Methods to determine thermal sensitivity of T-SAGE instrument for MICROSCOPE mission

Abstract

MICROSCOPE is a space mission launched in 2016 that aims to test the validity of the Equivalence Principle (EP), the main postulate of General Relativity (GR), with a precision never reached before (Touboul et al., 2001). EP states that two bodies of different compositions and masses fall with the same acceleration in the same gravitational field. In order to achieve this goal, MICROSCOPE's instrument is composed of two identical electrostatic differential accelerometers. MICROSCOPE will be the first lab to realize an experiment to test the EP in space which allows to break free from perturbations other than gravity. Those tests used to be presented in terms of the Eötvös ratio η . The first result published in December 2017 shows no evidence of violation higher than 1.3 ×10^-14 at 1 σ on η (Touboul et al., 2017). This result was obtained with only 7% of the whole data, so the statistical uncertainty would be improved with the analysis of the complete data. During the experiment some thermal variations could disturb the estimation of the Eötvös parameter. In order to better estimate the thermal systematic effect, the thermal sensitivity has to be determined. To do so, thermal stimulus are induced on the instrument by means of dedicated heaters and the response in the measured acceleration is analysed. Two methods were applied for theses analysis and will be presented in this paper. The first one operates in the time domain and the second one in the frequency domain. Those methods allow us to obtain a thermal systematic of 8.6 ×10^-16 which represents an improvement by one order of magnitude with respect to the result of Touboul et al. (2017).