Active narrowband disturbance rejection on an ultra quiet platform

Abstract

Vibration isolation on spacecraft is needed for imaging sensors, microgravity experiments, and other sensitive payloads. The preferred method thus far has been passive isolation because of its simplicity and low cost. Active vibration isolation and disturbance rejection will soon be more common as space qualified sensors, actuators and processors become more capable and affordable, and performance requirements increase. Spacecraft disturbances are typically periodic vibrations which are most effectively controlled through feedforward techniques. A popular choice of feedforward control methods for disturbance rejection is the Multiple Error Least Mean Squares (LMS) algorithm which requires a separately measured disturbance correlated signal in its implementation. A new technique called Clear Box makes extensive use of identification to bring out information that is normally hidden or not used by traditional control methods. It allows operation in an information rich environment with built in fault tolerance, the ability to control unanticipated disturbances, and the ability to select which modes to control (if saturation of the actuators is a possibility or concern), all without the need for a separately measured disturbance correlated signal. Experiments using both Multiple Error LMS and Clear Box on an Ultra Quiet Platform provide an effective demonstration of the advantages of the Clear Box Algorithm, including a new Adaptive Basis Method which allows control of rapidly varying frequencies.