Sputnik 1, launched on October 4, 1957, was the world's first artificial satellite.
It was also the first Soviet satellite programme and consisted of four Sputnik or "fellow traveller” satellites. It was relatively small having a mass of only 83.6 kg and its mission was to send back data concerning the density of the earth’s upper atmosphere, and ionosphere.
This it did but only for 21 days then it stopped transmitting signals.
The second Sputnik, Sputnik 2, was launched on November 3, in the same year and weighed in at 508.3 kilograms. However this time it was different. It carried a passenger on board. A dog called Laika. For just over a week scientists monitored Laika’s biological rhythms to see how a living body adapted to space.
Unfortunately they had not yet worked out how to return safely from space so Laika was put to sleep.
April 27, 1958 saw the launch of the third Sputnik satellite but it was destroyed only 88 seconds into its flight and as such it was not given a number.
This meant that Sputnik 3 was actualy the fourth sputnik launched. As it was on May 15, 1958. It was supposed to send back data on the results experiments carried out on the Earth's magnetic field, radiation belt, and ionosphere and this one weighed 1,327Kg.
It went on orbiting the earth and sending back data until the 6th of April 1960