John Glenn's official NASA portrait, 1961.

Marine pilot Maj. John H. Glenn Jr. prepares to step down from the F8UI Crusader at Floyd Bennet Field on July 16, 1957 after making the first non-stop supersonic flight from Los Angeles to New York. Glenn landed 3 hours, 23 minutes, 8.4 seconds after departure from Los Alamitos Naval air station in Ca., breaking the previous record set in 1955.

John Glenn poses for a portrait in his flight suit for the Mercury 6 mission in 1961.

John Glenn climbs into the Friendship 7 capsule with assistance from technicians to begin his historic flight on Feb. 20, 1962.

Astronaut John Glenn in the Friendship 7 capsule during the first manned orbital flight which lasted for 5 hours and orbited the Earth three times.

Astronaut John Glenn Jr. chats with his wife Annie Glenn, Vice President Lyndon Johnson and President John Kennedy on Feb. 23, 1962 at Cape Canaveral beside the capsule that he rode into orbit.

President John F. Kennedy talks with John Glenn and Vice President Lyndon Baines Johnson in Cape Canaveral, Feb. 23, 1962. Kennedy honored Glenn at a reception commemorating Glenn's Mercury-Atlas 6 space mission, also known as Friendship 7.

John Glenn Jr. rides in a car with President John F. Kennedy and General Leighton I. Davis in Cocoa Beach, Fla., following the successful MA-6 mission.

Astronaut John Glenn explains aspects of his three-orbital flight through space as he testifies before the Senate Space Committee in Washington on Feb. 28, 1962. He explained anew that last week's flight proved that man can operate a spacecraft in the new and strange environment of weightless outer space.

Jacqueline Kennedy and astronaut John Glenn water ski on Lewis Bay, Hyannis Port, Mass. on July 22, 1962. The boat was driven by Ethel Kennedy, wife of Robert F. Kennedy.

John Glenn serves as a pallbearer for assassinated Sen. Robert F. Kennedy at his funeral in Washington, D.C. on June 8, 1968.

Former astronaut John Glenn, flanked by his mother, Clara, and wife, Annie, smiles broadly on Dec. 11, 1969 while at a Columbus, Ohio news conference at which he announced he was seeking the Democratic party nomination for the U.S. Senate seat left vacant by the retirement of U.S. Senator Stephen Young.

John Glenn was elected as the Democratic Senator from Ohio in 1974 and served until 1999. Here, he poses in his office in Columbus, circa 1974.

Senator John Glenn stands with attorney Edward Bennett Williams on stage at the Democratic National Convention, New York City, July 13, 1976. Glenn was the Keynote Speaker and Williams the Chairman of the convention.

Sen. John Glenn speaks outdoors during his campaign for the Democratic Presidential nomination, Concord, New Hampshire, February 7, 1984.

Sen. John Glenn announces his return to the space program during a press conference at NASA headquarters in downtown Washington, D.C. on Jan. 16, 1998.

An official NASA portrait made on June 8, 1998 shows Sen. John Glenn wearing a partial pressure launch and entry suit in his role as Payload Specialist for Space Shuttle STS-95.

Sen. John Glenn rehearses launch readiness procedures on a crew trainer at the Johnson Space Center in Houston, Tx on June 9, 1998.

Space shuttle Discovery launches on Mission STS-95 on Oct. 29, 1998 with Sen. John Glenn on board, serving as Payload Specialist.

Former Senator John Glenn appears at a rally for US Democratic presidential candidate Senator Hillary Clinton at the Ohio State University in Columbus, Ohio, Feb. 14, 2008.

President Barack Obama awards a 2012 Presidential Medal of Freedom to astronaut and former U.S. Senator John Glenn during a ceremony in the East Room of the White House in Washington, May 29, 2012.

Buzz Aldrin, Annie Glenn and John Glenn visit before the memorial service for astronaut Neil Armstrong at the National Cathedral, Sept. 13, 2012, in Washington.

John Glenn, Annie Glenn and film director James Cameron attend the 109th Explorers Club Annual Dinner at The Waldorf-Astoria, March 16, 2013, in New York.

Explorer Don Walsh, left, John Glenn, retired U.S. astronaut, center, and mountaineer Jim Whittaker, gather for a group portrait at the Waldorf Astoria Hotel in New York, March 16, 2013. Walsh was the first to reach the ocean's deepest point in the Mariana Trench, Glenn was the first American to orbit the Earth, and Whitaker was the first American to reach the summit of Mount Everest.

John Glenn answers questions during an exclusive interview with The Associated Press at the Ohio Statehouse, May 14, 2015. Glenn said facts about scientific discovery should be taught in schools.

John Glenn, shakes hands with 8-year-old Josh Schick, left, before an event to mark the September 2016 renaming of Port Columbus International Airport to John Glenn Columbus International Airport in Columbus, Ohio, June 28, 2016.