COMMUNICATIONS SATELLITES

Advanced Technology has brought great changes in communications. Man has been successful in launching an artificial earth satellite into satellite into orbits around the earth. The communications satellites make it possible to send radio messages, telephone calls, and television programmers between distant parts of earth. Rockets boast it into orbit, and the force of gravity keeps it fro flying off into space.

This artificial earth satellite is used to send radio, telephone, television, or other electronic communications to any part of the world. Transmitting stations on earth bounce television signals to the satellite by means of special antennas. The satellites send the signals back to the earth. Communications by the satellite is more reliable than by ordinay short wave radio and it has better quality.

There are two kinds of communications satellites. They are passive or active depending on the way it sends signals back to the earth.

Passive communications satellites simply reflect signals, as a mirror reflect light. The signals send to passive satellites must be strong because radio waves weaken as they travel to a satellite and back to the earth. The satellite must be large to reflect the radio energy back to the ground or receiving stations on another continent or thousand of miles from the sending station.

Active communications satellites are equipped with a radio receiver and transmitter. They receive signals from the earth, ampifly (strengthen) them, and than transmit them back to the earth. Therefore, they do not need to be so large as passive satellites. Most active satellite are less than 3 meters high. The electric equipment gets its power from sunlight by means of solar batteries.
Television signals are sometimes blocked by mountains, by the earth’s curvature, or even by tall buildings. Therefore, they have to be relayed from one transmitter to another in order to tunnel long distances.

The first message transmitted by satellite was sent in 1958. It was a Christmas greeting by President Dwight D. Eisenhower. The first television pictures were relay to many parts of the world by satellite in 1969 from Apollo II astronauts on the moon.