Satellites orbit Earth and other celestial bodies. Natural satellites include Earth's moon and artificial satellites are human-made machines launched into space. There are over 2,787 active artificial satellites currently orbiting Earth that serve important roles like telecommunications, weather monitoring, Earth observation, navigation, military purposes, and more. They allow global connectivity through television and radio signals, phone calls, and internet access. Different types of orbits include low Earth orbit (LEO), medium Earth orbit (MEO), geostationary orbit (GEO), and highly elliptical orbit (HEO) depending on the satellite's purpose and distance from Earth.

1. SATELLITE
Nafizul Islam
nafizulislam2@gmail.com
Abstract
Satellite system definition, History, Application of
satellite system, Types of satellite system

2. What Is a Satellite?
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 space.
Earth and the moon are examples of natural satellites. Thousands of artificial, or man-made,
satellites orbit Earth. Some take pictures of the planet that help meteorologists predict weather and
track hurricanes. Some take pictures of other planets, the sun, black holes, dark matter or faraway
galaxies. These pictures help scientists better understand the solar system and universe.
Still other satellites are used mainly for communications, such as beaming TV signals and phone
calls around the world. A group of more than 20 satellites make up the Global Positioning System, or
GPS. If you have a GPS receiver, these satellites can help figure out your exact location.
Why Are Satellites Important?
The bird's-eye view that satellites have allows them to see large
areas of Earth at one time. This ability means satellites can
collect more data, more quickly, than instruments on the ground.
Satellites also can see into space better than telescopes at Earth's
surface. That's because satellites fly above the clouds, dust and
molecules in the atmosphere that can block the view from ground
level.
Before satellites, TV signals didn't go very far. TV signals only
travel in straight lines. So they would quickly trail off into space
instead of following Earth's curve. Sometimes mountains or tall
buildings would block them. Phone calls to faraway places were
also a problem. Setting up telephone wires over long distances or
underwater is difficult and costs a lot.
With satellites, TV signals and phone calls are sent upward to a
satellite. Then, almost instantly, the satellite can send them back
down to different locations on Earth.

3. Why Don't Satellites Crash Into Each
Other?
NASA and other U.S. and international organizations keep track
of satellites in space. Collisions are rare because when a satellite
is launched, it is placed into an orbit designed to avoid other
satellites. But orbits can change over time. And the chances of a
crash increase as more and more satellites are launched into
space.
In February 2009, two communications satellites - one American
and one Russian - collided in space. This, however, is believed to
be the first time two man-made satellites have collided
accidentally.
History of Satellite
 1945 Arthur C. Clarke – head of British Interplanetary Society publishes
article: "ExtraTerrestrial Relays” defines basic satellite concept - latter fame
as Sci-Fi author
 1955 John R. Pierce (AT&T researcher) publishes Article: "Orbital Radio
Relays” defines technical aspects for global telephony
 1957 Sputnik: Russia launches the first earth satellite. • 1960 First
reflecting communication satellite ECHO – aluminum coated balloon
 1962 AT&T TELSTAR (first active satellite) and RELAY launched (MEO) - for
voice/television/data
 1962 Communications Satellite Act (U.S.)
 1963 SYNCOM launched – first geosynchronous orbit satellite

4.  1964 INTELSAT formed International Telecommunications Satellite
Organization (part of UN) - aim provide global telecommunications
connectivity
 1965 COMSAT's EARLY BIRD: 1st commercial communications satellite: 240
duplex telephone channels or 1 TV channel, 1.5 years lifetime
 1969 INTELSAT-III series provides global coverage
 1972 ANIK: 1st Domestic Communications Satellite (Canada)
 1974 WESTAR: 1st U.S. Domestic Communications Satellite
 1975 RCA SATCOM: 1st operational body-stabilized Satellite
 1976 MARISAT: 1st mobile communications satellite
 1979 INMARSAT formed.
 1975 RCA SATCOM: 1st operational bodystabilized Satellite
 1976 MARISAT: 1st mobile communications satellite
 1979 INMARSAT formed. 1982 first mobile satellite telephone system
INMARSAT-A
 1988 first satellite system for mobile phones and data communication
INMARSAT-C
 1993 first digital satellite telephone system
 1998 global satellite systems for small mobile phones.
Satellite Basics Systems
 Earth Stations – antenna systems on or near earth
 Uplink – transmission from an earth station to a satellite
 Downlink – transmission from a satellite to an earth station

5.  Typically separated frequencies for uplink and downlink
(FDD)
 Transponder – electronics in the satellite that convert uplink
signals to downlink signals
Types of Satellite Systems
 GEO (Geostationary Earth Orbit) at about 36,000km
above the earth's surface.
 LEO (Low Earth Orbit) at about 500-1500km above the
earth's surface.
 MEO (Medium Earth Orbit) or ICO (Intermediate
Circular Orbit) at about 6000-20,000 km above the
earth's surface.
 HEO (Highly Elliptical Orbit)

6. GEO (Geostationary Earth Orbit)
 Geostationary satellites have a distance of almost 36,000
km to the earth. Examples are almost all TV and radio
broadcast satellites, any weather satellites and satellites
operating as backbones for the telephone network.
 Objects in GEO moves around the earth at the same
speed as the earth rotates. This means geostationary
satellites remain in the same position relative to the
surface of earth.
LEO (Low Earth Orbit)
 As LEOs circulate on a lower orbit, it is obvious that
they exhibit a much shorter period (the typical duration
of LEO periods are 95 to 120 minutes). Additionally,
LEO systems try to ensure a high elevation for every
spot on earth to provide a high quality communication
link.
 Each LEO satellite will only be visible from the earth for
about ten minutes.
 LEO satellites are much closer to earth than GEO
satellites, ranging from 500 to 1,500 km above the
surface. LEO satellites do not stay in fixed position
relative to the surface.

7. MEO (Medium Earth Orbit)
 A MEO satellite situates in orbit somewhere between
6,000 km to 20,000 km above the earth's surface.
 MEO satellites are similar to LEO satellites in the context
of functionality.
 MEO satellites are similar to LEO satellite in functionality.
 Medium earth orbit satellites are visible for much longer
periods of time than LEO satellites usually between 2 to 8
hours.
 MEO satellites have a larger coverage area than Low Earth
Orbit satellites.
HEO (High Earth Orbit)
 The High Earth orbit satellite is the only non-circular orbit
of the four types.
 HEO satellite operates with an elliptical orbit, with a
maximum altitude similar to GEO, and a minimum altitude
similar to the LEO.
 The HEO satellites used for the special applications where
coverage of high latitude locations is required.
Satellite Applications
2,787.Currently there are over 2,787 active artificial satellites
orbiting the Earth.

8.  Telecommunications
– global telephone connections
– backbone for global networks
– connections for communication in remote places or
underdeveloped areas
– global mobile communications
 Other Applications
– weather
– radio and TV broadcast satellites
– Earth observation (climate change, agricultural, etc.)
– military: surveillance, imaging, intelligence, early warning
– Navigation and localization: GPS(Global Positioning
System)