Design and control of lightweight, active space mirrors

Abstract

The success of the Hubble Space Telescope created a great interest in the next generation of space telescopes. To address this need, the University of Arizona (UA) has designed and built several lightweight prototype mirrors ranging in size from 0.5 m to 2 m in diameter. These mirrors consist of three key components: a thin, lightweight glass substrate holds the reflective surface; the surface accuracy is maintained by an array of position actuators; and the stiffness is maintained by a lightweight carbon-fiber/epoxy support structure. The UA mirrors are different from conventional mirrors in that they are actively-controlled: their figure may be changed after they leave the optics shop. This dissertation begins with an overview of the technical issues for placing large optics in space, and I also discuss the current state-of-the-art in active mirror design. Chapters 3 and 4 discuss ways to design mirrors such that the optical performance is maximized while the mass is minimized. Chapter 3 looks at the best way to distribute the mass between the reflective substrate and the actuators, and Chapter 4 looks at the optimum geometries for structured mirrors. The second half of this work looks at the practical aspects of controlling active mirrors. Chapter 5 discusses the University of Arizona's 2 m NMSD prototype mirror. Specifically, I review the system that I developed to measure and control the mirror. I also provide some details on using a least-squares solution to solve for the actuator commands. Chapter 6 discusses the UA ultralightweight 0.5 m prototype mirror. I describe the techniques that I developed for attaching loadspreaders to the reflective surface, the metrology system, and a software package used to remotely-control the mirror.