UGANDA CHRISTIAN UNIVERSITY

Group 10Name Reg NoOngodia Godfrey S08B23/607Tabaalya Phillip S08B23/802Ajuna Annet S08B23/003Nabude Belinda S08B23/506Murungi Brian S08B23/429Lumonya Miriam S08B23/362Nasamula Rachael S08B23/504

SATELLITES

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What is a satellite? A satellite is an electronic device that is set into space

and moves around the earth or another planet. It is used for communicating by radio, television and for providing information.

A satellite is also a natural object that moves around a larger natural object in space for example the moon is a satellite of the earth.

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CATEGORIES OF SATELLITESSatellite can be categorized according to;1. The distance from the earth These include; Low Earth Orbit satellites , Medium Earth Orbit

satellites , Geostationary Earth Orbit satellites2. Their functions Communication satellites: These provide worldwide linkup of

radio, television and telephone. Examples include Echo 1 launched in 1960, Relay 1 launched in 1962, Telstar 1 launched in 1962.

Weather satellites (meteorological satellites): These provide continuous up-to-date information about large scale atmospheric conditions such as cloud cover. Examples include Tiros 1 launched in 1960, GOES (Geostationary Operational Environmental Satellites)

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Low Earth Orbit Satellites LEO satellites are the closest to the earth, ranging from

500 to 1,500 km above the surface. LEO satellites must travel very fast to avoid gravity

forces. They travel at 17,000 miles per hour. LEO satellites don’t stay in fixed position relative to the

surface, and are only visible for 15 to 20 minutes each pass. These satellites can circle the whole earth in about one and a half hours and have a life expectancy of 7-10 years

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LEO Continued A network of 40 and beyond LEO satellites is necessary

for LEO satellites to be useful

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Advantages of LEO satellites 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.

A LEO satellite’s smaller area of coverage is less of a waste of bandwidth.

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Disadvantages of LEO satellites A network of LEO satellites is needed, which can be

costly

LEO satellites have to compensate for Doppler shifts cause by their relative movement.

Atmospheric drag affects LEO satellites, causing gradual orbital deterioration

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Medium Earth Orbit satellites A MEO satellite is in orbit somewhere between 8,000 km

and 18,000 km above the earth’s surface. These satellites are in line of sight for 2 hours and it

takes 8 hours to rotate around the earth. MEO satellites have a life expectancy of 10-15 years MEO satellites have a larger coverage area than LEO

satellites.

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Advantages of the MEO satellites A MEO satellite’s longer duration of visibility and

wider footprint means fewer satellites are needed in a MEO network than a LEO network.

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Disadvantages of MEO satellites 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.

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Geostationary Earth Orbit Satellite These satellites are in orbit 35,863 km above the earth’s

surface along the equator. A satellite in the Geosynchronous orbits the earth in 24

hours (the time it takes the earth to rotate one time). If these satellites are positioned over the equator and travel in the same direction as the earth rotates, they appear “fixed” with respect to a given spot on the earth.

GEO satellites have a life expectancy of 10-15 years 3 GEO satellites can cover the globe.

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Advantages of GEO satellites 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.

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Disadvantages of GEO satellites A GEO satellite’s distance also causes 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 broadcasting signals to near polar regions

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References

http://www.nasa.gov/audience/forstudents/8/features/what-is-a-satellite-58.html

http://www.howstuffworks.com/satellites

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