Minimizing actuator-induced errors in active space telescope mirrors
Author(s)Smith, Matthew William; Miller, David W.
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The trend in future space telescopes points toward increased primary mirror diameter, which improves resolution and sensitivity. However, given the constraints on mass and volume deliverable to orbit by current launch vehicles, creative design solutions are needed to enable increased mirror size while keeping mass and volume within acceptable limits. Lightweight, segmented, rib-stiffened, actively controlled primary mirrors have emerged as a potential solution. Embedded surface-parallel actuators can be used to change the mirror prescription onorbit, lowering mirror mass overall by enabling lighter substrate materials such as silicon carbide (SiC) and relaxing manufacturing constraints. However, the discrete nature of the actuators causes high spatial frequency residual errors when commanding low-order prescription changes. A parameterized finite element model is used to simulate actuator-induced residual error and investigate design solutions that mitigate this error source. Judicious specification of mirror substrate geometry and actuator length is shown to reduce actuator-induced residual while keeping areal density constant. Specifically, a sinusoidally-varying rib shaping function is found to increase actuator influence functions and decrease residual. Likewise, longer actuators are found to offer reduced residual. Other options for geometric shaping are discussed, such as rib-to-facesheet blending and the use of two dimensional patch actuators.
DepartmentMassachusetts Institute of Technology. Department of Aeronautics and Astronautics
Proceedings of SPIE--the International Society for Optical Engineering; v. 7731
Smith, Matthew W., and David W. Miller. “Minimizing actuator-induced errors in active space telescope mirrors.” Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave. Ed. Jacobus M. Oschmann et al. San Diego, California, USA: SPIE, 2010. 773122-14. © 2010 SPIE
Final published version