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1
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)
����
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