The Galileo for Science project: Precise Orbit Determination and force-modeling for the Galileo FOC satellites

The Galileo for Science Project (G4S_2.0) is an ongoing project funded by the Italian Space Agency that has several goals in the field of Fundamental Physics by exploiting the Galileo-FOC Constellation and, in particular, GSAT-0201 and GSAT-0202, the two FOC in elliptical orbit. The high eccentricity of their orbits and the accuracy of their atomic clocks allow to measure gravitational redshift and relativistic precessions of the orbits. These results will place new constraints on possible alternative theories of gravitation, both metric and non-metric in their structure. Furthermore, constraints on the presence of Dark Matter in our Galaxy can be placed by analysing data of the satellites’ atomic clocks.

In this framework a fundamental point is obtaining a suitable satellite orbit solution by performing an accurate Precise Orbit Determination (POD). To this purpose modeling, as better as possible, the complex effects of the Non-Gravitational Perturbations (NGPs) is essential. In particular, the direct Solar Radiation Pressure (SRP) represents the main source of error in determining the orbit of any GNSS spacecraft, as it is the largest NGPs perturbation.

Our final goal is to build a refined Finite Element Model (FEM) of the Galileo FOC spacecraft to compute the perturbing accelerations that will be used in the POD procedure.

As an intermediate step a Box-Wing (BW) model, as well as a 3D-CAD of the spacecraft, have been developed. We will present the results for the perturbing accelerations produced by SRP, Earth’s infrared radiation and Earth’s albedo in the case of a BW model built using the ESA Galileo metadata.

Moreover, accounting for multiple reflections and mutual shadowing effects is crucial to improve the POD and the scientific results. To this purpose we apply the so-called Ray Tracing technique to the spacecraft FEM. We will present our ongoing work on this technique by using the software COMSOL and Matlab on the current development we obtained for the FEM.

Finally, by using the residuals in the orbital elements obtained from a POD, we can test our new models and the improvements in the quality of the POD. In order to prove the reliability and robustness of the scientific results that will be obtained within G4S_2.0, we aim to exploit both GEODYN II and the Bernese software for the POD.