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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Measurement of stray radiance in the High Altitude Observatory's Skylab coronagraph

The paper outlines two techniques used for determining the instrumental stray radiance from orbital results obtained with the Skylab white light coronagraph. The first technique employs images of the lunar disk made near the time of solar eclipse to compare the apparent contrasts of maria and highlands recorded by the coronograph with those of previous studies and then determine the magnitude of the stray radiance and its variation along a radius. The second method determines the azimuthal variation of the stray radiance by measuring the change in the net radiance of a point in the coronal images as the image is rotated.

Csoeke-Poeckh, A.↗
NASA NTRS1977

Measurements of the reaction e/+/e/-/ yielding gamma-gamma at center-of-mass energies in the range 6.2-7.4 GeV

The cross section for the pair-annihilation reaction e(+)e(-) yields gamma-gamma were measured at center-of-mass energies in the range 6.2-7.4 GeV and at production angles close to 90 deg. The experimental apparatus consisted of two identical spectrometers which were set to view the luminous region at SPEAR-II from opposite directions at an azimuthal angle of 45 deg. In each spectrometer there was a NaI(TI) crystal 20 radiation lengths thick and 30 in. in diameter to measure the gamma-ray energies. Annihilation events were detected by an electronic trigger which required only the observation in coincidence of more than 0.2 GeV in each NaI(TI) crystal within + or - 15 nsec of the crossing beams. The observed rates of pair-annihilation events were found to be in agreement with those expected from quantum electrodynamics (QED) at all the center-of-mass energies used.

Hilger, E.↗
NASA NTRS1977

Boundary-value problem for plasma centrifuge at arbitrary magnetic Reynolds numbers

We solve in closed form the boundary-value problem for the partial differential equations which describe the (azimuthal) rotation velocity and induced magnetic fields in a cylindrical plasma centrifuge with ring electrodes of different radii and an external, axial magnetic field. The electric field, current density, and velocity distributions are discussed in terms of the Hartmann number H and the magnetic Reynolds number R. For small Hall coefficients, the induced magnetic field does not affect the plasma rotation. As a result of the Lorentz forces, the plasma rotates with speeds as high as 100,000 cm/sec around its axis of symmetry at typical conditions, so that the lighter (heavier) ion and atom components are enriched at (off) the center of the discharge cylinder.

Wilhelm, H. E.↗
NASA NTRS1977

Spiral approach navigation concepts for VTOL aircraft using a microwave landing system

Spiral approaches adjacent to the active runways of CTOL airports have been proposed as a means of effectively interfacing CTOL and VTOL landing operations. Assuming an airport equipped with a Microwave Landing System (MLS), a VTOL aircraft following a spiral approach path might, depending on the specific trajectory, pass alternatively in and out of the linear coverage of the MLS and thereby suffer degraded navigation performance. The objective of this study was to employ essentially state-of-the-art aided inertial navigation concepts to explore the expected navigation performance operating in the environment just described. Results show that aided inertial concepts utilizing simple body-mounted inertia systems may be adequate for an instrument landing if the MLS azimuth and Distance Measuring Equipment (DME) signal coverages extend to within a few feet of the ground.

Mcgee, L. A.↗
NASA NTRS1977

Radial variation of lunar crater rim topography

The paper presents results of determinations of variations of rim topography as a function of range from the crater rim for a group of morphologically fresh craters. It is found that the rate at which exterior crater topography converges with the surrounding surface is highly variable among different radial directions at individual craters as well as between different craters, and that at several craters, oblique impact appears to have contributed to azimuthal elevation/range variations.

Settle, M.↗
NASA NTRS1977

Dilation of force-free magnetic flux tubes

A general study is presented of the mapping functions which relate the magnetic-field profiles across a force-free rope in segments subjected to various external pressures. The results reveal that if the external pressure falls below a certain critical level (dependent on the flux-current relation which defines the tube), the magnetic profile consists of an invariant core sheathed in a layer permeated by an azimuthal magnetic field.

Frankenthal, S.↗
NASA NTRS1976

Mariner 10 interplanetary magnetic field results

Interplanetary magnetic field data obtained by Mariner 10 between November 1973 and March 1974 are examined. Though large variations in the field due to the effects of high speed streams and stream-stream interactions were observed, on average the large scale interplanetary magnetic field radial component was found to have a distance dependence of r to the minus 2.0 plus or minus 0.3, while the azimuthal field component was found to vary as r to the minus 1.3 plus or minus 0.4, and a dependence of r to the minus 1.4 plus or minus 0.6 was found for the component normal to the solar equatorial plane. A close correspondence was found between the magnetic field stream signatures and persistent but evolving coronal hole regions on the sun, and a clear pattern of large southward fields in stream interaction regions and high levels of field fluctuations within the high-speed streams was detected.

Behannon, K. W.↗
NASA NTRS1977

Construction and interpretation of a digital inertia image

An image representing the thermal inertia in the vicinity of Pisgah Crater and Lavic Lake in Southern California has been generated from visible, near IR, and thermal images taken from aircraft. Construction of the thermal inertia image required radiometric calibration and geometric rectification of the acquired images as well as registration to a topographic map. The Kahle thermal model used in the construction of the thermal inertia image requires specification of albedo, topographic slope and slope azimuth, diurnal temperature range and local meteorological conditions. Albedo information was derived from the visible image; digital topographic information was computed from digitized stereo aerial photographs; and thermal ranges were calculated by subtracting the predawn from the afternoon thermal image data. Our computed values of thermal inertia were in close agreement with published values for similar surface materials. Thermal inertia provides complementary information to conventional images of reflected solar radiation for use in lithologic mapping.

Gillespie, A. R.↗
NASA NTRS1979

Air-traffic surveillance systems

Passive ground-based radio-interferometry systems (RILS) monitor local air traffic by determining aircraft position in planes defined by surveillance area. Similar RILS arrangements are used to determine aircraft positions in three dimensions when combined with azimuth and range information obtained by radar. Information helps determine three-dimensional aircraft position without expensive encoding altimeters.

Macdoran, P. F.↗
NASA NTRS1977

Ground winds and winds aloft Edwards AFB, California

Ground level runway wind statistics cover crosswind, tailwind, and headwind reversal percentage frequencies with respect to month and hour for the two major runways. Also presented are bivariate normal wind statistics for a 90 degree flight azimuth for altitudes 0 through 27 km. Wind probability distributions, synthetic vector wind profiles, and statistics for any rotation of axes are computed from five given parameters.

Johnson, D. L.↗
NASA NTRS1977

Determination of particle size using measurement of scatter

Scatter measurements were taken from glass spheres of size 5 to 50 microns placed on a mirror to see whether such scatter data could be correlated with size. The spheres were illuminated with a laser whose wavelength was 0.62 microns. A Gonioreflectometer was used to vary the detector between the normal to the mirror and 85 deg from the normal and in the plane containing the normal to the mirror and the incident laser light. The azimuth of the detector with respect to the source was 180 deg. The light detector was driven by a step motor. The scatter was dark and bright lines. They appeared as minima and maxima on the output recorder. As the size of the beads increased the number of maxima increased.

Scott, R. L., Jr.↗
NASA NTRS1977

Investigation of techniques for inventorying forested regions. Volume 2: Forestry information system requirements and joint use of remotely sensed and ancillary data

The author has identified the following significant results. Effects of terrain topography in mountainous forested regions on LANDSAT signals and classifier training were found to be significant. The aspect of sloping terrain relative to the sun's azimuth was the major cause of variability. A relative insolation factor could be defined which, in a single variable, represents the joint effects of slope and aspect and solar geometry on irradiance. Forest canopy reflectances were bound, both through simulation, and empirically, to have nondiffuse reflectance characteristics. Training procedures could be improved by stratifying in the space of ancillary variables and training in each stratum. Application of the Tasselled-Cap transformation for LANDSAT data acquired over forested terrain could provide a viable technique for data compression and convenient physical interpretations.

Nalepka, R. F.↗
NASA NTRS1977

Radar backscattering from a sea having an anisotropic large-scale surface, part 2

A two scale scattering model was derived that combines specular reflections from sea waves and Bragg scattering in a manner consistent with energy conservation. The effect of the tilting of the small scale roughness by the large scale roughness was included, which accounted for the reduction of reflected power. The special case of backscattering for which the transmitted polarization equaled the received polarization was considered. An anisotropic large scale surface was used to specify the probability density function of the large scale surface normal. In order to isolate the azimuthal variation of the normalized radar cross section produced by the anisotropic probability density function, an isotropical small scale spectrum was assumed.

Wentz, F. J.↗
NASA NTRS1973

Heat pipe development

The objective of this program was to investigate analytically and experimentally the performance of heat pipes with composite wicks--specifically, those having pedestal arteries and screwthread circumferential grooves. An analytical model was developed to describe the effects of screwthreads and screen secondary wicks on the transport capability of the artery. The model describes the hydrodynamics of the circumferential flow in triangular grooves with azimuthally varying capillary menisci and liquid cross-sections. Normalized results were obtained which give the influence of evaporator heat flux on the axial heat transport capability of the arterial wick. In order to evaluate the priming behavior of composite wicks under actual load conditions, an 'inverted' glass heat pipe was designed and constructed. The results obtained from the analysis and from the tests with the glass heat pipe were applied to the OAO-C Level 5 heat pipe, and an improved correlation between predicted and measured evaporator and transport performance were obtained.

Bienart, W. B.↗
NASA NTRS1977

A low cost high temperature sun tracking solar energy collector

The design and economic evaluation of a low cost high temperature two axis sun tracking solar energy collector are described. The collector design is specifically intended for solar energy use with the freedom of motion about its two control axes being limited only to the amplitude required to track the sun. An examination of the performance criteria required in order to track the sun and perform the desired solar energy conversion is used as the starting point and guide to the design. This factor, along with its general configuration and structural aspect ratios, is the significant contributor to achieving low cost. The unique mechanical design allows the control system to counter wide tolerances that will be specified for the fabrication of the azimuth frame and perform within a small tracking error.

Perkins, G. S.↗
NASA NTRS1978

Ground winds and winds aloft for Edwards AFB, California (1978 revision)

Ground level runway wind statistics for the Edwards AFB, California area are presented. Crosswind, headwind, tailwind, and headwind reversal percentage frequencies are given with respect to month and hour for the two major Edwards AFB runways. Also presented are Edwards AFB bivariate normal wind statistics for a 90 degree flight azimuth for altitudes 0 through 27 km. Wind probability distributions and statistics for any rotation of axes can be computed from the five given parameters.

Johnson, D. L.↗
NASA NTRS1978

NASTRAN analysis of a wheel-rail loading on its foundation

One type of azimuth bearing for a large ground antenna (100 m) will consist of steel wheels, mounted at four corners of the alidade, rolling on a circular flat rail which provides the vertical restraints; a radial constraining bearing at the center of the alidade provides the horizontal restraints. One important design feature is the compressive stresses in the grout or concrete foundation under the wheel-rail load. A finite element analysis check was made of a particular design that consists of a steel rail resting on a concrete foundation. Symmetry was assumed as much as possible in order to minimize the models, but meaningful element sizes were used. Recently developed isoparametric hexahedron elements available in the NASTRAN computing program, which minimizes the number of elements required while maintaining the accuracy of the computed stresses, were used with two versions of NASTRAN. Test cases to check with the analytical solutions were made. A side loading was also applied to calculate the increase in the concrete stresses.

Katow, M. S.↗
NASA NTRS1977

Synthetic aperture radar correlator phase histories

This report supplements the design of the following subsystems: (1) zoom azimuth telescope, zooming range from 3X to 6X. (2) range curvature correcting lenses. (3) Sphero-cylindrical shift lens. (4) Auxiliary lenses (tilted cylinder and matching lens).

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