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Solar Sails Would Be Made From Carbon Nets

A report proposes that solar sails for spacecraft be made from nets of carbon fibers. The reason for choosing carbon nets over thin polymeric films is that nets offer greater capability for carrying tensile loads. The sails could be made from carbon-fiber nets of various thicknesses: nets used for high emissivity could be made from nanotube carbon fibers; nets for holding aluminum reflectors could be made from micron-thickness fibers; nets to carry tensile loads in sails could be made from fibers with thicknesses between 10 and 100 µm; and nets to carry large bulk loads and loads in high-stress areas could be made from fibers with thicknesses from 100 to 1,000 µm.

Posted in: Materials, Briefs, TSP

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Solar Sails Would Be Segmented To Minimize Stresses

A report proposes that solar sails for spacecraft be constructed in segments in such a way as to minimize stresses. The segments could be made of metallized fabric or film and could be connected by short, strong tethers. Alternatively, the segments could be like islands, held loosely in pockets bounded by fibers. For stowage during transport to outer space, the sails could be folded along the gaps between segments, so as to minimize folding stresses in the sail material. Because tensile and other stresses in the sail material would be minimal, the sail material could be made in a thickness of the order of a micron and could thus be very lightweight. In cases in which there are requirements for sails to sustain tensile stresses, carbon-fiber nets like those described in the preceding article could be used.

Posted in: Materials, Briefs, TSP

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Predicting Stresses in Thermal-Barrier Coatings

Creep, oxidation, differential thermal expansion, and interface roughness are taken into account. A methodology for predicting stresses and the resultant cracking in plasma-sprayed thermal-barrier coatings (TBCs) has been developed. The methodology is built around a computer code that implements a finite-element model that simulates the evolution of stresses, strains, and related phenomena in a TBC. The economic and technological value of the methodology lies in its potential to provide a more systematic basis for designing reliable and durable TBCs for advanced gas turbine engines by reducing the amount of time-consuming empirical testing needed to assess alternative TBC designs.

Posted in: Materials, Briefs, TSP

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Enhancing the Removal of Chlorocarbons From Groundwater

Sonication apparently removes corrosion products that inhibit dechlorination. Experiments have shown that ultrasound could be an effective means of enhancing the removal of chlorinated hydrocarbon contaminants from groundwater by the zero-valent-metal treatment process. This process, which has been a subject of research in recent years, is attractive because it does not involve above-ground treatment or the use of pumps, and because the materials needed to effect treatment are safe and relatively inexpensive.

Posted in: Materials, Briefs, TSP

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Multi-Shock Blankets for Protecting Spacecraft

A report discusses multi-shock blankets, which are under investigation for use in protecting spacecraft against orbiting debris from prior spacecraft missions. Multi-shock blankets are described in comparison with early protective metallic "bumpers" and with a somewhat more recent invention called the "multi-shock shield." A multi-shock blanket is a stand-alone, self-contained shield system that includes several layers of ceramic (or equivalent) shields separated by a flexible foam material.

Posted in: Materials, Briefs, TSP

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Study of High-Performance Polyimide Foams

This report describes an experimental study of thermal-stability, mechanical, and flammability properties of foams of several different densities made of three different polyimides. The study was performed because (1) prior such studies were performed on polyimide films rather than foams and (2) the synthesis of polyimide foams is a relatively recent development. There is a need to determine the suitability of each foam for potential applications — for example, as flame retarders, thermal and acoustic insulators, gaskets, seals, vibration-damping pads, spacers in adhesives and sealants, extenders, and flow and leveling aids.

Posted in: Materials, Briefs, TSP

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Obtaining Consistent, Reliable Results in Elastomer Seal Testing

Compression stress relaxation results help predict long-term sealing performance. Compression Stress Relaxation (CSR) is an important factor in evaluating elastomer materials and seal configurations for their ability to provide sealing force retention under a variety of conditions. Increasing emphasis on the performance and longevity of elastomer seals, used most often in aerospace and automotive applications, is strengthening the need for more accurate CSR testing procedures.

Posted in: Materials, Briefs

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