Sputnik Composite image of Sputnik the worlds first artificial satellite against a backdrop of the Moon above Earths horizon The Sun and the Earth are reflected on the satellites surface Sputnik was launched on th October by the former Soviet Union The name Sputnik is Russian for travel companion or satellite The body was a highly polished aluminium alloy sphere which measured centimetres in diameter and weighed kilograms It also had four long antennas attached Sputnik transmitted radio signals back to earth for a period of days The success of Sputnik prompted the US government to enter the Space Race with the launch of Explorer four months later