Sputnik
Sputnik is the Russian for "satellite" (literal meaning 'travel companion'). Sputnik 1 was the first artificial satellite to achieve geocentric orbit, and was launched on October 4th 1957. Its more formal name was Object PS - Prosteishii Sputnik, meaning simplest satellite, as it was decided to launch something much more simple and therefore lighter than originally planned as payload for the massive R-7 ICBM rocket in order to beat arch-rival America into space. In fact, the R-7 was designed to be capable of delivering a nuclear warhead anywhere in the world, but principally to be used against the USSR's 'main adversary.'
Both the USA and USSR were planning to launch satellites in International Geophysical Year, which ran from July 1957 to December 1958 to coincide the the 11 year cycle of maximum sunspot activity. The USA had signalled its intention in a 1955 press release and the Soviet government authorized development of an artificial satellite for peaceful scientific purposes in January 1956. The R-7 was capable of launching a payload of over 1 tonne and it was planned to allow 200 - 300 kg for the scientific instrumentation. However difficulties arose, both with the construction of the satellite (designated Object D) so the decision was made in November 1956 to delay the launch of Object D in favor of Object PS to comfortably enable launch within IGY. Sputnik 1 had a diameter of 0.58m and weighed 84 kg. It was fitted with a 1 watt transmitter which functioned for 22 days transmitting through two 2 beam antennas (one with 2.4m beams and the other 2.9m).
Sputnik 1 was pressurized with inert nitrogen at 1.3 atmospheres. The power for the transmitter etc was 3 silver-zinc batteries. If the temperature rose above 50 degrees Celsius or fell below 0 degrees then sensors were designed to trigger a change in Sputnik's signal. It re-entered the earth's atmosphere in January 1958.