difference between active and passive satellite in wikipedia
Communications satellite There are two major classes of communications satellites, passive and active. Passive satellites only reflect the signal coming from the source, toward the direction of the receiver. With passive satellites, the reflected signal is not amplified at the satellite, and only a very small amount of the transmitted energy actually reaches the receiver. Since the satellite is so far above Earth, the radio signal is attenuated due to free-space path loss, so the signal received on Earth is very, very weak. Active satellites, on the other hand, amplify the received signal before retransmitting it to the receiver on the ground.[3] Passive satellites were the first communications satellites, but are little used now. Telstar was the second active, direct relay communications satellite. Belonging to AT&T as part of a multi-national agreement between AT&T, Bell Telephone Laboratories, NASA, the British General Post Office, and the French National PTT (Post Office) to develop satellite communications, it was launched by NASA from Cape Canaveral on July 10, 1962, in the first privately sponsored space launch. Relay 1 was launched on December 13, 1962, and it became the first satellite to transmit across the Pacific Ocean on November 22, 1963.[8]
Retrograde and prograde motion In our Solar System, all of the planets and most of the other objects that orbit the Sun, with the exception of many comets, do so in the "prograde" direction, i.e. the same sense as the rotation of the Sun. In addition, the rotations of most planets are prograde, with the exceptions of Venus and Uranus, which have retrograde rotations. Most satellites of planets revolve around their planets in the prograde sense. (In the case of the satellites of Uranus, this means they revolve in the same sense as Uranus's rotation, which is retrograde relative to the Sun.) There are some satellites that orbit in the retrograde sense, but these are generally small and distant from their planets, except for Neptune's satellite Triton, which is large and close. It is thought that these retrograde satellites, including Triton, are bodies that have been captured into orbit around their planets, having been formed elsewhere.