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During its lifetime in space, the attitude and the orbit of a satellite are influenced by different perturbations resulting from the space environment. On the one hand, these natural boundary conditions have an impact on the design of the satellite, for instance thermal shielding or the design of the propulsion system. On the other hand, these disturbances may affect any data which is exchanged between a satellite and its ground station. Thus, the modelling and propagation of satellite motion is one of the central tasks in mission analysis. For this purpose, the High Performance satellite dynamics Simulator (HPS) is utilised, a tool that is developed by ZARM in cooperation with the DLR Institute of Space Systems.

It has been argued for quite some time that commonly used SRP models like the Cannonball and the Wing-Box model are not sufficient enough for an accurate SRP analysis if the involved geometries differ from a spherical shape or a standard bus and solar panel assembly. This paper will give a short overview on the implications of accurate SRP modelling for the example mission MICROSCOPE and the expected improvement of the implementation of non-gravitational disturbances modelling.

MICROSCOPE is a French space mission for testing the Weak Equivalence Principle (WEP). The mission goal is the determination of the Eötvös parameter with an accuracy of 10⁻¹⁵. This will be achieved by means of two high-precision capacitive differential accelerometers, that are built by the French institute ONERA. At the German institute ZARM drop tower tests are carried out to verify the payload performance. Additionally, the mission data evaluation is prepared in close cooperation with the French partners CNES, ONERA and OCA. Therefore a comprehensive simulation of the real system including the science signal and all error sources is built for the development and testing of data reduction and data analysis algorithms to extract the WEP violation signal. Currently, the High Performance Satellite Dynamics Simulator (HPS), a cooperation project of ZARM and the DLR Institute of Space Systems, is adapted to the MICROSCOPE mission for the simulation of test mass and satellite dynamics. Models of environmental disturbances like solar radiation pressure are considered, too. Furthermore detailed modeling of the on-board capacitive sensors is done.

The MICROSCOPE space mission aims at testing the Equivalence Principle (EP) with an accuracy of 10⁻¹⁵. This principle is one of the basis of the General Relativity theory; it states the equivalence between gravitational and inertial mass. The test is based on the precise measurement of a gravitational signal by a differential electrostatic accelerometer which includes two cylindrical test masses made of different materials. The accelerometers constitute the payload accommodated on board a drag-free micro-satellite which is controlled inertial or rotating about the normal to the orbital plane. The acceleration estimates used for the EP test are disturbed by the instruments physical parameters and by the instrument environment conditions on-board the satellite. These parameters are partially measured with ground tests or during the integration of the instrument in the satellite (alignment). Nevertheless, the ground evaluations are not sufficient with respect to the EP test accuracy objectives. An in-orbit calibration is therefore needed to characterize them finely. The calibration process for each parameter has been defined.