B-4-j- SATELLITE COMMUNICATIONS
In 1955, John R. Pierce proposed the use of satellites for communications. This proposal was preceded, however, by an earlier paper by Arthur C. Clark that was published in 1945, also proposing the idea of using an Earth-orbiting satellite as a relay point for communication between two Earth stations.
Clark calculated that satellites placed in a high orbit of 36,000 km would take exactly one day to go around the Earth. The positions of these satellites would appear motionless from the ground in a geostationary orbit.
Therefore, a minimum of three satellites, capable of receiving and transmitting radio signals and stationed 120 degrees apart, would enable almost total global coverage.
In the late 1950's, both the United States and the Soviet Union began developing satellites and the necessary launch vehicles to place them into orbit. The Soviet Union's successful launching of SPUTNIK 1 came in October of 1957, and was closely followed by the United States' EXPLORER 1 in January of 1958.
Shortly thereafter, in December 1958, the world's first active communications satellite, the U.S. Army-built SCORE, was launched.
The ECHO satellites that followed in the early sixties were passive. They merely reflected signals back to the earth. Active satellites TELSTAR and RELAY, which amplified signals from the earth and retransmitted them, were launched in 1962.
The rockets available in 1960 could boost satellites into orbits no higher than 10,000 km above the earth. The challenge was to increase the orbit to approximately 36,000 km. When located over the equator, the satellite at that height becomes geosynchonous, that is, it appears fixed in space relative to earth stations on the ground. This has the advantage of eliminating tracking electronics and position drives for antennas, thereby greatly simplifying the earth stations.
The first successful geosynchronous satellite was SYNCOM II, launched in 1963.
The commercial era in the United States opened with the Communications Satellite Act of 1962, which set up the Communications Satellite Corporation, or COMSAT, as the United States carrier for satellite communications. The formation of the International Satellite Organization, INTELSAT, and the launching of the "Early Bird" or INTELSAT in 1964 followed this.
Since SYNCOM, over 250 geosynchronous satellites have been launched, of which about 90% have been communications satellites.
The progressive increase in capacity and capabilities of the INTELSAT satellites illustrates the growth that is possible in satellite communications.
INTELSAT I, who was first operational in 1965, had an equivalent voice circuit capacity of 240 channels or one TV channel. It provided service between Europe and North America only. INTELSAT II had the same capacity. The capacity for INTELSAT III jumped to 1,500 channels and INTELSAT IV to 4,000 channels plus two TV signals.
INTELSAT IV-A, which was first operational in 1975, had a capacity of 6,000 channels plus two TV signals.
Today, the INTELSAT IX series deliver the largest satellite capacity in the INTELSAT system of up to 96 units of 36 MHz.
In 1993, the National Aeronautics and Space Administration, known as NASA, launched its Advanced Communication Technology Satellite, or ACTS. ACTS pioneered the testing of an all-digital, Ka-band, spot-beam, geosynchronous earth orbit satellite system capable of hundreds of megabits per second of bandwidth. A number of data optimized satellite networks is currently in operation providing global Internet access and corporate communications through VSAT terminals.
Satellite communications represent one solution to competition and to bringing advanced broadband services to consumers. Wire line technologies such as cable modems and wavelength division multiplexing are others that partly answer the demand.
The fact is the telecommunications industry is a growing market for many different technologies to coexist and flourish. In the USA Alone, spending on telecommunications equipment and services totaled $407 billion in 1997 rising 10% a year. It is communications technologies of all kinds that will connect the world.