What is a satellite??
• A satellite is an object that moves around a
• Earth and Moon are called “Natural” satellites.
• “Man-made” satellites are machines made by
• These machines are launched into space and
orbit 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
• 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
• 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.
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
• Many satellites carry cameras and scientific sensors.
They may gather information about Earth’s land, air
• Or they may collect data from the solar system and
First satellite in space!!
• The Soviet Union was the first to launch a
satellite into space.
• The satellite was launched in 1957 and was
called “Sputnik 1”.
• NASA has launched many satellites into space.
• The first was “Explorer 1” in 1958.
• Explorer was America’s first man-made
• 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
• The organization responsible for Indian
satellites is the Indian Space Research
• Launching satellites is not cheap business!!
• They cost a lot of money(in fact Millions of
Dollars) to design, construct, launch and to
• Running a satellite at a 36MHz bandwidth will
cost over $1.5 million a year!!
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
Geostationary Earth Orbit (GEO)
• These satellites are in orbit 35,863 km above
the earth’s surface along the equator.
• 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
A GEO satellite’s distance from earth gives it a
large coverage area, almost a fourth of the earth’s
GEO satellites have a 24 hour view of a particular
These factors make it ideal for satellite broadcast
and other multipoint applications.
A GEO satellite’s distance also cause it to have
both a comparatively weak signal and a time delay
in the signal, which is bad for point to point
GEO satellites, centered above the equator, have
difficulty broadcasting signals to near polar
Medium Earth Orbit (MEO)
• A MEO satellite is in orbit somewhere between 8,000 km and
18,000 km above the earth’s surface.
• 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.
• MEO satellites have a larger coverage area than LEO satellites.
A MEO satellite’s longer duration of visibility and
wider footprint means fewer satellites are needed
in a MEO network than a LEO network.
A MEO satellite’s distance gives it a longer time
delay and weaker signal than a LEO satellite,
though not as bad as a GEO satellite.
Low Earth Orbit (LEO)
• LEO satellites are much closer to the earth
than GEO satellites, ranging from 500 to 1,500
km above the surface.
• LEO satellites don’t stay in fixed position
relative to the surface, and are only visible for
15 to 20 minutes each pass.
• A network of LEO satellites is necessary for
LEO satellites to be useful
A LEO satellite’s proximity to earth compared to a
GEO satellite gives it a better signal strength and
less of a time delay, which makes it better for
point to point communication.
A LEO satellite’s smaller area of coverage is less of
a waste of bandwidth.
A network of LEO satellites is needed, which can
LEO satellites have to compensate for Doppler
shifts cause by their relative movement.
Atmospheric drag effects LEO satellites, causing
gradual orbital deterioration.
Types of Satellites
• Astronomical satellites are satellites used
for observation of distant
planets, galaxies, and other outer space
• Communications satellites are artificial
satellites stationed in space for the
purposes of telecommunications using
radio at microwave frequencies. Most
communications satellites use
geosynchronous orbits or neargeostationary orbits, although some recent
systems use low Earth-orbiting satellites.
• Earth observation satellites 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 satellites are satellites which use radio
time 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
• Reconnaissance satellites are Earth observation
satellite or communications satellite deployed for
military or intelligence applications.
• Space stations are man-made structures that are
designed for human beings to live on in outer
space. A space station is distinguished from other
manned spacecraft by its lack of major propulsion
or landing facilities - instead, other vehicles are
used as transport to and from the station. Space
stations are designed for medium-term living in
orbit, for periods of weeks, months, or even
• Weather satellites are satellites that primarily are
used to monitor the weather and/or climate of
• Drag-free satellites are satellites that offers an
environment that is as isolated as possible from
the forces of nature. A properly designed dragfree-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: mini
satellite (500-200kg), microsatellite (below
100kg), nanosatellite (below 10kg).
Applications of Sat. Comm.
Radio and TV broadcasting
Business radio and TV
Thin route or trunk telephony
Mobile satellite telephony
Data, broadband and multimedia services
IP over satellite for ISPs
Corporate or institutional VSAT networks
End-user services for home or small office
Mobile data communications
Advantages of Satellites
• Higher bandwidths are available for use.
• Satellite to satellite communication is very
• The coverage area of a satellite greatly
exceeds that of a terrestrial communication.
• Transmission cost of a satellite is independent
of the distance from the center of the
Disadvantages of satellites
• Launching satellites into orbits is costly.
• Satellite bandwidth is gradually becoming
• There is a larger propagation delay in satellite
communication than in terrestrial