Energy-Efficient Active Reflectors with Improved Mechanical Stability

Abstract

Active reflectors use an array of distributed actuators to control static surface deformations. In addition to meeting mission requirements with lower mass and lower costs, an active reflector adds robustness to a mission design by allowing for correction of unexpected orbital deformations. To control the wavefront of an active reflector, first the surface aberration is measured (via, e.g., a Shack-Hartmann sensor, direct imaging of the reflector surface, interferometric metrology, image-based PSF estimation, or other methods). Based on an actuator sensitivity matrix, a voltage profile is calculated that best reduces the observed aberration. In addition to controlling the static wavefront, piezoelectric actuators can easily be used to control structural vibrations in the frequency ranges of interest for active reflectors (50 to 2000Hz). Operational vibrations (e.g., microdynamics, ACS-induced vibrations, slew, thermally-induced stick-slip events) can effectively be rejected from the reflector system. Launch load vibrations are typically drivers for structural requirements, and typical mission concepts would have reflector actuators unpowered or shorted during launch. By incorporating a vibration control system into the actuator power circuitry, launch loads on the fragile reflector structure can be significantly reduced. By improving the electromechanical coupling and deliberately operating in a new nonlinear piezoelectric regime, we have optimized the surface correction and use the same actuators developed for surface control as structural control elements. This has yielded improved performance in terms of power draw and also enabled vibration suppression for launch load and operational disturbances.

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