A Short Overview of
Satellites
Dr Ayyem Pillai V
Professor, ECE, GRIET,
Hyderabad
What is a Satellite?
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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.
What is SatelliteContinued
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In the context of spaceflight, a
satellite is an artificial object
which has been intentionally
placed into orbit.
Such objects are sometimes called
artificial satellites to distinguish
them from natural satellites such
as Earth's Moon.
Types of Satellite
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Natural : Moon, Earth
Artificial or Man-made : Sputnik 1
(Russia, 1957), Explorer 1 (USA
1958), Asterix (France 1965),
Ohsumi (Japan 1970), Dong Fang
Hong (China 1970), Prospero (UK
1971), Rohini D1 (India 1980),
Ofeg 1 (Israel 1988), Insat(India),
Intelsat
Classification of Satellites
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Altitudes
Rotation centre
Applications
Classification of SatelliteAltitude
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Low Earth Orbit (LEO) Satellite
[500 – 2000 km]
Medium Earth Orbit (MEO)
Satellite [5000 – 20000 Km]
Geostationary (GEO) Satellite
[35786 Km]
Highly Elliptric Orbit (HEO)
Satellite
Classification of SatelliteRotation Centre
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Geocentric Orbit : An orbit around
the planet earth such as Moon,
Artificial satellite
Heliocentric Orbit : An orbit
around the sun such as all planets,
comets, Asteroids
Areocentric Orbit : An orbit around
the planet Mars such as moon,
Artificial satellite
Classification of SatelliteApplication
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Astronomical Satellite
Biosatellites
Communications satellites
Earth observation satellites
Navigational satellites
Reconnaissance satellites
Recovery satellites
Space stations
Tether satellites
Weather satellites
Astronomical Satellite
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An
astronomy
satellite
is
basically
a
really
big telescope floating in space. Because it is in orbit
above the Earth, the satellite's vision is not clouded by
the gases that make up the Earth's atmosphere, and its
infrared imaging equipment is not confused by the heat
of the Earth. Astronomy satellites, therefore, can "see"
into space up to ten times better than a telescope of
similar strength on Earth.
Astronomy satellites have many different applications:
They can be used to study stars, planets and black holes.
Biosatellites
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A biosatellite is an artificial satellite designed
to carry plants or animals in outer space.
They are used to research the effects of
space (cosmic radiation, weightlessness,
etc.) on biological matter.
The first satellite carrying an animal (a dog,
"Laika") was Sputnik 2 on November 3,
1957.
On August 20, 1960 Soviet Sputnik
5 launched and recovered dogs from Earth
orbit.
Communications satellites
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A communications satellite is an artificial satellite that
relays and amplifies radio telecommunication 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.
As of 1 January 2021, there are 2,224 communications
satellites in Earth orbit.
Most communications satellites are in geostationary
orbit.
Earth Observation
Satellites
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An
Earth
observation
satellite or Earth remote sensing
satellite is a satellite used or
designed
for
Earth
observation (EO) from orbit.
They detect changes in the Earth's
vegetation, atmospheric trace gas
content, sea state, ocean color,
and ice fields.
Navigational satellites
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A satellite navigation or satnav system is a
system that uses satellites to provide
autonomous geo-spatial positioning.
It allows small electronic receivers to
determine their location (longitude, latitude,
and altitude/elevation) to high precision
(within a few centimetres to metres)
using time signals transmitted along a line of
sight by radio from satellites.
Navigational satellitesContinued
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Global Positioning System
First launch year: 1978
The United States' Global Positioning System (GPS) consists of up to
32 medium Earth orbit satellites in six different orbital planes. The exact
number of satellites varies as older satellites are retired and replaced.
Operational since 1978 and globally available since 1994, GPS is the
world's most utilized satellite navigation system.
GLONASS
First launch year: 1982
The formerly Soviet, and
now Russian, Global'naya Navigatsionnaya Sputnikovaya Sistema, (GLObal
NAvigation Satellite System or GLONASS), is a space-based satellite
navigation system that provides a civilian radionavigation-satellite service
and is also used by the Russian Aerospace Defence Forces. GLONASS has
full global coverage since 1995 and with 24 satellites
Different Orbits
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The path in which satellite rotates
around the earth is called orbit.
Depending on the types of rotation
the orbits are classified
Equatorial Orbit
Polar Orbit
Different Orbits Continued
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Low earth Orbit (LEO) : 500 to 2000 Km, the period of
rotation is 90-120 minutes,
Medium earth Orbit (MEO) : 5000-20000 Km, the period
of rotation is 6 Hours.
Geostationary Orbit (GEO): 35786 Km, Radius : 42000
Km, Period : 24 hours, Equatorial Orbit. The period of
rotation is 24 hours. The period of the orbit equals one
sidereal day, coinciding with the rotation period of the
Earth. The speed is approximately 3,000 metres per
second (9,800 ft/s).
Different Orbits Continued
Parts of a Satellite
Attitude and Orbit Control
System
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The term attitude relative to satellite
communication
corresponds
to
the
orientation
of
satellite
(vehicle)
in
space. Attitude control is defined as
controlling the orientation of the axis of
satellites that are orbiting in space. So, the
complete set of devices forming a system
that helps to analyse and control the
orientation of satellites in space is known as
an attitude control system.
Thruster