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First U.S. satellite in orbit

January 30th, 2009
On Jan. 31, 1958, Explorer I was the first U.S. satellite to go into orbit. It was launched by a Jupiter-C rocket from Cape Canaveral, Fla., in response to the launch of the Soviet satellite Sputnik 1. It was the first spacecraft to detect the Van Allen radiation belt. 

The primary science instrument on Explorer 1 was a cosmic ray detector designed to measure the radiation environment in Earth orbit. Once in space this experiment, provided by Dr. James Van Allen of the University of Iowa, revealed a much lower cosmic ray count than expected. Van Allen theorized that the instrument may have been saturated by very strong radiation from a belt of charged particles trapped in space by Earth's magnetic field. The existence of these radiation belts was confirmed by another U.S. satellite launched two months later, and they became known as the Van Allen Belts in honor of their discoverer. 
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