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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The relationship between Jovian electrons and solar wind stream structure

Near-earth observations of above-0.22-MeV Jovian electrons by the APL/JHU experiments on IMP-7 and 8 during 1972-1975, a period of stable recurrent solar wind, reveals 19 of 26 events in good association with solar wind streams. This pattern of positive correlation with solar wind streams is also observed in 3-6 MeV data from 1965-1972 during well-defined electron events. During their pre-encounter periods Pioneers 10 and 11 were nearly radially aligned with Jupiter and direct magnetic connection was highly unlikely. Jovian electrons above about 5 MeV in the UCSD experiments on Pioneers 10 and 11 were anticorrelated with solar wind velocity from about 3-4 AU until encounter. Reconstructions of the large-scale interplanetary magnetic field suggest that the near-earth events result from direct connection with the Jovian magnetotail and corotation of quasi-trapped populations while for Pioneer events electrons propagate out from the magnetosphere to a solar wind stream interaction, in along the interaction, then in to Pioneer on undisturbed field lines.

Gold, R. E.↗
NASA NTRS1978

A note on the problem of jet stream formation

It is noted that the formation of 'jet streams', or narrow ringlike structures of small particles, in early planetary and satellite systems cannot result solely from inelastic collisions among the small particles. The possibility is considered that gravitational encounters between the particles will perturb them into more eccentric orbits and thus maintain the orbital coupling between particles (or jet streams) in neighboring orbits. It is found that when the gravitational effect of the particles is taken into account, the average eccentricity of the particles increases as agglomeration due to inelastic collisions proceeds. With respect to jet-stream formation, it is suggested that the ever-increasing orbital eccentricity of the particles will aid in coupling together the different 'sub-jet streams', so that large-scale orbital focusing toward the center of the whole system can continue. Alternative mechanisms leading to planetary accretion are briefly discussed.

Ip, W.-H.↗
NASA NTRS1972

Review of sonic-boom simulation devices and techniques.

Research on aircraft-generated sonic booms has led to the development of special techniques to generate controlled sonic-boom-type disturbances without the complications and expense of supersonic flight operations. This paper contains brief descriptions of several of these techniques along with the significant hardware items involved and indicates the advantages and disadvantages of each in research applications. Included are wind tunnels, ballistic ranges, spark discharges, piston phones, shock tubes, high-speed valve systems, and shaped explosive charges. Specialized applications include sonic-boom generation and propagation studies and the responses of structures, terrain, people, and animals. Situations for which simulators are applicable are shown to include both small-scale and large-scale laboratory tests and full-scale field tests. Although no one approach to simulation is ideal, the various techniques available generally complement each other to provide desired capability for a broad range of sonic-boom studies.

Edge, P. M., Jr.↗
NASA NTRS1972

Physical structure of the moon.

The moon has a much thicker lithosphere than the earth, as predicted by thermal models and as evidenced by the support of mascons, lack of surface folding, etc. More in question is whether the moon has a core (more properly, asthenosphere) of high temperature, as suggested by the volcanism 1.0-1.3 b.y. after origin and by the large low-degree harmonics in the gravity field. The moon is like the earth in having a large offset of center-of-mass from center-of-volume, apparently the residue of an early convective overturn associated with large-scale differentiation. The moon differs significantly from the earth in its lower iron content, gross homogeneity, much slower rate-of-change, and closer approach to isostatic equilibrium in the sense of stress-difference magnitudes.

Kaula, W. M.↗
NASA NTRS1972

Large-scale negative polarity magnetic fields on the sun and particle-emitting flares

Some observational facts about the large-scale patterns formed by solar negative polarity magnetic fields during the 19th and 20th cycles of solar activity are presented. The close relation of the position of occurrence of very large flares accompanied by cosmic ray and PCA events as well as other phenomena of solar activity during the declining part of the 19th cycle of the regularities in the internal structure of large scale negative polarity features are demonstrated.

Bumba, V.↗
NASA NTRS1973

On the decentralized control of large-scale systems

The decentralized control of stochastic large scale systems was considered. Particular emphasis was given to control strategies which utilize decentralized information and can be computed in a decentralized manner. The deterministic constrained optimization problem is generalized to the stochastic case when each decision variable depends on different information and the constraint is only required to be satisfied on the average. For problems with a particular structure, a hierarchical decomposition is obtained. For the stochastic control of dynamic systems with different information sets, a new kind of optimality is proposed which exploits the coupled nature of the dynamic system. The subsystems are assumed to be uncoupled and then certain constraints are required to be satisfied, either in a off-line or on-line fashion. For off-line coordination, a hierarchical approach of solving the problem is obtained. The lower level problems are all uncoupled. For on-line coordination, distinction is made between open loop feedback optimal coordination and closed loop optimal coordination.

Chong, C.↗
NASA NTRS1973

Internal constitution and evolution of the moon.

The composition, structure and evolution of the moon's interior are narrowly constrained by a large assortment of physical and chemical data. Models of the thermal evolution of the moon that fit the chronology of igneous activity on the lunar surface, the stress history of the lunar lithosphere implied by the presence of mascons, and the surface concentrations of radioactive elements, involve extensive differentiation early in lunar history. This differentiation may be the result of rapid accretion and large-scale melting or of primary chemical layering during accretion; differences in present-day temperatures for these two possibilities are significant only in the inner 1000 km of the moon and may not be resolvable.

Solomon, S. C.↗
NASA NTRS1975

Some aspects of control of a large-scale dynamic system

Techniques of predicting and/or controlling the dynamic behavior of large scale systems are discussed in terms of decentralized decision making. Topics discussed include: (1) control of large scale systems by dynamic team with delayed information sharing; (2) dynamic resource allocation problems by a team (hierarchical structure with a coordinator); and (3) some problems related to the construction of a model of reduced dimension.

Aoki, M.↗
NASA NTRS1974

Substituting telecommunications for travel - Feasible or desirable

This paper reviews recent advances in telecommunications and examines the detailed structure of travel to estimate the feasibility of substituting telecommunications for various travel objectives. The impact of travel is analyzed from a social, economic, energy, and pollution standpoint to assess the desirability of substitution. Perhaps 35-50% of the nation's travel could, in theory, be replaced by very advanced telecommunications (such as a much improved large-screen teleconferencing network), but public resistance would be massive. Much economic dislocation would result since, for example, over 25% of retail sales are travel-related. The energy savings would be modest since only 25% of the nation's energy is consumed by transportation. However, all pollution would be reduced substantially since transportation accounts for 75% of the carbon monoxide, 60% of the hydrocarbon, and 55% of the nitrogen oxide pollution in the nation. Problems related to the implementation of large-scale substitution are discussed.

Van Vleck, E. M.↗
NASA NTRS1976

Decentralization, stabilization, and estimation of large-scale linear systems

In this short paper we consider three closely related aspects of large-scale systems: decentralization, stabilization, and estimation. A method is proposed to decompose a large linear system into a number of interconnected subsystems with decentralized (scalar) inputs or outputs. The procedure is preliminary to the hierarchic stabilization and estimation of linear systems and is performed on the subsystem level. A multilevel control scheme based upon the decomposition-aggregation method is developed for stabilization of input-decentralized linear systems Local linear feedback controllers are used to stabilize each decoupled subsystem, while global linear feedback controllers are utilized to minimize the coupling effect among the subsystems. Systems stabilized by the method have a tolerance to a wide class of nonlinearities in subsystem coupling and high reliability with respect to structural perturbations. The proposed output-decentralization and stabilization schemes can be used directly to construct asymptotic state estimators for large linear systems on the subsystem level. The problem of dimensionality is resolved by constructing a number of low-order estimators, thus avoiding a design of a single estimator for the overall system.

Siljak, D. D.↗
NASA NTRS1976

Locally stabilizable large-scale systems

A class of large scale linear systems, stabilizable by local feedback control applied around each decoupled subsystem, is established. The control scheme, outlined in the paper, is based upon the decomposition-aggregation method, and involves only operations on the subsystem level. The systems, stabilized by the proposed method, have a tolerance to a wide class of non-linearities, and are reliable with respect to the structural perturbations.

Vukcevic, M. B.↗
NASA NTRS1976

Influence of planetary-scale topography on the diurnal thermal tide during the 1971 Martian dust storm

Data obtained with the Mariner 9 infrared spectroscopy experiment during the Martian dust storm of 1971-72 are examined for evidence of topographic influence on the atmospheric thermal structure. Temperature perturbations which are well correlated with the planetary-scale topography are found superposed on the large-amplitude diurnal thermal tide previously reported. Applications of tidal theory to the data indicate that the observed perturbations result from the kinematic interaction of the westward traveling diurnal wave with the large-scale components of topography. The dominant mode is excited by the wavenumber 2 topography component and is a vertically evanescent, eastward traveling wave with an equivalent depth comparable to the atmospheric-scale height. The principle dynamic effect of this mode is the enhancement of the amplitude of the near-surface diurnal wind to over 40 m/s in limited areas near 30 deg S latitude. Thus, it appears likely that dust was injected into the atmosphere in these regions during the storm. Other waves excited include vertically propagating modes which produce little effect in the lower atmosphere, but may represent a source of energy for the upper atmosphere during dust storm conditions.

Conrath, B. J.↗
NASA NTRS1977

Observations of intense velocity shear and associated electrostatic waves near an auroral arc

Simultaneous measurements of energetic particles and ac electric fields made by the javelin sounding rocket NASA 8:56 during the late expansion phase of a magnetic storm have revealed an intense shear in plasma flow of magnitude 20 (m/s)/m at the edge of an auroral arc. Structure with two characteristic scales sizes is displayed in the region of shear. Larger structures are of the order of several kilometers in size. Intense irregularities with characteristic wavelengths smaller than the scale size of the shear have also been detected. The large-scale changes in the orientation of the charge sheet at the edge of the arc may be due to the Kelvin-Helmholtz branch; shorter-wavelength modes may be related to the shear driven resistive drift wave. Observations are consistent with the suggestion that velocity shear instabilities may play a role in the formation of high-latitude irregularities.

Kelley, M. C.↗
NASA NTRS1978

Large scale telescopes for high resolution X-ray and gamma-ray astronomy

This paper shows that angular-resolution, energy-range, and structural constraints on image-modulated X-ray telescopes are not fundamental and that the limits on angular resolution can be overcome by constructing such telescopes on a very large spatial scale. It is proposed that widely separated satellites be used for the modulating mask and detector array. Implementation of this concept is discussed in terms of a simple system consisting of a pinhole camera (i.e., a hole in an opaque mask on one subsatellite and a detector array on another). Advantages and problems of such systems are briefly discussed, and a solar X-ray telescope intended for deployment from a Shuttle orbiter is described. It is noted that such large-scale telescopes can be constructed to image gamma rays and even energetic neutrons as well.

Hudson, H. S.↗
NASA NTRS1979

On the internal structure of the major satellites of the outer planets

The structures and thermal evolutions of the large icy-satellites of the outer solar system are considered. It is shown (for bodies comparable in size and mass to the Galilean satellites, having sizeable mass fraction of H2O, and with meteoritic abundances of radioactive materials contained within their silicate fractions) that the crust of solid ice over a liquid mantle predicted by conductive heat-transfer calculations is unstable to large-scale solid-state convection. For appropriate material parameters, convective heat-transfer rates are sufficient to freeze a large liquid mantle on a time scale that is short compared to the lifetime of the body. It is also concluded that the ice layer is convecting at the present time. A reevaluation of previous work, using improved values for material parameters and boundary conditions, reverses earlier conclusions and implies a rigid outer crust with resulting long-term stability of surface features to creep deformation. The combination of a rigid crust with active internal convection presents the additional possibility of surface features that are produced and maintained by dynamic internal processes.

Reynolds, R. T.↗
NASA NTRS1979

Potential utilization of the NASA/George C. Marshall Space Flight Center in earthquake engineering research

Earthquake engineering research capabilities of the National Aeronautics and Space Administration (NASA) facilities at George C. Marshall Space Flight Center (MSFC), Alabama, were evaluated. The results indicate that the NASA/MSFC facilities and supporting capabilities offer unique opportunities for conducting earthquake engineering research. Specific features that are particularly attractive for large scale static and dynamic testing of natural and man-made structures include the following: large physical dimensions of buildings and test bays; high loading capacity; wide range and large number of test equipment and instrumentation devices; multichannel data acquisition and processing systems; technical expertise for conducting large-scale static and dynamic testing; sophisticated techniques for systems dynamics analysis, simulation, and control; and capability for managing large-size and technologically complex programs. Potential uses of the facilities for near and long term test programs to supplement current earthquake research activities are suggested.

Scholl, R. E.↗
NASA NTRS1980

The stability properties of cylindrical force-free fields - Effect of an external potential field

A large-scale potential field with an embedded smaller-scale force-free structure gradient x B equals alpha B is studied in cylindrical geometry. Cases in which alpha goes continuously from a constant value alpha 0 on the axis to zero at large r are considered. Such a choice of alpha (r) produces fields which are realistic (few field reversals) but not completely stable. The MHD-unstable wavenumber regime is found. Since the considered equilibrium field exhibits a certain amount of magnetic shear, resistive instabilities can arise. The growth rates of the tearing mode in the limited MHD-stable region of k space are calculated, showing time-scales much shorter than the resistive decay time.

Chiuderi, C.↗