Two documents present updates on thin-shell, adjustable, curved mirrors now being developed for use in spaceborne imaging systems. These mirrors at an earlier stage of development were reported in “Nanolaminate Mirrors With Integral Figure-Control Actuators” (NPO-30221), NASA Tech Briefs, Vol. 26, No. 5 (May 2002), page 80. To recapitulate: These mirrors comprise metallic film reflectors on nanolaminate substrates that contain “in-plane” actuators for controlling surface figures with micronlevel precision. The actuators are integral parts of the mirror structures, typically fabricated as patches that are bonded onto the rear (nonreflective) surfaces of the mirror shells. The current documents discuss mathematical modeling of mirror deflections caused by actuators arranged in unit cells distributed across the rear mirror surfaces. One of the documents emphasizes an actuator configuration in which a mirror surface is divided into hexagonal unit cells. Each unit cell contains four rectangular actuator patches in an off-axis cruciform pattern to induce a combination of bending and twisting. For deflections to reduce certain optical aberrations, it is found that, relative to other configurations, this configuration involves a smaller areal density of actuators.
This work was done by Gregory Hickey, Shyh-Shiuh Lih, and Horn-Sen Tzou of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Materials category.
NPO-30748
This Brief includes a Technical Support Package (TSP).
Patched Off-Axis Bending/Twisting Actuators for Thin Mirrors
(reference NPO-30748) is currently available for download from the TSP library.
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Overview
The document discusses advancements in the development of innovative actuators for the distributed control of thin membrane shell structures, particularly in the context of aerospace applications. It highlights the need for lightweight, large optics to support future space missions, such as the Terrestrial Planet Finder, and addresses the limitations of conventional optical materials used in space optics, which are often heavy and expensive.
The research focuses on the design and implementation of a new class of optical mirror substrates that break away from traditional materials like ultra-low thermal expansion glass. These conventional materials, while effective, result in high-precision optics that are bulky and costly. The document outlines the evolution of optical systems from heavy glass mirrors to lightweight, non-actuated mirrors with complex core structures, aiming for a significant reduction in areal density.
A key innovation presented is the use of bending/twisting cell actuators, which are designed to provide precise control over the shape and surface figure of thin optical membranes. The actuators consist of four strip-like components arranged off-axis to generate bending and twisting forces, allowing for localized adjustments to surface aberrations. This design aims to enhance the performance of thin shell optics by enabling more effective micro-control actions and distributed control mechanisms.
The document also includes findings from finite element analysis that demonstrate the influence function of the unit actuators, showing a maximum displacement of approximately 7.5 microns with a 300 Volts DC input. This modeling has been validated through experimental testing, confirming the effectiveness of the actuator design.
Overall, the research aims to advance the state of the art in lightweight deployable space structures, moving away from bulky kinematic mechanisms towards more efficient and precise actuator systems. The findings have implications for the design of large optical aperture systems and other ultra-lightweight optical applications, addressing the challenges of dimensional stability and geometric constraints in space environments. The document serves as a technical support package under NASA's Commercial Technology Program, providing insights into the potential for broader technological and commercial applications of these developments.
