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Satellite Communications

Year 12 Engineering Studies - Telecommunications Assignment
by

Wei Kang

on 20 August 2013

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Transcript of Satellite Communications

Satellite
Historical Developments
of
Satellite Communication
The moon is a
natural
satellite
A
satellite
by definition is any object that revolves around a
planetary body
following a
circular or elliptical path
What we need is something a bit more useful communication.
Artificial
Satellites
Human built, and much more useful in terms of communication
Today, they are responsible for many modern day applications
GPS Navigation
Weather

Mapping
and
Imagery
Useless
Before we go into detail on how satellite works, lets take a look at how it got to the stage it is now
Sputnik I
First ever
artificial satellite
to orbit earth following an
elliptical path
on October 4th 1957
Started the "
Space Race
" between
USSR
and
U
S
A
Diameter of
58cm
with four antennas sending
low frequency radio
signals, orbited the Earth for 3 months.
Sputnik II
Just months after the the launch of Sputnik I, the
Soviet Union
on the 3rd of November 1957 launched its second satellite, Sputnik II.
It was a 4 meter high nose cone capsule with base diameter of 2 meters containing several instruments such as a Geiger counter and spectrophotometer
It is known for being the first satellite to have a
living passenger
on board during an orbit. The passenger was a dog named
Laika
.
Explorer
On January 31st, 1958 the
United

states
successfully launch their first first Satellite, officially known as Satellite 1958 Alpha.
It carried a small scientific payload that led to the discovery of the
Van Allen belt
remaining in orbit for 12 years.
Telestar I
Launched into
Low Earth orbit
on July 10 1962 becoming the first active satellite capable of
two way transmission
It was also the first satellite to transmit
live television imagery
between Europe and North America
Telestar also transmitted the first
call via
Satellite
Echo I & II
NASA in coordination with AT&T Bell's lab, developed their first project led by
John Robinson Pierce
, Echo I. It launched on August 12, 1960 consisting of no instruments, just the 30.5m
aluminium coated balloon
.
It could only
reflect signals
from the ground and hence was the first
passive satellite
Echo 2, with extremely
similar characteristics
as Echo I was launched on January 25, 1964
The only difference was that Echo 2 had a diameter of 41.5m
Syncom 2 & 3
Pirce also responsible for the development of the
travelling wave tube amplifier
, which enabled satellites to
receive, amplify and transmit
radio signals.
Following the failed launch of Syncom 1, the successful launch of
Syncom 2
on July 26, 1963 allowed for the first
Geosynchronous
orbital satellite
Syncom 3
was soon launched on August 19, 1964 becoming the first satellite in
Geostationary
orbit
Syncom 3
broadcast the 1964 Olympic Games
from Tokyo, Japan, to the United States, the first major sporting event broadcast via satellite.
Intelsat
Intelsat (
International Telecommunications Satellite Organization
) was formed on the August 20, 1964
The first Intelsat satellite to be launched was the
Early Bird
(Intelsat I) on April 6, 1965
Early Bird was the first
operational commercial satellite
providing
regular telecommunications and broadcasting services
between North America and Europe.
Early Bird was followed by Intelsat 2B and 2D, launched in 1967 and covering the
Pacific Ocean region
, and Intelsat 3 F-3, launched in 1969 and covering the
Indian Ocean region
.
Modern Day
The successful development of satellite technology paved the way for
modern global communications
. Presently, satellites serve variety of purposes through their differing orbits, frequencies and types of signals used to transmit information.
Satellites today have improved drastically since the Sputnik 1 and continue to rapidly progress into the future.

There are an estimate of
8,300 artificial satellites
that are currently orbiting the Earth.
How do
Satellite
work?
For a Satellite to do the work it intends on doing, it must first be placed into
orbit
All satellites get into
orbit
through riding a rocket. The rocket’s
pathway and velocity varies
depending on the type of orbit the satellite is designed for and situated in. The
inertial guidance system
of the rocket positions
horizontally
before
releasing the satellite
into its orbital state.
Now that the Satellite is in
orbit
around the Earth, it must now be able to
recieve signals
sent from ground and
retransmit
the signals back down
For this to occur, several
components
are vital for the satellite to act as a communication system
Antenna
and onboard
transponder
is responsible for receiving and transmitting of the signal
Power Package of
solar panels
and
batteries
are required to provide power for the Satellite
Propulsion system which includes
rockets
and
fuel
propel and realign the satellite.
In simple terms, a satellite communication works by a
ground
(earth)
station
sending a signal in the form of
low frequency microwaves
to the satellite. The satellite
receives
these microwaves and then uses the
transponders to boost the signal strength (active)
before
relaying it
another satellite or ground station.
Although most satellites operate the same, they exist in
different orbits
depending on the
purpose
of each satellite
There are
three main types
of
orbits
for Satellites:
Geostationary Orbit
Occur when the satellite orbits around the Earth remaining constantly
above a single point
on the Earth surface at all times.
They have an orbital period of 24 hours and an
orbital altitude of approximately 35,785km
.
Due to their high altitude, geostationary satellites are unaffected by mountains hence allowing over the horizon transmission making them suitable for
global communication, television broadcasting and weather satellites.
Asynchronous Orbit
Occur when the satellite
passes through different parts
of the globe at varying times.
They orbit at much
lower altitude
compared to Geostationary orbits of about
160km to 1,600km
and at a higher velocity aswell resulting in their period being drastically less than 24 hours.
Due to their low altitude orbit, they are commonly termed
Low Earth Orbits
(LEO) and are prone to atmospheric decay. They are used for
surveillance and spying purposes
as well as the
orbit in which space shuttles use
Polar Orbit
Like the name suggest, Polar orbits are orbits that
pass through the North and South poles
of the Earth
Similar to Low Earth Orbits, their
orbital altitude is fairly low at about 1,000km
The Polar orbit remains fixed in place while the Earth rotates underneath it allowing them to gain excellent coverage of the Earth's surface and hence are used for
mapping and photography purposes.
Lets now take a look at an
example of the application
of satellite communication in
intercontinental long distance telephone call
The analogue voice signal is carried across the wire telephone system where it undergoes
analogue to digital conversion
. The original analogue signal is modulated, multiplexed and
converted to digital
. It is then sent to the
ground station
where the signal is sent via
microwave
to the satellite.
Uplink

Signal sent via low frequency microwave signal
The
geostationary satellite
receives the signal and through the
integrated transponder
, amplifies it and retransmit it back down to the corresponding base station
Downlink

Low frequency microwaves
The
base station
receives the signal and is transmitted across the local telephone system where it undergoes digital to analogue conversion to the person receiving the call
Full transcript