In 1945, science novelist in England, Arthur C. Clarke, forecast that the world will have the satellite as a worldwide wireless communication system. Point of view, Arthur C. Clarke's forecast became true and satellites took the important role in the world technology at the present time. Satellites can be classified in many ways.

There are 11 kinds of satellites that are classifies by usability:

1. Satellite to communicate from point to point.
2. Satellite to communicate with other satellite.
3. Satellite for transportation (by land, by water and by air).
4. Satellite for radio and television.
5. Satellite to observe the natural resource.
6. Satellite to observe the space.
7. Satellite for the weather forecast.
8. Satellite to perform the special task in the space.
9. Satellite to mark the point on earth.
10. Satellite for boat navigation

ELEMENTS OF SATELLITE COMMUNICATIONS SYSTEM

• Space Segment

  i. Satellite (transponders etc)

  ii. Means for launching satellite

  iii. Satellite control centre for station keeping of the satellite

• Ground Segment

  i. Earth Stations

  ii. Rear Ward Communication links

  iii. User terminals and interfaces

  iv. Network control centre

  v. The Transponder (short-for Transmitter-responder) is the ―BRAIN of the satellite that provides connection between the satellite‘s Receive and Transmit antennas.

  vi. Satellites can have 12 to 96 transponders plus spares, depending on the size of the satellite.

  vii. A transponder bandwidth can frequently be 36 MHz, 54 MHz, or 72 MHz or it can be even wider.

  viii. A transponders function is to

  • Receive the signal, (Signal is one trillion times weaker then when transmitted)
  • Filter out noise,
  • Shift the frequency to a down link frequency (to avoid interference with uplink)
  • Amplify for retransmission to ground

There are specific frequency ranges used by commercial satellites.