presentation on space textiles

7/29/2019 presentation on space textiles

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satellites

satel l i tes

Subm it ted to:

Mr. Rohit Goel

Subm itted by:

vinesh

text i le 6thSem.


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contents

Types o f satel l i tes

Synchronous satel l ites

Frequency band al locat ionBand spectrum

Advantages and disadvantages of

satell i tes


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Appl icat ions


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Types o f satel l i tes

Satell i te orbi ts are also c lass i f ied based ontheir heigh ts above the earth:

GEO

LEO

MEO

Molniya Orbit

HAPs


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Geostat ionary earth orb it (GEO)

Orbi t is synchronouswith the earths rotat ion.

From the ground the

satell i te appears fixed .

Alt i tu de is abou t 23,000miles.

Coverage to 40% ofplanet per satel l i te.


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GEOs

Originally proposed by A rthu r C. Clarke

Circular orbi ts above the equator

Angular separat ion about 2 degrees - al low s 180

satell i tes

Orbital heigh t above the earth about 23000

miles/35000km.

GEO satel l ites require more power for commun ications

The signal to noise rat io for GEOs is worse because of

the distances invo lved.

A few GEOs can cover most of the su rface of the earth

Note that polar regions cannot be seen by GEOs


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Bas ic o f GEOs

Geostat ionary satel l ites are common ly used forcommun ications and weather-obs ervat ion.

The typical servic e li fe expectancy of a geos tat ionary

satel l i te is 10-15 years.

Becaus e geostat ionary satel l i tes cir cle the earth at the

equator , they are not able to pro vide coverage at theNorthernmost and Southernmost lat i tudes.


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Low earth orb i t (LEO)

LEO satel l ites are much

closer to the earth than

GEO satell i tes, rang ing

from 500 to 1,500 km

above the surface.

LEO satellites dont stayin f ixed posi t ion relative

to th e surface, and are

on ly vis ib le for 15 to 20

m inutes each pass. A network o f LEO

satel li tes is necessary

for LEO satel l i tes to be

usefu l

Revo lut ion t im e: 90 min - 3 hou rs


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Med ium earth orb i t (MEO)

A MEO satel l ite is in o rb it

somewhere between 8,000

km and 18,000 km above the

earths surface. These orb i ts are primarily

reserved for communications

satel li tes that cover the North

and South Pole.

Unl ike the circular orbi t of

the geostat ionary satel l i tes,

MEOs are placed in an

el lipt ical (oval-shaped) orb it.


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Synch ronous satel li tes OR

geo-synchronous satel li tes


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Synch ronous satel li tes

A geosynchronous orbi t is the one wi th an orbi tal

per iod (the t ime needed to orb i t once around the Earth)

that matches the rotat ion rate of th e Earth. This is a

sidereal day, wh ich is 23 hours 56 m inutes and 4

seconds in length. There is on ly one geosynch ronous earth o rbi t . It is

occupied by a large number of satel l i tes. In fact, the

geosynchronous orbi t is the most w idely used earth

orbi t for the obvious reason .

This st ipu lat ion equates to an angular separation of 4or m ore, wh ich l im i ts the number of satel l ite vehic les in

a geosynchronou s earth orbi t to less than 100.


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Satel li tes in geo-synch ronous

orb i t


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Geosynch ronous satel li tes

A geostat ionary orbi t is a special case of a

geosynchronous orb i t.

A satel l i te is in a geostat ionary orb it when it appearsstat ionary from the point of v iew of an ob server on the

Earth's su rface.


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Geostat ionary satell i tes

This can only occur when:

The orbi t is geosyn chronous.

The orbi t is a circu lar.

The orb it l ies in th e plane of the Earth's equator.

Thus, a geosynch ronous satel l ite w i l l be geostat ionaryon ly w ith the add i t ional restr ic t ions of i t being in acircu lar orb i t si tuated over the equator.

The satel l i te veloc ity in th is o rbit is 3075 m /s.

Operate in the 2.0 GHz to 18 GHz range.

When the incl inat ion and eccentr ic i ty of the orb i t iszero, the satel li te appears to be stat ionary to an

observer f rom ground.


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Geo-s tat ionary satel l i tes

Appl icat ions:

Telecommunicat ion systems

Radio

Data Transm ission sys tems


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Frequency Spectrum

concepts :

Frequency: Rate at which an electromagnetic wave reverts itspolar ity (oscil lates) in cycles per second or Hertz (H z).

Wavelength: distance between wavefronts in space. Given in

meters as: = c/f Where: c = speed of l ight (3x108m/s in vacuum)

f = frequency in Hertz

Frequency band: range of frequencies.

Bandwidth: Size or width (in Hertz) or a frequency band.

Electromagnetic Spectrum: ful l extent of al l frequencies from

zero to inf ini ty.


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Rad io Frequenc ies (RF)

RF Frequencies: Part of th e electrom agnetic

spectrum rang ing b etween 300 MHz and 300 GHz.

Interest ing propert ies:

Effic ient generat ion of signal power

Radiates into free space

Eff ic ient reception at a dif ferent po int.

Differences depend ing on the RF frequency

used: - Signal Bandwidth

- Propagation effects (dif fract ion, noise, fading )

- Antenna Sizes


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Microwave Frequencies

Sub-range of the RF frequencies approximately from 1GHz

to 30GHz. Main properties:

L ine of sight propagation (space and atmosphere).

Blockage by dense media (hil ls, buildings, rain)

Wide bandwidths compared to lower frequency bands.

Compact antennas, directional ity possible.

Reduced eff iciency of power ampli f ication as frequency

grows:

Radio Frequency Power OUT

Direct Current Power IN


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Spec trum Regu lat ion

I nternational Telecommunication Union (I TU): Members

from practical ly all countr ies around the wor ld.

Allocates frequency bands for different purposes and

distr ibute them around the planet.

Creates rules to l imit RF I nterference (RFI ) betweencountr ies that reuse same RF bands.

Mediates disputes and creates rules to deal with

harmful interference when it occurs.

Meets bi-annually with its members, to review rules

and allocations: World Radio Communication

Conference (WRC).


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Frequency band al locat ion

Different kind s of satel l ites use

di f ferent frequency bands.

L-band

S-band

C-band

X-band

Ku-band

Ka-band


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Early satel l i te commun icat ions

Used C band in the range 3.7-4.2 GHz

Could interfere with terrestr ial communicat ions

Beam-width is narrower w ith higher frequencies


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Rad io Frequency Spectrum

AM HF VHF UHF L S C X Ku Ka V Q

1 10 100 1

MHz GHz

Terrestrial Bands

Space Bands

Shared (Terrestrial and Space)

SHF

0.1 10010

Commonly Used Bands


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Commun icat ion frequenc ies

Microwave band term inology

L band 800 MHz - 2 GHz

S band 2-3 GHz

C band 3-6 GHz

X band 7-9 GHz

Ku band 10-17 GHz

Ka band 18-22 GHz


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Frequency bands

BandDownlink,

GHz

Uplink,

GHz

Bandwidth,

MHz

uses

L 1.5 1.6 15used by MSS

S 1.9 2.2 70

Used by MSS ,

NASA , deep

space research

C 4 6 500used by FSS

Ku 11 14 500used b y FSS and

BSS (DBS)

Ka 20 30 3500used by FSS


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Three bands are mos t ly used

6/4 Ghz band

14/12 Ghz band

20/30 Ghz band

6/4 band is mostly used. Because they offer the fewest

propagation problems

o Rain attenuation and sky noise is low , so it is easy tobuild low noise temp. in receiving system


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14/12 Ghz bando Crowding/congestion of 6/4 band with band width of 500

Mhz is high , to over come this problem 14/12 band is

used in commercial application

o Uplink freq. is 12.75 to 14.80 Ghz and downlink freq. is

10.7 to 12.3 Ghz

o Rain attenuation is a problem at this band.

20/30 Ghz bando For require higher capacities 20/30 Ghz band is used

with a band width of 2.5 Ghz

o Uplink is 27.50 to 31 Ghz

o

Downlink is 18.10 to 21.20 Ghz


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Advan tages o f satel l ites

Capable of transmitting high capacities over long distances.

Has a unique geometry, so it i s used as a broadcast medium to

transmit signs from one point to no. of points in coverage area i.e(

wide area broadcast).

I t can be install ed rapidly.

Has unique degree of f lexibil ity in interconnecting mobile vehicles.

So its good for mobile communication.


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Also useful for th in route remote area communicat ion. Lik(Hil ly area) Sikk im , Islands .

Can reach over large geog raphical area

Flexib le (i f transparent transponders)

Easy to ins tal l new circu i ts

Circui t costs independent of distance

1-for-N mult ipoint standby pos sib i l i t ies


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Commun ication path between transm it ter and receiver is

approximately 7500 km , w ith a veloci ty of 3x10^ 8m/s.

There is a delay of sec. b/w transm iss ion & reception .

Eff ic iency is reduced for long f i le transfers.

Disadvan tages o f satel l ites

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