Capacitive sensing for drag-free satellites

We report the key results of a study of the optimization of capacitive sensing for LISA. This work was a component of an ESA study into drag-free satellite control. We discuss the problems associated with the capacitive sensing and control of a proof mass which is electrically isolated and develop models for candidate non-resonant and resonant detection schemes. We calculate acceleration noise assuming an ideal control system whose only noise sources are the capacitive sensors and actuators. On the basis of this model it appears that the design goal of acceleration noise for the LISA mission is achievable using both resonant and non-resonant detection schemes. The residual acceleration noise on the proof mass is dominated by oscillator noise which produces force and displacement noise due to asymmetries in the electrode capacitance values and bridge components.