# Hybrid Electrostatic-Atomic Accelerometer for Future Space Gravity Missions
###### Abstract  
Long-term observation of Earth's temporal gravity field with enhanced temporal and spatial resolution is a major objective for future satellite gravity missions. Improving the performance of the accelerometers present in such missions is one of the main paths to explore. In this context, we propose to study an original concept of a hybrid accelerometer associating a state-of-the-art electrostatic accelerometer (EA) and a promising quantum sensor based on cold atom interferometry. To assess the performance potential of such an instrument, numerical simulations were performed to determine its impact in terms of gravity field retrieval. Taking advantage of the long-term stability of the cold atom interferometer (CAI), it is shown that the reduced drift of the hybrid sensor could lead to improved gravity field retrieval. Nevertheless, this gain vanishes once temporal variations of the gravity field and related aliasing effects are taken into account. Improved de-aliasing models or some specific satellite constellations are then required to maximize the impact of the accelerometer performance gain. To evaluate the achievable acceleration performance in-orbit, a numerical simulator of the hybrid accelerometer was developed and preliminary results are given. The instrument simulator was in part validated by reproducing the performance achieved with a hybrid lab prototype operating on the ground. The problem of satellite rotation impact on the CAI was also investigated both with instrument performance simulations and experimental demonstrations. It is shown that the proposed configuration, where the EA's proof-mass acts as the reference mirror for the CAI, seems a promising approach to allow the mitigation of satellite rotation. To evaluate the feasibility of such an instrument for space applications, a preliminary design is elaborated along with a preliminary error, mass, volume, and electrical power consumption budget. cold atom interferometer; electrostatic accelerometer; hybrid accelerometer; gravity mission; quantum space gravity; satellite geodes +
Footnote †: journal: remote sensing  
0000-0002-314-3273-222  
unique technique that enables the detection of sub-surface storage variations of groundwater or sub-glacial water mass exchanges, which are generally difficult to access from other remote sensing techniques. It also contributes to the quantification of all relevant processes of the global water cycle, allowing directly estimating their contribution to sea level rise. Future satellite gravity missions are expected to provide enhanced sustained observations with increased spatio-temporal resolution, higher accuracies, and new products that could directly be incorporated into operational services such as early warning of hydrological extremes and monitoring of geo-hazards. Moreover, the enhanced measurements shall contribute to the improvement of essential climate variables (ECV) with unprecedented quality for ground water, as well as unique measurements for climate applications, Earth energy balance closure, sea level change, mass balance of ice sheets and glaciers, heat and mass transport, etc. The largest error contributor of state-of-the-art missions that monitor the time-variable gravity field (e.g., GRACE and GRACE-FO) is the effect of temporal aliasing. This issue arises, on the one hand, from the poor observation geometry conditioned by the satellite pair's near-polar orbit, i.e., the east-west behavior of the gravity signal and its variations are known with a reduced accuracy. On the other hand, due to the limited temporal resolution, neighboring ground tracks may feature highly different signal content, which then manifests as typical north-south stripes in the gravity solution, as temporal variations are misinterpreted as spatial ones. The ESA/NASA MAGIC mission concept [1] is a well-designed satellite constellation that aims to tackle this limitation.