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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

An ET Origin for Stratospheric Particles Collected during the 1998 Leonids Meteor Shower

On 17 November 1998, a helium-filled weather balloon was launched into tfle strato- sphere, equipped with a xerogel microparticle collector. The three-hour flight was designed to sample the dust environment in the stratosphere during the Leonid meteor shower, and possibly to capture Leonid meteoroids. Environmental Scanning Election Microscope analyses of the returned collectors revealed the capture of a -30-pm particle. with a smooth, multigranular shape, and partially melted, translucent rims; similar to known Antarctic micrometeorites. Energy-dispersive X-ray Mass Spectroscopy shows en- riched concentrations of the non-volatile elements, Mg, Al, and Fe. The particle possesses a high magnesium to iron ratio of 2.96, similar to that observed in 1998 Leonids meteors (Borovicka, et al. 1999) and sharply higher than the ratio expected for typical material from the earth's crust. A statistical nearest-neighbor analysis of the abundance ratios Mg/Si, Al/Si, and Fe/Si demonstrates that the particle is most similar in composition to cosmic spherules captured during airplane flights throucrh the stratosphere. The mineralogical class is consistent with a stony (S) type of silicates. olivine [(Mg, Fe)2SiO4] and pyroxene [(Mg,Fe)SiO3]-or oxides, herecynite [(Fe,Mg) Al2O4]. Attribution to the debris stream of the Leonids' parent body, comet Tempel-Tuttle, would make it the first such material from beyond the orbit of Uranus positively identified on Earth.

Noever, David A.↗
NASA NTRS1999

Experimental and Numerical Study of Ammonium Perchlorate Counterflow Diffusion Flames

Many solid rocket propellants are based on a composite mixture of ammonium perchlorate (AP) oxidizer and polymeric binder fuels. In these propellants, complex three-dimensional diffusion flame structures between the AP and binder decomposition products, dependent upon the length scales of the heterogeneous mixture, drive the combustion via heat transfer back to the surface. Changing the AP crystal size changes the burn rate of such propellants. Large AP crystals are governed by the cooler AP self-deflagration flame and burn slowly, while small AP crystals are governed more by the hot diffusion flame with the binder and burn faster. This allows control of composite propellant ballistic properties via particle size variation. Previous measurements on these diffusion flames in the planar two-dimensional sandwich configuration yielded insight into controlling flame structure, but there are several drawbacks that make comparison with modeling difficult. First, the flames are two-dimensional and this makes modeling much more complex computationally than with one-dimensional problems, such as RDX self- and laser-supported deflagration. In addition, little is known about the nature, concentration, and evolution rates of the gaseous chemical species produced by the various binders as they decompose. This makes comparison with models quite difficult. Alternatively, counterflow flames provide an excellent geometric configuration within which AP/binder diffusion flames can be studied both experimentally and computationally.

Smooke, M. D.↗
NASA NTRS2002

A New Method for Estimating the Single Scattering Phase Functions of Regolith Grains

Hapke's photometric model has been widely used in solar system remote sensing applications for nearly two decades. Recently, Hapke extended his model to describe the coherent-backscatter opposition effect and multiple-scattering by particles with anisotropic single particle phase functions (SPPF's). A practical difficulty for retrieving Hapke's model parameters from typical planet, satellite, and asteroid photometry data sets is that the model employs a large number of adjustable parameters (at least eight) that can be reliably constrained only for a small number of planetary data sets in which both disk-resolved and whole-disk observations are available from opposition to very large phase angles. The present work aims to reduce the number of adjustable parameters and preserve (or even enhance) the model's accuracy and usefulness by expressing Hapke's parameters in terms of more fundamental physical properties on which they mutually depend. The most difficult part of this task, described here, is to develop a simple method for computing the effective SPPF for structurally complex regolith grains from optical constants, grain-size distribution, and average regolith porosity. The development of light-scattering models for irregularly shaped particles is a large, complex subject and many sophisticated methods, such as Discrete Dipole Approximation (DDA) and Monte-Carlo simulations, have been explored elsewhere. Many of these methods are computationally intensive and probably impractical for routine substitution in Hapke's model. Here, progress is reported in developing a practical, semi-empirical method for estimating the directional scattering behavior (i.e. SPPF) of irregular regolith grains. The method employs Optical Transfer Function (OTF) techniques to model how the structural complexity of regolith particles broaden and attenuate the angular distribution of scattered light relative to that expected from ideal spherical particles of equivalent size and composition.

Helfenstein, P.↗
NASA NTRS2003

JD 7: The Sun and the Heliosphere as an Integrated System

As knowledge of the Sun and the heliosphere grows, it is becoming not only possible but preferable to view the global structure, the interaction with the local interstellar medium, and changes over a solar cycle as the behavior of an integrated system. This consideration motivated Joint Discussion 7, which was meant both to summarize the state of art at the time of IAU XXVand to solicit interest in this kind of approach. The Joint Discussion was arranged in four sections, two on processes that, beginning from the Sun s interior, model and shape the heliosphere (From the Transition Region to the Corona and beyond and From the Sun to the interstellar Medium), one on elemental abundances and particles in the corona and the heliosphere (Energetic Particles, Energetic Neutral Atoms and Composition) and one on forthcoming solar and heliospheric space missions. In the following we give a brief summary of the contributions presented at the JD in each section. An ext.cnded discussion of the topics cov- ered by JD is expected to appear in a comprehensive book on the Sun and the Heliosphere which will be edited by us and printed by Kluwer in year 2004. Posters which were exhibited as part of the Joint Discussion are listed at the end of this summary.

Suess, Steven T.↗
NASA NTRS2007

Crystal Water on Mars: Insights from the Mars Exploration Rovers

The purpose of this paper is to constrain the total water contents from crystal H2O and OH in several materials analyzed by the Mars Exploration Rovers (MER). Crystal H2O is part of the unit cell and cannot be removed without changing the structure. Minerals that contain only OH in their structures are anhydrous minerals containing hydroxyls, although they are formed as a product of aqueous activity and will decompose with evolution of H2O when heated. The crystal water and OH contents of a bulk material at the MER landing sites can be estimated from mineralogical composition, which is determined by a combination of Fe-mineralogy obtained by the Mossbauer Spectrometer and mineral abundances based upon the chemical composition determined by the Alpha Particle X-ray Spectrometer. Jarosite, along with Ca- and Mg-sulfates, have been suggested as the sulfur-bearing phases in Meridiani Planum outcrop. Models of various hydration states of Fe-, Ca-, and Mg-sulfates and other possible secondary phases suggest that 6 to 22 wt.% of the outcrop may occur as crystal H2O and/or OH (Clark et al., 2005). This estimate of water is consistent with measurements from the Odyssey orbiter, where 7 % H2O-equivalent H was measured down to a depth of approximately 1 m for the region (Feldman et al., 2004).

Ming, D. W.↗
NASA NTRS2014

A Transmission Electron Microscope Investigation of Space Weathering Effects in Hayabusa Samples

The Hayabusa mission to asteroid 25143 Itokawa successfully returned the first direct samples of the regolith from the surface of an asteroid. The Hayabusa samples thus present a special opportunity to directly investigate the evolution of asteroidal surfaces, from the development of the regolith to the study of the more complex effects of space weathering. Here we describe the mineralogy, microstructure and composition of three Hayabusa mission particles using transmission electron microscope (TEM) techniques

Keller, Lindsay P.↗
NASA NTRS2014

Noachian Impact Breccias on the Rim of Endeavour Crater, Mars: Opportunity APXS Results

Mars Exploration Rover Opportunity has been investigating the geology of Meridiani Planum since January 2004, and is currently approx. 3830% into its primary mission. Opportunity reached the rim of 22 km diameter Endeavor crater at Spirit Point on the south end of Cape York on sol 2681 and began exploring the geology of Endeavour rim. She left Cape York on sol 3316 and arrived at the next rim remnant to the south, Solander Point, on sol 3387 to begin geological investigations at the contact and up onto Murray Ridge. The Burns fm. of Meridiani Planum lies near the top of the plains-forming unit of western Sinus Meridiani and onlaps onto the Endeavour rim rocks (hereafter rim rocks). Endeavour crater would have excavated approx. 4 km into the existing stratigraphy. Thus, the ejecta that form the rim rocks offer windows into the deeper lithologies of Sinus Meridiani. Here we discuss the polymict breccias of the Shoemaker fm. on Cape York and the breccias from Murray Ridge, with a focus on compositions determined by the Alpha Particle X-Ray Spectrometer (APXS).

Mittlefehldt, D. W.↗
NASA NTRS2019

Origin and Speciation of Sulfur Compounds in the Murray Formation, Gale Crater, Mars

The Mars Curiosity rover has traversed nearly 20 km and gained over 350 meters in elevation since landing in Gale crater in August 2012. Through 2250 sols of surface operations, Curiosity has spent approximately 60% of its time investigating the Murray formation, a unit of layered sediments. The occurrence of sulfur compounds in the Murray formation has been established by imaging of light-toned veins by MastCam and MAHLI, chemical compositions measured by the Alpha Particle X-ray Spectrometer (APXS) and ChemCam, crystalline phase identifications by the CheMin X-ray diffractometer, and evolved gas analyses from the Sample Analysis at Mars (SAM) instrument.

Yen, A. S.↗
NASA NTRS1992

Volatiles in interplanetary dust particles: A comparison with CI and CM chondrites

In an effort to classify and determine the origin of interplanetary dust particles (IDPs), 14 of these particles were studied using a laser microprobe/mass spectrometer. The mass spectra for these particles varied dramatically. Some particles released hydroxide or water which probably originated in hydroxide-bearing minerals or hydrates. Others produced spectra which included a number of hydrocarbons and resembled meteorite spectra. However, none of the individual IDPs gave spectra which could be matched identically with a particular meteorite type such as a CI or CM carbonaceous chondrite. We believe this was due to the fact that 10-20 micron size IDPs are too small to be representative of the parent body. To verify that the diversity was due primarily to the small particle sizes, small grains of approximately the same size range as the IDPs were obtained from two primitive meteorites, Murchison and Orgueil, and these small meteorite particles were treated exactly like the IDPs. Considerable diversity was observed among individual grains, but a composite spectrum of all the grains from one meteorite closely resembled the spectrum obtained from a much larger sample of that meteorite. A composite spectrum of the 14 IDPs also resembled the spectra of the CM and CI meteorites, pointing to a possible link between IDPs and carbonaceous chondrites. This also illustrates that despite the inherent diversity in particles as small as 10-20 micron, conclusions can be drawn about the possible origin and overall composition of such particles by looking not only at results from individual particles but also by including many particles in a study and basing conclusions on some kind of composite data.

Bustin, Roberta↗
NASA NTRS1975

Isotopic composition of cosmic ray nitrogen at 1.5 GeV/amu

For any location, the earth's magnetic field acts as a filter for incoming cosmic rays, allowing only particles above a certain rigidity. The relative isotopic composition of abundant elements can be measured with a detector sensitive to the velocity of particles in the penumbra of the earth's magnetic field. In this paper, the nitrogen velocity spectrum is compared with that of carbon plus oxygen as a reference, since in this case Z-dependent effects are minimal. The form of the energy spectrum of carbon, nitrogen, and oxygen, needed for proper correction, was measured in the same experiment. The results were obtained using a scintillator-Cerenkov counter telescope with a geometric factor of 0.25 sq in sr, flown twice on high-altitude balloons from Palestine, Texas, obtaining an exposure factor of 20 sq m sr hr. Results are presented on the isotopic composition of nitrogen at about 1.5GeV/amu.

Dwyer, R.↗
NASA NTRS1979

Program for plasma-sprayed self-lubricating coatings

A method for preparing composite powders of the three coating components was developed and a procedure that can be used in applying uniform coatings of the composite powders was demonstrated. Composite powders were prepared by adjusting particle sizes of the components and employing a small amount of monoaluminum phosphate as an inorganic binder. Quantitative microscopy (image analysis) was found to be a convenient method of characterizing the composition of the multiphase plasma-sprayed coatings. Area percentages and distribution of the components were readily obtained by this method. The adhesive strength of the coating to a nickel-chromium alloy substrate was increased by about 40 percent by a heat treatment of 20 hours at 650 C.

Walther, G. C.↗
NASA NTRS1999

Constraining the Global, Cloud-Free Reflected Solar Radiation Flux (RSRF) with Earth Observing System (EOS) Instruments

Variations in the top-of-atmosphere reflected solar radiation flux, and in the factors that determine its value, are among the most important diagnostic indicators of changes in Earth's energy balance. Data from the MISR (Multi-angle Imaging SpectroRadiometer), MODIS (Moderate-resolution Imaging Spectroradiometer), SAGE-3 (Stratospheric Aerosol and Gas Experiment), and CERES (Clouds and Earth's Radiant Energy System), all of which are spacecraft instruments scheduled for launch in 1999, will each constrain pieces of the RSRF budget. Prior to launch, we are performing studies to determine the sensitivity of these instruments to key factors that influence the cloud-free RSRF: aerosol optical depth, aerosol scattering properties, and surface visible bidirectional reflectance distribution function (BRDF). We are also assessing the ability of the aggregate of instruments to constrain the overall RSRF budget under natural conditions over the globe. Consider the MISR retrieval of aerosols: according to simulations over cloud-free, calm ocean, for pure particles with natural ranges of optical depth, particle size, and indices of refraction, MISR can retrieve column aerosol optical depth for all but the darkest particles, to an uncertainty of at most 0.05 or 20%, whichever is larger, even if the particle properties are poorly known. For one common particle type, soot, constraints on the optical depth over dark ocean are very poor. The simulated measurements also allow us to distinguish spherical from non-spherical particles, to separate two to four compositional groups based on indices of refraction, and to identify three to four distinct size groups between 0. 1 and 2.0 microns characteristic radius at most latitudes. Based on these results, we expect to distinguish air masses containing different aerosol types, routinely and globally, with multiangle remote sensing data. Such results far exceed current satellite aerosol retrieval capabilities, which provide only total optical depth for assumed particle properties; the new information will complement in situ data, which give details about aerosol size and composition locally. In addition, our team is using climatologies that reflect the constraints each instrument is expected to provide, along with ERBE (Earth Radiation Budget Experiment) data and a radiative transfer code, to study overall sensitivity to RSRF, helping us prepare for similar studies with new data from the EOS-era instruments.

Kahn, Ralph↗
NASA NTRS2004

Characterization of Individual Aerosol Particles Associated with Clouds (CRYSTAL-FACE)

The aim of our research was to obtain data on the chemical and physical properties of individual aerosol particles from near the bottoms and tops of the deep convective systems that lead to the generation of tropical cirrus clouds and to provide insights into the particles that serve as CCN or IN. We used analytical transmission electron microscopy (ATEM), including energy-dispersive X-ray spectrometry (EDS) and electron energy-loss spectroscopy (EELS), and field-emission electron microscopy (FESEM) to compare the compositions, concentrations, size distributions, shapes, surface coatings, and degrees of aggregation of individual particles from cloud bases and the anvils near the tropopause. Aggregates of sea salt and mineral dust, ammonium sulfate, and soot particles are abundant in in-cloud samples. Cirrus samples contain many H2SO4 droplets, but acidic sulfate particles are rare at the cloud bases. H2SO4 probably formed at higher altitudes through oxidation of SO2 in cloud droplets. The relatively high extent of ammoniation in the upper troposphere in-cloud samples appears to have resulted from vertical transport by strong convection. The morphology of H2SO4 droplets indicates that they had been at least yartiy ammoniated at the time of collection. They are internally mixed with organic materials, metal sulfates, and solid particles of various compositions. Ammoniation and internal mixing of result in freezing at higher temperature than in pure H2SO4 aerosols. K- and S-bearing organic particles and Si-Al-rich particles are common throughout. Sea salt and mineral dust were incorporated into the convective systems from the cloud bases and worked as ice nuclei while being vertically transported. The nonsulfate particles originated from the lower troposphere and were transported to the upper troposphere and lower stratosphere.

Buseck, Peter R.↗
NASA NTRS1980

The surface composition of Amalthea

It is proposed that charged particles from the Jovian magnetosphere, contaminants such as sulfur from Io, and high-velocity micrometeoritic matter, combine to darken, redden, and alter the surface of Amalthea revealed by Voyager; whose few isolated bright spots have a distinct greenish spectrum. A major finding of this analysis is that available spectral reflectance data contain little information about the bulk composition of the satellite. The effects of contamination by sulfur and its allotropes are shown to redden a variety of bulk compositions: carbonaceous material, refractory minerals, iron and iron sulfides, and moderate temperature silicates. The bright, greenish spots probably identify locations in which atypical alteration processes occur, such as variations in the amount of contaminant sulfur in micrometeoritic glasses or in the relative abundances of certain sulfur allotropes.

Gradie, J.↗
NASA NTRS1976

High-silica /greater than 60%/ lunar glasses in an Apollo 14 soil sample - Evidence for silicic lunar volcanism

The major-element compositions of 93 low-specific-gravity (less than 2.60) high-silica (greater than 60%) glass particles from a sample of lunar fines (14259,20) were determined by electron microprobe analyses. The size, shape, abundance, mineralogy, and major-element composition of more than 60% of the high-silica glasses is consistent with their being fragments of interstitial glass from mare basalts. However, one group of 30 glasses with between 72% and 78% SiO2 and an average of approximately 2.6% FeO can be distinguished from other high-silica glasses both chemically and petrographically. Glass particles with this composition do not contain crystalline inclusions and are fairly homogeneous not only within a single particle but also from particle to particle. The chemistry and petrology of these glasses suggest that they are not fragments of interstitial glass or shock-melted particles from a 'granitic' source rock. Rather, the homogeneity and lack of crystalline inclusions suggest that this group of high-silica glasses was the product of lunar acidic volcanism.

Glass, B. P.↗
NASA NTRS1978

High temperature resistant cermet and ceramic compositions

High temperature oxidation resistance, high hardness and high abrasion and wear resistance are properties of cermet compositions particularly to provide high temperature resistant refractory coatings on metal substrates, for use as electrical insulation seals for thermionic converters. The compositions comprise a sintered body of particles of a high temperature resistant metal or metal alloy, preferably molybdenum or tungsten particles, dispersed in and bonded to a solid solution formed of aluminum oxide and silicon nitride, and particularly a ternary solid solution formed of a mixture of aluminum oxide, silicon nitride and aluminum nitride. Ceramic compositions comprising a sintered solid solution of aluminum oxide, silicon nitride and aluminum nitride are also described.

Phillips, W. M.↗
NASA NTRS1994

The 8-13 micron spectra of comets and the composition of silicate grains

We have analyzed the existing spectra of seven comets which show an emission feature at 7.8-13 micrometers. Most have been converted to a common calibration, taking into account the SiO feature in late-type standard stars. The spectra are compared with spectra of the Trapezium, interplanetary dust particles (IDPs), laboratory mineral samples, and small particle emission models. The emission spectra show a variety of shapes; there is no unique 'cometary silicate'. A peak at 11.20-11.25 micrometers, indicative of small crystalline olivine particles, is seen in only three comets of this sample, P/Halley, Bradfield 1987 XXIX, and Levy 1990 XX. The widths of the emission features range from 2.6 to 4.1 micrometers (FWHM). To explain the differing widths and the broad 9.8 micrometers maximum, glassy silicate particles, including both pyroxene and olivine compositions, are the most plausible candidates. Calculations of emission models confirm that small grains of glassy silicate well mixed with carbonaceous material are plausible cometary constituents. No single class of chondritic aggregate IDPs exhibits spectra closely matching the comet spectra. A mixture of IDP spectra, particularly the glass-rich aggregates, approximately matches the spectra of comets P/Halley, Levy, and Bradfield 1987 XXIX. Yet, if comets are simply a mix of IDP types, it is puzzling that the classes of IDPs are so distinct. None of the comet spectra match the spectrum of the Trapezium. Thus, the mineralogy of the cometary silicates is not the same as that of the interstellar medium. The presence of a component of crystalline silicates in comets may be evidence of mixing between high- and low-temperature regions in the solar nebula.

Hanner, Martha S.↗
NASA NTRS1991

Fabrication of cast particle-reinforced metals via pressure infiltration

A new casting process for fabrication of particle-reinforced metals is presented whereby a composite of particulate reinforcing phase in metal is first produced by pressure infiltration. This composite is then diluted in additional molten metal to obtain the desired reinforcement volume fraction and metal composition. This process produces a pore-free as-cast particulate metal-matrix composite. This process is demonstrated for fabrication of magnesium-matrix composites containing SiC reinforcements of average diameter 30, 10 and 3 microns. It is compared with the compocasting process, which was investigated as well for similar SiC particles in Mg-10 wt pct Al, and resulted in unacceptable levels of porosity in the as-cast composite.

Klier, E. M.↗