January 31, 1958

1958: The Army launched Explorer I, the first US satellite in orbit, on a Jupiter-C from Cape Canaveral, Fla., into an orbit that circled the globe every 103.9 minutes (0345 GMT 1 Feb). Explorer 1 was designed and built by the Jet Propulsion Laboratory (JPL), while a Jupiter-C rocket was modified by the Army Ballistic Missile Agency (ABMA) to accommodate a satellite payload; the resulting rocket known as the Juno I. It discovered the Van Allen radiation belt. The satellite reentered the atmosphere over the South Pacific on 31 March 1970 after more than 58,000 revolutions of earth.