NASA / SCIENCE PHOTO LIBRARY NASA / SCIENCE PHOTO LIBRARY
Explorer 1. Launch of Explorer 1, America's first satellite, which discovered the Van Allen radiation belts around Earth. Explorer 1 was launched on 31 January 1958 by a modified Jupiter- C rocket. Explorer 1 (on top of the Jupiter-C) had an integral rocket which acted as the last stage booster. Explorer 1 carried instruments designed to gather data on cosmic rays and tiny meteoroids. It orbited every 107 minutes, transmitting until 23 May 1958. Its instruments showed that there were intense belts of radiation at altitudes above 965 kilometres, consisting of charged particles trapped by the Earth's magnetic field. Explorer 1's orbit decayed on 31 March 1970.
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