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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 397 records · Page 22
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NASA NTRS1986

High precision GPS orbit determination using March 1985 demonstration data

Preliminary orbit determination for satellites in the U.S. Department of Defense's Global Positioning System has been performed using GPS carrier phase data collected in March-April 1985 at 10 sites in the continental United States. The data were analyzed using a new data processing software package called GIPSY (GPS Inferred Positioning SYstem) and with existing covariance analysis software. Data from one day have been processed with average formal position errors of 1.4 to 3.6 meters. The true errors are probably somewhat larger. Covariance results are presented which suggest that the orbits can be obtained with formal errors under 2 meters after certain software issues are resolved.

Bertiger, W.↗
NASA NTRS1993

Pinatubo and Pre-Pinatubo Optical-Depth Spectra: Mauna Loa Measurements, Comparisons, Inferred Particle Size Distributions, Radiative Effects, and Relationship to Lidar Data

The Ames airborne tracking sunphotometer was operated at the National Oceanic and Atmospheric Administration (NOAA) Mauna Loa Observatory (MLO) in 1991 and 1992 along with the NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) automated tracking sunphotometer and lidar. June 1991 measurements provided calibrations, optical-depth spectra, and intercomparisons under relatively clean conditions; later measurements provided spectra and comparisons for the Pinatubo cloud plus calibration checks. June 1991 results are similar to previous MLO springtime measurements, with midvisible particle optical depth tau(sub p)(lambda = 0.526 microns) at the near-background level of 0.012 +/- 0.006 and no significant wavelength dependence in the measured range (lambda = 0.38 to 1.06 microns). The arrival of the Pinatubo cloud in July 1991 increased midvisible particle optical depth by more than an order of magnitude and changed the spectral shape of tau(sub p)(lambda) to an approximate power law with an exponent of about -1.4. By early September 1991, the spectrum was broadly peaked near 0.5 microns, and by July 1992, it was peaked near 0.8 microns. Our optical-depth spectra include corrections for diffuse light which increase postvolcanic midvisible tau(sub p) values by 1 to 3% (i.e., 0.0015 to 0.0023). NOAA- and Ames Research Center (ARC)-measured spectra are in good agreement. Columnar size distributions inverted from the spectra show that the initial (July 1991) post-Pinatubo cloud was relatively rich in small particles (r less than 0.25 microns), which were progressively depleted in the August-September 1991 and July 1992 periods. Conversely, both of the later periods had more of the optically efficient medium-sized particles (0.25 less than r less than 1 micron) than did the fresh July 1991 cloud. These changes are consistent with particle growth by condensation and coagulation. The effective, or area-weighted, radius increased from 0.22 +/- 0.06 micron in July 1991 to 0.56 +/- 0.12 micron in August-September 1991 and to 0.86 +/- 0.29 micron in July 1992. Corresponding column mass values were 4.8 +/- 0.7, 9.1 +/- 2.7, and 5.5 +/- 2 micro g/sq cm, and corresponding column surface areas were 4.4 +/- 0.5, 2.9 +/- 0.2, and 1.1 +/- 0.1 sq micron/sq cm,. Photometer-inferred column backscatter values agree with those measured by the CMDL lidar on nearby nights. Combining lidar-measured backscatter profiles with photometer-derived backscatter-to-area ratios gives peak particle areas that could cause rapid heterogeneous loss of ozone, given sufficiently low particle acidity and suitable solar zenith angles (achieved at mid- to high latitudes). Top-of-troposphere radiative forcings for the September 1991 and July 1992 optical depths and size distributions over MLO are about -5 and -3 W 1/sq m, respectively (hence comparable in magnitude but opposite in sign to the radiative forcing caused by the increase in manmade greenhouse gases since the industrial revolution). Heating rates in Pinatubo layer over MLO are 0.55 +/- 0.13 and 0.41 +/- 0.14 K/d for September 1991 and July 1992, respectively.

Russell, P. B.↗
NASA NTRS1986

The isotopes of hydrogen and helium in the Galactic cosmic radiation - Their source abundances and interstellar propagation

A self-consistent model describing the interstellar propagation of Galactic cosmic radiation is developed using low-energy measurements and calculations of the effects of interstellar propagation and solar modulation. The source ratio H-1/He-4 at constant energy per nucleon is determined to be 12.2 + or - 1.5, and the mean path length for an exponential path length weighting function required to account for the data is 7.2 + or - 1.0 g/sq cm. The measured H-2/He-4 and He-3/He-4 ratios do not vary by more than about 30 percent over the solar cycle. The behavior of the ratios during the solar cycle reflects the energy dependence of the local interstellar ratios, and leads to an energy dependence of the mean path length below 1 GeV per nucleon weaker than that inferred from boron/carbon. The source ratio H-1/He-4 inferred from the low-energy data is consistent both with the value inferred from high-energy cosmic ray data using a model of rigidity-dependent confinement and with the solar system abundance ratio.

Beatty, James J.↗
NASA NTRS1987

An inference engine for embedded diagnostic systems

The implementation of an inference engine for embedded diagnostic systems is described. The system consists of two distinct parts. The first is an off-line compiler which accepts a propositional logical statement of the relationship between facts and conclusions and produces data structures required by the on-line inference engine. The second part consists of the inference engine and interface routines which accept assertions of fact and return the conclusions which necessarily follow. Given a set of assertions, it will generate exactly the conclusions which logically follow. At the same time, it will detect any inconsistencies which may propagate from an inconsistent set of assertions or a poorly formulated set of rules. The memory requirements are fixed and the worst case execution times are bounded at compile time. The data structures and inference algorithms are very simple and well understood. The data structures and algorithms are described in detail. The system has been implemented on Lisp, Pascal, and Modula-2.

Fox, Barry R.↗
NASA NTRS1971

The earth and the moon /Harold Jeffreys Lecture/.

The internal structures of the earth and the moon are compared in the light of the latest extensive data on the earth structure, mobility of the earth outer layers, and the properties of lunar crust. The Monte Carlo method is applied to develop an earth model by a stepwise process beginning with a random distribution of two elastic velocities and the density as a function of de pth. Lunar seismic, magnetic, and rock analysis data are used to infer the properties of the moon. The marked planetological contrast between the earth and the moon is shown to consist in that the earth is highly differentiated and still undergoes a large-scale differentiation, while the moon has lost its volatiles in its early history and has a cold dynamically inactive shell which has been without basic changes for three billion years.

Press, F.↗
NASA NTRS1973

Finite deformation of elasto-plastic solids

A theoretical basis is established for analysis of finite deformation of metals. The observation that finite deformation of such elastoplastic materials may be viewed as a process rather than an event leads to derivation of a complete initial and boundary value problem distinguished by its quasilinear nature. This feature of the formulation motivates adoption of an incremental approach to numerical problem solving. Numerical solution capability is established for problems of plane stress and plane strain. The validity of the theory and numerical analysis is demonstrated by consideration of a number of problems of homogeneous finite deformation for which analytic solutions are available. Subsequently the analysis is employed for the investigation of necking in flat metal tensile bars. The results of this investigation provide the first full numerical solutions for tensile necking in plane stress and plane strain. In addition a basis is provided for assessment of the validity of stress-strain relations inferred from tensile test data.

Osias, J. R.↗
NASA NTRS1973

A first look at atmospheric dynamics and temperature variations on Titan.

Pollack (1973) has used a radiative equilibrium model to match radiometric data for Titan and infers the atmospheric mass, composition, opacity, and gross vertical thermal structure. These results are used to estimate the atmospheric temperature variations by means of scaling analysis, taking into account dynamics both for a baroclinic wave regime and for an axially symmetric circulation regime. Horizontal temperature variations of the atmosphere and surface are found to be very small, and the circulation is found to be weak and probably axially symmetric. The small temperature variations appear to preclude the storage of volatiles in polar caps, so that the present atmospheric methane content may be due to a balance between outgassing and photodissociation.

Leovy, C. B.↗
NASA NTRS1973

Radial thickness variation in impact crater ejecta - Implications for lunar basin deposits

An expression is proposed for radial thickness variations in lunar impact crater ejecta. The expression was inferred from available cratering data and semi-empirical calculations for approximate modeling of variations in ejecta thickness with the increasing range of lunar craters. A table of predicted stratigraphic sections for the Apollo Landing sites is included. The predictions were made by using this expression. The results suggest that the pre-Nubium crustal material at upland Apollo sites lies at depths of above 280 up to 1940 m.

Mcgetchin, T. R.↗
NASA NTRS1974

External field effects on solidification - Macroscopic and microscopic models

Comparison of theoretical effects of magnetic and gravitational fields on melts of metals and semiconductors provides two kinds of insight into space processing materials problems. First, the task of comparing effects of the two fields yields mathematical models which may be used to estimate material properties and responses to processing under various field conditions. Then, by using these models, microgravity effects can be inferred from magnetic field data already obtained in laboratories on earth. Magnetohydrodynamics (static and oscillating fields) and the Free Volume Model are used to study macroscopic effects, and Sekerka's interface stability theory is used to show how external fields can affect microsegregation. It is demonstrated that the mathematical formalism is essentially the same for describing macroscopic effects of both microgravity and magnetic fields.

Miller, R. I.↗
NASA NTRS1976

Radioactivity in the galactic plane

The paper reports the detection of a large concentration of interstellar radioactivity during balloon-altitude measurements of gamma-ray energy spectra in the band between 0.02 and 12.27 MeV from galactic and extragalactic sources. Enhanced counting rates were observed in three directions towards the plane of the Galaxy; a power-law energy spectrum is computed for one of these directions (designated B 10). A large statistical deviation from the power law in a 1.0-FWHM interval centered near 1.16 MeV is discussed, and the existence of a nuclear gamma-ray line at 1.15 MeV in B 10 is postulated. It is suggested that Ca-44, which emits gamma radiation at 1.156 MeV following the decay of radioactive Sc-44, is a likely candidate for this line, noting that Sc-44 arises from Ti-44 according to explosive models of supernova nucleosynthesis. The 1.16-MeV line flux inferred from the present data is shown to equal the predicted flux for a supernova at a distance of approximately 3 kpc and an age not exceeding about 100 years.

Walraven, G. D.↗
NASA NTRS1977

Lunar gravity determinations and their implications

Mass distributions inferred from lunar gravity data are studied, with emphasis on mascons as mass excesses in topographic lows in all the near-side ringed basins, with best representation as near-surface disks with excess loads of 800 kg per sq cm. The gravity data are derived from earth-based radiometric data on speed variations of orbiting Apollo spacecraft observed from the earth. Mass deficits are found in the case of large 100 km craters (Langrenus, Theophilus, Copernicus), and are consistent with crater volume. Earlier states of the moon are hypothesized on the basis of the small gravitational anomaly associated with the Apennine mountains, and on the basis of lunar isostasy, plasticity, and maria flooding and filling.

Sjogren, W. L.↗
NASA NTRS1979

Airframe noise component interaction studies

Acoustic wind tunnel tests were conducted to examine the noise-generating processes of an airframe during approach flight. The airframe model was a two-dimensional wing section, to which highlift leading and trailing edge devices and landing gear could be added. Far field conventional microphones were utilized to determine component spectrum levels. An acoustic mirror directional microphone was utilized to examine noise source distributions on airframe components extended separately and in combination. Measured quantities are compared with predictions inferred from aircraft flyover data. Aeroacoustic mechanisms for each airframe component are identified. Component interaction effects on total radiated noise generally were small (within about 2 dB). However, some interactions significantly redistributed the local noise source strengths by changing local flow velocities and turbulence levels. Possibilities for noise reduction exist if trailing edge flaps could be modified to decrease their noise radiation caused by incident turbulent flow.

Fink, M. R.↗
NASA NTRS1980

Energy loss by resonance line photons in an absorbing medium

The mean path length of photons undergoing repeated scatterings in media of large optical thickness is calculated from accurate numerical solutions of the transfer equation including the effect of frequency redistribution characteristic of combined Doppler and natural broadening. Energy loss by continuous absorption processes, such as ionization or dust absorption, is discussed, and asymptotic scaling laws for the energy loss, the mean path length, and the mean number of scatterings are inferred from the numerical data.

Hummer, D. G.↗
NASA NTRS1982

Light scattering calculations for the nephelometer experiment on the 1981/1982 Jupiter Orbiter-Probe mission

A variety of studies were carried out to help establish the accuracy of quantities describing physical characteristics of cloud particles (such as size, shape, and composition) that are to be inferred from light scattering data obtained with the nephelameter experiment on the Galileo spacecraft. The objectives were to provide data for validating and testing procedures for analyzing the Galileo nephelameter data with light scattering observations in a variety of on-going laboratory and field measurement programs for which simultaneous observations of the physical characteristics of the scattering particles were available.

Grams, G. W.↗
NASA NTRS1983

Geodynamics of the Baikal-Stanovoy seismic belt

The convection generated tensional stress field in the earth, as inferred from satellite gravity data, reveals an anomalous lens of upwelling mantle rocks under the Baikal rift zone. The point of no strain at 56 deg N 116 deg E forms a seismic gap along the Baikal-Stanovoy seismic belt. East of this point, the stress field changes from extension to compression. Therefore, the position of no strain at the eastern termination of the rift accounts for the dying-out of the rift zone and for the appearance of a compressive structure in the Stanovoy Range.

Liu, H.-S.↗
NASA NTRS1983

The large scale dust distribution in the inner galaxy

Initial results are presented from a new large-scale survey of the first quadrant of the galactic plane at wavelengths of 160, 260, and 300 microns. The submillimeter wavelength emission, interpreted as thermal radiation by dust grains, reveals an optically thin disk of angular width about 0.09 deg (FWHM) with a mean dust temperature of 23 K and significant variation of the dust mass column density. Comparison of the dust column density with the gas column density inferred from CO survey data shows a striking spatial correlation. The mean luminosity per hydrogen atom is found to be 2.5 x 10 to the -30th W/H, implying a radiant energy density in the vicinity of the dust an order of magnitude larger than in the solar neighborhood. The data favor dust in molecular clouds as the dominant submillimeter radiation source.

Hauser, M. G.↗
NASA NTRS1984

Antarctic sea ice microwave signatures and their correlation with in situ ice observations

The general characteristics and microwave radiative properties of sea ice in the Weddell Sea region during the onset of spring are studied by using the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) and other satellite sensors, in conjunction with in situ observations from the Mikhail Somov. The position of the ice edge, the gradient of ice concentration, and the width of the Marginal Ice Zone are inferred from the microwave data, and are found to be consistent with ship observations, especially at 18 GHz. The sensitivities of the various SMMR frequencies to surface and other effects are investigated by using multispectral cluster analysis. The results show considerable variability in emissivity, especially at 37 GHz, likely associated with varying degrees of surface wetness. Ice concentrations are derived by using two methods: one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed. Using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations.

Comiso, J. C.↗