Title: A Simplified Gravitational Reference Sensor for Future Geodosy Missions                    
Presenting Author: John Conklin
Organization: University of Florida
Co-Author(s): Eric Bradley, Joseph Controy, Anthony Dávila Álvarez, Stephen Bennett, Riccardo Bevilacqua, Neil Doughty, Joseph Footdale, Zane Forrester, Paul Fulda, John Hanson, Harold Hollis, Moad Isteita, Victoria Kennedy, Ryan Kinzie, Guido Mueller, James Leitch, Jennifer Lee, Glenn McDaniel, Cole Perkins, Jose Sanjuan, John Siu, Robert Spero, Mark Storm, Brent Ware, Peter Wass, David Wiese

Abstract:
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 non-drag-compensated platforms, is also under study as a potential technology demonstration on NASA's Mass Change mission. This presentation will describe the S-GRS, its development timeline, and performance estimates.