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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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Making Ion-Accelerator Grids From Ti Instead of Mo

Titanium grids last longer, cost less, and have greater strength/weight ratios. Titanium has been found to offer several advantages over molybdenum as the material used to construct electrostatic-accelerator and -screen grids for ion thrusters for spacecraft. These advantages could also be expected to extend to the manufacture of grids for ion accelerators used in scientific research and the fabrication of semiconductors.

Posted in: Materials, Briefs, TSP

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Thermal Insulation Would Use CO2 in the Martian Environment

A report describes the development of a lightweight thermal insulation system for Martian surface applications. The ambient Martian atmosphere, which is predominantly carbon dioxide at a pressure of 10 torr, is used as the insulation medium with a modest multiple radiation shield enclosure. The carbon dioxide has a thermal conductivity that is very close to traditional insulation, and the carbon dioxide is naturally available on the Martian surface. Preformed Mylar spacers that are affixed to the hardware create the necessary standoff distance from the enclosure.

Posted in: Materials, Briefs, TSP

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Filled Skutterudites as Thermoelectric Materials

The highest known thermoelectric figure of merit was observed in one of these materials. Filled skutterudites have shown promise as semiconducting materials with superior thermoelectric properties at temperatures up to at least 650 °C. This finding is a breakthrough in a continuing investigation of the potential utility of skutterudites as thermoelectric materials. Previous results of this investigation were reported in several articles in NASA Tech Briefs; namely, "Skutterudite Compounds for Power Semiconductor Devices" (NPO-19378), NASA Tech Briefs, Vol. 20, No. 3 (March 1996), page 60; "Two Potentially Useful Ternary Skutterudite Compounds" (NPO-19409), NASA Tech Briefs, Vol. 20, No. 11 (November 1996), page 66; and "Preparation and Some Properties of n-Type IrxCo1 — xSb3" (NPO-19852), NASA Tech Briefs, Vol. 20, No. 11 (November 1996), page 94.

Posted in: Materials, Briefs, TSP

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Lithium Alkoxide Electrolyte Additives for Lithium-Ion Cells

These additives help to extend operating temperatures to as low as –40 °C. Alkoxides of lithium have been found to be useful as electrolyte additives to improve the low-temperature performance of rechargeable lithium-ion electrochemical cells. As explained below, an additive of this type exerts beneficial electrochemical effects both within the bulk of the electrolyte and on the surface of the carbon anode, such that the low-temperature electrical characteristics of the cell are improved.

Posted in: Materials, Briefs, TSP

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