It's no wonder.
"I guess it's been a rare day that somebody hasn't brought up something about that," said Glenn, who at age 80 is the first astronaut to reach the 40-year milestone. (All four of his space predecessors have died.)
CBS Radio News Correspondent Peter King reports Glenn says although his Friendship 7 flight was a life-changing experience, he never imagined that he would become one of the most celebrated Americans in history.
It wasn't just about the science, or the adventure of outer space.
Glenn was a Cold War hero, who got the job done for the U.S. at a time when the Soviets had been leading in the space exploration race.
Glenn recalls that it wasn't easy catching up to the Russians but the publicity over the U.S. space program's successes helped win the taxpayer and political support NASA ultimately used to fuel trips to the moon, space shuttle missions, and the building of the International Space Station.
The question Glenn is asked most frequently about the Feb. 20, 1962, flight is: "Were you scared?"
After all, he was only the third American and the fifth person in the world to rocket into space, and the first to ride the Mercury Atlas into orbit.
No, he was not afraid, but he was apprehensive.
Statistical studies at the time gave him a 90 percent chance of returning alive, Glenn said.
At the time, psychiatrists feared weightlessness might prove so euphoric he would not want to return to Earth; they called it the breakaway phenomenon. But Glenn said he thought it was nonsense.
"I can laugh about them now, but they were serious then, I'll tell you," he said in an interview last week.
During the five-hour, three-orbit flight, Glenn had to overcome problems with the capsule's automatic control system and contend with grave concerns about the spacecraft's heat shield.
Glenn, who made a comeback as the world's oldest spaceman in 1998 aboard space shuttle Discovery, said he is disappointed NASA has yet to sign up another senior citizen to help produce more data on the effects of space on older astronauts.
Born in Cambridge, Ohio in 1921, Glenn moved two years later to nearby New Concord, home of Muskingum College, his alma mater. He was an Ohio senator for 24 years, retiring in 1998.
Glenn still flies his own plane and takes an active role in The John Glenn Institute at Ohio State University, created to promote public service and policy.
He will mark his 40th space anniversary with a sold-out lecture at the Smithsonian Institution's National Air and Space Museum and a call to the crew of the international space station. On Sunday, he will be reunited at Cape Canaveral with the three other surviving Mercury astronauts.
Glenn intends to be around for his 50th anniversary, maybe even his 60th. "Getting old is two things, attitude and exercise, tat keep you going," he said.
© MMII, CBS Worldwide Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report