Title: Advancement of a Simplified Gravitational Reference Sensor for Future Geodesy Missions
Presenting Author: John W. Conklin
Organization: University of Florida
Co-Author(s): Stephen Apple, Lea Bischof, Joseph Conroy, Anthony Dávila Álvarez, Stephen Bennett, Riccardo Bevilacqua, Joseph Footdale, Zane Forrester, Paul Fulda, Jacob Gambrill, Bill Gavert, John Hanson, Victoria Kennedy, Ryan Kinzie, Andres Leyton, Cole Perkins, Jose Sanjuan, Thomas Schwarze, John Siu, Chad Sypolt, 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 Embry-Riddle Aeronautical University 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 ~20 times more sensitive than the GRACE accelerometers and ~100 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. We are currently developing the TRL 6 version of the S-GRS and optimizing it for non-drag-compensated platforms. A potential microsatellite technology demonstration mission, called GRATTIS (Gravity Recovery Advanced Technology Test In Space), has been proposed for the second half of this decade. This presentation will describe the S-GRS, its development timeline, and the prospects for testing the performance of the sensor in low Earth orbit.