A Simplified Gravitational Reference Sensor for NASA’s Mass Change Mission and Beyond

The University of Florida, is leading a team that includes Caltech/JPL, Ball Aerospace, Fibertek, Inc, CrossTrac Engineering, Texas A&M University, and the University of Central Florida to develop a Simplified Gravitational Reference Sensor (S-GRS), an ultra-precise inertial sensor optimized for future Earth geodesy missions. Inertial sensors like the S-GRS are used to measure or compensate for all non-gravitational accelerations of the host spacecraft so that they can be removed in the data analysis to recover spacecraft motion due to Earth’s gravity field, the main science observable. Low-low satellite-to-satellite tracking missions like GRACE-FO that utilize laser ranging interferometers are technologically limited by the acceleration noise performance of their electrostatic accelerometers, as well as temporal aliasing associated with Earth’s dynamic gravity field. The S-GRS is estimated to be at least 40 times more sensitive than the GRACE accelerometers and more than 500 times more sensitive if operated on a drag-compensated platform. The S-GRS concept is a simplified version of the flight-proven LISA Pathfinder GRS. Our performance estimates are based on models vetted during the LISA Pathfinder flight and the expected Earth orbiting spacecraft environment based on flight data from GRACE-FO. The improved performance is enabled by removing the small grounding wire used in the GRACE accelerometers and replacing it with a UV photoemission-based charge management system, enabling more massive test masses and larger gaps between the test mass and its housing. We have shown that the increased S-GRS performance allows future missions to take full advantage of the improved sensitivity of the GRACE-FO Laser Ranging Interferometer (LRI) over microwave ranging systems in the gravity recovery analysis. A specific version of the S-GRS, optimized for NASA’s Mass Change Mission, is also under study as part of that mission’s Phase A development. This presentation will describe the S-GRS, its development timeline and performance estimates.