Satellite systems are composed of a space segment and an earth segment. Earth stations send information via radio signals or microwaves to the satellite. The satellite receives, amplifies and transmits these signals to another earth station or satellite. It acts as a relay device. Early communications satellites were described as passive repeaters because they simply reflected signals.
Modern satellites are active reapeaters because they also amplify the signal they receive.
The idea for satellites came from Arthur C. Clarke in 1945. After much research and testing, mankind was able to implement Clarke's vision. Score consisted of two radio receivers and two transmitters. Since then, many more satellites have been launched into space. There are also weather satellites, which transmit complex images of cloud patterns and global positioning satellites that tell you your location on earth and allow for navigation.