Today, a lot of money has been invested in communications satellites. It is a satellite that can relay radio, telephone and television signals. They allow telephone conversations, telegraph messages and television shows to travel across the world. Without satellites, massive networks of cables would be needed to enjoy the same benefits and at a much greater cost. 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.