satellite intro

1. SATELLITE ORBITS AND
SYSTEMS
• Orbits and Launching Methods:Kepler‘s Law,
Orbital Elements , Apogee and Perigee
Heights , Orbit Perturbations, The
Geostationary Orbit: Introduction , Antenna
Look Angles The Polar Mount Antenna ,
Limits of Visibility , Near Geostationary Orbits
, Earth Eclipse of Satellite , Sun Transit
Outage ,Launching Orbits, Radio Wave
Propagation: Atmospheric Losses
,Ionospheric Effects , Rain Attenuation , Other
Propagation Impairments
2/6/2023 1

2. Introduction : History of
Satellites
• Communicating through a satellite first appeared in the
short story titled “The Brick Moon,” written by Edward
Everett Hale and published in The Atlantic Monthly in
1869–70.
• The first practical concept of satellite communication was
proposed by Royal Air Force officer Arthur C. Clarke in a
paper titled “Extra-Terrestrial Relays: Can Rocket Stations
Give World-wide Radio Coverage?” published in the
October 1945 issue of Wireless World.
• In October 1957 communications stations started picking
up a regular beeping noise coming from space.
• The signals were coming from Russia's Sputnik 1, the
world's first man-made satellite.
• It was January 1958, before a Jupiter rocket successfully
launched Explorer 1, the first American satellite.

3. Introduction : History of
Satellites
• In July 1963 the Hughes Aircraft Corporation
launched the experimental Syncom 2 for NASA, the
world's first geosynchronous communications
satellite
– It carried the first live two-way satellite call
between heads of state when President John F.
Kennedy in Washington, D.C., telephoned
Nigerian Prime Minister Abubaker Balewa in
Africa.
• The third Syncom satellite transmitted live television
coverage of the 1964 Olympic Games from Tokyo.

4. Introduction : History of
Satellites
• The world's first commercial communications
satellite was Early Bird, built for the
Communications Satellite Corporation (COMSAT)
by Hughes.
• It was launched on April 6, 1965, and placed in
commercial service after moving into
geosynchronous orbit 36,000 Km above the
equator.
• That meant it was always on station to provide line
of sight communications between Europe and
North America.
• Early Bird didn't have a battery - and worked only
when its solar panels were exposed to the sun.

5. Introduction : History of
Satellites
• The launch of the Intelsat 3 satellites in
1969 created a global TV and speech
communications network that spanned the
Atlantic, Pacific and Indian Oceans.
• The introduction of multiple-beam
antennas in the 1980s brought new
improvements in efficiency, as a satellite's
power could now be concentrated on small
regions of the Earth, making possible
smaller-aperture (coverage area), lower-
cost ground stations.
• The Capacity (the number of
simultaneous television and speech
channels carried) grew as well.

6. Introduction : How
Satellites Work
1. A Earth Station sends
message in GHz range.
(Uplink)
2. Satellite Receive and
retransmit signals back.
(Downlink)
3. Other Earth Stations
receive message in
useful strength area.
(Footprint)

7. Advantages of Satellite
communication
• Satellite links are unaffected by the
propagation variations that interfere with HF
radio.
• Free from the high attenuation of wire or
cable facilities
• Capable of spanning long distances.
• The numerous repeater stations required for
line-of-sight or troposcatter links are no
longer needed.
• They furnish the reliability and flexibility of
service that is needed to support a military
operation.

8. Advantages of Satellite
communication
• The system is capable of handling
thousands of communications channels.
• Frequencies are not dependent upon
reflection or refraction and are affected
only slightly by atmospheric
phenomena.
• Destruction of a single communication
satellite would be quite difficult and
expensive.
• A high degree of freedom from jamming

9. Disadvantage of satellite
communication
• With the Satellite in position the communication
path between the terrestrial transmitter and
receiver is approximately 75000 km long.
• There is a delay of 0.25 sec between the
transmission and reception of a signal because the
velocity of electromagnetic wave is 3* 10^5
Km/second.
• The time delay reduces the efficiency of satellite in
data transmission and long file transfer, which
carried out over the satellites.
• Over-crowding of available bandwidth due to low
antenna gains is occurred.
• High atmosphere losses above 30 GHz limit the
carrier frequency.

10. Services provided by satellites
Name of the satellite Services
Fixed satellite service • Telephone Networks
• Transmitting TV signals to
cable companies
Broadcasting satellite service Direct Broad cast service or
DTH
Mobile satellite services • Land Mobile
• Maritime mobile
• Aeronautical Mobile
Navigational satellite services GPS
Meteorological satellite
services
Search and rescue services

11. Frequency Band Designations
used at present for DBS,
and it is also used for
certain fixed satellite
services.
(14/12 GHz)
used for FSS and no direct
broadcast services are
allowed (6/4 GHz)
used for mobile and
navigational services and
for data transfer from
weather satellites.
used for mobile satellite
services and navigation
systems.

12. Frequency Allocations for
Satellite Services
• International Telecommunication Union
Region 1:
Europe,
Africa,
what was
formerly
the Soviet
Union,
and
Mongolia
Region 2:
North and
South
America
and
Greenland
Region 3:
Asia,
Australia,
and the
southwes
t Pacific

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49. Orbits : Low-Earth-Orbit (LEO)
• Altitude (375-1000 miles)
• 0.8 GHz – 30 GHz range
• Revolution time: 90 min - 3 hours.
• Advantages:
– Reduces transmission delay
– Small, low-cost
– Eliminates need for bulky receiving
equipment.
– Handles Broad band data
• Disadvantages:
– Smaller coverage area.
– Shorter life span (5-8 yrs.) than GEOs
(10 yrs).
• Subdivisions: Little, Big, and Mega (Super)
LEOs.
• Application : Vehicle tracking, environmental
monitoring and two-way data communication.
Used for short, narrowband communications

50. Middle-Earth-Orbiting (MEO)
• MEOs orbits between the altitudes of
5,600 and 9,500 miles.
• These orbits are primarily reserved for
communications satellites that cover the
North and South Pole.

51. Geosynchronous-Earth-Orbit
(GEO)
• Orbit is synchronous with the earths
rotation.
• From the ground the satellite appears
fixed.
• Altitude is about 36000 km.
• Coverage to 40% of planet per satellite.

52. Polar Orbiting Satellites
• Orbit the earth to cover the north and
south polar regions.

53. The polar orbiters
• Able to track weather conditions and
provide a wide range of data,
– Includes visible and infrared radiometer
data for imaging purposes
– radiation measurements, and
– temperature profiles.
• They carry ultraviolet sensors that
measure ozone levels,
• They monitor the ozone hole over
Antarctica.

54. Definitions of Terms for Earth-Orbiting
Satellites

55. Apogee The
point farthest
from earth.
Perigee The point of
closest approach to
earth.
Line of apsides : The line
joining the perigee and
apogee through the center
of the earth.
Inclination The angle
between the orbital plane
and the earth’s equatorial
plane. It is measured at the
ascending node from the
equator to the orbit, going
from east to north.

56. Ascending node The
point where the orbit
crosses the equatorial
plane going from
south to north.
Descending node The
point where the orbit
crosses the equatorial
plane going from north to
south.
Line of nodes The line
joining the ascending
and descending nodes
through the center of the
earth.

57. • Prograde orbit:
An orbit in which
the satellite
moves in the
same direction as
the earth’s
rotation .
• It is also known
as a direct orbit.
• The inclination of
the orbit always
lies between 0
and 90°.
• Most satellites are
launched in this
orbit .
• Because the
earth’s rotational
velocity provides
part of the orbital
velocity with a
consequent
saving in launch
energy.

58. Retrograde orbit An
orbit in which the
satellite moves in a
direction counter to
the earth’s rotation,
The inclination of a
retrograde
orbit always lies
between 90 and 180°.

59. Argument of perigee The
angle from ascending node to
perigee, measured in the orbital
plane at the earth’s center, in the
direction of satellite motion.

60. Right ascension of the
ascending node :
For an absolute measurement
of an orbit , a fixed reference
in space is required.
The reference chosen is the
first point of Aries,
otherwise known as the
vernal, or spring, equinox.
It occurs when the sun
crosses the equator going
from south to north,
An imaginary line is drawn
from this equatorial crossing
through the center of the sun
points to the first point of
Aries (symbol ).
This is the line of Aries.
The right ascension of the
ascending node is then the
angle measured eastward,
in the equatorial plane,
from the line to the
ascending node.

61. True anomaly
• The true anomaly is the angle from
perigee to the satellite position,
measured at the earth’s center. (μ)
• This gives the true angular position of
the satellite in the orbit as a function of
time.

62. Mean Anomaly
• Mean anomaly “M” gives an average
value of the angular position of the
satellite with reference to the perigee.
• For a circular orbit, M gives the angular
position of the satellite in the orbit.
• For elliptical orbit, the position is much
more difficult to calculate, and M is used
as an intermediate step in the
calculation.

63. Orbital
elements
A set of mathematical parameters that enables
us to accurately describe satellite motion
Purpose:
• Discriminate one satellite from other satellites
• Predict where a satellite will be in the future or
has been in the past
• Determine amount and direction of maneuver
or perturbation

64. The Six Keplerian Elements
1. Size/Period
2. Shape (Circular or
Ellipse)
3. Inclination
4. Right Ascension
5. Argument of
Perigee
6. True Anomaly

65. 1. Size/Period
• Size is how big or small your satellite’s orbit is….
• Defined by semi-major axis “a”
• There are basically 4 sizes of orbits satellites use:
– Low Earth Orbit (LEO): approx 120 – 1200 miles above
Earth
– Medium Earth Orbit (MEO) or Semi-synchronous Orbit:
approx 12,000 miles above Earth
– Highly Elliptical Orbit (HEO): altitude varies greatly! From
100 miles to sometimes several hundred thousand miles
– Geo-synchronous or Geo-stationary Orbit
(GEO): approx 22,300 miles from Earth

66. Location of Orbits
• Equatorial – Prograde (towards the
east) or Retrograde (towards the west)
• Polar – Over the Poles!!
• A very Important Point:
ALL ORBITS OF SATELLITES MUST
INTERSECT THE CENTER OF THE
EARTH

67. 2. Shape
• Orbit shapes are either circular or not
circular: some sort of an Ellipse!!
• How elliptical an orbit, is called
Eccentricity

68. Circular
Orbits
• Characteristics
– Constant speed
– Nearly constant altitude
• Typical Missions
– Reconnaissance/Weather (DMSP)
– Manned
– Navigational (GPS)
– Geo-synchronous (Comm sats)

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Elliptical Orbits
• Characteristics
• Varying speed
• Varying altitude
• Asymmetric Ground Track
• Typical Missions
• Deep space surveillance (Pioneer)
• Communications (Polar comm.)
• Ballistic Missiles

70. Eccentricity “e”
e = 0.75
e = .45
e = 0

71. 3. Inclination “i”
• Inclination is the tilt of your orbit
• At 0 degrees of inclination, you are
orbiting the equator
• At 90 degrees of inclination, you are in a
polar orbit
Orbital Plane
Equatorial Plane
Inclination
Inclination: Is this angle, measured
in degrees

72. Inclination “i”
Equatorial: i = 0 or 180
Polar: i = 90
Prograde: 0
 i < 90
Retrograde: 90
 i < 180

73. 4. Right Ascension “Ω”
• Right Ascension is the twist of your tilt,
as measured from a fixed point in
space, called the First Point of Aries
i
Right
Ascensio
n of the
Ascendin
g Node
()
First
Point
of
Aries
()
i

74. Right Ascension “Ω”
Inclination
First
Point
of
Aries
()
• Right Ascension will determine where your satellite will
cross the Equator on the ascending pass
• It is measured in degrees
Right Ascension is this angle, measured in
degrees

75. 5. Argument of Perigee “ω”

Inclination

Perige
e
Argumen
t of
Perigee:
Is this
angle,
measure
d in
degrees
• Argument of Perigee is a measurement from a fixed point in
space to where perigee occurs in the orbit
• It is measured in degrees
Apoge
e

76. 6. True Anomaly
Direction of
satellite
motion
True Anomaly is a measurement from a fixed point in space to the
actual satellite location in the orbit
It is measured in degrees True
Anomaly:
Is this
angle,
measured
in degrees
Fixed
point in
space

77. Summery of Keplerian
elements
• Earth-orbiting artificial satellites are defined by six orbital
elements referred to as the Keplerian element set.
1. the semimajor axis a
2. the eccentricity e
3. the mean anomaly M0, gives the position of the satellite in
its orbit at a reference time known as the epoch.
4. The argument of perigee ω, gives the rotation of the orbit’s
perigee point relative to the orbit’s line of nodes in the
earth’s equatorial plane.
5. the inclination i and
6. the right ascension of the ascending node Ω , relate the
orbital plane’s position to the earth.

78. Orbit Perturbations
• Effects of a nonspherical earth
• For a spherical earth of uniform mass,
Kepler’s third law gives the nominal
mean motion n0 as
• The 0 subscript is included as a
reminder that this result applies for a
perfectly spherical earth of uniform
mass.

79. Effects of a nonspherical earth
• However not practically
– K1 is a constant which evaluates to 66,063.1704 km2.
• The earth’s oblateness has negligible effect on the
semi major axis a,
• If a is known, the mean motion is readily calculated.
• The orbital period taking into account the earth’s
oblateness is termed the anomalistic period

80. Effects of a nonspherical earth
• The anomalistic period is
– where n is in radians per second.
• If the known quantity is “n” one can
solve the above Eq. for “a” , keeping in
mind that n0 is also a function of “a”.
• The above equation may be solved for
“a” by finding the root of the following
equation:

81. Problem
• A satellite is orbiting in the equatorial plane with a
period from perigee to perigee of 12 h. Given that the
eccentricity is 0.002, calculate the semimajor axis.
The earth’s equatorial radius is 6378.1414 km.

82. Answer
• Non perturbed value a = 26597 km
• Perturbed Value a = 26598.6 km

83. Effects of a nonspherical earth
• The oblateness of the earth also produces
two rotations of the orbital plane.
• regression of the nodes,
– where the nodes appear to slide along the
equator.
– In effect, the line of nodes, which is in the
equatorial plane, rotates about the center of
the earth.
– Thus , the right ascension of the ascending
node, shifts its position.

84. Effects of a nonspherical earth
• If the orbit is prograde the
nodes slide westward,
• if retrograde, they slide
eastward.
• As seen from the ascending
node, a satellite in
prograde orbit moves
eastward, and in a
retrograde orbit,westward.
• The nodes therefore move
in a direction opposite to
the direction of satellite
motion, hence the term
regression of the nodes.
• For a polar orbit (i = 90°),
the regression is zero.

85. Effects of a nonspherical earth
• The second effect is rotation of apsides
in the orbital plane,
• Both effects depend on the mean
motion n, the semimajor axis a, and the
eccentricity e

86. Atmospheric Drag
• For satellites below 1000 km, the effects of
atmospheric drag are significant.
• Because the drag is greatest at the perigee,
• The drag acts to reduce the velocity at this
point, resulting the satellite not to reach the
same apogee height on successive revolutions.
• As a result the semi major axis and the
eccentricity are both reduced.
• Drag does not noticeably change the other
orbital parameters, including perigee height.

87. Atmospheric Drag
• An approximate expression for the
change of major axis is
• The mean anomaly is also changed.
• An approximate expression for the
amount by which it changes is

88. Inclined Orbits
• Determination of the look angles and
range involves the following quantities and
concepts:
1. The orbital elements,
2. Various measures of time
3. The perifocal coordinate system, which is
based on the orbital plane
4. The geocentric-equatorial coordinate system,
which is based on the earth’s equatorial
plane
5. The topocentric-horizon coordinate system,
which is based on the observer’s horizon
plane

89. Inclined Orbits
The two major coordinate transformations
which are needed are as follows:
• The satellite position measured in the
perifocal system is transformed to the
geocentric-horizon system in which the earth’s
rotation is measured, thus enabling the
satellite position and the earth station
location to be coordinated.
• The satellite-to-earth station position
vector is transformed to the topocentric-
horizon system, which enables the look
angles and range to be calculated.

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91. INTELSAT

92. INTELSAT
• International Telecommunication
Satellite
• Created in 1964
• Has 140 member countries
• 40 investing entities
• satellites are in geostationary orbit,
• geostationary satellites orbit in the
earth’s equatorial plane and that their
position is specified by their longitude.
• Life time is 10 to 15 years

93. INTELSAT
INTELSAT covers three main regions, the
• Atlantic Ocean Region (AOR),
• the Indian Ocean Region (IOR), and
• the Pacific Ocean Region (POR).
• Traffic in the AOR is about three times that
in the IOR and about twice that in the IOR
and POR combined.
• Thus the system design is tailored mainly
around AOR requirements (Thompson and
Johnston, 1983)

94. INTELSAT

95. Evolution of some of the INTELSAT
satellites.

96. Intel sat VII capacity
Parameters VII VII/A
Two way telephone
circuits
1800 22500
TV channels 3 3
Two way telephone
circuits achieved with
digital circuit
multiplication
9000
0
11250
0
Life time is for 14 to 17 years
Intel sat IX is for self study

97. U.S Domsat – Domestic
satellite
• Used to provide various
telecommunications services, such as:
– voice, data & video transmissions, within a
country.
• Situated in geostationary orbit.
• Wide selection of TV channels for the
home entertainment market
• A large amount of commercial
telecommunications traffic is also
handeled

98. Domsat
• Provides a DTH television service
• Can be classified broadly as
– high power,
– medium power, and
– low power
• the primary purpose of satellites in the high-power
category is to provide a DBS service.
• In the medium-power category, the primary
purpose is point-to-point services, but space may
be leased on these satellites for the provision of
DBS services.
• In the low-power category, no official DBS services
are provided.

101. Minimum Orbital Spacing -
DOMSAT
• In 1983, the U.S. Federal
Communications Commission (FCC)
adopted a policy objective.
• 2° as the minimum orbital spacing for
satellites operating in the 6/4-GHz band
and
• 1.5° for those operating in the 14/12-
GHz band (FCC, 1983).
• It is clear that interference between
satellite circuits is likely to increase as

102. The orbital plane
• The position vector r and the
velocity vector v specify the motion
of the satellite
• the magnitude of the position
vector is required which is given as
• Eq 1:
• The true anomaly v is a function of
time, and determining it is one of
the more difficult steps in the
calculations

103. The sub satellite point
• The point on the earth vertically
under the satellite is referred to as
the subsatellite point.
• The latitude and longitude of the
subsatellite point and the height of
the satellite above the subsatellite
point can be determined from a
knowledge of the radius vector r.
• The height of the terrain above the
reference ellipsoid at the
subsatellite point is denoted by HSS
• The height of the satellite above
this, by hSS.
• Thus the total height of the satellite
above the reference ellipsoid is
• h = HSS+hSS

104. The subsatellite point
IJK
frame r replaces R, the height to the
point of interest is h rather than
H, and the subsatellite latitude
λSS is used

105. The subsatellite point
• The equation can be rewritten as
• We now have three equations in three
unknowns, LST, λE, and h,
• The east longitude is found by EL =
LST - GST

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Applications
• Traditionally
– weather satellites
– radio and TV broadcast satellites
– military satellites
– satellites for navigation and localization (e.g., GPS)
• Telecommunication
– global telephone connections
– backbone for global networks
– connections for communication in remote places or
underdeveloped areas
– global mobile communication
•  satellite systems to extend cellular phone
systems (e.g., GSM or AMPS)
replaced by fiber optics

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base station
or gateway
Classical satellite systems
Inter Satellite Link
(ISL)
Mobile User
Link (MUL) Gateway Link
(GWL)
footprint
small cells
(spotbeams)
User data
PSTN
ISDN GSM
GWL
MUL
PSTN: Public Switched
Telephone Network

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Inclination
inclination d
d
satellite orbit
perigee
plane of satellite orbit
equatorial plane

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Elevation
Elevation:
angle e between center of satellite beam
and surface
e
minimal elevation:
elevation needed at least
to communicate with the satellite

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Atmospheric attenuation
Example: satellite systems at 4-6 GHz
elevation of the satellite
5° 10° 20° 30° 40° 50°
Attenuation of
the signal in %
10
20
30
40
50
rain absorption
fog absorption
atmospheric
absorption
e

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Orbits II
earth
km
35768
10000
1000
LEO
(Globalstar,
Irdium)
HEO
inner and outer Van
Allen belts
MEO (ICO)
GEO (Inmarsat)
Van-Allen-Belts:
ionized particles
2000 - 6000 km and
15000 - 30000 km
above earth surface

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Overview of LEO/MEO systems
Iridium Globalstar ICO Teledesic
# satellites 66 + 6 48 + 4 10 + 2 288
altitude
(km)
780 1414 10390 ca. 700
coverage global 70° latitude global global
min.
elevation
8° 20° 20° 40°
frequencies
[GHz
(circa)]
1.6 MS
29.2 
19.5 
23.3 ISL
1.6 MS 
2.5 MS 
5.1 
6.9 
2 MS 
2.2 MS 
5.2 
7 
19 
28.8 
62 ISL
access
method
FDMA/TDMA CDMA FDMA/TDMA FDMA/TDMA
ISL yes no no yes
bit rate 2.4 kbit/s 9.6 kbit/s 4.8 kbit/s 64 Mbit/s 
2/64 Mbit/s 
# channels 4000 2700 4500 2500
Lifetime
[years]
5-8 7.5 12 10
cost
estimation
4.4 B$ 2.9 B$ 4.5 B$ 9 B$