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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 127 records · Page 7
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NASA NTRS1977

A two-scale scattering model with application to the JONSWAP '75 aircraft microwave scatterometer experiment

The general problem of bistatic scattering from a two scale surface was evaluated. The treatment was entirely two-dimensional and in a vector formulation independent of any particular coordinate system. The two scale scattering model was then applied to backscattering from the sea surface. In particular, the model was used in conjunction with the JONSWAP 1975 aircraft scatterometer measurements to determine the sea surface's two scale roughness distributions, namely the probability density of the large scale surface slope and the capillary wavenumber spectrum. Best fits yield, on the average, a 0.7 dB rms difference between the model computations and the vertical polarization measurements of the normalized radar cross section. Correlations between the distribution parameters and the wind speed were established from linear, least squares regressions.

Wentz, F. J.↗
NASA NTRS1978

Quasi-microscope concept for planetary missions - Stereo

The quasi-microscope has been used for stereo pictures using a small aperture placed at the right and left over the entrance aperture. A 16-degree stereo view angle yields an enhanced stereo effect. When viewed upward through a transparent support, all grains come into focus. The technique may be used for determining mineral constituents on the basis of cleavage and fracture patterns, grain details, and surface slopes used in estimating single-particle albedo and the illumination of scattering profiles.

Burcher, E. E.↗
NASA NTRS1979

A modification to linearized theory for prediction of pressure loadings on lifting surfaces at high supersonic Mach numbers and large angles of attack

A new linearized-theory pressure-coefficient formulation was studied. The new formulation is intended to provide more accurate estimates of detailed pressure loadings for improved stability analysis and for analysis of critical structural design conditions. The approach is based on the use of oblique-shock and Prandtl-Meyer expansion relationships for accurate representation of the variation of pressures with surface slopes in two-dimensional flow and linearized-theory perturbation velocities for evaluation of local three-dimensional aerodynamic interference effects. The applicability and limitations of the modification to linearized theory are illustrated through comparisons with experimental pressure distributions for delta wings covering a Mach number range from 1.45 to 4.60 and angles of attack from 0 to 25 degrees.

Carlson, H. W.↗
NASA NTRS1979

Modal Interpolation Program, L 215 (INTERP): Supplemental System Design and Maintenance Document - Volume 2

The design, structure, and usage of the modal interpolation program L215 are presented. The program uses modal data sets of arrays containing interpolation coefficients. The interpolation arrays are used to determine displacements at various aerodynamic control points. The displacements consist of translations normal to the aerodynamic surface and surface slopes that are parallel and perpendicular to the free stream direction. Five different interpolation methods are available.

Hirayama, M. Y.↗
NASA NTRS1979

Modal interpolation program, L215 (INTERP). Volume 1: Engineering and usage

The usage of the Modal Interpolation Program L215 (INTERP) is described. The program uses modal data to form sets of arrays containing interpolation coefficients. The interpolation arrays can then be used to determine displacements at various aerodynamic surface and surface slopes that are parallel and perpendicular to the freestream direction. Five different interpolation methods are available. A description of the data manipulation and the interpolation methods is presented.

Kroll, R. I.↗
NASA NTRS1979

Viking bistatic radar observations of the Hellas basin on Mars - Preliminary results

Preliminary reduction of Viking bistatic radar data gives root-mean-square surface slopes in the Hellas basin on Mars of about 4 deg on horizontal scales averaged over 10 centimeters to 100 meters. This roughness decreases slightly with position along the ground track, south to north. The dielectric constant in this area appears to be approximately 3.1, greater than the Martian average. These values are characteristic of lunar maria and are similar to those found near the Viking Lander site in Chryse with the use of earth-based radar.

Simpson, R. A.↗
NASA NTRS1979

Low cost point focus solar concentrator, phase 1

Design concepts and plans for mass-production facilities and equipment, field installation, and maintenance were developed and used for cost analysis of a pneumatically stabilized plastic film point focus solar concentrator which has potential application in conjunction with Brayton cycle engines or supply of thermal energy. A sub-scale reflector was fabricated and optically tested by laser ray tracing to determine focal deviations of the surface slope and best focal plane. These test data were then used for comparisons with theoretical concentrator performance modeling and predictions of full-scale design performance. Results of the economic study indicate the concentrator design will have low cost when mass-produced and has cost/performance parameters that fall within current Jet Propulsion Laboratory goals.

Source record↗
NASA NTRS1979

Comparative study of solar optics for paraboloidal concentrators

Different analytical methods for computing the flux distribution on the focal plane of a paraboloidal solar concentrator are reviewed. An analytical solution in algebraic form is also derived for an idealized model. The effects resulting from using different assumptions in the definition of optical parameters used in these methodologies are compared and discussed in detail. These parameters include solar irradiance distribution (limb darkening and circumsolar), reflector surface specular spreading, surface slope error, and concentrator pointing inaccuracy. The type of computational method selected for use depends on the maturity of the design and the data available at the time the analysis is made.

Wen, L.↗
NASA NTRS1980

Estimation of wing nonlinear aerodynamic characteristics at supersonic speeds

A computational system for estimation of nonlinear aerodynamic characteristics of wings at supersonic speeds was developed and was incorporated in a computer program. This corrected linearized theory method accounts for nonlinearities in the variation of basic pressure loadings with local surface slopes, predicts the degree of attainment of theoretical leading edge thrust, and provides an estimate of detached leading edge vortex loadings that result when the theoretical thrust forces are not fully realized.

Carlson, H. W.↗
NASA NTRS1981

High-speed photometry of the 11 December 1979 Juno occultation

The occultation of SAO 115946 by Juno on 11 December 1979 was observed from two sites in southern California with portable two-color, high-speed photometers. A composite light curve was constructed from the data by suitable scaling of individual observations, using an astrometric solution for the location of the contact points on Juno's limb. The preliminary astrometric solution used here has a semiminor axis of 118 km and a semimajor axis of 145 km at position angle 75.5 deg. The composite light curve is compatible with a stellar radius of (1.6 + or - 0.8) x 10 to the -4th arcsec, consistent with the radius estimated from the color and visual magnitude. There is no evidence for any companions to SAO 115946 or Juno. The prospects for use of asteroid occultations to determine stellar radii and asteroid surface slopes are discussed as compared with the lunar occultation technique.

Reitsema, H. J.↗
NASA NTRS1980

Pioneer Venus radar results - Altimetry and surface properties

A topographic map of 93% of the Venus globe was depicted by the radar altimeter of the Pioneer Venus orbiter with a resolution better than 150 km. Extremes in relief expressed as a center-of-mass-to-surface radius extend from 6049 to 6062 km; the elevated terrain is dominated by a massive equatorial area equal in size to South America. The distribution of average meter-scale surface slopes is determined for the same regions in the 1 to 10 deg range; elevated areas have higher slopes, so that most features observed in the earth-based images are also evident in the vertical-incidence spacecraft measurements.

Pettengill, G. H.↗
NASA NTRS1980

Seasat orbital radar imagery for geologic mapping - Tennessee-Kentucky-Virginia

The purpose of the reported study is to analyze Seasat SAR imagery of a heavily vegetated mountainous land surface and to determine the potential of this microwave imaging system for geologic mapping. It is found that geologic mapping using orbital Seasat SAR imagery is feasible in the Appalachian Valley and Ridge province, where the radar system is highly sensitive to change of surface slope. Image tones and textures correlate with distinctive topography, from which generalized lithologic and structural interpretations are derived. Major and minor linear topographic features are easily mapped from the SAR images. The SAR sensor suppresses subdued geomorphic lineaments that strike parallel with or near to the radar look direction. This deficiency is partly compensated by the dual directions of radar illumination obtainable from the Seasat imaging system.

Ford, J. P.↗
NASA NTRS1981

Viscoplastic lubrication of asperities

Theoretical analyses for the lubrication of rigid wedge-shaped asperities by a viscoplastic fluid are developed for geometries in which either wedge or squeeze action are dominant. The load support in the wedge action geometry is severly limited by lubricant shear, although the squeeze geometry maintains high load support at small film thicknesses. Results suggest that in cases where macroscopic hydrodynamic lubrication is inadequate, lubricant film breakdown will be promoted by low lubricant shear strength, high sliding speed, low surface roughness, and high surface slope. In addition, results are compared with previous investigations of the factors influencing susceptibility to lubrication failure.

Sheu, S.↗
NASA NTRS1981

Satellite radar altimeters - Present and future oceanographic capabilities

Satellite radar altimeters have the ability to provide information related to ocean wave heights, wind speed, and currents. The present investigation has the objective to demonstrate the current capabilities and to indicate ways to increase the information content of the altimeter return through the use of wider bandwidth, higher pulse repetition frequencies (PRF), and multibeam. Altimeters aboard Skylab, Geos-3, and Seasat-1 have provided investigators with valuable experience in translating the radar observables into oceanic parameters. Basically, an altimeter transmits a narrow pulse and measures the time interval until the return energy from the ocean surface is received. That direct measure of the satellite altitude can be interpreted in terms of surface topography. Attention is given to altimeter oceanographic measurements, altimeter return pulse characteristics, satellite pointing and surface slopes, the adaptive tracker for terrain mapping, and a multibeam altimeter.

Townsend, W. F.↗
NASA NTRS1983

An investigation to model radar backscatter from ridged first year sea ice for the period ending December 31, 1981

The response of the microwave scatterometer to meter scale roughness of first year sea ice was investigated. An empirical, one dimensional model was developed to predict the back scattered power from ridged first year sea ice of known surface topography, by interpreting the surface as a series of angular facets and summing the proportional power from each facet. The model is evaluated by comparing the predicted values to scatterometer measurements obtained during NASA's Sea Ice Radar Experiment (SIRE). The input to the model is surface slope, which for SIRE was calculated from the ice topography, as measured by an airborne laser profiler. The correlation between the predicted and the measured power is .62 to .68. It is concluded that the model adequately describes the backscatter from regions of first year sea ice whose dimensions are of a few tens of meters.

Jackson, B. L. W.↗
NASA NTRS1984

A new type of overshoot phenomenon in wind wave development and its implication in remote sensing of the ocean

Laboratory measurements using both wave probes (contact and optical) and radar confirm the existence of a new type of overshoot phenomenon in the wind-wave development processes. This type of overshoot, which occurs at gravity-capillary wavelengths, is practically a function of local wind stress only. It is named the overshoot phenomenon of the third kind. With the existence of this overshoot it becomes obvious that the assumed simple power-law relationship between the rms value of surface slope at a fixed wavelength and the wind stress is untenable. Since such a relationship is one of the key assumptions invoked in the development of algorithms used in scatterometry, the published scatterometer data are reexamined, pointing out the implications of this overshoot phenomenon. Recommendations for improvement of the performance of the scatterometer are also made in light of this new understanding of the wind-wave development processes.

Huang, N. E.↗
NASA NTRS1984

Sulfur volcanoes on Io?

The unusual rheological properties of sulfur are discussed in order to determine the distinctive volcanic flow morphologies which indicate the presence of sulfur volcanoes on the Saturnian satellite Io. An analysis of high resolution Voyager imagery reveals three features which are considered to be possible sulfur volcanoes: Atar Patera, Daedalus Patera, and Kibero Patera. All three features are distinguished by circular-to-oval central masses surrounded by irregular widespread flows. The central zones of the features are interpreted to be domes formed of high temperature sulfur. To confirm the interpretations of the satellite data, molten sulfur was extruded in the laboratory at a temperature of 210 C on a flat surface sloping 0.5 deg to the left. At this temperature, the sulfur formed a viscous domelike mass over the event. As parts of the mass cooled to 170 C the viscosity decreased to a runny stage, forming breakout flows. It is concluded that a case can be made for sulfur volcanoes on Io sufficient to warrant further study, and it is recommended that the upcoming Galileo mission examine these phenomena.

Greeley, R.↗
NASA NTRS1986

Convection without eddy viscosity: An attempt to model the interiors of giant planets

In the theory of hydrostatic quasi-geostrophic flow in the Earth's atmosphere the principal results do not depend on the eddy viscosity. This contrasts with published theories of convection in deep rotating fluid spheres, where the wavelength of the fastest growing disturbance varies as E sup 1/3, where E, the Ekman number, is proportional to the eddy viscosity. A new theory of quasi-columnar motions in stably stratified fluid spheres attempts to capture the luck of the meteorologists. The theory allows one to investigate the stability of barotropic and baroclinic zonal flows that extend into the planetary interior. It is hypothesized that the internal heat Jupiter and Saturn comes out not radially but on sloping surfaces defined by the internal entropy distribution. To test the hypothesis one searches for basic states in which the wavelength of the fastest-growing disturbance remains finite as E tends to zero, and is which the heat flux vector is radially outward and poleward.

Ingersoll, A. P.↗