VDE-SAT Ranging for Critical Navigation
Characteristics of Experimental VDE-SAT Ranging Signals and System Performance Analysis for Critical Navigation
Øyvind Pettersen (TU Delft - Aerospace Engineering)
Jose van den Van Den Ijssel – Mentor (TU Delft - Astrodynamics & Space Missions)
Sven-Ingve Rasmussen – Graduation committee member (Space Norway)
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Abstract
Traditional Global Navigation Satellite Systems (GNSS) are subject to intentional or unintentional disturbances in the northern regions of Norway, leading to loss of critical infrastructure. The novel VHF Data Exchange System (VDES) has been suggested as an alternative positioning, navigation and timing (PNT) system for a possible GNSS contingency service, based on signal simulations and statistical estimates. However, an empirical investigation into the feasibility of such a GNSS contingency service remains to be done, and has only recently become possible after the launch of the NorSat-TD satellite with purpose-designed VDES ranging capabilities. This paper presents an analysis of the characteristics of empirical VDE-SAT range measurements and a system-level performance analysis of a GNSS-contingency system based on the signal performance of empirical ranging data gathered from NorSat-TD. Using the equated error level of the signal, the positioning performance of simulated autonomous systems of VDE-SAT PNT-sources is analysed, followed by an assessment of the combination of the empirical VDE-SAT range measurements and traditional GNSS measurements in a critical GNSS contingency scenario. In total, 236 VDE-SAT pseudorange observations obtained from eleven satellite passes recorded in July 2023 were used. Residual analysis shows that these observations have a large and constant mean error of about 416 km, with a standard deviation of 260.8 m. The previously neglected atmospheric propagation effects on a VDE-SAT range measurement is shown to be significant, and the largest effect is likely to be the time-delay due to the ionosphere. The system performance analysis shows that VDE-SAT as a PNT-source could be used as a possible future general navigation backup system, with a positioning accuracy within 1000 m. Finally, an important conclusion is that a contemporary GNSS-contingency system is possible with the measured signal performance, where NorSat-TD acting as a PNT-source can, under the correct geometric conditions, allow a positioning accuracy within 1000 m in combination with partial GNSS coverage at the user.