Sputnik 1, artwork. This Soviet spacecraft, the first ever spacecraft to reach Earth orbit, was launched on 4 October 1957 by the Soviet Union. The hammer and sickle symbol of the USSR's flag is in the background at left. Sputnik 1 was a highly polished aluminium alloy sphere, 58 centimetres in diameter, with four long antennas attached to it. It transmitted radio signals back to Earth for a period of 23 days. The following year, Sputnik 1 burned up as it re-entered Earth's atmosphere on 4 January 1958. The launch of Sputnik 1 took the USA by surprise, starting what became known as the Space Race between the USA and USSR.