6 craft came within inches of Gemini 7, carrying Frank Borman and James A. Lovell Jr., and orbited alongside it.

On his final mission, in October 1968, Captain Schirra commanded Apollo 7, the first manned mission in the Apollo program, the quest to land men on the moon. The Apollo 7 crew, which also included Donn F. Eisele and Walter Cunningham, flew for 163 orbits and provided the first televised pictures from an American spacecraft.

The mission is also remembered for the head colds the three astronauts caught during their almost 11 days in space. They took decongestants and returned without bursting their eardrums, as NASA had feared might happen.

Captain Schirra’s death leaves former Senator John Glennand M. Scott Carpenter as the remaining survivors of the original Mercury astronauts, figures celebrated for their courage and, in the eyes of many, for their bravado in forging a new American frontier amid the cold war competition with the Soviet Union.

These were the men profiled by Tom Wolfe in “The Right Stuff” and in the 1983 movie adaptation of the book in which Captain Schirra was portrayed by Lance Henriksen.

But for Captain Schirra, who logged more than 295 hours in space, the missions were hardly all glamour.

“Mostly it’s lousy out there,” he told The Associated Press in 1981. “It’s a hostile environment, and it’s trying to kill you. The outside temperature goes from a minus 450 degrees to a plus 300 degrees. You sit in a flying Thermos bottle.”

Walter Marty Schirra Jr., a native of Hackensack, N.J., came from a family of fliers. His father, an officer in the Army Signal Corps, flew bombing and reconnaissance missions over Germany in World War I and later performed stunts in a bi-plane at county fairs in New Jersey. His wife, Florence, sometimes stood on the wing.

Walter Jr. first took a plane’s controls at age 13, handed over by his father at 3,000 feet above Teterboro Airport in New Jersey. Captain Schirra graduated from the United States Naval Academy in 1945 and became a naval aviator three years later. He flew 90 missions in the Korean War, mainly low-level bombing and ground-strafing operations, and downed a Russian MIG fighter. He later helped develop the Sidewinder air-to-air missile as a Navy test pilot.

As he told it in “The Real Space Cowboys” (Apogee Books, 2005), written with Ed Buckbee, his goal was to be “a hot shot test pilot, not just a scarf and goggles type, but one who could use his engineering confidence to work on systems and make the best airplane, ever.”

“I didn’t really volunteer for Project Mercury,” he said, but he became a candidate after being ordered to Washington to hear a presentation. “We were listening to a pair of engineers and a psychologist describing the feeling when you’re on top of a rocket in a capsule and going around the world,” he remembered. “I was immediately looking for the door, and they said, ‘Not to worry, we’ll send a chimpanzee first!’ There’s no way a test pilot would volunteer for something like that.”

On April 9, 1959, he was named a Mercury astronaut, together with Mr. Glenn, Mr. Carpenter, Alan B. Shepard Jr., Virgil I. Grissom, L. Gordon Cooper Jr. and Donald K. Slayton.

Captain Schirra specialized in developing life-support systems for the Mercury astronauts, his tasks including testing their pressurized suits. On Oct. 3, 1962, he piloted the capsule Sigma 7 on a six-orbit mission lasting a bit more than nine hours. The third orbital flight by an American, it showed that an astronaut could manage the limited amounts of electricity and maneuvering fuel needed for longer, more complex flights.

Captain Schirra later helped develop the Gemini program, and on Dec. 12, 1965, he and the pilot, Thomas Stafford, were on the launching pad in their Gemini 6 spacecraft atop a Titan II booster rocket when it ignited, then shut down. Captain Schirra had to make an immediate decision on whether to activate controls to eject the two astronauts, but he chose to remain in the craft. Technicians found that the booster was not about to explode; the problem was a loose electrical plug.

Three days later, the two astronauts lifted off, and in less than six hours they completed their nondocking rendezvous with Gemini 7 some 170 miles above the Mariana Islands in the Pacific.

Commanding Apollo 7, which lifted off on Oct. 11, 1968, Captain Schirra and two other astronauts tested systems that had been redesigned after the January 1967 Apollo 1 launching pad fire that killed Mr. Grissom and his fellow astronauts Ed White and Roger Chaffee.

Captain Schirra retired from the Navy and left NASA in July 1969 to become president of Regency Investors, a financial company based in Denver. He was involved in various business enterprises after that. He is survived by his wife, Josephine; a son, Walter III, and a daughter, Suzanne.

In 1984, Captain Schirra took part in founding the Mercury Seven Foundation, which creates college scholarships for science and engineering students. On Aug. 1, 1998, he spoke at NASA’s Johnson Space Center in Houston at a ceremony honoring Alan Shepard, the first American in space, who died at 74 the previous month.

Captain Schirra told the gathering, “The brotherhood we have will endure forever.”

Walter M Schirra