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Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS)

Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS). Murat Hasani. Introduction.

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Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS)

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  1. Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) Murat Hasani

  2. Introduction • French microwave tracking system and an uplink radio system based on the Doppler principle, requiring a host satellite (for the space segment package) and a global network of ground-based tracking stations, called Doris beacons. • DORIS system has been designed and optimized by the French space agency CNES, IGN (InstitutGéographique National), and GRGS (Groupe de Recherches en GéodésieSpatiale) to perform high precision orbit determination and beacon positioning.

  3. History • Developed in the framework of the TOPEX/POSEIDON oceanographic altimetry mission • Planning for the system started in 1983 and DORIS has been operated since 22nd Jan. 1990, when the first technology demonstration system (prototype payload) was launched on board the SPOT-2 spacecraft • The quality, density and homogeneity of the DORIS network have continuously improved throughout its 20 year evolution • The main evolution was the implementation of a Real-Time Precise Orbit Determination capacity called DIODE (Doris Immediate on-board Orbit Determination). It is advanced function of the DORIS receiver that computes the position and the velocity of the satellite. This capacity is embedded in the DORIS receivers since SPOT4

  4. Architecture • The DORIS system mainly consists of Space Segment where belongs satellites, then Ground segment with 3 types of centers and DORIS instrument.

  5. SpaceSegment • The Doris system was primarily designed for the precise orbit computation required for observing the oceans by altimetry. • DORIS receivers are flown on LEO satellites for precise orbit determination as well as for geodetic applications Table 1- Doris contributor satellites

  6. The orbit of SPOT satellites is polar, circular, sun-synchronous and phased Figure 1 - Satellites with the Doris system onboard and applications. Credits CLS/Cnes.

  7. GroundSegment • Ground Segment is responsible for the maintenance and operation of the DORIS constellation. The ground segment is comprised of the following elements: ●A beacon installation and management center at IGN coordinating the global network of orbit determination beacons (ODB) ●TheSSALTO (Segment Sol Altimetrie et Orbitographie) multi mission control center is operated by CLS (CollecteLocalisation Satellites) on behalf of CNES. ●Three master beacon sites - able to upload commands to the instrument: Toulouse, Kourou, and Hartebeetshoek. The master beacon sites are tied to an atomic clock, enabling synchronization of the DORIS system with TAI (International Reference Time)

  8. The ground stations in the various countries are generally hosted by the following institutions: National survey organizations; space agencies; institutes of astronomy, geophysics, or oceanography; universities; telecommunication stations; and meteorological stations Figure 2- Overview of the DORIS network as of 2007 and co-locations with other IERS techniques (image credit: CNES, IGN)

  9. DORIS Instruments • DORIS instrument is on-board DORIS receiver, developed by TAS (Thales Airborne Systems), receives the signals of the DORIS ground network through two RF chains (amplifiers, filters, mixers) at the frequencies: f1 =2036.25 MHz, and f2 = 401.25 MHz • With more satellites carrying the Doris instrument, the system will make more accurate than before • Doris system includes all the instruments onboard the carrying satellite (antenna, receiver, oscillator), an international network of autonomous stations spread around the globe and a control and processing center that calculates the orbit of the satellites.

  10. The DORIS on-board package includes: ●Two redundant processing chains, performing Doppler measurements and receiving auxiliary data from the beacons ●A fixed dual-frequency Omni-directional antenna ●A USO (Ultra Stable Oscillator) delivering the reference frequency with a specified stability of < 5 x 10-13 over periods from 10 to 100 seconds Table 3-Doris on-board package characteristics

  11. Diode, created by Cnes in 1991, is integrated software to the Doris instrument that calculates real-time location and very precise velocity of the satellite • Every 10 seconds, Diode runs a program that: ●acknowledges commands ●predicts the satellite's position using a model of its motion ●corrects the predicted position on the basis of Doris measurements (when the satellite is within view of a ground beacon) ●corrects the predicted position on the basis of Doris measurements (when the satellite is within view of a ground beacon) ●delivers the calculated position to the ground station

  12. Operation • In summary, the ground beacons broadcast signals, the Doris receiver onboard satellites makes the Doppler shift measurements and stores them in its internal memory • The data are relayed to the ground on each pass of the satellite over a station. Then they are sent to SSALTO at regular interval, the Doris mission control center in Toulouse, France • Since 1990 up to 2006, Doris has acquired over 100 million measurements for the international scientific community

  13. Services • The prime objective is to provide precise measurements for POD (Precise Orbit Determination) services and geodesy applications • The system concept is based on accurate measurements of the Doppler shifts on a radiofrequency signal (2 GHz and 400 MHz) transmitted by ground stations and received on-board orbiting satellites, carrying DORIS receivers, when they are in visibility of a station • The system can locate customer ground beacons with precision up to 1 cm depending on the duration and local observation conditions • The number of DORIS carrier satellites is unlimited

  14. The measurements and on-board products provided by the DORIS receivers can be used in the following applications: ●POD support for altimetry and other missions ●Orbit control (either on-board or on ground) ●Ground beacon positioning ●Geophysical modeling (Earth gravity field, atmosphere, ionosphere, Earth pole motion monitoring, etc.) ●Integrity control of the DORIS system. Table 2- DORIS beam positioning performance

  15. Signal specifications • As was mentioned system is using two frequencies: VHS band signal at 400Mhz and S-band frequency 2Ghz for measurement. Antenna has right hand circular polarization • The power transmitted at transmitter box output is 7 W ± 1 W on the 400 MHz channel and 15 W ± 1 W on the 2 GHz channel • Modulation is synchronous with the carrier signal as both are generated from reference clock signal. Used modulation is PCM/SPL/PM bi-phase. The bit rate is 200 bits/s synchronous with the reference clock (USO or external atomic clock)

  16. Thank you for your attention

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