Drift mode accelerometry for spaceborne gravity measurements

Abstract

A drift mode accelerometer is a precision device that overcomes the much of the acceleration noise and readout dynamic range limitations of traditional electrostatic accelerometers. It has the potential of achieving acceleration noise performance of drag-free systems over a restricted frequency band without the need for external drag-free control or spacecraft propulsion. Like traditional accelerometers, the drift mode accelerometer contains a high-density test mass surrounded by an electrode housing, which can control and sense all six degrees of freedom of the test mass. Unlike traditional accelerometers, the suspension system is operated with a low duty cycle so that the limiting suspension force noise only acts over brief, known time intervals, which can be neglected in the data analysis. The readout is performed using a laser interferometer which is immune to the dynamic range limitations of even the best voltage references typically used to determine the inertial acceleration of electrostatic accelerometers. The drift mode accelerometer is related to the like-named operational mode of the LISA Pathfinder spacecraft, which will be used to estimate the acceleration noise associated with the LISA Pathfinder front end electronics. This paper describes operation of such a device, develops models for its performance with respect to satellite geodesy and gravitational wave astrophysics applications, and discusses methods for testing its performance using torsion pendula in the laboratory and the LISA Pathfinder mission in space.