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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Study of inverted-V auroral precipitation events

The macroscopic properties of inverted V events measured by the Atmospheric Explorer-D satellite are described, along with the spatial distributions and the extents of individual events. The satellite carried 19 detectors, each comprising a cylindrical electrostatic analyzer followed by an electron multiplier. A total of 430 events was recorded, none of which occurred in cusp precipitation. The observed characteristics of the inverted V events are compared with particle distribution properties predicted by a double layer mechanism, an electrostatic shock model, extended field-aligned potential, and anomalous resistivity. Widespread, continuous electric fields were found parallel to the magnetic field lines, and anomalous resistivity was determined as the most favorable mechanism for producing the electron precipitation structure observed.

Hoffman, R. A.↗
NASA NTRS1982

High-pressure LOX/hydrocarbon preburner injector investigation

The NASA-MSFC program to furnish a high-pressure LOX/hydrocarbon turbine drive combustor technology base for future booster engine programs is discussed. The program evaluated the LOX/RP-1 and LOX/methane preburner and gas generator performance and gas property prediction methods for fuel-rich and oxidizer-rich operating conditions. A small-scale hardware test program, which included 42 hot-fire tests of fuel-rich LOX/methane and LOX/RP-1 and oxidizer-rich LOX/methane, supplied information to reduce uncertainties in prediction techniques. The hot-fire results show that theoretical computer model features should be modified to support curves generated from experimental data.

Huebner, A. W.↗
NASA NTRS1980

Fabrication and evaluation of brazed titanium-clad Borsic/aluminum compression panels

Processes for brazing Borsic/aluminum composite materials that eliminate diffusion of braze alloy constituents into the aluminum matrix developed. One brazing study led to the development of a hybrid composite which combines high strength Borsic/aluminum and ductile titanium to form a material identified as titanium clad Borsic/aluminum. The titanium foil provides the Borsic/aluminum with a durable outer surface and serves as a diffusion barrier which alleviates fiber and matrix degradation during brazing. Titanium clad Borsic/aluminum skin panels were joined to titanium clad Borsic/aluminum stringers by brazing and were tested in end compression at room and elevated temperatures. The data include failure strength, buckling strength, and the effects of brazing on the material properties. Predicted buckling loads are compared with experimental data.

Royster, D. M.↗
NASA NTRS1986

Assessment of simplified composite micromechanics using three-dimensional finite-element analysis

Three-dimensional finite-element analyses are used to assess the accuracy of simplified composite micromechanics equations (SME) for hygral, thermal, and mechanical properties of unidirectional composites with orthotropic fibers. The properties predicted by the SME are in reasonably good agreement with those predicted by the three-dimensional finite-element analyses. This correlation demonstrates that the SME can be used with confidence in predicting the hygral, thermal, and mechanical behavior of unidirectional fiber composites.

Caruso, J. J.↗
NASA NTRS1986

Mechanical properties characterization of composite sandwich materials intended for space antenna applications

The composite materials proposed for use in the Advanced Communications Technology Satellite (ACTS) Program contains a new, high modulus graphite fiber as the reinforcement. A study was conducted to measure certain mechanical properties of the new fiber-reinforced material as well as of a composite-faced aluminum honeycomb sandwich structure. Properties were measured at -157, 22, and 121 C. Complete characterization of this material was not intended. Longitudinal tensile, picture-frame shear, short-beam shear, and flexural tests were performed on specimens of the composite face-sheet materials. Unidirectional, cross-plied, and quasi-isotropic fiber composite ply layup designs were fabricated and tested. These designs had been studied by using NASA's Integrated Composite Analyzer (ICAN) computer program. Flexural tests were conducted on (+/- 60/0 deg) sub s composite-faced sandwich structure material. Resistance strain gages were used to measure strains in the tensile, picture-frame, and sandwich flexural tests. The sandwich flexural strength was limited by the core strength at -157 and 22 C. The adhesive bond strength was the limiting factor at 121 C. Adhesive mechanical properties are reflected in sandwich structure flexural properties when the span-to-depth ratio is great enough to allow a significant shear effect on the load-deflection behavior of the sandwich beam. Most measured properties agreed satisfactorily with the properties predicted by ICAN.

Bowles, Kenneth J.↗
NASA NTRS1987

Application of satellite data in observational and theoretical studies of the evolving structure of baroclinic waves

A variety of observational and theoretical studies were performed which were designed to clarify the relationship between satellite measurements of cloud and radiation and the evolution of transient and stationary circulation in middle latitudes. Satellite outgoing longwave radiation data are used to: (1) estimate the generation of available potential energy due to infrared radiation, and (2) show the extent to which these data can provide the signature of high and low frequency weather phenomena including blocking. In a significant series of studies the nonlinear, energetical, and predictability properties of these blocking situations, and the ralationship of blocking to the planetary, scale longwave structure are described. These studies form the background for continuing efforts to describe and theoretically account for these low frequency planetary wave phenomena in terms of their bimodal properties.

Saltzman, Barry↗
NASA NTRS1988

Point mass deflectors in gravitational lenses

The observed properties of the six systems generally accepted as gravitational lenses are compared with the properties predicted for the images of point-mass and distributed mass deflectors. Taken as a statistical distribution, the characteristics of the six known systems strongly suggest the existence of a super-massive black hole as the effective deflecting mass in one or more of these systems. If the deflecting mass in a gravitational lens is a black hole, the distance to the deflecting mass can be determined directly from the difference in light travel time along the separate image paths. (No direct solution for the distance to the deflecting mass exists when the deflecting mass is a galaxy or a cluster of galaxies). Geometric parallaxes of objects at 1000 Mpc distance are of obvious importance in a wide variety of cosmological studies.

Dolan, Joseph F.↗
NASA NTRS1989

Mechanical properties characterization of composite sandwich materials intended for space antenna applications

The composite materials proposed for use in the Advanced Communications Technology Satellite (ACTS) program contains a new, high modulus graphite fiber as the reinforcement. A study was conducted to measure certain mechanical properties of the new fiber-reinforced material as well as of a composite-faced aluminum honeycomb sandwich structure. Properties were measured at -157, 22, and 121 C. Complete characterization of this material was not intended. Longitudinal tensile, picture-frame shear, short-beam shear, and flexural tests were performed on specimens of the composite face-sheet materials. Unidirectional, cross-plied, and quasi-isotropic fiber composite ply layup designs were fabricated and tested. These designs had been studied by using NASA's Integrated Composite Analyzer (ICAN) computer program. Flexural tests were conducted on (+/- 60/0 deg) sub s composite-faced sandwich structure material. Resistance strain gages were used to measure strains in the tensile, picture-frame, and sandwich flexural tests. The sandwich flexural strength was limited by the core strength at 157 and 22 c. The adhesive bond strength was the limiting factor at 121 C. Adhesive mechanical properties are reflected in sandwich structure flexural properties when the span-to-depth ratio is great enough to allow a significant shear effect on the load-deflection behavior of the sandwich beam. Most measured properties agreed satisfactorily with the properties predicted by ICAN.

Bowles, Kenneth J.↗
NASA NTRS1992

Monte Carlo simulation of a near-continuum shock-shock interaction problem

A complex shock interaction is calculated with direct simulation Monte Carlo (DSMC). The calculation is performed for the near-continuum flow produced when an incident shock impinges on the bow shock of a 0.1 in. radius cowl lip for freestream conditions of approximately Mach 15 and 35 km altitude. Solutions are presented both for a full finite-rate chemistry calculation and for a case with chemical reactions suppressed. In each case, both the undisturbed flow about the cowl lip and the full shock interaction flowfields are calculated. Good agreement has been obtained between the no-chemistry simulation of the undisturbed flow and a perfect gas solution obtained with the viscous shock-layer method. Large differences in calculated surface properties when different chemical models are used demonstrate the necessity of adequately representing the chemistry when making surface property predictions. Preliminary grid refinement studies make it possible to estimate the accuracy of the solutions.

Carlson, Ann B.↗
NASA NTRS1992

Distant magnetotails of the outer magnetic planets

The distant planetary magnetotails of Jupiter, Saturn, Uranus, and Neptune are assumed to be partially open, hot, long plasma cavities generally in pressure equilibrium with the solar wind. Most of the magnetosheath magnetic field lines drape around the magnetotails. Conservation of momentum density, magnetic field, plasma density, and energy density fluxes are invoked at the tail boundaries to determine the shape of the magnetotails and the variations of plasma and magnetic field characteristics with distance down the magnetotail. Voyager observations are used to initialize calculations in the near-planet portions of each magnetotail. Estimates of magnetotail cross sections, magnetic field strengths, and plasma densities are described as a function of downstream distance. The model accurately predicts properties of the Jovian magnetotail at least as far as Saturn's orbit.

Macek, W. M.↗
NASA NTRS1993

Organic Materials For Optical Switching

Equations predict properties of candidate materials. Report presents results of theoretical study of nonlinear optical properties of organic materials. Such materials used in optical switching devices for computers and telecommunications, replacing electronic switches. Optical switching potentially offers extremely high information throughout in compact hardware.

Cardelino, Beatriz H.↗
NASA NTRS1992

How life affects the geochemical cycle of carbon

Developing a quantitative understanding of the biogeochemical cycles of carbon as they have worked throughout Earth history on various time scales, how they have been affected by biological evolution, and how changes in the carbon content of ocean and atmosphere may have affected climate and the evolution of life are the goals of the research. Theoretical simulations were developed that can be tuned to reproduce such data as exist and, once tuned, can be used to predict properties that have not yet been observed. This is an ongoing process, in which models and results are refined as new data and interpretations become available and as understanding of the global system improves. Results of the research are described in several papers which were published or submitted for publication. These papers are summarized. Future research plans are presented.

Walker, James C. G.↗
NASA NTRS1993

Clumpy Langmuir waves in type III radio sources - Comparison of stochastic-growth theory with observations

Detailed comparisons are made between the Langmuir-wave properties predicted by the recently developed stochastic-growth theory of type III sources and those observed by the plasma wave experiment on ISEE 3, after correcting for the main instrumental and selection effects. Analysis of the observed field-strength distribution confirms the theoretically predicted form and implies that wave growth fluctuates both spatially and temporally in sign and magnitude, leading to an extremely clumpy distribution of fields. A cutoff in the field-strength distribution is seen at a few mV/m, corresponding to saturation via nonlinear effects. Analysis of the size distribution of Langmuir clumps yields results in accord with those obtained in earlier work and with the size distribution of ambient density fluctuations in the solar wind. This confirms that the inhomogeneities in the Langmuir growth rate are determined by the density fluctuations and that these fluctuations persist during type III events.

Robinson, P. A.↗
NASA NTRS1993

Superconducting terahertz mixer using a transition-edge microbolometer

We present a new device concept for a mixer element for THz frequencies. This uses a superconducting transition-edge microbridge biased at the center of its superconducting transition near 4.2 K. It is fed from an antenna or waveguide structure. Power from a local oscillator and an RF signal produce a temperature and resulting resistance variation at the difference frequency. The new aspect is the use of a very short bridge in which rapid (less than 0.1 ns) outdiffusion of hot electrons occurs. This gives large intermediate frequency (IF) response. The mixer offers about 4 GHz IF bandwidth, about 80 ohm RF resistive impedance, good match to the IF amplifier, and requires only 1-20 nW of local oscillator power. The upper RF frequency is determined by antenna or waveguide properties. Predicted mixer conversion efficiency is 1/8, and predicted double-sideband receiver noise temperatures are 260 and 90 K for transition widths of 0.1 and 0.5 Tc, respectively.

Prober, D. E.↗
NASA NTRS1992

Development of nontoxic heat transport fluids for habitat two-phase thermal control systems

A computational chemistry approach based on pattern recognition techniques is used to correlate molecules thermodynamic and chemical properties with its molecular structure. The potential to develop a suitable two-phase nontoxic heat transport working fluid for the spacecraft habitat environment is discussed. It is concluded that the perfluorocarbons represent a potentially useful class to consider as a source of the working fluids because of their low toxicity, thermal stability, and chemical inertness. The ADAPT software program is considered to be adequate to make structural and property predictions.

Parrish, Clyde F.↗
NASA NTRS1993

Origin of outflows and winds

Recent developments concerning the accretion-outflow connection and the role of magnetic fields are examined. It is argued that the weakly ionized wind most likely represents an MHD outflow driven centrifugally from the disk surfaces or from the boundary between the disk and the star. Specific wind models for each of these alternatives are presented, and it is contended that both provide a natural explanation of the observed correlation between accretion and outflow. The kinematic, thermal, and chemical wind properties predicted by these models are described and their observational implications are considered. It is suggested that the wind characteristics may be reflected in the observed forbidden line and IR continuum emission of T Tauri stars and in the measured abundances of various molecular species.

Koenigl, Arieh↗
NASA NTRS1993

Quantification of processing artifacts in textile composites

One of the greatest difficulties in developing detailed models of the mechanical response of textile reinforced composites is an accurate model of the reinforcing elements. In the case of elastic property prediction, the variation of fiber position may not have a critical role in performance. However, when considering highly localized stress events, such as those associated with cracks and holes, the exact position of the reinforcement probably dominates the failure mode. Models were developed for idealized reinforcements which provide an insight into the local behavior. However, even casual observations of micrographical images reveals that the actual material deviates strongly from the idealized models. Some of the deviations and causes are presented for triaxially braided and three dimensionally woven textile composites. The necessary modeling steps to accommodate these variations are presented with some examples. Some of the ramifications of not accounting for these discrepencies are also addressed.

Pastore, Christopher M.↗
NASA NTRS1995

Geometrical modelling of textile reinforcements

The mechanical properties of textile composites are dictated by the arrangement of yarns contained within the material. Thus, to develop a comprehensive understanding of the performance of these materials, it is necessary to develop a geometrical model of the fabric structure. This task is quite complex, as the fabric is made from highly flexible yarn systems which experience a certain degree of compressibility. Furthermore there are tremendous forces acting on the fabric during densification typically resulting in yarn displacement and misorientation. The objective of this work is to develop a methodology for characterizing the geometry of yarns within a fabric structure including experimental techniques for evaluating these models. Furthermore, some applications of these geometric results to mechanical property predictions models are demonstrated.

Pastore, Christopher M.↗