Six-degree-of-freedom magnetically suspended fine-steering mirror

Fine-steering mirrors (FSM) have been used for many years to provide accurate pointing and image motion compensation. The major limitation to the device is the flexure suspension system. These flexures limit the angular travel of the mirror and represent a single-point failure if they break, thus requiring careful design to reduce stress. To eliminate these design and performance issues, Ball Aerospace has developed a magnetically suspended fine-steering mirror (MSFSM). This mechanism eliminates the need for the flexure suspension system and requires acceptable amounts of power by using high-efficiency electromagnetic actuators. Other benefits include the elimination of destabilizing suspension bending modes and the ability to control telescope focus and collimation with this single device. This paper discusses a 6-DOF MSFSM, completed in 1990, that matches the operational capabilities of high- performance flexure-mounted FSMs. It addresses the critical design issues, servo control algorithms, and the device's performance capabilities and limitations.