Improved test of the Weak Equivalence Principle: First scientific results of the MICROSCOPE mission
Final Report Abstract
The space mission MICROSOCPE was launched in April 2016 in order to test the Weak Equivalence Principle (WEP) with an accuracy never achieved before. The WEP is the central principle underlying General Relativity and in the focus of experimental physics since many decades. In the German scientific community, only ZARM has primary access to the mission data which allows the participation in the first science data analysis of MICROSCOPE. The focus of the project activities at ZARM was on the preparation of an end-to-end simulation environment for the MICROSCOPE mission. Therefore, a Matlab/Simulink model including all mission specific parameters and the related framework has been implemented and tested, including the development and integration of source code. A coupled differential equation system describes the motion of five bodies in the Earth’s gravitational field: (i) the satellite and (ii) the four test masses. Their geodesic motion is disturbed by the influence of several environmental conditions, e.g. the Earth’s atmosphere, the magnetic field of the Earth, and the Solar Radiation Pressure (SRP). Furthermore internal errors and noises have to be considered within the mission simulation approach. Therefore, suitable noise models based on mission design documents have been implemented. The completed mission simulator has been used to create so-called mock data sets based on specificly chosen simulation scenarios. These mock data sets are assumed to be the best artificially produced data sets because they contain all available information about the mission design and the orbital environment as well as onbord coupling effects. Mock data sets are of critical importance for a deeper understanding of the influence of disturbances and for the testing of data evaluation procedures. The mock data challenge (MDC) proposed in the original application could not be carried out as planned, since a sensible execution needs two teams (or at least more than one person) involved in this task. A MDC is thought to test the data evaluation procedures without any investigator knowledge of the composition of the mock data files. Consequently, a restriction to one person involved in this task made a MICROSCOPE MDC ineffective. Nevertheless, mock data sets have been used to test the developed Flight Data Evaluation Tool (FDET). This tool is used for the science data analysis at ZARM during and after the operational phase of the mission. It is developed based on algorithms which are used to (i) transcript binary data files and to (ii) combine their content with linked attributes into a new “ZARM”-format. This data format is the basis of the ZARM data analysis. Furthermore, so-called wavelet transformation methods have been studied and have been found useful to complete the FDET. This method allows to determine whether there are disturbing non-stationary events within the data sets. This analysis approach was not included within the initial proposal. Though, after first promising results we decided to pursue this approach. Besides the completion of the MICROSCOPE mission simulator and the works regarding mock data and wavelet analysis, a detailed study of the impact of disturbances acting on the satellite due to SRP has been performed. It was shown that the forecast of disturbances connected to SRP strongly depends on the chosen geometry model of the satellite. A more detailed geometry model based on finite elements offers the opportunity to additionally take into account surface properties including material degradation effects. This may result in a modulation of science signals because of periodically changing SRP drag force due to oscillating illumination conditions on the satellite’s surface. This particular work was not initially proposed. However, present publications reveal a strong interest on SRP dependent disturbances in orbit. The preliminary science result of the MICROSCOPE mission is confidential until its official announcement on December 4th, 2017. In parallel, the accuracy of this WEP test will also be published in the renowned journal Physical Review Letters. This procedure is based on an internal agreement signed by all participating organisations.
Publications
- Analysis of the impact of temporal disturbances on the science signals of the space mission MICROSCOPE by using wavelet transformation tools, Proceedings of the 66th International Astronautical Congress, Jerusalem, Israel (2015)
H. Selig, A. Gierse, S. Bremer, M. List, B. Rievers
- Modelling of solar radiation pressure effects: Parameter analysis for the MICROSCOPE mission, International Journal of Aerospace Engineering vol.2015, 14 (2015)
M. List, S. Bremer, B. Rievers, H. Selig
(See online at https://doi.org/10.1155/2015/928206) - Advanced Thermal Radiation Pressure modeling and its benefits for the MICROSCOPE mission, Adv. Astro. Sci. 158 (2016)
B. Rievers, M. List, S. Bremer
- Extended Analysis on The Free-Molecular Flow Effects on a GRACE-Like Satellite, Adv. Astro. Sci. 158, 2983–2996 (2016)
T. Kato, F. Wöske, B. Rievers, M. List
- Generic Computation Method of Free-Molecular Flow Effects on Space Objects, Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan 14 (ISTS 30), 105–110 (2016)
T. Kato, B. Rievers, M. List
(See online at https://doi.org/10.2322/tastj.14.Pd_105) - Wavelet analysis for the MICROSCOPE mission, Proceedings of the 67th International Astronautical Congress, Guadalajara, Mexico (2016)
H. Selig, A. Gierse, S. Bremer, B. Rievers, M. List
