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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

The influence of dynamics on two-dimensional model results - Simulations of C-14 and stratospheric aircraft NO(x) injections

The influence of dynamics on model results is investigated via a 2D photochemical model. Three representations of atmospheric transport are tested in order to simulate total ozone and C-14 amounts after nuclear tests in the early 1960s. Three scenarios of NO(x) injections from a proposed fleet of stratospheric aircraft and their effects on ozone are simulated. The three dynamical formulations used are Dynamics A, a base dynamics used in previous work with this model; Dynamics B, a strong circulation dynamics discussed by Jackman et al. (1989); and Dynamics C, the dynamics used by Shia et al. (1989). The advective component of the stratosphere to the troposphere mass exchange rate is largest for Dynamics B (5.8 x 10 exp 17 kg/yr) and smallest for Dynamics C (1.4 x 10 exp 17 kg/yr), with the advective strat/trop exchange rate for Dynamics A (2.4 x 10 exp 17 kg/yr) being these two extremes. Ozone depletion from NO(x) injections of stratospheric aircraft showed a strong sensitivity to dynamics.

Jackman, Charles H.↗
NASA NTRS1972

Experimental nuclear cross sections for spacecraft shield analysis

Experiments have been performed to validate and to supplement the intranuclear cascade model as a method for estimating cross sections of importance to spacecraft shield design. The experimental situation is inconclusive particularly for neutron-producing reactions, but is relatively sound for reaction cross sections and for proton spectra at several hundred MeV at medium forward angles. Secondary photon contributions are imprecisely known.

Peelle, R. W.↗
NASA NTRS1986

Spectral energy distributions of active galactic nuclei between 0.1 and 100 microns

The 0.1-100-micron line-free spectral energy distributions of 29 AGN are characterized by fitting simple models to data from IRAS and IUE observations and ground-based NIR and optical spectrophotometry. The data are presented in tables and graphs and discussed in detail. It is found that nuclear dust does not play a major role in most of the Seyfert 1 galaxies and QSOs, which can be described by a model with four spectral components.

Edelson, R. A.↗
NASA NTRS1985

Numerical simulation of comet nuclei. I - Water-ice comets

A one-dimensional numerical model of pure water-ice cometary nuclei is presented, and the influence of the nuclear interior as a heat reservoir on the behavior of the nuclear surface is examined. It is shown that a number of effects, including the thermal inertia due to heat stored in the core and the release of latent heat, which goes entirely into heating the adjacent layers or into sublimation on passing through a phase transition from amorphous to crystalline ice, can help to explain such characteristics as the asymmetrical lightcurve of Comet Halley. Results are given for the cases of Comet Schwassmann-Wachmann 1 and Comet Encke. Consideration is also given to the insulating effect of an evolving dust mantle. The role of this mantle in determining the surface temperature of the ice core is studied as a function of the mass fraction of the dust in the ice-dust mixture and the thermal conductivity of the nucleus. The loose-lattice model of Mendis and Brin (1977) indicates that both high dust to ice ratios and high-core conductivities inhibit mantle blowoff.

Herman, G.↗
NASA NTRS2014

Comparison of Martian Surface Radiation Predictions to the Measurements of Mars Science Laboratory Radiation Assessment Detector (MSL/RAD)

For the analysis of radiation risks to astronauts and planning exploratory space missions, detailed knowledge of particle spectra is an important factor. Detailed measurements of the energetic particle radiation environment on the surface of Mars have been made by the Mars Science Laboratory Radiation Assessment Detector (MSL-RAD) on the Curiosity rover since August 2012, and particle fluxes for a wide range of ion species (up to several hundred MeV/u) and high energy neutrons (8 - 1000 MeV) have been available for the first 200 sols. Although the data obtained on the surface of Mars for 200 sols are limited in the narrow energy spectra, the simulation results using the Badhwar-O'Neill galactic cosmic ray (GCR) environment model and the high-charge and energy transport (HZETRN) code are compared to the data. For the nuclear interactions of primary GCR through Mars atmosphere and Curiosity rover, the quantum multiple scattering theory of nuclear fragmentation (QMSFRG) is used, which includes direct knockout, evaporation and nuclear coalescence. Daily atmospheric pressure measurements at Gale Crater by the MSL Rover Environmental Monitoring Station are implemented into transport calculations for describing the daily column depth of atmosphere. Particles impinging on top of the Martian atmosphere reach the RAD after traversing varying depths of atmosphere that depend on the slant angles, and the model accounts for shielding of the RAD by the rest of the instrument. Calculations of stopping particle spectra are in good agreement with the RAD measurements for the first 200 sols by accounting changing heliospheric conditions and atmospheric pressure. Detailed comparisons between model predictions and spectral data of various particle types provide the validation of radiation transport models, and thus increase the accuracy of the predictions of future radiation environments on Mars. These contributions lend support to the understanding of radiation health risks to astronauts for the planning of various mission scenarios.

Kim, Myung-Hee Y.↗
NASA NTRSDate not supplied

SR-1 Freedom Thermal Architecture Challenges

The SR-1 Freedom mission aims to demonstrate nuclear electric propulsion (NEP) and deliver the Skyfall helicopter payload to Mars. Repurposing the existing Gateway Power and Propulsion Element (PPE) spacecraft and combining it with a 20 kWe-class nuclear power module (NPM) presents a variety of thermal architecture challenges. These include unprecedented waste heat rejection requirements, integration with a spacecraft bus originally designed for a different mission profile, and novel packaging constraints. This presentation will describe the simplified concept of operations as it relates to on-orbit thermal environments, early-phase architecture trades and supporting analyses, and planned forward work. We will also discuss our strategy for integrated thermal modeling of the complete spacecraft and examples of interface challenges necessitated by this ambitious effort.

Thermal↗
NASA NTRS1992

Analysis of the photospheric epoch spectra of type 1a supernovae SN 1990N and SN 1991T

This paper presents an LTE analysis of the photospheric epoch optical and IUE UV spectra of the recent Type Ia supernovae SN 1990N and SN 1991T. It is found that SN 1990N has matter moving as fast as 40,000 km/s, while SN 1991T has matter moving as fast as 20,000 km/s. The exponential density profile with e-folding velocity of 3160 km/s suggested by deflation and delayed/late-detonation explosion models is adequate for calculating fits to the observed spectra. Findings on the iron peak elements suggest that in both SNe some nuclear burning continues into the outer ejecta or the newly synthesized elements are mixed into the outer ejecta. The observed spectra of SN 1990N are consistent with a composition of the inner envelope like that of model W7. Intermediate-mass elements with abundances higher than solar are probably in the outer ejecta of both SNe, while silicon, sulfur, and calcium are underabundance in SN 1991T relative to SN 1990N by factors of order 3, 3, and 120, respectively.

Jeffery, David J.↗
NASA NTRS2022

Global Food Insecurity and Famine From Reduced Crop, Marine Fishery and Livestock Production Due to Climate Disruption From Nuclear War Soot Injection

Atmospheric soot loadings from nuclear weapon detonation would cause disruptions to the Earth’s climate, limiting terrestrial and aquatic food production. Here, we use climate, crop and fishery models to estimate the impacts arising from six scenarios of stratospheric soot injection, predicting the total food calories available in each nation post-war after stored food is consumed. In quantifying impacts away from target areas, we demonstrate that soot injections larger than 5 Tg would lead to mass food shortages, and livestock and aquatic food production would be unable to compensate for reduced crop output, in almost all countries. Adaptation measures such as food waste reduction would have limited impact on increasing available calories. We estimate more than 2 billion people could die from nuclear war between India and Pakistan, and more than 5 billion could die from a war between the United States and Russia—underlining the importance of global cooperation in preventing nuclear war.

Atmospheric soot↗
NASA NTRS2000

Atomic-Based-Combined-Cycle Analysis

Atomic-based-combined-cycle (ABCC) engine combines an air-breathing ramjet engine with an atomic reactor to increase the mission-averaged specific impulse and thereby increasing the dry-mass ratio. ABCC engine is similar to RBCC engine except that energy needed for the propulsive power is derived from nuclear reaction rather than chemical combustion used in the RBCC engine. The potential performance improvement of an ABCC engine over a RBCC engine comes from two factors. Firstly, the energy density of nuclear reaction is several order of magnitudes higher than the chemical combustion. Secondly, hydrogen can produce much higher nozzle exit velocity because of its small molecular weight. A one-dimensional, transient numerical model was used to analyze a generic scramjet engine and it is used as a baseline to evaluate an imaginary ABCC engine performance. A nuclear reactor is treated as a black box energy source that replaces the role of the primary rocket and the chemical combustion chamber in a RBCC engine. Hydrogen is heated by the reactor and accelerated to produce high-speed ejection velocity. The ejection velocity up 10,000 m/sec is theoretically possible because of high energy density from the reactor and large gas constant of the hydrogen. Oxygen contained in the entrained air reacts with hydrogen and produces propulsive power for ejector mode operation. To provide enough thrust for initial acceleration, relatively large amount of hydrogen must be pumped through the reactor. Amount of oxygen contained in the entrained air may not be sufficient to burn all hydrogen and consequently combustion could occur at the end of exit nozzle. It is assumed that this combustion process is constant-pressure combustion at 1.0 atmospheric pressure and thus not affects the nozzle exit condition.

Han, Sam↗
NASA NTRS1999

Atomic-Based-Combined-Cycle Analysis

Atomic-based-combined-cycle (ABCC) engine combines an air-breathing ramjet engine with an atomic reactor to increase the mission-averaged specific impulse and thereby increasing the dry-mass ratio. ABCC engine is similar to RBCC engine except that energy needed for the propulsive power is derived from nuclear reaction rather than chemical combustion used in the RBCC engine. The potential performance improvement of an ABCC engine over a RBCC engine comes from two factors. Firstly, the energy density of nuclear reaction is several order of magnitudes higher than the chemical combustion. Secondly, hydrogen can produce much higher nozzle exit velocity because of its small molecular weight. A one-dimensional, transient numerical model was used to analyze a generic RBCC engine and it is used as a baseline to evaluate an imaginary ABCC engine performance. A nuclear reactor is treated as a black box energy source that replaces the role of the primary rocket and the chemical combustion chamber in a RBCC engine. The performance of a generic ABCC engine along a flight path (q0 =10 (exp 3) lbf per square ft) shows that the mission averaged-specific impulse is about twice larger than RBCC engine and the dry mass-ratio is about 50% larger. Results of the present ABCC engine performance are based on the assumptions that the flow passage of working fluids is identical to that of RBCC engine and that a nuclear reactor is treated as an energy black box. Preliminary heat transfer calculation shows that the rate of heat transfer to the working fluids is within the limit of turbulent convective heat transfer regimes. The flow passage of realistic ABCC engine must be known for a better prediction of ABCC engine performance. Also, critical heat transfer calculations must be performed for the ejector mode and ramjet mode operations. This is possible only when the details of a reactor configuration are available.

Han, Samuel S.↗
NASA NTRS1981

Nucleosynthesis of neutron-rich heavy nuclei during explosive helium burning in massive stars

The production of heavy nuclei during explosive helium burning has been calculated using a hydrodynamical model of a 15-solar mass (Type II) supernova and an n-process nuclear reaction network. It is found that the resulting neutron-rich heavy nuclei are not produced in the relative abundances of solar-system r-process material, especially in the vicinity of Pt, nor are any actinides produced. These deficiencies reflect an inadequate supply of neutrons. However, some neutron-rich isotopes, normally associated with the r-process, are produced which may be significant for the production of isotopic anomalies in meteorites.

Blake, J. B.↗
NASA NTRS1984

Propagation of heavy cosmic-ray nuclei

Techniques for modeling the propagation of heavy cosmic-ray nuclei, and the required atomic and nuclear data, are assembled in this paper. Emphasis is on understanding nuclear composition in the charge range Z = 3-83. Details of the application of 'matrix methods' above a few hundred MeV/nucleon, a new treatment of electron capture decay, and a new table of cosmic ray-stable isotopes are presented. Computation of nuclear fragmentation cross sections, stopping power, and electron stripping and attachment are briefly reviewed.

Letaw, J. R.↗
NASA NTRS1985

Nucleus precession of periodic comet Comas Sola

The nuclear properties of the periodic comet Comas Sola are studied based on a precession model applied previously to the periodic comets Encke, Kopff, and Giacobini-Zinner. The results imply that, for a few revolutions about the sun, Comas Sola was precessing more rapidly than any comet studied to date. An explanation is offered for this behavior in terms of a perturbation in the comet's obliquity shortly after the 1952 passage through perihelion. The equatorial radius of the nucleus is close to 1 km and its rotation period is 1.5-2.3 days, according to the model results. The calculated shape of the nucleus is compared with those of other comets studied using this technique.

Sekanina, Z.↗
NASA NTRS1988

Carbon and helium abundances in Wolf-Rayet WC stars determined from optical recombination lines

Carbon to helium ratios and ionization fractions are derived for 74 WC stars in the Galaxy and the LMC from optically thin recombination lines at visual wavelengths. The range of C/He ratios is 0.13 to 0.79 by number, similar to the ratios calculated by Nugis (1975) and about 20 times greater than the ratios of Smith and Willis (1982). These ratios also agree with the abundances determined in the most recent evolutionary models of massive stars, which include mass loss, convective dredge-up, and new nuclear reaction rates. The range of values found for the C/He ratios implies that the convective cores of WC stars do not occupy a very large mass fraction. The C/He ratio differs within a subtype by a factor of three or less, but the mean tends to increase toward earlier subtypes, although the standard deviation from the mean is large enough to allow the interpretation that the C/He ratio is constant for all WC subtypes.

Torres, Ana V.↗
NASA NTRS1993

On magnetodynamic effects initiated by a high-speed impact of a large cosmic body upon the Earth's surface

The impact of a large cosmic body with typical size R approximately = 1 km (mass M approximately = 4-10 Gt for a stony or icy body) moving with velocity V approximately = 50-70 km/s (kinetic energy of the order of 10 exp 21 J or 10 exp 6 Mt of TMT) on the Earth's surface leads to a full vaporization of a body and of a significant part of substance of the upper layers of the Earth and even to the ionization of this vapor cloud. As a result, a hypersonic jet of air and erosion plasma is formed. The kinetic energy E sub J is far above the total energy of the geomagnetic field of the Earth (approximately equivalent to the energy of 100 Mt) and the total mass of a fast-moving part of the jet M sub j approximately = 10 exp 12 kg is far above the mass of atmosphere in the jet expansion cone. Thus, the jet will propagate practically inertially with the constant mean velocity U approximately = 10-20 km/s and even higher. The interaction of this plasma jet with the Earth's magnetic field causes magnetodynamic effects similar to those which are produced by cosmic nuclear explosions but of a larger scale. The preliminary results of experimental and numerical modeling of the plasma jet-magnetosphere interaction are presented.

Nemchinov, I. V.↗
NASA NTRS1996

Microscopic optical model calculations of 4He, 12C-nucleus absorption cross sections

Calculations of absorption cross sections using a microscopic first-order optical potential for heavy-ion scattering are compared with experiments. In-medium nucleon-nucleon (NN) cross sections were used to calculate the two-body scattering amplitude. A medium-modified first-order optical potential was obtained for heavy-ion scattering using the in-medium two-body scattering amplitude. A partial wave expansion of the Lippmann-Schwinger equation in momentum space was used to calculate the absorption cross sections for various systems. The results are presented for the absorption cross sections for 4He-nucleus and 12C-nucleus scattering systems and are compared with the experimental values in the energy range 18-83A MeV. The use of the in-medium NN cross sections is found to result in significant reduction of the free space absorption cross sections in agreement with experiment.

NASA Discipline Radiation Health↗