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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Optical properties of mercury ion thruster exhaust plumes Significance for candidate SEP science instruments

Emission from the exhaust plume of a 30 cm mercury ion thruster was measured from 160 to 600 nm as a function of axial and radial distance from the thruster discharge chamber. The spectrally dispersed absolute intensities were used to construct an empirical volume emission rate function. The function was integrated along a typical instrument field of view, and the resulting apparent brightness was compared with instrument sensitivities to evaluate the extent of optical interference. The intensity levels degraded rapidly with distance from the thruster so that optical interference was negligible for fields of view not intercepting the beam axis. The operation of only one instrument, a zodiacal photopolarimeter was considered incompatible with simultaneous thruster operation.

Goldstein, R.↗
NASA NTRS1975

Combustion instability with partial length acoustic liners

The development is discussed of analytical techniques and numerical methods for the prediction of the stability behavior of liquid propellant rocket combustors with partial length acoustic liners, injector face baffles, and nonlinear combustion responses. Three primary objectives included: (1) extension of the Green's Function integral-iteration technique previously developed so that nonlinear three dimensional wave propagation effects could be included in stability predictions; (2) development of an analytical technique and a computer program for the prediction of the damping effects caused by injector face baffles; and (3) inclusion of a nonlinear, wave distortation dependent, combustion response model in the global stability analysis and determination of its effect on combustor stability.

Mitchell, C. E.↗
NASA NTRS1976

Diatomic molecule variations

The rotational energy is separated from vibrational energy in the two-particle, steady-state wave equation and to first order the solutions are harmonic oscillator functions. The classical phase integral gives a partition function valid only at high temperature, but the quantum summation is easily performed to give analytic expressions for all the thermodynamic properties of the harmonic oscillator at all temperatures. Anharmonic effects are treated by small perturbation solutions to the wave equation and the relation between energy levels and a series expansion of the perturbation potential is derived. Next, the quantum solutions for an oscillator with a Morse-function potential are derived in terms of Laguerre polynomials.

Source record↗
NASA NTRS1976

Steady incompressible variable thickness shear layer aerodynamics

A shear flow aerodynamic theory for steady incompressible flows is presented for both the lifting and non lifting problems. The slow variation of the boundary layer thickness is considered. The slowly varying behavior is treated by using multitime scales. The analysis begins with the elementary wavy wall problem and, through Fourier superpositions over the wave number space, the shear flow equivalents to the aerodynamic transfer functions of classical potential flow are obtained. The aerodynamic transfer functions provide integral equations which relate the wall pressure and the upwash. Computational results are presented for the pressure distribution, the lift coefficient, and the center of pressure travel along a two dimensional flat plate in a shear flow. The aerodynamic load is decreased by the shear layer, compared to the potential flow. The variable thickness shear layer decreases it less than the uniform thickness shear layer based upon equal maximum shear layer thicknesses.

Chi, M. R.↗
NASA NTRS1976

Doppler noise considered as a function of the signal path integration of electron density

The hypothesis is advanced that observed Doppler noise during solar conjunctions is proportional to total columnar electron content along the signal path. This assumption leads directly to a geometrical model (ISED) for observed Doppler noise which is shown to be in very good agreement with Doppler noise data accumulated during the 1975 Pioneer 10, Pioneer 11 and Helios 1 solar conjunctions. An augmented model is constructed which quantitatively indicates correlation between earth observed sunspot activity and systematic, cyclical deviations from the ISED model.

Berman, A. L.↗
NASA NTRS1976

Long period coupling terms for Lagrange's equations

A generalization of that portion of the work of Berger, which deals with the long period coupling effect of certain pairs of zonal harmonics. Long period terms arising from the short short period coupling of zonal harmonics are derived for Lagrange's equations. The formulation is general so that the results are valid for any pairs of zonal harmonics. Formulas are given to generate the various functions and integrals needed for the results given. Checks have been made against the work of Kozai.

Source record↗
NASA NTRS1976

Solid rocket motor internal insulation

Internal insulation in a solid rocket motor is defined as a layer of heat barrier material placed between the internal surface of the case propellant. The primary purpose is to prevent the case from reaching temperatures that endanger its structural integrity. Secondary functions of the insulation are listed and guidelines for avoiding critical problems in the development of internal insulation for rocket motors are presented.

Twichell, S. E.↗
NASA NTRS1978

Remote water monitoring system

A remote water monitoring system is described that integrates the functions of sampling, sample preservation, sample analysis, data transmission and remote operation. The system employs a floating buoy carrying an antenna connected by lines to one or more sampling units containing several sample chambers. Receipt of a command signal actuates a solenoid to open an intake valve outward from the sampling unit and communicates the water sample to an identifiable sample chamber. Such response to each signal receipt is repeated until all sample chambers are filled in a sample unit. Each sample taken is analyzed by an electrochemical sensor for a specific property and the data obtained is transmitted to a remote sending and receiving station. Thereafter, the samples remain isolated in the sample chambers until the sampling unit is recovered and the samples removed for further laboratory analysis.

Grana, D. C.↗
NASA NTRS1978

NASTRAN implementation of an isoparametric doubly-curved quadrilateral shell element

A quadrilateral shell element, CQUAD4, was added to level 15.5 and subsequently to level 16.0 of NASTRAN. The element exhibited doubly curved surfaces and used biquadratic interpolation functions. Reduced integration techniques were used to improve the performance of the element in thin shell problems. The creation of several new bulk data items is discussed, along with a special module, GPNORM, to process SHLNORM bulk data cards. In addition to the theoretical basis for the element stiffness matrix, consistent mass and load matrices are presented. Several potential sources of degenerate behavior of the element were investigated. Guidelines for proper use of the element were suggested. Performance of the element on several widely published classical examples was demonstrated. The results showed a significant improvement over presently available NASTRAN shell elements for even the coarsest meshes. Potential applications to two classes of practical problems are discussed.

Potvin, A. B.↗
NASA NTRS1979

The classical solution of a definite integral occurring in the satellite theory in the extended phase space

A method of integrating the functions defined by Scheifele and Graf (1974), arising in the elimination of time from the arguments of satellite theory using Delaunay elements in the extended phase space, is proposed. By repeated applications of an identity of Stiefel and Scheifele (1971), neglecting certain terms, and assuming a solution in the form of a product of Bessel functions, a solution expanded in the eccentricity is obtained.

Bond, V. R.↗
NASA NTRS1978

Contribution to solving the energy crisis - Simulating the prospects for low cost energy through silicon solar cells

PECAN (Photovoltaic Energy Conversion Analysis) is a highly interactive decision analysis and support system. It simulates the prospects for widespread use of solar cells for the generation of electrical power. PECAN consists of a set of integrated APL functions for evaluating the potential of terrestrial photovoltaics. Specifically, the system is a deterministic simulator, which translates present and future manufacturing technology into economic and financial terms, using the production unit concept. It guides solar cell development in three areas: tactical decision making, strategic planning, and the formulation of alternative options.

Kran, A.↗
NASA NTRS1979

Two-stream theory of reflectance of snow

Spectral reflectance of snow under diffuse illumination is studied using the two-stream approximation of the radiative transfer equation. The scattering and absorption parameters of the radiative transfer equation - the single scattering albedo, the optical depth, and the integrated phase function are obtained from the grain size and density of snow. Analytical expressions for the intensity within the snowpack, the reflectance, and the asymptotic flux extinction coefficient, are given. Good agreement is shown between the theory and available experimental data on visible and near-infrared reflectance, and the asymptotic flux extinction coefficient. The theory may also be used to explain the observed effect of aging on the snow reflectance.

Choudhury, B. J.↗
NASA NTRS1982

An accurate method for evaluating the kernel of the integral equation relating lift to downwash in unsteady potential flow

The method is capable of generating approximations of arbitrary accuracy. It is based on approximating the algebraic part of the nonelementary integrals in the kernel by exponential functions and then integrating termwise. The exponent spacing in the approximation is a geometric sequence. The coefficients and exponent multiplier of the exponential approximation are computed by least squares so the method is completely automated. Exponential approximates generated in this manner are two orders of magnitude more accurate than the exponential approximation that is currently most often used for this purpose. The method can be used to generate approximations to attain any desired trade-off between accuracy and computing cost.

Desmarais, R. N.↗
NASA NTRS1983

Interpretation of 2-probe turbulence measurements in an axisymmetric contraction

Simultaneous measurements of the streamwise and radial velocity components at two points, one on and one off the centerline with variable radial separation, were digitally recorded and processed at several stations along a four to one contraction with controlled upstream turbulence conditions. Various statistical quantities are presented including spectra and coherence functions. The integral L sub ux, L sub um, L sub vx, L sub vm were also estimated and their variation along the contraction is examined.

Marion-Moulin, C.↗
NASA NTRS1983

A theory of rotating stall of multistage axial compressors. III - Limit cycles

A theory of rotating stall, based on single parameters for blade-passage lag and external-flow lag and a given compressor characteristic yields limit cycles in velocity space. These limit cycles are governed by Lienard's equation with the characteristic playing the role of nonlinear damping function. Cyclic integrals of the solution determine stall propagation speed and the effect of rotating stall on average performance. Solution with various line-segment characteristics and various throttle settings are found and discussed. There is generally a limiting flow coefficient beyond which no solution is possible; this probably represents stall recovery. This recovery point is independent of internal compressor lag, but does depend on external lags and on the height-to-width ratio of the diagram. Tall diagrams and small external lags (inlet and diffusor) favor recovery. Suggestions for future theoretical and experimental research are discussed.

Moore, F. K.↗
NASA NTRS1984

Signal-to-noise ratio for the wide field-planetary camera of the Space Telescope

Signal-to-noise ratios for the Wide Field Camera and Planetary Camera of the Space Telescope were calculated as a function of integration time. Models of the optical systems and CCD detector arrays were used with a 27th visual magnitude point source and a 25th visual magnitude per arc-sq. second extended source. A 23rd visual magnitude per arc-sq. second background was assumed. The models predicted signal-to-noise ratios of 10 within 4 hours for the point source centered on a signal pixel. Signal-to-noise ratios approaching 10 are estimated for approximately 0.25 x 0.25 arc-second areas within the extended source after 10 hours integration.

Zissa, D. E.↗
NASA NTRS1984

The infrared properties of galaxy clusters - IRAS observations of the Hercules Cluster (Abell 2151)

A total of 41 sources have been detected at 60 microns to a level of 50 mJy in a 1.6 x 0.5 deg field centered on the rich galaxy cluster Abell 2151. Twenty-four of these sources can be identified with late-type spiral galaxies of estimated photographic magnitude 17 or brighter. Galaxies classified as E or S0 are notably absent in the infrared data. Within the field, eleven of the IRAS sources cannot be easily identified with galaxies in the Hercules Cluster. If the brightest 60 micron cluster source (NGC 6045) is neglected, the integral luminosity function in the far-infrared can be fitted well with two power laws of slope -1.1 and -2.5.

Young, E.↗