A document proposes self-deploying spacecraft radar antennas based on cold hibernated elastic memory (CHEM) structures. Described in a number of prior NASA Tech Briefs articles, the CHEM concept is one of utilizing open-cell shape-memory-polymer (SMP) foams to make lightweight structures that can be compressed for storage and can later be expanded, then rigidified for use. A CHEM-based antenna according to the proposal would comprise three layers of microstrip patches and transmission lines interspersed with two flat layers of SMP foam, which would serve as both dielectric spacers and as means of deployment. The SMP foam layers would be fabricated at full size at a temperature below the SMP glass-transition temperature (Tg). The layers would be assembled into a unitary structure, which, at temperature above Tg, would be compacted to much smaller thickness, then rolled up for storage. Next, the structure would be cooled to below Tg and kept there during launch. Upon reaching the assigned position in outer space, the structure would be heated above Tg to make it rebound to its original size and shape. The structure as thus deployed would then be rigidified by natural cooling to below Tg.
This work was done by Witold Sokolowski, John Huang, and Reza Ghaffarian of Caltech for NASA's Jet Propulsion Laboratory. NPO-30742
This Brief includes a Technical Support Package (TSP).
CHEM-Based Self-Deploying Spacecraft Radar Antenna
(reference NPO30742) is currently available for download from the TSP library.
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Overview
The document presents a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing the development of a novel ultra-light, self-deployable radar antenna structure utilizing cold hibernated elastic memory (CHEM) technology. This innovative approach employs shape memory polymers in an open cellular foam material system, enabling the creation of advanced radar antennas suitable for space applications.
The CHEM technology operates by fabricating the structure in a hard state below the glass transition temperature (Tg). The structure is then warmed above the Tg to allow for compression and stowing, followed by cooling below the Tg to induce a hibernation state. Once in space, the structure "remembers" its original shape when warmed again, allowing it to deploy and then cool to achieve rigidity. This process offers flexibility in selecting a wide range of Tg values for deployment and rigidization.
The proposed radar antenna design features a flat L-band array composed of microstrip patches and microstrip transmission lines, designed to achieve dual polarizations with an 80 MHz bandwidth. The antenna consists of a three-layer membrane structure: the top layer includes 18 x 6 radiating square patches, the middle layer serves as the ground plane, and the bottom layer contains the power dividing transmission lines. Each layer is made from 2-mil thick polyimide material with 5-micron copper deposited on it. The spacing between the layers is precisely defined, with the top layer spaced 1.27 cm from the middle layer and the bottom layer spaced 0.63 cm from the ground plane.
To facilitate deployment, shape memory polymer foam material is incorporated between the three membrane layers, serving both as spacers and as part of the antenna's deployment mechanism. The entire assembly can be compressed into a very thin structure for stowage and, during deployment, the shape memory foam returns to its original shape, unrolling the structure to form a flat antenna.
This document is part of NASA's Commercial Technology Program, aimed at disseminating aerospace-related developments with broader technological, scientific, or commercial applications. It emphasizes the potential of CHEM technology in enhancing the capabilities of radar antennas for future space missions. Further information can be accessed through NASA's Scientific and Technical Information Program Office.
