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At least 793 records · Page 44

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NASA NTRS1971

Combustion of a premixed system in stagnation flow. I - Theoretical.

The theoretical steady-state and transient characteristics of a premixed combustible system in laminar axisymmetric stagnation flow are studied by way of numerical solution of the governing boundary-layer equations. Computations, which are based on the oxidation reaction of carbon monoxide in humid air, invoke a minimum of simplifying assumptions. Steady-state results include prediction of (1) profiles of the state variables, (2) extinction of blow-off conditions, (3) ignition conditions, and (4) the heat flux to the stagnation point. Computer simulations of the unsteady state provide an indication of the stability of a given steady state to perturbations. Comparisons between some of the predictions of the mathematical model and the results of laboratory experiments will be reported in Part II.

Smith, H. W.↗

NASA NTRS1972

Quantifying parameters influencing the spacing of geostationary satellites.

Parameters affecting satellite spacing must be investigated to fully exploit the limited capacity of the geostationary orbit. The usefulness of laboratory experiments, analytic methods, and space environment experiments in quantifying these factors is discussed. It is concluded that space environment experiments are required to evaluate the effects of operationally related parameters including antenna gain patterns, polarization, and antenna instabilities. A unique method of measuring the time-variant effects of the earth station antenna characteristics on satellite spacing is described as a possible space environment experiment. The proposed experiment uses a single satellite to obtain the required data.

Henry, V. F.↗

NASA NTRS1972

Microcraters on lunar rocks.

Lunar microcraters may consist of a central, glass-lined pit, a halo of microfractured material surrounding the pit and a larger, generally concentric, spall area. A classification of microcraters is based on the presence or absence of a pit and a spall. The change from one crater type to another is gradational. Comparison with laboratory experiments indicates that a primary microcrater may be identified by the presence of melted host rock associated with the crater. Most microcraters are the result of the high-speed impact of primary, extralunar particles. Microcratering represents the small-scale end of a continuum of impact cratering as a process.

Hartung, J. B.↗

NASA NTRS1972

Detection of soil microorganism in situ by combined gas chromatography mass spectrometry

Experimental tests were made to determine whether analysis of volatile metabolic products, formed in situ, is a viable procedure for an extraterrestrial life detection system. Laboratory experiments, carried out under anaerobic conditions with addition of carbon source, extended to include a variety of soils and additional substrates. In situ experiments were conducted without amendment using a vacuum sampling system.

Alexander, M.↗

NASA NTRS1972

Eutectic Experiment Development for Space Processing

A ground base test plan and a specimen evaluation scheme have been developed for the aluminum-copper eutectic solidification experiment to be run in the M518 multipurpose electric furnace during the Skylab mission. Besides thermal and solidification studies a detailed description is given of the quantitative metallographic technique which is appropriate for characterizing eutectic structures. This method should prove a key tool for evaluating specimen microstructure which is the most sensitive indicator of changes produced during solidification. It has been recommended that single grain pre-frozen eutectic specimens be used to simplify microstructural evaluation and to eliminate any porosity in the as-cast eutectic specimens. High purity (99.999%) materials from one supplier should be employed for all experiments. Laboratory studies indicate that porosity occurs in the MRC as-cast eutectic ingots but that this porosity can be eliminated by directional freezing. Chemical analysis shows that the MRC ingots are slightly Al rich and contain about .03% impurity. Because of the impurity content the lower cooldown rate (1.2 C/min) should be used for eutectic freezing if MRC material is used in the M518 furnace.

Hopkins, R. H.↗

NASA NTRS1972

Evolution from amino acids - Lunar occurrence of their precursors.

Review of the present state of experimentally based concepts of organic evolution from amino acids. Earlier studies of the synthesis of amino acid precursors from meteoritic material, lunar dust, and terrestrial lava are briefly summarized, and laboratory experiments in which polymers of amino acids were obtained either by direct heating of dry amino acids or by heating aqueous solutions of mixtures of amino acids are described. In particular, a process is described by which alpha-amino acids were made to react to form linear chains of proteinoids. It is concluded that a proteinoid microsystem was a common ancestor of all life on earth.

Fox, S. W.↗

NASA NTRS1973

Ultrafiltration by a compacted clay membrane. I - Oxygen and hydrogen isotopic fractionation. II - Sodium ion exclusion at various ionic strengths.

Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disk compacted to a porosity of 35% by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5% and in O-18 by 0.8% relative to the residual solution. No additional isotopic fractionation due to a salt-filtering mechanism was observed at NaCl concentrations up to 0.01N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role. The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins. It is shown how it is possible to proceed from the ion exchange capacity of clay minerals and, by means of the Donnan membrane equilibrium concept and the Teorell-Meyer-Siever theory, develop a theory to explain why and to what extent ultrafiltration occurs when solutions of known concentration are forced to flow through a clay membrane.

Coplen, T. B.↗

NASA NTRS1973

A study of selected radiation and propagation problems related to antennas and probes in magneto-ionic media

Research consisted of computations toward the solution of the problem of the current distribution on a cylindrical antenna in a magnetoplasma. The case of an antenna parallel to the applied magnetic field was investigated. A systematic method of asymptotic expansion was found which simplifies the solution in the general case by giving the field of a dipole even at relatively short range. Some useful properties of the dispersion surfaces in a lossy medium have also been found. A laboratory experiment was directed toward evaluating nonlinear effects, such as those due to power level, bias voltage and electron heating. The problem of reflection and transmission of waves in an electron heated plasma was treated theoretically. The profile inversion problem has been pursued. Some results are very encouraging, however, the general question of stability of the solution remains unsolved.

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NASA NTRS1973

Engineering studies related to geodetic and oceanographic remote sensing using short pulsed techniques

Theoretical basis is presented for a feasibility study of measuring global ocean surface current pattern from satellites and aircraft. The analysis is supported by some preliminary laboratory experiments. Since the ultimate goal is to establish an operational routine for monitoring the global current pattern, a nondisturbing remote sensing device using a laser probe was developed. Detailed construction of the measuring system and the results of some preliminary observations are also presented.

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NASA NTRS1974

Processing eutectics in space

Studies which have been done in an earth-based laboratory environment have generally not yielded specimens with the degree of perfection required of the eutectic microstructure to provide test data to evaluate their nonstructural applications. It has been recognized that the low-g environment of an orbiting space laboratory provides a unique environment to re-examine the process of solidification with the goal of producing better microstructures. The objective of this program is to evaluate the feasibility of using the space environment for producing eutectics with microstructures which can be of value on earth. In carrying out this objective, evaluative investigations were carried out on the technology of solidification in a 1-g environment to provide sound baseline data for planning space laboratory experiments.

Douglas, F. C.↗

NASA NTRS1973

Vitrification darkening of rock powders - Implications for optical properties of the lunar surface

Laboratory experiments show that albedoes as low as those on the moon can be produced by vacuum vitrification and associated chemical fractionation of ordinary terrestrial basaltic material. Vitrification is established as an unequivocal process that can account for the low albedo and apparent local darkening with age of the lunar surface. The spectral reflectance curves of glass powders are significantly different than those of the parent rock mineralogy; thus, the presence of ubiquitous glass in lunar surface material complicates compositional determinations by interpretation of spectral reflectance curves. Vitrification of rocks on the moon may highly modify the chemical composition of the resulting glass; thus, glass fragments found in lunar fines cannot be assumed to represent bulk parent rock material. Progressive impact vitrification of lunar surface material throughout the moon's history may have led to a fine-grain, opaque, refractory-rich material we call 'ultimate glass.' This unidentified and, at this point, hypothetical component may exist in dark regolith material; if found, it may be a useful indicator of regolith maturity.

Nash, D. B.↗

NASA NTRS1973

The Apollo program and amino acids

Apollo lunar sample analyses designed to detect the presence of organic compounds are reviewed, and the results are discussed from the viewpoint of relevance to laboratory experiments on the synthesis of amino acids and to theoretical models of cosmochemical processes resulting in the formation of organic compounds. Glycine, alanine, glutamic acid, aspartic acid, serine, and threonine have been found repeatedly in the hydrolyzates of hot aqueous extracts of lunar dust. These compounds represent an early step in the sequence of events leading to the rise of living material and were probably deposited by the solar wind. The results of the Apollo program so far suggest that the pathway from cosmic organic matter to life as it evolved on earth could have been pursued on the moon to the stage of amino acid precursors and then may have been terminated for lack of sufficient water.

Fox, S. W.↗

NASA NTRS1974

A chondrule - Evidence of energetic impact unlikely

It had been concluded by Lange and Larimer (1973) that the morphology and mineralogy of an unusual chondrule from the Ngawi meteorite are the results of a highly energetic impact within the solar nebula. The evidence for this conclusion is examined. It is found that the chondrule does not show evidence of high relative velocities in the solar nebula. It is pointed out that arguments against chondrule production by impact on planetary surfaces on the basis of ejection velocities are not supported by laboratory experiments.

Vedder, J. F.↗

NASA NTRS1973

Instrumentation for one-way satellite PTTI applications

A review of general principles and operational procedures illustrates how the typical passive user and omni receiving antenna can recover Precise Time and Time Interval (PTTI) information from a low altitude navigation satellite system for clock calibration and synchronization. Detailed discussions of concepts and theory of the receiver design are presented. The importance of RF correlation of the received and local PN encoded sequences is emphasized as a means of reducing delay uncertainties of the instrumentation to values compatible with nanosecond to submicrosecond PTTI objectives. Two receiver configurations were fabricated for use in satellite-to-laboratory experiments. In one receiver the delay-locked loop for PN signals synchronization used a dithered amplitude detection process while the second receiver used a complex sums phase detection method for measurement of delay error. The necessity for compensation of Doppler shift is discussed. Differences in theoretical signal acquisition and tracking performance of the design concepts are noted.

Osborne, A. E.↗

NASA NTRS1974

Annoyance and acceptability judgements of noise produced by three types of aircraft by residents living near JFK Airport

A random sample of selected communities near JFK Airport were interviewed. Subsamples, with differing feelings of fear of aircraft crashes and different locations of residence were invited to participate in a laboratory experiment. The subjects were exposed to tape recordings of simulated flyovers of aircraft in approach and departure operations at nominal distances from the airport. The subjects judged the extent of noise annoyance and acceptability of the aircraft noises. Results indicate that level of noise is most significant in affecting annoyance judgements. Subjects with feelings of high fear report significantly more annoyance and less acceptability of aircraft noise than subjects with feelings of low fear.

Borsky, P. N.↗

NASA NTRS1975

Raman backscatter measurement research on water vapor systems

Raman backscatter techniques proved to be a useful remote sensing tool, whose full potential has not been realized. The types of information available from laser probes in atmospheric studies are reviewed. Detection levels for known Raman cross sections are calculated using the laser radar equation. Laboratory experiments performed for H2O, N2, SO2, O2 and HCL indicate that accurate wavelength cross sections need to be obtained, as well as more emphasis on obtaining accurate Raman cross sections of molecular species at wavelengths in the ultraviolet spectra.

Workman, G. L.↗

NASA NTRS1975

Remote measurement of ocean temperature from depolarization in Raman scattering

Ocean temperatures may be mapped in three dimensions from an aircraft down to depths of 2 to 4 attenuation lengths by monitoring Raman radiation backscattered from a laser beam. This paper describes laboratory experiments on the temperature dependence of Raman spectra of saline solutions and calculations of the expected performance of a field system. The Raman technique is of greatest potential utility in coastal and estuarine waters where gradients are relatively high. It is estimated that seawater temperature may be measured to a statistical precision of 0.5 C at depths to four attenuation lengths in two meter water, using one Joule of transmitted laser energy.

Chang, C. H.↗

NASA NTRS1975

Na-D line emission from rock specimens by proton bombardment - Implications for emissions from Jupiter's satellite Io

The effectiveness of low-keV range protons in producing Na line emission from selected sodium-bearing rock and mineral samples is examined. Laboratory experiments show that substantial Na-D line emission is produced by 3- to 5-keV proton bombardment of silicate and halite rock powders. It is found that emission intensity and energy efficiency are directly proportional to sodium content and are dependent on total dose, dose rate, and proton energy. Na-D photon emission is considered to emanate predominantly from sputtered sodium slightly above the target surfaces. It is concluded that the Na-D line emission directly excited during surface sputtering by Jovian magnetospheric protons appears to be an observable component in the Jovian satellite Io emission.

Nash, D. B.↗