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Commercial Communications Satellites

Deployment and operation of communications satellites on a commercial basis began with the founding of the Communications Satellite Corporation (COMSAT) in 1963. When the International Telecommunications Satellite Organization (INTELSAT) was formed in 1964, COMSAT became the U.S. member. Based in Washington, D.C., INTELSAT is owned by more than 120 nations. Intelsat 1, known as Early Bird, launched in 1965, provided either 2400 voice circuits or one two-way television channel between the United States and Europe. During the 1960s and 1970s, message capacity and transmission power of the Intelsat 2, 3, and 4 generations were progressively increased by beaming the satellite power only to the earth and segmenting the broadcast spectrum into transponder units of a certain bandwidth. The first of the Intelsat 4s, launched in 1971, provided 4000 voice circuits. With the Intelsat 5 series (1980), introduction of multiple beam operation resulted in additional increases in capacity. A satellite's power could now be concentrated on small regions of the earth, making possible smaller-aperture, lower-cost ground stations. An Intelsat 5 satellite can typically carry 12,000 voice circuits. The Intelsat 6 satellites, which entered service in 1989, can carry 24,000 circuits and feature dynamic on-board switching of telephone capacity among six beams, using a technique called SS-TDMA (satellite-switched time division multiple access). By the early 1990s, Intelsat had 15 satellites in orbit, providing the world's most extensive telecommunications system. Other systems also provide international service in competition with Intelsat. By 1997, all regulatory restraints to such competition will have been lifted. The growth of international systems has been paralleled by domestic and regional systems, such as the U.S. Telstar, Galaxy, and Spacenet programs and Europe's Eutalsat and Telecom.

Services

Commercial satellites provide a wide range of communications services. Television programs are relayed internationally, giving rise to the phenomenon known as the "global village." Satellites also relay programs to cable television systems as well as to homes equipped with dish antennas. In addition, very small aperture terminals (VSATs) relay digital data for a multitude of business services. Intelsat satellites now carry over 100,000 telephone circuits, with growing use of digital transmission. Digital source coding methods (see Telecommunications) have resulted in a ten-fold reduction in the transmission rate needed to carry a voice channel, thus enhancing the capacity of existing facilities and reducing the size of ground stations that provide telephone service.

The International Mobile Satellite Organization (INMARSAT), founded in 1979 as the International Maritime Satellite Organization, is a mobile telecommunications network, providing digital data links, telephone, and facsimile transmission, or fax, service between ships, offshore facilities, and shore-based stations throughout the world. It is also now extending satellite links for voice and fax transmission to aircraft on international routes.


Date: 2016-01-14; view: 725


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