The first satellite to relay messages from one Earth Station to another was SCORE (Signal Communicating by Orbiting Relay Equipment) launched December 18, 1958. These early satellites, because they were visible from both sides of the Atlantic Ocean simultaneous for only a short time could provide only a period of five hours a day for communications.
Early United States Satellites
In 1960 the United States launched the Echo satellite, a metallic balloon that reflected signals. Later satellites, such as Telestar and Relay, included electronic relay equipment called transponders. Syncom II, the first satellite to be placed in a synchronous orbit, was launched in 1963. The first commercial communications satellites were launched in 1965.
Passive and Active Communication Satellites
Communications through satellites are either passive or active. The first communications satellites were passive. Signals from Earth were merely reflected from the orbiting metallic sphere. Later types of satellites are active. Active communication satellites receive signals from Earth, electronically strengthen the signals, and transmit the signals to Earth.
Relaying of Signals
This relaying of signals from one Earth Station to another is done through the satellite’s transponder. Most communications satellites have more than one transponder and antenna so that they can relay several users of radio waves or signals at the same time.
Launch of Communication Satellites
Communications satellites are launched by rockets or carried into space by the Space Shuttle. Once in space, small engines on the satellites guide the satellite into orbit and help keep them there. Most communications satellites are placed in orbit at an altitude of 22,300 miles above the Earth. This is known as a geostationary or synchronous orbit. This allows the satellite to orbit the Earth at the same speed as the rotation of the Earth. As a result, the satellite appears to be stationary above the same location on Earth.
Satellite Broadcast Range
Broadcasts from a satellite in synchronous orbit can cover only about one third of the Earth’s surface. To send signals anywhere in the world, three communications satellites in geostationary orbit are needed.
Communications satellites will be used to link all the regions and people of the world. This is a giant step from the early uses of communication satellites. “What at the beginning of the decade, was no more than a concept in the minds of a few engineers had, by the end, become a fully commercial system providing global communication system” (Fishlock 23). This global system will consist of many satellites, positioned in geostationary orbit, providing high bandwidth capacity, interconnect many highly specialized Earth Stations operating in more than thirty countries. This network, already in progress by consortiums headed by Motorola (Iridium) will provide the framework and capability for anyone in the world to communicate with anyone else, regardless of location.
The experimental communication satellites were Score, Echo, Telestar, Relay, Syncom. They were all launched by the U.S. between 1958 and 1963. Since then, with the advances in satellite communications, many countries have developed or purchased their own communications satellites, with many others planning to do the same. “More and more large companies with extensive telephone and computer needs are turning to an economical alternative to conventional transmissional methods” (Beatty 275).
Intelsat Satellite Telecommunication Satellite
Intelsat Telecommunication is the biggest worldwide satellite communication network. “It has over 110 nations, and operates powerful communications satellites, such as Intelsat 6, over the Atlantic, Pacific, and Indian Oceans” (Cayne 50). The Intelsat spans the globe, and domestic satellites such as the USSR’s Molniya satellites. Western Union’s Westar, and Canada’s Anik – serve individual countries. The Intelsat V is the latest in its space-craft series, it can handle 12,000 telephone circuits and two color television transmission simultaneously.
Teledesic Satellite Network
A company called Teledesic intends to create a $9 billion wireless data network requiring the launch of more than 810 satellites or “birds”. Other proposed systems would employ fewer, but still significant number of birds.
Telestar, the experimental satellite designed by Bell Telephone Laboratories and placed in an elliptical inclined medium altitude orbit by NASA in 1962. LEO Satellites take less than two hours to orbit the planet. This spacecraft maybe able to serve a user on the ground only a few minutes before it travels out of range.
Satcomes, a different name for communication satellites are being used increasingly to handle long distance telephone, television, and other transmission around the world.
Weather forecasting has been revolutionized by the use of satellites. They are able to scan the whole Earth and the atmosphere continuously. The entire Earth has been photographed at least once daily on a continuous basis for use in weather prediction. Satellite’s data provide information about the ocean, desert, and polar areas of the Earth where conventional weather reports are unavailable or limited. The satellites can show how weather systems are developing anywhere in the world, even where there are no ground stations. Some weather satellites such as the U.S. Goes and European Meteosat, circle in geostationary orbit. Other satellites, such as the U.S. NOAA series, are launched into a polar orbit, over the North and South Poles. These satellites can scan the whole Earth every 12 hours.
Radio transmissions are also conducted through satellite facilities. Amateur radio operators, or “hams” have built several Orbital Satellites Caring Amateur Radios (OSCARS) that take advantage of leftover payload space on other missions to get a free ride into orbit. Other communications satellites listen for distress signals from ships and aircraft, then relay the victims’ location to rescue teams.
TV Broadcasting System
One of the best known uses of communications satellites is for the transmission of video, television. High bandwidth can easily be provided using satellites which allow easy sending of television broadcasts. In addition, developments in broadcast technology allow different types of transmissions to be sent, taking advantage of sharing the same satellite signal. “The cost to the viewers must be small, and this requirement could best be met if satellites transmissions employed vestigial sideband amplitude modulation of frequencies in or near the existing UHF broadcasting bands” (Fishlock 45). Using receivers, amplifiers and transmitters and the electronic techniques of multiplying, these communication satellites can simultaneously relay many telephone and television signals.
For telecommunications, orbiting switchboards (communications satellites) have helped to reduce costs of long distance telephone calls dramatically. It is predicted that users in the future will spend 65 cents a minute to be hooked via satellites into the wired phone network. Long- distance phone charges over land line networks will be added to that figure. “Iridium, which will bypass long distance land lines with its inter-satellite communication, expects to charge $3 per minute for delivering a call “from anywhere to anywhere” (Mannes 69).
Satellite vs. Terrestrial Cost
Communications satellites are more economical to build and use than more traditional terrestrial methods. For example, in 1983, seven undersea cables linked North America and Europe. The last cable cost $175 million. In comparison, a modern communications satellite costs roughly $80 million (including payment for launching it into orbit). It handles more than 3 times as many calls.
The use of satellite technology, particularly in the use of communications satellites has grown rapidly in the past thirty years. Each day more and more uses for the satellites are being discovered. Feeding this is the rapid advancement of technology that allows the quick implementation of these uses.
Communications satellites will not only help out a person in distress but allow a person walking the street in Manhasset N.Y. USA to use their cellular phone to speak with someone in China. More and more satellites are being launched each year to support new and growing uses for business, military and communication needs. Satellite communications will continue in the right direction, UP.