Two BeiDou-3 navigation satellites that previously struggled with orbit inconsistencies due to solar radiation pressure are now operating with vastly improved precision, thanks to an innovative hybrid modeling approach developed by researchers from Chang'an University.
Illustration of a Beidou-3 satellite above the Earth. Credit: CASC
The anomalies in the satellites, C223 and C222, arose after they were equipped with Medium Earth Orbit Search and Rescue (MEOSAR) payloads. These payloads, which were added to enhance satellite functionality, disrupted the satellites' symmetry and created challenges in accurately modeling the effects of solar radiation pressure (SRP). Standard models like ECOM2 were unable to adequately account for these changes, leading to inconsistencies in orbit predictions.
To address this, the team combined a physically-based Adjustable Box-Wing (ABW) model with the empirical ECOM2 framework. This hybrid approach significantly reduced laser ranging residuals by more than 60%, vastly improving the reliability of real-time orbit predictions. The new model accounts for the unique way sunlight interacts with the asymmetric MEOSAR payloads, which had previously caused inaccuracies.
Published on June 2, 2025, in Satellite Navigation, the study introduced two ABW variants—ABWX and ABWMX—each tailored to different payload orientations (+X or -X side). The researchers tested these against traditional methods, developing four hybrid strategies (S1-S4) that incorporated the ABW-derived solar force estimations into the ECOM2 model. This combination resulted in a dramatic reduction in residual standard deviations, from 7.8 cm to 3 cm, and significantly improved short-term orbit prediction accuracy and boundary continuity.
The study found that the configuration where the payload was mounted on the +X side delivered the best performance. Furthermore, the team devised a method for operational integration, creating a priori SRP models using Fourier-transformed ABW data, which allows for precise orbit corrections without adding extra computational burden.
"This study resolves a long-standing issue in satellite orbit modeling," said Prof. Guanwen Huang, the corresponding author of the study. "By identifying the root cause of the orbit inconsistencies and developing a strategy that updates with each orbit arc, we've greatly improved the reliability of BeiDou-3. Our approach not only enhances these specific satellites but sets a new standard for how satellites with complex or asymmetric payloads should be modeled in the future."
The hybrid modeling technique has broader implications beyond BeiDou-3. Its precision and adaptability make it a promising solution for future Global Navigation Satellite Systems (GNSS), including updates to the Galileo and GPS constellations. With its balance of physical accuracy and real-time applicability, the new approach represents a significant leap forward for satellite navigation systems worldwide.
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