introduction to satellite

CONTENTS : What’s mean by satellite ? History of Satellites : Layer Of Atmosphere : Generalized communication system : What are the components of a satellite? How Satellites Work ? How do satellite stay in orbit ? Why satellite are launched 36,000 Km from centre of earth ? Types of bands : Types of orbits : Global position system : Advantages And Disadvantages Of satellite : Uses of satellite : References :

what’s mean by sATELLITE ?

Passive Satellites Active satellitesI. Natural satellites II. artificial satellites.• A passive satellite only

reflects received signals back to earth.

• Ex.moon is a natural satellite of earth

• Active satellites are complicated structures having a processing equipment called Transponder .

• An active satellite acts as a REPEATER

A Satellite is a solid object which revolves around some body due

to the effect of gravitational forces ORa satellite is an object which has been placed into orbit by human endeavour.

History of Satellites :

• First satellite that was used for communication purpose in INDIA was -ARYABHATTA (19 April 1975)

• The first geostationary communication satellite -SYNCOM 3(19 Aug 1963).

• Father of geostationary communication satellite is

-HAROLD ROSEN (Aircraft engineer)

The world's first artificial satellite is the Sputnik 1

was launched in 1957

Layer Of Atmosphere : TROPOSPHERE :

STRATOSPHERE :

MESOSPHERE :

THERMOSPHERE :

EXOSPHERE :

INFORMATION

SOURCE

Uses of informa

tion

TRANNSMITTE

R

ReceiverChannel

1 2 3 4

1= Message signal.

2 = tranmitted signal.

3 = received signal.

4 = message signal.

Generalized communication system :

NOISE OCCUR

What are the components of a satellite?

• Many satellites are powered by rechargeable batteries.

• Small thrusters provide attitude i.e. stabilize the satellite's position in space.

How Satellites Work :

I. A Earth Station sends message in GHz range (Uplink).

II. Satellite Receive and retransmit signals back. (Downlink)

III. Difference between Downlink and Uplink frequency is

2 GHz.

Why geostationary satellite are launched

36,000 km from the center of the earth?

• 1.Gravitational force= attraction between any two objects, given by

• 2.Centrifugal force=an outward-directed force that normally balances the inward-directed centripital force

There are two relevant forces involved in this problem

Equate that 2 eqn=

i.e.

The tangential velocity of the satellite (vs) is related to its orbital period, T so,

Eqating that 2 eqn=

As we know

Then T=? and sqaring

We know:G = 6.67 x 10-11 Nm2kg-2

me = 5.97 x 1024 kgwe = 7.29 x 10-5 rad s-1

Hence, substituting the above constants into

gives:

R = 35,786 km for center of earthNear about 36,000 km.

How do satellites stay in orbit?

Satellites stay in orbit due to the balance of two factors:

i. Velocity andii. Gravitational pull

between the Earth and the satellite.

Satellites never fall into the Earth this because Earth is round and curves.

Satellite Frequency Bands :

There is a inverse relationship between frequency and wavelength.

• Different kinds of satellites use different frequency bands.

• L–Band: 1 to 2 GHz, • S-Band: 2 to 4 GHz• C-Band: 4 to 8 GHz• X-Band: 8 to 13 GHz• Ku-Band: 13 to 18 GHz• K-Band: 18 to 28 GHz• Ka-Band: 28 to 40 GHz

As wavelength increases (and frequency decreases), larger antennas (satellite dishes) are necessary to gather the signal.

C-band :• C-band is the most common frequency spectrums used by today’s satellite.

• C-band satellite transmissions occupy the 4 to 8 GHz frequency range.

• C-band antenna is approximately 2-3 meters in diameter

Ku-band :• Ku-band satellite

transmissions occupy the 13

to 18 GHz frequency range.

• Ku-band antennas can be as

small as 18 inches in diameter

•  These very high frequency

transmissions mean very

small wavelengths and very

small diameter receiving

antennas.

TYPES OF ORBITS

Low-Earth-Orbit (LEOs)

Medium-Earth-Orbit (MEOs)

Geostationary (GEOs)

Low-Earth-Orbit (LEO) Altitude (600-1000 KM) satellite gives it a better signal

strength

Advantages: Reduces transmission

delay

Disadvantages: Smaller coverage area.Shorter life span (5-8 yrs.)

Little LEOs Applications

0.8 GHz range

Small, low-cost

Used for short communications.

Middle-Earth-Orbiting (MEO)

MEOs orbits between the altitudes of 8,000 - 20,000 km above the earth.

MEO satellites have a larger coverage.These orbits are primarily reserved for communications satellites that cover the North and South Pole.

MEOs are placed in an elliptical (oval-shaped) orbit.

Geosynchronous-Earth-Orbit (GEO)

From the ground level the satellite appears fixed.

GEO satellites have a 24 hour view of a particular area.

Coverage to 40% of area Of planet by this satellite

The Global Positioning System :

EQUATORIAL ORBIT :

POLAR CIRCULAR ORBIT :

INCLINED ORBIT :

EACH SATELLITE COVER 40% AREA

SATELLITE MAKES AN ANGLE OF 120 WITH EACH OTHER.

ADVANTAGES AND DISADVANTAGES OF

SATELLITE: ADVANTAGES :

DISADVANTAGES :• Make repeated

observations over a given area .

• At a time satellites observe a larger coverage

• Minimum Satellite lifetime is about 10-15 years.

• Poor spatial resolution in the polar regions.

– Launching satellites into orbit is costly.

Uses of satellite:• IT IS USED FOR LONG DISTANCE COMMUNICATION.

• IT IS SPEEDY AND RELIABLE.

• IT IS USED FOR WEATHER FORECASTING.

(study of atmosphere ,rain ,sunshine at any place at perticular time)

• IT IS USED FOR TRANSMIT T.V. SIGNAL OVER LARGE DISTANCE COMMUNICATION.

• POLAR SATELLITE IS USED FOR REMOTE SENSING.

REFERENCES :

• http://en.wikipedia.org/wiki/Geosynchronous_satellie

• Geostationary Satellite(Author- Louis E.Frenzel)

(Edition- Third) (Publication- Tata McGraw-Hill)

• http://web.mit.edu/invent/iow/rosen.html

-- >>BY SWAPNIL G. THAWARE