Cold atom interferometer accelerometry for future satellite gravimetry missions

Kurzfassung

For more than a decade satellite gravimetry missions like GRACE, currently GRACE-FO and in the future planned missions like NASA's GRACE-II and ESAs NGGM measure the change of the global gravity field. These gravity field solutions, typically with a monthly temporal resolution, show the mass redistribution in the ice shields, the oceans and on land on scales of a few hundreds of kilometres. Additionally, measurements of individual sensors of the satellites are used, e.g., to determine properties of the atmosphere by analysing the non-gravitational forces acting on the satellite, which are measured with the accelerometer at its centre of mass. After the improvement of the GRACE ranging system by the implementation of a laser ranging interferometer (LRI) in GRACE-FO, the focus of current developments is on the advancement of the accelerometers used in future missions to increase spatial and temporal resolution. In recent years, cold-atom interferometry (CAI) based inertial sensors have matured from laboratory sized experiments to robust transportable instruments, including first commercial applications, for terrestrial gravimetry. CAI was also demonstrated in challenging environments on sounding rockets and the International Space Station, making this technique the prime candidate for the next generation accelerometer on a satellite by offering absolute and drift-free measurements. We investigate different scenarios of GRACE type missions, based on the LRI and CAI accelerometers in combination with classical electrostatic sensors. Potentially, the CAI accelerometer also offers the possibility to better determine degree 2 gravity field coefficients, due to its long-term stability. A closed-loop simulator has been developed to test different scenarios of orbit configurations and system/instrument parameters. Regarding the orbit configurations, parameters like inter-satellite distance, orbit altitude and repeat cycle are varied. The results will be evaluated based on recovered gravity fields. As a further benefit, the concept of a CAI based drag-free control system is investigated and its impact on possible satellite orbits for NGGMs and the resulting gravity fields is discussed. As the control system is of critical importance for the success of the mission, key parameters are analysed. Furthermore, the requirement for drag compensation depends on the knowledge of the accelerometer's scale factor. Related to this aspect, requirements on drag compensation are derived for different scenarios. We will present first results of the simulation studies. H.W. acknowledges support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy - EXC 2123 "QuantumFrontiers, Project-ID 390837967". A.K. acknowledges initial funding for the DLR Institute by the Ministry of Science and Culture of the German State of Lower Saxony from "Niedersächsisches Vorab".