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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Mesosiderites and howardites - Igneous formation and possible genetic relationships

Neutron activation data are presented for major, minor, and trace elements in whole rock howardites and silicates from mesosiderites. Compositions of howardites and mesosiderites are similar and intermediate between those of eucrites and diogenites. It is indicated that mesosiderites have a higher normative silica component than howardites. It appears that this results partly from a higher content of a highly evolved igneous component and partly from in situ reduction of FeO to Fe followed by magnetic separation of metal prior to analysis. It is shown that light rare earth elements are enriched in some mesosiderites.

Mittlefehldt, D. W.↗
NASA NTRS1980

Induction powered biological radiosonde

An induction powered implanted monitor for epidurally measuring intracranial pressure and telemetering the pressure information to a remote readout is disclosed. The monitor utilizes an inductance-capacitance (L-C) oscillator in which the C comprises a variable capacitance transducer, one electrode of which is a small stiff pressure responsive diaphragm. The oscillator is isolated from a transmitting tank circuit by a buffer circuit and all electric components in the implanted unit except an input and an output coil are shielded by a metal housing.

Fryer, T. B.↗
NASA NTRS1980

Research on graphite reinforced glass matrix composites

High levels of mechanical performance in tension, flexure, fatigue, and creep loading situations of graphite fiber reinforced glass matrix composites are discussed. At test temperatures of up to 813 K it was found that the major limiting factor was the oxidative instability of the reinforcing graphite fibers. Particular points to note include the following: (1) a wide variety of graphite fibers were found to be comparable with the glass matrix composite fabrication process; (2) choice of fiber, to a large extent, controlled resultant composite performance; (3) composite fatigue performance was found to be excellent at both 300 K and 703 K; (4) composite creep and stress rupture at temperatures of up to 813 K was limited by the oxidative stability of the fiber; (5) exceptionally low values of composite thermal expansion coefficient were attributable to the dimensional stability of both matrix and fiber; and (6) component fabricability was demonstrated through the hot pressing of hot sections and brazing using glass and metal joining phases.

Prewo, K. M.↗
NASA NTRS1981

Ion source design for industrial applications

The more frequently used design techniques for the components of broad-beam electron bombardment ion sources are discussed. The approach used emphasizes refractory metal cathodes and permanent-magnet multipole discharge chambers. Design procedures and sample calculations are given for the discharge chamber, ion optics, the cathodes, and the magnetic circuit. Hardware designs are included for the isolator, cathode supports, anode supports, pole-piece assembly, and ion-optics supports. A comparison is made between two-grid and three-grid optics. The designs presented are representative of current technology and are adaptable to a wide range of configurations.

Kaufman, H. R.↗
NASA NTRS1982

Metamorphism in mesosiderites

Previous studies of mesosiderites have identified a metamorphic overprint in these meteorites. However, the effects and implications of this overprint have not yet been explored in detail. The present study documents several important textural and chemical features of the mesosiderites. The components of mesosiderites are examined, taking into account orthopyroxenites, olivine in clasts, mesosiderite mafic clasts, and metal. The characteristics of the silicate matrix of the mesosiderites is explored, and textural and chemical evidence of metamorphism is discussed, giving attention to coronas on olivine clasts, overgrowths on Mg-pyroxene clasts, rims on iron rich pyroxene grains, poikiloblasts of plagioclase, and resorption of clasts. Aspects of redox formation of merrillite are considered along with the causes and the implications of metamorphism. It is found that metamorphism has radically changed the texture of the silicate fraction of the mesosiderites.

Delaney, J. S.↗
NASA NTRS1988

Development of a unit cell for a Ge:Ga detector array

Two modules of gallium-doped germanium (Ge:Ga) infrared detectors with integrated multiplexing readouts and supporting drive electronics were designed and tested. This development investigated the feasibility of producing two-dimensional Ge:Ga arrays by stacking linear modules in a housing capable of providing uniaxial stress for enhanced long-wavelength response. Each module includes 8 detectors (1x1x2 mm) mounted to a sapphire board. The element spacing is 12 microns. The back faces of the detector elements are beveled with an 18 deg angle, which was proved to significantly enhance optical absorption. Each module includes a different silicon metal-oxide semiconductor field effect transistor (MOSFET) readout. The first circuit was built from discrete MOSFET components; the second incorporated devices taken from low-temperature integrated circuit multiplexers. The latter circuit exhibited much lower stray capacitance and improved stability. Using these switched-FET circuits, it was demonstrated that burst readout, with multiplexer active only during the readout period, could successfully be implemented at approximately 3.5 K.

Source record↗
NASA NTRS1988

Antarctic ozone - Meteoric control of HNO3

Atmospheric circulation leads to an accumulation of debris from meteors in the Antarctic stratosphere at the beginning of austral spring. The major component of meteoric material is alkaline, comprised predominantly of the oxides of magnesium and iron. These metals may neutralize the natural acidity of stratospheric aerosols, remove nitric acid from the gas phase, and bond it as metal nitrates in the aerosol phase. Removal of nitric acid vapor has been previously shown to be a critical link in the photochemical depletion of ozone in the Antarctic spring, by allowing for increased catalytic loss from chlorine and bromine.

Prather, Michael J.↗
NASA NTRS1991

An overview of the first results on the solar array passive LDEF experiment (sample), AO171

Space environmental effects were visibly obvious on components of experiment AO171 which contained solar cells, composites, polymeric thin films, solar reflectors, protective coatings, metals, paints , and elastomers. Micrometeoroid/space debris impacts were observed on all experiment elements. Luminescence of polyimide, silicone, and polyurethane materials occurred under black light examination. Outgassing of RTV511 occurred mainly as a result of insufficient thermal vacuum bakeout. Solar cell degradation was predominantly below 10 percent. Elastomers lost mass and discolored; composites showed evidence of atomic oxygen attack, and unprotected thin polymer films eroded away.

Whitaker, Ann F.↗
NASA NTRS1991

Method of making carbide/fluoride/silver composites

A composition containing 30 to 70 percent chromium carbide, 5 to 20 percent soft noble metal, 5 to 20 percent metal fluorides, and 20 to 60 percent metal binder is used in a powdered metallurgy process for the production of self-lubricating components, such as bearings. The use of the material allows the self-lubricating bearing to maintain its low friction properties over an extended range of operating temperatures.

Sliney, Harold E.↗
NASA NTRS1994

Leveraging metal matrix composites to reduce costs in space mechanisms

Advanced metal matrix composites may be one of the most promising technologies for reducing cost in structural components without compromise to strength or stiffness. A microlight 12.50 N (2.81 lb), two-axis, solar array drive assembly (SADA) was made for the Advanced Materials Applications to Space Structures (AMASS) Program flight experiment. The SADA had both its inner and outer axis housings fabricated from silicon carbide particulate reinforced alumimun. Two versions of the housings were made. The first was machined from a solid billet of material. The second was plaster cast to a near net shape that required minimal finish machining. Both manufacturing methods were compared upon completion. Results showed a cost savings with the cast housing was possible for quantities greater than one and probable for quantities greater than two. For quantities approaching ten, casting resulted in a reduction factor of almost three in the cost per part.

Nye, Ted↗
NASA NTRS1994

ASCA observations of Cassiopeia A

The ASCA Observatory provides the first capability to map a diffuse X-ray source in individually resolved emission lines. We have applied this capability to the Cas A supernova remnant, measuring the mean energies and equivalent widths of 14 line features in three distinct spatial regions. The northwest (NW) and southeast (SE) regions provide the large fraction of the X-ray emission at energies below 4 keV, and define the axis of a Doppler map of the remnant constructed by measuring the peak energy of the prominent Si-K feature. Using restoration techniques to obtain image quality equivalent to 30 sec full width at half maximum (FWHM), we present restored images in the two brightest line features, and in two continuum bands. An emission region in the west is increasingly prominent at higher energies, and its markedly lower metallicity and correlation with radio emission suggest that its X-ray emission has a larger component from fore-shocked material than do the NW and SE regions where the emission is presumed to be dominated by reverse-shocked material.

Holt, Stephen S.↗
NASA NTRS2001

Lightweight Chambers for Thrust Assemblies

The Marshall Space Flight Center (MSFC) of the National Aeronautics and Space Administration (NASA) has successfully applied new materials and fabrication techniques to create actively cooled thrust chambers that operate 200-400 degrees hotter and weigh 50% lighter than conventional designs. In some vehicles, thrust assemblies account for as much as 20% of the engine weight. So, reducing the weight of these components and increasing their operating range will benefit many engines and vehicle designs, including Reusable Launch Vehicle (RLV) concepts. Obviously, copper and steel alloys have been used successfully for many years in the chamber components of thrust assemblies. Yet, by replacing the steel alloys with Polymer Matrix Composite (PMC) and/or Metal Matrix Composite (MMC) materials, design weights can be drastically reduced. In addition, replacing the traditional copper alloys with a Ceramic Matrix Composite (CMC) or an advanced copper alloy (Cu-8Cr-4Nb, also known as GRCop-84) significantly increases allowable operating temperatures. Several small MMC and PMC demonstration chambers have recently been fabricated with promising results. Each of these designs included GRCop-84 for the cooled chamber liner. These units successfully verified that designs over 50% lighter are feasible. New fabrication processes, including advanced casting technology and a low cost vacuum plasma spray (VPS) process, were also demonstrated with these units. Hot-fire testing at MSFC is currently being conducted on the chambers to verify increased operating temperatures available with the GRCop-84 liner. Unique CMC chamber liners were also successfully fabricated and prepared for hot-fire testing. Yet, early results indicate these CMC liners need significantly more development in order to use them in required chamber designs. Based on the successful efforts with the MMC and PMC concepts, two full size "lightweight" chambers are currently being designed and fabricated for hot-fire testing at MSFC in 2001. These "full size" chambers will be similar in size to those used on the X33 engine (RS2200). One will be fabricated with a MMC structural jacket, while the other uses a PMC jacket. Each will be designed for thrust levels of 15,000 pounds in an oxygen/hydrogen environment with liquid hydrogen coolant. Both chambers will use GRCop-84 for its channel wall liner. Each unit is expected to be at least 60% lighter than a conventional design with traditional materials. Hot-fire testing on the full size units in late 2001 will directly compare performance results between a conventional chamber design and these "lightweight" alternatives. The technology developed and demonstrated by this effort will not only benefit next generation RLV programs, but it can be applied to other existing and future engine programs, as well. Efforts were sponsored by the Advanced Space Transportation Program for RLV Focused Technologies. The task team was led by MSFC with additional members from NASA-Glenn Research Center and the Rocketdyne Division of The Boeing Company. Specific materials development and fabrication processes were provided by Aerojet, Lockheed Martin Astronautics, Composite Optics, Inc., Hyper-Therm, Ceramic Composites, Inc., MSE Technology Applications, and Plasma Processes, Inc.

Elam, Sandra K.↗
NASA NTRS2004

Development of Thin Film Ceramic Thermocouples for High Temperature Environments

The maximum use temperature of noble metal thin film thermocouples of 1100 C (2000 F) may not be adequate for use on components in the increasingly harsh conditions of advanced aircraft and next generation launch technology. Ceramic-based thermocouples are known for their high stability and robustness at temperatures exceeding 1500 C, but are typically found in the form of rods or probes. NASA Glenn Research Center is investigating the feasibility of ceramics as thin film thermocouples for extremely high temperature applications to take advantage of the stability and robustness of ceramics and the non-intrusiveness of thin films. This paper will discuss the current state of development in this effort.

Wrbanek, John D.↗
NASA NTRS2005

Effects of Control Mode and R-Ratio on the Fatigue Behavior of a Metal Matrix Composite

Composite Because of their high specific stiffness and strength at elevated temperatures, continuously reinforced metal matrix composites (MMC's) are under consideration for a future generation of aeropropulsion systems. Since components in aeropropulsion systems experience substantial cyclic thermal and mechanical loads, the fatigue behavior of MMC's is of great interest. Almost without exception, previous investigations of the fatigue behavior of MMC's have been conducted in a tension-tension, load-controlled mode. This has been due to the fact that available material is typically less than 2.5-mm thick and, therefore, unable to withstand high compressive loads without buckling. Since one possible use of MMC's is in aircraft skins, this type of testing mode may be appropriate. However, unlike aircraft skins, most engine components are thick. In addition, the transient thermal gradients experienced in an aircraft engine will impose tension-compression loading on engine components, requiring designers to understand how the MMC will behave under fully reversed loading conditions. The increased thickness of the MMC may also affect the fatigue life. Traditionally, low-cycle fatigue (LCF) tests on MMC's have been performed in load control. For monolithic alloys, low-cycle fatigue tests are more typically performed in strain control. Two reasons justify this choice: (1) the critical volume from which cracks initiate and grow is generally small and elastically constrained by the larger surrounding volume of material, and (2) load-controlled, low-cycle fatigue tests of monolithics invariably lead to unconstrained ratcheting and localized necking--an undesired material response because the failure mechanism is far more severe than, and unrelated to, the fatigue mechanism being studied. It is unknown if this is the proper approach to composite testing. However, there is a lack of strain-controlled data on which to base any decisions. Consequently, this study addresses the isothermal, LCF behavior of a [0]_32 MMC tested under strain- and load-controlled conditions for both zero-tension and tension-compression loading conditions. These tests were run at 427 C on thick specimens of SiC-reinforced Ti-15-3. For the fully-reversed tests, no difference was observed in the lives between the load- and strain-controlled tests. However, for the zero-tension tests, the strain-controlled tests had longer lives by a factor of 3 in comparison to the load-controlled tests. This was due to the fact that under strain-control the specimens cyclically softened, reducing the cracking potential. In contrast, the load-controlled tests ratcheted toward larger tensile strains leading to an eventual overload of the fibers. Fatigue tests revealed that specimens tested under fully-reversed conditions had lives approximately an order of magnitude longer than for those specimens tested under zero tension. When examined on a strain-range basis, the fully reversed specimens had similar, but still shorter lives than those of the unreinforced matrix material. However, the composite had a strain limitation at short lives because of the limited strain capacity of the brittle ceramic fiber. The composite also suffered at very high lives because of the lack of an apparent fatigue limit in comparison to the unreinforced matrix. The value of adding fibers to the matrix is apparent when the fatigue lives are plotted as a function of stress range. Here, the composite is far superior to the unreinforced matrix because of the additional load-carrying capacity of the fibers.

Source record↗
NASA NTRS2008

Polymer Coats Leads on Implantable Medical Device

Langley Research Center s Soluble Imide (LaRC-SI) was discovered by accident. While researching resins and adhesives for advanced composites for high-speed aircraft, Robert Bryant, a Langley engineer, noticed that one of the polymers he was working with did not behave as predicted. After putting the compound through a two-stage controlled chemical reaction, expecting it to precipitate as a powder after the second stage, he was surprised to see that the compound remained soluble. This novel characteristic ended up making this polymer a very significant finding, eventually leading Bryant and his team to win several NASA technology awards, and an "R&D 100" award. The unique feature of this compound is the way that it lends itself to easy processing. Most polyimides (members of a group of remarkably strong and incredibly heat- and chemical-resistant polymers) require complex curing cycles before they are usable. LaRC-SI remains soluble in its final form, so no further chemical processing is required to produce final materials, like thin films and varnishes. Since producing LaRC-SI does not require complex manufacturing techniques, it has been processed into useful forms for a variety of applications, including mechanical parts, magnetic components, ceramics, adhesives, composites, flexible circuits, multilayer printed circuits, and coatings on fiber optics, wires, and metals. Bryant s team was, at the time, heavily involved with the aircraft polymer project and could not afford to further develop the polymer resin. Believing it was worth further exploration, though, he developed a plan for funding development and submitted it to Langley s chief scientist, who endorsed the experimentation. Bryant then left the high-speed civil transport project to develop LaRC-SI. The result is an extremely tough, lightweight thermoplastic that is not only solvent-resistant, but also has the ability to withstand temperature ranges from cryogenic levels to above 200 C. The thermoplastic s unique characteristics lend it to many commercial applications; uses that Bryant believed would ultimately benefit industry and the Nation. "LaRC-SI," he explains, "is a product created in a government laboratory, funded with money from the tax-paying public. What we discovered helps further the economic competitiveness of the United States, and it was our goal to initiate the technology transfer process to ensure that our work benefited the widest range of people." Several NASA centers, including Langley, have explored methods for using LaRC-SI in a number of applications from radiation shielding and as an adhesive to uses involving replacement of conventional rigid circuit boards. In the commercial realm, LaRC-SI can now be found in several commercial products, including the thin-layer composite unimorph ferroelectric driver and sensor (THUNDER) piezoelectric actuator, another "R&D 100" award winner (Spinoff 2005).

Source record↗
NASA NTRS2012

Analysis of Direct Samples of Early Solar System Aqueous Fluids

Over the past three decades we have become increasingly aware of the fundamental importance of water, and aqueous alteration, on primitive solar-system bodies. Some carbonaceous and ordinary chondrites have been altered by interactions with liquid water within the first 10 million years after formation of their parent asteroids. Millimeter to centimeter-sized aggregates of purple halite containing aqueous fluid inclusions were found in the matrix of two freshly-fallen brecciated H chondrite falls, Monahans (1998, hereafter simply "Monahans") (H5) and Zag (H3-6) (Zolensky et al., 1999; Whitby et al., 2000; Bogard et al., 2001) In order to understand origin and evolution of the aqueous fluids inside these inclusions we much measure the actual fluid composition, and also learn the O and H isotopic composition of the water. It has taken a decade for laboratory analytical techniques to catch up to these particular nanomole-sized aqueous samples. We have recently been successful in (1) measuring the isotopic composition of H and O in the water in a few fluid inclusions from the Zag and Monahans halite, (2) mineralogical characterization of the solid mineral phases associated with the aqueous fluids within the halite, and (3) the first minor element analyses of the fluid itself. A Cameca ims-1270 equipped with a cryo-sample-stage of Hokkaido University was specially prepared for the O and H isotopic measurements. The cryo-sample-stage (Techno. I. S. Corp.) was cooled down to c.a. -190 C using liquid nitrogen at which the aqueous fluid in inclusions was frozen. We excavated the salt crystal surfaces to expose the frozen fluids using a 15 keV Cs+ beam and measured negative secondary ions. The secondary ions from deep craters of approximately 10 m in depth emitted stably but the intensities changed gradually during measurement cycles because of shifting states of charge compensation, resulting in rather poor reproducibility of multiple measurements of standard fluid inclusions of +/- 90 0/00(2 sigma) for delta D, and +/- 29 0/00 (2 sigma) for delta O-18. On the other hand, the reproducibility of Delta O-17 is plus or minus 8 /00 (2 sigma ) because the observed variations of isotope ratios follow a mass dependent fractionation law. Variations of delta D of the aqueous fluids range over sog,a 330(90; 2 sigma ) to +1200(90) 0/00 for Monahans and delta 300(96) 0/00 to +90(98)0/00 for Zag. Delta O-17 of aqueous fluids range over delta 16(22) 0/00 to +18(10) 0/00 for Monahans and +3(10) 0/00 to +27(11) 0/00 for Zag. These variations are larger than the reproducibility of standard analyses and suggest that isotope equilibria were under way in the fluids before trapping into halite. The mean values of delta D and Delta O-17 are +290 0/00 and +9 0/00, respectively. The mean values and the variations of these fluids are different from the representative values of ordinary chondrites, verifying our working hypothesis that the fluid inclusion-bearing halites were not indigenous to the H chondrite parent-asteroid but rather represent exogenous material delivered onto the asteroid from a separate cryovolcanically-active body. This initial isotopic work has demonstrated the feasibility of the measurements, but also revealed sample processing and analytical shortcomings that are now being addressed. Examination of solid mineral inclusions within Monahans and Zag halite grains by confocal Raman spectroscopy at the Carnegie Geophysical Laboratory has revealed them to be metal, magnetite, forsteritic olivine (Fo.98), macromolecular carbon (MMC), pyroxenes, feldspar with Raman spectral affinity to anorthoclase and, probably, fine-grained lepidocrocite (FeO(OH)). In addition, one inclusion features aliphatic material with Raman spectral features consistent with a mixture of short-chain aliphatic compounds. We have initiated analyses of the bulk composition of the fluids within the inclusions in Zag and Monahans halites at Virginia Tech by LA ICPMS using angilent 7500ce quadrupole ICPMS and a Lambda Physik GeoLas 193 nm excimer laser ablation system. Preliminary results reveal that the inclusion aqueous fluids contain highly charged cations of Ca, Mg and Fe. The minerals and compounds discovered thus far within Monahans/Zag halites are indicative of an originating body at least partly composed of unequilibrated anhydrous materials (high Fo olivine, pyroxenes, feldspars, possibly the metal) which were subjected to aqueous alteration (the halite parent brine) and containing a light organic component (the short-chain aliphatic compounds). This material was ejected from the originating body with little or no disruption, as evidenced with the presence of fluid inclusions. An actively geysering body similar to modern Enceladus (Postberg et al., 2011) may be a reasonable analogue in this respect. Also, the originating body should have been within close proximity to the H chondrite parent in order to generate the number of halite grains seen in Monahans and Zag. Other candidates for Monahans/Zag halite parent bodie(s) may include a young Ceres with its possible liquid ocean, or Main Belt comets.

Zolensky, Michael E.↗
NASA NTRS2012

Multicolor Detectors for Ultrasensitive Long-Wave Imaging Cameras

A document describes a zeptobolometer for ultrasensitive, long-wavelength sensors. GSFC is developing pixels based on the zeptobolometer design that sense three THz wavelengths simultaneously. Two innovations are described in the document: (1) a quasiparticle (QO) filter arrangement that enables a compact multicolor spectrum at the focal plane, and (2) a THz antenna readout by up to three bolometers. The innovations enable high efficiency by greatly reducing high, frequency-dependent microstrip losses, and pixel compactness by eliminating the need for bulky filters in the focal plane. The zeptobolometer is a small TES bolometer, on the scale of a few microns, which can be readily coupled through an impedance-matching resistor to a metal or dielectric antenna. The bolometer is voltage-biased in its superconducting transition, allowing the use of superconducting RF multiplexers to read out large arrays. The antenna is geometrically tapped at three locations so as to efficiently couple radiation of three distinct wavelengths to the individual TESs. The transition edge hot electrons in metals offer a simple, compact arrangement for antenna readout, which can be crucial in the THz where line losses at high frequencies can be substantial. A metallic grill filter acts as a high-pass filter and directs the low-frequency components to a location where they will be absorbed. The absorption spectrum shows that three well-separated THz bands are feasible. The filters can be made from high-purity dielectrics such as float zone silicon or sapphire.

Brown, Ari↗
NASA NTRS2018

Composite Overwrapped Pressure Vessel (COPV) Life Test

Recent attention has been focused on how NASA and its commercial partners have been placing less emphasis on testing and have become more dependent on analytical methods when evaluating design margins for fracture-critical components. Of high concern is the possible misuse of such analytic models for thin-walled metallic liners for composite overwrapped pressure vessels (COPVs). The NASA Engineering and Safety Center (NESC) has initiated an assessment to understand the limitations of linear-elastic fracture mechanics (LEFM) computational methods used to predict fatigue crack growth rate behavior of small cracks in thin metal liners for COPVs. It has been observed that fabrication of some thin metallic liners results in a wide variation in microstructure morphology, which results in varying microscale crack growth mechanisms. The ultimate goal is to develop and demonstrate a test-based methodology validating the safe-life requirements for COPVs with thin, elastically responding metal liners where LEFM methods are not appropriate.

Russell, Richard↗