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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Organic analysis of the Antarctic carbonaceous chondrites

Thus far, organic analysis of carbonaceous chondrites has proven the only fruitful means of examining complex organic matter of extraterrestrial origin. The present paper presents the results of organic analysis of two Antarctic meteorites, Allan Hills (77306) and Yamato (74662), which may be considered free from terrestrial contamination. Ion-exchange chromatography, gas chromatography and mass spectrometery of meteorite samples reveal the presence in Yamato of 15 and in Allan Hills of 20 protein and nonprotein amino acids, the most abundant of which are glycine and alanine. Abundances of the D and L enantiomers of each amino acid are also found to be nearly equal. Data thus indicate an abiotic extraterrestrial origin for the matter, and confirm a lack of terrestrial contamination.

Kotra, R. K.↗
NASA NTRS1984

Air-sampling inlet contamination by aircraft emissions on the NASA CV-990 aircraft

Results of an experimental investigation of the contamination of air sampling inlets by aircraft emissions from the NASA CV-990 research aircraft are presented. This four-engine jet aircraft is a NASA facility used for many different atmospheric and meteorological experiments, as well as for developing spacecraft instrumentation for remote measurements. Our investigations were performed to provide information on which to base the selection of sampling locations for a series of multi-instrument missions for measuring tropospheric trace gases. The major source of contamination is the exhaust from the jet engines, which generate many of the same gases that are of interest in atmospheric chemistry, as well as other gases that may interfere with sampling measurements. The engine exhaust contains these gases in mixing ratios many orders of magnitude greater than those that occur in the clean atmosphere which the missions seek to quantify. Pressurized samples of air were collected simultaneously from a scoop located forward of the engines to represent clean air and from other multiport scoops at various aft positions on the aircraft. The air samples were analyzed in the laboratory by gas chromatography for carbon monoxide, an abundant combustion by-product. Data are presented for various scoop locations under various flight conditions.

Condon, E. P.↗
NASA NTRS1984

Colloidally separated samples from Allende residues - Noble gases, carbon and an ESCA-study

Results are presented which strengthen the hypothesis of heterogeneity among the carbon- and nitrogen-bearing phases of the Allende meteorite. These data also highlight the possibility of performing physical separations yielding samples in which some of the noble gas- and carbon-bearing phases are extraordinarily predominant over others. The conclusion, based on mass and isotope balance arguments, that a significant portion of the carbonaceous matter in Allende is likely to be gas-poor or gas-free need not weaken the case for carbonaceous carriers for the major noble gas components. The concept that acid-soluble carbonaceous phases contain a multiplicity of components, each of which may have formed under a multiplicity of different physical-chemical conditions, is reemphasized by the results of the present study.

Ott, U.↗
NASA NTRS1986

Tropospheric HO determination by FAGE

In the detection of tropospheric HO by laser excited fluorescence, and alternative air-sampling method, named FAGE (Fluorescence Assay with Gas Expansion) was introduced. Here the air is expanded through a nozzle prior to excitation, in order to improve the ratio of the HO signal to the scattered, fluorescent, and photolytic backgrounds. The improvement comes from the differing pressure dependence of the intensities of these four terms, as well as the distinguishability of their temporal waveforms at low pressures when excited by a pulsed laser. HO has been excited by a YAG/dye laser. Other lasers and pumping paths may perform as well or better in this method. With FAGE, chemical modulation of the HO signal was achieved by hydrocarbon addition to the nozzle flow, converting photolytic HO from an interference to a background. Chemical calibration of the instrumental response to external HO was also achieved, by hydrocarbon decay, at HO concentrations within the ambient range.

Hard, T. M.↗
NASA NTRS1985

Thermophoretically enhanced mass transport rates to solid and transpiration-cooled walls across turbulent (law-of-the-wall) boundary layers

Convective-diffusion mass transfer rate predictions are made for both solid wall and transpiration-cooled 'law-of-the-wall' nonisothermal turbulent boundary layers (TBLs), including the mechanism of thermophoresis, i.e., small particle mass transport 'down a temperature gradient'. The present calculations are confined to low mass-loading situations but span the entire particle size range from vapor molecules to particles near the onset of inertial ('eddy') impaction. It is shown that, when Sc is much greater than 1, thermophoresis greatly increases particle deposition rates to internally cooled solid walls, but only partially offsets the appreciable reduction in deposition rates associated with dust-free gas-transpiration-cooled surfaces. Thus, efficient particle sampling from hot dusty gases can be carried out using transpiration 'shielded' probe surfaces.

Gokoglu, Suleyman A.↗
NASA NTRS1989

Hydrogen-silicon carbide interactions

A study of the thermochemistry and kinetics of hydrogen environmental attack of silicon carbide was conducted for temperatures in the range from 1100 C to 1400 C. Thermodynamic maps based on the parameters of pressure and oxygen/moisture content were constructed. With increasing moisture levels, four distinct regions of attack were identified. Each region is defined by the thermodynamically stable solid phases. The theoretically stable solid phases of Region 1 are silicon carbide and silicon. Experimental evidence is provided to support this thermodynamic prediction. Silicon carbide is the single stable solid phase in Region 2. Active attack of the silicon carbide in this region occurs by the formation of gases of SiO, CO, CH4, SiH4, and SiH. Analysis of the kinetics of reaction for Region 2 at 1300 C show the attack of the silicon carbide to be controlled by gas phase diffusion of H2O to the sample. Silicon carbide and silica are the stable phases common to Regions 3 and 4. These two regions are characterized by the passive oxidation of silicon carbide and formation of a protective silica layer.

Eckel, Andrew J.↗
NASA NTRS1990

Scattered-light scanner measurements of cryogenic liquid-jet breakup

The effect of highly turbulent Mach 1 gas flow and high thermal gradients on drop size measurements was investigated with a scattered light scanner. The instrument, developed at NASA-Lewis, was used to measure characteristic drop diameters or cyrogenic liquid sprays. By correcting for gas turbulence and thermal gradient affects, it was possible to obtain good reproducible data with the scattered light scanner. Tests were conducted primarily in the aerodynamic-stripping regime of liquid atomization and it was found that the loss of small droplets due to vaporization and dispersion had a marketed effect on drop size measurements. The nitrogen gas flow rate exponent of 1.33 is the same as that predicted by atomization theory for liquid jet breakup in high velocity gas flow. However, when the sprays were sampled farther downstream of the atomizer, at axial distances of 2.5 and 4.5 cm, the exponent for W sub n decreased 1.2 and 0.9, respectively. This was attributed to the loss of small droplets due to vaporization when values of downstream axial distances exceeded 1.3 cm.

Ingebo, Robert D.↗
NASA NTRS1990

Catalysts for ultrahigh current density oxygen cathodes for space fuel cell applications

The objective of this research was to identify promising electrocatalyst/support systems for the oxygen cathode in alkaline fuel cells operating at relatively high temperatures, O2 pressures and current densities. A number of materials were prepared, including Pb-Ru and Pb-Ir pyrochlores, RuO2 and Pt-doped RuO2, and lithiated NiO. Several of these were prepared using techniques that had not been previously used to prepare them. Particularly interesting is the use of the alkaline solution technique to prepare the Pt-doped Pb-Ru pyrochlore in high area form. Well-crystallized Pb(2)Ru(2)O(7-y) was used to fabricate high performance O2 cathodes with relatively good stability in room temperature KOH. This material was also found to be stable over a useful potential range at approximately 140 C in concentrated KOH. Other pyrochlores were found to be either unstable (amorphous samples) or the fabrication of the gas-fed electrodes could not be fully optimized during this project period. Future work may be directed at this problem. High area platinum supported on conductive metal oxide supports produced mixed results: small improvements in O2 reduction performance for Pb(2)Ru(2)O(7-y) but a large improvement for Li-doped NiO at room temperature. Nearly reversible behavior was observed for the O2/OH couple for Li-doped NiO at approximately 200 C.

Tryk, D.↗
NASA NTRS1990

Hydrogen-silicon carbide interactions

A study of the thermochemistry and kinetics of hydrogen environmental attack of silicon carbide was conducted for temperatures in the range from 1100 C to 1400 C. Thermodynamics maps based on the parameters of pressure and oxygen/moisture content were constructed. With increasing moisture levels, four distinct regions of attack were identified. Each region is defined by the thermodynamically stable solid phases. The theoretically stable solid phases of region 1 are silicon carbide and silicon. Experimental evidence is provided to support this thermodynamic prediction. Silicone carbide is the single stable solid phase in region 2. Active attack of the silicon carbide in this region occurs by the formation of gases of SiO, CO, CH4, SiH4 and SiH. Analyses of the kinetics of reaction for region 2 at 1300 C show the attack of the silicon carbide to be controlled by gas phase diffusion of H2O to the sample. Silicon carbide and silica are the stable phases common to regions 3 and 4. These two regions are characterized by the passive oxidation of silicon carbide and formation of a protective silica layer.

Eckel, Andrew J.↗
NASA NTRS1992

CVD of SiC and AlN using cyclic organometallic precursors

The use of cyclic organometallic molecules as single-source MOCVD precursors is illustrated by means of examples taken from our recent work on AlN and SiC deposition, with particular focus on SiC. Molecules containing (AlN)3 and (SiC)2 rings as the 'core structure' were employed as the source materials for these studies. The organoaluminum amide, (Me2AlNH2)3, was used as the AlN source and has been studied in a molecular beam sampling apparatus in order to determine the gas phase species present in a hot-wall CVD reactor environment. In the case of SiC CVD, a series of disilacyclobutanes (Si(XX')CH2)2 (with X and X' = H, CH3, and CH2SiH2CH3), were examined in a cold-wall, hot-stage CVD reactor in order to compare their relative reactivities and prospective utility as single-source CVD precursors. The parent compound, disilacyclobutane, (SiH2CH2)2, was found to exhibit the lowest deposition temperature (ca. 670 C) and to yield the highest purity SiC films. This precursor gave a highly textured, polycrystalline film on the Si(100) substrates.

Interrante, L. V.↗
NASA NTRS1995

Gaseous Vortices in Barred Spiral Galaxies

During the course of examining many two-dimensional, as well as a smaller sample of three-dimensional, models of gas flows in barred spiral galaxies, we have been impressed by the ubiquitous presence fo vortex pairs, oriented roughly perpendicular to their bars, with one vortex on each side. The vortices are obvious only when viewed in the bar frame, and the centers of their velocity fields usually are near Lagrangian points L(sub 4,5). In all models that we have studied, the vortices form on essentially the same time scale as that for the development of gaseous spiral arms, typically two bar rotations. Usually the corotation radius, r(sub c), lies slightly beyond the end of the bar. Depending upon the mass distributions of the various components, gas spirals either into, or out of, the vortices: In the former case, the vortices become regions of high density, whereas the opposite is true if the gas spirals out of a vortex. The models described in this paper have low-density vortices, as do most of the models we have studied. Moreover, usually the vortex centers lie approximately within +/- 15 deg of L(sub 4,5). In the stellar dynamic limit, when pressure and viscous forces are absent, short-period orbits exist, centered on L(sub 4,5). These orbits need not cross and therefore their morphology is that of gas streamlines, that is, vortices. We believe that the gas vortices in our models are hydrodynamic analogues of closed, short-period, libration orbits centered on L(sub 4,5).

England, Martin N.↗
NASA NTRS2008

25th Space Simulation Conference. Environmental Testing: The Earth-Space Connection

Topics covered include: Methods of Helium Injection and Removal for Heat Transfer Augmentation; The ESA Large Space Simulator Mechanical Ground Support Equipment for Spacecraft Testing; Temperature Stability and Control Requirements for Thermal Vacuum/Thermal Balance Testing of the Aquarius Radiometer; The Liquid Nitrogen System for Chamber A: A Change from Original Forced Flow Design to a Natural Flow (Thermo Siphon) System; Return to Mercury: A Comparison of Solar Simulation and Flight Data for the MESSENGER Spacecraft; Floating Pressure Conversion and Equipment Upgrades of Two 3.5kw, 20k, Helium Refrigerators; Affect of Air Leakage into a Thermal-Vacuum Chamber on Helium Refrigeration Heat Load; Special ISO Class 6 Cleanroom for the Lunar Reconnaissance Orbiter (LRO) Project; A State-of-the-Art Contamination Effects Research and Test Facility Martian Dust Simulator; Cleanroom Design Practices and Their Influence on Particle Counts; Extra Terrestrial Environmental Chamber Design; Contamination Sources Effects Analysis (CSEA) - A Tool to Balance Cost/Schedule While Managing Facility Availability; SES and Acoustics at GSFC; HST Super Lightweight Interchangeable Carrier (SLIC) Static Test; Virtual Shaker Testing: Simulation Technology Improves Vibration Test Performance; Estimating Shock Spectra: Extensions beyond GEVS; Structural Dynamic Analysis of a Spacecraft Multi-DOF Shaker Table; Direct Field Acoustic Testing; Manufacture of Cryoshroud Surfaces for Space Simulation Chambers; The New LOTIS Test Facility; Thermal Vacuum Control Systems Options for Test Facilities; Extremely High Vacuum Chamber for Low Outgassing Processing at NASA Goddard; Precision Cleaning - Path to Premier; The New Anechoic Shielded Chambers Designed for Space and Commercial Applications at LIT; Extraction of Thermal Performance Values from Samples in the Lunar Dust Adhesion Bell Jar; Thermal (Silicon Diode) Data Acquisition System; Aquarius's Instrument Science Data System (ISDS) Automated to Acquire, Process, Trend Data and Produce Radiometric System Assessment Reports; Exhaustive Thresholds and Resistance Checkpoints; Reconfigurable HIL Testing of Earth Satellites; FPGA Control System for the Automated Test of MicroShutters; Ongoing Capabilities and Developments of Re-Entry Plasma Ground Tests at EADS-ASTRIUM; Operationally Responsive Space Standard Bus Battery Thermal Balance Testing and Heat Dissipation Analysis; Galileo - The Serial-Production AIT Challenge; The Space Systems Environmental Test Facility Database (SSETFD), Website Development Status; Simulated Reentry Heating by Torching; Micro-Vibration Measurements on Thermally Loaded Multi-Layer Insulation Samples in Vacuum; High Temperature Life Testing of 80Ni-20Cr Wire in a Simulated Mars Atmosphere for the Sample Analysis at Mars (SAM) Instrument Suit Gas Processing System (GPS) Carbon Dioxide Scrubber; The Planning and Implementation of Test Facility Improvements; and Development of a Silicon Carbide Molecular Beam Nozzle for Simulation Planetary Flybys and Low-Earth Orbit.

Packard, Edward↗
NASA NTRS2011

A CFD Analysis of Hydrogen Leakage During On-Pad Purge in the ORION/ARES I Shared Volume

A common open volume is created by the stacking of the Orion vehicle onto the Ares I Upper Stage. Called the Shared Volume, both vehicles contribute to its gas, fluid, and thermal environment. One of these environments is related to hazardous hydrogen gas. While both vehicles use inert purge gas to mitigate any hazardous gas buildup, there are concerns that hydrogen gas may still accumulate and that the Ares I Hazardous Gas Detection System will not be sufficient for monitoring the integrated volume. This Computational Fluid Dynamics (CFD) analysis has been performed to examine these topics. Results of the analysis conclude that the Ares I Hazardous Gas Detection System will be able to sample the vent effluent containing the highest hydrogen concentrations. A second conclusion is that hydrogen does not accumulate under the Orion Service Module (SM) avionics ring as diffusion and purge flow mixing sufficiently dilute the hydrogen to safe concentrations. Finally the hydrogen concentrations within the Orion SM engine nozzle may slightly exceed the 1 percent volume fraction when the entire worse case maximum full leak is directed vertically into the engine nozzle.

Ajmani, Kumud↗
NASA NTRS2014

Submillimeter Galaxies as Progenitors of Compact Quiescent Galaxies

Three billion years after the big bang (at redshift z = 2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low-redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3 < z < 6). Simulations show that gas-rich major mergers can give rise to such starbursts, which produce dense remnants. Submillimeter-selected galaxies (SMGs) are prime examples of intense, gas-rich starbursts.With a new, representative spectroscopic sample of compact, quiescent galaxies at z = 2 and a statistically well-understood sample of SMGs, we show that z = 3-6 SMGs are consistent with being the progenitors of z = 2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses, and internal velocities. Assuming an evolutionary connection, their space densities also match if the mean duty cycle of SMG starbursts is 42(sup+40) −29 Myr (consistent with independent estimates), which indicates that the bulk of stars in these massive galaxies were formed in a major, early surge of star formation. These results suggest a coherent picture of the formation history of the most massive galaxies in the universe, from their initial burst of violent star formation through their appearance as high stellar-density galaxy cores and to their ultimate fate as giant ellipticals.

Cosmology - Observations↗
NASA NTRS2015

Determining the Covering Factor of Compton-Thick Active Galactic Nuclei with NuSTAR

The covering factor of Compton-thick (CT) obscuring material associated with the torus in active galactic nuclei (AGNs) is at present best understood through the fraction of sources exhibiting CT absorption along the line of sight (N(sub H) greater than 1.5 x 10(exp 24) cm(exp −2)) in the X-ray band, which reveals the average covering factor. Determining this CT fraction is difficult, however, due to the extreme obscuration. With its spectral coverage at hard X-rays (greater than 10 keV), Nuclear Spectroscopic Telescope Array (NuSTAR) is sensitive to the AGNs covering factor since Compton scattering of X-rays off optically thick material dominates at these energies. We present a spectral analysis of 10 AGNs observed with NuSTAR where the obscuring medium is optically thick to Compton scattering, so-called CT AGNs. We use the torus models of Brightman and Nandra that predict the X-ray spectrum from reprocessing in a torus and include the torus opening angle as a free parameter and aim to determine the covering factor of the CT gas in these sources individually. Across the sample we find mild to heavy CT columns, with N(sub H) measured from 10(exp 24) to 10(exp 26) cm(exp −2), and a wide range of covering factors, where individual measurements range from 0.2 to 0.9. We find that the covering factor, f(sub c), is a strongly decreasing function of the intrinsic 2-10 keV luminosity, L(sub X), where f(sub c) = (−0.41 +/- 0.13)log(sub 10)(L(sub X)/erg s(exp −1))+18.31 +/- 5.33, across more than two orders of magnitude in L(sub X) (10(exp 41.5) - 10(exp 44) erg s(exp −1)). The covering factors measured here agree well with the obscured fraction as a function of LX as determined by studies of local AGNs with L(sub X) greater than 10(exp 42.5) erg s(exp −1).

NGC 4945↗
NASA NTRS2017

Chemical, Structural, and Microstructural Changes in Metallic and Silicon-Based Coating Materials Exposed to Iodine Vapor

The chemical, structural and microstructural behavior of steels (304, 316 and A36), titanium-aluminum alloy (Ti-Al, (6Al-4V)), aluminum-magnesium alloy (Al-Mg, 6061), and coatings (Silcolloy and Dursan (SilcoTek Corporation)) were probed after exposure to iodine laminar flow. Exposures were carried out in a custom-built Iodine Vapor RIG (IVR) at 300 degrees C to an iodine laminar vapor flow of 1 mg min(exp. -1), carried by 145 mL-min(exp. -1) argon gas, for 5, 15 and 30 days. Samples were characterized before and after the experiment by gravimetric analysis, X-ray diffraction (XRD) and cross section electron microscopy analysis coupled with energy dispersive X-ray spectroscopy (EDS). All steels exposed for 30 days formed scales consisting mainly of metal (Cr, Fe, Ni) oxides showing different chemistry, microstructure and crystalline phases. Elemental iodine was only detected by EDS analysis in the scales of stainless steels 304 and 316. After 30 days, the Ti-Al exhibited no detectable scale, suggesting only a very thin film was formed. A scale consisting mainly of aluminum, iodine, and oxygen formed on the Al-Mg sample exposed to 30 days. Some pockets rich in magnesium, iodine and oxygen also formed in this Al-Mg alloy. Stainless steel 316, low carbon steel A36 and Ti-Al alloy coated with Silcolloy and stainless steel 304 coated with Dursan that were exposed for 30 days exhibited no oxidation. Stainless steel 304 coated with Silcolloy exposed for 30 days did not exhibit corrosion although the sample gained weight and the coating exhibited expansion. The weight gain per area performance of the materials exposed in iodine lamina flow containing oxygen at impurity level for 10, 15 and 30 days are reported from the lowest to the highest weight gain per area as follows: Steels: Less than 316 less than 304 less than A36; Ti-Al-Mg based alloys: Al-Mg less than Ti-Al: Considering the experimental uncertainties, no weight change was observed for Stainless steel 316, low carbon steel A36 and Ti-Al alloy coated with Silcolloy and stainless steel 304 coated with Dursan. The corrosion of the alloys is catalyzed by iodine in the presence of oxygen as impurity.

Costa, Gustavo C. C.↗
NASA NTRS2018

Outgas and Vacuum Storage Testing for MAV Hybrid Fuel Grain

As a part of the Mars Ascent Vehicle mission, NASA MSFC has formulated a new hybrid fuel grain from a paraffin blend, named SP-7. As a part of the necessary preparation for the mission, this material must be tested for any outgassing behavior or other property changes due to vacuum exposure. This type of testing had not yet been conducted for this material. The goal of this project was to set up and begin automated analysis of this material, which would then run over the course of a year. To accomplish this goal, a few primary objectives were necessary-construction of a vacuum chamber to house the test, implementation of an automated gas analyzer system, preparation of SP-7 samples, and test initialization.

Mars Ascent Vehicle↗
NASA NTRSDate not supplied

Latest Results from NASA Ames’ COSmIC and Optical Constants Facility (OCF): Determining Optical Constants for Titan, Pluto and Protoplanetary Disks Applications

The NASA Ames COsmic SImulation Chamber (COSmIC) is a unique experimental facility that can be used, among many applications, to produce solid particles from gas phase molecular precursors at low temperature (150 K) using a plasma discharge to induce the chemistry in the stream of a free jet expansion. The choice of the initial gas mixture used to produce the solid sample allows the simulation of either cold planetary atmospheres like Titan or Pluto (with N2/CH4-based initial mixtures), or circumstellar environments (with Ar/CxHy-based initial mixtures). The Ames Optical Constants Facility (OCF) allows the determination of optical constants covering a broad wavelength range with high spectral resolution for solid materials, analogs of organic refractory materials formed in planetary and astrophysical environments. The core of the OCF is a Fourier transform infrared (FTIR) spectrometer that allows the continuous characterization of solid samples in the visible to far-infrared (FIR) range (0.59–200 μm, 16,950–50 cm−1). Modeling of the laboratory measurements conducted with the OCF allows the determination of accurate optical constants, n and k, over the full vis-FIR range. Here we present the latest results of two studies that combined (1) experiments performed with COSmIC to produce analogs of aerosols forming in Titan’s atmosphere and analogs of cosmic grains forming in circumstellar envelops, and (2) the characterization of these analogs with the OCF to provide the real and imaginary parts of their refractive indices, n + ik, to the community, from the visible to the FIR. These optical constants can be used as critical input parameters in radiative transfer, atmospheric and reflectance models to interpret observational data of, e.g., Titan’s atmosphere and protoplanetary disks. Providing optical constants for various materials of different compositions allows to explore a broad range of composition by simulating mixtures of materials. We also present a new project to produce analogs of Pluto’s atmospheric aerosols with COSmIC and determine their optical constants with OCF, to be used in reflectance spectra models for the interpretation of New Horizons observations of Lowell Regio, Sputnik Planitia and Cthulhu.

COsmic SImulation Chamber (COSmIC)↗