Joseph Locantore and Franco Gottifredi, WAY4WARD s.r.l., Italy

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Abstract:

The recent interest in the exploitation of GNSS for Lunar missions has brought new challenges not only in the development of products for the faced scenario, but also in the tests of the new implemented algorithms. This work proposes the application of the GNSS Outer Orbits Data Simulator (GOOD Sim) tool, internally developed by WAY4WARD s.r.l., for the generation of trajectory, GNSS visibility and raw data measurements aimed at the preliminary validation of orbit and attitude determination products. The GOOD Sim consists of three main modules: the Trajectory Definition, the Visibility Analysis, the Raw Data Generator; each of them with a dedicated User Interface (UI). The first module includes an orbit propagator for the estimation of the receiver satellite’s trajectory, in the inertial reference frame, through the numerical integration of the geocentric orbital equations of motion for a Moon Transfer Orbit (MTO). Currently, the dynamic model includes the gravity’s acceleration of the Earth, Sun and Moon as well as the Solar Radiation Pressure, but additional forces have been planned to be introduced in the future versions. The Visibility Analysis module provides the GNSS Space Vehicles’ orbits, geometric and electromagnetic satellite’s visibility divided for receiver antennas, transmitter lobes and ionosphere affected signals. The Raw Data Generator computes the measurement’s errors at the selected frequency and combines them with the true range according to the visibility analysis estimating the raw GNSS measurements code phase (pseudorange) and carrier phase for the chosen mission scenario. The proposed tool has been adopted for the test of the Enhanced Precise Orbit Determination (EPOD) algorithm for lunar mission that is based on an Extended Kalman Filter with a single frequency Ionosphere-free multi constellation measurement’s model and whose performance are presented in the paper.