What is a satellite??

• An artificial body placed in orbit round the earth or another planet in order to collect the information or for communication.

• Earth and Moon are called “Natural” satellites.

• “Man-made” satellites are machines made by scientists.

• These machines are launched into space and to orbit the Earth or another body in space.

Why are satellites important?

• Satellites fly high in the sky, So they can see large areas of earth at one time.

• Satellites also have a clear view of space.

• Before the invention of satellites, TV signals didn’t go very far.

• TV signals only travel in straight lines. So they would go off into space instead of following Earth’s curve.

Contd..

• Sometimes they would be blocked by mountains or tall buildings.

• Phone calls to far away places were also a problem. It costs a lot and it is hard to set up telephone wires over long distances or underwater!!

• With satellites, TV signals and phone calls can be sent up to a satellite. The satellite can then send them back down to different spots on Earth.

TYPES OF SATELLITES

• Astronomy satellite

• Atmospheric satellite

• Communication satellite

• Navigation satellite

• Reconnaissance satellite

• Remote sensing satellite

• Search & Rescue satellite

• Space exploration satellite

• Weather satellites

Incredible India

• India has launched 64 satellites (as of 25 February 2013) of many types.

• The first satellite was Aryabhata launched on 19-04-1975. It is a experimental/small satellite.

• The organization responsible for Indian satellites is the Indian Space Research organization (ISRO).

8-Nov-14 Satellite Communications 8

First Launching Of Satellites By

Country

What are the parts of a satellite??

• Satellites come in many shapes and sizes. But most have at least two parts in common. They are 1)an antenna and 2)a power source.

• The antenna is used to send and receive information.

• The power source can be a solar panel or battery.• Solar panels make power by turning sunlight into

electricity.• Many satellites carry cameras and scientific

sensors. They may gather information about Earth’s land, air and water.

Components of a satellite

How do satellites work??

• Two stations on earth want to communicate through radio broadcast but are too far away to use conventional means.

• The two stations can use satellite as a relay station for their communication.

• One Earth Station sends a transmission to the satellite. This is called Uplink.

• The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink

• A communications satellite is a radio relay

station in orbit above the earth.

• It receives, amplifies, and redirects analog and

digital signals carried on a specific radio

frequency.

• Satellite communications play a vital role in

the global telecommunications system.

• Two major elements of Satellite Communications

Systems are:

– Space Segment

– Ground Segment

• Space Segment includes:

– Satellite

– Means for launching satellite

– Electrical Power System

– Mechanical structure

– Communication transponders

– Communication Antennas

– Attitude and orbit control

system

• The ground segment consists of

– Earth Stations

– Rear Ward Communication links

– User terminals and interfaces

– Network control centre

– Transmit equipment.

– Receive equipment.

– Antenna system.

• Satellite Control Centre function:

– Tracking of the satellite

– Receiving data

– Eclipse management of satellite

Conti…..

– Commanding the Satellite for station keeping.

– Determining Orbital parameters from Tracking

and Ranging data

– Switching ON/OFF of different subsystems as per

the operational requirements

• The path a Satellite follows around a planet is

defined as an orbit.

• Satellite Orbits are classified in two broad

categories :

– Non-Geostationary Orbit (NGSO)

– Geo Stationary Orbit (GSO)

GEO: 35,786 km above the earth

MEO: 8,000-20,000 km above the earth

LEO: 500-2,000 km above the earth

• During early 1950s, both passive and active satellites were

considered for the purpose of communications over a large

distance.

• Passive satellites though successfully used in the early years of

satellite communications, with the advancement in technology

active satellites have completely replaced the passive

satellites.

Passive Satellites

• The first artificial passive satellite Echo-I of NASA was launched in August 1960.

Active Satellites

• In active satellites, it amplify or modify and retransmit the signal

from the earth.

• Satellites which can transmit power are called active satellite.

• Have several advantages over the passive satellites.

– Require lower power earth station.

– Less costly.

– Not open to random use.

– Directly controlled by operators from ground.

Active Satellites

• Universal: Satellite communications are available

virtually everywhere.

• Versatile: Satellites can support all of today's

communications needs .

Conti…..

• RELIABLE: Satellite is a proven medium for supporting a

company's communications needs.

• SEAMLESS: Satellite's inherent strength as a broadcast

medium makes it perfect.

• FAST: Since satellite networks can be set up quickly,

companies can be fast-to-market with new services.

• Telephone

• Television

• Digital cinema

• Radio

• Internet access

• Military

• Etc………

• Future communication satellites will have

– more onboard processing capabilities,

– more power, and

– larger-aperture antennas

that will enable satellites to handle more bandwidth.

• The demand for more bandwidth will ensure the long-term

viability of the commercial satellite industry well into the 21st

century.

• In addition, other technical innovations such as low-cost reusable launch

vehicles are in development.

• Further improvements in satellites’ propulsion and power systems will

increase their service life to 20–30 years from the current 10–15 years.

Disadvantages of satellites

• Launching satellites into orbits 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

Stability

Power

Communications

Harsh Environment

8-Nov-14 Satellite Communications 38

• By going through the above slides we came to know

that satellite is mostly responsible for:

– Telecommunication transmission

– Reception of television signals

– Whether forecasting

• Which is very important in our daily life.