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What is a satellite??

A satellite is an object that moves around a

larger object.

Earth and Moon are called Natural satellites.

Man-made satellites are machines made by

scientists.

These machines are launched into space andorbit Earth or another body in space.

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Why are satellites important?

Satellites fly high in the sky, So they can see

large areas of earth at one time.

Satellites also have a clear view of space.

Before the invention of satellites, TV signals

didnt go very far.

TV signals only travel in straight lines. So theywould go off into space instead of following

Earths curve.

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Contd..

Sometimes they would be blocked by mountains

or tall buildings.

Phone calls to far away places were also a

problem. It costs a lot and it is hard to set uptelephone wires over long distances or

underwater!!

With satellites, TV signals and phone calls can besent up to a satellite. The satellite can then send

them back down to different spots on Earth.

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First satellite in space!!

The Soviet Union was the first to launch a

satellite into space.

The satellite was launched in 1957 and was

called Sputnik 1.

NASA has launched many satellites into space.

The first was Explorer 1 in 1958. Explorer was Americas first man-made

satellite.

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The SPUTNIK 1

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Incredible India

India has launched 64 satellites (as of 25

February 2013) of many types.

The first satellite was Aryabhata launched on

19-04-1975. It is a experimental/small

satellite.

The organization responsible for Indian

satellites is the Indian Space Research

organization (ISRO).

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Cost

Launching satellites is not cheap business!!

They cost a lot of money(in fact Millions of

Dollars) to design, construct, launch and to

monitor.

Running a satellite at a 36MHz bandwidth will

cost over $1.5 million a year!!

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How do satellites work??

Two stations on earth want to communicatethrough radio broadcast but are too far away touse conventional means.

The two stations can use satellite as a relaystation for their communication.

One Earth Stationsends a transmission to thesatellite. This is called Uplink.

The satellite Transponder converts the signal andsends it down to the second earth station. This iscalled a Downlink

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Satellite orbits

GEO(Geo stationary Earth Orbit)

MEO(Medium Earth Orbit)

LEO(Low Earth Orbit)

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Geostationary Earth Orbit (GEO)

These satellites are in orbit 35,863 km above

the earths surface along the equator.

Objects in Geostationary orbit revolve around

the earth at the same speed as the earth

rotates. This means GEO satellites remain in

the same position relative to the surface of

earth.

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GEO (cont.)

Advantages

A GEO satellites distance from earth gives it a

large coverage area, almost a fourth of the earths

surface.

GEO satellites have a 24 hour view of a particular

area.

These factors make it ideal for satellite broadcastand other multipoint applications.

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GEO (cont.)

Disadvantages

A GEO satellites distance also cause it to have

both a comparatively weak signal and a time delay

in the signal, which is bad for point to pointcommunication.

GEO satellites, centered above the equator, have

difficulty broadcasting signals to near polar

regions

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Medium Earth Orbit (MEO)

A MEO satellite is in orbit somewhere between 8,000 km and

18,000 km above the earths 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.

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MEO (cont.)

Advantage

A MEO satellites longer duration of visibility and

wider footprint means fewer satellites are needed

in a MEO network than a LEO network.

Disadvantage

A MEO satellites 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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Low Earth Orbit (LEO)

LEO satellites are much closer to the earth

than GEO satellites, ranging from 500 to 1,500

km above the surface.

LEO satellites dont 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

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LEO (cont.)

Advantages

A LEO satellites proximity to earth compared to a

GEO satellite gives it a better signal strength and

less of a time delay, which makes it better forpoint to point communication.

A LEO satellites smaller area of coverage is less of

a waste of bandwidth.

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LEO (cont.)

Disadvantages

A network of LEO satellites is needed, which can

be costly

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

Atmospheric drag effects LEO satellites, causing

gradual orbital deterioration.

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Types of Satellites

Astronomical satellitesare satellites used

for observation of distant planets, galaxies,and other outer space objects.

Communications satellitesare artificial

satellites stationed in space for thepurposes of telecommunicationsusing

radio at microwave frequencies. Most

communications satellites usegeosynchronous orbits or near-

geostationary orbits, although some recent

systems use low Earth-orbiting satellites.

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Earth observation satellitesare satellitesspecifically designed to observe Earth from orbit,

similar to reconnaissance satellites but intendedfor non-military uses such as environmentalmonitoring, meteorology, map making etc.

Navigation satellitesare satellites which use radio

time signals transmitted to enable mobilereceivers on the ground to determine their exactlocation. The relatively clear line of sight betweenthe satellites and receivers on the ground,combined with ever-improving electronics, allowssatellite navigation systems to measure locationto accuracies on the order of a few meters in realtime.

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Reconnaissance satellitesare Earth observation

satellite or communications satellite deployed for

military or intelligence applications.

Space stationsare man-made structures that are

designed for human beings to live on in outer

space. A space station is distinguished from other

manned spacecraft by its lack of major propulsionor landing facilities - instead, other vehicles are

used as transport to and from the station. Space

stations are designed for medium-term living in

orbit, for periods of weeks, months, or evenyears.

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Weather satellitesare satellites that primarily areused to monitor the weather and/or climate of

the Earth. Drag-free satellitesare satellites that offers an

environment that is as isolated as possible fromthe forces of nature. A properly designed drag-

free-satellite proof mass is uncoupled from therest of the Universe to a remarkable degree.

Miniaturized Satellitesare satellites of unusuallylow weights and small sizes. New classifications

are used to categorize these satellites: minisatellite (500-200kg), microsatellite (below100kg), nanosatellite (below 10kg).

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Applications of Sat. Comm.

Radio and TV broadcasting Business radio and TV Telephony Thin route or trunk telephony

Mobile satellite telephony LEO-based telephony GEO-based telephony Data, broadband and multimedia services IP over satellite for ISPs Corporate or institutional VSAT networks End-user services for home or small office Mobile data communications

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Advantages of Satellites

Higher bandwidths are available for use.

Satellite to satellite communication is very

precise.

The coverage area of a satellite greatly

exceeds that of a terrestrial communication.

Transmission cost of a satellite is independent

of the distance from the center of the

coverage area.

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Disadvantages of satellites

Launching satellites into orbits is costly.

Satellite bandwidth is gradually becoming

used up.

There is a larger propagation delay in satellite

communication than in terrestrial

communication.

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