Prof. ANITA MISHRA
A satellite is an object that orbits another object (known as it
primary). The term is often used to describe an artificial satellite(as
opposed to natural satellites, or moons).
All masses that are part of the solar system, including the Earth, are
satellites of the Sun, or satellites of those objects, such as the Moon.
The first artificial satellite was the Soviet Sputnik 1, launched on
October 4, 1957.
There are about 750 satellite in the space,most of them are used for
A communications satellite (sometimes abbreviated to comsat) is an
artificial satellite stationed in space for the purposes of
telecommunications using radio at microwave frequencies. In other
words, in satellite communication, signal transferring between the sender
and receiver is done with the help of satellite.
In this process, the signal which is basically a beam of modulated
microwaves is sent towards the satellite. Then the satellite amplifies the
signal and sent it back to the receiver’s antenna present on the earth’s
surface. So, all the signal transferring is happening in space. Thus this type
of communication is known as space communication.
Satellite communications are comprised
of 2 main components:
The Ground Station.
Earth station is the common name for every installation located on the
Earth's surface and intended for communication with one or more satellites.
Earth stations include all devices and installations for satellite
communications: handheld devices for mobile satellite telephony.
The term Earth station refers to the collection of equipment that is needed
to perform communications via satellite: the antenna (often a dish) and the
associated equipment (receiver/decoder, transmitter).
The two main parts in the sky common to all satellites
are called the payload and the bus.
Payload: transponders, antennas
Bus: physical platform, remote control
The payload represents all equipment a satellite needs to do its
job. This can include antennas, cameras, radar and electronics.
The payload is different for every satellite. For example, the
payload for a weather satellite includes cameras to take pictures of
cloud formations, while the payload for a communications satellite
includes large antennas to transmit TV or telephone signals to Earth
The bus is the part of the satellite that carries the payload
and all its equipment into space. It is the physical
platform that holds all the satellite's parts together and
that provides electrical power, navigation, control and
propulsion to the spacecraft. The bus also contains
equipment that allows the satellite to communicate with
Earth, a kind of 'remote control'.
There are three types of satellite communication orbits:-
G.E.O.(Geostationary Earth Orbit)
L.E.O.(Low Earths Orbit)
M.E.O.(Medium Earths Orbit)
L .E . O (LOWER EARTHS
LEO satellites don’t stay in fixed
position relative to the surface, and
are only visible for 15 to 20 minutes
EARTH ORBITS) :
Objects in Geostationary orbit revolve
around the earth at the same speed as the
earth rotates. This means GEO satellites
remain in the same position relative to the
surface of earth.
M.E.O.(Medium Earths Orbit):MEO satellites are similar to LEO satellites in functionality.
MEO satellites are visible for much longer periods of time than LEO
satellites, usually between 2 to 8 hours
How do communication satellite works?
Two Stations on Earth want to communicate through radio broadcast but
are too far away to use conventional means.
The two stations can use a satellite as a relay station for their
One Earth Station sends a transmission to the satellite. This is called a
The satellite Transponder converts the signal and sends it down to the
second earth station. This is called a Downlink.
Astronomical satellites are satellites used for observation of
distant planets, galaxies, and other outer space objects.
Communication Satellites are artificial satellites stationed in
space for the purposes of telecommunications systems use low
Earth observation satellites:
Earth observation satellite are satellites specifically designed to observe Earth
from orbit, similar to reconnaissance satellites but intended for non-military
uses such as environmental monitoring, meteorology, map making etc.
Navigation Satellite are satellites which use radio signals transmitted to
enable mobile receivers on the ground to determine their exact location. The
relatively clear line of sight between the satellites and receivers on the
ground, combined with ever-improving electronics, allows satellite navigation
systems to measure location to accuracies on the order of a few meters in real
Weather satellites are satellites that primarily are used to monitor
the weather and/or climate of the Earth.
Drag – fee satellites are satellites that offers an environment that is
as isolated as possible from the forces of nature. A properly designed
drag-free-satellite proof mass is uncoupled from the rest of the
Universe to a remarkable degree.
Miniaturized satellites are satellites of unusually low weights and
small sizes. New classifications are used to categorize these satellites:
minisatellite (500-200kg), microsatellite (below100kg),
nanosatellite (below 10kg).
Radio & TV broadcasting:
a. TV satellites deliver hundreds of television channels every day throughout the world. These
satellites are even used to supply television signals to stations for further distribution to the
home, or to exchange signals between television studios.
b. The bandwidth required to transmit multiple programmes at the same time can easily be
provided using satellites.
Mobile Satellite telephony:
Mobile telephony allows the user to make telephone calls and to transmit and receive data
from wherever he/she is located. Digital cellular mobile telephony such as GSM has
become a worldwide standard for mobile communications, but its services lack coverage
over areas that are sparsely populated or uninhabited(mountains, jungle, sea), because it is
not economically viable or practical for the network operators to build antennas there.
a. With satellites, forecasters can see weather across the whole globe: the
oceans, continents, and poles. Satellites show cloud formations, large weather events such as
hurricanes, and other global weather systems.
b. Recent satellite data is very detailed, even to the point of showing states and counties.
Military Applications :
Communications satellites are used for military communications applications, such
as Global command & Control systems. Examples of military systems that use
communication satellites for eg: the Defens eSatellite Communications System
Scientific research satellites provide us with meteorological information, land survey
data , and other different scientific research applications such as earth science, marine
The area coverage through satellite transmission is quit large.
The laying & maintenance of intercontinental cable is difficult and expensive and
this is where the satellite provides alternative.
Satellites can cover large areas of earth. This is particularly useful sparsely populated
Satellite Costs are independent of distances.
Quality of signal is independent of distances.
The high investment cost and insurance cost associated with significant
probability of failure.
Launching satellites into orbit is costly.
There is a larger propagation delay in satellite communication than in terrestrial
Satellites remain the best utilization used for
communications due to their speed and other