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Satellite Adnan Qamar 1
SATELLITE
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Satellite Adnan Qamar 3
What exactly is a satellite?
The word satellite originated from the Latinword Satellit- meaning an attendant, one who
is constantly covering around & attending to a
master or big man.
For our own purposes however a satellite is
simply any body that moves around another
(usually much larger) one in a mathematically
predictable path called an orbit.
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Satellite Adnan Qamar 5
Types of Satellite
Weather Satellites
Communication Satellites
Navigation Satellite
Observing Satellite
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WEATHER SATELLITE
A weather satellite
called the
Geostationary
Operational
EnvironmentalSatellite observes
atmospheric
conditions over a
large area to help
scientists study and
forecast the weather
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Satellite Adnan Qamar 7
COMMUNICATION SATLLITE
A communications
satellite, such as
the Tracking and Data
Relay Satellite(TDRS) shown here,
relays radio,
television, and other
signals between
different points in
space and on Earth
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Satellite Adnan Qamar 8
A navigation
satellite, like this
Global Positioning
System (GPS)
satellite, sendssignals that
operators of
aircraft, ships, and
land vehicles and
people on foot can
use to determine
their location
NAVIGATION SATELLITE
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Satellite Adnan Qamar 9
OBSERVING SATELLITE
An Earth observingsatellite surveys ourplanet's resources.This satellite, Aqua,
helps scientistsstudy oceanevaporation and otheraspects of themovement anddistribution ofEarth's water
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Satellite Adnan Qamar 10
How do Satellites Work?
Two Stations on Earth want tocommunicate through radiobroadcast but are too far awayto use conventional means.
The two stations can use asatellite as a relay station
for their communication.
* One Earth Station transmitsthe signals to the satellite.Up linkfrequency is thefrequency at which GroundStation is communicating withSatellite.
* The satellite Transponderconverts the signal and sendsit down to the second earthstation. This frequency iscalled a Downlink.
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Transponders
The transponder is the brains of the satellite - provides the
connection between the satellites receive and transmit antennas.
Satellites can have 12 to 96 transponders plus spares, depending on
the size of the satellite.
A transponder bandwidth can frequently be 36 MHz, 54 MHz, or
72 MHz or it can be even wider.
A transponders function is to
Receive the signal, (Signal is one trillion times weaker then when transmitted) Filter out noise,
Shift the frequency to a down link frequency (to avoid interference w/uplink)
Amplify for retransmission to ground
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How Satellites Work1. A Earth Station sends
message in GHz range.(Uplink)
2. Satellite Receive andretransmit signals back.(Downlink)
3. Other Earth Stationsreceive message inuseful strength area.(Footprint)
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Satellite Adnan Qamar 13
Launching the satellite
Space shuttles carry some
satellites into space, butmost satellites arelaunched by rockets thatfall into the ocean aftertheir fuel is spent. Manysatellites require minoradjustments of their orbitbefore they begin toperform their function.Built-in rockets calledthrusters make theseadjustments. Once asatellite is placed into a
stable orbit, it canremain there for a longtime without furtheradjustment.
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How does a satellite stay in its orbit?
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Satellite frequency band
BandDownlink,
GHz
Uplink,
GHz
Bandwidth,
MHz
L 1.5 1.6 15
S 1.9 2.2 70
C 4 6 500
Ku 11 14 500
Ka 20 30 3500
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Satellite Frequency Bands andAntennas (Dishes)
The size of Satellite Dishes (antennas) arerelated to the transmission frequency.
There is a inverse relationship betweenfrequency and wavelength.
As wavelength increases (and frequency
decreases), larger antennas (satellite dishes) arenecessary to gather the signal.
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Satellite Frequency Bands andAntennas (Dishes)
C-Band Ku-Band
Most commonly used bands: C-band (4 to 8 GHz) , Ku-band (11 to 17 GHz) , and Ka-band (20 to 30 GHz ).
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Satellite Adnan Qamar 19
Classification of orbits:
* Circular orbits are simplest
* Inclined orbits are useful for coverage of
equatorial regions
* Elliptical orbits can be used to givestationary behavior viewed from earth using 3
or 4 satellites
* Orbit changes can be used to extend the life of
satellites
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Satellite Adnan Qamar 20
Categories of satellites
Satellite orbits are also classified
based on their heights above the earth:
LEO(Low earth orbit satellite)
MEO(Medium earth orbit satellite)
GEO(Geostationary orbit)
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Satellite Adnan Qamar 21
Satellite orbit Altitudes
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Low-Earth-Orbit (LEO) Altitude (375-1000 miles)
Revolution time: 90 min - 3 hours.
Advantages:
Reduces transmission delay
Eliminates need for bulkyreceiving equipment.
Disadvantages:
Smaller coverage area.
Shorter life span (5-8 yrs.)than GEOs (10 yrs).
Subdivisions: Little, Big, and Mega(Super) LEOs.
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Low Earth Orbits Satellite Arrays Satellite arrays
Launching a set of
satellites into lowearth orbits
Each point in groundhas at least onesatellite overhead
Satellites in an arraycommunicate withone another
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In LEO polarorbits are used
Altitude:500 to2000 km
Period:90 to 120min
Speed:20,000 to25,000 kmph
Footprint:8000km
diameter
25
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Little LEOs Applications
0.8 GHz range
Small, low-cost
Vehicle tracking,environmental
monitoring and two-waydata communication.Used for short,narrowbandcommunications.
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Big LEOs Applications 2 GHz or above range
Can offer global services, whichcan be subject to regulatoryrequirements.
Used for technology devices suchas high-speed, high-bandwidthdata communications, and videoconferencing. They carry voice
and high-speed data services.The main uses are datacommunications and real-timevoice delivery to hand-helddevices.
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Mega (Super) LEOs Applications
20-30 GHz range
Mainly handles broadband
data. These systems areoptimized for packet-switched data rather thanvoice. They share the sameadvantages and drawbacks
of other LEOs and areintended to operate withinter-satellite links tominimize transmission timesand avoid dropped signals.
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Example of LEO:
Iridium sytem:A project started by
Motorola in the year 1990 with theobjective of providing worldwide Voiceand Data communication
29
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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 theNorth and South Pole.
Unlike the circular orbit of the
geostationary satellites, MEOs are placed
in an elliptical (oval-shaped) orbit.Approximately a dozen medium Earth
orbiting satellites are necessary to
provide continuous global coverage 24
hours a day.
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Geosynchronous-Earth-Orbit (GEO)
Orbit is sychroneous withthe earths rotation.
From the ground the
satellite appears fixed.
Altitude is about 23,000miles.
Coverage to 40% ofplanet per satellite.
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Basics of GEOs
Geostationary satellites are commonly used forcommunications and weather-observation.
The typical service life expectancy of a geostationary
satellite is 10-15 years.
Because geostationary satellites circle the earth at theequator, they are not able to provide coverage at theNorthernmost and Southernmost latitudes.
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GEOs and Weather
The altitude is chosen sothat it takes the satellite24 hours to orbit theEarth once, which is alsothe rotation rate of theEarth.
This produces the cloudanimations you see on TV.
Can take imagesapproximately everyminute.
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GEOs
Satellites arepositioned every 4-8degrees.
Aproximately 300 GEOsatellites are in orbit.
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Satellite Adnan Qamar 36
Apogee & Perigee
Apogee is the point at
which a satellite in an
elliptical orbit is
furthest from the Earth.
At its apogee, the
satellite travels slowerthan at any other point in
its orbit.
Perigee is the point at
which a satellite in an
elliptical orbit isclosest to the Earth.
At its perigee, the
satellite travels faster
than at any other point in
its orbit.
Definition of terms for earth
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Definition of terms for earth-orbiting satellite
ApogeeThe point farthest from earth.Apogee height is shown as hain Fig
PerigeeThe point of closest approach toearth. The perigee height is shown as hp
Line of apsidesThe line joining the perigeeand apogee through the center of the earth.
Ascending nodeThe point where the orbitcrosses the equatorial plane going from south
to north. Descending nodeThe point where the orbit
crosses the equatorial plane going from northto south.
Line of nodesThe line joining the ascendingand descending nodes through the center ofthe earth.
InclinationThe angle between the orbitalplane and the earths equatorial plane. It is
measured at the ascending node from theequator to the orbit, going from east to north.The inclination is shown as iin Fig.
Mean anomaly M gives an average value ofthe angular position of the satellite withreference to the perigee.
True anomaly is the angle from perigee tothe satellite position, measured at the earthscenter. This gives the true angular position of
the satellite in the orbit as a function of time.
D fi iti f t f
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Prograde orbitAn orbit in which the satellite moves inthe same direction as the earths rotation. Theinclination of a prograde orbit always lies between 0and 90.
Retrograde orbitAn orbit in which the satellite movesin a direction counter to the earths rotation. Theinclination of a retrograde orbit always lies between 90and 180.
Argument of perigeeThe angle from ascending nodeto perigee, measured in the orbital plane at the earthscenter, in the direction of satellite motion.
Definition of terms forearth-orbiting satellite
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Satellite Adnan Qamar 39
Components of a satellite
There are 3 major
components in a
satellite, they are :
Transponder andantenna system-
Power Package-
Control and
information system &
rocket thrustersystem
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Basics: Advantages of Satellites
The advantages of satellitecommunication 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 thecenter of the coverage area.
Satellite to Satellite communication is veryprecise.
Higher Bandwidths are available for use.
Disadvantage
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Disadvantage
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 terrestrialcommunication.
Security can be an issue
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THE END