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GENERAL OVERVIEW of

TELECOM SATELLITES

GENERAL OVERVIEW of

TELECOM SATELLITES

Daniel HERNANDEZ

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NEED or MISSION DEFINITIONNEED or MISSION DEFINITION

Example : « Offer over main land France High data rate links for Business tobusiness communications »

MAIN LAND FRANCE���� Shape of the coverage

BUSINESS TO BUSINESS communications���� Small dimension (and cost) ground stations (« Permis de construire : building licence»)

HIGH DATA RATE���� channel number / bandwidth���� utilisation mode : T.D.M.A, Spread spectrum, ...

����

E.I.R.P. on board����

antenna /transmission power of the satellite

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LINK BUDGETLINK BUDGET

����• Transmission Power ���� type of Transmitter

� existing or not� TWT or SSPA� Radiating collector or not

• Type of feed / reflector� multi or monofeed� fixed antenna, unfoldable, ...� traditional or bifrequencies or bipolarisation…

• Pointing Performances required� body or antenna pointed

• Station keeping window� On board transmission power� + satellite antenna gain� + satellite antenna pointing accuracy� +station keeping window (and/or ground antenna pointing)� + type of ground antennas �

NEED

CONSTRAINT

FRANCE COVERAGE + TRAFIC+

POSSIBLE SATELLITE CONFIGURATION (size, number of antennas)

LINK BUDGET

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TRAFFICTRAFFIC

• Channel bandwidth Total power• Power to be radiated ���� (consumed,• Channel number dissipated)• Utilisation mode

� TDMA � pulsed power demand� pointing « on demand » :

multifeeds + on board switching + connection matrix� eclipse or not � power supply architecture� permanent operations or not � Thermal conception

type of redundancies heatpipes

GENERAL ARCHITECTURE OF THE PAYLOAD

� Mass / power

� Constraints pointingpower supplythermalTM/TCstructures - mechanisms

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MISSION + LAWS���� CHOICE of an ORBITAL POSITION

MISSION + LAWS���� CHOICE of an ORBITAL POSITION

MISSION� See, from the covered zone, the satellite under a convenient angle� Choice of the eclipse hour (ex. in TV)

LAWS� Orbital Position predefined by international agreements � formerly TV (WARC 77)

Example : Western Europe at 19°W1user having an antenna oriented towards 19°W would have been able to receive France,Germany, Belgium, Luxembourg, Switzerland, Italy, Netherlands…

� Orbital Position where no other satellite is using the same frequencies in the sameearth direction � otherwise risks of interference

Orbital position chosen ���� declaration ���� negotiationWindow for station keeping���� rules O,1° in TV for instance� technical necessity : gain, pointing of users antennas

ORBITAL Position ���� GO and KEEP

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ORBITAL POSITION ϕϕϕϕ = - 7°ORBITAL POSITION ϕϕϕϕ = - 7°

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ORBITAL POSITION ϕϕϕϕ = -18°ORBITAL POSITION ϕϕϕϕ = -18°

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POSITION ORBITALE ϕϕϕϕ = - 25°POSITION ORBITALE ϕϕϕϕ = - 25°

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GEO satellites in orbit

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ORBITAL POSITION ���� GO ORBITAL POSITION ���� GO

LAUNCH• Compatibility with the launcher : mechanical, thermal, safety…• Transport to the launch base• Finish integration , test, fuel filling on the launch base• Launch windowTRANSFERT ORBITapogee, perigee, inclination, nodes position (of the sun)

� Can be adjusted to certain extend as a function of the mass to be launched, of the fuelsavailable in the spacecraft

� Ariane places on an orbit of approx. 200 - 36 000 km

STS was placing the satellites on a circular orbit of approximately 200 km

Proton has the possibility of injecting directly in GEO

� To reach the GEO orbit, it is then necessary to have :� on Ariane and most launchers, 1 apogee engine to circularise at 36 000 km� on STS, 1 perigee kick motor to raise the orbit at 200-36000 km + 1 apogee engine to

circularise at 36000 km

� Ariane places the satellites on an orbit inclined by approximately 7°launchers from US pads on an orbit inclined by 28°5

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LOCALISATION - ATTITUDE CONTROL OF the SATELLITE - CONFIGURATION

CHOICE OF ORBITS, OF FIRINGS INSTANTS, CHOICE OF the NETWORK OF GROUND STATIONS(for 1 satellite, 1 station theoretically sufficient for placing the satellite in position but...

ORBITAL POSITION ���� KEEP (to follow)ORBITAL POSITION ���� KEEP (to follow)

� To get to the geostationnary orbit, it is necessary to correct the inclination to 0° ���� PKMand/or AKM fired :� in the adequate direction� at the orbit node (i.e. at the right time)

� Apogee and orbit node are very close� Network of stations must permit a good visibility of the satellite in all critical manoeuvres,

especially at motor firings� Circularisation to be done close to the official and final orbital position to avoid a long

drift period� Limitation of the transfer orbit number because :

� braking due to the drag by the atmosphere at the perigee � the orbit must be quickly raised� crossing of the Van Allen belts � degradation of the electronics� thermal problems, batteries discharge

CHOICE OF ORBITS, OF FIRINGS INSTANTS, CHOICE OF the NETWORK OF GROUND STATIONS(for 1 satellite, 1 station theoretically sufficient for placing the satellite in position but…)

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ATTITUDE DURING THE TRANSFER ORBITATTITUDE DURING THE TRANSFER ORBIT

PROBLEMS

� Direction of the apogee engine at firing� thermal budget� power budget� TT&C (TM/TC) link budget ���� antenna configuration / transmission power

Note :� If high thrust (solid propellant), at firing, stabilisation by rotation is needed

� If unstable configuration� 3 axes control or active control of nutation

� If low thrust and low rotation speed of the satellite� possibility to unfold appendices such as Solar generator, antennas...

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DRIFT ORBITDRIFT ORBIT

After apogee motor firing ���� orbit is quasi circular

⊗ slow drift of the spacecraft

⊗ once the satellite on station, drift is suppressed

During the drift orbits, the satellite is progressively put inoperational configuration (antennas - SG - attitude)

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On station ���� keep positionOn station ���� keep position

Window for station keeping ex. 0,1° TV 0,05° TC2

� because « link budget » : pointing of user antennas� because « laws » : no interference

PROBLEMS :

• of accurate localisation� distance measurement� angular measurement� relative speed measurement(Doppler)

���� Station + computation

• of movement forecast���� Models + computation

• of movement capability - direction / amplitude ���� Ejection of mater

����

� perturbation of the satellite attitude � need to pilot� fuel storage� 6 engines eventually redunded (x, -x, y, -y, z, -z)

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KEEP THE ATTITUDEKEEP THE ATTITUDE

� Pointing the antennas towards the Earth

� Pointing the solar generator to the Sun

besides the satellite movements :• 1 turn / day around the Earth• perturbation on the attitude :

� due to solar pressure� generated by the satellite itself (expulsion of fuel)

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STABILISATION + PROPULSION

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CONSTRAINTSCONSTRAINTS

LAUNCHER

� Capacity : mass in orbit� Size of the fairing ���� - volume for satellite

- dimensions of antennas� Launch window ���� - satellite configuration� Safety rules : Especially for STS� mechanical, thermal environment…� Others : launch base…

REGULATIONS� International agreements� W.R.C./ I.T.U.� etc…

� Find an orbital position proper for the mission and not subjected to interference� Frequencies for TT&C (TM/TC) - Transmission Power� Satellite Coverage (ex. direct TV SL)

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SPACENET F1 SATELLITE in the ARIANE 1 FAIRINGSPACENET F1 SATELLITE in the ARIANE 1 FAIRING

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CONFIGURATION for SATELLITE LAUNCHCONFIGURATION for SATELLITE LAUNCH

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GENERAL CONFIGURATIONwith SYLDA in the FAIRING

GENERAL CONFIGURATIONwith SYLDA in the FAIRING

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G-STAR 1 AND TELECOM 1B in the ARIANE 3 FAIRING and SYLDAG-STAR 1 AND TELECOM 1B in the ARIANE 3 FAIRING and SYLDA

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POSSIBLE STANDARD FAIRINGS(volume offered)

POSSIBLE STANDARD FAIRINGS(volume offered)

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PERFORMANCE IN ELLIPTICAL ORBITS90° INCLINAISON (injection close to perigee)PERFORMANCE IN ELLIPTICAL ORBITS

90° INCLINAISON (injection close to perigee)

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CONSTRAINTS (continuation)CONSTRAINTS (continuation)

SPACE ENVIRONMENT

• Vacuum• Gravity• Sun / shadow• Eclipse : Earth, Moon• Radiations and particles

TEST FACILITIES - TRANSPORTATION MEANS

COST and DELAYS

� Reuse of the existing technologyex. : Reuse of existing buses

� Lifetime Reliability / RedundanciesAvailability Safety - Maintainability

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CONSTRAINTS FOR the LAUNCH WINDOWCONSTRAINTS FOR the LAUNCH WINDOW

� ORBIT CORRECTION AT APOGEEin visibility of 2 stations of the network and limited transfer duration

� LAUNCHER PERFORMANCES(including deviations)

� SOLAR ASPECT ANGLE (from injection to apogee)because problems :

- of power- of thermal management- of attitude determination

� ECLIPSE DURATION IN TRANSFERT ���� PERIGEE

� launch at 12 h impossible close to equinox� PRECISION OF THE ATTITUDE DETERMINATION

Attitude defined by directions of Earth and Sun� must be well separated

� APOGEE in the EQUATORIAL PLAN

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SEQUENCE for DEPLOYMENT in ORBIT of a 3 AXES SATELLITE :TRANSFER ORBIT

(first orbit)

SEQUENCE for DEPLOYMENT in ORBIT of a 3 AXES SATELLITE :TRANSFER ORBIT

(first orbit)

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THE DIFFERENT SUB-SYSTEMSOF A SATELLITE

THE DIFFERENT SUB-SYSTEMSOF A SATELLITE

BUS (or PLATFORM)

• Stabilisation• Propulsion• Apogee engine• Power• Structure - Mechanisms - Pyrotechnic• Thermal Control• Telemetry / Telecommand (TM/TC)• Harness

PAYLOAD

• Repeater• Antennas

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The VEHICLE and the PAYLOADto SERVE the MISSION

The VEHICLE and the PAYLOADto SERVE the MISSION

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OPERATIONS of the VARIOUS SUB-SYSTEMSOPERATIONS of the VARIOUS SUB-SYSTEMS