Glenn, who served four terms as a U.S. senator from Ohio, was one of NASA's original seven Mercury astronauts. His flight on Friendship 7 on Feb. 20, 1962, showed the world that America was a serious contender in the space race with the Soviet Union.Oct. 29, 1998, when he was 77, made him the oldest human to venture into space. On Discovery he participated in a series of tests on the aging process. The aging population was one focus of his work as a U.S. senator.