Satellite Communication Module 1. Anna university syllabus

EC8094 Satellite Communication

A Satellite is a physical object that
revolves (or) more around a larger
object in space
(It is a Microwave repeater in the
space)
★ Satellite communication system is very much afact of every day life.
★ Satellites are specifically made for telecommunication purpose.
★ They are used for mobile applications such as communication to
■ ships, vehicles, planes, hand -held terminals and for TV and radio
broadcasting
★ There are about 6000 satellites in the space, most of them are used for communication.
They are: Wide area coverage of the earth’s surface.
Transmission delay is about 0.3 sec.
Transmission cost is independent of distance

R1 : Europa,Africa,Mongolia
R2: North & South America,Greenland
R3:Asia,Australia & South-West Pacific

Global Communication
Three Geosynchronous Satellites (Geo Stationary Satellite) are required to
cover world for communication

Origin of Satellite communication
The idea of satellite communication was conceived by Arthur C.Clarke famous
British Science fiction writer in 1945
How many countries have sent a Satellite into space? More than 75 countries
https://www.youtube.com/watch?v=g2WaJdflqT0
https://www.youtube.com/watch?v=PVLh9Huw4AU
2,666 operational satellites circled the globe in April of 2020

Sputnik 1
SCORE
First artificial satellite
LEO type
4th
October 1957
Soviet Union
From American Atlas
rocket
Telstar in 1962
It provided the very first live
transatlantic television feed
It is still in orbit
First satellite to
achieve a
geosynchronous orbit
Syncom 1 in 1963

November 3, 1957, barely a month after the Soviet
Union sent humanity’s first artificial satellite into orbit
sputnik 2
LAIKA
Apollo 11 Saturn V space vehicle lifts off with Astronauts Neil A. Armstrong,
Michael Collins and Edwin E. Aldrin Jr. at 9:32 a.m. EDT July 16, 1969
First Artificial Satellite of the
Moon
Luna
Apollo

Mariner 9 was launched successfully on May 30,
1971, and became the first artificial satellite of Mars
Chandrayaan-1, India's first mission to the Moon
was launched on 22 October 2008
Mars Orbiter Mission (MOM)-Mangalyaan

Satellite Communication Module 1. Anna university syllabus

Three Common usual Bands are :
1. C Band : 4-8 GHZ
2. Ku Band : 12-18 GHZ K Band (18 -27 GHZ ) ← DBS
3. Ka Band : 26-40 GHZ
Txion TV Signal - Cable company -
Cable System)
DBS/DTH
Land Mobile ,Maritime Mobile,Aeronautical Mobile

C Band Antenna
Ku Band Antenna
Ka Band Antenna
K Band Antenna

Uplink
A Signal from earth station to
the satellite is known as
uplinked
Frequency range is 5.9 GHZ
to 6.4 GHZ.
Transponder is used to
convert 6 GHZ signal into 4
GHZ signals.
It converts the signal and
sends it down to the second
earth station
Downlink
A signal from satellite to
earth station is known as
downlink signals
Frequency range is 3.7 GHZ
to 4.2 GHZ.

Reason for the Downlink Frequency to be lower than the Uplink Frequency
1. Output power amplifier in Transponder [ Generates more power at lower
frequency]
2. Effective area of the receiving antenna [ More energy ]
3. Path Loss (Lower frequency < Higher frequency)
4. Beam width (wider at Low Frequency)

Orbit : Any body that means around another one
in a mathematically predictable path

LEO : Low Earth Orbit
MEO: Middle (Medium) Earth Orbit
HEO: High Elliptical Orbit
GEO: Geo Synchronous Earth Orbit
Apogee : The point farthest from earth (ha)
Perigee : The point closest approach to earth (hp)

Characteristics LEO MEO GEO HEO
Altitude 300-1500 Km 5000-10000 Km 36000 Km 20000-47000 Km
Rotation Period 90 Mins 5 -12 Hrs 24 Hrs > 24 Hrs
Satellite Life 3 to 7 Years 10 to 15 Years 10 to 15 Years 10 to 15 Years
No.of Satellites 40-80 8-20 3 4-20
Frequency Range 1 GHz- 2.5 GHz 1.2 - 1.66 GHz 1.5 – 1.67 GHz --
Example Iridium, GlobalStar GPS,Glonass VSAT Molnya, Ellipso
Uses
Earth Monitoring
Weather Satellites
Global Communication
(Email,Fax,Telephony)
Direct TV
Point to Multipoint
(Cable TV)
Satellite Radio
Remote Sensing
Astronomical
observations
Advantages
Lower Transmit Power
Smaller Antenna
Less Packet delay
Simple Design
Cover Larger Area
Few Handover
Almost 3 satellite
can cover entire
world
High latitude and polar
coverage
Dis Advantages
For Global coverage
need more satellites
Complex Design
High Power
Special Antenna needed
High Power
Fixing cost is more
Larger Antenna
Selected area
coverage
High propagation delay

Earth
Satellite
Kepler’s First Law (Law of orbit)
It states that the path followed by a satellite around the primary will be an ellipse
A ellipse has two focus points F1 & F2
Apogee
Perigee
Eccentricity
0<e<1 Elliptical
🡪
e =0 Circle
🡪
a & e - Size and shape of orbit parameters
Ovalness

Argument of Perigee (ω)
The angle formed between the perigee
& the ascending node.
I, w,Ω - Position of satellite in orbit parameters

Inclination (i)
The angle between the orbital plane and the earths
equatorial plane (going from east to north)

Kepler’s Second Law (Law of Areas)
It states that for equal time
interval, a satellite will sweep out equal
areas in its orbital plane, focused at the
center
1 Month
1 Month
Earth
Satellite
Perigee
Apogee
Right Ascension of ascending node (Ω)
It is the angle between line of Aries and ascending node towards east direction in equatorial plane.

Kepler's Third Law (Law of Periods)
It states that square of the periodic time of
orbit is proportional to the cube of the mean distance
between the two bodies

Sub Satellite path
This is the path traced out on the earth’s surface directly below the satellite
Mean anomaly (M)
It gives the average value to the angular
position of the satellite with reference to the
perigee.
True anomaly
It is the angle from point of perigee to the
satellite s position, measure at the Earth s centre.
‟ ‟
It is an angular parameter that defines the position of
a body moving along a Keplerian orbit. It is the
angle between the direction of periapsis and the
current position of the body,
la
True anomaly - Location of satellite according to time parameter

Newton’s law:
Every particle in the Universe attracts every other particle with a force that is directly
proportional to the product of the masses and inversely proportional to the square of the
distance between them
Satellite has its forward thrust, which is offset by the pull of gravity
towards the earth. This keeps the satellite circling in its orbit.

Newton's second law
Acceleration is produced when a force acts on a mass. The greater the mass (of
the object being accelerated) the greater the amount of force needed (to accelerate the
object).
F=ma
Newton's second law of motion, the net force acting upon the satellite is directed in the same
direction as the acceleration - towards the focus of the ellipse.
Once more, this net force is supplied by the force of gravitational attraction between
the central body and the orbiting satellite.

1. Major Axis (a)
2. Eccentricity (e)
[a & e - Size and shape of orbit parameters]
3. Inclination angle (i)
The angle between orbital plane & earths equatorial plane (going from east to north)
4. Argument of Perigee (ω)
The angle formed between the perigee & the ascending node
5. Right Ascension of ascending node (Ω)
Angle between line of Aries and ascending node towards east direction in equatorial
plane
[I, w,Ω - Position of satellite in orbit parameters]
6. True anomaly
It is the angle from point of perigee to satellite s position, measure at the Earth s centre
‟ ‟
True anomaly - Location of satellite according to time parameter
Orbital Parameters

Perturbation - Deviation or Disturbing
Theoretically, an orbit described by Kepler is ideal as Earth is considered to be a perfect
sphere and the force acting around the Earth is the centrifugal force.
This force is supposed to balance the gravitational pull of the earth
In practice, other forces also play an important role and affect the motion of the satellite
1. Asymmetry or the Earth Gravitational Field - More pronounced for LEO
2. The Gravitational field of the Sun and Moon - More pronounced on GEO
3. Solar radiation pressures -Affects large GEO satellites which uses large solar
arrays
4. Atmospheric drag - More pronounced for LEO
Orbital Perturbations

1.Effects of non-Spherical Earth
As the shape of Earth is not a perfect ellipse, it causes some variations in the path
followed by the satellites.
Earth is flattened at the poles
Equatorial radius is not constant
Non regular features of earth there are regions where the average density of earth appears
to be higher - Regions of mass consideration or Mascon
Above factors lead non uniform gravitational field around the earth
As the Earth is bulging from the equatorial belt, and keeping in mind that an orbit is
not a physical entity, and it is the forces resulting from an oblate Earth which act on the satellite
produce a change in the orbital parameters.
1.Regression of the nodes & the latitude of perigee(point closest to the Earth).
2.Rotation of the line of apsides.
3.Argument of perigee & Right ascension of ascending node.
Due to the non-spherical shape of Earth, one more effect called as the “Satellite Graveyard”
It leads to the small value of eccentricity (10-5) at the equatorial plane.
This causes a gravity gradient on GEO satellite and makes them drift to one of the two
stable points which coincide with minor axis of the equatorial ellipse.
Longitudinal changes -->In plane changes

Due to the position of the Mascons & Equatorial bulges there are four equilibrium points
(Two Stable points (Bottom of Valley) & Two Unstable points (Top of hill) )

inclination change → out of plane changes
Rate of change hihger than average
(Sun & Moon same side of satellite orbit)
Less than average
(Sun & Moon opposite of satellite orbit)

Atmospheric Drag
For Low Earth orbiting satellites, the effect of atmospheric drag is more
pronounces. The impact of this drag is maximum at the point of perigee.
Drag(pull towards the Earth) has an effect on velocity of Satellite (velocity
reduces).
This causes the satellite to not reach the apogee height successive revolutions.
This leads to a change in value of semi-major axis and eccentricity (a & e)
Satellites in service are maneuvered by the earth station back to their original orbital
position.

Station Keeping
Station keeping is the process of maintenance of the satellite’s orbit against different factors that
Cause temporal drift
Satellite drift is typically in the range of 0.5 -3o
Per day
Satellites need to have their orbits adjusted time to time because the satellite, even though initially
placed in the correct orbit, can undergo a progressive drift due to some natural forces
Gravitational perturbations due to the sun and moon
Solar radiation pressure,
Earth being an imperfect sphere etc
The orbital adjustments are usually made by releasing jets of gas or firing small rockets tied
to the body of satellite. It is maintained as every 2 or 3 weeks
Satellites have a supply of fuel allocated for station keeping and this fuel is used gradually
over a planned lifetime period of 7 to 15 years to keep the satellite within typically +/- 0.15 deg east
west and +/-0.15 deg north/south of its nominal orbit position. The equatorial ellipticity of the earth
causes GEO satellite to drift slowly along the orbit, to 75°E and to 105°W
Station Keeping it is important that a geostationary satellite be kept in its correct orbital slot

Station keeping in the North - South station
keeping (N-S) is maintained by firing thrusters
parallel to the spin axis in a continuous
Station keeping in the East - West station keeping
(E-W) is obtained by firing thrusters perpendicular
to the spin axis
In body or 3 axis stabilization firing thrusters E-w &
N-S in continuous mode
Station Keeping Satellites in the 6/4-GHz C band
must be kept within ±0.1° and the 14/12-GHz Ku
band, within ±0.05°of the designated longitude
North-south station-keeping maneuvers much
more expensive in fuel than are east-west station-
keeping maneuvers.
Station Keeping Orbital correction is carried out by
command from the TT&C (Telemetry, Tracking and
Command) earth station, which monitors the
satellite position.
Each loop cycle (sidereal period)
represents one day.
Satellite crosses the equator twice a day
The best time to do this adjustment is
when the satellite goes through the exact
Centre of the station keeping box.
Often satellites are maintained with little or no N-S station keeping to extend on orbit life

Sub satellite Point
The point on the earth vertically under the satellite is referred to as the sub satellite point.
Point at which a line between the satellite and the center of the Earth intersects the Earth’s
surface
Location of the point expressed in terms of latitude and longitude
If one is in the US it is common to use
o Latitude (λE) – degrees north from equator
o Longitude (ΦE) – degrees west of the Greenwich meridian
Location of the sub satellite point may be calculated from coordinates of the rotating system
EL = LST – GST
EL - East Longitude
LST – Local Sidereal Time
GST – Greenwich sidereal Time

Location
Northern Hemisphere
Southern Hemisphere
Latitude and longitude make up the grid system that helps us identify absolute, or exact, locations
on the Earth's surface. we can use latitude and longitude to identify specific locations.
Latitude and longitude are also helpful in identifying landmarks

Sub Satellite Point
It is location on the surface that lies directly between the satellite and centre of the Earth
Nadir Direction
The pointing direction from satellite to subsatellite point
Zenith Direction
The pointing direction from subsatellite point to satellite

Look Angle Determination
The coordinates to which an earth station antenna must be pointed to communicate a satellite are
called the Look Angles
1.Azimuth (Az)
2.Elevation (El)
Satel
lite
Elevation Angle
It is from center of Earth ,where is the position of satellite
It is measured up from the local Horizontal plane to the Orbital plane
Angle between 00
& 900
Azimuth Angle
Angle between North towards East ,where the satellite points for
plane
Angle between 00
& 3600

Azimuth angle is generally referenced north (0°) or to south (180°) in clockwise
+ive Angle - Ive Angle
North Latitude South Latitude
East Longitude West Longitude

The following information is needed to determine the look angles of geostationary
orbit.
1. Earth Station Latitude: λE
2. Sub satellite Point Latitude : λss
3. Earth Station Longitude: ΦE
4. Sub-Satellite Point s Longitude: Φ
‟ SS
5. ES: Position of Earth Station
6. SS: Sub-Satellite Point
7. S: Satellite
8. d: Range from ES to S
9. ζ: angle to be determined
Side a: angle between North Pole & radius of SS point.
Side b: angle between radius of Earth and radius of the SS
Side c: angle between radius of Earth and the North Pole
a = 900
c = 900
- λE

Elevation Calculation
Azimuth Calculation
1.An earth station is located at latitude 35°N & longitude 100°W.Calculate the antenna look angles
for a satellite at 67°W.
2.An earth station is located at latitude 12°S & longitude 52°W.Calculate the antenna look angles
for a satellite at 70°W.
3.An earth station is located at latitude 35°N & longitude 65°E.Calculate the antenna look angles
for a satellite at 19°E.
4.An earth station is located at latitude 30°S & longitude 130°E.Calculate the antenna look angles
for a satellite at 156°E.
R = 6371 Km
aGSO=42164 Km

σmin= 900
+ El min
Limits of Visibility
The east and west limits of geostationary are visible from any given Earth station.
These limits are set by the geographic coordinates of the Earth station and antenna elevation.
The lowest elevation is zero (in theory) when the antenna is pointing along the horizontal but in
practice, to avoid reception of excess noise from Earth. Some finite minimum value of elevation is
issued (Elmin)
The earth station can see a satellite over a
geostationary arc bounded by ±81.30
about the earth
station longitude
The limiting angle is given by
Earth station at equator with the antenna pointing
either east or west along the horizontal

Earth Eclipse of satellite
It occurs when Earth s equatorial plane coincides with the plane of the Earth s orbit
‟ ‟
around the sun. An Eclipses is said to occur When the sun light fails to reach the satellite solar
panel
Near the time of spring and autumnal equinoxes, when the sun is crossing the equator, the
satellite passes into sun s shadow. This happens for some duration of time every day.
‟
Equinox Making night and day of approximately equal length all over the earth and occurring
🡪
about March 20-21 (vernal equinox or spring equinox ) and September 22-23
(autumnal equinox).
These eclipses begin 23 days before the equinox
and end 23 days after the equinox.
They last for almost 10 minutes at the beginning
and end of equinox and increase for a maximum
period of 72 minutes at a full eclipse.

A satellite east of the earth station enters eclipse during daylight & early evening (busy hours) at
the earth station.
A Satellite west of earth station enters eclipse during night & early morning (non busy hours).
The solar cells of the satellite become
non-functional during the eclipse period
& the satellite is made to operate with the
help of power supplied from the
batteries.
Modern satellites are well equipped with
batteries for operation during eclipse.

Sun Transit Outage
Sun transit outage is an interruption in or distortion of geostationary satellite signals caused by
interference from solar radiation (Hot)
During the equinoxes is the transit of the satellite between earth & sun
When this happens, Sun appears to be an extremely noisy source which completely blanks out
the signal from satellite. [Temporarily blanking the communication]
This effect lasts for 6 days around the equinoxes. Sun Outage occurs two times in a year
They occur for a maximum period of 10 minutes.
Generally, sun outages occur in February, March & September, October (Northern Hemisphere)
March, April & August, September (Southern Hemisphere) around the time of the
equinoxes.
At these times, the apparent path of the sun across the sky takes it directly behind the line of
sight between an earth station and a satellite.
As the sun radiates strongly at the microwave frequencies used to communicate with satellites
(C-band, Ka band and Ku band) the sun swamps(heat) the signal from the satellite.
The effects of a sun outage can include partial degradation

The traffic of satellite may be shifted to other satellite during sun transit
outage

Case1
Case 2
Case 2
Case 3 Working of sun outage
Case1
1 2

Launch Vehicles & Propulsion
The launching of a satellite into orbit is extraordinary complex & costly operation
Satellite launch vehicles are nothing but Multi stage Rockets
Rocket – To put satellite into orbit which are above 120 miles from earth station
Two types of satellite launch vehicles.
1.Expendable Launch Vehicles (ELV) – [Delta & Ariane Rockets]
2.Reusable Launch Vehicles (RLV) – [Space Shuttle]

Expendable Launch Vehicles
ELV is uses to carry a payload into space
It is used only onec i.e Their components are not recovered for reuse after launch
ELV contains three stages
1st
& 2nd
stage of ELV raise the satellite to an about 50 miles and 100 miles.
3rd
stage of ELV places the satellite in transfer orbit.
The task of ELV will be completed and its spare parts will be fallen to earth, when the satellite
reached to transfer orbit.
Reusable Launch Vehicles
RLV is capable of launching a payload into space more than once(Multiple Times)
i.e Partially reusable (Space Shuttle main engines & Two Solid Rocket Boosters)
The functions of space shuttle are similar to the functions of 1st & 2nd stages of ELV
Satellite along with the 3rd stage of space shuttle are mounted in the cargo bay
It is ejected from the cargo bay when the space shuttle reaches to about 150 to 200 miles.
3rd stage of space shuttle gets fired and places the satellite into a transfer orbit.
After this, the space shuttle will return back to earth for reuse.

Satellite must be placed into transfer orbit between initial LEO & High Altitude Orbit

Placing Satellites into Geostationary Orbit
1
2
3.Direct Insertion to GEO

TTC – Tracking Telemetry & Command Functions
✔Throughout the launch & acquisition phases
✔Network of Ground Station
✔Spread across the Earth

Launching of Satellites
The process of placing the satellite in a proper orbit is known as launching process.
During this process, from earth stations we can control the operation of satellite. Mainly, there are
four stages in launching a satellite.
First Stage − The first stage of launch vehicle contains rockets and fuel for lifting the satellite along
with launch vehicle from ground.
Second Stage − The second stage of launch vehicle contains smaller rockets. These are ignited
after completion of first stage. They have their own fuel tanks in order to send the
satellite into space.
Third Stage − The third (upper) stage of the launch vehicle is connected to the satellite fairing. This
fairing is a metal shield, which contains the satellite and it protects the satellite.
Fourth Stage − Satellite gets separated from the upper stage of launch vehicle, when it has been
reached to out of Earth's atmosphere. Then, the satellite will go to a “transfer
orbit”. This orbit sends the satellite higher into space.
When the satellite reached to the desired height of the orbit, its subsystems like solar
panels and communication antennas gets unfurled. Then the satellite takes its position in the orbit
with other satellites. Now, the satellite is ready to provide services to the public.

Functions
&
Process
4th
stage
Final Reoriented
✔ Orbit & Attitude
✔ Velocity Correction
🡪Deploy Solar Arrays
🡪Sun Acquisition
🡪Earth Capture
🡪Station Acquisition
3rd
stage
Coast into Perigee
Coast into Apogee
AKM attitude & Fired
Near GEO
2nd
stage
Separate from PKS
2nd
upper stage burned
Post Injection
✔ Align space craft
✔ Separate space craft
✔ Reoriented & Tracked
1st
stage
✔ Launch
✔ Lift off
✔ Booster Space
1st
upper stage burned
Into parking orbit
(Near Equator)
PKS motor fired
Into Transfer orbit
https://www.youtube.com/watch?v=ebhOnf65N9Q
https://www.youtube.com/watch?v=QQB1Iw3zJbc
https://www.tutorialspoint.com/satellite_communication

Indian Satellites
https://www.isro.gov.in/launchers
https://www.youtube.com/watch?v=FiCFj4fcrWQ
https://www.youtube.com/watch?v=--8ORixBXQE

Satellite Communication Module 1. Anna university syllabus

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