Development and manufacture of an adaptive lightweight mirror for space application

Abstract

Currently, scientific space missions based on interferometric optical and infrared astronomical instruments are under development in the United States as well as in Europe. These instruments require optical path length accuracy in the order of a few nanometres across structural dimensions of several metres. This puts extreme demands on static and dynamic structural stability. It is expected that actively controlled, adaptive structures will increasingly have to be used for these satellite applications to overcome the limits of passive structural accuracy. Based on the evaluation of different piezo-active concepts, analysis and design of an adaptive lightweight satellite mirror primarily made of carbon fibre reinforced plastic with embedded piezoceramic actuators for shape control is described. Simulation of global mirror performance takes different wavefront sensors and controls for several cases of loading into account. Extensive finite-element optimization of various structural details was performed while testing of active sub-components served as a basis for a final update of finite-element models. Local material properties of sub-assemblies or geometry effects at the edges of the structure were investigated with respect to their impact on mirror performance. The major result of the analysis was the lay-out of the adaptive mirror and the specific design of embedded piezoceramic actuators. Manufacture of structural components and successfully completed mirror integration is described. The paper concludes with an outline of testing, and space qualification of the demonstrator of an actively controllable lightweight satellite mirror currently under way.

Minimizing actuator-induced errors in active space telescope mirrors

“…In such arrangements, two dimensional "patch" actuators bonded to reflective surfaces are used to locally alter mirror curvature. Dürr et al 18 and Shepherd et al 10 provide two examples.…”

Modular bimorph mirrors for adaptive optics

“…There are several actuation technologies available for flexible AO mirrors, depending on their size and stroke: linear actuators pushing at the back of the mirror, 7 piezoelectric bimorph mirrors, 8,9 electrostatic actuators, 10, 11 electromagnetic actuators 12 and carbon fibre reinforced plastic mirrors with embedded piezoceramic actuators. 13 Piezoelectric actuators exhibit hysteresis, while electrostatic actuators are nonlinear; electromagnetic actuators tend to require more space and weight than the others. MEMS mirrors are all electrostatic; they can achieve a very small pitch, but they are limited to very small sizes.…”

Adaptronic Systems for Aerospace Applications (Adaptronische Systeme für Anwendungen in der Luftfahrt)

“…5). Recent work [15] has been dealing with the use of piezofibre actuators completed as pre-encapsulated patches which have been integrated into a lightweight honeycomb core satellite mirror. Optimum actuator shapes were determined numerically, realised and integrated into the real structure.…”