Ad Astra: Simultaneous Tracking and Navigation With Megaconstellation LEO Satellites
Zaher M. Kassas, Nadim Khairallah, Sharbel Kozhaya
Abstract
A framework to exploit megaconstellation low Earth orbit (LEO) satellite signals of opportunity for navigation is developed. This framework, termed simultaneous tracking and navigation (STAN), estimates the navigating vehicle's states simultaneously with the states of orbiting LEO satellites. STAN employs a cognitive receiver that exploits megaconstellation LEO satellite downlink signals to produce navigation observables: pseudorange, Doppler, and/or carrier phase. These observables are fused through an extended Kalman filter (EKF) to aid the vehicle's inertial navigation system (INS) in a tightly coupled fashion. Simulation results are presented demonstrating the efficacy of the STAN framework. These simulations assumed the aerial vehicle to be equipped with an altimeter and a tactical-grade inertial measurement unit (IMU), navigating for 15.43 km in 300 seconds, in which GNSS signals were only available for the first 60 seconds. It is demonstrated that the final three-dimensional (3-D) position error and position root mean squared error (RMSE) of a typical tightly-coupled GNSS-aided INS grows to 1,536 m and 897 m, respectively. In contrast, the STAN framework with 77 LEO satellites (resembling Orbcomm, Iridium NEXT, and Starlink constellations) achieved a final 3-D position error and position RMSE of 15.2 m and 7.3 m, respectively with pseudorange measurements, and 37.1 m and 10.6 m, respectively with Doppler measurements. In addition, the first multi-constellation LEO navigation experimental results of their kind are presented of a ground vehicle traversing 4.15 km in 150 seconds, in which GNSS signals were only available for the first 80 seconds. It is shown that while the final 3-D position error of the vehicle's GNSS-aided INS with a tactical-grade IMU and an altimeter grew to 472.7 m and the 3-D position RMSE grew to 118.5 m; in contrast, the final 3-D position error and position RMSE of the STAN framework with received signals from 2 Orbcomm, 1 Iridium NEXT, and 3 Starlink LEO satellites were 27.1 m and 18.4 m, respectively.