1. SATELLITE- COMMUNICATIONPresented by, R-THANDAIAH PRABU M.E.,

2. Working of satellite 3. Satellite The word satellite originated from the Latin word Satellit- meaning an attendant, one who is constantly covering around & attending to a master or big man Earth Stations antenna systems on earth Uplink transmission from an earth station to a satellite Downlink transmission from a satellite to an earth station Transponder electronics in the satellite that convert uplink signals to downlink signals 4. Frequency Allocation for Satellite CommunicationBandUplink (GHz)Downlink (GHz)C64Ku1412Ka3020X8.27.5S4020Q4421L1.525 to 1.5591.626 to 1.660First satellite launched into space: Sputnik (1957). 5. Frequency Bands Available for Satellite Communications 6. APPLICATIONS 1. Global Telecommunications : Land, Sea, Air 2. Broadcasting : Sound, TV, Multimedia, Cable TV, DTH, DTU, DBS, DVB 3. Navigation : Global Positioning System (GPS) 4. Remote Sensing Earth Observation 5. Weather 6. Emergency Communication Services Disasters 7. Mobile Communication Services 8. Corporate Communications Virtual Private Network (VPN) - VSAT Technology 9. Military Communications 7. Applications 8. Different services of satellite systems *Fixed satellite services *Broadcasting satellite services *Mobile satellite services *Navigational satellite services *Meteorological satellite services. 9. Communication process 10. Satellite Orbits Polar OrbitLow Earth Equatorial OrbitGeostationary OrbitMolniya Orbit 11. north celestial polenorth poleequator equator south poleMajor Axissouth celestial polecelestial sphere 12. Motion of Space Objects 13. Three classes of Satellite orbits: Satellites orbits vary depending on:1) altitude2) inclination3) orbital periodAn orbit is the path that a satellite follows as it revolves around Earth1) Low Earth Orbit (LEO) up to 2,000km altitude remote sensing satellites, altimeter satellites, other 2) Medium Earth Orbit (MEO) altitudes between 5,000km 20,000km GPS satellites (12hr period twice a day) 3) Geostationary Earth Orbit (GEO) 24hr period appears fixed altitudes of 36,000km communication satellites 14. Satellite orbit altitudes 15. GEO Orbit Advantages of the the GEO orbit No problem with frequency changes Tracking of the satellite is simplified High coverage area Disadvantages of the GEO orbit Weak signal after traveling over 35,000 km Polar regions are poorly served Signal sending delay is substantial 16. LEO Satellite Characteristics Circular/slightly elliptical orbit under 2000 km Orbit period ranges from 1.5 to 2 hours Diameter of coverage is about 8000 km Round-trip signal propagation delay less than 20 ms Maximum satellite visible time up to 20 min System must cope with large Doppler shifts Atmospheric drag results in orbital deterioration 17. MEO Satellite Characteristics Circular orbit at an altitude in the range of 5000 to 12,000 km Orbit period of 6 hours Diameter of coverage is 10,000 to 15,000 km Round trip signal propagation delay less than 50 ms Maximum satellite visible time is a few hours 18. Orbital location and footprint The location of a geostationary satellite is referred to as its orbital location. International satellites are normally measured in terms of longitudinal degrees East ( E) from the Prime Meridian of 0 The geographic area of the Earth's surface over which a satellite can transmit to, or receive from, is called the satellite's "footprint." 19. Motion of Space Objects 1473 -1543 Copernicus Heliocentric (sun in the center) Orbit 1546 1601 Tycho Brahe Before telescope followed the planets (acquired quality data) 1571 1630 Johannes Kepler Discovered orbital path to be elliptical around focus point Keplers 3 laws of planetary motion 1642 1727 Sir Isaac Newton Physical Principals Universal law of Gravitation 20. Keplers 3 (empirical) laws of Planetary Motion First Law (elliptical orbit) The orbital path of a planet takes the shape of an ellipse, with the Sun located at one of its focal points. 21. Keplers Second Law The line from the sun to a planet sweeps out equal areas in equal time intervals. t1 t2areaA t4aphelion (slowest)perihelion (fastest) areaBareaA = areaB if t2-t1 = t4-t3t3 22. Keplers Third Law The ratio of the square of the planets orbital period and the cube of the mean distance from the Sun is constant(D1/D2)3 = (P1/P2)2 Planets far from the sun take longer to orbit the sun than do planets nearer the sun. 23. Geometry of an Ellipse Semi-major axis of the satellite orbit Eccentricity of the satellite orbit (deviation from a circle) A satellite is closest to the earth at a point called Perigee A satellites farthest point from the earth is called apogeeGPS orbital period of 12 hours based on Keplers third law corresponds to a satellite altitude of about 20,000km above the surface of the earth 24. Apogee Inclination VDefinitions & orbital parameters:Apogee: Farthest from earthPerigeeRight AscensionPerigee: Closest approach to earth Line of apsides: Joining perigee & apogee through center of the earth Ascending node: Point where the orbit crosses the equatorial plane going from south to north Descending node: Point where the orbit crosses the equatorial plane going from north to south Line of nodes: Line joining the ascending and descending node through the center of the earth 25. Inclination: Angle between the orbital plane and earths equatorial plane Prograde orbit: Satellite moves in the same direction as the earths rotation ( 0 to 90) Retrograde orbit: Satellite moves in the counter direction to the earths rotation Mean anomaly: Average value of the angular position of the satellite with reference to the perigee True anomaly: Angle from perigee to the satellite position measured at the earths center. 26. Sources of Orbital Perturbations Several external forces cause perturbation to spacecraft orbit 3rd body effects, e.g., sun, moon, other planets Unsymmetrical central bodies Space Environment: Solar Pressure, drag from rarefied atmosphere 27. Orbit perturbations1) Keplers three laws of planetary motion Apply to any orbiting object (Satellites) 2) GPS Satellites orbit the earth in an elliptical path 3) Earth becomes the focal points 28. Mean motion of the orbital period is called as anomalistic period P=2/n sec perturbation which must be accounted for. Main effects: Regression of nodes Rotation of apsides 29. Orbital Perturbation Effects: Regression of Nodes Regression of Nodes: Equatorial bulge causes component of gravity vector acting on SC to be slightly out of orbit plane This out of orbit plane component causes a slight precession of the orbit plane.The resulting orbital rotation is called regression of node. Note: Although regression rate is small for Geo., it must be accounted. 30. Orbital Perturbation: Rotation of Apsides Rotation of apsides caused by earth oblateness is similar to regression of nodes. The phenomenon is caused by a higher acceleration near the equator and a resulting overshoot at periapsis. This only occurs in elliptical orbits. 31. Satellites in geosynchronous orbit 32. Uses of Geostationary Orbits Geostationary orbits are primarily used for two functions: Weather monitoring Telecommunications & Broadcasting Commercial growth is focused on: DTH TV (Direct To Home: Sky TV) Phone, Fax, Video, Data services Mobile Communications VSAT & USAT Digital Radio 33. Three conditions are required for an orbit to be geostationary: The satellite must travel eastward at the same rotational speed as the earth The orbit must be circular The inclination of the orbit must be zero 34. How To File for a Geo Position Only Allocated to National Governments Go to National Government Request Orbital Position (s) US Companies (Non Governmental Entities) work through FCC UK through UK Radiocommunications Agency Prepare ITU Paperwork File & Coordinate First Come, First Served = Priority! 35. To determine the look angles for the geostationary orbit we need The earth station latitude The earth station longitude The longitude of the sub satellite point The average of radius R=6378 km polar antenna A single actuator is used which moves the antenna in a circular arc ie known as polar mount antenna. 36. Declination The angle of tilt is often referred to as the declination which must not be confused with the magnetic declination used in correcting compass readings. Limits of Visibility: The limits will be set by the geographic coordinates of the earth station and the antenna elevation.