Explorer 1 was the first American satellite to reach Earth orbit, launching on January 31, 1958.
The satellite was developed by the Jet Propulsion Laboratory and the Army Ballistic Missile Agency. It launched from Cape Canaveral, Florida, aboard a Juno I rocket, only months after the Soviet Union had launched Sputnik 1 and Sputnik 2.
Explorer 1 carried scientific instruments designed to study the space environment. Its most important discovery was the Van Allen radiation belts, zones of charged particles trapped by Earth’s magnetic field. The finding demonstrated that satellites could make major contributions to space science as well as national prestige.
The satellite remained in orbit until March 31, 1970. Its launch followed an earlier failure of the U.S. Navy’s Vanguard TV-3 mission, making Explorer 1 especially important in the opening phase of the Space Race. The mission was sometimes called Satellite 1958 Alpha by its scientific designation.