Satellite Orbit Determination with the Global Educational Network for Satellite Operations

1. Satellite Orbit Determination with theGlobal Educational Network for Satellite Operations • AMSAT-UK Colloquium 2010 • Ivo Klinkert, PA1IVO

2. Project Overview • MSc project Computer Science Nice combination of part-time study and hobby besides daily job • 'Two alternative approaches to orbit determination' • Orbit determination because: 1. 'NORAD‘ might stop providing TLEs 2. Scientifically interesting 3. Help during LEOP (not exactly topic of my research) • Based on GENSO ground station network Will work with any collection of amateur radio like ground stations

3. Orbit Determination with GENSO • Is GENSO able to create TLEs by itself? Problem statement of the research project • GENSO not designed for orbit determination Uses prediction based on TLEs, does not measure • GENSO has a lot of resources, connected together Collect many low-accuracy observations • No operational GENSO available during research

4. Orbit Determination Problems for Project • No distance measurements possible • No direct angle measurements possible • No direct frequency measurements possible Doppler shift should give speed relative to ground station • Relatively low-profile ground stations In principle un-calibrated measurements Low-profile with respect to orbit determination

5. Simulation Model of GENSO (1) • Simulation model required Testing of orbit determination methods • Simulation of satellite reception by GENSO Ground stations, antennas, receivers, satellite, reception,… Combination of theory and practice (thanks to many HAMs) • SGP4 to simulate satellite position and speed Integration of existing SGP4 Java library (thanks to Dave G4DPZ) One SGP4 instance to simulate 'real' orbit • Configurable Different experiments can be performed Too many parameters to do all combinations!

6. Simulation Model of GENSO (2) Ground stations – based on Delfi-C3 RX reports (thanks!)

7. Simulation Model of GENSO (3) Simulation model system architecture

8. Orbit Determination Algorithms (1) • Two different methods/algorithms for my project • First method: 'Static mode' orbit determination No initial information about orbit Based on ground track reconstruction principle • Second method: ‘tracking mode' orbit determination Some signals will be received with the initial TLE Based on artificial intelligence search principle

9. Orbit Determination Algorithms (2) • Simplification: circular orbit No determination of argument of perigee and eccentricity For LEO orbits only a small error • Based on reception of satellite signals only Most generic approach, a satellite will at least transmit some data • Many other were considered, but not used AFC, discriminator readings, SDRs, … • Only basic equipment Unmodified IC-910H/TS-2000/…., standard antennas • Central entity for orbit determination 'control'

10. Static Mode Orbit Determination – Principles (1) • Insufficient information to track satellite Only frequency of satellite is known • Wait for satellite to pass over Antennas up, fixed receiver frequency: 'static' • Observations measure 'position' and time Averaging of observations, average point-in-time • The orbit is reconstructed Reconstruction based on ground track reconstruction

11. Static Mode Orbit Determination – Principles (2) • One observation filtered out per pass • Longitude correction For rotation of the Earth For nodal regression (in iterations)

12. Longitude-corrected (inclination visible) Static Mode Orbit Determination – Principles (3) Uncorrected

13. Static Mode Orbit Determination – Principles (4) • Orbital period Find multiple time period between nearly the same locations • Inclination Projection of rotated observations Least-squares fit • RAAN / MA

14. Static Mode Orbit Determination: Results After 2 days, TLEs are obtained that could be used to track satellites with GENSO.

15. Tracking Mode Orbit Determination (1) • Usable TLE is available • Ground stations track the satellite Following with antenna and receiver: 'tracking' • Trial-and-error hill-climbing search By varying orbital parameters in TLEs Mutual influences on parameter values One parameter searched at a time • Different ground stations test different TLEs • Smart quality measurement Comparison between predicted and the real observations

16. Tracking Mode Orbit Determination (2)

17. Tracking Mode Orbit Determination (3)

18. Tracking Mode Orbit Determination: Results After 5 to 7 days, reception quality between 90 and 100%, except for some low inclination orbits.

19. Conclusions and Future Work • Proof-of-concept for orbit determination with GENSO • Methods developed for entire lifetime of satellite • Not as accurate as NORAD, but sufficient • Static mode better than tracking mode But during tracking mode reception of data is possible • Test when GENSO gets operational • Adapt to real-world behavior of GENSO

20. Acknowledgements • ESA For the organization and sponsoring of GENSO • People from GENSO For good discussions and the work done so far • Radio amateurs from AMSAT For good discussions and advices. Thanks folks! • AMOLF For support in time, money, and offering flexibility • Family For support now and in the past

21. Questions? Thesis at: http://www.xs4all.nl/~ivok/genso-ou/ThesisOrbitDetermination.pdf