Sensor and performance modelling of an optical accelerometer for future gravity field missions

Abstract

Electrostatic accelerometers (EA) are one of the limiting factors of space gravimetry missions dominating the error contribution at low frequencies (<10e-3Hz). The focus of this study is on the modelling of an optical accelerometer that can improve gravity field retrieval to unprecedented accuracy. Contrary to GRACE(-FO) or GOCE accelerometers, optical accelerometers sense the motion of the test mass (TM) in one or more axes by applying laser interferometry. Combination of sensing in multiple directions and of several test masses would lead to enhanced gradiometry which would improve the determination of the static gravity field to a higher spatial resolution. Modelling of the above-mentioned accelerometer blocks in Matlab Simulink allows to simulate various TM measurement scenarios for satellite missions under different conditions, e.g. dedicated satellite configurations, various non-gravitational forces, etc. This research is based on very promising results of the mission LISA-Pathfinder (LPF) which has demonstrated the benefit of a drag-free system in combination with optical accelerometry that allowed sensing of non-gravitational accelerations several orders of magnitude more accurate than those of current gravity missions like GRACE-FO. This research project is carried out in close collaboration with the IGP and the DLR-SI, to provide - on the long run - a roadmap for improved angular and linear accelerometry for the next generation of gravity field missions. In this presentation, we now introduce a functional model of 6 degrees-of-freedom (DoF) optical accelerometer and compare its output with the measurements of electrostatic accelerometers for the dual satellite configuration, i.e. GRACE-FO mission. Also, the current state of the Simulink implementation of the accelerometer model which are mainly developed by IGP are presented. Finally, the simulated gravity gradients from the novel gradiometer based on the optical accelerometers are demonstrated as well as benefits that can be acquired from this sensor.