Farewell to the First U.S. Satellite

Forty years ago today — March 31, 1970 — Explorer-1 burned up in the Earth’s atmosphere. The first successful U.S. satellite, it had been launched on January 31, 1958.

Explorer-1’s primary scientific instrument, a cosmic ray detector, returned lower than expected results, which led Dr. James Van Allen to postulate 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.

During its lifetime, Explorer-1 orbited the Earth over 58,000 times and traveled 1.66 billion miles (2.67 billion kilometers).

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