Solar Radiation Pressure Modeling for the QZS1 Satellite

Kurzfassung

Solar Radiation Pressure (SRP) is the dominant non-gravitational perturbation of Global Navigation Satellite Systems (GNSSs). The system considered in this thesis is the Japanese regional satellite navigation system QZSS that is currently made up of one single satellite, called QZS-1. The good accuracy of the Earth gravity fields makes the modeling of the non-gravitational perturbations significant for the Precise Orbit Determination (POD). The SRP modeling is therefore an important goal to improve the navigation performance of a satellite such as QZS-1. The SRP depends on the surfaces of the satellite involved, in particular it depends on the optical and geometrical properties of the surfaces. In the absence of detailed information about these properties and, therefore, in the absence of detailed models, empirical SRP, such as the Empirical CODE Orbit Model (ECOM), are used for GNSS orbit determination. The problem is that it requires a significant number of parameters to describe in a good way the real motion. Two different models of the SRP are developed: an analytical model and a ray-tracing model. The first one is a generic box-wing model based on the previous work of DLR about the SRP analysis for the European Galileo system while the second one is built up the previous work about the SRP analysis for the GOCE satellite at the University of Padova. A new reference frame is introduced in the analytical description of the SRP in order to consider both the attitudes used by QZS-1, the Yaw-Steering mode and the Orbit-Normal mode. The box-wing model is related to the corresponding parameters of the ECOM. The validation of the box-wing model in a Precise Orbit Determination gives as result an a priori model of the SRP for the QZS-1 satellite. The orbits obtained using this model show a consistent improvements in the quality of the orbit for both YS and ON attitude modes, in terms of Day Boundary Discontinuities (DBDs), SLR residuals and clock residuals. The ray-tracing approach gives an accurate model based on a CAD geometry of the spacecraft. The comparison between the two models in orbit determination suggests that the a more accurate model, such as the ray-tracingmodel, could improve the POD of QZS-1 even more than a box-wing model. Nevertheless to completely explain the remaining discrepancies between the analytical model and the observed orbital perturbations a more detailed modeling of thermal re-radiation, more detailed information about the true attitude, and offsets between the nominal and actual solar panels are needed.