  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.
