Explorer 1 was the first United States satellite launched into orbit.
Explorer 1 launched on January 31, 1958, from Cape Canaveral, Florida, aboard a Juno I rocket. The United States sent it into orbit during the early Space Race, several months after the Soviet Union launched Sputnik 1. The satellite was designed by the Jet Propulsion Laboratory and built under the direction of scientist William H. Pickering, while James Van Allen led the scientific team.
Explorer 1 carried instruments that detected the radiation belts surrounding Earth. These regions became known as the Van Allen radiation belts. The discovery was a major scientific result, not merely a symbolic response to Sputnik. Explorer 1 remained in orbit until March 31, 1970, when it reentered Earth's atmosphere.
Vanguard 1, launched in March 1958, was another early American satellite, but it was not the first. The satellite's launch vehicle, Juno I, was derived from the Jupiter-C rocket developed for the U.S. Army.