On constellation design of multi-GNSS radio occultation mission

The FORMOSAT-3/COSMIC mission which is a joint Taiwan-US mission for meteorological, climatological, ionospheric, and geodetic studies has successfully provided a significant amount of GPS radio occultation (RO) data for better modeling of climate model, forecasting of weather, and monitoring of ionosphere. Owing to the success of the FORMOSAT-3 program, the follow-on FORMOSAT-7 mission is being planned. In the perceivable future, sources for RO mission can be originated from multiple global navigation satellite systems (GNSSs) including GPS, Galileo, GLONASS, and Beidou as well as several regional navigation satellite systems (RNSSs) and space-based augmentation systems (SBASs). To facilitate the operational capability for weather forecast and space weather monitoring, the FORMOSAT-7 constellation must be designed to ensure a sufficient and uniform distribution in space and time for GNSS/RNSS/SBAS RO events. In addition, it is desired that the RO events in certain region can be maximized to account for severe weather. As the distribution of RO events due to GNSS, RNSS, and SBAS are distinct and the requirements appear to be multi-objective, the constellation design becomes very complicated. The paper applies genetic algorithm (GA) to design constellation parameters. It is shown that the adopted approach can be used to account for non-uniform distribution of RO events due to RNSSs and SBASs. The GA-based design approach is demonstrated to result in constellations that are superior in both global distribution and regional emphasis of RO events to those of the existing baseline design.