GNSS-Based Dual-Constellation and Dual-Frequency Real-Time Reduced-Dynamics P2OD for LEO Satellites

Francesco Darugna, Stefano Casotto, Massimo Bardella, Mauro Sciarratta, Paolo Zoccarato, Pietro Giordano

Abstract: Onboard GNSS-based satellite navigation is becoming a reality due to the need for current and planned Earth observation missions to be equipped with real-time, high-accuracy positioning. In this perspective, an existing Precise Onboard Orbit Determination (P2OD) software (SW) tool, developed at the University of Padua, has been used as a starting point for an upgrade to a higher level of performance to meet the needs of real-time onboard navigation. The current features of the SW are presented along with a solution quality analysis. The SW is based on Extended Kalman Filter (EKF) using a reduced-dynamics approach. The force model implemented is comparable to those used in high-accuracy, ground-based processing, employing empirical accelerations to take into account residual force mismodeling. A test case using Sentinel-3A GPS dual-frequency data is analyzed. The computed orbit has been compared to the official ESA precise ephemeris over an 18-days period, showing a 7.6 cm and a 14.5 cm 3D RMS difference when using IGS final products and IGC products, respectively. Moreover, we investigate the use of stale ancillary data (Earth Orientation Parameters (EOP) and Solar And Geomagnetic Activity (SAGA) data) with a latency of several days—a relatively common situation for missions not supported by an extensive ground-station network. It is described how outdated ancillary data impact the solution depending on the reference frame used to model empirical accelerations. The reduced-dynamics approach is exploited to ensure the state vector prediction capability also during GNSS data outage. Here, we report on the results obtained for a selenocentric orbit (LRO mission data), showing a 3D RMS difference w.r.t. published estimated orbits lower than 5 m after three orbital periods. Finally, the current developments are described in the context of the onboard technology demonstration ESA/GOMspace GOMX-5 CubeSat mission within the DEIMOS G3PSTAR GNSS receiver in the second half of 2022. These include the capability to process dual-constellation, i.e., GPS and Galileo data, and the Galileo High Accuracy Service (HAS) corrections.
Published in: Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021)
September 20 - 24, 2021
Union Station Hotel
St. Louis, Missouri
Pages: 1004 - 1017
Cite this article: Darugna, Francesco, Casotto, Stefano, Bardella, Massimo, Sciarratta, Mauro, Zoccarato, Paolo, Giordano, Pietro, "GNSS-Based Dual-Constellation and Dual-Frequency Real-Time Reduced-Dynamics P2OD for LEO Satellites," Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021), St. Louis, Missouri, September 2021, pp. 1004-1017. https://doi.org/10.33012/2021.18033
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