Sputnik 1 (/ˈspʌtnɪk, ˈspʊtnɪk/; "Satellite-1", or "PS-1", Простейший Спутник-1 or Prosteyshiy Sputnik-1, "Elementary Satellite 1")^[​6] was the first artificial Earth satellite.^[​7] The Soviet Union launched it into an elliptical low Earth orbit on 4 October 1957. It orbited for three weeks before its batteries died and then orbited silently for two months before it fell back into the atmosphere on the 25th December 1957.

It was a polished metal sphere 58 cm (23 in) in diameter with four external radio antennas to broadcast radio pulses. Its radio signal was easily detectable by radio amateurs,^[​8] and the 65° inclination and duration of its orbit made its flight path cover virtually the entire inhabited Earth.