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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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Burning solid ammonium perchlorate composite propellants surface structure observation to assess heterogeneous or subsurface reactions, using scanning electron microscope
Traveling wave propagation, modal vibrations and elastic transmission medium studies from theoretical seismograms for realistic gravitating heterogeneous spherical earth model
Crystal growth method based on controlled power reduction under stabilizing thermal gradients, eliminating chemical heterogeneities
Unmanned lunar rover exploration objectives and requirements, considering heterogeneous surface
Spectrometric data were used to gain information for computation of the flux-energy spectra of bremsstrahlung inside the Gemini spacecraft and to determine if energetic electrons are able to penetrate the vehicle walls. The spectra were compared with computer predicted bremsstrahlung spectra by the use of data from beta spectrometers flown on Gemini 10 and 12 missions. The calculations of bremsstrahlung radiation involved uncertainties because of the small amount of information available on cross-section interaction and because of the complex, heterogeneous composition of the spacecraft. The bremsstrahlung detector was designed for time-differentiated measurement of the electron-induced gamma rays over a large section of the vehicle. Preliminary analysis of the data obtained during the missions was indicative that electrons did penetrate the spacecraft wall.
The application of remote sensors for obtaining geophysical information of the Arctic regions is discussed. Two significant requirements are to acquire sequential, synoptic imagery of the Arctic Ocean during all weather and seasons and to measure the strains in the sea ice canopy and the heterogeneous character of the air and water stresses acting on the canopy. The acquisition of geophysical data by side looking radar and microwave sensors in military aircraft is described.
Materials development topics include: development of analysis techniques to adjust heterogeneous data; determination of thermal conductivity for AISI 347 stainless steel and elastic moduli and Poisson's ratio for Inconel 718 and Ti 5Al-2.5Sn; embrittlement effects of 1400 psi gaseous hydrogen for alloy 718 and Ti 5Al-2.5Sn; cryogenic radiation damage of Ti 5Al-2.5Sn; and evaluation of prepreg, impregnation, and fabric materials for optimum fibrous graphite properties. Component support topics include: tensile design allowable development of Ti 5Al-2.5Sn for turbopump applications; evaluation of fatigue, fracture toughness, and stress corrosion properties of AA 7039-T63 for pressure vessel applications; development of AISI 347 sheet tensile and creep properties for nozzle applications; evaluation of orbital weld techniques for aluminum line fabrication; material selection of shield materials; development of high load friction and wear properties of hard chrome/gold plate combinations; and evaluation of weld processes for NASS duct coolant channel fabrication.
Synthesis of sugars by Ca(OH)2 catalyzed formaldehyde condensation (the formose reaction) has produced branched carbohydrates that do not occur in nature. The kinetics and mechanisms of the homogeneously catalyzed autocatalytic condensation were studied and analogies between homogeneous and heterogeneous rate laws have been found. Aldol condensations proceed simultaneously with Cannizzaro and crossed-Cannizzaro reactions and Lobry de Bruyn-Van Eckenstein rearrangements. The separate steps as well as the interactions of this highly complex reaction system were elucidated. The system exhibits instabilities, competitive catalytic, mass action, and equilibrium phenomena, complexing, and parallel and consecutive reactions. Specific finding that have been made on the problem will be of interest for synthesizing sugars, both for sustained space flight and for large scale food manufacture. A contribution to methodology for studying complex catalyzed reactions and to understanding control of reaction selectivity was a broad goal of the project.
Research has been conducted by means of laboratory experiments to enhance understanding of the fundamental mechanisms of heterogeneous and homogeneous chemical reactions taking place during ablative processes that accompany the reentry or manned space vehicles into planetary atmospheres. Fundamental mechanisms of those chemical reactions believed to be important in the thermal degradation of ablative plastic heat shield materials, and the gases evolved, are described.
The analysis provides insight into the failure mechanics of these materials and defines criteria which serve as tools for preliminary design material selection and for material reliability assessment. The model incorporates both dispersed and propagation type failures and includes the influence of material heterogeneity. The important effects of localized matrix damage and post-failure matrix shear stress transfer are included in the treatment. The model is used to evaluate the influence of key parameters on the failure of several commonly used fiber-matrix systems. Analyses of three possible failure modes were developed. These modes are the fiber break propagation mode, the cumulative group fracture mode, and the weakest link mode. Application of the new model to composite material systems has indicated several results which require attention in the development of reliable structural composites. Prominent among these are the size effect and the influence of fiber strength variability.
Results of grain-size measurements in Permalloy platings suggest that recrystallization is possible at temperatures as low as 200 C, but that it is an extremely heterogeneous process. No worthwhile correlation was found to exist between observed grain size and magnetic dispersion in samples aged in the temperature range from 180 to 230 C. It is suggested that the magnetic aging which occurs under these conditions may be due to some other diffusion-controlled process than recrystallization; a process such as chemical homogenization is tentatively preferred.
Exploration of available information concerning carbon on the moon, following review of what is known about carbon on the earth, and consideration of the results of studies of meteorites, which have provided the first direct clues about extraterrestrial carbon. Carbon and carbon isotope composition data taken from Apollo 11 samples are tabulated. Carbon compounds produced by pyrolysis, extracted with benzene-methanol, extracted with water, and freed by acid treatment are discussed. Carbon and carbon compounds in lunar rocks and soils appear to be distributed heterogeneously.
Diverse lunar soil fragments returned from the Luna 16 mission were examined for evidence in shock metamorphism in order to evaluate the role of meteorite impact in forming the lunar regolith at a new site relatively distant from the Apollo landing sites. It was found that shock metamorphic effects, characteristic of meteorite impact and virtually identical to those observed in Apollo samples, are common in the Luna 16 fragments. Two types of shock effects are present - i.e., a deformation and partial melting features in rock and mineral fragments, and heterogeneous glasses and glassy breccias produced by shock melting. It is concluded that these shock metamorphic effects indicate that regolith formation by meteorite impact has occurred in Mare Fecunditatis and is a general process over the entire moon.
Investigation of the effects of sensor spatial resolution on estimating the amount of clouds covering the earth by simulating various cloud distributions and sizes, and measuring the known cloud amount with resolution of different sizes using a cloud-no cloud threshold technique often applied in automatic data processing. Cloud amount statistics have been tabulated for a three-orders-of-magnitude range in the ratio (R) of areal cloud size to areal resolution size for seven cloud amounts between 6 and 90%. Three different cloud patterns were used. These were 1) a regularly spaced pattern of homogeneous dots arranged in rows and columns (to simulate cloud streets), 2) a randomly spaced pattern of the same dots (to simulate randomly oriented cumulus clouds), and 3) a heterogeneous cloud size distribution irregularly spaced (to simulate a view of different cloud types and sizes). Two cloud amount estimation techniques were tested. Cloud amounts of 100% (method 1) and 50% (method 2) were assigned to partially filled resolution elements. Using criteria applicable to some studies carried out in the past, it is shown that cloud amount estimations can be in error by as much as 86 and 38%, respectively, for the two methods. Nomograms have been developed which subtantially improve the estimate of the true cloud cover for R less than 100, provided that R can be determined.
A computational method has been developed for the study of the post-ignition transients in hybrid rocket systems. The particular system chosen consisted of a gaseous oxidizer flowing within a tube of solid fuel, resulting in heterogeneous combustion. With the appropriate assumptions, two-dimensional, time-dependent conservation equations were derived for the reacting gas phase, and for the solid phase, in a cylindrical coordinate system. These were then programmed for numerical computation, using two implicit finite-difference schemes, the Lax-Wendroff scheme for the gas phase, and the Crank-Nicolson scheme for the solid phase. Appropriate initial and boundary conditions were represented, including heat and mass conservation at the interface between gas and solid. Initially, no attempt was made to relate the recession rate at the surface to the surface temperature, or to include heat transfer by radiation. A simple case was selected for preliminary calculations, with aluminum and oxygen as fuel and oxidizer, and aluminum oxide as the product.
Electron microprobe examination revealed that glassy lunar fragments had inclusions as well as boundaries between mineral glasses of different compositions. Glassy lunar spherules showed detectable heterogeneity less marked than that of the fragments. The room-temperature refractive indices and densities of the spherules are changed by heat-treating them at 500 to 700 C. The large increases (as much as 2% in density and 0.7% in index of refraction) are difficult to explain on the basis of classical glass-transition phenomena alone unless extremely rapid cooling rates are assumed. Further, the spherules darkened significantly when they were heated in air or a medium vacuum above 625 C.
This experimental study is concerned with the mixing in the initial region of turbulent coaxial streams. The investigation is limited to the low-speed incompressible case with the inner stream of lower velocity than the outer stream. Velocity ratios ranged from infinity to one. The inner to outer stream density ratio was either 4 or 1. Experimental measurements were made with a hot-wire anemometer system, static pressure probes, and shadowgraphy. The data show that a backflow region is formed in this particular apparatus at outer to inner stream velocity ratio of 13 for the homogeneous case and at outer to inner stream velocity ratio of 26 for the heterogeneous case. For higher velocity ratio, a circulating toroidal vortex is established which enhances mixing between the inner and outer streams. This vortex pattern exhibits similarity of velocity with velocity ratio variations.
The reactions were studied with the aid of a mass spectrometer. A pinhole bleed system provided continuous sampling of the gas mixture in the cell during the reaction. It was found that the homogeneous reactions of nitric oxide and nitrogen dioxide with hydrogen peroxide are too slow to be of any significance in the upper atmosphere. However, the heterogeneous reactions may be important in the conversion of nitric oxide to nitrogen dioxide in the case of polluted urban atmospheres.