Performance Demonstration of Gravitational Reference Sensors using a Torsion Pendulum

The University of Florida is developing a Simplified Gravitational Reference Sensor (S-GRS), an ultra-precise inertial sensor optimized for future geodetic missions. These sensors enable recovery of spacecraft motion due to Earth's gravity field by measuring and compensating for all non-gravitational accelerations in data post-processing. Our torsion pendulum facility allows for on-ground testing of the GRS with a force sensitivity on order of pN/Hz^-1/2, and is equipped with full electrostatic actuation authority and sensing with a broadband noise performance of 30 nm/Hz^-1/2. A novel contactless UV-photoemission based device for precision charge control of the Test Mass (TM) is also integrated within the system. Originally designed for GRS testing of the Laser Interferometer Space Antenna (LISA) space-based gravitational wave detector, it allows for investigation and characterization of all facets of the GRS head that will be implemented on the new Gravitational Reference Advanced Technology Test In Space (GRATTIS) mission.

The pendulum can be used to simulate non-gravitational accelerations such as drag and environmental effects by imparting a physical torque on the torsional member. This is then compensated for using feedback-controlled electrostatic actuation to keep the TM centered. In this presentation, an analytical model is compared with experimental results to build a comprehensive understanding of these effects.