Development of a virtual environment for quantum technologies on satellite based next-generation gravimetry missions

The success of GRACE-FO and its predecessors has demonstrated to the scientific community the benefits of satellite gravimetry for monitoring mass variations on the Earth’s surface and its interior. However, the demand for increasingly higher spatial and temporal resolution of gravity field solutions has brought into focus the need for next-generation gravimetry missions (NGGMs). To this end, the German Aerospace Center (DLR) has established the Institute for Satellite Geodesy and Inertial Sensing, which investigates the potential of quantum technologies for NGGMs. Currently, quantum sensors for gravity field satellite missions are being developed, which include cold atom interferometry (CAI) gradiometers and optical clocks. In addition, quantum accelerometers and quantum inertial sensors are being studied for the application on satellites. NGGM concepts are analyzed using the Hybrid Simulation Platform for Space Systems (HPS) developed by ZARM (University of Bremen) and DLR. With the adaptation of HPS for the French MICROSCOPE mission, HPS was already capable of simulating the dynamics of the satellite and its test masses on a helio-synchronous orbit in an altitude of 700 km. The simulation included environmental models for the atmosphere, magnetic field, radiation, and gravity field, as well as a detailed model of the on-board capacitive sensors. Efforts have been made to extend the simulation platform to include quantum sensors. This introduces new challenges for pointing accuracy and noise determination, which place more stringent requirements on the computation of environmental disturbances in lower orbits suitable for NGGMs. Therefore, satellite vibration and thermal models are being investigated for use in HPS, with the goal of providing a complete testbed for quantum technologies in gravimetry missions. This paper presents the current status of the research

Kalman-Filter Based Hybridization of Classic and Cold Atom Interferometry Accelerometers for Future Satellite Gravity Missions

Proof-of-principle demonstrations have been made for cold atom interferometer (CAI) sensors. Using CAI-based accelerometers in the next generation of satellite gravimetry missions can provide long-term stability and precise measurements of the non-gravitational forces acting on the satellites. This would allow a better understanding of climate change processes and geophysical phenomena which require long-term monitoring of mass variations with sufficient spatial and temporal resolution. The proposed accuracy and long-term stability of CAI-based accelerometers appear promising, while there are some major drawbacks in the long dead times and the comparatively small dynamic range of the sensors. One interesting way to handle these limitations is to use a hybridization with a conventional navigation sensor. This study discusses one possible solution to employ measurements of a CAI accelerometer together with a conventional Inertial Measurement Unit (IMU) using a Kalman filter framework. A hybrid navigation solution of these two sensors for applications on ground has already been demonstrated in simulations. Here, we adapt this method to a space-based GRACE-like gravimetry mission. A simulation is performed, where the sensitivity of the CAI accelerometer is estimated based on state-of-the-art ground sensors and further published space scenarios. Our results show that the Kalman filter framework can be used to combine the measurements of conventional inertial measurement units with the CAI accelerometers measurements in a way to benefit from the high accuracy of the conventional IMU measurements in higher frequencies together with the high stability of CAI measurements in lower frequencies. We will discuss the challenges, potential solutions, and the possible performance limits of the proposed hybrid accelerometry scenario

Reference mirror misalignment of cold atom interferometers on satellite-based gravimetry missions

The success of GRACE-FO and its predecessors has demonstrated the benefits of satellite gravimetry for monitoring mass variations on the Earth’s surface and its interior. However, the demand for increasingly higher spatial and temporal resolution of gravity field solutions has brought into focus the need for next-generation gravimetry missions (NGGMs). Therefore, we investigate the hybridization of electrostatic accelerometers (E-ACC) with cold atom interferometers (CAI), which can reduce the instrumental error contribution of the E-ACC, e.g. by enabling in-flight estimation of E-ACC bias parameters, and reduce systematic effects in gravity field solutions by proving drift free measurements. However, these sensors introduce more stringent requirements on the computation of environmental disturbances in lower Earth orbits, as the alignment of the CAI’s reference mirror has to be controlled precisely. Therefore, the movement of the CAI’s reference mirror inside the satellite is analyzed using the Hybrid Simulation Platform for Space Systems (HPS) developed by DLR and ZARM (University of Bremen). Misalignments and vibrations of the reference mirror cause an additional CAI phase shift, which introduces measurement inaccuracies. Our work examines the translational displacement, rotational misalignment and angular velocity of the reference mirror, due to forces transferred by the coupling link between mirror and satellite. This helps to compare different hybridization concepts and to improve noise and signal models for CAI accelerometers

The Benefit of Accelerometers Based on Cold Atom Interferometry for Future Satellite Gravity Missions

Satellite gravity missions, like GRACE and GRACE Follow-On, successfully map the Earth's gravity field and its change over time. With the addition of the laser ranging interferometer (LRI) to GRACEFO, a significant improvement over GRACE for intersatellite ranging was achieved. One of the limiting factors is the accelerometer for measuring the non-gravitational forces acting on the satellite. The classical electrostatic accelerometers are affected by a drift at low frequencies. This drawback can be counterbalanced by adding an accelerometer based on cold atom interferometry (CAI) due to its high long-term stability. The CAI concept has already been successfully demonstrated in ground experiments and is expected to show an even higher sensitivity in space. In order to investigate the potential of the CAI concept for future satellite gravity missions, a closed-loop simulation is performed in the context of GRACE-FO like missions. The sensitivity of the CAI accelerometer is estimated based on state-of-the-art ground sensors and predictions for space applications. The sensor performance is tested for different scenarios and the benefits to the gravity field solutions are quantitatively evaluated. It is shown that a classical accelerometer aided by CAI technology improves the results of the gravity field recovery especially in reducing the striping effects. The non-gravitational accelerations are modelled using a detailed surface model of a GRACE-like satellite body. This is required for a realistic determination of the variations of the non-gravitational accelerations during one interferometer cycle. It is demonstrated that the estimated error due to this variation is significant. We consider different orbit altitudes and also analyze the effect of drag compensation

Quantum technology for future earth observation from space - gradiometry case

In various geoscience disciplines, there is a huge interest in knowing the mass variations of the Earth with high resolution and accuracy. It is vital for monitoring climate change processes to define corresponding requirements for the sensor technology and for possible satellite missions. The future satellite missions will strongly depend on the advancement of novel technology and beneficial observation concepts of the Earth gravitational field. In this study, various quantum and hybrid gradiometer concepts are first characterized and corresponding error properties are described. Here, special attention is paid to Cold Atom Interferometry (CAI) accelerometers and gradiometers that will perfectly supplement the classical electrostatic concepts due to their white noise behavior at low frequencies. Those, accelerometers and gradiometers using atom interferometry have great potential for increasing the accuracy of future gravity satellite missions. We will compare hybrid with classical electrostatic gradiometers (as also used in GOCE) and illustrate their different spectral behavior as well as their mutual benefit. Using simulated atom-interferometric and hybrid gradient measurements along one or more gradiometer axes in GOCE-like orbits, we determine the gravity field in spherical harmonics coefficients for the various cases and discuss the pros and cons of the selected concepts

Cold Atom Interferometry Accelerometers for Future Low-Low Satellite-to-Satellite Tracking and Gradiometry Missions

The interest in a higher spatial and temporal resolution of the Earth's gravity field is large in various disciplines and especially important in relation to climate change. We analyze possible improvements of the accelerometers for future satellite gravity missions. The classical electrostatic accelerometers suffer from their low-frequency drift and are the limiting factor on the instrument side. The Cold Atom Interferometry (CAI) accelerometers with their long-term stability would complement the classical accelerometers very well. Different accelerometer performance models are tested within a closed-loop simulation and the corresponding gravity field solution is recovered. An improvement and the reduction of the North-South striping effects are shown when using a hybrid accelerometer. However, the low sampling rate of the CAI sensor leads to aliasing effects due to the variation of the acceleration signal. The well know scale factor of the CAI measurements, on the contrary, is a great advantage. According to these two aspects, several altitudes and drag compensation scenarios are investigated. Furthermore, a combination of the two measurement concepts low-low Satellite-to-Satellite Tracking and gradiometry is studied. A more isotropic error pattern is achieved when adding to a low-low Satellite-to-Satellite Tracking a hybrid gradiometer in cross-track direction

Cold Atom Interferometry Accelerometry for Future Low-Low Satellite-to-Satellite Tracking and Cross-track Gradiometry Satellite Gravity Missions

Satellite gravity missions give unprecedented insights in the Earth system. However, a further improvement in spatial and temporal resolution is required to better monitor the various geo-processes. When considering the sensors of satellite missions, the accelerometers are the limiting factors. Cold Atom Interferometry (CAI) accelerometers are characterized by their long-term stability and an accurate knowledge of the scale factor. Closed-loop simulations are performed in order to quantify the influence of different accelerometer performances on the gravity field recovery. The impact of the scale factor knowledge on the acceleration measurement is evaluated in terms of a requirement based on the non-gravitational acceleration signal and the accelerometer noise. Furthermore, the variation of the non-gravitational acceleration signal within one interferometer cycle is studied. It is demonstrated that both aspects are significant. The impact on the acceleration measurements can be reduced to an acceptable level by drag compensation. Moreover, the addition of a CAI cross-track gradiometer to a low-low Satellite-to-Satellite Tracking mission is investigated, as supplemental observations in east-west direction are provided. This combination enhances the estimation of the high-degree coefficients and reduces the striping effects in north-south direction. We acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project-ID 434617780 - SFB 1464 and under Germany's Excellence Strategy - EXC-2123 Quantum-Frontiers - 390837967 and the support by Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) for the projects Q-BAGS and QUANTGRAV

Cold atom interferometry accelerometry for future low-low satellite-to-satellite tracking and cross-track gradiometry satellite gravity missions

International audienc

Cold atom interferometry accelerometry for future low-low satellite-to-satellite tracking and cross-track gradiometry satellite gravity missions

International audienc