On March 26, 1958, the United States launched its third satellite into space. Explorer 3 was almost identical to Explorer 1, the first satellite the U.S. ever launched. Explorer 3 was the first successful launch in the series after Explorer 1.
Explorer 3 launched on a Juno I rocket from Cape Canaveral, Florida and entered an eccentric orbit. This means it was following a long elliptical path around the Earth. Its payload included a cosmic ray counter and a micrometeorite detector.
The data from Explorer 3 and Explorer 1 led to the discovery of the Van Allen radiation belt. This is a region around the Earth where charged particles from the sun get trapped by Earth’s magnetic field. Explorer 3 spent 93 days orbiting the Earth before its orbit decayed.
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