Modeling of non-conservative forces for the Galileo-FOC spacecraft

Suboptimal modeling of direct Solar Radiation Pressure (SRP) is currently the main source of error in determining the orbit of any type of spacecraft of the Global Navigation Satellite System (GNSS). The complex shape of these satellites (bus and wings) combined with their particular attitude law – which requires the face of the satellite that collects the different antennas to continuously point to the nadir and deep space the face near which the atomic clocks are located, while at the same time the array of solar panels must continuously point towards the Sun for energy reasons – make the modeling of this perturbation and its optimal insertion into the Precise Orbit Determination (POD) process a non-trivial issue. We will present the results for the perturbative accelerations produced by solar and terrestrial (albedo and infrared) radiation in the case of a Box-Wing model built using the ESA Galileo metadata. The Yaw Steering law for the spacecraft attitude was also include in our model. The Box-Wing model and a 3D model of the satellite were also incorporated into the s/w COMSOL for a preliminary activity on the use of the Ray-tracing technique. Our final aim is, in fact, to build a Finite Element Model of the satellite and apply an ad hoc Ray-tracing for the calculation of the different perturbations related to the radiation pressure, also considering umbra and penumbra effects and multiple reflections. This activity is part of those of the Galileo for Science project (G4S 2.0) funded by ASI. The main objectives of G4S 2.0 are in the field of Fundamental Physics and a POD of the Galileo satellites based on a reliable dynamic model, in particular for Doresa and Milena, the two satellites in elliptical orbit, is of primary importance.