Communication
Satellites
Communications Satellites have been around since 1958. A communications
satellite is a spacecraft that orbits the Earth and relays messages, radio,
telephone and television signals. Stations on the ground, called earth stations,
transmit signals to the satellite, which then relays the signal to other earth
stations. As a newer form of communications, communications satellites are very
useful in bringing the people in the world together. Communications between
people that used to take days or even months, now take only minutes or seconds
using satellites.
First Satellites
The first satellite to relay messages from one Earth Station to another was
SCORE (Signal Communicating by Orbiting Relay Equipment) launched December 18,
1958. These early satellites, because they were visible from both sides of the
Atlantic Ocean simultaneous for only a short time could provide only a period of
five hours a day for communications.
Early United States Satellites
In 1960 the United States launched the Echo satellite, a metallic balloon
that reflected signals. Later satellites, such as Telestar and Relay, included
electronic relay equipment called transponders. Syncom II, the first satellite
to be placed in a synchronous orbit, was launched in 1963. The first commercial
communications satellites were launched in 1965.
Passive and Active Communication Satellites
Communications through satellites are either passive or active. The first
communications satellites were passive. Signals from Earth were merely reflected
from the orbiting metallic sphere. Later types of satellites are active. Active
communication satellites receive signals from Earth, electronically strengthen
the signals, and transmit the signals to Earth.
Relaying of Signals
This relaying of signals from one Earth Station to another is done through
the satellite's transponder. Most communications satellites have more than one
transponder and antenna so that they can relay several users of radio waves or
signals at the same time.
Launch of Communication Satellites
Communications satellites are launched by rockets or carried into space by
the Space Shuttle. Once in space, small engines on the satellites guide the
satellite into orbit and help keep them there. Most communications satellites
are placed in orbit at an altitude of 22,300 miles above the Earth. This is
known as a geostationary or synchronous orbit. This allows the satellite to
orbit the Earth at the same speed as the rotation of the Earth. As a result, the
satellite appears to be stationary above the same location on Earth.
Satellite Broadcast Range
Broadcasts from a satellite in synchronous orbit can cover only about one
third of the Earth's surface. To send signals anywhere in the world, three
communications satellites in geostationary orbit are needed.
Communication
Communications satellites will be used to link all the regions and people of
the world. This is a giant step from the early uses of communication satellites.
"What at the beginning of the decade, was no more than a concept in the
minds of a few engineers had, by the end, become a fully commercial system
providing global communication system" (Fishlock 23). This global system
will consist of many satellites, positioned in geostationary orbit, providing
high bandwidth capacity, interconnect many highly specialized Earth Stations
operating in more than thirty countries. This network, already in progress by
consortiums headed by Motorola (Iridium) will provide the framework and
capability for anyone in the world to communicate with anyone else, regardless
of location.
Telecommunications
The experimental communication satellites were Score, Echo, Telestar, Relay,
Syncom. They were all launched by the U.S. between 1958 and 1963. Since then,
with the advances in satellite communications, many countries have developed or
purchased their own communications satellites, with many others planning to do
the same. "More and more large companies with extensive telephone and
computer needs are turning to an economical alternative to conventional
transmissional methods" (Beatty 275).
Intelsat Satellite Telecommunication Satellite
Intelsat Telecommunication is the biggest worldwide satellite communication
network. "It has over 110 nations, and operates powerful communications
satellites, such as Intelsat 6, over the Atlantic, Pacific, and Indian
Oceans" (Cayne 50). The Intelsat spans the globe, and domestic satellites
such as the USSR's Molniya satellites. Western Union's Westar, and Canada's Anik
- serve individual countries. The Intelsaat V is the latest in its space-craft
series, it can handle 12,000 telephone circuits and two color television
transmission simultaneously.
Teledesic Satellite Network
A company called Teledesic intends to create a $9 billion wireless data
network requiring the launch of more than 810 satellites or "birds".
Other proposed systems would employ fewer, but still significant number of
birds.
Telestar
Telestar, the experimental satellite designed by Bell Telephone Laboratories
and placed in an elliptical inclined medium altitude orbit by NASA in 1962. LEO
Satellites take less than two hours to orbit the planet. This spacecraft maybe
able to serve a user on the ground only a few minutes before it travels out of
range.
Satcomes
Satcomes, a different name for communication satellites are being used
increasingly to handle long distance telephone, television, and other
transmission around the world.
Weather Satellites
Weather forecasting has been revolutionized by the use of satellites. They
are able to scan the whole Earth and the atmosphere continuously. The entire
Earth has been photographed at least once daily on a continuous basis for use in
weather prediction. Satellite's data provide information about the ocean,
desert, and polar areas of the Earth where conventional weather reports are
unavailable or limited. The satellites can show how weather systems are
developing anywhere in the world, even where there are no ground stations. Some
weather satellites such as the U.S. Goes and European Meteosat, circle in
geostationary orbit. Other satellites, such as the U.S. NOAA series, are
launched into a polar orbit, over the North and South Poles. These satellites
can scan the whole Earth every 12 hours.
Radio Satellites
Radio transmissions are also conducted through satellite facilities. Amateur
radio operators, or "hams" have built several Orbital Satellites
Caring Amateur Radios (OSCARS) that take advantage of leftover payload space on
other missions to get a free ride into orbit. Other communications satellites
listen for distress signals from ships and aircraft, then relay the victims'
location to rescue teams.
TV Broadcasting System
One of the best known uses of communications satellites is for the
transmission of video, television. High bandwidth can easily be provided using
satellites which allow easy sending of television broadcasts. In addition,
developments in broadcast technology allow different types of transmissions to
be sent, taking advantage of sharing the same satellite signal. "The cost
to the viewers must be small, and this requirement could best be met if
satellites transmissions employed vestigial sideband amplitude modulation of
frequencies in or near the existing UHF broadcasting bands" (Fishlock 45).
Using receivers, amplifiers and transmitters and the electronic techniques of
multiplying, these communication satellites can simultaneously relay many
telephone and television signals.
CostCommunication
For telecommunications, orbiting switchboards (communications satellites)
have helped to reduce costs of long distance telephone calls dramatically. It is
predicted that users in the future will spend 65 cents a minute to be hooked via
satellites into the wired phone network. Long- distance phone charges over land
line networks will be added to that figure. "Iridium, which will bypass
long distance land lines with its inter-satellite communication, expects to
charge $3 per minute for delivering a call "from anywhere to anywhere"
(Mannes 69).
Satellite vs. Terrestrial Cost
Communications satellites are more economical to build and use than more
traditional terrestrial methods. For example, in 1983, seven undersea cables
linked North America and Europe. The last cable cost $175 million. In
comparison, a modern communications satellite costs roughly $80 million
(including payment for launching it into orbit). It handles more than 3 times as
many calls.
Conclusion
The use of satellite technology, particularly in the use of communications
satellites has grown rapidly in the past thirty years. Each day more and more
uses for the satellites are being discovered. Feeding this is the rapid
advancement of technology that allows the quick implementation of these uses.
Communications satellites will not only help out a person in distress but
allow a person walking the street in Manhasset N.Y. USA to use their cellular
phone to speak with someone in China. More and more satellites are being
launched each year to support new and growing uses for business, military and
communication needs. Satellite communications will continue in the right
direction, UP.
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