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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 37 records · Page 2
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NASA NTRS1974

Photo-polarization study of lunar samples: Negative branch

Polarization measurements with a telescope for the degree of polarization of light reflected by planetary surfaces, and comparative measurement of terrestrial minerals, meteorites, and returned lunar samples are reported. The polarization curve plots of the dependence of the degree of polarization on the phase angle V are plotted and compared with each other to determine the optical characteristics of the planetary surfaces.

Dollfus, A.↗
NASA NTRS1928

Wind Tunnel Tests on Autorotation and the "Flat Spin."

This report deals with the autorotational characteristics of certain differing wing systems as determined from wind tunnel tests made at the Langley Memorial Aeronautical Laboratory. The investigation was confined to autorotation about a fixed axis in the plane of symmetry and parallel to the wind direction. Analysis of the tests leads to the following conclusions: autorotation below 30 degree angle of attack is governed chiefly by wing profile, and above that angle by wing arrangement. The strip method of autorotation analysis gives uncertain results between maximum C subscript L and 35 degrees. The polar curve of a wing system, and to a lower degree of accuracy the polar of a complete airplane model are sufficient for direct determination of the limits of rotary instability, subject to strip method limitations. The results of the investigation indicate that in free flight a monoplane is incapable of flat spinning, whereas an unstaggered biplane has inherent flat-spinning tendencies. The difficulty of maintaining equilibrium in stalled flight is due primarily to rotary instability, a rapid change from stability to instability occurring as the angle of maximum lift is exceeded. (author)

Knight, Montgomery↗
NASA NTRS1973

Polarimetry of Pluto.

Pluto has been observed at a solar phase of 0.8 deg and found to have a degree of polarization of 0.27 percent (probable error 0.02 percent) and a position angle of polarization of 156 deg (probable error 2 deg). The observations indicate that Pluto has a polarization curve with a deep negative branch and, therefore, that its surface is likely to be microscopically rough. The observed polarization is compatible with the small geometric albedo of Pluto. No convincing evidence of variable polarization associated with Pluto's rotation has been found.

Kelsey, L. A.↗
NASA NTRS1980

Theory and application of the polarization-albedo rules

The paper reports results of a computer calculation of the scattering of light from porous particulate surfaces such as those of the moon, asteroids, and airless planets. The scattered-light intensity and polarization are computed as a function of phase angle, and plots are constructed corresponding to the observed empirical rules for deducing albedo from the slope, maximum, and minimum of polarization curves. The approximate linearity of these rules on a log-log plot is confirmed for most solar system objects. The theory shows that the albedo vs. polarization plots correspond directly to a plot in two dimensions of the real vs. imaginary index of refraction of these soils, using curved axes.

Wolff, M.↗
NASA NTRS2011

Gamma-Ray Pulsar Light Curves in Offset Polar Cap Geometry

Recent studies have shown that gamma-ray pulsar light curves are very sensitive to the geometry of the pulsar magnetic field. Pulsar magnetic field geometries, such as the retarded vacuum dipole and force-free magnetospheres, used to model high-energy light curves have distorted polar caps that are offset from the magnetic axis in the direction opposite to rotation. Since this effect is due to the sweepback of field lines near the light cylinder, offset polar caps are a generic property of pulsar magnetospheres and their effects should be included in gamma-ray pulsar light curve modeling. In slot gap models (having two-pole caustic geometry), the offset polar caps cause a strong azimuthal asymmetry of the particle acceleration around the magnetic axis. We have studied the effect of the offset polar caps in both retarded vacuum dipole and force-free geometry on the model high-energy pulse profile~. We find that. corn pared to the profile:-; derived from :-;ymmetric caps, the flux in the pulse peaks, which are caustics formed along the trailing magnetic field lines. increases significantly relative to the off-peak emission. formed along leading field lines. The enhanced contrast produces greatly improved slot gap model fits to Fermi pulsar light curves like Vela, which show very little off-peak emIssIon.

Harding, Alice K.↗
NASA NTRS1995

An experimental study of light scattering by large, irregular particles

The intensity and polarization of light scattered by a variety of types of artificial partices large compared to the wavelength were measured as a function of phase angle. Shape, surface roughness, absorption coefficient, and internal scattering coefficient were varied systematically and their effects studied. Scattering by clear, smooth-surfaced spheres is in quantitative agreement with the predictions of the geometrical optics (ray theory) approximation to physical optics (Mie theory). The phase functions of almost all of the particles measured have both forward and backward scattering lobes. A two-parameter, double Henyey-Greenstein function generally provides reasonably good descriptions of the data, while keeping the number of free parameters to the minimum necessary. On a double Henyey- Greenstein parameter plot all of the particles fall into an L-shaped area of restricted size in which the location is characteristic of the particle type. Formalisms based on the equivalent slab model are also given for estimating the scattering efficiency of a large, irregular particle. For most dielectric particles the transmitted, forward scattered light is partially negatively polarized. It is this component that is respopnsible for the well-known maximum in the polarization curves of planetary regoliths at phase angles around 100 deg. For phase angles between about 30 deg and 70 deg the internally scattered light is found to be randomly polarized in the particles studied here, so that the only contribution to the second component of the Stokes vector is by Fresnel reflection from the particle surface. If this empirical result is general, measurement of the second Stokes vector of the light scattered from a regolith at these angles may provide a method of remotely measuring the mean refractive index.

Mcguire, Audrey F.↗
NASA NTRS1992

Testing Metal Chlorides For Use In Sodium-Cell Cathodes

Cyclic voltammetric curves of transition-metal wires in molten NaAlCl4 electrolyte used to eliminate suitability of transition metals as cathodes in sodium cells. Cyclic voltammetry used in conjunction with measurement of galvanostatic polarization curves determines whether given metal chloride suitable as cathode material in such cell. Cells useful in such high-energy-density and high-power-density applications as leveling loads on electric-power plants, supplying power to electric ground vehicles, and aerospace applications.

Bugga, Ratnakumar V.↗
NASA NTRS1989

Interstellar circular polarization and the dielectric nature of dust grains

The implications of the observed relationship between the wavelength dependence of interstellar circular and linear polarization were reexamined. Mie theory calculations for grains with various optical constants demonstrate that any population of grains which matches the observed wavelength dependence of linear polarization also yields the correct cross-over wavelength of circular polarization. The coincidence of the peak wavelength of linear polarization and the cross-over of circular polarization is therefore independent of the optical constants of the grains and cannot be used as a critical constraint on grain properties. The observed relationship instead reflects a more fundamental connection between linear and circular polarization which was derived from the Kramers-Kronig relations by Shapiro (1975). Numerical results fully support Shapiro's conclusions and demonstrate that the apparent upper limit on the visual absorptivity of polarizing grains deduced from earlier Mie theory calculations (Martin, 1972) was spurious and resulted from a violation of the Kramers-Kronig relations in the assumed optical constants of the particles. The Kramers-Kronig interpretation of circular polarization can be used to place constraints on linear polarization outside the wavelength range in which it was observed. This approach was used to show that the peak observed in the visual is likely to be the only significant feature in the linear polarization curve, which therefore appears to be well approximated at all wavelengths by the Serkowski formula. A synthesis of available laboratory data was used to analyze the properties of dielectric core-mantel grains as the source of visual extinction and polarization.

Chlewicki, Grzegorz↗
NASA NTRS1928

A few more mechanical-flight formulas without the aid of polar diagrams

The reliability of the assumption of a parabolic shape of the polar curve is investigated and found satisfactory for all practical purposes. It is further shown that the aerodynamically best possible or "ideal" airplane is produced on this assumption. Lastly, detailed suggestions are given on the possibilities of application of this method of calculation. It especially simplifies the design and evaluation of structural changes and the determination of the limits of technical possibilities. The present report deals only with the relations of the airfoils. The mutual action of the airfoils, engine and propeller will be treated in a subsequent report.

FORMULAS - PERFORMANCE↗
NASA NTRS1972

The Nasa earth resources spectral information system: A data compilation, first supplement

The NASA Earth Resources Spectral Information System and the information contained therein are described. It is intended to be used as a supplement to the NASA Earth Resources Spectral Information System: A Data Compilation, N72-28366. This supplement includes approximately 500 rock and mineral, 100 soil, and 30 vegetation bidirectional and directional reflectance, transmittance, emittance, and degree-of-polarization curves in the optical region from 0.2 to 22.0 microns. The data have been categorized by subject and each curve plotted on a single graph. For some rocks and minerals, all curves of the same type, differing only in particle size, have been plotted on one grid as a composite plot. Each graph, composite or single, is fully titled to indicate curve source and is indexed by subject to facilitate user retrieval.

Leeman, V.↗
NASA NTRS1981

Computing diffuse reflection from particulate planetary surface with a new function

An equation is derived to compute the amount of diffuse light reflected by a particulate surface, such as on Mars or an asteroid. The method traces the paths of rays within an ensemble of randomly shaped grains and finds the eventual probability of emission. The amount of diffuse, unpolarized emitted light is obtained in terms of the real index of refraction, the imaginary index, and the average diameter of particles making up the surface. The equation is used to compute the empirical rule for obtaining the planetary albedo from the slope of its polarization curve. Accuracy of the equation, estimated at + or - 4%, seems justified because of quantitative agreement with experimental measures of the empirical rule. It is also shown that the equation can be applied to bubble-enclosing surfaces such as volcanic foams. Results for the indices of the moon, Mars, Io, and Europa are obtained and compared with other data.

Wolff, M.↗
NASA NTRS1987

The indirect electrochemical refining of lunar ores

Recent work performed on an electrolytic cell is reported which addresses the implicit limitations in various approaches to refining lunar ores. The cell uses an oxygen vacancy conducting stabilized zirconia solid electrolyte to effect separation between a molten salt catholyte compartment where alkali metals are deposited, and an oxygen-evolving anode of composition La(0.89)Sr(0.1)MnO3. The cell configuration is shown and discussed along with a polarization curve and a steady-state current-voltage curve. In a practical cell, cathodically deposited liquid lithium would be continuously removed from the electrolytic cell and used as a valuable reducing agent for ore refining under lunar conditions. Oxygen would be indirectly electrochemically extracted from lunar ores for breathing purposes.

Semkow, Krystyna W.↗
NASA NTRS1990

Fundamental studies on the metal chloride cathodes in sodium batteries

The authors report studies of the passivation of the NiCl2 electrode during reduction, its effect on the electrochemical rate kinetics for the reduction, and its dependence on the state of charge of the electrode. NiCl2 exhibits passive behavior more readily at lower states of charge due to a decrease in the electrochemical area, resulting from NaCl deposited during reduction. The passive behavior is evident from the DC polarization curves as well as AC impedance plots at the same potentials, implying a correlation between them. The results of the studies are presented in detail.

Ratnakumar, B. V.↗
NASA NTRS1992

Polarimetric observations of comet Levy 1990c and of other comets: Some clues to the evolution of cometary dust

The evolution with the phase angle alpha of the polarization degree P of light scattered by comet Halley's dust is well documented. No significant discrepancy is found between Halley and Levy polarization curves near the inversion point. From all available cometary observations, we have derived polarimetric synthetic curves. Typically, a set of about 200 data points in the red wavelengths range exhibits a minimum for (alpha approximately equals 10.3 degrees, P approximately equals 1.8 percent) and an inversion point for (alpha approximately equals 22.4 degrees, P = 0 percent), with a slop of about 0.27 percent per degree. A significant spreading of some data (comets Austin 1982VI, Austin 1989c1, West 1976VI) is found at large phase angles. The analysis of our polarimetric maps of Levy reveals that the inner coma is heterogeneous. The increase of the inversion angle value with increasing distance from the photometric center is suspected to be due to the evolution with time of grains ejected from the nucleus. A fan like structure could be produced by a jet of grains freshly ejected.

Levasseur-Regourd, Anny-Chantal↗
NASA NTRS1941

Wind-tunnel investigation of NACA 23012, 23021, and 23030 airfoils equipped with 40-percent-chord double slotted flaps

Report presents the results of an investigation conducted in the NACA 7 by 10-foot win tunnel to determine the effect of the deflection of main and auxiliary slotted flaps on the aerodynamic section characteristics of large-chord NACA 23012, 23021, 23030 airfoils equipped with 40-percent-chord double slotted flaps. The complete aerodynamic section characteristics and envelope polar curves are given for each airfoil-flap combination. The effect of airfoil thickness is shown, and comparisons are made of single slotted flaps with double slotted flaps on each of the airfoils.

Harris, Thomas A↗