Solar heating has been proposed as a means of deployment of structures of the type described in "Cold Hibernated Elastic Memory (CHEM) Expandable Structures," (NPO-20394), NASA Tech Briefs, Vol. 23, No. 2 (February 1999), page 56. A few examples of structures that would be amenable to the CHEM approach include expandable shelters, tanks, rafts, and thermally insulating boxes for storing food and drinks.

To recapitulate from the cited prior article: The CHEM concept is one of utilizing open-cell foams of shape-memory polymers (SMPs) to make lightweight, reliable, simple, and inexpensive structures that can be alternately (1) compressed and stowed compactly and later (2) expanded and rigidified for use. A CHEM structure of any shape is compacted to a small volume while in the rubbery state above the glass-transition temperature (Tg) of the SMP. After compaction, the structure is cooled below Tg where it is frozen in the glassy state of the SMP. The compacting force can then be released and the structure remains compact as long as the temperature is kept below Tg. Upon subsequent heating of the structure above Tg to the rubbery state of the SMP, the simultaneous elastic recovery of the foam and its shape-memory effect cause the structure to expand to its original size and shape. Once thus deployed, the structure can be rigidified by cooling below Tg to the glassy state. Once deployed and rigidified, the structure could be heated and recompacted. In principle, there should be no limit on the achievable number of compaction/deployment/rigidification cycles.

The attractiveness of the CHEM structure is the wide range of Tg resulting in a variety of potential space and terrestrial applications. Experiments have confirmed the feasibility of this innovative, self-deployable, and rigidizable structure.

The disadvantage of CHEM structures is that heat is needed for deployment. The proposed use of solar heat would eliminate the need to deplete other energy sources. According to the proposal, a CHEM structure would be wrapped in a blanket made of a material with a high ratio between solar absorptivity and infrared emissivity. Upon exposure to solar radiation, the structure inside the blanket would become heated because the blanket would absorb more heat than it would reradiate. Eventually, the temperature of the wrapped structure would increase beyond Tg, causing the structure to deploy itself by expanding to its full size and shape. After full deployment, the blanket would be removed, causing the structure to become cooled below Tg and thus rigidified. Thermal analysis confirmed a feasibility of this concept in the Mars environment. This concept will also work for applications on Earth and perhaps perform even better than on Mars.

This work was done by Witold Sokolowski, Art Chmielewski, and Henry Awaya of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.

NPO-20961