Performance of a Large Reaction Compensated Fast Steering Mirror

In this paper, the performance of a Fast Steering Mirror (FSM) is measured and compared to the predictions of a simple set of coupled differential equations. The FSM has a 24-cm diameter optical element, is capable of ±3 mrad angular motion, and uses a reaction mass to cancel torques arising from the mirror motion that would otherwise couple into an optical bench. Local position sensors provide feedback for closed-loop control. Quantities such as angular stroke versus input signal, mechanical assembly frequency response, power consumption versus frequency and effective resistance and inductance as a function of frequency are presented and compared to the theoretical predictions. Reaction attenuation characteristics are covered in some detail. In addition, control system measurements (open loop response, closed loop response, and error attenuation) are given and compared to expectations. Very good agreement between theoretical predictions and experimental results were achieved in most areas.