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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 289 records · Page 16
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NASA NTRS1978

Thermal response behavior of boundary-layer flows

This paper presents an approximate, but general, analysis for the thermal response behavior of incompressible, constant property, laminar boundary layer flow over a smooth object of arbitrary shape. It encompasses the classic time-dependent Leveque problem as its special case. Comparisons with available data show that, for fluids with Prandtl number of the order of unity or larger, this analytical solution is able to provide reasonably accurate results for most engineering applications. Under certain restrictive conditions, it can also be used to predict the thermal response of a compressible boundary layer flow.

Lin, F. N.↗
NASA NTRS1978

The 3 K blackbody radiation, Dirac's Large Numbers Hypothesis, and scale-covariant cosmology

A program is described which is intended to derive a generalized system of gravitational equations that allow (but do not require) G to vary, to use the 3-K blackbody radiation to fix the relation between G and the gauge function, and to employ Dirac's (1937) Large Numbers Hypothesis to derive the geometry of the universe. Einstein's equations are retained in their total integrity, but the specification is made that they are valid only when gravitational units are used. A scale-invariant form of Einstein's equations is obtained, and from this are derived the energy conservation law, the baryon-number conservation law, and the appropriate cosmological equations. Dirac's proposals of 1937 and 1973 are incorporated into the formalism, and a gauge based on consolidation of the 3-K blackbody radiation is presented. A unique solution for the geometry of the universe is determined for zero curvature solely from the 3-K radiation and the Large Numbers Hypothesis; this solution predicts a deceleration parameter exactly equal to unity.

Canuto, V.↗
NASA NTRS1980

Improved flaw-detection method

Holographic detection of unbonded or delaminated surfaces of materials and structures is improved by using helium instead of air in vacuum test chamber. Helium has index of refraction closer to vacuum (unity) than air. Therefore changes in chamber pressure during test do not alter index of refraction as much as they do with air. With air, much of detail is lost, particularly in curved areas.

Platt, R. J., Jr.↗
NASA NTRS1978

Magnetosphere of Saturn

Models of the Saturnian magnetosphere based on the application of magnetospheric scaling relations to a spin-aligned planetary magnetic dipole, that produces a surface equatorial field strength in the range 0.5 to 2 gauss, exhibit the following properties: (1) The orbit of Titan lies inside of the magnetosphere essentially all of the time, even when variations in the size of the magnetosphere resulting from solar wind pressure changes are taken into account; (2) the Brice-type planetary plasmasphere reaches a peak density of about 10 protons cm/3 at L approximately 7 (L = planetocentric distance in units of planetary radii); (3) Saturn's rings have a profound effect on the energetic particle population and the plasmaspheres derived from interstellar neutrals and Titan's torus; (4) the model calculation suggests that the Titan-derived plasmasphere may be self-amplifying with a feed-back factor greater than unity, which implies the possibility of a non-linearly saturated, highly inflated Saturnian magnetosphere; and (5) this same source can have important eroding effects on the outer edge of the rings determined by Brown-Lauzerotti sputtering rates.

Siscoe, G. L.↗
NASA NTRS1979

Friction and wear with a single-crystal abrasive grit of silicon carbide in contact with iron base binary alloys in oil: Effects of alloying element and its content

Sliding friction experiments were conducted with various iron-base binary alloys (alloying elements were Ti, Cr, Mn, Ni, Rh, and W) in contact with a rider of 0.025-millimeter-radius, single-crystal silicon carbide in mineral oil. Results indicate that atomic size and content of alloying element play a dominant role in controlling the abrasive-wear and -friction properties of iron-base binary alloys. The coefficient of friction and groove height (wear volume) general alloy decrease, and the contact pressure increases in solute content. There appears to be very good correlation of the solute to iron atomic radius ratio with the decreasing rate of coefficient of friction, the decreasing rate of groove height (wear volume), and the increasing rate of contact pressure with increasing solute content C. Those rates increase as the solute to iron atomic radius ratio increases from unity.

Miyoshi, K.↗
NASA NTRS1977

The effect of a visual/motion display mismatch in a single axis compensatory tracking task

The frequency response of visual systems is typically unity from 0 to 20 rad/sec, while that of motion systems typically falls off in the vicinity of 6 rad/sec. The question arises as to what effect, if any, such a difference in servomechanism performance has on the simulation. Is pilot performance reduced by the conflict between displays? Would a more realistic simulation occur if the visual servomechanisms were degraded to match the motion servomechanisms? Does the pilot need and use the higher frequency information present in the visual display? The purpose of the experiment is to take a step forward toward answering these questions. Work already in the literature which bears on these questions is outlined. A description is then given of an experiment used to check for the effects of a difference in the performance of the visual and motion servomechanisms (the experiment uses a single-axis, compensatory, roll-tracking task). The results of the experiment are then presented and analyzed.

Shirachi, D. K.↗
NASA NTRS1979

The friction and wear of metals and binary alloys in contact with an abrasive grit of single-crystal silicon carbide

Sliding friction experiments were conducted with various metals and iron-base binary alloys (alloying elements Ti, Cr, Mn, Ni, Rh and W) in contact with single crystal silicon carbide riders. Results indicate that the friction force in the plowing of metal and the groove height (corresponding to the wear volume of the groove) decrease linearly as the shear strength of the bulk metal increases. The coefficient of friction and groove height generally decrease, and the contact pressure increases with an increase in solute content of binary alloys. There appears to be very good correlation of the solute to iron atomic ratio with the decreasing rate of change of coefficient of friction, the decreasing rate of change of groove height and the increasing rate of change of contact pressure with increasing solute content. These rates of change increase as the solute to iron atomic radius ratio increases or decreases from unity.

Miyoshi, K.↗
NASA NTRS1979

Growth of silicon carbide crystals on a seed while pulling silicon crystals from a melt

A saturated solution of silicon and an element such as carbon having a segregation coefficient less than unity is formed by placing a solid piece of carbon in a body of molten silicon having a temperature differential decreasing toward the surface. A silicon carbide seed crystal is disposed on a holder beneath the surface of the molten silicon. As a rod or ribbon of silicon is slowly pulled from the melt, a supersaturated solution of carbon in silicon is formed in the vicinity of the seed crystal. Excess carbon is emitted from the solution in the form of silicon carbide which crystallizes on the seed crystal held in the cool region of the melt.

Ciszek, T. F.↗
NASA NTRS1979

Prediction of ion drift effects on spacecraft floating potentials

The plasma environment of high altitude spacecraft was observed to involve ion drift velocities which sometimes become comparable to ion mean thermal speeds. Such drifts may cause an electrically isolated spacecraft surface to float at a substantially increased negative potential if it is simultaneously shaded and downstream relative to the drift direction. The results showed that: (1) the ion speed ratio at which drift effects become important (i.e. change the floating potential by at least 10 percent) can be as low as 0.1, and may be decreased if the ambient electrons are non-Maxwellian; (2) the effects of ion speed ratio increase with increasing ion-to-electron temperature ratio; and (3) negative floating potentials for drifting Maxwellian ion velocity distributions with speed ratio unity are typically about twice as large as the corresponding potentials for nondrifting conditions.

Chang, J. S.↗
NASA NTRS1979

Antenna feedhorn software upgrade

The HYBRIDHORN computer program was developed to serve as an item of general purpose antenna feedhorn design and analysis software. The formulation contains a small flare angle approximation which is subject to question for designs such as the S- and X-band feedhorn. Additionally, the original formulation did not allow azimuthal variation indexes other than unity. The HYBRIDHORN program was upgraded to correct both of these deficiencies. A large flare angle formulation was found. In the upgrade, all of the major program elements were converted to Univac 1108 compatible structured FORTRAN (SFTRAN) for ease of software maintenance. The small and large angle formulations are described and sample numerical results are presented.

Potter, P. D.↗
NASA NTRS1978

Winston Solar Concentrators and Evaluation Support. Phase 2: Non-imaging Concentrators for Space Applications

A 4.67X, plus or minus 5 deg. compound parabolic concentrator (CPC) for a large photovoltaic array in space was analyzed. The design was demonstrated to be effective in achieving a net power gain which can be varied from more than a factor of 3 down to approximately unity. A method for reducing nonuniformities in illumination to a given desired level was found. The effectiveness of this method, which involves the introduction of a degree of non-specularity in the reflector surface, was confirmed by direct measurements with prepared foil reflectors in a CPC in terrestrial sunshine as well as by computer ray tracing. Further ray tracing confirms that the CPC design is extremely tolerant to pointing and alignment errors, minor distortions, etc. A two stage non-imaging design was shown, by preliminary measurements and analysis, to provide both the desired angular tolerance and the required degree of intensity uniformity if higher concentrations (4X-10X) are necessary.

Winston, R.↗
NASA NTRS1978

The convection electric field model for the magnetosphere based on Explorer 45 observations

Large-scale electric fields in the magnetosphere, represented by the scalar potentials of corotation and convection fields, are examined in order to interpret both plasmapause positions at different local times and energetic particle penetrations inside the plasmapause observed by the Explorer 45 (S3-A) dc E field measurements and particle detectors. The Volland-Stern type convection electric field is assumed. A uniform dawn-dusk convection electric field which corresponds to an exponent (gamma) of unity is not consistent with the observational data, but the Volland-Stern model with gamma = 2 more likely represents the convection electric field during the hours of electric field increases during magnetic activity. In the time-independent case, the shape of the plasmapause does not depend on the intensity of the convection electric field, so that by using two plasmapause distances at different local times along the S3 outbound and inbound orbits the shape factor gamma of the convection field could be determined. The average value of gamma for 42 cases was found to be 2.4.

Ejiri, M.↗
NASA NTRS1978

The solar power satellite concept evaluation program

The paper describes in detail one of the preliminary baseline concepts for the solar power satellite (SPS). A large space freighter with payload capacity of 424 metric tons will deliver the material to a construction base in low earth orbit where the eight modules of the satellite are constructed. Electric thrusters will propel the modules to a smaller geosynchronous base, where the modules are docked and the solar arrays are deployed to form a satellite capable of providing 5 GW power from each of two end-mounted antennas to the two ground rectennas. The solar array is 5.3 km by 21.3 km to provide a total platform area of 113 sq km. The solar array employs silicon solar cells with a concentration ratio of unity. Details on transportation, construction bases, rectenna, and solar array design are given along with material requirements and cost estimates.

Piland, R. O.↗
NASA NTRS1978

Inversion of data from diffraction-limited multiwavelength remote sensors. I - Linear case

The remote sensing inverse problem is considered in which the sensor does not necessarily view the same area on the earth at each wavelength, and spatial correlations of the geophysical parameters may be present. Under the conditions of linearity and stationary statistics, the minimum mean-square error solution to the problem of inverting such data is a spatial filter of the Wiener-Kolmogorov class. The resulting remote-sensing system can be characterized by an impulse response matrix in ordinary space or by a transfer matrix in frequency space. A signal-to-noise matrix for the geophysical parameters to be sensed is also defined; this matrix depends on the postulated a priori statistics and on the characteristics of the remote-sensing instrument. The system transfer matrix and the signal-to-noise matrix are simultaneously diagonalizable. The optimum transfer matrix filters out of the estimate vector those eigenparameters for which eigenvalues of the signal-to-noise matrix are less than unity.

Rosenkranz, P. W.↗
NASA NTRS1979

Io - An intense brightening near 5 micrometers

Spectrophotometric observations of the Jovian satellite Io on February 20 and 21, 1978, (Universal Time) were made from 1.2 to 5.4 micrometers. Io's brightness at 4.7 to 5.4 micrometers was found to be three to five times greater at an orbital phase angle of 68 deg than at orbital phase angles of 23 deg (5.5 hours before the brightening) and 240 deg (20 hours after the brightening). Since the 5-micrometer albedo of Io is near unity under ordinary conditions, the observed transient phenomenon must have been the result of an emission mechanism. Although several such mechanisms were examined, the actual choice is not clear.

Witteborn, F. C.↗
NASA NTRS1979

The near-wake structure of the Atmosphere Explorer C /AE-C/ satellite - A parametric investigation

Measurements of ion current, electron temperature, and values of space potential obtained from the cylindrical electrostatic probe on board the Atmosphere Explorer C (AE-C) satellite were used to examine, in a parametric manner, the angular distribution of charge around the satellite. Interest is focused on nighttime equatorial data in the altitude range 275-620 km, which yields a wide range for the parameter R sub D (the radius of the satellite divided by the ambient value of the Debye lengths), including R sub D greater than 100, which is of practical significance to large space platforms. The variations of normalized ion current in the wake zone of the AE-C satellite appear to display an exponential dependence on R sub D for 'constant' values of other relevant parameters. The angular variations of electron temperature and space potential in the close vicinity of the satellite's surface were examined and compared with results from the Explorer 31 satellite. The variation of the ratio of measured to computed space potential with electron temperature was examined using data from both the AE-C and Explorer 31 satellites. It was found that the ratio is greater than unity. Possible causes for the above inequality are discussed.

Samir, U.↗
NASA NTRS1979

The radius and albedo of Hyperion

A measurement of the 20-micron thermal flux from Hyperion is reported, and the radius and surface geometric albedo of this outer satellite of Saturn are computed by the photometric/radiometric method. A corrected and normalized 20-micron thermal flux of 0.033 + or - 0.012 Jy is determined. A radius of 112 + or - 15 km and a surface geometric albedo of 0.47 + or - 0.11 are obtained by assuming values of unity for the phase integral, emissivity, and bolometric/visual geometric-albedo ratio. The sensitivity of the photometric/radiometric method to the assumed values of the parameters involved is discussed, and the results are compared with similar studies of Triton. It is concluded that neither Hyperion nor Triton appears to have a geometric albedo in the lower end of the distribution of small bodies in the solar system.

Cruikshank, D. P.↗
NASA NTRS1979

The emission-line spectrum of 3C 48

The spectrum and absolute energy distribution of the quasar 3C 48 are analyzed, yielding the following results. The forbidden lines are blueshifted with respect to the permitted lines by 600 km/s. The Balmer lines can be decomposed into a narrow and a broad component, with the narrow component having the redshift of the forbidden lines. The Mg II profile fits well the broad components of H-beta and H-gamma along with the Fe II profiles, and the forbidden O II profile fits well the profiles of forbidden O III and higher-ionization forbidden lines. The spatial coverage in the broad-line region is large, ranging from 0.1 to 0.4, and the optical depth at the Lyman limit is much greater than unity; the electron density is greater than 10 million per cu cm. The forbidden-line region has a lower density (less than 1 million per cu cm) and is subdivided into a low-excitation (forbidden O II) and high-excitation (forbidden O III) zone. The helium abundance appears to be normal.

Thuan, T. X.↗