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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Crater size-shape profiles for the moon and Mercury - Terrain effects and interplanetary comparisons

Crater size-shape data were compiled for 221 fresh lunar craters and 152 youthful Mercurian craters. Terraces and central peaks develop initially in fresh craters on the moon in the 0-10 km diameter interval. Above a diameter of 65 km all craters are terraced and have central peaks. Swirl floor texture is most common in craters in the size range 20-30 km, but it occurs less frequently as terraces become a dominant feature of crater interiors. For the moon there is a correlation between crater shape and geomorphic terrain type. These crater data suggest that there are significant differences in substrate and/or target properties between maria and highlands. Size-shape profiles for Mercury show that central peak and terrace onset is in the 10-20 km diameter interval; all craters are terraced at 65 km, and all have central peaks at 45 km. The crater data for Mercury show no clearcut terrain correlation. Comparison of lunar and Mercurian data indicates that both central peaks and terraces are more abundant in craters in the diameter range 5-75 km on Mercury. Differences in crater shape between Mercury and the moon may be due to differences in planetary gravitational acceleration.

Smith, E. I.↗
NASA NTRS1979

Supercritical wing design using numerical optimization and comparisons with experiment

A numerical minimization scheme is used in conjunction with two-dimensional and three-dimensional inviscid transonic flow analysis codes to provide procedures for wing leading edge aerodynamic design. The procedures are demonstrated in the design of a new leading edge to improve C-141 cruise performance. For the high aspect ratio moderately swept C-141 wing, the 2-D procedure is shown to yield results which are in close agreement with those obtained using the 3-D technique. Although the 2-D approach uses much less computation time than the 3-D technique, the latter requires fewer manhours than the former. Comparisons of predicted and wind tunnel measured performance improvements are presented which verify the design procedures.

Lores, M. E.↗
NASA NTRS1979

Numerical comparisons of panel methods at subsonic and supersonic speeds

Numerical comparisons between some recently developed surface panel methods and well-established methods are made to assess their accuracy at subsonic and supersonic speeds. The results at subsonic speeds indicate similar improvements for the methods investigated over the low order source method. At supersonic speeds, stable and accurate results were obtained with the surface panel methods. Significant differences between tangential mass flux and tangential velocity boundary conditions occurred, especially at low fineness ratios and higher Mach numbers. The advantages of the general source/doublet panel formulation at both subsonic and supersonic speeds are noted.

Thomas, J. L.↗
NASA NTRS1978

IMF structures between 0.3 and 1 A.U. - A comparison of two-spacecraft observations

Interplanetary-magnetic-field observations by Helios 1 and IMP 8 have been compared for a period of time (corresponding to four solar rotations) in which the radial and latitudinal separations between spacecraft, respectively, ranged between 0 and 0.69 AU and 0 and 14.5 degrees. The correspondence between macrostructural features is good even when the observing spacecraft are located at opposite sides of the solar equatorial plane. Unipolar regions of the interplanetary magnetic field are confirmed as steady-state, corotating structures and are also mostly consistent with a quite regular extension of the field polarities of the observed coronal holes. There are, however, interesting examples of recurrent unipolar regions which are not associated with the recurrent pattern of high-velocity streams. A comparison of two field enhancements suggests that these structures do not experience significant modifications with the heliocentric distance.

Villante, U.↗
NASA NTRS1979

Preliminary flight and wind tunnel comparisons of the inlet/airframe interaction of the F-15 airplane

Preliminary flight and wind tunnel comparison data are presented for the F-15 inlet/airframe interactions program. Test conditions and instrumentation for both the model and the aircraft are described. Flight and wind tunnel inlet drag data (for a 0-deg angle of attack and Mach numbers of 0.6, 0.9, and 1.2), derived by using nearly identical pressure integration equations, are compared. The effects of a movable cowl, movable ramps, and other system components on pressure flow fields along the airframe are discussed. Excellent agreement between wind tunnel and flight pressure-integrated drags is found at all three Mach numbers. The wind tunnel data show good agreement for pressure-integrated and force-balance-measured inlet drag, except at Mach 0.6. Flight-measured pressure-integrated inlet lift is lower than that measured in the wind tunnel.

Webb, L. D.↗
NASA NTRS1979

Comparison of backscatter ultraviolet /BUV/ and ground-based total ozone fields for December 1970

For the period December 1970, comparison is made between the monthly average analyses (mapped fields) of the backscatter ultraviolet (BUV) total ozone data and the ground-based observations. In particular, significant differences of over 50 Dobson units are noted over the region of the North Atlantic Ocean with the BUV of greater magnitude than the ground-based data. As part of the overall verification program, both analyses are compared against the 100 mb height fields. The results indicate that the BUV analysis in the region of question is the more consistent of the two.

Miller, A. J.↗
NASA NTRS1978

Comparison of modal test methods on the Voyager payload

A comparison of the performance of modern modal data analysis methods on test data from the Voyager Jupiter/Saturn payload is presented. Four different test/data-analysis combinations are compared - multiple-point sine excitation tests, single-point random-excitation tests using two different techniques of manipulating Fourier transform data, and a time-domain method for analyzing random data. Results indicate that all four methods can give comparable results. Of the four, the time-domain approach detects more modes in the test data and, at the same time, shows the greatest promise for reducing the time and cost of modal testing.

Hanks, B. R.↗
NASA NTRS1978

The comparison between the synthetic aperture radar imageries and the surface truth of ocean waves

Ocean waves measured offshore of Marineland, Florida, by the synthetic aperture radar (SAR) are compared with the surface truth data. The Fourier transform of SAR imageries are taken and the corrections of the wave directions and wave lengths due to the relative velocities between SAR and waves are considered. Favorable comparisons are obtained for the peak frequencies, wave directions, and directional distributions. However, the one-dimensional SAR spectra are quite different from the surface truth wave height spectra.

Hsiao, S. V.↗
NASA NTRS1979

Comparison of quasi-specular radar scatter from the moon with surface parameters obtained from images

Quasi-specular radar data used to determine apparent surface roughness of geologic surfaces displays a variable wavelength dependence. The strongest changes with wavelength are observed in lunar maria, while scatter from lunar highlands is nearly wavelength independent. Commonly used, gently undulating surface models for electromagnetic scatter predict no wavelength dependence. Wavelength dependence occurs whenever a significant fraction of the surface has local radii of curvature comparable to the observing wavelength. This condition can be determined by comparison of the value of the integrated surface curvature spectrum with the radar wave number, multiplied by a constant that depends on the geometry. Variations in curvature statistics calculated from photogrammetric reduction of lunar images are consistent with the observed variations in quasi-specular scatter between wavelengths of 13 and 116 cm at the same locations. Variations in the strength of the wavelength dependence are correlated with the sizes of lunar craters that lie near the upper size limit for the local steady-state distribution. This correlation is also consistent with variations in the curvature spectrum calculated from crater size-frequency distributions.

Tyler, G. L.↗
NASA NTRS1979

Comparison of projected critical currents in PbMo6S8 and Nb3Ge

Critical current densities, Jc, of sputtered Chevrel phase PbMo6S8 films have been measured as a function of field to 19 T at several temperatures. The pinning forces were found to obey a scaling law. Assuming an effective upper critical field Bc2 = 45 T, an effective critical temperature Tc = 13 K, together with empirical estimates of numerical factors in the scaling law, the upper limits for critical current density Jc in PbMo6S8 are estimated. Comparisons are made with estimates of Jc for Nb3Ge at 4.2 K. A crossover of Jc vs. B is found for B of the order of 25 to 30 T. Below this point, Nb3Ge is projected to have a higher critical current density. Thus practical use of Chevrel materials in high field magnets only appears to be competitive with Nb3Ge for fields above 25 to 30 T.

Alterovitz, S. A.↗
NASA NTRS1979

Initial comparison of single cylinder Stirling engine computer model predictions with test results

A NASA developed digital computer code for a Stirling engine, modelling the performance of a single cylinder rhombic drive ground performance unit (GPU), is presented and its predictions are compared to test results. The GPU engine incorporates eight regenerator/cooler units and the engine working space is modelled by thirteen control volumes. The model calculates indicated power and efficiency for a given engine speed, mean pressure, heater and expansion space metal temperatures and cooler water inlet temperature and flow rate. Comparison of predicted and observed powers implies that the reference pressure drop calculations underestimate actual pressure drop, possibly due to oil contamination in the regenerator/cooler units, methane contamination in the working gas or the underestimation of mechanical loss. For a working gas of hydrogen, the predicted values of brake power are from 0 to 6% higher than experimental values, and brake efficiency is 6 to 16% higher, while for helium the predicted brake power and efficiency are 2 to 15% higher than the experimental.

Tew, R. C., Jr.↗
NASA NTRS1978

Mare Crisium area topography - A comparison of earth-based radar and Apollo mapping camera results

An earth-based radar topography (ERT) map has been constructed of the Mare Crisium area. Systematic and random sources of error are discussed. A comparison between the ERT map and Lunar Topographic Orthophotomaps shows a random mean discrepancy of less than 100 m between the two maps, except for small-scale (20 km or less in diameter) features, where systematic smoothing reduces the ERT elevation contrast

Zisk, S.↗
NASA NTRS1979

A one-dimensional model describing aerosol formation and evolution in the stratosphere. I - Physical processes and mathematical analogs. II - Sensitivity studies and comparison with observations

A new time-dependent one-dimensional model of the stratospheric sulfate aerosol layer is developed. The model treats atmospheric photochemistry and aerosol physics in detail and includes the interaction between gases and particles explicitly. It is shown that the numerical algorithms used in the model are quite precise. Sensitivity studies and comparison with observations are made. The simulated aerosol physics generates a particle layer with most of the observed properties. The sensitivity of the calculated properties to changes in a large number of aeronomic aerosol parameters is discussed in some detail. The sensitivity analysis reveals areas where the aerosol model is most uncertain. New observations are suggested that might help resolve important questions about the origin of the stratospheric aerosol layer.

Turco, R. P.↗
NASA NTRS1978

Comparisons between observed and predicted cosmogenic noble gases in lunar samples

Comparisons are made between cosmogenic production rates and isotopic ratios predicted on the basis of nuclear systematics with those observed in well-documented lunar samples. Although some significant differences are found, the agreement in general is surprisingly good. The predicted production rates for Ar-38 and Xe-126 agree reasonably well with observation but the predicted rate for Ne-21 appears to be too high; in most cases the predicted rate for Kr-83 agrees to within 50%, although some larger differences are apparent. There are some prominent cases in which predicted isotopic compositons differ from observation: Kr-78/Kr-83 trends in the wrong sense with the Zr/Sr ratio; Xe-124/Xe-126 is too large by about 13%; Xe-128/Xe-126 is too small by about 6%; Xe-130/Xe-126 is too low by 30-40%.

Hohenberg, C. M.↗
NASA NTRS1978

A comparison of contour maps derived from independent methods of measuring lunar magnetic fields

Computer-generated contour maps of strong lunar remanent magnetic fields are presented and discussed. The maps, obtained by previously described (Eliason and Soderblom, 1977) techniques, are derived from a variety of direct and indirect measurements from Apollo 15 and 16 and Explorer 35 magnetometer and electron reflection data. A common display format is used to facilitate comparison of the maps over regions of overlapping coverage. Most large scale features of either weak or strong magnetic field regions are found to correlate fairly well on all the maps considered.

Lichtenstein, B. R.↗
NASA NTRS1979

A comparison of WFTA and FFT programs

Bounds on the minimum number of data transfers (i.e., loads and stores) required by WFTA (Winograd Fourier Transform Algorithm) and FFT programs are presented. The analysis is applicable to those general-purpose computers with a small number of general processor registers (e.g., the IBM370, PDP-11, etc.). It is shown that the 1008-point WFTA requires about 21% more data transfers than the 1024-point radix-4 FFT; on the other hand, the 120-point WFTA has about 22% fewer data transfers than the 128-point radix-2 FFT. Finally, comparisons of the 'total' program execution times (multiplications, additions, and data transfers, but not indexing or permutations) are presented.

Nawab, H.↗
NASA NTRS1979

Comparison of seasonal variations of upper stratospheric ozone concentrations revealed by Umkehr and Nimbus 4 BUV observations

This paper reports the results of a comparison between upper stratospheric ozone concentration profiles in the region between 22 and 1.4 mbar, as determined from surface-based Umkehr observations and satellite Nimbus 4 BUV observations. The Umkehr data, consisting of monthly averages of observations extending over several years or longer, were obtained at three stations located in the Northern Hemisphere and two in the Southern Hemisphere. The BUV data were obtained during the period from May 1970 to March 1971. Aside from some bias in the magnitudes of the Umkehr and BUV data, marked annual cycles of ozone concentration in the upper stratosphere are clearly revealed. Above 4 mbar the profiles show a summer minimum and a winter maximum, while below 4 mbar the annual variation is reversed from this pattern. In the Northern Hemisphere the winter maximum is accompanied by a secondary minimum of 1- to 2-month duration near 3 mbar. This short-term minimum is much less obvious in the Southern Hemisphere data. Some of the problem of attempting to monitor long-term changes in the upper stratosphere are discussed briefly.

Deluisi, J. J.↗
NASA NTRS1979

The auroral ionosphere - Comparison of a time-dependent model with composition measurements

A time-dependent model of the auroral ionosphere including the odd nitrogen species, NO, N(D-2), and N(S-4), is used for comparison with data from a coordinated rocket-satellite measurement of an auroral event. The chemical scheme and the adopted rate coefficients have been shown to be compatible with daytime mid-latitude ionospheric chemistry. The electron flux and neutral atmospheric parameters measured on the satellite are used to compute the appropriate ionization and dissociation rates. The calculated NO(plus), O2(plus), O(plus), Ne, and NO densities agree well with the rocket measurements. The calculated N2(plus) densities are larger than the measured densities by a factor of 3 at most altitudes. The calculations show that the nitric oxide content of the aurora (about 1.2 times 10 to the 9th NO molecules/cu cm at 105 km) is below the saturation value.

Gerard, J.-C.↗