The Galileo for science (G4S_2.0) project: non-gravitational perturbations models and precise orbit determination with SLR data

The G4S_2.0 project, funded by the Italian Space Agency, aims to test fundamental physics in the terrestrial field using the satellites of the Galileo FOC Constellation and, in particular, the two satellites GSAT0201 and GSAT0202 in eccentric orbit. Three Italian research centers are involved in the project: ASI-CGS in Matera, Politecnico di Torino and IAPS-INAF at Roma Tor Vergata. We present some of the ongoing activities at IAPS-INAF, which is Prime of the project. The activities undertaken have as main final objectives: i) the measurement of the relativistic precessions of the orbits of the satellites, ii) to place constraints on a possible violation of the Local Position Invariance (LPI) through an accurate measurement of the Gravitational Redshift, iii) to place constraints on the presence of dark matter in our Galaxy, and iv) to develop a new concept of accelerometer for a future generation of Galileo satellites. These activities therefore concern both the analysis of the orbits of satellites and those of the atomic clocks they carry. In particular, an activity is underway to improve the dynamic model of the orbits of satellites starting from the direct solar radiation pressure (SRP), the largest non-gravitational perturbation (NGP) on Galileo satellites and in general on all satellites of the Global Navigation Satellite Systems (GNSS) constellations. We have developed a Box-Wing (BW) model of the satellite using the information provided by ESA and a 3D model of the same to be used for a finite element analysis based on the ray-tracing technique, once all surfaces and elements of the satellite will be adequately characterized. We also started preliminary analyses of the orbits of Galileo FOC satellites based on laser tracking data. Our goal from this point of view is to improve the Precise Orbit Determination (POD) of the satellites by jointly using laser tracking data (in particular the Full Rate ones) and the microwave tracking data. For this goal, as underlined, a key role will be played by the improved dynamic model of the spacecraft: we plan to use increasingly sophisticated BW models up to the construction, if possible, of a finite element model (FEM) of the satellite. We will present the preliminary results obtained in the development of the spacecraft model and those obtained for the satellites orbit determination.