NASA / SCIENCE PHOTO LIBRARY NASA / SCIENCE PHOTO LIBRARY
Explorer 1. Engineers check 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 had an integral last-stage booster rocket. It was 2 metres long and weighed 14 kilogrammes. It 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; these consist of charged particles that are trapped by the Earth's magnetic field. Explorer 1's orbit decayed on 31 March 1970.
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