Hybrid deployable radio antennas and reflectors of a proposed type would feature rigid narrower apertures plus wider adjoining apertures comprising reflective surfaces supported by open-cell polymeric foam structures (see figure). The open-cell foam structure of such an antenna would be compressed for compact stowage during transport. To initiate deployment of the antenna, the foam structure would simply be released from its stowage mechanical restraint. The elasticity of the foam would drive the expansion of the foam structure to its full size and shape.
There are several alternatives for fabricating a reflective surface supported by a polymeric foam structure. One approach would be to coat the foam with a metal. Another approach would be to attach a metal film or a metal-coated polymeric membrane to the foam. Yet another approach would be to attach a metal mesh to the foam.
The hybrid antenna design and deployment concept as proposed offers significant advantages over other concepts for deployable antennas:
- In the unlikely event of failure to deploy, the rigid narrow portion of the antenna would still function, providing a minimum level of assured performance. In contrast, most other concepts for deploying a large antenna from compact stowage are of an “all or nothing” nature: the antenna is not useful at all until and unless it is fully deployed.
- Stowage and deployment would not depend on complex mechanisms or actuators, nor would it involve the use of inflatable structures. Therefore, relative to antennas deployed by use of mechanisms, actuators, or inflation systems, this antenna could be lighter, cheaper, amenable to stowage in a smaller volume, and more reliable. An open-cell polymeric (e.g., polyurethane) foam offers several advantages for use as a compressible/expandable structural material to support a large antenna or reflector aperture. A few of these advantages are the following:
- The open cellular structure is amenable to compression to a very small volume — typically to 1/20 of its full size in one dimension.
- At a temperature above its glass-transition temperature (Tg), the foam strongly damps vibrations. Even at a temperature below Tg, the damping should exceed that of other materials.
- In its macroscopic mechanical properties, an open-cell foam is isotropic. This isotropy facilitates computational modeling of antenna structures.
- Through chemical formulation, the Tg of an open-cell polyurethane foam can be set at a desired value between about - 100 and about 0 °C. Depending on the application, it may or may not be necessary to rigidify a foam structure after deployment. If rigidification is necessary, then the Tg of the foam can be tailored to exceed the temperature of the deployment environment, in conjunction with providing a heater to elasticize the foam for deployment. Once deployed, the foam would become rigidified by cooling to below Tg.
- Techniques for molding or machining polymeric foams (especially including open-cell polyurethane foams) to desired sizes and shapes are well developed.
This work was done by Tommaso Rivellini, Paul Willis, Richard Hodges, and Suzanne Spitz of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Electronics/Computers category. NPO-30819
This Brief includes a Technical Support Package (TSP).
Hybrid Deployable Foam Antennas and Reflectors
(reference NPO-30819) is currently available for download from the TSP library.
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Overview
The document discusses the development of hybrid deployable foam antennas and reflectors, as outlined in NASA's Technical Support Package NPO-30819. The primary motivation for this innovation stems from the need for large antennas that can be stored in limited volumes, particularly in applications like spacecraft where deployment failure can lead to significant operational risks. Traditional antenna deployment systems often result in an all-or-nothing performance, which is inadequate for critical missions.
The proposed hybrid antenna system combines a small, fixed rigid reflector with a larger deployable foam reflector. This design ensures a minimum performance capability even if the larger foam surface fails to deploy, thereby providing a fail-safe performance floor. The hybrid system offers several advantages over existing technologies, including lighter weight, reduced cost, increased reliability, and a smaller stowage volume. Unlike mechanically deployed systems, this design does not rely on complex mechanisms or actuators, which enhances its reliability and simplifies testing.
The foam used in the antenna is pre-shaped and has a thin layer of open-celled foam attached to its back surface. This foam provides a restoring force that helps maintain the correct shape of the reflector film, eliminating the need for an inflation canopy, which is a common requirement in current designs. The elimination of the inflation system reduces mass and addresses material challenges associated with canopy materials, such as the need for lightweight, strong, and UV-resistant properties.
Additionally, the document highlights the tear resistance of polymer films, which is a common weakness. The attachment of the polymer foam to the film helps prevent the initiation and propagation of tears, enhancing the durability of the antenna.
Overall, the hybrid deployable foam antenna system represents a significant advancement in antenna technology, offering a reliable and efficient solution for applications requiring large antennas in constrained environments. The document emphasizes the potential for various antenna types to be hybridized, including horns and microstrip-fed patch antennas, showcasing the versatility and design flexibility of this innovative approach.
