Hindustan University, Chennai
• Working principle
• Types of satellite
• Recent Development
A satellite is a moon, planet or machine that
orbits a planet or star. For example, Earth is a
satellite because it orbits the sun. Likewise,
the moon is a satellite because it orbits Earth.
Usually, the word "satellite" refers to a
machine that is launched into space and
moves around Earth or another body in
a. Synchronous orbit
It lies in the equatorial plane
of the earth. This orbit is
most useful orbit for
b. Polar orbit
c. Inclined orbit
The path along which satellite moves in the space around earth are
called orbits. A Satellite can move in three types of orbits namely:-
Nearest point on the orbit of a
satellite from earth.
It is determined by the angle it
makes with the equator.
Characteristics of orbit are
Farthest point on the orbit of a satellite from earth.
The synchronous orbit is further classified into
• Geostationary Orbit:
An orbit in which a satellite appears stationary relative to any
point on earth. A satellite in such an orbit is at an altitude of
approximately 35,786 km (22,236 mi) above mean sea level.
An object in such an orbit has an orbital period equal to the
Earth's rotational period and thus appears motionless, at a fixed
position in the sky, to ground observers. Communication
satellites and Weather satellites are often placed in
• Geosynchronous Orbit:
A Satellite whose period of revolution equals to period of
rotation of earth about its axis. In this, Satellite has 24 hours
non-equatorial orbit. If a Satellite has a time period of 24
hours, then height of Satellite above earth may be determined
• The antenna can simply be pointed at the satellite and remain
in a fixed position. With this arrangement, continuous
communications are possible. Approximately
40% of the earth’s surface can be
accessed from such a satellite.
Hence, three such synchronous
satellites are required to cover the
entire earth. Three synchronous
Satellite are placed in such a way to
provide 100% earth coverage.
Types of Satellite
Natural: Such as the
moon orbiting around the
international space station
orbiting the earth
A communications satellite is an artificial satellite
that relays and amplifies radio telecommunications
signals via a transponder; it creates a
communication channel between a source
transmitter and a receiver at different locations on
Earth. Communications satellites are used for
television, telephone, radio, internet, and military
applications. There are over 2,000 communications
satellites in Earth’s orbit, used by both private and
The major subsystem of satellite are
1. Solar panels:
They charge the batteries and supply the electric power for
2. Communication subsystems:
This is a set of transponders that receive the uplink signals and
transmit them to the earth.
3. Telemetry, tracking and command subsystem:
It monitors onboard conditions such as temperature and
battery voltage and transmit them to ground station for
4.Attitude control subsystem:
It provides stabilization in orbit and senses change in
5. Propulsion subsystem:
The jet thrusters and apogee kick motor (AKM) are part of
propulsion subsystem and are commanded from ground.
Advantages of satellite over
The coverage area of a satellite greatly
exceeds that of a terrestrial system.
Transmission cost of a satellite is
independent of the distance from the center of
the coverage area.
Satellite to Satellite communication is very
Higher Bandwidths are available for use.
Launching satellites into orbit is costly.
Satellite bandwidth is gradually becoming used up.
There is a larger propagation delay in satellite communication
than in terrestrial. communication.
Major problems for satellites
Positioning in orbit
Satellite Transmission Bands
C Band are mostly used. It’s capacity is low and terrestrial interference is problem. In Ku band, rain
interference is the problem. In Ka band, equipment needed to use the band is very expensive.
Frequency Band Downlink Uplink
C 3.7-4.2 GHz 5.92-6.42 GHz
Ku 11.7-12.2 GHz 14.0-14.5 GHz
Ka 17.7-21.2 GHz 27.5-31.0 GHz