Lecture _1 (Satellite Technology)

8/8/2019 Lecture _1 (Satellite Technology)

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Satellite Technology 1

SATELLITE TECHNOLOGY

Instructor:

Muhammad Aneel BEIT-7


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SATELLITE TECHNOLOGY


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CONTENTS

Ov er viewApplicationsOrbitsInjection into orbitOrbital velocity

Orbital maintenance and maneu veringPakistan satellite program


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OVERVIEW

An artificial satellite is a spacecraft orbiting around the Earthcaring se veral instruments pertaining to its mission.

De velopment in rocket and missile technology led to the satellitetechnology.

Three or more stage rocket engine is necessary to achie ve the

required velocity to inject the satellite in the orbit .

The satellites are tracked and controlled by ground based radiostation.


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OVERVIEW

1957 first satellite SPUTN IK by USSR

1960 first reflecting communication satellite ECH O

1963 first geostationary satellite SYNC OM

1965 first commercial geostationary satellite Early Bird ( INTELSAT I) 1982 first mobile satellite telephone system INM ARSAT-A

1988 first satellite system for mobile phones and data communicationINM ARSAT-C

1998 global satellite systems for small mobile phones


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APPLICATIONS

Traditionallyweather satellitesradio and TV broadcast satellitesmilitary satellites

satellites for na vigation and localization (e.g., GPS )Telecommunication

global telephone connectionsbackbone for global networksconnections for communication in remote places or

underde veloped areasglobal mobile communication

satellite systems to extend cellular phone systems (e.g., GS M or AMPS )


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APPLICATIONSSpace explorationNatural resource explorationGeo- Mapping


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SATELLITE ORBITS

Satellite orbit has two characteristics.

Its angle w.r.t equator plane. The angle of the orbit plane determinesthe extent to which it will co ver the parts of the globe.

Perigee and apogee of elliptical orbit.

The minimum altitude required for orbiting a satellite is155

km,which is well outside the atmosphere.


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SATELLITE ORBITS

T = ( 2 T r )/( Q ) 3 /2 1 /2


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ORBITS

Four different types of satellite orbits can be identified depending onthe shape and diameter of the orbit:

GEO: geostationary Earth orbit, 36000 km abo ve earth surface

LEO: (Low Earth Orbit): 500 - 1500 km

M EO: (Medium Earth Orbit) or ICO (Intermediate Circular Orbit):6000 - 20000 km

HEO: (Highly Elliptical Orbit) elliptical orbitsEARTH RADIUS: Mean earth radius is 6338 .137 km and GE Oradius from the centre of the earth is 4 216 4. 17 km.


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ORBITS

earth

35786 km

10000

1000

LEO (Globalstar,

Irdium )

HEO

inner and outer Van Allen belts

MEO (ICO)

GE O (Inmarsat )


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ORBITSGE O O rbit altitude is 35786 km

Three properly positioned communication satellites co ver theentire globe. Geostationary orbit is a specific orbit, it lies in theequator plane i.e. zero inclination and the satellites remain fixover the region they are employed for.

LEO orbit altitude is 500 -1500 km

Visibility of satellite is 10 - 4 0 minutes. Many satellites arenecessary for global co verage. Iridium ( start 1998 , 66 satellites ).Global star ( start 1999 , 4 8 satellites )

Iridium is currently in operation system utilizing 66 satellites insix 8 4.4 degree inclined orbital planes at the height of 780 kmwith an orbital period of 100 miutes and 28 second.


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ORBITSLEO satellites system is a complex system due to mo vingsatellites. Atmospheric drag results in orbital deterioration andthe life of the satellite is dramatically reduced.

MEO orbit altitude is 5000 20000 km.

It is simpler to design a system for this orbit. Less number of slow mo ving satellites is required.

INM ARSAT is in operation in ICO ( Intermediate circular orbit )at the height of 10000 km. Modest number of satellites in 2 to 3

planes are required for global co verage. Satellite orbital period is6 hrs and its visibility time o ver the local horizon is of the order of few hrs.


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ORBITS


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IRIDIUM SYSTE M OF SATELLITES


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ORBITS

GPS ( Global positioning system ) is a prime example of MEO system.It uses satellites and computers to measure position anywhere on theEarth.GPS system comprises 2 4 satellites in six orbital planes.

It allows land, sea and airborne users to determine their position,velocity and time 2 4 hrs. a day, in all weather, any where in the world.


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M EO SYSTE M S


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INJECTION INTO ORBIT

There is a specific velocity required for attaining a specific orbitat a gi ven altitude.

There are two methods to inject the satellite into proper orbit. ( 1 )

Direct injection ( 2 ) step injection.

After launch the spacecraft is separated from the launch vehicleat a particular altitude with a particular velocity in a particular direction.


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INJECTION INTO ORBIT


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INJECTION INTO ORBIT Additional Velocity Imparted here

Parking Orbit

Impulse

application

Final Orbit


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INJECTION INTO ORBITIf the spacecraft encounters no disturbance then the energy andmomentum of the spacecraft will remain constant through thelife time of the spacecraft.

The spacecraft energy and momentum determine the orbitaltitude as a function of time. As the spacecraft loses energy, itslows down and comes down into the lower orbit, its velocityincreases at the less altitude and imbalance between C.P andC. F results in satellite destruction in atmosphere.


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ORBITAL VELOCITY

Smi measure axis (a ) Smi measure axis (a )

Focus

Perigee

Radius, r p Apogee

Radius, r a


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ORBITAL VELOCITY

Elliptical Orbital Velocity

V = [(2/r1/a)]

Circular Orbital Velocity

V = (/r)

Escape Velocity

V = (2/r)Q = G M e

e Orbit

0 Circle (a = r ) [ra = rp]

0 ) [rp > 0 ]

1 Parabola [a $ g (undefined )]

[rp = 0 ]

>1 Hyperbola (a < 0 )

e = eccentricity = ( r a r p ) / (r a + r p )

1/2

1/2

1/2

el

es

c


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ORBITAL VELOCITY

Vc = velocity in circular Orbit


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ORBITAL VELOCITY

According to Keplers first law two bodies in space interactinggra vitationally will re volve in elliptical or circular orbit,if there isno gra vitational attraction between them then orbit will behyperbola. Mathematically it is as, v =(2/r1/a) where v is thevelocity of the satellite, = MeG Me is the mass of the Earth, Gis the constant of gra vity, a is the semi- major axis of the orbitand r is the distance between the satellite and the Earth center.

For circular orbit r = a, so circular orbit velocity is = (/r).

For escape velocity a = infinity, so escape velocity is = (2/r)


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ORBITAL M ANEUVERING AND

M AINTENANCESometimes plane change or transfer of a satellite from one orbitto another by means of change in velocity is required becauseof safety or launch site cannot launch the satellite in that plane.

Orbit change can be achie ved by the addition of the velocitycomponent ( v that is necessary to change the direction of theinitial velocity vector.


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ORBITAL M ANEUVERING AND

M AINTENANCE

| ( v | = 2 | v | sin U/2


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PAKISTAN SATELLITE PROGRA MM

SUPARC O built communication satellites Badar 1 and Badar b andthey were launched on Chinese long march rocket in 1990 andRussian Zenit 2 rocket in 2001 respecti vely but launching was notsuccessful.

Pakistan is stri ving to de velop the indigenous SLV to place thesatellite in the orbit. SLV would be deri ved from an already a vailablemissile launching system. All the experiments necessary to readythe SLV are in process. In march 2005 , president Per vez Mushraf

emphasized on the research and de velopment of an indigenouslaunch capability which would place domestically built satellitePaksat- IR. Howe ver date of completion of this project is not gi ven.


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PAKISTAN SATELLITE PROGRA MM

SUPARC O (Space and Upper Atmosphere Research Commission )has outlined their future programs like remote sensing andgeographic satellites. In this regard SUPARC O has established a

RS-G IS centre in Karachi.

Satellite application programs are being studied. For instance,


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PAKISTAN SATELLITE PROGRA MMRemote sensing applicationSpace and atmospheric sciences

Global na vigation satellite system application.

Tele-medicine and Tele- education.

Pakistan has been allocated geostationary orbit at38

degree eastlongitude. Pakistan has leased an in- orbit satellite H-G-S- 3 fromM/S Hughes Global Ser vice. The HGS- 3 renamed as paksat- 1 isalready pro viding ser vices to a number of users. This satellitepro vides high quality communication to Pakistan, Africa and MiddleEast. Paksat- 1 has two beams in each C and KU bands; C 1 ,C 2 in CK1 ,K2 in KU band respecti vely. C 1 co vers mainly Africa and Middle

East. C2

co vers South Asia, Middle East, Africa, central Asia andSouth Europe. In KU band K1 co vers mainly Middle East, andEastern Africa. K2 co vers South East and central Asia.

Pakistan is de veloping a new satellite the PA KSAT- IR which willreplace the leased paksat- 1 communication satellite.


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THANK YOU

Documents

Lecture _1 (Satellite Technology)