Sputnik 1 stamp. Artwork of Sputnik 1, the world's first artificial satellite, on a stamp issued by the communist government of the former Soviet Union. Sputnik 1 was launched on October 4th, 1957. The name Sputnik is Russian for 'travel companion' or satellite. The body was a highly polished aluminium alloy sphere which measured 58 centimetres in diameter and weighed 83.5 kilograms. It also had four long antennas attached. Sputnik 1 transmitted radio signals back to earth for a period of 21 days. The success of Sputnik 1 prompted the US government to enter the Space Race with the launch of Explorer-1 four months later.