The simplest type of satellite is a passive reflector which is a device that simply bounces signals from one place to another . A passive satellite reflects signals back to earth as there are no gain devices on board to amplify or modify the signals. The moon is a natural satellite of earth , visible by reflection of sunlight and having a slightly elliptical orbit. Consequently , the moon became the first passive satellite in1954, when the U.S Navy successfully transmitted the first message over this earth to moon to earth communications systems . In 1956, a relay service was established between Washington, D.C and Hawaii and, unit 1962 , offered reliable long distance radio communications service limited only by the availability of the moon. Over time, however , the moon proved to be an inconvenient and unreliable communications satellite, as it is above the horizon only half the time and its position relative to earth is constantly changing.
An obvious advantage of passive satellite is that they o not required sophisticated electronic equipment on board, although they are not necessarily void of power. Some passive satellite required radio beacon transmitters for tracking and ranging purposes. A beatcon is a continuously transmitted un modulated carrier that an earth station can lock on to and use to determine the exact location of a satellite so the earth station can align its antennas . Another disadvantages of passive satellite is thier inefficient use of transmitted power .
In 1957, Russia launched Sputnik I the first active earth satellite. An active satellite is capable of receiving , amplifying ,reshaping, regenerating, and retransmitting information. Sputnik I transmitted telemetry information for 21 days, later in the same year the United State launched Explore I , which transmitted telementry information for nearly five months. In 1958, NASA launched Score a 150 pound conical -shaped satellite . With an on board tape recording ,score rebroadcast President Eisenhower's 1958 Christmas message.
In 1960, NASA in conjunction with Bell Telephone Laboratories and the Jet Propulsion Laboratory lunched Echo, a 100-foot-diameter plastic balloon with an aluminum coating. Echo, passively reflected radio signals it received from large earth station antennas. Eacho was simple and realiable but required extremely high power transmitters at the earth stations . The forst transatlantic transmission using a satellite was accomplished using Echo. The Syncom project s, a number of using geosynchronous satellites.
Since the Syncom projects a number of nations and private corporations have successfully launched satellite that are currently being used to provide national as well as regional and international global communications . Today's , there are several hundred satellite communications systems operations operating in virtually every corner of the world . There companies provide worldwide , fixed common- carrier telephone and data ciruits: point to point television broadcasting ; network television distribution; music broadcasting ; mobile telephone servies; navigation services; and private communications networks for large corporations, governemt agencies, and military applications.
Intelset I was the first commercial telecommunications satellite. It was launched from Cape Kennedy in 1965 and used two transponders and a 25-mhz band width to simultaneously carry one television signal and 480 voice channels. Intelsat stands for international Telecommunications Satellite Organization. Intelsat is a commercial global satellite network that manifested in 1964 from within the United Nations. Intelsat is a consortium of over 120 nations with the commitment to provide worldwide, non discriminatory satellite communications using four basic service categories; international public switched telephony , broadcasting, private- line business networks and domestic communications. Between 1966 and 1987 Intelsat launched a series of satellite designated Intelsat II ,III,IV,V, ans VI . Intelsat VI has a capacity of 80,000 voice channels. Intelsat s most recent satellite launches include the 500,600,700, and 800 series space vehicles.
The former Soviet Union launched the first set of domestic satellites in 1966 and called them Molniya , meaning lightning. Domsats are satellites that are owned operated and used by a single country. In 1972 Canada launched its first commercial satellite designated Anik , which is an Inuit word meaning 'little brother". Western Union launched their first westar satellite in 1974 and radio corporation of America launched its first Satcom satellites in 1975.
In the United States today a publicly owned company called communications satellite corporation regulates the use and the operation of U.S satellite and also sets their tariffs. Although a company or government may own a satellite , its utilities are generally made available to anyone willing to pay for them. The United States currently utilizes the largest share of available worldwide satellite time ; Great Britain is second with 13percent followed by France with 6 percent.
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