Page 190 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes Introduction

Today’s satellite operators are planning to be in the business for the long-term. Providers are
investing heavily in developing new platforms capable of carrying large communication
payloads. A satellite is basically any object that revolves around a planet in a circular or
elliptical path. Although anything that is in orbit around Earth is technically a satellite, the
term “satellite” is typically used to describe a useful object placed in orbit purposely to perform
some specific mission or task. Meteor burst communication is a way of communicating using
the ionized trails made by meteors as they enter the earth’s atmosphere. It is also called Meteor
scatter communication. The Earth encounters thousands of tiny bits of meandering space debris
(rock, sand) every day. The number, and perhaps the average size, of these particles increases
sharply during meteor showers, but there is significant meteor activity almost every day.
12.1 Satellites

A satellite is basically a self-contained communications system with the ability to receive
signals from Earth and to retransmit those signals back with the use of a transponder—an
integrated receiver and transmitter ofradio signals. A satellite has to withstand the shock of a
launch into orbit at 28,100 km (17,500 miles) an hour and a hostile space environment where it
can be subject to radiation and extreme temperatures for its projected operational life, which
can last up to 20 years. In addition, satellites have to be light, as the cost of launching a satellite
is quite expensive and based on weight. To meet these challenges, satellites must be small and
made of lightweight and durable materials. They must operate at a very high reliability of more
than 99.9 percent in thevacuum of space with no prospect of maintenance or repair.

Satellite communication, in telecommunications, the use of artificial satellites to provide
communication links between various points on Earth. Satellite communications play a vital role
in the global telecommunications system.

Did u know? Approximately 2,000 artificial satellites orbiting Earth relay analog and digital
signals carrying voice, video, and data to and from one or many locations worldwide.
The main components of a satellite consist of the communications system, which includes
theantennas and transponders that receive and retransmit signals, the power system, which
includes the solar panels that provide power, and the propulsion system, which includes
therockets that propel the satellite. A satellite needs its own propulsion system to get itself
to the right orbital location and to make occasional corrections to that position. A satellite
ingeostationary orbit can deviate up to a degree every year from north to south or east to west of
its location because of the gravitational pull of the Moon and Sun. A satellite has thrusters that
are fired occasionally to make adjustments in its position. The maintenance of a satellite’s orbital
position is called “station keeping,” and the corrections made by using the satellite’s thrusters
are called “attitude control.” A satellite’s life span is determined by the amount of fuel it has to
power these thrusters. Once the fuel runs out, the satellite eventually drifts into space and out of
operation, becoming space debris.
A satellite in orbit has to operate continuously over its entire life span. It needs internal power
to be able to operate its electronic systems and communications payload. The main source of
power is sunlight, which is harnessed by the satellite’s solar panels. A satellite also has batteries
on board to provide power when the Sun is blocked by Earth.

!
Caution The batteries are recharged by the excess current generated by the solar panels when
there is sunlight.

184 LOVELY PROFESSIONAL UNIVERSITY