Precise Orbit Determination of Satellites with Low-Cost, Single Frequency Receivers in raPPPid

Abstract

Nanosatellites, particularly CubeSats, are being extensively used for Earth observation, scientific experimentation, atmospheric research, communication, and emerging LEO-based PNT (Positioning, Navigation, and Timing) missions. Hence, precise knowledge of satellite position and velocity is crucial to support both standalone CubeSat missions and large constellations. In this work, we present enhancements to the open source raPPPid software package to perform Precise Orbit Determination (POD) for LEO platforms using an Extended Kalman Filter (EKF). The state prediction is performed by incorporating the satellite’s dynamical model, and observation correction is implemented by pseudo-range and carrier-phase measurements. Group and Phase Ionospheric Correction (GRAPHIC) Linear Combination (LC) method is implemented to mitigate the ionospheric delay, and Doppler measurements are used for robust cycle-slip detection to accurately estimate float ambiguities, in low-cost, single-frequency receivers. Observation weighting and exclusion are governed by elevation angle and boresight angle criteria. Boresight angle criterion improves orbit accuracy and performs efficient observation handling, especially, for satellites with rear-facing antennas. Validation is conducted on the Astrocast nanosatellite constellation, where low-cost receiver results yield a 3-D root mean square error (RMSE) of the post-fit residuals on the order of a few decimeters. As for high-quality geodetic receivers, such as the GNSS receiver onboard the Sentinel-3A satellite, the RMSE reduces to a few centimeters. The resulting ephemerids archive, formatted in SP3c, supports future space-based applications, e.g. measuring the dynamics of composition and density of Earth’s upper atmosphere, and holds promise for real-time onboard application, e.g. by incorporating the Galileo High Accuracy Service (HAS) into orbit determination approach. These developments open the door for more autonomous, effective, and scalable navigation systems in future space missions, and highlight the possibility of low-cost GNSS-based POD for nanosatellites.