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At least 145 records · Page 8

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NASA NTRSDate not supplied

In-Situ Resource Utilization Modeling of a Lunar Water Processing System

A key element of achieving a sustained surface presence, such as defined in NASA’s Artemis plan, is In-Situ Resource Utilization (ISRU). ISRU is the practice of using local resources to provide mission consumables that reduce system launch mass requirements, and regenerate resources (chiefly, water and oxygen) for propulsion and life support supporting both Lunar and Martian missions. ISRU systems require multiple complex processes, such as excavation, chemical reactors, and electrolysis subsystems that must operate in harmony to optimize the overall system process from beginning to end. The Mission Analysis and Integration Tool (MAIT) was previously developed with MATLAB in FY22 to connect individual subsystem models into a customized, flexible framework for the purpose of technology downselect, optimization, and end-to-end process planning. Beginning in FY24, MAIT was updated and became the capital program in the Systems Engineering and Integration (SE&I) ISRU Modeling and Analysis (SIMA) project. Prior work was leveraged and evolved using MATLAB/Simulink due to its ability to communicate with a vast number of other programming languages and makes up the backbone of data flow between inputs and outputs to the subsystem models. MAIT initially evaluated a suite of ISRU-related technologies, including the water processing Lunar Auger Dryer for ISRU (LADI) system with integrated upstream excavation and downstream electrolysis subsystems. With individual models consolidated, the MAIT tool generated over 5,000 cases during its first round of parametric sweeps on the water processing architecture at multiple production targets; the system analysis produced valuable insight into the optimal LADI geometry that minimized energy demands, estimated effects to cold trap size and radiator requirements, and calculated the power dynamics of the electrolysis unit and liquid oxygen storage volume. Additional efforts are being made to demonstrate the ability to scale ISRU technologies supporting the Space Technology Mission Directorate’s (STMD) commercialization strategy and increase the MAIT software capability. Work is ongoing to handle a wide array of ISRU system models beyond the Lunar environment, e.g. production of propellant for a Martian lander.

Avery Carlson↗

NASA NTRSDate not supplied

In-Situ Resource Utilization Modeling of a Lunar Water Processing System

Avery Carlson↗

NASA NTRS1980

Changes in surface chemistry of silicon carbide (0001) surface with temperature and their effect on friction

Friction studies were conducted with a silicon carbide (0001) surface contacting polycrystalline iron. The surface of silicon carbide was pretreated: (1) by bombarding it with argon ions for 30 minutes at a pressure of 1.3 pascals; (2) by heating it at 800 C for 3 hours in vacuum at a pressure of 10 to the minus eighth power pascal; or (3) by heating it at 1500 C for 3 hours in a vacuum of 10 to the minus eighth power pascal. Auger emission spectroscopy was used to determine the presence of silicon and carbon and the form of the carbon. The surfaces of silicon carbide bombarded with argon ions or preheated to 800 C revealed the main Si peak and a carbide type of C peak in the Auger spectra. The surfaces preheated to 1500 C revealed only a graphite type of C peak in the Auger spectra, and the Si peak had diminished to a barely perceptible amount. The surfaces of silicon carbide preheated to 800 C gave a 1.5 to 3 times higher coefficient of friction than did the surfaces of silicon carbide preheated to 1500 C. The coefficient of friction was lower in the 11(-2)0 direction than in the 10(-1)0 direction; that is, it was lower in the preferred crystallographic slip direction.

Miyoshi, K.↗

NASA NTRS1991

Plasma-deposited germanium nitride gate insulators for indium phosphide metal-insulator-semiconductor field-effect transistors

Plasma-deposited germanium nitride was investigated for the first time as a possible gate insulator for InP compound semiconductor metal-insulator-semiconductor FET (MISFET) technology. The germanium nitride films were successfully deposited in a capacitively coupled parallel plate reactor at 13.56 MHz operation using GeH4/N2/NH3 and GeH4/N2 mixtures as reactant gases. The former process produced better quality films with enhanced uniformity, increased deposition rates, and increased resistivity. The breakdown field strength of the films was greater than 10 to the 6th V/cm. Auger electron spectroscopy did not indicate significant chemical composition differences between the two processes. For MISFETs with 2-micron channel lengths fabricated on InP, the device transconductance and threshold voltage for the GeH4/N2/NH3 process were 17 mS/mm and -3.6 V, respectively. The drain-source breakdown voltages were greater than 10 V.

Johnson, Gregory A.↗

NASA NTRS1999

Characterization of In-Situ BN Interface Formed by Nitridation of Nextel 312

Treatment of Nextel (TM) 312 in a reactive environment has been used as a low cost approach to the formation of BN on the fiber surface. Although the BN enriched surface region is extremely thin (less than 40 run), it is effective in providing debonding and composite behavior. Variation in mechanical behavior of Nextel (TM) 312/BN/Blackglas (TM) composites has been noted among panels fabricated with AF-10 cloth treated in different nitridation runs, Understanding this variation became the rationale for undertaking a detailed characterization of the nitrided fiber using field emission scanning electron microscopy, low voltage energy dispersive x-ray and Auger electron spectroscopy. Chemical composition and surface morphology are discussed in relation to observed mechanical behavior of NeXtel (TM) 312/Blackglas (TM) composites tested in bending.

Hurwitz, Fances I.↗

NASA NTRS1984

Thermal oxidation of 3C silicon carbide single-crystal layers on silicon

Thermal oxidation of thick single-crystal 3C SiC layers on silicon substrates was studied. The oxidations were conducted in a wet O2 atmosphere at temperatures from 1000 to 1250 C for times from 0.1 to 50 h. Ellipsometry was used to determine the thickness and index of refraction of the oxide films. Auger analysis showed them to be homogeneous with near stoichiometric composition. The oxide growth followed a linear parabolic relationship with time. Activation energy of the parabolic rate constant was found to be 50 kcal/mole, while the linear rate constant was 74 kcal/mole. The latter value corresponds approximately to the energy required to break a Si-C bond. Electrical measurements show an effective density of 4-6 x 10 to the 11th per sq cm for fixed oxide charges at the oxide-carbide interface, and the dielectric strength of the oxide film is aproximately 6 x 10 to the 6th V/cm.

Fung, C. D.↗

NASA NTRSDate not supplied

Probing the Properties of Superheavy Dark Matter Annihilating or Decaying into Neutrinos With Ultra-High Energy Neutrino Experiments

The evidence for dark matter particles,x, is compelling based on Galactic to cosmological scale observations. Thus far, the promising weakly interacting massive particle scenario have eluded detection, motivating alternative models of dark matter. We consider scenarios involving super-heavy dark matter (SHDM) that potentially can decay or annihilate to neutrinos and antineutrinos. In the mass range m(sub x) =10(exp 7) −10(exp 15) GeV, we evaluate the sensitivities of future observatories PO-EMMA and GRAND for indirect dark matter detection via the measurement of neutrino-induced extensive air showers (EAS), compute the Auger and ANITA limits using their last up-to-date sensitivities, and compare them with IceCube limits. We also show that the uncertainties related to the dark matter distribution in the Galactic halo have a large impact on the neutrino flux. We show that a ground-based radio detector such as GRAND can achieve high sensitivities due to its large effective area and high duty cycle. Space-based Cherenkov detectors such as POEMMA that measure the EAS optical Cherenkov signal have the advantage of full-sky coverage and rapid slewing, enabling an optimized SHDM observation strategy focusing on the Galactic Center. We show that increasing the field of view of the Cherenkov detectors can significantly enhance the sensitivity. Moreover, POEMMA’s fluorescence observation mode that measures EAS above20EeV will achieve state-of-the-art sensitivity to SHDM properties at the highest mass scales.

Claire Guepin↗

NASA NTRS1986

Sliding Seal Materials for Adiabatic Engines, Phase 2

An essential task in the development of the heavy-duty adiabatic diesel engine is identification and improvements of reliable, low-friction piston seal materials. In the present study, the sliding friction coefficients and wear rates of promising carbide, oxide, and nitride materials were measured under temperature, environmental, velocity, and loading conditions that are representative of the adiabatic engine environment. In addition, silicon nitride and partially stabilized zirconia disks were ion implanted with TiNi, Ni, Co, and Cr, and subsequently run against carbide pins, with the objective of producing reduced friction via solid lubrication at elevated temperature. In order to provide guidance needed to improve materials for this application, the program stressed fundamental understanding of the mechanisms involved in friction and wear. Electron microscopy was used to elucidate the micromechanisms of wear following wear testing, and Auger electron spectroscopy was used to evaluate interface/environment interactions which seemed to be important in the friction and wear process. Unmodified ceramic sliding couples were characterized at all temperatures by friction coefficients of 0.24 and above. The coefficient at 800 C in an oxidizing environment was reduced to below 0.1, for certain material combinations, by the ion implanation of TiNi or Co. This beneficial effect was found to derive from lubricious Ti, Ni, and Co oxides.

Lankford, J.↗

NASA NTRS1986

Dry etching of beta-SiC in CF4 and CF4 + O2 mixtures

Dry etching of cubic (100) beta-SiC single-crystal thin films produced via chemical-vapor deposition (CVD) has been performed in CF4 and CF4 + O2 mixtures, in both the reactive-ion-etching (RIE) and plasma-etching modes. The latter process yielded measurable etch rates, but produced a dark surface layer which appears, from the results of secondary-ion mass spectrometry, to be residual SiC. The RIE samples had no residual layer, but Auger electron spectroscopy did reveal a C-rich surface. The optimal RIE conditions were obtained with 10 sccm of pure CF4 at 40 mtorr and a power density of 0.548 W/sq cm, giving an etch rate of 23.3 nm/min. Neither the increase of temperature between 293 and 573 K, nor the incremental addition of O2 to CF4 to 50 percent, produced any strong effect on the etch rates of SiC during RIE. Pictorial evidence of fine line structures produced by RIE of beta-SiC films are also presented.

Palmour, J. W.↗

NASA NTRS1979

XPS and SAM studies of the surface chemistry of lunar impact glasses including 12054

We report and discuss quantitative X-ray photoemission (XPS) analyses of mm size areas and qualitative scanning Auger microprobe (SAM) analyses of micron size areas on the surfaces of impact glass coatings found on fragments in the 14161 coarse fines and on the top surface, and a reentrant crack surface of rock 12054. The data suggest that some segregation occurs during impact glass formation leading to surface enrichments in Si and depletions in Mg, Al, Ca, and Ti. The magnitude of the effect appears fairly small, although the complexity of the surfaces severely complicates the data analysis. Because of the complexity of the surfaces, both XPS and SAM data were essential. A search for direct evidence of either solar wind sputter erosion or vapor deposition on the exposed top surface of 12054 provided interesting results which we cannot yet fully interpret. Both this surface and the surface from the re-entrant crack showed enrichments of more than a factor of two in Fe with respect to the bulk.

Housley, R. M.↗

NASA NTRS1978

Research on lunar materials

Abstracts of 14 research reports relating to investigations of lunar samples are presented. The principal topics covered include: (1) optical properties of surface and core samples; (2) chemical composition of the surface layers of lunar grains: Auger electron spectroscopy of lunar soil and ground rock samples; (3) high frequency electrical properties of lunar soil and rock samples and their relevance for the interpretation of lunar radar observations; (4) the electrostatic dust transport process; (5) secondary electron emission characteristics of lunar soil samples and their relevance to the dust transportation process; (6) grain size distribution in surface soil and core samples; and (7) the optical and chemical effects of simulated solar wind (2keV proton and a particle radiation) on lunar material.

Gold, T.↗

NASA NTRS1978

The effect of minor additions of titanium on the fracture toughness of Fe-12Ni alloys at 77K

Titanium additions ranging from 0.18 to 0.99 atomic percent and heat treatments of 2 hours at 550, 685 and 820 C respectively followed by a water quench were considered. Cubic and rectangular shaped inclusions were noted in the SEM fractographs of the alloys with the Ti additions. A fine precipitate was observed by TEM for the Fe-12Ni-0.18Ti alloys heat treated at 550 C; this precipitate was not observed for the 685 and 820 C heat treatments of the same alloy. Auger mappings of the fracture surfaces indicated a weak to moderate association of the interstitials C, N and O with Ti, the degree of which depended on the particular interstitial and the heat treatment temperature.

Conrad, H.↗

NASA NTRS1987

A high flux source of swift oxygen atoms

A source of swift oxygen atoms is described which has several unique features. A high current ion beam is produced by a microwave discharge, accelerated to 10 keV and the mass selected by a modified Du Pont 21-110 mass spectrometer. The O(+) beam exciting the mass spectrometer is focused into a rectangular shape with an energy spread of less than 1 eV. The next section of the machine decelerates the ion beam into a counterpropagating electron beam in order to minimize space charge effects. After deceleration, the ion beam intersects at 90 deg, a neutral oxygen atom beam, which via resonant charge exchange produces a mixture of O(+) and O. Any remaining O(+) are swept out of the beam by an electric field and differentially pumped away while the desired O beam, collimated by slits, impinges on the target. In situ monitoring of the target surface is done by X-ray photoelectron or Auger spectroscopy. Faraday cups provide flux measurements in the ion sections while the neutral flux is determined by a special torsion balance or by a quadrupole mass spectrometer specially adapted for swift atoms. While the vacuum from the source through the mass spectrometer is maintained by diffusion pumps, the rest of the machine is UHV.

Fink, M.↗

NASA NTRS1983

Sputtering of the gallium-indium eutectic alloy in the liquid phase

Watson and Haff (1980) have discussed a theory which is designed to explain quantitatively isotopic fractionation effects observed during sputtering of simple or complex targets. This theory is based on the assumption that most of the atoms sputtered from a surface originate in the top monolayer. The present investigation is mainly concerned with a direct experimental test of that assumption. The sputtering of both solid and liquid phases of gallium, indium, and the gallium-indium eutectic alloy is studied. Results obtained with the aid of ion scattering and Auger spectroscopy show that, in agreement with rough theoretical expectations, the surface monolayer of a gallium-indium alloy with 16.5 percent indium in bulk contains more than 94 percent indium, while the next layer can be only slightly enriched.

Dumke, M. F.↗

NASA NTRS1973

K-LL Auger transition probabilities for elements with low and intermediate atomic numbers

Radiationless K-LL transition probabilities have been calculated nonrelativistically in j-j coupling and in intermediate coupling, without and with configuration interaction, for elements with atomic numbers from 13 to 47. The system is treated as a coupled two-hole configuration. The single-particle radial wave functions required in the calculation of radial matrix elements, and in the calculation of mixing coefficients in the intermediate-coupling scheme, were obtained from Green's atomic independent-particle model. Comparison with previous theoretical work and with experimental data is made. The effects of intermediate coupling, configuration interaction, and relativity are noted.

Chen, M. H.↗

NASA NTRS1987

Sodium hydroxide anodization of Ti-Al-4V adherends

The use of sodium hydroxide anodization (SHA) for Ti-6Al-4V adherends is examined. The SHA surface is evaluated using SEM, X-ray photoelectron spectroscopy, and Auger electron spectroscopy. The SHA procedures of Kennedy et al. (1983) were employed in this experiment. The photomicrographs of the SHA (sandblasted) and PSHA (sandblasted and pickled) oxide surface reveal that the two surfaces differ. The PSHA is patchy and similar to a chromic acid anodization surface and the porosity of the PSHA is more uniform than the SHA surface. The compositions of the surfaces are studied. It is noted that SHA is an effective pretreatment for Ti-6Al-4V adherends.

Filbey, Jennifer A.↗

NASA NTRS1972

Metallurgical evaluation of factors influencing the ductility of aged T-111

The metallurgical factors influencing the ductility of T-111 (Ta-8W-2Hf) alloy following long-time exposures of GTA welds and tubing in the temperature range 982 C (1800 F) through 1316 C (2400 F) were evaluated by means of scanning and transmission electron microscopy, Auger electron emission spectroscopy, and optical metallographic procedures. No classical aging response occurs in the alloy over the temperature range studied. The ductility impairment implied by previous investigations is not the result of microstructural response of the alloy to thermal exposures. Intergranular failure in the GTA sheet welds appears the result of random contamination by silicon, potassium, and/or fluorine at the grain boundaries of the fusion zones. Exposure to lithium at high temperatures had no adverse effects on the ductility of T-111 tubing. These materials were, however, sensitive to post-age handling and testing procedures.

Gold, R. E.↗

NASA NTRS1996

Electronic and Interfacial Properties of PD/6H-SiC Schottky Diode Gas Sensors

Pd/SiC Schottky diodes detect hydrogen and hydrocarbons with high sensitivity. Variation of the diode temperature from 100 C to 200 C shows that the diode sensitivity to propylene is temperature dependent. Long-term heat treating at 425 C up to 140 hours is carried out to determine the effect of extended heat treating on the diode properties and gas sensitivity. The heat treating significantly affects the diode's capacitive characteristics, but the diode's current carrying characteristics are much more stable with a large response to hydrogen. Scanning Electron Microscopy and X-ray Spectrometry studies of the Pd surface after the heating show cluster formation and background regions with grain structure observed in both regions. The Pd and Si concentrations vary between grains. Auger Electron Spectroscopy depth profiles revealed that the heat treating promoted interdiffusion and reaction between the Pd and SiC dw broadened the interface region. This work shows that Pd/SiC Schottky diodes have significant potential as high temperature gas sensors, but stabilization of the structure is necessary to insure their repeatability in long-term, high temperature applications.

Chen, Liang-Yu↗