Tech Briefs

Composite-Material Tanks With Chemically Resistant Liners

Liner materials are chosen for compatibility with reactive and/or unstable fluids. Lightweight composite-material tanks with chemically resistant liners have been developed for storage of chemically reactive and/or unstable fluids — especially hydrogen peroxide. These tanks are similar, in some respects, to the ones described in — Lightweight Composite-Material Tanks for Cryogenic Liquids — (MFS-31379), NASA Tech Briefs, Vol.25, No.1 (January, 2001), page 58; however, the present tanks are fabricated by a different procedure and they do not incorporate insulation that would be needed to prevent boil-off of cryogenic fluids.

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Improved BN Coatings on SiC Fibers in SiC Matrices

Outside debonding would be favored over inside debonding. Modifications of BN-based coatings that are used as interfacial layers between the fibers and matrices of SiC-fiber/SiC-matrix composite materials have been investigated to improve the thermomechanical properties of these materials. Such interfacial coating layers, which are also known as interphases (not to be confused with "interphase" in the biological sense), contribute to strength and fracture toughness of a fiber/matrix composite material by providing for limited amounts of fiber/matrix debonding and sliding to absorb some of the energy that would otherwise contribute to the propagation of cracks.

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Simulating Operation of a Planetary Rover

Simulating Operation of a Planetary Rover Rover Analysis, Modeling, and Simulations (ROAMS) is a computer program that simulates the operation of a robotic vehicle (rover) engaged in exploration of a remote planet. ROAMS is a rover-specific extension of the DARTS and Dshell programs, described in prior NASA Tech Briefs articles, which afford capabilities for mathematical modeling of the dynamics of a spacecraft as a whole and of its instruments,actuators, and other subsystems. ROAMS incorporates mathematical models of kinematics and dynamics of rover mechanical subsystems, sensors, interactions with terrain, solar panels and batteries, and onboard navigation and locomotion-control software. ROAMS provides a modular simulation framework that can be used for analysis, design, development, testing,and operation of rovers. ROAMS can be used alone for system performance and trade studies. Alternatively, ROAMS can be used in an operator-in-the-loop or flight-software closed-loop environment. ROAMS can also be embedded within other software for use in analysis and development of algorithms,or for Monte Carlo studies, using a variety of terrain models, to generate performance statistics. Moreover, taking advantage of real-time features of the underlying DARTS/Dshell simulation software, ROAMS can also be used for real-time simulations.

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Silicone-Rubber Microvalves Actuated by Paraffin

Relative to other microvalves, these would be simpler. Microvalves containing silicone-rubber seals actuated by heating and cooling of paraffin have been proposed for development as integral components of microfluidic systems. In comparison with other microvalves actuated by various means (electrostatic, electro-magnetic, piezoelectric, pneumatic, and others), the proposed valves (1) would contain simpler structures that could be fabricated at lower cost and (2) could be actuated by simpler (and thus less expensive) control systems.

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Flexible Shields for Protecting Spacecraft Against Debris

A report presents the concept of Flexshield —a class of versatile, light-weight, flexible shields for protecting spacecraft against impacts by small meteors and orbiting debris. The Flexshield concept incorporates elements of, but goes beyond, prior space-craft-shielding concepts, including those of Whipple shields and, more recently, multi-shock shields and multi-shock blankets. A shield of the Flexshield type includes multiple outer layers (called “bumpers” in the art) made, variously, of advanced ceramic and/or polymeric fibers spaced apart from each other by a lightweight foam.As in prior such shields, the bumpers serve to shock an impinging hypervelocity particle, causing it to disintegrate, vaporize, and spread out over a larger area so that it can be stopped by an innermost layer (back sheet). The flexibility of the fabric layers and compressibility of the foam make it possible to compress and fold the shield for transport,then deploy the shield for use. The shield can be attached to a spacecraft by use of snaps, hook-and-pile patches,or other devices. The shield can also contain multilayer insulation material, so that it provides some thermal protection in addition to mechanical protection.

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Controllable Curved Mirrors Made From Single-Layer EAP Films

A document proposes that light-weight, deployable, large- aperture, controllable curved mirrors made of reflectively coated thin electroactive-polymer (EAP) films be developed for use in spaceborne microwave and optical systems. In these mirrors, the EAP films would serve as both structures and actuators. EAPs that are potentially suit- able for such use include piezoelectric, electrostrictive, ferroelectric, and di-electric polymers. These materials exhibit strains proportional to the squares of applied electric fields. Utilizing this phenomenon,a curved mirror according to the proposal could be made from a flat film, upon which a nonuniform electrostatic potential (decreasing from the center toward the edge) would be imposed to obtain a required curvature. The effect would be analogous to that of an old-fashioned metalworking practice in which a flat metal sheet is made into a bowl by hammering it repeatedly, the frequency of hammer blows decreasing with distance from the center. In operation, the nonuniform electrostatic potential could be imposed by use of an electron gun. Calculations have shown that by use of a single-layer film made of a currently available EAP, it would be possible to control the focal length of a 2m-diameter mirror from infinity to 1.25 m.

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Thermally Conductive Metal-Tube/Carbon-Composite Joints

Modified solder joints accommodate differential thermal expansion. An improved method of fabricating joints between metal and carbon-fiber-based composite materials in lightweight radiators and heat sinks has been devised. Carbon-fiber-based composite materials have been used in such heat-transfer devices because they offer a combination of high thermal conductivity and low mass density. Metal tubes are typically used to carry heat-transfer fluids to and from such heat-transfer devices. The present fabrication method helps to ensure that the joints between the metal tubes and the composite-material parts in such heat-transfer devices have both (1) the relatively high thermal conductances needed for efficient transfer of heat and (2) the flexibility needed to accommodate differences among thermal expansions of dissimilar materials in operation over wide temperature ranges.

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