Glenn, John Herschel, Jr., 1921-, American astronaut and politician, b. Cambridge, Ohio. On Feb. 20, 1962, he became the first American and the third person to orbit the earth, circling the globe three times in a vehicle launched from Cape Canaveral, Fla. After leaving the space program, Glenn entered Ohio politics and was elected to the U.S. Senate as a Democrat in 1974. Known for his work on military issues, he campaigned unsuccessfully for the Democratic Presidential nomination in 1984. In Oct., 1998, Glenn went into orbit again, on a space shuttle mission, to test effects of space on the elderly. In 1999 he retired from the Senate.