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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 469 records · Page 26
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NASA NTRS1976

Scattering in the atmosphere of Venus. I - Line profiles and curves of growth for isotropic scattering

Line profiles and curves of growth were computed for both reflected and transmitted radiation for typical lines in CO2 bands (in the photographic infrared) which occur in the spectrum of Venus. In the model, the pressure variation with altitude was considered, and the base of the cloud deck was set at the 2 bar level. The temperature was held constant at 250 K, and a Voigt profile was used for the line shape. It was also assumed that the scale height of the cloud particles was equal to the scale height of the gas. The calculations were made for four values of the scattering optical thickness (0.1, 1.0, and 100) using a continuum single-scattering albedo of 0.9975 (which gives a Bond albedo of 0.896 for a scattering optical thickness of 100, the value observed for Venus at these wavelengths). Curves of growth are also presented for reflected radiation which has been averaged over the visible disk for three values of the Venus phase angle (0, 86, and 166 deg).

Young, L. D. G.↗
NASA NTRS1977

The photometric functions of Phobos and Deimos. II - Surface photometry of Deimos

Mariner 9 television pictures of Deimos are used to study the uniformity of a certain photometric scattering parameter over the surface of the satellite. It is shown that the photometric data considered satisfy the reciprocity principle and that the Hapke-Irvine scattering law is adequate for describing the surface. Phase functions for Deimos are obtained from scans along the photometric equator, and the photometric behavior of the brightest and darkest areas on the satellite's disk is examined. The results indicate that the surface of Deimos is covered uniformly by a dark and texturally complex material whose photometric behavior is well-represented by the Hapke-Irvine law, that the intrinsic phase coefficient of this material is about 0.017 mag/deg over the phase-angle range from 20 to 80 deg, and that slightly brighter material is present near some craters. Since enhanced brightening was not observed at the specular point of the photometric equator in any of the pictures studied, it is concluded that large exposures of solid rock are absent from the Mars-facing side of Deimos.

Noland, M.↗
NASA NTRS1977

The photometric functions of Phobos and Deimos. III - Surface photometry of Phobos

Mariner 9 television pictures of Phobos are used to study the uniformity of a certain photometric scattering parameter over the surface of the satellite, assuming that the scattering law for Phobos can be represented by the Hapke-Irvine equation. Ways of avoiding topographically irregular areas are discussed, phase functions for Phobos are obtained from scans along the photometric equator, and the photometric behavior of selected areas not along this equator is examined. Searches are conducted for anomalously bright areas and evidence of solid rock on the surface. The results indicate that: (1) at least three large regions on the surface of Phobos are covered by a dark material of complex texture which scatters light according to the Hapke-Irvine law; (2) the average intrinsic phase coefficient of this material is 0.020 mag/deg over the phase-angle range from 20 to 80 deg; (3) even the topographically irregular areas have photometric properties similar to those of the three smooth regions; (4) the surface of Phobos is rougher than that of Deimos on the largest scale; and (5) apparent bright patches are most likely caused by local tilts of the surface.

Noland, M.↗
NASA NTRS1976

Dynamic stiffness and damping of externally pressurized gas lubricated journal bearings

A rigid vertical shaft was operated with known amounts of unbalance at speeds up to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. The measured stiffness was proportional to the supply pressure, while damping was little affected by supply pressure. Damping dropped rapidly as the fractional frequency whirl threshold was approached. A small eccentricity analysis overpredicted the stiffness by 4 to 55 percent. Predicted damping was close to measured at low speeds but higher at high speeds

Fleming, D. P.↗
NASA NTRS1977

The infrared photometric function of Mars and its bolometric albedo

The photometric properties of local areas on Mars are studied using Minnaert's rule of surface scattering to analyze Mariner 6 and 7 Infrared Spectrometer data. Several bright deserts, Hellas, and the south polar cap are found to obey Minnaert's function well. Observed bright regions all have similar values of limb-darkening coefficient k, except for Hellas and the south polar cap. The lower k of Hellas is apparently caused by microscopic effects rather than by large-scale roughness due to cratering. The higher k of the cap is similar to terrestrial snows in the visual at the same phase angle.

Pleskot, L. K.↗
NASA NTRS1977

Experimental studies of trailing-edge conditions on an oscillating airfoil at frequency parameters of up to one

This paper describes an investigation to find the range of reduced frequencies over which the classical Kutta-Joukowsky condition is valid and the nature of deviations beyond this range. An NACA 64A010 airfoil with a 15-cm chord is supported between the side walls of a 25-cm x 35-cm low-speed wind tunnel and oscillated over reduced frequencies ranging from 0.05 to 1.2. The experimentally determined loading near the trailing edge is measured and compared with unsteady incompressible small-disturbance theory. Experimental data are obtained both with and without a boundary-layer trip. It is observed that application of the Kutta-Joukowsky condition in the theoretical analysis is valid below a reduced frequency of about 0.6 in predicting the loading in the trailing-edge region. At reduced frequencies beyond 0.8, the predicted results underestimate the measured loading near the trailing edge, and the deviations increase further with reduced frequency. Similarly, the experimental phase angle of the loading in the trailing-edge region agrees reasonably with the linear theory up to k = 0.8 but lags the predicted value beyond k = 0.8.

Satyanarayana, B.↗
NASA NTRS1977

Fluctuating loads on the flap surfaces of an externally-blown-flap configuration

An experimental program to obtain the fluctuating loads on the surfaces of a triple-slotted externally-blown-flap powered-lift STOL configuration was conducted. A large model of a wing/flap system and a TF-34 medium bypass ratio engine was investigated. Measurements of the fluctuating pressure, static pressure, and surface temperature resulting from the jet impingement were obtained at several locations on the surfaces of the second and third flaps. Fluctuating pressure data include overall level, power-spectral density (PSD), cross-correlation coefficient, coherency, and phase angle of the cross power-spectral density. These data indicate that more than one mechanism contributes to the fluctuating pressure levels on the flaps. In the immediate area above the intersection of the engine centerline and the flap, low frequency pressures dominate the overall fluctuating pressure levels. In other areas, such as below this intersection and outboard on the flaps, the PSD curve reaches a peak value at a Strouhal number ranging from 0.22 to 0.45.

Schoenster, J. A.↗
NASA NTRS1977

Calculation of unsteady two-dimensional laminar and turbulent boundary layers with fluctuations in external velocity

A numerical method is proposed for calculating unsteady two-dimensional laminar and turbulent boundary layers with allowance for fluctuations in external flow velocity. An eddy-viscosity formulation is used to model the Reynolds shear stress term appropriate to turbulent flow, and the governing boundary layer equations are solved by a two-point finite-difference scheme. For illustration, the method is applied to the calculation of the phase angles between the shear stress at the wall and an oscillating external laminar boundary layer on a flat plate. The effectiveness of the method (for engineering purposes) is demonstrated by comparing calculations for turbulent flows with experimental data.

Cebeci, T.↗
NASA NTRS1977

Polarimetry of satellite surfaces

Available polarization observations of the satellites are reviewed, and the question of what information about satellite surfaces such observations contain is discussed critically. For satellites with negligible atmospheres, polarization measurements should provide useful information on surface texture and on the opacity of the surface materials. However, they are unlikely to yield specific compositional information. For Titan, the only satellite known to have an extensive atmosphere, polarimetry indicates the presence of optically thick clouds; it should be possible to deduce the cloud particle characteristics from such data, especially if more extensive observations, covering the full range of available phase angles and wavelengths, are obtained.

Veverka, J.↗
NASA NTRS1977

Io's sodium emission profiles - Variations due to Io's phase and magnetic latitude

We present recent measurements of high-resolution sodium D2 emission line profiles of Io's atmosphere and cloud. The high-velocity skirts of these profiles are strongest when Io is on the magnetic equator where protons and heavy ions, which sputter atoms from Io's surface, are concentrated. The skirts are most prominent on the long-wavelength side of the line when Io is west of Jupiter, and they are most prominent on the short-wavelength side of the line when Io is east of Jupiter. Our observations also indicate that there is a shift in the emission peak with respect to Io which is correlated with Io's orbital phase angle.

Trafton, L.↗
NASA NTRS1977

An explication of the radiometric method for size and albedo determination

A radiometric model for determination of diameters, albedos, and temperatures of asteroids and other airless planets is presented. Integrated photometry of planets is reviewed, and attention is given to problems of stellar calibration, monochromatic corrections, and corrections for the temperature variations across the planetary sphere. A previous model, which assumes that an asteroid emits infrared radiation as a smooth sphere, is modified to account for observed sunward beaming of infrared emissions, apparently due to craters. In contrast to some studies of the lunar emission, the observable flux ratio between a cratered sphere and a smooth sphere is calculated for large ranges of wavelength, temperature, and phase angle. Revised diameters based on the crater model are given for 84 asteroids. The systematic discrepancy between radiometrically- and polarimetrically-obtained albedos is accounted for; further areas of disagreement between radiometry and polarimetry are discussed, and research to resolve them is suggested.

Hansen, O. L.↗
NASA NTRS1977

An improved Venus cloud model

An inhomogeneous cloud model for Venus is presented in which a (transparent) sulfuric acid aerosol extends above the tropopause, but an (absorbing) sulfur aerosol consisting of much larger particles does not. It is shown that the temperature dependence of the absorption spectrum of sulfur, combined with the lapse rate in the planet's atmosphere, can explain the color of Venus. A simple 'black-white' radiative-transfer model is developed, the spectral reflectance of the cloud model is computed for the 60-km level in Marov's (1972) model atmosphere, and strong evidence is obtained that sulfur is the UV absorber on Venus. The wavelength variation of contrast in UV cloud features is analyzed, and absorption is found to increase with depth at every wavelength due to the inward increase in temperature. The black-white model is applied to CO2 absorption, variations in CO2 and UV absorption with phase angle are compared, and line profiles are calculated for pressure-broadened CO2 lines. The theoretical results are compared with Venera 9 and 10 data.

Young, A. T.↗
NASA NTRS1979

Optimizing multislot feeds for reflecting antennas

Multislot feed corrects phase errors in reflecting antennas. Variables are reduced by considering symmetry and corrective effect of each phase mode. Overall computation concerning calculation of correct phase angles while optimizing main beam efficiency is simplified by analysis used parabolic torus reflector aboard Space Shuttle.

Waineo, D. K.↗
NASA NTRS1977

Synthesis of blade flutter vibratory patterns using stationary transducers

Flutter frequency was determined and rotor vibratory amplitude and phase distributions during flutter were reconstructed from stationary aerodynamic type measurements. A previously reported optical method for measuring blade-tip displacement during flutter was extended by means of digital analysis. Displacement amplitudes and phase angles were determined based on this method. For selected blades, spectral results were also obtained from strain gage measurements. The results from these three types of measurement were compared and critically evaluated.

Kurkov, A.↗
NASA NTRS1977

An analysis of the rotor blade stresses of the three stage compressor of the Ames Research Center 11- by 11-foot transonic wind tunnel

The static and dynamic rotor blade stresses of the three stage compressor were measured. Data are presented in terms of total blade stress for the complete operational range of compressor speeds and tunnel total pressures. Modal frequencies and variations with tunnel conditions were measured. Phase angles and coherences between various gage combinations are also presented. Recommendations for improvements are given for future rotor blade experimental investigations.

Dods, J. B., Jr.↗
NASA NTRS1978

Preliminary results of study of infrared spectra of Venus from the orbital spacecraft Venera-9 and Venera-10

The infrared spectrum of Venus in the spectral range 1.6 to 2.8 was measured by means of the spectrometers aboard 'Venera-9' and 'Venera-10' orbital spacecrafts. Approximately 20 series of measurements were made near the pericenter of the orbit, each of which contains 150 spectra for each path intersecting the planet from the terminator to the limb. Phase angles lie within the limits from 60 to 120 deg.

Gnedykh, V.↗
NASA NTRS1977

Viking Imaging of Phobos and Deimos: An Overview of the Primary Mission

During the Viking primary mission the cameras on the two orbiters acquired about 50 pictures of the two Martian moons. The Viking images of the satellites have a higher surface resolution than those obtained by Mariner 9. The typical surface resolution achieved was 100-200 m, although detail as small as 40 m was imaged on Phobos during a particularly close passage. Attention is given to color sequences obtained for each satellite, aspects of phase angle coverage, and pictures for ephemeris improvement.

Duxbury, T. C.↗