Tuning In The Global Village : EXPLORING THE WORLD OF SATELLITE TELEVISION

There are 2,004 satellites of all types orbiting the Earth on behalf of various governments and commercial and scientific organizations, according to the U.S. Space Command at Petersen Air Force Base in Colorado Springs, Colo.

* Weather and spy satellites look down to gather information and intelligence.

* Astronomy satellites peer into deep space, gathering scientific information.

* Communications satellites link distant parts of the planet, transmitting data and telephone conversations as well as radio and television broadcasts to homes and offices.

Types of Communications Satellites

The 125 such satellites now deployed are of four basic types:

1) Global trunk line (19)

* Highest capacity: Up to 48 channels

* Example: Intelsat

2) Domestic or regional (94; 29 U.S.)

* Lower capacity: 24 to 36 channels

* Example: Galaxy (U.S.), Arabsat (Middle East)

3) Direct broadcast (8)

* Highest power: Makes possible smaller receiving antennas

* Example: Astra 1A and 1B (Western Europe)

4) Marine (4)

* Services ships at sea, aircraft and portable telephones

* Example: Inmarsat

Global Trunk Line Communications Satellite

1) Solar panels convert sunlight into electricity to run crucial systems.

2) Antennas receive broadcasts in the form of microwave signals from ground stations and transmit them to other ground stations far away.

*Small, high-power KU-band antennas offer greater signal strength and are favored for television broadcasts.

*Large, low-power C-band antennas carry most telephone conversations.

3) Transponders or individual satellite channels route incoming signals and amplify them for transmission back to Earth. Geostationary Orbit Geostationary satellites orbit at a height of 22,300 miles, moving at the same speed as the Earth rotates so that they are always over the same fixed point on the surface.

Vital Statistics (for typical model, Intelsat VI)

Diameter: 12 feet

Length: 39 feet

Dry weight: 4,202 pounds

Cost: $157 million

Added cost to launch: $90 million to $115 million

Lifespan: 13 years

Transponders: 38 C band; 10 KU band

Normal capacity: Three color television channels and 120,000 telephone circuits.

Some Satellite Systems Used in TV Broadcasting

1) International

* Intelsat: 19 satellites carrying nearly all live TV broadcasts and 80% of transoceanic TV. Transmits to more than 150 Earth stations in 135 user nations.

2) Regional

* Arabsat: 21-nation consortium formed in 1976. Provides telephone and television coverage to Middle East and parts of southern Europe, Asia, and Africa.

* Eutelsat: Includes 29 European nations and seven satellites. Formed in 1977.

* Intersputnik International: Links former Soviet Union and 13 former Socialist Bloc nations via Statsionar satellites.

* Asiasat: Serving area from Tokyo to Jakarta, covering the Asian subcontinent, Middle East and Central Europe.

* PanAmSat: Covers North and South America and Europe for a variety of national customers.

3) National

* Telesat (Canada): Uses three Anik satellites.

* Satcom (U.S.): Five-satellite system of General Electric Co. serving all 50 states and Puerto Rico. Began in 1975.

* BS System (Japan): Five-satellite system covering entire Japanese archipelago. Government-controlled. Began in 1978.

* JCSAT (Japan): First privately owned satellite operator in Japan.

* Superbird (Japan): Second private satellite operator.

* Palapa (Indonesia): Three satellites covering about 60% of populated archipelago, as well as Assn. of Southeast Asian Nations, Papua New Guinea and North Australia. Began in 1976.

* Insat (India): Includes three satellites with capacity to deliver signals to 528 terrestrial TV stations. Launched in 1982.

* Telecom (France): Three satellites serving French mainland, Martinique and French Guyana.

* AUSSAT (Australia): Three-satellite system serving Australia and Papua New Guinea.

* Brazilsat (Brazil): Two satellites.

* Statsionar System (CIS): 26-satellite network serving former Soviet Union.

How Images Get to Your TV Set Satellite Dish

Individuals who own their dish antennas receive unscrambled satellite television signals directly.

Cable

The cable company receives the satellite signal through a dish antenna, then distributes programs to subscriber homes by coaxial or fiber optic cable.

Antenna

A television station receives satellite programming and rebroadcasts it over the air, enabling viewers to receive the signal with “rabbit ears” or conventional rooftop antennas.

The Double Hop

Bouncing a TV signal from one side of the globe to the other--from Moscow, say, to Los Angeles--requires sending the signal up and down between orbiting satellites and ground relay stations more than once.

Where The Footprints Fall

Each transponder or group of transponders on a communications satellite covers a specific area on the ground, known as its “footprint.” The map shows the footprints of some major satellites that carry Cable News Network programs:

Astra 1B Intelsat VI

Arabsat 1

Intelsat F8

Palapa B2P

Superbird Sources: International Telecommunications Satellite Organization (Intelsat); MLE Inc., publisher of World Satellite Almanac; Cable News Network.