Published on January 29, 2014
Satellite Systems Presented By Sorath Asnani Mehran University of Engineering & Technology, Jamshoro
Contents • • • • • • • • • • • Introduction to Satellites Major types of Satellites Working of Satellites Satellite Communication Satellite Frequency Bands Satellite Orbits Geocentric Orbits Types of Satellites Uses and Applications of Satellites Conclusion References 2
What is satellite? • Any object that revolves around a larger object in space is called a satellite. • A satellite travels in a special path, called its orbit. Figure 1. Satellite orbiting the Earth 3
Major types of Satellite 1. Natural Satellites 2. Artificial Satellites Figure 2. Natural Satellite Figure 3. Artificial Satellite 4
Natural Satellites • There are about 173 known natural satellites orbiting planets in the Solar System. • All the planets that revolve around the Sun are Natural Satellites. • The Moon is the only Natural Satellite of the Earth. Figure 4. Earth revolving around Sun Figure 5. Moon revolving around Earth 5
First Artificial Satellite • The world's first artificial satellite, the Sputnik 1, was launched by the Soviet Union on October 4, 1957. • It's primary purpose was to send back temperatures of space. • It was about the size of a basketball, weighed only 183 pounds, and took about 98 minutes to orbit the Earth on its elliptical path. Figure 6. The Sputnik 1 6
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 transmits the signals to the satellite. Up link frequency is the frequency at which Ground Station is communicating with Satellite. • The satellite Transponder converts the signal and sends it down to the second earth station. This frequency is called a Downlink frequency. • The area which receives a signal of useful strength from the satellite is known as the satellite's footprint. 7
Satellite Communication Advantages: The advantages of satellite communication over terrestrial communication are: • The coverage area of a satellite is greater than that of a terrestrial system • Transmission cost of a satellite is independent of the distance from the center of the coverage area • Higher Bandwidths are available for use 8
Satellite Communication Cont.. Disadvantages: The disadvantages of satellite communication are: • Cost involved in launching satellites into orbit is too high • There is a larger propagation delay in satellite communication than in terrestrial communication 9
Basics of Satellites Figure 7. Working of Satellite 10
Satellite Frequency Bands Table 1. Satellite Frequency Bands 11
Satellite Frequency Bands Cont.. • The three most commonly used satellite frequency bands are: 1. C-band 2. Ku-band 3. Ka-band • C-band and Ku-band are the two most common frequency spectrums used by today's satellites. • There is an inverse relationship between frequency and wavelength--when frequency increases, wavelength decreases and vice versa. • As wavelength increases (and frequency decreases), larger antennas (satellite dishes) are necessary to gather the signal. 12
C - Band • • • C-band satellite transmissions occupy the 4 to 8 GHz frequency range. These relatively low frequencies translate to larger wavelengths than Ku-band or Ka-band. These larger wavelengths of the C-band mean that a larger satellite antenna is required to gather the minimum signal strength, and therefore the minimum size of an average C-band antenna is approximately 2-3 meters in diameter. Figure 8. C – Band Satellite Antenna 13
Ku - Band • Ku-band satellite transmissions occupy the 11 to 17 GHz frequency range. • These relatively high frequency transmissions correspond to shorter wavelengths and therefore a smaller antenna can be used to receive the minimum signal strength. • Ku-band antennas can be as small as 18 inches in diameter. Figure 9. Ku – Band Satellite Antenna 14
Ka - Band • Ka-band satellite transmissions occupy the 20 to 30 GHz frequency range. • These very high frequency transmissions mean very small wavelengths and very small diameter receiving antennas. Figure 10. Ka – Band Satellite Antenna 15
Satellite Orbits • Satellites travels around the Earth in different orbits. Figure 11. Satellite Orbits 16
Geocentric Orbits A Geocentric orbit involves any object orbiting the Earth, such as the Moon or artificial satellites. Figure 12. Geocentric Orbits 17
Types of Geocentric Orbits • • • • • LEO (Low Earth Orbit) MEO (Medium Earth Orbit) GSO (Geo Synchronous Orbit) GEO (Geostationary Earth Orbit) HEO (Higher Earth Orbit) 18
Types of Geocentric Orbits Cont.. Figure 13. Satellite orbits 19
Low Earth Orbit (LEO) Satellite Systems • A low Earth orbit (LEO) is an orbit with an altitude between 160 kilometers and 2,000 kilometers. • At 160 km, one revolution takes approximately 90 minutes, and the circular orbital speed is 8,000 meters per second (26,000 ft/s). • The majority of artificial satellites, have been in LEO. • Earth observation satellites and spy satellites use LEO as they are able to see the surface of the Earth more clearly as they are not so far away. 20
LEO Cont.. Advantages: • better signal strength • Short propagation delays (10 – 15 msec) • less of a time delay, which makes it better for point to point communication • Low transmission power required • Low price for satellite and equipment Disadvantages: • A network of LEO satellites is needed, which can be costly • Small coverage spot • High system complexity 21
Medium Earth Orbit (MEO) Satellite Systems • MEO, sometimes called Intermediate Circular Orbit (ICO), is the region of space around the Earth above LEO (altitude of 2,000 kilometers) and below geostationary orbit (altitude of 35,786 kilometres). • The most common use for satellites in this region is for navigation, communication, and space environment science. • The most common altitude is approximately 20,200 kilometres (12,552 mi)), which yields an orbital period of 12 hours, as used, for example, by the Global Positioning System (GPS). 22
MEO Cont.. Advantages: • MEO satellites have a larger coverage area than LEO satellites. • fewer satellites are needed in a MEO network than a LEO network. Disadvantages: • 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. 23
Geo-Synchronous Orbit (GSO) Satellite Systems • A geosynchronous orbit (GSO) is an orbit around the Earth with an orbital period of one sidereal day (approximately 23 hours 56 minutes and 4 seconds), matching the Earth's sidereal rotation period. • When an object is in a geosynchronous orbit it means that it is traveling around the Earth at the same speed that the Earth is rotating. • To someone on the Earth, the object will always appear in the same region in the sky but it might move slightly north or south. • Sidereal day: The time for one complete rotation of the earth relative to a particular star, about 4 minutes shorter than a mean solar day. 24
Geostationary Earth Orbit (GEO) Satellite Systems • A geostationary orbit is a special type of geosynchronous orbit. • When an object is in geostationary orbit, it is orbiting at the same speed as the Earth rotates, but it orbits around the equator. • From the Earth’s surface, an object in a geostationary orbit looks like it is not moving at all. • GEO is a circular orbit about 35,786 kilometres (22,236 mi) above the Earth's equator. • Communications satellites and weather satellites are often given geostationary orbits, so that the satellite antennas that communicate with them do not have to move to track them, but can be pointed permanently at the position in the sky where they stay. 25
GEO Cont.. Figure 14. Geostationary Earth Orbit Satellite System 26
GEO Cont.. 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. 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 in broadcasting signals near polar regions 27
GEO Cont.. • Only 3 satellites in Geostationary orbit can coveer the entire globe. Figure 15. Tri state satellite system 28
High Earth Orbit (HEO) Satellite Systems • A high Earth orbit is a geocentric orbit with an altitude entirely above that of a geosynchronous orbit (35,786 kilometres (22,236 mi)) • Not widely used. 29
Types of Satellites & their Uses Astronomy satellites • An astronomy satellite is basically a really big telescope floating in space. • Used for space observation. • • Figure 16. Astronomy Satellite 30
Types of Satellites & their Uses Cont.. Atmospheric studies satellites • Used to study the Earth’s atmosphere. • • Figure 17. Atmospheric studies Satellite 31
Types of Satellites & their Uses Cont.. Communication satellites • Communications satellites allow radio, television, and telephone transmissions to be sent live anywhere in the world. • • Figure 18. Communication Satellite 32
Types of Satellites & their Uses Cont.. Navigation satellites • Use to determine location of any object. • The GPS system is the first core element of the satellite navigation system widely available to civilian users. Figure 19. Navigation Satellite 33
Types of Satellites & their Uses Cont.. Weather satellites • Used to find out the weather anywhere in the world any time of the day. • Weather forecasting is done by using the Weather Satellites. Figure 20. Weather Satellite 34
Conclusion • Satellites are most widely used in almost every field. • Today most of the advancement in various technologies are due to the satellite systems. 35
References • • • • • • • • • • • • • • http://searchmobilecomputing.techtarget.com/definition/satellite http://en.wikipedia.org/wiki/Satellite http://people.bridgewater.edu/~lwilliam/Chapter%2004/sld049.htm http://www.jisc.ac.uk/whatwedo/themes/network/sat/report3.aspx http://www.scribd.com/doc/7140701/52/Principal-Satellite-TransmissionBands https://www.google.com/images http://www.youtube.com/watch?v=S22u7_Eq26g http://www.youtube.com/watch?v=m2WrY1GdQ74 http://www.youtube.com/watch?v=xv9dRENgDoc http://www.youtube.com/watch?v=m2WrY1GdQ74 http://www.williamcraigcook.com/satellite/work.html http://www.howstuffworks.com/satellite.htm http://www.satellites.spacesim.org/english/engineer/copy/ http://www.stmary.ws/highschool/physics/97/MHALLETT.HTM 36
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