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DIODE: On-Board Orbit Determination for Satellite Positioning and Velocity Assessment

DIODE function on-board satellites provides real-time position/velocity data and TAI time-tagging with quality assessments. It offers ancillary products like Doppler reduction and is valuable for both platform and payload operations, as well as for ground processing. DIODE has been successfully used by various users for optical terminal pointing, image rectification, and vegetation-related tasks. The system employs a Kalman filter, Runge-Kutta numerical integration, and ionospheric error measurements for accurate orbit determination. The on-orbit results show high accuracy, availability, and reliability, meeting specified requirements. The DIODE system continuously evolves and offers improved functionalities for different missions and satellites.

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DIODE: On-Board Orbit Determination for Satellite Positioning and Velocity Assessment

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  1. DIODE • On-Board Orbit Determination function, providing : • satellite position/velocity (plus a quality assessment), • TAI time-tagging (plus a quality assessment), • ancillary products (next beacon, expected Doppler, …), • elaborated on-board and in real-time every ten seconds. • Products are useful for : • platform and payload, • ground processing of the data (images, altimetry, …), • DORIS receiver (self-programming and reduction of Doppler tolerances).

  2. DIODE / SPOT4 • A probatory experiment ... • validation of the concept (routine filter only), • limited amount of memory on a dedicated card, • software completed in June 1995. • … but already with users of the products : • POAM (NRL, for optical terminal pointing), • SPOT IMAGE (ground immediate and precise rectification), • VEGETATION (idem), • DIODE monitoring and R&D evolutions.

  3. DIODE / SPOT4 : main features • Only the routine Kalman filter : • prediction/correction every ten seconds, • state vector : position, velocity, frequency & tropospheric biases. • Extrapolation model : • Runge-Kutta numerical integration (Gill), • force model = 15x15 E.G.F., nominal thrust accel. • Measurement model : • ionospheric error (two-frequency measurement), • on-board clock estimated with Master Beacons.

  4. DIODE/SPOT4 on-orbit results

  5. DIODE / SPOT4 conclusions • After more than two years : • accuracy = a few meters RMS, • availability > 99.6% (unavailable 62h over 750 days), • meet specifications (200 m MAX) > 99.7%), • good behaviour during manœuvers (see paper). • users of the products : • POAM several times a day (near poles), • SPOT IMAGE : DIODE is the nominal source for image positionning, • VEGETATION (permanent since July 1999).

  6. DIODE / Jason-1 • Complete mission, including : • improved dynamical model, • improved autonomy : • self-initialisation (« lost in space »), • self-programming of the DORIS receiver, • TAI (or TUC) time-tagging of external events. • Users of the products : • quick-look processing of altimetric data, • possible use by the platform, • and by (SPOT5) the ground Control Center.

  7. DIODE / Jason-1 : main evolutions • New functionnalities : • self-initialisation algorithm (4 passes, two filters), • receiver programming (prediction of the next-to-come beacon, optimal choice, Doppler shift). • Improved models : • adjusted : Earth pole coordinates, Hill accelerations, thrust accelerations, • force model = 40x40 optimised E.G.F., moon&sun attractions, solar pressure (box&wings), air drag, • improved quality assessments.

  8. DIODE/TOPEX ground results • (64 bits SPARC processor)

  9. DIODE / Jason-1 objectives • Performances : • routine accuracy : goal = 1m RMS 3D, a few centimeters radial RMS (between 5 and 14), • self-initialisation mean time =1 hour, • time determination (goal= a few microseconds), • operationnal use of the self-programming mode. • Availability : • goal = 100 % .

  10. DIODE future perspectives • Already planned : Jason-1, SPOT5, ENVISAT, • T.B.C : PLEIADES (SPOT follow-on), • On Skybridge, DORIS/DIODE has been evaluated as technically acceptable, • Currently under study : • ISS (ACES), ATV, CRYOSAT, ALTIKA, • Navigation dedicated DORIS receivers...

  11. DIODE/TOPEX cy 232 radial errors • (64 bits SPARC processor)

  12. DIODE/TOPEX radial errors • (64 bits SPARC processor)

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