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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Calculations of the effects of angular momentum on the early evolution of Jupiter

Early phases in the evolutionary development of a rotating cloud of gas and dust are investigated to determine whether physically reasonable initial conditions are likely to produce a planet-satellite system with the values of specific orbital angular momentum currently observed for Jupiter and its inner satellites. Spherically symmetric computations of Jupiter's evolutionary history are reviewed, and transport of angular momentum is considered along with evolutionary sequences of individual differentially rotating models with decreasing values of equatorial radius. The problem of accounting for the present specific orbital angular momenta of Jupiter and its regular satellites is examined qualitatively, and a range of possible angular-momentum distributions in an initially tidally unstable cloud is assessed. The results show that particular physically plausible angular-momentum distributions, which could either be established as initial conditions or be caused by angular-momentum transport, will lead to favorable situations for the formation of a central planet and a surrounding rotating cloud with specific angular momentum comparable to that of the regular satellites.

Bodenheimer, P.↗
NASA NTRS1977

Ion sheath effects on RF plasma probes - Experimental results in laboratory plasmas

Laboratory work dealing with the frequency characteristic of the plasma impedance of spherical and cylindrical electrode systems is reported. The influence of the ion sheath on various features of the impedance characteristic is emphasized. Those features are the series and parallel resonance as well as additional resonances due to the excitation of electroacoustic and cyclotron harmonic waves. The dependence of the series and parallel resonances on dc biasing leads to a method of determining the ion sheath capacity for a cylindrical electrode system. The obtained values agree fairly well with those obtained from a theoretical model for the density and potential distribution in the sheath of a cylindrical sensor aligned with a supersonic plasma flow. The amplitude of resonances due to excitation of longitudinal plasma waves (electroacoustic and cyclotron harmonic) is reduced or even vanishes for sufficiently negative dc bias. Positive bias first leads to an increased amplitude up to a certain dc bias value above which, however, the amplitude decreases again due to electron absorption at the sensor surface.

Kist, R.↗
NASA NTRS1977

A note on the assumption of quasiequilibrium in semiconductor junction devices

It is shown that the quasi-equilibrium theory for p-n junctions, as originally proposed by Shockley (1949), does not apply under conditions involving an application of comparatively low external voltages. A numerical example indicates that the quasi-equilibrium assumption must be discarded as soon as the voltage is increased beyond a certain critical value, although the system may still be in a low-level injection regime. It is currently not known which set of simplifying assumptions may replace the quasi-equilibrium assumptions. Possible analytic simplification relations applicable to moderate or high injection levels can, perhaps, be based on an approach considered by Mari (1968) and Choo (1971, 1972).

Von Roos, O.↗
NASA NTRS1979

Mathematical model for steady state, simple ampholyte isoelectric focusing: Development, computer simulation and implementation

The elimination of Ampholine from the system by establishing the pH gradient with simple ampholytes is proposed. A mathematical model was exercised at the level of the two-component system by using values for mobilities, diffusion coefficients, and dissociation constants representative of glutamic acid and histidine. The constants assumed in the calculations are reported. The predictions of the model and computer simulation of isoelectric focusing experiments are in direct importance to obtain Ampholine-free, stable pH gradients.

Palusinski, O. A.↗
NASA NTRS1979

Optical infrared sky survey instrumentation

An unusual, highly modified, Baker reflector-corrector class telescope has been adapted for wide field survey photography in the near infrared. This optical system uses a full field corrector plate and a field flattening lens to provide a flat field subtending about 4.5 deg on the sky. The small aperture telescope (20 inch primary) has been modified for use in the Newtonian focus configuration while preserving the optical elements of the Prime focus configuration. The telescope has been further modified to accept a very large format (146mm diameter photocathode) image intensifier camera to serve as a detector. The camera output is recorded photographically on film rather than glass plates. This unique instrument system is used in a program of sky survey photography in the optical infrared (8000-9000A bandpass) supplemented by visual bandpass photography. The photographs obtained with this system are of value not only for the extreme redness of the band but also because of their high resolution and their freedom from hydrogen emission.

Craine, E. R.↗
NASA NTRS1979

Multivariable control altitude demonstration on the F100 turbofan engine

The control system designed under the Multivariable Control Synthesis (MVCS) program for the F100 turbofan engine is described. The MVCS program, applied the linear quadratic regulator (LQR) synthesis methods in the design of a multivariable engine control system to obtain enhanced performance from cross-coupled controls, maximum use of engine variable geometry, and a systematic design procedure that can be applied efficiently to new engine systems. Basic components of the control system, a reference value generator for deriving a desired equilibrium state and an approximate control vector, a transition model to produce compatible reference point trajectories during gross transients, gain schedules for producing feedback terms appropriate to the flight condition, and integral switching logic to produce acceptable steady-state performance without engine operating limit exceedance are described and the details of the F100 implementation presented. The engine altitude test phase of the MVCS program, and engine responses in a variety of test operating points and power transitions are presented.

Lehtinen, B.↗
NASA NTRS1979

Hydrogen-fueled diesel engine without timed ignition

Experiments were carried out to investigate the feasibility of converting a diesel engine to hydrogen-fueled operation without providing a timed ignition system. Use was made of a glow plug and a multiple-strike spark plug. The glow plug was found to provide reliable ignition and smooth engine operation. It caused the hydrogen to ignite almost immediately upon the start of injection. Indicated mean effective pressures were on the order of 1.3 MPa for equivalence ratios between 0.1 and 0.4 at a compression ratio of 18. This is significantly higher than the corresponding result obtained with diesel oil (about 0.6 MPa for equivalence ratios between 0.3 and 0.9). Indicated thermal efficiencies were on the order of 0.4 for hydrogen and 0.20-0.25 for diesel oil. Operation with the multiple-strike spark system yielded similar values for IMEP and efficiency, but gave rise to large cycle-to-cycle variations in the delay between the beginning of injection and ignition. Large ignition delays were associated with large amplitude pressure waves in the combustion chamber. The measured NO(x) concentrations in the exhaust gas were of the order of 50-100 ppm. This is significantly higher than the corresponding results obtained with premixed hydrogen and air at low equivalence ratios. Compression ignition could not be achieved even at a compression ratio of 29.

Homan, H. S.↗
NASA NTRS1979

Decametric radio measurement of Jupiter's rotation period

Results of determinations of Jupiter's average decametric-wave rotation period are reported. The residual longitude drift of 18, 20 and 22.2 GHz emission observed at stations in Florida and Chile was calculated from measurements of the longitudes of source A peak centers for apparitions separated by 12 years; the drift was assumed to be the longitude shift which maximizes the cross correlation of histograms of occurence probability as a function of System III (1957.0) central meridian longitude. The weighted mean rotation period observed is 9 h 55 min 29.689 sec (standard deviation 0.005 sec), which is 0.022 sec less than the System III (1965) value. It is suggested that, if measurements are continued through the next maximum of Jovicentric earth declination, a secular drift in Jupiter's magnetic field may be observable.

May, J.↗
NASA NTRS1980

Iterative methods based upon residual averaging

Iterative methods for solving boundary value problems for systems of nonlinear partial differential equations are discussed. The methods involve subtracting an average of residuals from one approximation in order to arrive at a subsequent approximation. Two abstract methods in Hilbert space are given and application of these methods to quasilinear systems to give numerical schemes for such problems is demonstrated. Potential theoretic matters related to the iteration schemes are discussed.

Neuberger, J. W.↗
NASA NTRS1979

Analysis of solar radiation pressure induced coupled librations of a gravity stabilized axisymmetric satellite

This paper presents an analysis of solar radiation pressure induced coupled librations of gravity stabilized cylindrical spacecraft with a special reference to geostationary communication satellites. The Lagrangian approach is used to obtain the corresponding equations of motion. The solar induced torques are assumed to be free of librational angles and are represented by their Fourier expansion. The response and periodic solutions are obtained through linear and nonlinear analyses, using the method of harmonic balance in the latter case. The stability conditions are obtained using Routh-Hurwitz criteria. To establish the ranges of validity the analytic response is compared with the numerical solution. Finally, values of the system parameters are suggested to make the satellite behave as desired. Among these is a possible approach to subdue the solar induced roll resonance. It is felt that the approximate analysis presented here should significantly reduce the computational efforts involved in the design and stability analysis of the systems.

Shrivastava, S. K.↗
NASA NTRS1981

Eastern Regional Remote Sensing Applications Conference

The roles and activities of NASA and the National Conference of State Legislatures in fostering remote sensing technology utilization by the states and in promoting interstate communication and cooperation are reviewed. The reduction and interpretation of LANDSAT MSS and aerial reconnaissance data for resources management and environment assessment are described as well as resource information systems, and the value of SEASAT synthetic aperture radar and LANDSAT 4 data.

Short, N. M.↗
NASA NTRS1984

Analog simulation of flux-summing servo-model, phases 1 and 2

The analog simulation was developed for a closed-loop system having an electrohydraulic flux-summing servo valve and actuator with associated inertial load. One-fourth of the system's total forward gain is carried by each of four channels. The present study successfully applied failure mode management techniques to the problem of channel failure. Digital logic circuitry was developed to maintain the overall forward gain of the system at a constant value, in the presence of channel failure. Finally, the stability of the system was verified, and performance characteristics were determined through the use of frequency response methods.

Hriber, E. J.↗
NASA NTRS1987

Echocardiographic evaluation of Space Shuttle crewmembers

Echocardiographic measurements of left ventricular volume were obtained from 17 members of four Space Shuttle crews before and after 5- to 8-day space flights. Measurements obtained 1 h after landing indicated increases in the heart rate (HR), mean arterial pressure, and systemic vascular resistance values. On the other hand, the end-diastolic volume index (EDVI) fell 17 ml/sq m, and the stroke volume index (SVI) fell 15 ml/sq m. Measurements taken 1-2 weeks later demonstrated that the HR values returned to normal, but the EDVI and SVI values remained significantly below preflight levels, despite the ability of the subjects to ambulate and exercise. The results indicate that a space flight induces significant changes in heart volume affecting the left-ventricle function. It is suggested that the prolonged recovery period is related to the high level of aerobic conditioning in these subjects.

Bungo, M. W.↗
NASA NTRS1986

Model reference adaptive attitude control of spacecraft using reaction wheels

A nonlinear model reference adaptive control law for large angle rotational maneuvers of spacecraft using reaction wheels in the presence of uncertainty is presented. The derivation of control law does not require any information on the values of the system parameters and the disturbance torques acting on the spacecraft. The controller includes a dynamic system in the feedback path. The control law is a nonlinear function of the attitude error, the rate of the attitude error, and the compensator state. Simulation results are prsented to show that large angle rotational maneuvers can be performed in spite of the uncertainty in the system.

Singh, Sahjendra N.↗
NASA NTRS1987

Attitude control of a three rotor gyrostat in the presence of uncertainty

A nonlinear control law for large angle rotational maneuvers of spacecraft using reaction wheels in the presence of uncertainty is presented. The derivation of this suboptimal control law does not require any information on the values of the system parameters and the disturbance torques acting on the spacecraft. The controller includes a dynamic system in the feedback path. The control law is a nonlinear function of the attitude error, the rate of the attitude error and the compensator state. Simulation results are presented to show that large angle rotational maneuvers can be performed in spite of the uncertainty in the system.

Singh, Sahjendra N.↗
NASA NTRS1988

A review of test results on parabolic dish solar thermal power modules with dish-mounted Rankine engines and for production of process steam

This paper presents results of development testing of various solar thermal parabolic dish modules and assemblies. Most of the tests were at modules and assemblies that used a dish-mounted, organic Rankine cycle turbine for production of electric power. Some tests were also run on equipment for production of process steam or for production of electricity using dish-mounted reciprocating steam engines. These tests indicate that early modules achieve efficiencies of about 18 percent in converting sunlight to electricity (excluding the inverter but including parasitics). A number of malfunctions occurred. The performance measurements, as well as the malfunctions and other operating experience, provided information that should be of value in developing systems with improved performance and reduced maintenance.

Jaffe, Leonard D.↗
NASA NTRS1988

A review of test results on solar thermal power modules with dish-mounted Stirling and Brayton cycle engines

This paper presents results of development tests of various solar thermal parabolic dish modules and assemblies that used dish-mounted Brayton or Stirling cycle engines for production of electric power. These tests indicate that early modules achieve net efficiencies up to 29 percent in converting sunlight to electricity, as delivered to the grid. Various equipment deficiencies were observed and a number of malfunctions occurred. The performance measurements, as well as the malfunctions and other test experience, provided information that should be of value in developing systems with improved performance and reduced maintenance.

Jaffe, Leonard D.↗
NASA NTRS1990

Micromechanics analysis of space simulated thermal deformations and stresses in continuous fiber reinforced composites

Space simulated thermally induced deformations and stresses in continuous fiber reinforced composites were investigated with a micromechanics analysis. The investigation focused on two primary areas. First, available explicit expressions for predicting the effective coefficients of thermal expansion (CTEs) for a composite were compared with each other, and with a finite element (FE) analysis, developed specifically for this study. Analytical comparisons were made for a wide range of fiber/matrix systems, and predicted values were compared with experimental data. The second area of investigation focused on the determination of thermally induced stress fields in the individual constituents. Stresses predicted from the FE analysis were compared to those predicted from a closed-form solution to the composite cylinder (CC) model, for two carbon fiber/epoxy composites. A global-local formulation, combining laminated plate theory and FE analysis, was used to determine the stresses in multidirectional laminates. Thermally induced damage initiation predictions were also made.

Bowles, David E.↗