Page 21 - Satellite Communications, Fourth Edition

Chapter
1

Overview of Satellite Systems

1.1 Introduction
The use of satellites in communications systems is very much a fact of
everyday life, as is evidenced by the many homes equipped with anten-
nas, or “dishes,” used for reception of satellite television. What may not
be so well known is that satellites form an essential part of telecom-
munications systems worldwide, carrying large amounts of data and
telephone traffic in addition to television signals.
Satellites offer a number of features not readily available with other
means of communications. Because very large areas of the earth are vis-
ible from a satellite, the satellite can form the star point of a commu-
nications net, simultaneously linking many users who may be widely
separated geographically. The same feature enables satellites to provide
communications links to remote communities in sparsely populated
areas that are difficult to access by other means. Of course, satellite sig-
nals ignore political boundaries as well as geographic ones, which may
or may not be a desirable feature.
To give some idea of cost, the construction and launch cost of the
Canadian Anik-E1 satellite (in 1994 Canadian dollars) was $281.2
million, and that of the Anik-E2, $290.5 million. The combined launch
insurance for both satellites was $95.5 million. A feature of any satel-
lite system is that the cost is distance insensitive, meaning that it
costs about the same to provide a satellite communications link over
a short distance as it does over a large distance. Thus a satellite com-
munications system is economical only where the system is in contin-
uous use and the costs can be reasonably spread over a large number
of users.
Satellites are also used for remote sensing, examples being the
detection of water pollution and the monitoring and reporting of
1