Simplified Precise Orbital Determination Approaches and Results from GPS Measurements Onboard Low Earth Orbiting Satellites

Ning Zhou and Yanming Feng

Abstract:	Precise Orbit Determination (POD) is a well-defined enabling technology for determination of satellite orbit states to the accuracy of 1 meter or better for GNSS satellites or low earth orbit satellites using GNSS measurements. However, the existing POD strategies normally involve sophisticated dynamics models, large number of parameters, complicated estimation algorithms, and require long arcs of observations to achieve the centimetre accuracy. The process normally is undertaken on ground, resulting in considerable solutions latency. This research develops so-called “simplified precise orbit determination” (SPOD) strategies in order to address near-real time or real time onboard GPS-based LEO orbit determination requirements. Targeting the 3D orbit accuracy of sub-metre to metre level using flight measurements, the simplification strategies are applied to the dynamical models and integration, measurement standardisation and estimation aspects. This paper covers two major aspects: dynamical model simplifications and short-arc orbit estimations. To orbital dynamical models, simplification focuses on implementation of the gravity approximation algorithms following the pseudo-centre strategy. Numerical results have confirmed that we can still retain the accuracy of a full model with the computing load equivalent to that of a 5 5× gravity model, at a cost of additional few Mbytes storage. A short-arc least-square filter with sliding-window processing method was used and tested to assure stable solutions while keeping the computing time short. In addition, the short-arc technique can tolerate dynamic orbital modelling errors, allowing good orbit accuracy with simplified precise orbit models. Results from GPS SAC-C flight data have shown that with a data arc of 2 hour (1 orbit period= 100 minutes), the 3D position RMS accuracy of 1.2 m can be achieved at latency of 10 ~ 20 minutes. The 3D RMS accuracy of 80cm was reached with the same data set of 24 hours, but the computing time is about 30 times longer. In general, the proposed simplification strategies for precise orbit determination have performed well for the testing data. Relying on flight GPS data only, the approaches are applicable for ground-based real time satellite tracking and onboard orbit determination.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1180 - 1190
Cite this article:	Zhou, Ning, Feng, Yanming, "Simplified Precise Orbital Determination Approaches and Results from GPS Measurements Onboard Low Earth Orbiting Satellites," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1180-1190.
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