Explorer

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U.S. Explorer 10 satellite shown undergoing testing in a National Aeronautics and Space Administration laboratory. Explorer 10 was launched March 25, 1961, and relayed magnetic field data from a high Earth orbit. The satellite was one of more than 50 scientific spacecraft launched as part of the Explorer program between 1958 and 1975.

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Explorer

satellites

Written and fact-checked by The Editors of Encyclopaedia Britannica

Article History

Key People:: Wernher von Braun; William Hayward Pickering

Related Topics:: Earth satellite

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Explorer, any of the largest series of unmanned U.S. spacecraft, consisting of 55 scientific satellites launched between 1958 and 1975. Explorer 1 (launched Jan. 31, 1958), the first space satellite orbited by the United States, discovered the innermost of the Van Allen radiation belts, two zones of charged particles that surround Earth. Explorer 1’s discovery of the Van Allen belts was the first scientific discovery made by an artificial satellite. Explorer 6 (launched Aug. 7, 1959) took the first pictures of Earth from orbit. Other notable craft in the series include Explorer 38 (launched July 4, 1968; also known as Radio Astronomy Explorer), which measured galactic radio sources and studied low frequencies in space, and Explorer 53 (launched May 7, 1975; also known as Small Astronomy Satellite-C), which was sent out to explore X-ray sources both inside and outside the Milky Way Galaxy.

This article was most recently revised and updated by Erik Gregersen.