The Galileo for science (G4S_2.0) project: a new concept of accelerometer for future Galileo satellites

The G4S_2.0 project, funded by the Italian Space Agency (ASI), aims to test fundamental physics in the field of the Earth by using the satellites of the Galileo FOC Constellation. Three Italian research centers are involved in the project: ASI-CGS in Matera, Politecnico di Torino and IAPS-INAF in Rome which is the project lead institution. We will present one of the ongoing activities at IAPS-INAF, regarding the development of a new accelerometer for a next generation of Galileo satellites. As well known in the literature of the Global Navigation Satellite Systems (GNSS), the precise modeling of the Non-Gravitational Perturbations (NGPs) represents today the most important challenge for a further and significant improvement of the Precise Orbit Determination (POD) of all navigation satellites and, consequently, of all products that can be obtained from the analysis of the orbits and clocks of the satellites of the GNSS. Indeed, the suboptimal modeling of the direct Solar Radiation Pressure (SRP) ⎯ the largest NGPs on the orbit of Galileo FOC satellites and in general of all navigation satellites ⎯ is currently the main source of error in determining their orbit. 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 continuously pointsto the nadir while the face near the atomic clocks points to the deep space and 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 POD process a non-trivial issue. Consequently, the capability to perform direct measurement, by means of an onboard accelerometer, of the accelerations produced by the complex and subtle non-gravitational forces acting on the satellite's surfaces is considered an extremely important and significant system improvement for the direct impact it would have on the accuracy of the POD of satellites and on the products that the GNSS community derives from it in the fields of positioning, timing, geophysics and fundamental physics. We will present the main characteristics of the accelerometer concept under development, giving an overview of its working principle and expected measurement performance. Furthermore, we will introduce a methodology to remove the thermal disturbances on the accelerometer readings at low frequencies.