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SATELLITE COMMUNICATION

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					SATELLITES
•What is satellite?
•Launching &working.
•History of satellites.
•Types of satellites:
     Basing on working:
     Basing on type of orbit:
•Applications of satellites
     Satellite communication:
•Limitations in using satellite
•conclusion
             What is a satellite?
 In general,a satellite is anything that orbits something
    else,as,for example:the moon orbits the earth.
   In a communication context, a satellite is a
    specialized wireless receiver/transmitter that is
    launched by a rocket and placed in orbit around the
    earth.
   The path a satellite follows is an orbit.
   The velocity required for a satellite to move in an orbit
    is termed as orbital velocity.
   The velocity required for a satellite to flee away from
    the earth is called as escape velocity.
LAUNCHING SATELLITE
•How does a satellite stay in an orbit?
 HOW DOES A SATELLITE WORK?
Consider the light bulb example:
           HISTORY OF SATELLITES
Satellite technology has progressed
 tremendously over the last 50 years since
 Arthur C.Clarke first proposed its idea in 1945
 in his article in wireless World.
The first active satellite was launched by
 Russia in 1957
 The first Indian satellite- Aryabhatta satellite
 was launched in 1975.
          TYPES OF SATELLITES
 Basing on function:
              • Passive satellite
              • Active satellite


   Passive satellite:
   •it is just a plastic balloon having a metal coated
   over it.
   •This sphere reflects the coming microwave signals
   coming from one part of the earth to other part.
   •This is also known as passive sphere.
   •Our earth also has a passive satellite i.e. moon.
               TYPES OF SATELLITES
 Active satellite:
 It basically does the work of amplifying the microwave
    signals coming.
   In active satellites an antenna system, transmitter, power
    supply and a receiver is used.
   These satellites are also called as transponders.
   The transmitters fitted on the earth generate the
    microwaves.
   These rays are received by the transponders attached to the
    satellite.
   Then after amplifying, these signals are transmitted back to
    earth.
   This sending can be done at the same time or after some
    delay.
 The first active satellite was launched by Russia in 1957
       TYPES OF SATELLITE( cont.)


 Basing on type of orbit:
 GEO STATIONARY EARTH ORBIT( GEO )
 LOW EARTH ORBIT ( LEO )
 MEDIUM EARTH ORBIT ( MEO )
 GEO: GEO STATIONARY EARTH ORBIT
 These satellites are in orbit 35,863 km above the
  earth’s surface along the equator.
 It is also termed as geo-synchronous earth orbit.
 What are the requirements for a satellite to be
  geostationary?
 Its revolutionary direction must be same as that of
  the earth, i.e. from west to east.
 The time period of satellite’s revolution must be same
  to the time period of the rotation of earth along its
  polar axis, which is equal to 24 hours.
 The equatorial plane of earth must be coplanar with
  the orbital plane of the satellites revolution.
GEO
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.
Disadvantages:
 Its distance from the earth may cause the signal
  delay.
 a single GEO-satellite can cover only 40%of earth’s
  surface,due to the curvature of earth.
 So 3 geo satellites placed at 120 to each other are
  used to cover the entire civilized World.
LEO:    LOW EARTH ORBIT
 LEO satellites are much closer to the earth than GEO
  satellites, ranging from 500 to 1,500 km above the
  surface.
 LEO satellites don’t stay in fixed position relative to
  the surface, and are only visible for 15 to 20 minutes
  each pass.
 A network of LEO satellites is necessary for LEO
  satellites to be useful.
LEO

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.
Disadvantages:
 A network of LEO satellites is needed, which can be
  costly
 Atmospheric drag effects LEO satellites, causing
  gradual orbital deterioration.
MEO:     MEDIUM EARTH ORBIT
 A MEO satellite is in orbit somewhere between 8,000
  km and 18,000 km above the earth’s surface.
 MEO satellites are similar to LEO satellites in
  functionality.
 MEO satellites are visible for much longer periods of
  time than LEO satellites, usually between 2 to 8 hours.
 MEO satellites have a larger coverage area than LEO
  satellites.
MEO
Advantages:
 MEO satellites are visible for longer duration than LEO
  satellites.
 MEO satellites are hence required in smaller number
  than LEO satellites.


Disadvantages:
 A MEO satellite’s distance gives it a longer time delay
 MEO Satellite gives a weaker signal than a LEO
 satellite, though not as bad as a GEO satellite
S.NO TYPE OF THE ORBIT          DETAILS                ADVANTAGES         DISADVANTAGES


 1.   GEOSTATIONARY        HEIGHT:35,863KM.         LARGE COVERAGE          SIGNAL
       EARTH ORBIT       TIMEPERIOD: 24 HOURS.       AREA (ALMOST 4 TH)       DELAY
                                                    24 HOUR VIEW OF         3GEO
                                                     AREA                     SATELLITES
                                                                              ARE
                                                                              REQUIRED
 2.   LOW EARTH ORBIT     HEIGHT:500-1500KM.        BETTER SIGNAL           AN
                         TIMEPERIOD:15-20 MIN.       STRENGTH.                EXPENSIVE
                                                    LESS TIME DELAY.         NETWORK.
                                                                             ATMOSPHERIC
                                                                              DRAG.

 3.   MEDIUM EARTH       HEIGHT:8000-18000KM.       LONGER VISIBILITY.      DISTANT-
         ORBIT           TIMEPERIOD:2-8 HOURS.      LESS NUMBER ENOUGH       TIME DELAY.
                                                                             WEAKER
                                                                              SIGNAL THAN
                                                                              LEO
Satellite orbits
             Applications of satellite:
 used for long distance communication
 high speed data transmission
 many receiver stations can receive signal from the
    same sender station
   are used for detecting where nuclear weapons are
    launched
   take pictures to help predict the weather
   used for GPS(global positioning system) and for
    guiding ships and airplanes
   Mobile communication-what we are all using right now.
   For research and developments in the field of
    Navigation and Security
Applications of satellites
           Satellite communication
 In satellite communication, signal transferring between the
  sender and receiver is done with the help of satellite.
 In this process, the signal which is basically a beam of
  modulated microwaves is sent towards the satellite.
 Then the satellite amplifies the signal and broadcasts
  it another frequency to avoid interference.
 So, all the signal transferring is happening in space.
 Thus this type of communication is known as space
  communication.
 The first satellite with radio transmitter was in 1957.
                       Limitations
 The major limitations in using satellites:
 EXPENSIVE:
            It’s initial cost as well as maintenance is
  expensive
 SIGNAL DELAY:
            as it is at a very large distance from earth’s
  surface there is a scope of signal delay.

 IMPOSSIBILITY TO REPAIR AND MAINTAIN:
              if any components fail to work there is no
  scope of repair.
            CONCLUSION
 That is how various types of satellites help
  us meet our requirements……
 Without our satellites, our great
  technological age would be brought to a
  stand still.
 In further decades the applications of
  satellites in different fields will be more
  and more.
THINK ……….
HOW TO REDUCE
ITS LIMITATIONS

				
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posted:1/30/2013
language:English
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