2. Glenn and six other military fliers were selected in 1959 to become the first American astronauts as part of Project Mercury. NASA put the “Mercury 7” through a grueling series of medical and psychological tests. Glenn is seen here being outfitted with a biosensor during astronaut training activities at Cape Canaveral, Fla., in 1961.

ss-120216-john-glenn-03n_48fd50bd923fded87507ffc79400aa23-nbcnews-ux-1024-900NASA