Fine surface control of flexible space mirrors using adaptive optics and robust control

Abstract

Future space telescopes will contain lightweight, flexible, segmented mirrors. Traditional control approaches for mirror alignment and shape control may be inadequate due to flexibilities and low natural frequencies. Using adaptive optics for space telescopes presents a possible solution. This research proposes innovative H[infinity] robust control techniques for these types of systems. An H[infinity] controller is synthesized for a complex analytical model with 997 inputs, 936 outputs, and 332 states. To accomplish this, a new technique for model reduction using Zernike polynomials was developed. The H[infinity] controller was able to achieve a minimum 15 Hz control bandwidth. The previous integral controller was unable to meet the 10 Hz bandwidth requirement. The H[infinity] design process used was validated on a simpler adaptive optics testbed. The experimental verification also showed that the robust control techniques outperformed the classical control techniques in the presence of disturbances. The significant contributions are a Zernike polynomial method for model reduction, robust controller synthesis for a complex adaptive optics analytical model, and experimental verification on an AO testbed. Although the robust control design is more complex, it provides improved performance in the presence of uncertainty in the disturbances and modeling.