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Sputnik 1 (/ˈspʌtnɪk, ˈspʊtnɪk/, Russian: Спутник-1, Satellite 1), often referred to as simply Sputnik, was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program. It sent a radio signal back to Earth for three weeks before its three silver-zinc batteries became depleted. Aerodynamic drag caused it to fall back into the atmosphere on 4 January 1958.