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At least 289 records · Page 16
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NASA NTRS2000

Airbreathing Propulsion System Analysis Using Multithreaded Parallel Processing

In this paper, parallel processing is used to analyze the mixing, and combustion behavior of hypersonic flow. Preliminary work for a sonic transverse hydrogen jet injected from a slot into a Mach 4 airstream in a two-dimensional duct combustor has been completed [Moon and Chung, 1996]. Our aim is to extend this work to three-dimensional domain using multithreaded domain decomposition parallel processing based on the flowfield-dependent variation theory. Numerical simulations of chemically reacting flows are difficult because of the strong interactions between the turbulent hydrodynamic and chemical processes. The algorithm must provide an accurate representation of the flowfield, since unphysical flowfield calculations will lead to the faulty loss or creation of species mass fraction, or even premature ignition, which in turn alters the flowfield information. Another difficulty arises from the disparity in time scales between the flowfield and chemical reactions, which may require the use of finite rate chemistry. The situations are more complex when there is a disparity in length scales involved in turbulence. In order to cope with these complicated physical phenomena, it is our plan to utilize the flowfield-dependent variation theory mentioned above, facilitated by large eddy simulation. Undoubtedly, the proposed computation requires the most sophisticated computational strategies. The multithreaded domain decomposition parallel processing will be necessary in order to reduce both computational time and storage. Without special treatments involved in computer engineering, our attempt to analyze the airbreathing combustion appears to be difficult, if not impossible.

Schunk, Richard Gregory↗
NASA NTRS1979

Scaling and the start-up phase of space industrialization

By terrestrial standards very little mass is needed to construct the space portion of a 10,000 megawatt (10 GW) power system. Use of lunar materials makes it reasonable to consider alternatives to silicon solar cells for conversion of sunlight to electricity and thereby avoid present major problems associated with solar cell production. Machinery needed on the moon to excavate lunar materials and deliver them to a transport system, to beneficiate lunar materials, to produce glasses and ceramics from lunar materials and to chemically process lunar materials into their major oxides and elements are minor mass fractions of the total mass of equipment needed in space to produce an SPS. In addition the processing equipment can throughput several hundred times their own mass each year with very little requirement for makeup mass from earth.

Criswell, D. R.↗
NASA NTRS2005

How Does Abundance Affect the Strength of UV Emission in Elliptical Galaxies?

This program used the Far Ultraviolet Spectroscopic Explorer (FUSE) to observe elliptical galaxies with the intention of measuring the chemical abundances in their hot stellar populations. It was designed to complement an earlier FUSE program that observed elliptical galaxies with strong UV emission. The current program originally planned observations of two ellipticals with weak UV emission (M32 and M49). Once FUSE encountered pointing control problems in certain regions of the sky (particularly Virgo, which is very unfortunate for the study of ellipticals in general), M49 was replaced with the bulge of M31, which has a similar UV-to-optical flux ratio as the center of M49. As the closest elliptical galaxy and the one with the weakest UV-to-optical flux ratio, M32 was an obvious choice of target, but M49 was the ideal complementary target, because it has a very low reddening (unlike M32). With the inability of FUSE to point at Virgo, nearly all of the best elliptical galaxies (bright galaxies with low foreground extinction) were also lost, and this severely hampered three FUSE programs of the PI, all focused on the hot stellar populations of ellipticals. M31 was the best replacement for M49, but like M32, it suffers from significant foreground reddening. Strong Galactic ISM lines heavily contaminate the FUSE spectra of M31 and M32. These ISM lines are coincident with the photospheric lines from the stellar populations (whereas M49, with little foreground ISM and significant redshift, would not have suffered from this problem). We have reduced the faint (and thus difficult) data for M31 and M32, producing final co-added spectra representing all of the exposures, but we have not yet finished our analysis, due to the complication of the contaminating ISM. The silver lining here is the set of CHI lines at 1175 Angstroms, which are not significantly contaminated by the ISM. A comparison of the M31 spectrum with other galaxies observed by FEE showed a surprising result: the hot stars in M31 seem to have a similar carbon abundance to those stars in galaxies with much brighter UV emission. The fraction of these hot stars in a population should be a strong function of chemical abundances, so this finding warrants further exploration, and we are proceeding with our analysis. Because the UV emission in these galaxies comes from a population of extreme horizontal branch stars, the PI (Brown) presented this result at a June 2003 conference on such stars.

Sonneborn, George↗
NASA NTRS2011

Z-Pinch Magneto-Inertial Fusion Propulsion Engine Design Concept

Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human spaceflight missions. Magneto-Inertial Fusion (MIF) is an approach which has been shown to potentially lead to a low cost, small fusion reactor/engine assembly (1). The Z-Pinch dense plasma focus method is an MIF concept in which a column of gas is compressed to thermonuclear conditions by an estimated axial current of approximately 100 MA. Recent advancements in experiments and the theoretical understanding of this concept suggest favorable scaling of fusion power output yield as I(sup 4) (2). The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this is repeated over short timescales (10(exp -6) sec). This plasma formation is widely used in the field of Nuclear Weapons Effects (NWE) testing in the defense industry, as well as in fusion energy research. There is a wealth of literature characterizing Z-Pinch physics and existing models (3-5). In order to be useful in engineering analysis, a simplified Z-Pinch fusion thermodynamic model was developed to determine the quantity of plasma, plasma temperature, rate of expansion, energy production, etc. to calculate the parameters that characterize a propulsion system. The amount of nuclear fuel per pulse, mixture ratio of the D-T and nozzle liner propellant, and assumptions about the efficiency of the engine, enabled the sizing of the propulsion system and resulted in an estimate of the thrust and Isp of a Z-Pinch fusion propulsion system for the concept vehicle. MIF requires a magnetic nozzle to contain and direct the nuclear pulses, as well as a robust structure and radiation shielding. The structure, configuration, and materials of the nozzle must meet many severe requirements. The configuration would focus, in a conical manner, the Deuterium-Tritium (D-T) fuel and Lithium-6/7 liner fluid to meet at a specific point that acts as a cathode so the Li-6 can serve as a current return path to complete the circuit. In addition to serving as a current return path, the Li liner also serves as a radiation shield. The advantage to this configuration is the reaction between neutrons and Li-6 results in the production of additional Tritium, thus adding further fuel to the fusion reaction and boosting the energy output. To understand the applicability of Z-Pinch propulsion to interplanetary travel, it is necessary to design a concept vehicle that uses it. The propulsion system significantly impacts the design of the electrical, thermal control, avionics, radiation shielding, and structural subsystems of a vehicle. The design reference mission is the transport of crew and cargo to Mars and back, with the intention that the vehicle be reused for other missions. Several aspects of this vehicle are based on a previous crewed fusion vehicle study called Human Outer Planet Exploration (HOPE), which employed a Magnetized Target Fusion (MTF) propulsion concept. Analysis of this propulsion system concludes that a 40-fold increase of Isp over chemical propulsion is predicted. This along with a greater than 30% predicted payload mass fraction certainly warrants further development of enabling technologies. The vehicle is designed for multiple interplanetary missions and conceivably may be suited for an automated one-way interstellar voyage.

Miernik, Janie H.↗
NASA NTRS1997

Chemical Vapor Deposited SiC (SCS-0) Fiber-Reinforced Strontium Aluminosilicate Glass-Ceramic Composites

Unidirectional SrO Al2O3 2SiO2 glass-ceramic matrix composites reinforced with uncoated Chemical Vapor Deposited (CVD) SiC (SCS-0) fibers have been fabricated by hot-pressing under appropriate conditions using the glass-ceramic approach. Almost fully dense composites having a fiber volume fraction of 0.24 have been obtained. Monoclinic celsian, SrAl2Si2O8, was the only crystalline phase observed in the matrix by x-ray diffraction. No chemical reaction was observed between the fiber and the matrix after high temperature processing. In three-point flexure, the composite exhibited a first matrix cracking stress of approx. 231 +/- 20 MPa and an ultimate strength of 265 +/- 17 MPa. Examination of fracture surfaces revealed limited short length fiber pull-out. From fiber push-out, the fiber/matrix interfacial debonding and frictional strengths were evaluated to be approx. 17.5 +/- 2.7 MPa and 11.3 +/- 1.6 MPa, respectively. Some fibers were strongly bonded to the matrix and could not be pushed out. The micromechanical models were not useful in predicting values of the first matrix cracking stress as well as the ultimate strength of the composites.

Bansal, Narottam P.↗
NASA NTRS2004

On the Origin of GEMS

GEMS (glass with embedded metal and sulfides) are a major component of anhydrous interplanetary dust particles (IDPs) their physical and chemical characteristics show marked similarities to contemporary interstellar dust. Recent oxygen isotopic measurements confirm that at least a small fraction (less than 5%) of GEMS are demonstrably presolar, while the remainder have ratios that are indistinguishable from solar values. GEMS with solar oxygen isotopic compositions either (1) had their isotopic compositions homogenized through processing in the interstellar medium (ISM), or (2) formed in the early solar system. Isotopic homogenization necessarily implies chemical homogenization, so (interstellar) GEMS compositions should reflect the average composition of dust in the local ISM. We performed a systematic examination of the bulk chemistry of GEMS in primitive IDPs in order to test this hypothesis.

Keller, L. P.↗
NASA NTRS2014

Mass Dependency of Isotope Fractionation of Gases Under Thermal Gradient and Its Possible Implications for Planetary Atmosphere Escaping Process

Physical processes that unmix elements/isotopes of gas molecules involve phase changes, diffusion (chemical or thermal), effusion and gravitational settling. Some of those play significant roles for the evolution of chemical and isotopic compositions of gases in planetary bodies which lead to better understanding of surface paleoclimatic conditions, e.g. gas bubbles in Antarctic ice, and planetary evolution, e.g. the solar-wind erosion induced gas escaping from exosphere on terrestrial planets.. A mass dependent relationship is always expected for the kinetic isotope fractionations during these simple physical processes, according to the kinetic theory of gases by Chapman, Enskog and others [3-5]. For O-bearing (O16, -O17, -O18) molecules the alpha O-17/ alpha O-18 is expected at 0.5 to 0.515, and for S-bearing (S32,-S33. -S34, -S36) molecules, the alpha S-33/ αlpha S-34 is expected at 0.5 to 0.508, where alpha is the isotope fractionation factor associated with unmixing processes. Thus, one isotope pair is generally proxied to yield all the information for the physical history of the gases. However, we recently] reported the violation of mass law for isotope fractionation among isotope pairs of multiple isotope system during gas diffusion or convection under thermal gradient (Thermal Gradient Induced Non-Mass Dependent effect, TGI-NMD). The mechanism(s) that is responsible to such striking observation remains unanswered. In our past studies, we investigated polyatomic molecules, O2 and SF6, and we suggested that nuclear spin effect could be responsible to the observed NMD effect in a way of changing diffusion coefficients of certain molecules, owing to the fact of negligible delta S-36 anomaly for SF6.. On the other hand, our results also showed that for both diffusion and convection under thermal gradient, this NMD effect is increased by lower gas pressure, bigger temperature gradient and lower average temperature, which indicate that the nuclear spin effect may not be the significant contributor as the energies involved in the hyperfine effect are much smaller than those with molecular collisions, especially under convective conditions.

Sun, Tao↗
NASA NTRS1999

Mineralogy of the Solar System

The coming decade will witnesses the first sample return missions from solar system bodies in 30 years. These samples will all be very small, some missions return only a few milligrams of total mass. Fortunately, the capability of modem methods to characterize ultra-small samples is well established from analysis of interplanetary dust particles (IDPs), interstellar grains recovered from meteorites, and other materials requiring ultra-sensitive analytical capabilities. Powerful analytical techniques are available that require, under favorable circumstances, single particles of only a few nanograms for entire suites of fairly comprehensive characterizations. A returned sample of greater than 1,000 particles with total mass of just one microgram permits comprehensive quantitative geochemical measurements that are impractical to can-y out in situ by flight instruments. With the Galileo flybys of Gaspra and Ida, it is now recognized that even very small airless bodies have indeed developed a particulate regolith. Acquiring a sample of the bulk regolith, a simple sampling strategy, provides two critical pieces of information about the body. Regolith samples are excellent bulk samples since they normally contain all the key components of the local environment, albeit in particulate form. Furthermore, since this fine fraction dominates remote measurements, regolith samples also provide information about surface alteration processes and are a key link to remote sensing of other bodies. Studies indicate that a statistically significant number of nanogram-sized particles should be able to characterize the regolith of a primitive asteroid, although the presence of larger components within even primitive meteorites (e.g.. Murchison), e.g. chondrules, CAI, large crystal fragments, etc., points out the limitations of using data obtained from nanogram-sized samples to characterize entire primitive asteroids. However, most important asteroidal geological processes have left their mark on the matrix, since this is the finest-grained portion and therefore most sensitive to chemical and physical changes. Thus, the following information can be learned from this fine grain size fraction alone: (1) mineral paragenesis; (2) regolith processes, (3) bulk composition; (4) conditions of thermal and aqueous alteration (if any); (5) relationships to planets, comets, meteorites (via isotopic analyses, including oxygen; (6) abundance of water and hydrated material; (7) abundance of organics; (8) history of volatile mobility, (9) presence and origin of presolar and/or interstellar material.

Zolensky, Michael E.↗
NASA NTRS1984

The chemistry and origin of the ordinary chondrites Implications from refractory-lithophile and siderophile elements

Thirty-eight ordinary chondrites (17 H, 20 L, and 1 LL) have been analyzed for major and selected trace elements. These data indicate that the lithophile elements Mg, Ca, Al, Cr, and V normalized to Si are in higher abundance in the H than in the L chondrites. The siderophile elements Ni, Co, and Fe show very good correlation within, as well as between, the two major ordinary chondrite groups. Twenty-four of the analyses are of Antarctic finds, while ten are samples of falls. Comparing the Antarctic data with the fall data reveals no evidence that any of the elements studied here have been mobilized by terrestrial weathering processes. Within the H and L chondrite groups there is little chemical variation, indicating that the source of these samples is remarkably homogeneous. Equilibrium condensate fractionation from a nebula of CI composition can result in the observed ordinary chondrite compositions. The fractionation of metal at about 1440 K (and 0.001 atm) into high and low iron groups, followed by a gas-solid fractionation at about 1380 K with the H group losing more solids than the L, will produce the observed H and L compositions and intragroup trends.

Fulton, C. R.↗
NASA NTRS1992

A subgrid mixing model for LES of nonpremixed turbulent combustion

A new sub-grid mixing model for use in large eddy simulations of turbulent combustion is presented and applied to a hydrogen-air diffusion flame. The sub-grid model is based on Kerstein's Linear Eddy Model (1988). The model is first used to predict the mixing of a conserved scalar in a turbulent shear flow. The model correctly predicts the behavior of the pdf of the scalar field and displays a nonmarching peak at the preferred mixture fraction as the shear layer is traversed. It is then illustrated how a reduced chemical mechanism can be implemented within the linear eddy subgrid model formulation. The model is used to predict NO formation in hydrogen-air diffusion flame using a reduced chemical mechanism involving nine reactive scalars.

Mcmurtry, P. A.↗
NASA NTRS1995

Modeling of turbulent chemical reaction

Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.

Chen, J.-Y.↗
NASA NTRS1977

Chemical characterization of lunar core 60010

Twenty-eight major, minor, and trace-element abundances have been determined in nine fines fractions of core 60010 by instrumental thermal and 14 MeV neutron activation analysis. With the exception of the elements Fe, Co, and Ni, core section 60010 exhibits a much more uniform composition than the lower section (60009) of the double drive tube collected at the Apollo 16 LM site. The siderophilic meteorite indicator elements Fe, Co, and Ni are significantly enriched in subsample 40, which is located 3.0-4.5 cm below the lunar surface, and are highly variable throughout the 60010 core section. Microscopic examination of subsample 40 revealed the presence of numerous metallic fragments including an approximately 1-mm metal fragment exhibiting only Fe, Co, Ni, and Ir gamma-ray peaks and having a composition typical of a coarse octahedrite. Composition profiles of 60010 exhibit small variations in lithophilic element abundances which can be related to most of the seven stratigraphic units of Duke and Nagle (1976). Although the basal portion of 60010 has been described as texturally similar to the upper unit of 60009, the present chemical studies show a marked compositional difference at this interface.

Ali, M. Z.↗
NASA NTRSDate not supplied

Constraints on triple oxygen isotope kinetics

The general assumption that systems are in equilibrium is convenient, but imperfect. Instead, the partial or full expression of kinetic reaction steps may need to be determined. Using an isotope fractionation Monte-Carlo model under the harmonic approximation (Figure 1 envelopes), we find the range of kinetic isotope effects (i.e., resulting from unidirectional chemical reactions) contains and exceeds the range of accessible equilibrium isotope effects. For the 16O-17O-18O system, accessible kinetic isotope effects can yield Δ′17O variations as large 0.8‰ from a single kinetic fractionation step. Reactions that yield the largest deviations from equilibrium are those with the largest molecular mass difference between decomposition fragments, typically the two products, such as a gas and solid generated from the thermal decomposition of an initial solid. For example, previously published experiments on the thermal decomposition of calcite (CaCO3) and dehydroxylation of brucite (Mg(OH)2) are matched by density functional theory models of each kinetic isotope effect, thus revealing their origin in mass-dependent reaction. Beyond oxygen, our approach applies to any system with more than two isotopes.

Oxygen isotopes↗
NASA NTRS2014

Assessing the Origins of Aliphatic Amines in the Murchison Meteorite from their Compound-Specific Carbon Isotopic Ratios and Enantiomeric Composition

The study of meteoritic organic compounds provides a unique window into the chemical inventory of the early Solar System and prebiotic chemistry that may have been important for the origin of life on Earth. Multiple families of organic compounds have been extracted from the Murchison meteorite, which is one of the most thoroughly studied carbonaceous chondrites. The amino acids extracted from Murchison have been extensively analyzed, including measurements of non-terrestrial stable isotopic ratios and discoveries of L-enantiomeric excesses for alpha-dialkyl amino acids, notably isovaline. However, although the isotopic signatures of bulk amine-containing fractions have been measured, the isotopic ratios and enantiomeric composition of individual aliphatic amines, compounds that are chemically related to amino acids, remain unknown. Here, we report a novel method for the extraction, separation, identification and quantitation of aliphatic monoamines extracted from the Murchison meteorite. Our results show a complete suite of structural isomers, with a larger concentration of methylamine and ethylamine and decreasing amine concentrations with increasing carbon number. The carbon isotopic compositions of fourteen meteoritic aliphatic monoamines were measured, with delta C-13 values ranging from +21% to +129%, showing a decrease in C-13 with increasing carbon number, a relationship that may be consistent with the chain elongation mechanism under kinetic control previously proposed for meteoritic amino acids. We also found the enantiomeric composition of sec-butylamine, a structural analog to isovaline, was racemic within error, while the isovaline extracted from the same Murchison piece showed an L-enantiomeric excess of 9.7; this result suggested that processes leading to enantiomeric excess in the amino acid did not affect the amine. We used these collective data to assess the primordial synthetic origins of these meteoritic aliphatic amines and their potential linkage to meteoritic amino acids.

prebiotic chemistry↗
NASA NTRS1988

Infrared spectroscopy of Jupiter and Saturn

High resolution infrared spectoscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn. The 5 micrometer spectral region, which is transparent to deep levels, is particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. These are tracers of convective and strongly non-equilibrium processes in the atmosphere. High resolution ground-based spectroscopy complements Voyager and Galileo measurements. Spectroscopy is sensitive to lower mixing levels for selected molecules, while the on-board mass spectrometers probe molecules that are spectroscopically inaccessible. Analysis and modeling of the 4.7 micrometer carbon monoxide in Jupiter was completed. CO is present at a mole fraction of 1.6 plus or minus 0.3 x 10 to the 9th power and concentrated in the troposphere. At this abundance, it must be convected upward from much deeper levels in Jupiter where the temperature is near 1100 K. Thus CO is a tracer of the deep atmosphere which is otherwise unobservable. The oxygen abundance in Jupiter (as measured by the CO abundance) is near solar. Chemical or physical process must deplete the major oxygen carrier, water. Germane, GeH4, was discovered on Saturn at amole fraction of 4 plus or minus 2 x 10 to the 10th power.

Knacke, Roger↗
NASA NTRS1975

Micrometeoroid velocity-and-trajectory analyzer

By adding potential energy of charged capacitor to kinetic energy of impacting particle, new technique causes major fraction of atoms in microscopic particle impacting on particle-receiving surface to be ionized. Chemical constituents of impacting particle are represented by generated ion mass spectrum in approximately correct proportions.

Auer, S. O.↗
NASA NTRS1975

On the origin of high-Ti mare basalts

Analyses were conducted of sixteen Apollo 17 mare basalts for alkali, alkaline-earth, and rare-earth elements, Co, and Sc. The obtained data were utilized in a study concerning the nature of the igneous processes responsible for the chemical variations among the high-Ti, low-K basalts. Estimates were obtained regarding the abundances of the large-ion, lithophile elements in the source regions for the basalts. It is shown that the source regions could plausibly have been produced by processes believed to have occurred during the early history of the moon. Attention is given to chemical variations among the Apollo 17 mare basalts, near-surface (low-pressure) crystal fractionation, partial melting, limits on the extent of partial melting, and a summary of possible events leading to formation of high-Ti mare basalts.

Shih, C.-Y.↗