<Tr> <Td_colspan="2"> Radio transmitter (20,005 MHz - 40,002 MHz) </Td> </Tr> <Tr> <Td_colspan="2"> Sputnik program ← None Sputnik 2 → </Td> </Tr> <P> Sputnik 1 (/ ˈspʊtnɪk / or / ˈspʌtnɪk /; "Satellite - 1", or "PS - 1", Простейший Спутник - 1 or Prosteyshiy Sputnik - 1, "Elementary Satellite 1") was the first artificial Earth satellite . The Soviet Union launched it into an elliptical low Earth orbit on 4 October 1957, orbiting for three weeks before its batteries died, then silently for two more months before falling back into the atmosphere . It was a 58 cm (23 in) diameter polished metal sphere, with four external radio antennas to broadcast radio pulses . Its radio signal was easily detectable even by radio amateurs, and the 65 ° inclination and duration of its orbit made its flight path cover virtually the entire inhabited Earth . This surprise success precipitated the American Sputnik crisis and triggered the Space Race, a part of the Cold War . The launch ushered in new political, military, technological, and scientific developments . </P> <P> Tracking and studying Sputnik 1 from Earth provided scientists with valuable information . The density of the upper atmosphere could be deduced from its drag on the orbit, and the propagation of its radio signals gave data about the ionosphere . </P>

When was the first satellite sent into space