Tech Briefs

Isogrid Membranes for Precise, Singly Curved Reflectors

Reinforcing meshes of fibers would prevent wrinkles and ripples. A new type of composite material has been proposed for membranes that would constitute the reflective surfaces of planned lightweight, single curvature (e.g., parabolic cylindrical) reflectors for some radar and radio communication systems. The proposed composite materials would consist of polyimide membranes containing embedded grids of high strength (e.g., carbon) fibers. The purpose of the fiber reinforcements, as explained in more detail below, is to prevent wrinkling or rippling of the membrane.

Posted in: Materials, Briefs, TSP

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Photocatalytic Coats in Glass Drinking-Water Bottles

According to a proposal, the insides of glass bottles used to store drinking water would be coated with films consisting of or containing TiO2. In the presence of ultraviolet light, these films would help to remove bacteria, viruses, and trace organic contaminants from the water.

Posted in: Materials, Briefs

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Automated Rapid Prototyping of 3D Ceramic Parts

Unlike in prior rapid-prototyping processes, there is no manual stacking of sheets. An automated system of manufacturing equipment produces three-dimensional (3D) ceramic parts specified by computational models of the parts. The system implements an advanced, automated version of a generic rapid-prototyping process in which the fabrication of an object having a possibly complex 3D shape includes stacking of thin sheets, the outlines of which closely approximate the horizontal cross sections of the object at their respective heights. In this process, the thin sheets are made of a ceramic precursor material, and the stack is subsequently heated to transform it into a unitary ceramic object.

Posted in: Manufacturing & Prototyping, Briefs

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High-Temperature, High-Load-Capacity Radial Magnetic Bearing

Speed and temperature limits of rolling element bearings can be exceeded. A radial heteropolar magnetic bearing capable of operating at a temperature as high as 1,000 °F (≈540 °C) has been developed. This is a prototype of bearings for use in gas turbine engines operating at temperatures and speeds much higher than can be withstood by lubricated rolling-element bearings.

Posted in: Mechanical Components, Briefs, TSP

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Improving Control in a Joule-Thomson Refrigerator

A report discusses a modified design of a Joule-Thomson (JT) refrigerator under development to be incorporated into scientific instrumentation aboard a spacecraft.In most other JT refrigerators (including common household refrigerators), the temperature of the evaporator (the cold stage) is kept within a desired narrow range by turning a compressor on and off as needed. This mode of control is inadequate for the present refrigerator because a JT-refrigerator compressor performs poorly when the flow from its evaporator varies substantially, and this refrigerator is required to maintain adequate cooling power. The proposed design modifications include changes in the arrangement of heat exchangers, addition of a clamp that would afford a controlled heat leak from a warmer to a cooler stage to smooth out temperature fluctuations in the cooler stage, and incorporation of a proportional + integral + derivative (PID) control system that would regulate the heat leak to maintain the temperature of the evaporator within a desired narrow range while keeping the amount of liquid in the evaporator within a very narrow range in order to optimize the performance of the compressor. Novelty lies in combining the temperature- and cooling-power-regulating controls into a single control system.

Posted in: Mechanics, Mechanical Components, Briefs, TSP

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Gifford-McMahon/Joule-Thomson Refrigerator Cools to 2.5 K

This system is relatively simple. A compact refrigerator designed specifically for cooling a microwave maser low noise amplifier is capable of removing heat at a continuous rate of 180 mW at a temperature of 2.5 K. This refrigerator is a combination of (1) a commercial Gifford-McMahon (GM) refrigerator nominally rated for cooling to 4 K and (2) a Joule-Thomson (J-T) circuit. The GM refrigerator pre-cools the J-T circuit, which provides the final stage of cooling. The refrigerator is compact and capable of operating in any orientation. Moreover, in comparison with a typical refrigerator heretofore used to cool a maser to 4.5 K, this refrigerator is simpler and can be built at less than half the cost.

Posted in: Mechanics, Mechanical Components, Briefs, TSP

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Integrated Structural Analysis and Test Program

An integrated structural-analysis and structure-testing computer program is being developed in order to: • Automate repetitive processes in testing and analysis; • Accelerate pre-test analysis; • Accelerate reporting of tests; • Facilitate planning of tests; • Improve execution of tests; • Create a vibration, acoustics, and shock test database; and • Integrate analysis and test data.

Posted in: Test & Measurement, Briefs

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