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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

The He I emission lines of SN 1987A

We model the evolution of the He I lines, especially He I 1.083 micrometers and He I 2.058 micrometers, from the envelope of SN 1987A during the first 3 yr after the explosion. The He I metastable 2(sup 3)S and 2(sup 1)S states are populated by fast electrons resulting from energy deposition by gamma rays and depopulated by electron collisions and two-photon decay. The 2.058 micrometer line is excited mainly by nonthermal electrons at all times. The 1.083 micrometer line is excited mainly by thermal electron impact for t less than or approximately = 450 days and by recombination afterward. We can fit the observed evolution of He I 2.058 micrometers with a model in which approximately 3 solar mass of nearly pure helium and approximately 11 solar mass of hydrogen mixed with primordial helium occupy the volume emitting most of the light (v less than or approximately = 2500 km/s). For t less than or approximately = 450 days, trace carbon in the inner part of the helium suppresses the He I 2.058 micrometer line by photoabsorbing He I lambda 584 and depopulating the 2(sup 1) P(sup 0) state. The observed 1.08 micrometer line is a blend of He I 1.083 micrometers and (S I) 1.082 micrometers. We estimate that He I 1.083 micrometers contributes 40% of the observed flux for t less than or approximately = 550 days and approximately 60% thereafter.

Li, Hongwei↗
NASA NTRS2000

Minimum Energy Requirements for Sustained Microbial Activity in Anoxic Sediments

Currently understood mechanisms of biochemical energy conservation dictate that, in order to be biologically useful, energy must be available to organisms in "quanta" equal to, at minimum one-third to one-fifth of the energy required to synthesize ATP in vivo. The existence of this biological energy quantum means that a significant fraction of the chemical amp on Earth cannot be used to drive biological productivity, and places a fundamental thermodynamic constraint on the origins, evolution, and distribution of life. We examined the energy requirements of intact microbial assemblages in anoxic sediments from Cape Lookout Bight, NC, USA, using dissolved hydrogen concentrations as a non-invasive probe. In this system, the thermodynamics of metabolic processes occurring inside microbial cells is reflected quantitatively by H2 concentrations measured outside those cells. We find that methanogenic archaea are supported by energy yields as small as 10 kJ per mol, about half the quantity calculated from studies of microorganisms in culture. This finding implies that a significantly broader range of geologic and chemical niches might be exploited by microorganisms than would otherwise be expected.

Hoehler, Tori M.↗
NASA NTRS2021

FUMES. II. Ly α Reconstructions of Young, Active M Dwarfs

The H I Ly α (1215.67 Å) emission line dominates the far-UV spectra of M dwarf stars, but strong absorption from neutral hydrogen in the interstellar medium makes observing Ly α challenging even for the closest stars. As part of the Far-Ultraviolet M-dwarf Evolution Survey, the Hubble Space Telescope has observed 10 early-to-mid M dwarfs with ages ranging from ∼24 Myr to several Gyr in order to evaluate how the incident UV radiation evolves through the lifetime of exoplanetary systems. We reconstruct the intrinsic Ly α profiles from STIS G140L and E140M spectra, and achieve reconstructed fluxes with 1σ uncertainties ranging from 5% to a factor of two for the low-resolution spectra (G140L) and 3%–20% for the high-resolution spectra (E140M). We observe broad, 500–1000 km s −1 wings of the Ly α line profile, and analyze how the line width depends on stellar properties. We find that stellar effective temperature and surface gravity are the dominant factors influencing the line width with little impact from the star's magnetic activity level, and that the surface flux density of the Ly α wings may be used to estimate the chromospheric electron density. The Ly α reconstructions on the G140L spectra are the first attempted on λ/Δλ ∼ 1000 data. We find that the reconstruction precision is not correlated with the signal-to-noise ratio of the observation—rather, it depends on the intrinsic broadness of the stellar Ly α line. Young, low-gravity stars have the broadest lines and therefore provide more information at low spectral resolution to the fit to break degeneracies among model parameters.

Allison Youngblood↗
NASA NTRS1987

The evolution of red clump stars - Theoretical sequences

Two grids of horizontal-branch evolutionary sequences are presented which extend the grid of Sweigart and Gross (1976) to higher masses and higher metallicities. These two grids were constructed specifically for the study of red clump stars observed in intermediate-age star clusters in the Magellanic Clouds and in the Galaxy. An additional evolutionary track, with a thick hydrogen-burning shell which simulates the effect of a modest amount of mixing from the helium core into the shell at the time of the helium-core flash, is also presented. It is found that a small amount of mixing does not alter in a significant way the standard course of horizontal-branch evolution.

Seidel, E.↗
NASA NTRS1996

Spatial Variation of the 3.29 and 3.40 Micron Emission Bands Within Reflection Nebulae and The Photochemical Evolution of Methylated Polycyclic Aromatic Hydrocarbons

Spectra of 3 microns emission features have been obtained at several positions within the reflection nebulae NGC 1333 SVS3 and NGC 2023. Strong variations of the relative intensities of the 3.29 microns feature and its most prominent satellite band at 3.40 microns are found. It is shown that: (1) the 3.40 microns band is too intense with respect to the 3.29 microns band at certain positions to arise from hot band emission alone, (2) the 3.40 microns band can be reasonably well matched by new laboratory spectra of gas-phase polycyclic aromatic hydrocarbons (PAHs) with alkyl (-CH3) side groups, and (3) the variations in the 3.40 microns to 3.29 microns band intensity ratios are consistent with the photochemical erosion of alkylated PAHs. We conclude that the 3.40 microns emission feature is attributable to -CH3 side groups on PAH molecules. We predict a value of 0.5 for the peak intensity ratio of the 3.40 and 3.29 microns emission bands from free PAHs in the diffuse interstellar medium, which would correspond to a proportion of one methyl group for four peripheral hydrogens. We also compare the 3 microns spectrum of the proto-planetary nebula IRAS 05341 + 0852 with the spectrum of the planetary nebula IRAS 21282 + 5050. We suggest that a photochemical evolution of the initial aliphatic and aromatic hydrocarbon mixture formed in the outflow is responsible for the changes observed in the 3 microns emission spectra of these objects.

Joblin, C.↗
NASA NTRS1996

Spatial variation of the 3.29 and 3.40 micron emission bands within reflection nebulae and the photochemical evolution of methylated polycyclic aromatic hydrocarbons

Spectra of 3 micrometers emission features have been obtained at several positions within the reflection nebulae NGC 1333 SVS3 and NGC 2023. Strong variations of the relative intensities of the 3.29 micrometers feature and its most prominent satellite band at 3.40 micrometers are found. It is shown that (i) the 3.40 micrometers band is too intense with respect to the 3.29 micrometers band at certain positions to arise from hot band emission alone, (ii) the 3.40 micrometers band can be reasonably well matched by new laboratory spectra of gas-phase polycyclic aromatic hydrocarbons (PAHs) with alkyl (-CH3) side groups, and (iii) the variations in the 3.40 micrometers to 3.29 micrometers band intensity ratios are consistent with the photochemical erosion of alkylated PAHs. We conclude that the 3.40 micrometers emission feature is attributable to -CH3 side groups on PAH molecules. We predict a value of 0.5 for the peak intensity ratio of the 3.40 and 3.29 micrometers emission bands from free PAHs in the diffuse interstellar medium, which would correspond to a proportion of one methyl group for four peripheral hydrogens. We also compare the 3 micrometers spectrum of the proto-planetary nebula IRAS 05341+0852 with the spectrum of the planetary nebula IRAS 21282+5050. We suggest that a photochemical evolution of the initial aliphatic and aromatic hydrocarbon mixture formed in the outflow is responsible for the changes observed in the 3 micrometers emission spectra of these objects.

NASA Center ARC↗
NASA NTRS1972

Thermogravity system designed for use in dispersion strengthening studies

A thermogravimetry system designed to study the reduction of oxides in metal and alloy powders to be used in dispersion strengthened materials is described. The apparatus was devised for use at high temperatures with controlled atmospheres. Experimental weight change and moisture evolution results for the thermal decomposition of calcium oxalate monohydrate in dry helium, and experimental weight change results for the reduction of nickel oxide in dry hydrogen and hydrogen containing 15,000 PPM water vapor are presented. The system is currently being successfully applied to the evaluation of the reduction characteristics and the removal of impurities from metals and alloys to be used for dispersion strengthening.

Herbell, T. P.↗
NASA NTRS1972

Thermogravimetry system designed for use in dispersion strengthening studies.

A thermogravimetry system, designed to study the reduction of oxides in metal and alloy powders to be used in dispersion strengthened materials, is described. The apparatus was devised for use at high temperatures with controlled atmospheres. Experimental weight change and moisture evolution results for the thermal decomposition of calcium oxalate monohydrate in dry helium, and experimental weight change results for the reduction of nickel oxide in dry hydrogen and hydrogen containing 15,000 p.p.m. water vapor are presented. The system is currently being successfully applied to the evaluation of the reduction characteristics and the removal of impurities from metals and alloys to be used for dispersion strengthening.

Herbell, T. P.↗
NASA NTRS1973

Ultraviolet selection pressure on the earliest organisms

It had been proposed by Sagan (1957, 1961) that UV light, partially penetrating the primitive reducing atmosphere of the earth, posed a major problem for the earliest evolution of life. This argument is now updated and refined. The picture of a secondary reducing atmosphere is presented. It is assumed that an excess of hydrogen from this atmosphere has already escaped to space. The genetic material surrounded itself as a solution to the UV selection pressure with bases or nucleotides having no function whatever in replication or protein synthesis.

Sagan, C.↗
NASA NTRS1986

Structural integrity and durability for Space Shuttle main engine and future reusable space propulsion systems

NASA is conducting a program which will establish a technology base for the orderly evolution of reusable space propulsion systems. As part of that program, NASA initiated a Structural Integrity and Durability effort for advanced high-pressure oxygen-hydrogen rocket engine technology. That effort focuses on the development of: (1) accurate analytical models to describe flow fields; aerothermodynamic loads; structural responses; and fatigue/fracture, from which life prediction codes can be evolved; and (2) advanced instrumentation with capabilities to verify the codes in an SSME-like environment as well as the potential for future use as diagnostic sensors for real-time condition monitoring of critical engine components.

Marsik, S. J.↗
NASA NTRS1986

Structural integrity and durability for Space Shuttle main engine and future reusable space propulsion systems

NASA is conducting a program which will establish a technology base for the orderly evolution of reusable space propulsion systems. As part of that program, NASA initiated a Structural Integrity and Durability effort for advanced high-pressure oxygen-hydrogen rocket engine technology. That effort focuses on the development of: (1) accurate analytical models to describe flow fields; aerothermodynamic loads; structural responses; and fatigue/fracture, from which life prediction codes can be evolved; and (2) advanced instrumentation with capabilities to verify the codes in an SSME-like environment as well as the potential for future use as diagnostic sensors for real-time condition monitoring of critical engine components.

Marsik, S. J.↗
NASA NTRS1993

Moessbauer spectrometer for mineralogical analysis of the Mars surface: Moessbauer source considerations

Development of space rocketry and cosmic instrument making has made it possible to create interplanetary stations to be sent to the solar system bodies. In the last decade of the century the planet Mars will be in the focus of planetary science problems. Russia, USA (the NASA) and Europe (the ESA) plan to do a new step in the study of the planetary system by spacecraft missions to Mars. One part of the programs of these missions is Martian surface measurements of iron, which is a dominant element in both the Martian soil and rocks (about 13 percent by weight). The chemistry of iron in space is strongly coupled to the chemistry of abundant elements (to begin with hydrogen, carbon, oxygen) and it is this coupling of chemical cycles of abundant elements that gives us the possibility of understanding some features of the chemical evolution of matter. In this connection of extremely great importance for the understanding of the evolution of the solar system are the oxidation state of the iron and its mineral composition of the Mars surface. Being highly successful, the Viking landers had no instrumentation to answer these questions. Such instrumentation has to be specifically sensitive to mineralogy. For this purpose the back scattering Moessbauer spectrometer (MS-96) was proposed to be installed on a rover to be launched on board the Russian spacecraft Mars-96 mission to Mars. Due to power and mass restrictions three systems of the device MS-96 (velocity transducer, detector and electronic components) have been extremely miniaturized in comparison to a standard system. In this paper we intend to place for consideration a radioactive source to find out what characteristics it should have to be suitable for purposes of the experiment.

Evlanov, E. N.↗
NASA NTRS1995

Insights to primitive replication derived from structures of small oligonucleotides

Available information on the structure of small oligonucleotides is surveyed. It is observed that even small oligomers typically exhibit defined structures over a wide range of pH and temperature. These structures rely on a plethora of non-standard base-base interactions in addition to the traditional Watson-Crick pairings. Stable duplexes, though typically antiparallel, can be parallel or staggered and perfect complementarity is not essential. These results imply that primitive template directed reactions do not require high fidelity. Hence, the extensive use of Watson-Crick complementarity in genes rather than being a direct consequence of the primitive condensation process, may instead reflect subsequent selection based on the advantage of accuracy in maintaining the primitive genetic machinery once it arose.

Review↗
NASA NTRS1997

Mineral induced phosphorylation of glycolate ion--a metaphor in chemical evolution

Bilateral surface-active minerals with excess positive charge concentrate glycolate and trimetaphosphate ion from l0(-3) m aqueous solution to half-saturation of the internal surface sites, and induce phosphorylation of glycolate ion in the mineral with trimetaphosphate, sorbed from l0(-2) m solution. By utilizing reactants from dilute solution at near-neutral pH, and eliminating the need for participating organic nitrogen compounds, the reaction comprises several elements considered necessary for geochemical realism in models for molecular evolution.

NASA Discipline Exobiology↗
NASA NTRS2010

SSME - Materials and Methods for Addressing High-Pressure Hydrogen Embrittlement

From the humid, corrosion-friendly atmosphere of KSC, to the extreme heat of ascent, to the cold vacuum of space, the Space Shuttle faced one hostile environment after another. One of those harsh environments the hydrogen environment existed within the shuttle itself. Liquid hydrogen was the fuel that powered the shuttle s complex, powerful, and reusable main engine. Hydrogen provided the high specific impulse the bang per pound of fuel needed to perform the shuttle s heavy lifting duties. Hydrogen, however, was also a potential threat to the very metal of the propulsion system that used it. The diffusion of hydrogen atoms into a metal can make it more brittle and prone to cracking a process called hydrogen embrittlement. This effect can reduce the toughness of carefully selected and prepared materials. A concern that exposure to hydrogen might encourage crack growth was present from the beginning of the Space Shuttle Program, but the rationale for using hydrogen was compelling. This paper outlines the material characterization, anomaly resolution, and path to understanding of hydrogen embrittlement on superalloys through the course of the SSME program. Specific examples of nickel alloy turbine housings and single crystal turbine blades are addressed. The evolution of fracture mechanics analytical methods is also addressed.

Matejczk, Daniel↗
NASA NTRS1985

Advanced research and technology programs for advanced high-pressure oxygen-hydrogen rocket propulsion

A research and technology program for advanced high pressure, oxygen-hydrogen rocket propulsion technology is presently being pursued by the National Aeronautics and Space Administration (NASA) to establish the basic discipline technologies, develop the analytical tools, and establish the data base necessary for an orderly evolution of the staged combustion reusable rocket engine. The need for the program is based on the premise that the USA will depend on the Shuttle and its derivative versions as its principal Earth-to-orbit transportation system for the next 20 to 30 yr. The program is focused in three principal areas of enhancement: (1) life extension, (2) performance, and (3) operations and diagnosis. Within the technological disciplines the efforts include: rotordynamics, structural dynamics, fluid and gas dynamics, materials fatigue/fracture/life, turbomachinery fluid mechanics, ignition/combustion processes, manufacturing/producibility/nondestructive evaluation methods and materials development/evaluation. An overview of the Advanced High Pressure Oxygen-Hydrogen Rocket Propulsion Technology Program Structure and Working Groups objectives are presented with highlights of several significant achievements.

Marsik, S. J.↗