Introduction to
Satellite
Communications
Engr. Cyrill O. Escolano
Contract of Service Instructor
College of Engineering
Southern Luzon State University
Satellite
 The word satellite is defined as a physical object
that orbits or revolve around another physical
body.
Types of Satellites
 Natural Satellite
 Artificial Satellite
Basics: 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 a satellite as a relay station for
their communication
 One Earth Station sends a transmission to the satellite.
This is called a Uplink.
 The satellite Transponder converts the signal and sends
it down to the second earth station. This is called a
Downlink.
Basics: Advantages of Satellites
 The advantages of satellite communication over
terrestrial communication are:
 The coverage area of a satellite greatly exceeds that
of a terrestrial system.
 Transmission cost of a satellite is independent of the
distance from the center of the coverage area.
 Satellite to Satellite communication is very precise.
 Higher Bandwidths are available for use.
Basics: Disadvantages of Satellites
 The disadvantages of satellite communication:
 Launching satellites into orbit is costly.
 Satellite bandwidth is gradually becoming used up.
 There is a larger propagation delay in satellite
communication than in terrestrial communication.
Satellite Applications
Once placed into its intended orbit, a satellite can be
used for the following applications:
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Communications
Spying
Weather
Space exploration
Scientific research
Search and rescue operation
Navigation
Communications Satellite
 A spacecraft placed in orbit around Earth that
carries onboard transmitting and receiving
equipments capable of relaying signals back to
Earth.
The Components of the Satellite
A satellite system basically consists of the following
components:
 Space Segment
 Ground Segment
Space Segment
Contains the satellite and all terrestrial facilities for
the control and monitoring of the satellite.
 Satellite Payload
 Platform
 Electric power supply
 tracking and telemetry command
(TT&C) equipments
 temperature control
 Altitude and orbit control
Ground Segment
 Consists of all the Erath station that are most
often connected to the end-user’s equipment by
a terrestrial network.
Brief Historical Account
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1945
1955
1957
1960
 1961
 1962
 1963
 1964
:Arthur C. Clarke Article: “Extra-Terrestrial Relays.
:John R. Pierce Article: “Orbital Radio Relays
:Sputnik: Russia launches the first Earth satellite
:AT&T applies to FCC for experimental satellite
communications license
:Formal start of TELSTAR, RELAY, and SYNCOM
Programs
:Communications Satellite Act (US)
:SYNCOM was launched
:INTELSAT was formed
Brief Historical Account
 1965
 1972
 1974
 1975
 1975
:INTELSAT-III series provides global coverage
:ANIK – 1st Domestic Communications Satellite
(Canada)
:WESTAR – 1st U.S. Domestic Communications
Satellite
:INTELSAT-IVA – 1st use of dual-polarization
:RCA SATCOM – 1st operational body-stabilized
communications satellite
Brief Historical Account
 1976
 1976
 1979
 1997
:MARISAT – 1st mobile communications
satellite
:PALAPA – 3rd country to launch domestic
satellite
:INMARSAT formed
:AGILA 2 Satellite Launched – Philippines
 SCORE
(Signal Communications by
Orbiting Relay Equipment )
December 18, 1958
 Project Echo
 Echo 1 (May 13, 1960)
 Echo 2 (January 25,
1964)
 SYNCOM 3
(August 19, 1964)
AGILA 2
How satellites are classified?
Types of Service Offered
 Fixed Satellite Services (FSS)
 Mobile Service
 Broadcast Services
Orbital Locations (Satellite Elevation Category
Low Earth Orbit (LEO) Satellite
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Orbit height
:100 – 300 mi
Orbital Velocity (ave)
:17,500 mph
Orbital Time (period)
:1.5 hours
Satellite Availability
:15 min per orbit
Typical operating frequency:1 GHz – 2.5 GHz
Leo: Advantages
 Advantages
 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.
Leo: Disadvantages
 Disadvantages
 A network of LEO satellites is needed, which can be
costly
 LEO satellites have to compensate for Doppler shifts
cause by their relative movement.
International Space Station
Crew
6
Launch
1998 – 2012
Mass
approximately 450,000 kg (990,000 lb)
Length
51 m (167.3 ft)
Width
109 m (357.5 ft)
Height
20 m (66 ft)
Volume
837 m3 (29,600 cu ft)
Perigee
352 km (190 nmi)
Apogee
355 km (192 nmi)
Orbital Inclination
51.6 degrees
Average Speed
7,706.6 m/s
Orbital Period
91 minutes
No. of Orbits
73789
Orbital Locations (Satellite Elevation Category
Medium Earth Orbit (MEO) Satellite
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Orbit height
:6,000 – 12,000 mi
Orbital Velocity (ave)
:9,580 mph
Orbital Time (period)
:5 to 12 hours
Satellite Availability
:2 to 4 hours per orbit
Typical operating frequency:1.2 GHz – 1.66 GHz
Meo: (cont..)
 Advantage
 A MEO satellite’s longer duration of visibility and wider
footprint means fewer satellites are needed in a MEO
network than a LEO network.
 Disadvantage
 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.
Orbital Locations (Satellite Elevation Category
Geostationary or Geosynchronous (GEO) Satellite
 Orbit height
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:22,300 mi
(within 19,000 – 25,000 mi)
Orbital Velocity (ave)
:6,879 mph
Orbital Time (period)
:24 hours
Satellite Availability
:24 hours per orbit
Typical operating frequency:2 GHz – 18 GHz
Geo: Advantages
 Advantages
 A GEO satellite’s distance from earth gives it a large
coverage area, almost a fourth of the earth’s surface.
 GEO satellites have a 24 hour view of a particular
area.
 These factors make it ideal for satellite broadcast and
other multipoint applications.
Geo: Disadvantage
 Disadvantages
 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 communication.
 GEO satellites, centered above the equator, have
difficulty broadcasting signals to near polar regions
Satellite Classification
Territorial Coverage
 Global Satellite System
 Regional Satellite System
 National or Domestic Satellite System
Satellite Footprints
 Spot Beam
 Zonal Beam
 Earth coverage
The Orbital Pattern
 Equatorial Orbit
 Polar Orbit
 Inclined Orbit
Equatorial Orbit
Polar Orbit
Inclined Orbit
Molniya Orbit
The Orbital Direction
 Prograde or Posigrade Orbit
 Retrograde Orbit
Size, Mass and Cost of Satellites: An Estimate
Size
Mass (kg)
Cost (Millions)
Large
Satellites
Small
Satellites
Mini Satellites
>1,000
>$100
500 – 1,000
$500 – 1,000
100 – 500
$5 – 20
10 – 100
$2 – 3
<10
<$1
Micro
Satellites
Nano
Satellites
The Orbital Dynamics
The Kepler’s Law
 First Law
A satellite will orbit around a primary body like Earth
following an elliptical path.
The Orbital Dynamics
The Kepler’s Law
 Second Law
For equal intervals of time, a satellite will sweep out
equal areas in the orbital plane, focused at the
barycentre. This is known as the “law of areas”.
The Orbital Dynamics
The Kepler’s Law
 Third Law
The square of the periodic time of orbit is
proportional to the cube of the mean distance
between the primary and the satellite. “This is known
as the “harmonic law”.
The Orbital Dynamics
The Kepler’s Law
 Third Law
α = semi-major axis (km)
A = constant (unitless) = 42242.0979 for Earth
P = mean solar Earth days [ratio of the time of one sidereal day
(23 hours 56 minutes and 4.091 seconds) to the time of one
revolution of Earth (24 hours)] = 0.9972
Forces that keep satellite in orbit
 Every point mass attracts every single other point
mass by a force pointing along
the line intersecting both points. The force
is proportional to the product of the
two masses and inversely proportional to
the square of the distance between them:
V
Satellite
Orbit
Forces that keep the satellite in orbit
ms = mass of the satellite
me= mass of Earth
(5.98 x 1024kg)
v = satellite velocity in orbit
R = Earth’s radius
(3960 mi or 6371 km)
G = Gravitational constant
(6.674 x 10-11 N-m2/kg2)
Forces that keep the satellite in orbit
 The Satellite Velocity in Orbit
 The Satellite Height
T = satellite period (hrs)
g = gravitational acceleration
(9.81 x 10-3 km/s2)
R = Earth’s radius (km)
H = satellite height (km)
Example
 In a satellite communications, what is the height
of a satellite from the Earth’s surface if the
sidereal period is 20 hours?
Example
 Find the gravitational force exerted by a 800-kg
geostationary satellite orbiting the Earth.
 Find the orbital period of a satellite in a circular
orbit 600 km above the surface of the Earth.