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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1967

Light from reflection nebulae. I.

Models of reflection nebulae light for single scattering, pure or modified by internal nebular extinction, on spherical grains imitating dielectric or metallic particles

ASTRONOMICAL MODEL↗
NASA NTRS1992

Probing Infrared Sources By Computer Modeling

The Infrared Astronomical Satellite (IRAS) has yielded a large and uniform sample of high quality data for various infrared sources. To interpret the IRAS observations, complementary theoretical studies have been undertaken which often involve modeling in detail the scattering, absorption, and emission of photons by dust grains. In the past decade, significant progress has been made at Rensselaer in the development of radiation transport models for infrared sources. Models with increasing degree of physical realism have been constructed. We review recent progress made in the modeling of infrared sources. Directions for future research in this area are briefly discussed.

Leung, Chun Ming↗
NASA NTRS1977

Experimental measurement and computer analysis of stray radiation in a telescope

A description is presented of an experimental measurement system for the study of the stray radiation performance of a 50-cm aperture astronomical telescope model. The model incorporates a very high performance baffle system. To simulate the space environment of the actual orbiting telescope, the telescope model was placed in a vacuum chamber. The stray radiation source for the experiment was a ruby laser system. A photomultiplier tube was used for the detector. A minicomputer system was used to control the experiment and to gather and process the data. A computer program was used to model the telescope baffle system. Experimentally and analytically determined stray radiation attenuation data are compared.

Hunt, G. H.↗
NASA NTRS1980

Radio emission evolution of nonstationary sources in the Hedgehog model

Correlations are obtained for numerical calculation of flux F sub v and polarized radiation intensity of a cloud of arbitrary geometry, consisting of ultrarelativistic electrons that dissipate in a radial magnetic field of the nucleus at a random angle to the observer. It is possible that some of the variable extragalactic objects that were previously described by the Shklovskiy model are young formations in the examined model. Radio astronomical observations would permit a determination of their distance, age, and lifetime.

Kovalev, Y. A.↗
NASA NTRS1981

Studies in astronomical time series analysis. I - Modeling random processes in the time domain

Several random process models in the time domain are defined and discussed. Attention is given to the moving average model, the autoregressive model, and relationships between and combinations of these models. Consideration is then given to methods for investigating pulse structure, procedures of model construction, computational methods, and numerical experiments. A FORTRAN algorithm of time series analysis has been developed which is relatively stable numerically. Results of test cases are given to study the effect of adding noise and of different distributions for the pulse amplitudes. A preliminary analysis of the light curve of the quasar 3C 272 is considered as an example.

Scargle, J. D.↗
NASA NTRS1982

Planetary geology: Impact processes on asteroids

The fundamental geological and geophysical properties of asteroids were studied by theoretical and simulation studies of their collisional evolution. Numerical simulations incorporating realistic physical models were developed to study the collisional evolution of hypothetical asteroid populations over the age of the solar system. Ideas and models are constrained by the observed distributions of sizes, shapes, and spin rates in the asteroid belt, by properties of Hirayama families, and by experimental studies of cratering and collisional phenomena. It is suggested that many asteroids are gravitationally-bound "rubble piles.' Those that rotate rapidly may have nonspherical quasi-equilibrium shapes, such as ellipsoids or binaries. Through comparison of models with astronomical data, physical properties of these asteroids (including bulk density) are determined, and physical processes that have operated in the solar system in primordial and subsequent epochs are studied.

Chapman, C. R.↗
NASA NTRS1984

Satellite ephemerides for the Voyager Uranus encounter

Uranian satellite ephemerides are needed by the Voyager project to support both navigation and acquisition of scientific data. This paper presents the approach being taken to develop the ephemerides and details the initial phase of the development. That phase involves the analytical modeling of the satellites' motion and the adjustment of the model to fit astronomical observations. The paper describes the model and gives the result of a fit to 71 years of observations.

Jacobson, R. A.↗
NASA NTRS1990

Studies in astronomical time series analysis. IV - Modeling chaotic and random processes with linear filters

While chaos arises only in nonlinear systems, standard linear time series models are nevertheless useful for analyzing data from chaotic processes. This paper introduces such a model, the chaotic moving average. This time-domain model is based on the theorem that any chaotic process can be represented as the convolution of a linear filter with an uncorrelated process called the chaotic innovation. A technique, minimum phase-volume deconvolution, is introduced to estimate the filter and innovation. The algorithm measures the quality of a model using the volume covered by the phase-portrait of the innovation process. Experiments on synthetic data demonstrate that the algorithm accurately recovers the parameters of simple chaotic processes. Though tailored for chaos, the algorithm can detect both chaos and randomness, distinguish them from each other, and separate them if both are present. It can also recover nonminimum-delay pulse shapes in non-Gaussian processes, both random and chaotic.

Scargle, Jeffrey D.↗
NASA NTRS1996

Astronomical Performance of the Engineering Model rsted Advanced Steller Compass

The Danish geomagnetic microsatellite, rsted, is an autonomous sciencecraft which is scheduled for a May 1997 launch into polar orbit. It is produced by a consortium of universities, industry, and government and is Denmark's first national spacecraft. NASA support includes JPL real sky evaluation of its star tracker, the Advanced Stellar Compass (ASC).

mission↗
NASA NTRS2019

Astrochemical Bistability: Autocatalysis in Oxygen Chemistry

The origin of bistable solutions in the kinetic equations describing the chemistry of dense interstellar clouds is explained as being due to the autocatalysis and feedback of oxygen nuclei from the oxygen dimer (O2). We identify four autocatalytic processes that can operate in dense molecular clouds, driven respectively by reactions of H+, He+, C+, and S+ with O2. We show that these processes can produce the bistable solutions found in previous studies, as well as the dependence on various model parameters such as the helium ionization rate, the sulfur depletion and the H+ electron recombination rate. We also show that ion–grain neutralizations are unlikely to affect the occurrence of bistability in dense clouds. It is pointed out that many chemical models of astronomical sources should have the potential to show bistable solutions.

Dufour, Gwenaelle C.↗
NASA NTRS2019

Astrochemical Bistability: Autocatalysis in Oxygen Chemistry

The origin of bistable solutions in the kinetic equations describing the chemistry of dense interstellar clouds is explained as being due to the autocatalysis and feedback of oxygen nuclei from the oxygen dimer (O2).We identify four autocatalytic processes that can operate in dense molecular clouds, driven respectively by reactions of H(+), He(+), C(+), and S(+) with O2. We show that these processes can produce the bistable solutions found in previous studies, as well as the dependence on various model parameters such as the helium ionization rate, the sulfur depletion and the H3(+) electron recombination rate. We also show that ion–grain neutralizations are unlikely to affect the occurrence of bistability in dense clouds. It is pointed out that many chemical models of astronomical sources should have the potential to show bistable solutions.

Gwénaëlle Dufour↗
NASA NTRS2019

Astrochemical Bistability: Autocatalysis in Oxygen Chemistry

The origin of bistable solutions in the kinetic equations describing the chemistry of dense interstellar clouds is explained as being due to the autocatalysis and feedback of oxygen nuclei from the oxygen dimer (O2). We identify four autocatalytic processes that can operate in dense molecular clouds, driven respectively by reactions of H+, He+, C+, and S+ with O2. We show that these processes can produce the bistable solutions found in previous studies, as well as the dependence on various model parameters such as the helium ionization rate, the sulfur depletion and the ${{\rm{H}}}_{3}^{+}$ electron recombination rate. We also show that ion–grain neutralizations are unlikely to affect the occurrence of bistability in dense clouds. It is pointed out that many chemical models of astronomical sources should have the potential to show bistable solutions.

astrochemistry – ISM: abundances – ISM: molecules ↗
NASA NTRS2016

Providing Comprehensive and Consistent Access to Astronomical Observatory Archive Data: The NASA Archive Model

Since the turn of the millennium a constant concern of astronomical archives have begun providing data to the public through standardized protocols unifying data from disparate physical sources and wavebands across the electromagnetic spectrum into an astronomical virtual observatory (VO). In October 2014, NASA began support for the NASA Astronomical Virtual Observatories (NAVO) program to coordinate the efforts of NASA astronomy archives in providing data to users through implementation of protocols agreed within the International Virtual Observatory Alliance (IVOA). A major goal of the NAVO collaboration has been to step back from a piecemeal implementation of IVOA standards and define what the appropriate presence for the US and NASA astronomy archives in the VO should be. This includes evaluating what optional capabilities in the standards need to be supported, the specific versions of standards that should be used, and returning feedback to the IVOA, to support modifications as needed. We discuss a standard archive model developed by the NAVO for data archive presence in the virtual observatory built upon a consistent framework of standards defined by the IVOA. Our standard model provides for discovery of resources through the VO registries, access to observation and object data, downloads of image and spectral data and general access to archival datasets. It defines specific protocol versions, minimum capabilities, and all dependencies. The model will evolve as the capabilities of the virtual observatory and needs of the community change.

Virtual observatory; data archives; standards; IVO↗