Modelling and simulation of the space mission MICROSCOPE

Abstract

MICROSCOPE is a French space mission for testing the weak equivalence principle (WEP). The mission goal is the determination of the Eötvös parameter $\eta$ with an accuracy of 10⁻¹⁵. The French space agency CNES is responsible for the satellite which is developed and produced within the Myriade series. The satellite's payload T-SAGE (Twin Space Accelerometer for Gravitation Experimentation) is developed and built by the French institute ONERA. It consists of two high-precision capacitive differential accelerometers. One accelerometer is used as reference sensor with two test masses of platinum, the science sensor contains a platinum and a titanium proof mass. The detection of the test mass movement and their control is done via a complex electrode system. As a member of the MICROSCOPE performance team, the German department ZARM will be involved in the data analysis of the MICROSCOPE mission. For this purpose, mission simulations and the preparation of the mission data evaluation in close cooperation with the French partners CNES, ONERA and OCA are realised. The development status of the simulation tool which will represent the complex spacecraft dynamics and all error sources in order to design and test data reduction procedures is presented and some features are discussed in detail.

Introduction

The French MICROSCOPE mission is designed to test the weak equivalence principle (WEP) by the determination of the Eötvös factor $\eta$ with an accuracy of 10⁻¹⁵ [1], [2]. This parameter describes the difference of the ratio of gravitational to inertial mass of two macroscopic bodies:

$$\eta ={\left(\frac{m_{\mathrm{g}}}{m_i}\right)}_{\mathrm{mass}1}-{\left(\frac{m_{\mathrm{g}}}{m_i}\right)}_{\mathrm{mass}2}\text{.}$$

The WEP states that the Eötvös parameter turns out to zero.

The mission will be carried out on a CNES satellite that will use drag-free technology to compensate for all non-gravitational accelerations. The payload T-SAGE (Twin Space Accelerometer for Gravitation Experimentation) [3] consists of two high-precision capacitive differential accelerometers and is developed and built by the French institute ONERA. This instrument is also part of the satellite's drag-free control system. In order to achieve the mission objective this system has to reduce the residual drag to less than $3\times {10}^{-10}\mathrm{m}{\mathrm{s}}^{-2}/\sqrt{\mathrm{Hz}}$ [4].

At the Center of Applied Space Technology and Microgravity (ZARM) two different work packages are executed. As part of the pre-mission test program free-fall tests in the drop tower are used to study the instrument performance and to verify its functionality [5]. In order to prepare the mission analysis a comprehensive simulation of the satellite and instrument dynamics as well as the interaction with the space environment is developed at ZARM. Therefore the High Performance Satellite Dynamics Simulator (HPS) is adapted and refined for the MICROSCOPE mission. This paper focuses on this simulation tool, presenting the overall architecture, showing first steps of the integration of the MICROSCOPE instrument and giving some details on the modelling of surface forces.