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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 1,315 records · Page 73
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NASA NTRS1975

Magnetospheric plasma regions and boundaries

The boundaries of the various regions of the magnetospheric plasma are considered, taking into account the bow shock, the magnetopause, the outer boundary of the plasma sheet, the inner boundary of the plasma sheet, and the trapping boundary for energetic particles. Attention is given to the steady state, or quasi-steady state, to substorm effects in which temporal changes are important, and to primary auroral processes. A description is presented of the high latitude lobes of the magnetotail. The characteristics of magnetic field topology associated with interconnected interplanetary and geomagnetic field lines are illustrated with the aid of a graph.

Heikkila, W. J.↗
NASA NTRS1976

Isotopic composition of nitrogen - Implications for the past history of Mars' atmosphere

Models are presented for the past history of nitrogen on Mars, based on Viking measurements showing that the atmosphere is enriched in N-15. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N2 and by dissociative recombination of N2(+). The initial partial pressure of N2 should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO2 and HNO3.

Mcelroy, M. B.↗
NASA NTRS1977

Geologic evolution of the terrestrial planets

The paper presents a geologic comparison of the terrestrial planets Mercury, Venus, Earth, the Moon and Mars, in the light of the recent photogeologic and other evidence gathered by satellites, and discusses the relationships between their regional terrain types, ages, and planetary evolution. The importance of the two fundamental processes, impact cratering and volcanism, which had formed these planets are stressed and the factors making the earth unique, such as high planetary evolution index (PEI), dynamic geological agents and the plate tectonics, are pointed out. The igneous processes which dominate earth and once existed on the others are outlined together with the planetary elevations of the earth which has a bimodal distribution, the moon which has a unimodal Gaussian distribution and Mars with a distribution intermediate between the earth and moon. Questions are raised concerning the existence of a minimum planetary mass below which mantle convection will not cause lithospheric rifting, and as to whether each planet follows a separate path of evolution depending on its physical properties and position within the solar system.

Head, J. W.↗
NASA NTRS1977

A search for helium ions in the recovery phase of a magnetic storm

Data from an energetic ion mass spectrometer experiment on the low-latitude polar-orbiting satellite 1971-89A were examined for evidence of helium ions in the region of the ring current during the recovery phase of the December 17-18, 1971 magnetic storm. The principal precipitating ion species with energies between 0.7 and 12 keV were observed to be O+ and H+. No evidence for He+ was obtained. Inferences about the composition of the trapped population are made on the basis of simultaneous observations in the equatorial plane by Explorer 45. Coordinated observations with Explorer 45 and the Fritz Peak Observatory during the period of a stable auroral red arc have provided some information on the ionospheric and magnetospheric processes associated with the arc. A comparison of charge exchange and precipitation lifetimes during the recovery phase of the December 17-18 storm has shown both processes to be of comparable importance as ring current decay mechanisms in the energy range of the observations.

Sharp, R. D.↗
NASA NTRS1979

Application of advanced on-board processing concepts to future satellite communications systems

An initial definition of on-board processing requirements for an advanced satellite communications system to service domestic markets in the 1990's is presented. An exemplar system architecture with both RF on-board switching and demodulation/remodulation baseband processing was used to identify important issues related to system implementation, cost, and technology development.

Katz, J. L.↗
NASA NTRS1980

On-board processing concepts for future satellite communications systems

The initial definition of on-board processing for an advanced satellite communications system to service domestic markets in the 1990's is discussed. An exemplar system with both RF on-board switching and demodulation/remodulation baseband processing is used to identify important issues related to system implementation, cost, and technology development. Analyses of spectrum-efficient modulation, coding, and system control techniques are summarized. Implementations for an RF switch and baseband processor are described. Among the major conclusions listed is the need for high gain satellites capable of handling tens of simultaneous beams for the efficient reuse of the 2.5 GHz 30/20 frequency band. Several scanning beams are recommended in addition to the fixed beams. Low power solid state 20 GHz GaAs FET power amplifiers in the 5W range and a general purpose digital baseband processor with gigahertz logic speeds and megabits of memory are also recommended.

Brandon, W. T.↗
NASA NTRS1980

Association reactions of C/+/ ions with H2 and D2 molecules at 78 and 300 K

The paper deals with an investigation of associated reactions of C(+) ions with H2 and D2 molecules, using drift-tube-mass spectrometer techniques. It is found that at H2 and D2 densities of 1 x 10 to the 16th per cu cm, the reactions proceed by three-body association, the rate coefficients at 300 and 78 K being somewhat higher for D2 than for H2. The measurements place an upper limit on the rate coefficients for radiative association, a process thought to constitute an important step in the formation of molecules in interstellar gas clouds

Johnsen, R.↗
NASA NTRS1980

Social issues and implications of remote sensing applications: Paradigms of technology transfer

The transfer of technology from one federal agency to another was observed in the case of the move of LANDSAT to NOAA. An array of unanticipated consequences was found that have important impacts on both the process and outcome of the transfer. When the process was studied from viewpoint of the ultimate recipient, a set of expectations and perceptions were found that figure more in a final assessment than do the attributes of the technology being transfered. The question of how to link a technology with a community of potential users was studed in detail.

Hoos, I. R.↗
NASA NTRS1981

A diagonal form of an implicit approximate-factorization algorithm

A modification of an implicit approximate-factorization finite-difference algorithm applied to partial differential equations is presented. This algorithm is applied to the two- and three-dimensional Euler equations in general curvilinear coordinates. The modification transforms the coupled system of equations into an uncoupled diagonal form that requires less computational work. For steady-state applications, the resulting diagonal algorithm retains the stability and accuracy characteristics of the original algorithm. The diagonal algorithm reduces the storage requirement of the implicit solution process and therefore has an important effect on the application of implicit finite-difference schemes to vector processors. Results are presented for realistic two-dimensional transonic flow fields about airfoils. Computation costs are reduced to 24-34%.

Pulliam, T. H.↗
NASA NTRS1982

Numerical prediction of the Mid-Atlantic states cyclone of 18-19 February 1979

A series of forecast experiments was conducted to assess the accuracy of the GLAS model, and to determine the importance of large scale dynamical processes and diabatic heating to the cyclogenesis. The GLAS model correctly predicted intense coastal cyclogenesis and heavy precipitation. Repeated without surface heat and moisture fluxes, the model failed to predict any cyclone development. An extended range forecast, a forecast from the NMC analysis interpolated to the GLAS grid, and a forecast from the GLAS analysis with the surface moisture flux excluded predicted weak coastal low development. Diabatic heating resulting from oceanic fluxes significantly contributed to the generation of low level cyclonic vorticity and the intensification and slow rate of movement of an upper level ridge over the western Atlantic. As an upper level short wave trough approached this ridge, diabatic heating associated with the release of latent heat intensified, and the gradient of vorticity, vorticity advection and upper level divergence in advance of the trough were greatly increased, providing strong large scale forcing for the surface cyclogenesis.

Atlas, R.↗
NASA NTRS1982

Doppler line profiles measurement of the Jovian Lyman Alpha emission with OAO-C

Observation of Jupiter made with the high resolution ultraviolet spectrometer of the Orbiting Astronomical Observatory copernicus in April and May, 1980, yield a Jovian Lyman alpha emission intensity of 7 + or 2.5 RR. This indicates a decrease by about a factor of two since the Voyager ultraviolet spectrometer measurements, nearly a year earlier. An unusually high column abundance of hydrogen atoms above the methane homopause at the Voyager epoch is indicated. Since the auroral charged particle bombardment of molecular hydrogen is expected to contribute significantly to the global population of the hydrogen atoms, it is suggested that at the time of the Voyager Jupiter encounter unusually high auroral activity existed, perhaps d to the high concentration of the Io plasma torus. The temporal variation of the Saturn lyman alpha emission, when contrasted with the Jovian data, reveals that the auroral processes are not nearly as important in determining the Saturn Lyman alpha intensity in the nonauroral region.

Barker, E. S.↗
NASA NTRS1982

Fragmentation of Fe-56 nuclei on CH2, carbon, and hydrogen targets - Individual charge changing and total cross sections

Elemental and isotopic differences between cosmic rays coming from different sources may have important implications for the nucleosynthesis process occurring in the stars that ultimately produce the galactic cosmic rays. The cosmic-ray composition observed at earth is modified from that accelerated in the source regions by passage through approximately 6 g/sq cm of interstellar matter consisting of approximately 90% H and 10% He by number. The extrapolation of the observed composition at earth to the sources requires an accurate understanding of the fragmentation cross sections in H. With the recent acceleration of heavy nuclei up to Fe to relativistic energies, the direct measurement of the astrophysically interesting cross section is now possible. The present investigation is concerned with a determination of the individual elemental cross sections, Fe-56 incident on H, taking into account the application of the elemental cross section data to the cosmic-ray propagation problem.

Webber, W. R.↗
NASA NTRS1983

Analysis of defect structure in silicon. Characterization of SEMIX material. Silicon sheet growth development for the large area silicon sheet task of the low-cost solar array project

Statistically significant quantitative structural imperfection measurements were made on samples from ubiquitous crystalline process (UCP) Ingot 5848 - 13C. Important correlation was obtained between defect densities, cell efficiency, and diffusion length. Grain boundary substructure displayed a strong influence on the conversion efficiency of solar cells from Semix material. Quantitative microscopy measurements gave statistically significant information compared to other microanalytical techniques. A surface preparation technique to obtain proper contrast of structural defects suitable for quantimet quantitative image analyzer (QTM) analysis was perfected and is used routinely. The relationships between hole mobility and grain boundary density was determined. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density.

Natesh, R.↗
NASA NTRS1984

Analysis of SSME HPOTP rotordynamics subsynchronous whirl

The causes and remedies of vibration and subsynchronous whirl problems encountered in the Shuttle Main Engine SSME turbomachinery are analyzed. Because the nonlinear and linearized models of the turbopumps play such an important role in the analysis process, the main emphasis is concentrated on the verification and improvement of these tools. It has been the goal of our work to validate the equations of motion used in the models are validated, including the assumptions upon which they are based. Verification of th SSME rotordynamics simulation and the developed enhancements, are emphasized.

Source record↗
NASA NTRS1984

The nonlinear gyroresonance interaction between energetic electrons and coherent VLF waves propagating at an arbitrary angle with respect to the earth's magnetic field

A theory is presented of the nonlinear gyroresonance interaction that takes place in the magnetosphere between energetic electrons and coherent VLF waves propagating in the whistler mode at an arbitrary angle psi with respect to the earth's magnetic field B-sub-0. Particularly examined is the phase trapping (PT) mechanism believed to be responsible for the generation of VLF emissions. It is concluded that near the magnetic equatorial plane gradients of psi may play a very important part in the PT process for nonducted waves. Predictions of a higher threshold value for PT for nonducted waves generally agree with experimental data concerning VLF emission triggering by nonducted waves.

Bell, T. F.↗
NASA NTRS1985

Theoretical Thermodynamics of Mixtures at High Pressures

The development of an understanding of the chemistry of mixtures of metallic hydrogen and abundant, higher-z material such as oxygen, carbon, etc., is important for understanding of fundamental processes of energy release, differentiation, and development of atmospheric abundances in the Jovian planets. It provides a significant theoretical base for the interpretation of atmospheric elemental abundances to be provided by atmospheric entry probes in coming years. Significant differences are found when non-perturbative approaches such as Thomas-Fermi-Dirac (TFD) theory are used. Mapping of the phase diagrams of such binary mixtures in the pressure range from approx. 10 Mbar to approx. 1000 Mbar, using results from three-dimensional TFD calculations is undertaken. Derivation of a general and flexible thermodynamic model for such binary mixtures in the relevant pressure range was facilitated by the following breakthrough: there exists an accurate nd fairly simple thermodynamic representation of a liquid two-component plasma (TCP) in which the Helmholtz free energy is represented as a suitable linear combination of terms dependent only on density and terms which depend only on the ion coupling parameter. It is found that the crystal energies of mixtures of H-He, H-C, and H-O can be satisfactorily reproduced by the same type of model, except that an effective, density-dependent ionic charge must be used in place of the actual total ionic charge.

Hubbard, W. B.↗
NASA NTRS1985

Development of algorithms for using satellite meteorological data sets to study global transport of stratospheric aerosols and ozone

The utilization of stratospheric aerosol and ozone measurements obtained from the NASA developed SAM II and SAGE satellite instruments were investigated for their global scale transports. The stratospheric aerosols showed that during the stratospheric warming of the winter 1978 to 1979, the distribution of the zonal mean aerosol extinction ratio in the northern high latitude exhibited distinct changes. Dynamic processes might have played an important role in maintenance role in maintenance of this zonal mean distribution. As to the stratospheric ozone, large poleward ozone transports are shown to occur in the altitude region from 24 km to 38 km near 55N during this warming. This altitude region is shown to be a transition region of the phase relationship between ozone and temperature waves from an in-phase one above 38 km. It is shown that the ozone solar heating in the upper stratosphere might lead to enhancement of the damping rate of the planetary waves due to infrared radiation alone in agreement with theoretical analyses and an earlier observational study.

Want, P. H.↗
NASA NTRS1985

Euler computations of AGARD Working Group 07 airfoil test cases

In an attempt to provide a set of accurate standard test problems for computational code developers, a series of inviscid airfoil test cases were chosen by the AGARD Working Group 07, a subpanel of the AGARD Fluid Dynamics Panel. The cases include three different airfoils at transonic to supersonic conditions. A large number of international experts responded in this effort with computations that have been contrasted for accuracy and consistency. This paper is a summary of the authors' contribution to this study. In particular, the important aspects of the solution process that made it possible to obtain the high level of accuracy needed in this study are stressed.

Pulliam, T. H.↗