Explorer 1 was the first U.S. satellite, launched on January 31, 1958.
The satellite was built by the Jet Propulsion Laboratory and the Army Ballistic Missile Agency. It flew aboard a Jupiter-C rocket from Cape Canaveral, Florida, after the Soviet Union had already launched Sputnik 1 and Sputnik 2. Explorer 1’s successful launch marked the United States’ entry into the space age.
Explorer 1 carried scientific instruments designed by a team at the University of Iowa led by James Van Allen. The instruments detected charged particles trapped by Earth’s magnetic field, leading to the discovery of the radiation belts now known as the Van Allen belts.
Explorer 1 remained in orbit until March 31, 1970. It is often confused with Vanguard 1, which was the first solar-powered satellite and remains the oldest artificial satellite still in orbit, although it was not the first U.S. satellite.