Determination of Spherical Test Mass Kinematics with Modular Gravitational Reference Sensor

Abstract

A modular gravitational reference sensor is stand-alone sensor for gravitational wave detection, inertial navigation, and fundamental physics experiments in space. In a modular design, measurement of the mass center of a drag-free test mass is made with respect to reference surfaces fixed to the spacecraft. In a gravitational wave detection scheme, the same reference surfaces are used to independently measure the distance between sensors on separate spacecraft. A single spinning spherical test mass is used as the gravitational reference, with several interferometers used to measure the mass center location relative to the spacecraft housing. This paper develops an analytical model for the modular gravitational reference sensor output including all first-order contributions. With this model, we evaluate systematic errors in the mass center measurement due to geometric variations which place requirements on spacecraft attitude and test mass dynamics. We also present a fast and reliable algorithm for recovering the mass center location and spin frequency of the test mass, in real time, to the required level of accuracy from the sensor data.