COMMUNICATION SATELLITES

COMMUNICATION SATELLITES. Artificial communication satellites can relay television, radio, and telephone communication between any two places on the globe and from space to other objects in space or on earth. The military, commercial companies, and amateurs from over twenty nations have hundreds of communication satellites orbiting the earth. This has been accomplished in a mere forty-five years.

The origin of artificial communications satellites began over a century ago with Guglielmo Marconi's electric waves transmission in 1896. The possibilities for satellites improved gradually with advances in short wave communication and radar in the 1930s, and with the possibilities of rocket flight after Robert H. Goddard's rocket demonstration in the 1920s. In 1945, British scientist and science fiction author Arthur C. Clarke published an article in which he predicted the launching of orbital rockets that would relay radio signals to earth. At last, on 4 October 1957, the Soviet Union launched Sputnik I, the first artificial satellite. Clarke's seemingly far-fetched prediction had come true in about ten years. It took over fifty years from the early possibilities to the first satellite, but the next forty-five years saw tremendous and rapid technical advancement and proliferation of worldwide satellite communication.

Early Communication Satellites

The United States entered the Space Age when it launched the Explorer 1 satellite in January 1958. At the end of 1958, an Atlas B rocket launched a SCORE communications satellite, which contained two radio receivers, two transmitters, and two tape recorders. It broadcast a taped Christmas greeting from President Dwight D. Eisenhower. Then, in August 1960, the National Aeronautics and Space Administration (NASA) launched Echo 1, a giant, ten-story Mylar balloon reflector that relayed voice signals. It was so bright it could be seen by the naked eye. Echo 1 launched the American satellite communication era.

At that time, there were two principal viewpoints toward satellite relay. One side favored the Echo passive satellite system, artificial "moons" that would reflect electromagnetic energy. The other view favored active satellites, which would carry their own equipment for reception and transmission. Courier 1B, launched in October 1960 shortly after Echo 1, was the first active transmitter and used solar cells and not chemical batteries for power. Telstar 1, the first commercial satellite, was built by AT&T and launched by NASA in 1962. It provided direct television transmission between the United States and Japan and Europe and proved the superiority of active satellite communication, as well as the capability of commercial satellites (COMSATS) to provide multi channel, wideband transmission.

Satellites receive signals from a ground station, amplify them, and then transmit them at a different frequency to another station. Most ground stations have huge antennas to receive transmissions. Smaller antennas than used in years past have been placed closer to the user, such as on top of a building. By using frequencies allocated solely to a satellite, rather than going through the earth microwave stations, communications are much faster. This allows for teleconferencing and for computer to computer communications.

International Communications

In 1962, President John F. Kennedy signed legislation to create the Communications Satellite Corporation to represent the United States in a worldwide satellite system. In 1964, under United Nations auspices, the International Telecommunications Satellite Consortium (Intelsat) was formed. From then on, communication satellites had synchronous, high-altitude, elliptical orbits, which improved communications. The Intelsat 1 (Early Bird) was launched in 1965 for transatlantic communication service. It could transmit 240 simultaneous telephone calls or one color television channel between North America and Europe.

By 1970, the Intelsat 4s provided 4,000 voice circuits each; by 1990, each satellite could carry over 24,000 circuits. As of 2002, there were 19 Intelsats in orbit, as well as many other competing satellite communications systems in the United States and Europe. Intelsats can communicate with each other and with other satellite systems as well. For instance, Intelsats and the Russian satellites provide the hotline between Washington, D.C., and Moscow.

Development in communication satellites systems results from many sources. The first ham, or amateur, radio satellites were launched in 1961. By 1991, thirty-nine amateur communications satellites had been launched, many sent free as ballast on government rockets. As of 2002, there were six countries that owned their own communications satellites for domestic telephone service and some twenty-four countries that leased from the Intelsat systems for domestic service. Commercial satellites have been developed by some twenty countries and provide many communications services. Television programs can be transmitted internationally by beaming off satellites. Satellites also relay programs to cable television systems and homes equipped with dish antennas, until recently only a possibility for sophisticated military use.

New Technology

One new technique of the 1990s is called frequency reuse, which expands the capabilities of satellites in several ways. It allows satellites to communicate with a number of ground stations using the same frequency. The beam widths can be adjusted to cover different-sized areas—from as large as the United States to as small as a single small state. Additionally, two stations far enough apart can receive different messages transmitted on the same frequency. Also, satellite antennas have been designed to transmit several beams of different sizes in different directions.

The satellite communications systems of NASA, called Tracking and Data Relay Satellites (TDRS), which began in 1983, provide links between space shuttles and ground control. By 1990 one TDRS satellite could relay all the data in a twenty-four volume encyclopedia in five seconds. The new TDRS converts solar energy to electricity and uses antennas to transmit up to 300 million bits of information per second per radio channel. The latest versions allow communication between spacecrafts, between a shuttle and a space station, or with the Hubble Space Telescope.

There is also now a mobile telecommunications network which provides data digital links and telephone and fax communication between ships or with airplanes on international flights. Ships can also use two satellites at two different locations for navigation purposes. Laser beams, operating in the blue-green wavelength which penetrates water, have been used for communication between satellites and submarines.

In the early 2000s, developments in satellites use networks of small satellites in low earth orbit (1,200 miles or less above the earth) to provide global telephone communications. The special telephones used allow access to regular telephone networks from anywhere on the globe, creating a true "global village."

BIBLIOGRAPHY

Curtis, Anthony R. ed. Space Almanac. Houston: Gulf Publishing Co., 1992.

McGraw Hill Encyclopedia of Space. West Germany: Editions Rombaldi, 1967.

Diane NagelPalmer

communications satellite one of two types of orbiting vehicle that relays signals between communications stations:
1. active communications satellite a satellite that receives, regenerates, and retransmits signals between stations.

2. passive communications satellite a satellite that reflects communications signals between stations.

Communications Satellite (COMSAT) Private company that provides worldwide satellite communications systems. COMSAT, established by the US Congress, began with the launch of the Early Bird satellite in 1965. Many other nations now participate in COMSAT projects.