Advanced control systems that include built-in smart-material elastic-deformation structural actuators have been proposed for deployable thin-shell structures that are required to be maintained in precise shapes once deployed. This approach to structural shape control was conceived to enable the development of lightweight telescope mirrors, radar reflectors, and the like that could be stowed compactly for launching and transport, then deployed in outer space to required precise shapes at much larger dimensions (of the order of 10 m). The concept may also be applicable to similar, but probably smaller structures for terrestrial use.

A typical shell structure according to the proposal (see figure) would include (1) a flexible single- or multiple-layer face sheet that would include a reflective mirror surface; (2) structural supports in the form of stiffeners made of shape-memory alloys; and (3) bimorph-type piezoelectric actuators, possibly of a variety of sizes and shapes. The actuators, together with an electronic control subsystem, would implement a concept of hierarchical distributed control: The shape-memory actuators would be used for global shape control and would generate the large deformations needed for the deployment process. The piezoelectric actuators would generate smaller deformations and would be used primarily to effect fine local adjustments of the shape of the mirror.

Because of the geometric and material nonlinearities of shell structures, this work considers the essential nonlinearity of the large deformations needed for stowage and deployment, and the further complexity and nonlinearity that obtains in structures that include flexible membranes. This research and development effort will serve as a foundation for designing and building such structures integrated with hierarchical distributed control systems. The proposed work will take advantage of recent advances in mathematical modeling, dynamics, and distributed sensing and control of structures that exhibit nonlinear responses and undergo large deformations.

This work was done by Gregory Hickey and Shyh-Shiuh Lih of Caltech and Horn-Sen Tzou of the University of Kentucky for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at  under the Physical Sciences category.


This Brief includes a Technical Support Package (TSP).
Deployable Shell Structures with Shape-Control Actuators

(reference NPO-21138) is currently available for download from the TSP library.

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This article first appeared in the December, 2001 issue of NASA Tech Briefs Magazine.

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