Tech Briefs

Asymmetric Bulkheads for Cylindrical Pressure Vessels

These bulkheads would offer advantages over prior concave, convex, and flat bulkheads. Asymmetric bulkheads are proposed for the ends of vertically oriented cylindrical pressure vessels. These bulkheads, which would feature both convex and concave contours, would offer advantages over purely convex, purely concave, and flat bulkheads (see figure). Intended originally to be applied to large tanks that hold propellant liquids for launching spacecraft, the asymmetric-bulkhead concept may also be attractive for terrestrial pressure vessels for which there are requirements to maximize volumetric and mass efficiencies.

Posted in: Briefs, Mechanical Components, Mechanics, Bulkheads

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Code Assesses Risks Posed by Meteoroids and Orbital Debris

BUMPER II version 1.92e is a computer code for assessing the risk of damage from impacts of micrometeoroids and orbital debris on the International Space Station (ISS), including those parts of the ISS covered by shielding that affords partial protection against such impacts. (Other versions of BUMPER II have been written for other spacecraft.) Bumper II quantifies the probability of penetration of shielding and the damage to spacecraft equipment as functions of the size, shape, and orientation of the spacecraft; the parameters of its orbit; failure criteria that quantify impact damage at the threshold of failure for each spacecraft surface; and the impact-damage resistance of each spacecraft surface as defined by “ballistic limit equations” that return the size of a failure causing particle as a function of target parameters (including materials, configurations, thicknesses, and gap distances) and impact conditions (impact velocity and the density and shape of the impactor). BUMPER II version 1.92e contains several dozen ballistic limit equations that are based on results from thousands of hypervelocity impact tests conducted by NASA on ISS shielding and other hardware, and on results from numerical simulations of impacts.

Posted in: Briefs, Mechanical Components, Mechanics, Computer software and hardware, Risk assessments, Spacecraft

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Self-Regulating Water-Separator System for Fuel Cells

This system would not depend on hydrophobic or hydrophilic surfaces. A proposed system would perform multiple coordinated functions in regulating the pressure of the oxidant gas (usually, pure oxygen) flowing to a fuel-cell stack and in removing excess product water that is generated in the normal fuel-cell operation. The system could function in the presence or absence of gravitation, and in any orientation in a gravitational field.

Posted in: Briefs, Mechanical Components, Mechanics, Fuel cells

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Self-Advancing Step-Tap Drills

It is not necessary to apply axial drilling forces.Self-advancing tool bits that are hybrids of drills and stepped taps make it possible to form threaded holes wider than about 1/2 in. (about 13 mm) without applying any more axial force than is necessary for forming narrower pilot holes. These self-advancing stepped-tap drills were invented for use by space-suited astronauts performing repairs on reinforced carbon/carbon space-shuttle leading edges during space walks, in which the ability to apply axial drilling forces is severely limited. Self-advancing stepped-tap drills could also be used on Earth for making wide holes without applying large axial forces.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Tools and equipment, Drilling

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Array of Bolometers for Submillimeter-Wavelength Operation

This is a prototype of arrays for astrophysical imaging and photometry. A feed-horn-coupled monolithic array of micromesh bolometers is undergoing development for use in a photometric camera. The array is designed for conducting astrophysical observations in a wavelength band centered at 350 μm. The bolometers are improved versions of previously developed bolometers comprising metalized Si3N4 micromesh radiation absorbers coupled with neutron-transmutation-doped Ge thermistors. Incident radiation heats the absorbers above a base temperature, changing the electrical resistance of each thermistor. In the present array of improved bolometers (see figure), the thermistors are attached to the micromesh absorbers by indium bump bonds and are addressed by use of lithographed, vapor-deposited electrical leads. This architecture reduces the heat capacity and minimizes the thermal conductivity to 1/20 and 1/300, respectively, of earlier versions of these detectors, with consequent improvement in sensitivity and speed of response.

Posted in: Briefs, TSP, Physical Sciences, Architecture, Imaging and visualization, Optics

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Delta-Doped CCDs as Detector Arrays in Mass Spectrometers

Improved performance is obtained with reduced size, mass, and power. Delta-doped, back-illuminated charge-coupled devices (CCDs) are used as detector arrays in high-performance double- focusing miniature mass spectrometers of Mattauch-Herzog design (described below). The uses of delta-doped CCD detector arrays eliminates the need for microchannel plates (MCPs) and the high-voltage power supplies, that, heretofore, have been used in detection schemes in mass spectrometers; this makes it possible to reduce the sizes, masses, and power demands of mass spectrometers. The use of delta-doped CCDs enables the direct and simultaneous measurement of ions with different masses separated along the focal plane.

Posted in: Briefs, TSP, Physical Sciences, Measurements, Charge coupled devices, Spectroscopy

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Arrays of Bundles of Carbon Nanotubes as Field Emitters

Area-averaged current densities exceed those of arrays of single nanotubes. Experiments have shown that with suitable choices of critical dimensions, planar arrays of bundles of carbon nanotubes (see figure) can serve as high-current-density field emitter (cold-cathode) electron sources. Whereas some hot-cathode electron sources must be operated at supply potentials of thousands of volts, these cold-cathode sources generate comparable current densities when operated at tens of volts. Consequently, arrays of bundles of carbon nanotubes might prove useful as cold-cathode sources in miniature, lightweight electron-beam devices (e.g., nanoklystrons) soon to be developed.

Posted in: Briefs, TSP, Physical Sciences, Materials properties, Nanomaterials, Test procedures

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