presentation on space textiles
TRANSCRIPT
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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