Seasonal variations in the thermosphere and exosphere, 1968-70
Seasonal density variations in thermosphere and exosphere, obtaining model from Explorers 19 and 39 drag measurements for comparison with OGO-6 mass spectroscopy
Keating, G. M.↗
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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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A new cosmological model - Formation of organic molecules, planets, and comets.
A new model is proposed based on studies of plasma instabilities in a magnetic field, which suggests that the inside region of a star is quantized into smaller regions, each of which is rotating in the magnetic field of a central rotating stellar core. Numerous applications of such a model are explored and some, such as the earth, evaluated in detail.
Johnson, F. M.↗
The interplanetary acceleration of energetic nucleons
Co-rotating proton and electron streams are the dominant type of low-energy (0.1-10 MeV/nucleon) particle event observed at 1 A.U. The radial dependence of these events was studied between 1 and 4.6 A.U. using essentially identical low-energy detector systems on IMP 7, Pioneer 10 and Pioneer 11. It was expected that at a given energy, the intensity of these streams would decrease rapidly with heliocentric distance due to the effects of interplanetary adiabatic deceleration. Instead it was found that from event to event the intensity either remains roughly constant or increases significantly (more than an order of magnitude) between 1 and 3 A.U. It appears that interplanetary acceleration processes are the most plausible explanation. Several possible acceleration models are explored.
Mcdonald, F. B.↗
Galactic winds driven by cosmic rays
Cosmic rays traveling through a magnetized plasma with mean velocity greater than the Alfven speed can become coupled to the plasma by the emission of magnetohydrodynamic waves. Using a time-independent, spherically symmetric, hydrodynamic treatment, we show that cosmic rays escaping from a galaxy can carry along thermal gas and produce a 'galactic wind'. Solutions indicate that a typical galaxy can lose mass at a rate of about 1 to 10 million solar masses per year and energy at a rate of about 10 to the 40th to 10 to the 42nd ergs per sec. The possible role of galactic winds in radio and X-ray sources is explored. A model is proposed to explain the X-ray emission observed from clusters of galaxies.
Ipavich, F. M.↗
Toward autonomous spacecraft
Ways in which autonomous behavior of spacecraft can be extended to treat situations wherein a closed loop control by a human may not be appropriate or even possible are explored. Predictive models that minimize mean least squared error and arbitrary cost functions are discussed. A methodology for extracting cyclic components for an arbitrary environment with respect to usual and arbitrary criteria is developed. An approach to prediction and control based on evolutionary programming is outlined. A computer program capable of predicting time series is presented. A design of a control system for a robotic dense with partially unknown physical properties is presented.
Fogel, L. J.↗
The role of modern control theory in the design of controls for aircraft turbine engines
The development, applications, and current research in modern control theory (MCT) are reviewed, noting the importance for fuel-efficient operation of turbines with variable inlet guide vanes, compressor stators, and exhaust nozzle area. The evolution of multivariable propulsion control design is examined, noting a basis in a matrix formulation of the differential equations defining the process, leading to state space formulations. Reports and papers which appeared from 1970-1982 which dealt with problems in MCT applications to turbine engine control design are outlined, including works on linear quadratic regulator methods, frequency domain methods, identification, estimation, and model reduction, detection, isolation, and accommodation, and state space control, adaptive control, and optimization approaches. Finally, NASA programs in frequency domain design, sensor failure detection, computer-aided control design, and plant modeling are explored
Zeller, J.↗
The intercrater plains of Mercury and the Moon: Their nature, origin and role in terrestrial planet evolution. Estimated thickness of ejecta deposits compared to to crater rim heights
The area of the continuous ejecta deposits on mercury was calculated to vary from 2.24 to 0.64 times the crater's area for those of diameter 40 km to 300 km. Because crater boundaries on the geologic map include the detectable continuous ejecta blanket, plains exterior to these deposits must consist of farther-flung ejecta (of that or other craters), or volcanic deposits flooding the intervening areas. Ejecta models are explored.
Leake, M. A.↗
Compressibility effects in turbulence modeling
Numerical turbulence modeling is discussed with attention given to fluid property variations caused by compressibility in an adiabatic flow. The models are considered in terms of integral quantities expressed by ordinary differential equations and by those formulated as partial differential equations. Compressibility corrections for both integral and partial differential methods are reviewed. Eddy-viscosity models are explored for their capability to characterize the mass-weighted Reynolds stress, which can be accounted for with primitive and/or mass-weighted variables. Compressible flow simulations are currently constrained to low Re and zero mean dilation. The effects of compressibility are defined in wave number space by resolving the Fourier transforms of the velocity vectors into components which are perpendicular and parallel to the wave number vector. Statistical correlations then permit obtaining a value for each contribution.
Rubesin, M. W.↗
Inferences on the Thermodynamic Characteristics of a Star from the Observed Distinctive Radial Sequences of the Distinctive Atmospheric Regions Comprising that Stellar Atmosphere
The implications of observational findings on atmospheric and subatmospheric taxonomy, diagnostics, and modeling are explored. The correlations between distinctive radial sequences in stellar atmospheres and the thermodynamic properties of the stars in which they appear are discussed.
Source record↗
Exploring the use of structural models to improve remote sensing agricultural estimates
Satellite estimates of agricultural characteristics often are not sufficiently precise for reliable use in small geographical regions. The precision of estimates of agricultural characteristics such as crop proportions and leaf area indexes can be increased by modeling ground observations as a function of satellite estimates. Linear regression models using least squares estimators of the model parameters are most often advocated as an appropriate methodology; however, least squares estimation requires that the predictor variables are measured without error, an unreasonable assumption for this application. An alternative estimation methodology which assumes that both the response variables (ground observations) and the predictor variables (satellite estimates) are measured with error involves the use of linear structural models. The application of linear structural models to the estimation of agricultural characteristics using satellite spectral measurements is examined.
Gunst, R. F.↗
Narrow Absorption Components in Be Star Winds
The stars omega Ori (B2 IIIe), 66 Oph (B2 IVe), and 59 Cyg (B1.5 IVe) are discussed. The extent to which the narrow absorption components in these Be stars differs from narrow components in the O stars and gamma Cas is explored. Any models or mechanisms for the formation of narrow absorption features in the UV resonance lines of Be star spectra must account for the presence of multiple narrow absorption features which are variable in number, radial velocity, and strength. Models predicting a high and low density structure to the stellar wind caused by instabilities in a flow driven by radiation pressure or by variable mass loss may be more successful in describing the behavior of winds in early Be stars. These models appear to be capable of producing single absorption components in the velocity range observed for O stars and very early Be stars.
Grady, C. A.↗
Cruise noise of counterrotation propeller at angle of attack in wind tunnel
The noise of a counterrotation propeller at angle of attack was measured in the NASA Lewis 8- by 6-Foot Supersonic Wind Tunnel at cruise conditions. Noise increases of as much as 4 dB were measured at positive angles of attack on the tunnel side wall, which represented an airplane fuselage. These noise increases could be minimized or eliminated by operating the counterrotation propeller with the front propeller turning up-inboard. This would require oppositely rotating propellers on opposite sides of the airplane. Noise analyses at different bandwidths enabled the separate front- and rear-propeller tones, as well as the total noise, at each harmonic to be determined. A simplified noise model was explored to show how the observed circumferential noise patterns of the separate propeller tones might have occurred. The total noise pattern, which represented the sum of the front- and rear-propeller tones at a particular harmonic, showed trends that would be hard to interpret without the separate-tone results. Therefore it is important that counterrotation angle-of-attack noise data be taken in such a manner that the front- and rear-propeller tones can be separated.
Dittmar, J. H.↗
The applicability of satellite altimetry data to tidal models
The characteristics of satellite altimetry data are reviewed, and techniques for incorporating them into numerical tide models are discussed. The relationship between the geocentric tides observed by satellites and the ocean tides measured by gages or predicted by models is explored, and particular attention is given to the differences between deep-water, shelf, and estuarine tidal regimes. It is concluded that a separate tidal solution should always be performed before assimilating satellite data, including calculation of the tides along a single repeated ground track in the case of shelf and estuarine regions. The potential value of the altimetry to be provided by Topex/Poseidon (scheduled launch in 1991) is indicated.
Parke, Michael E.↗
The far-ultraviolet spectra of early-type galaxies
New and revised ultraviolet energy distributions ar presented based on 97 IUE spectra of 31 early-type galaxies and the bulge of M31. Based on optical spectra and morphology, the sample galaxies are divided into star-forming galaxies, active galaxies, and quiescent galaxies. A well-defined nonlinear relationship between (1550-V) color and Mg2 for the 24 quiescent galaxies is obtained. The ultraviolet spectra of these galaxies can be modeled as a sum of two components: a normal, cool stellar population of main-sequence and giant branch stars that is redder at high Mg2, plus a very blue population having a steeply rising UV flux below 2000 A that increases in strength with metallicity. The UV spectra of star-forming galaxies are significantly flatter than the very blue component of quiescent galxies and are consistent with aging bursts of star formation. Two sample population models are explored for the blue stellar component of quiescent galaxies: postasymptotic giant branch stars and young stars from continuing star formation.
Burstein, David↗
Martian seismicity
The design and ultimate success of network seismology experiments on Mars depends on the present level of Martian seismicity. Volcanic and tectonic landforms observed from imaging experiments show that Mars must have been a seismically active planet in the past and there is no reason to discount the notion that Mars is seismically active today but at a lower level of activity. Models are explored for present day Mars seismicity. Depending on the sensitivity and geometry of a seismic network and the attenuation and scattering properties of the interior, it appears that a reasonable number of Martian seismic events would be detected over the period of a decade. The thermoelastic cooling mechanism as estimated is surely a lower bound, and a more refined estimate would take into account specifically the regional cooling of Tharsis and lead to a higher frequency of seismic events.
Phillips, Roger J.↗
The dynamics of hydroponic crops for simulation studies of the CELSS initial reference configurations
The goal of this research is to develop a progressive series of mathematical models for the CELSS hydroponic crops. These models will systematize the experimental findings from the crop researchers in the CELSS Program into a form useful to investigate system-level considerations, for example, dynamic studies of the CELSS Initial Reference Configurations. The crop models will organize data from different crops into a common modeling framework. This is the fifth semiannual report for this project. The following topics are discussed: (1) use of field crop models to explore phasic control of CELSS crops for optimizing yield; (2) seminar presented at Purdue CELSS NSCORT; and (3) paper submitted on analysis of bioprocessing of inedible plant materials.
Volk, Tyler↗
Modeling and analysis tools
The topics covered are presented in viewgraph form and include the following: the effect of the Mars environment on systems; the design of models and modeling tools; space environment interaction information dissemination; tools used in the development and validation of models; Space Exploration Initiative planning; and systems integration.
Jongeward, Gary↗
Overturn of magma ocean ilmenite cumulate layer: Implications for lunar magmatic evolution and formation of a lunar core
We explore a model for the chemical evolution of the lunar interior that explains the origin and evolution of lunar magmatism and possibly the existence of a lunar core. A magma ocean formed during accretion differentiates into the anorthositic crust and chemically stratified cumulate mantle. The cumulative mantle is gravitationally unstable with dense ilmenite cumulate layers overlying olivine-orthopyroxene cumulates with Fe/Mg that decreases with depth. The dense ilmenite layer sinks to the center of the moon forming the core. The remainder of the gravitationally unstable cumulate pile also overturns. Any remaining primitive lunar mantle rises to its level of neutral buoyancy in the cumulate pile. Perhaps melting of primitive lunar mantle due to this decompression results in early lunar Mg-rich magmatism. Because of its high concentration of incompatible heat producing elements, the ilmenite core heats the overlying orthopyroxene-bearing cumulates. As a conductively thickening thermal boundary layer becomes unstable, the resulting mantle plumes rise, decompress, and partially melt to generate the mare basalts. This model explains both the timing and chemical characteristics of lunar magmatism.
Hess, P. C.↗