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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Noble gas isotopes and halogens in volatile-rich inclusions in diamonds

Application of the (40)Ar-(39)Ar method and noble gas studies to diamonds has increased our understanding of their age relationships to the host kimberlite or lamproite, and of the source and composition of volatile-rich fluids in the upper mantle. The properties of diamond (inert, high mechanical strength and low gas diffusivities) means they are especially useful samples for studying gases trapped deep within the earth (less than 150 km) as they are unlikely to have undergone loss or exchange of entrapped material since formation. Volatile-rich fluids (H2O-CO2) are important agents for metasomatic processes in the upper mantle, and the noble gases and halogens preferentially partition into this phase leading to a strong geochemical coherence between these groups of elements. The abundances of the halogens in the major reservoirs of the Earth shows a marked progression from chlorine, concentrated in the oceans, through to iodine which, through its affinity to organic material, is concentrated mainly in sediments. Abundances in the upper mantle are low. This is particularly true for iodine which is of special interest in view of its potential significance as an indicator of sediment recycling and by way of its link to (129)Xe amomalies in the mantle through the low extinct isotope (129)I. Extensions of the (40)Ar-(39)Ar technique enable measurements of halogens and other elements (K, Ca, Ba, U) by production of noble gas isotopes from these species during neutron irradiation. Samples analyzed in this way include 15 coated stones from an unknown source in Zaire, 3 boarts from the Jwaneng and 1 boart from the Orapa kimberlites, both in Botswana.

Burgess, Raymond↗
NASA NTRS1994

Volatiles, rheology, and mantle convection: Comparing Earth, Venus, and Mars

Silicate rheology is controlled in part by volatile content. The variation of viscosity with position in the mantle will influence the nature of mantle convection; hence, modeling mantle convection and its effect on surface observables such as the geoid places constraints on the viscosity structure of a planet's mantle and may indirectly constrain the volatile distribution. Models of viscous mantle flow and the Earth's geoid indicate that there is roughly a two order of magnitude variation in viscosity between the upper and lower mantles, although there is some disagreement over the depth of the viscosity minimum in the upper mantle. Some studies of post-glacial rebound also support such a viscosity contrast between the upper and lower mantles. On Venus, several highland regions appear to be supported by mantle plumes. Modeling of the geoid and topography of these regions indicates that if these features are plume-related, then the mantle of Venus can not have an Earth-like low viscosity zone in its upper mantle. On Mars, the Tharsis volcanic province has alternatively been explained as supported either by mantle convection or by flexure of a thick lithosphere. If the convective model is correct, then the large geoid anomaly requires that Mars can not have a low viscosity zone in its upper mantle.

Kiefer, Walter S.↗
NASA NTRS1995

Fixture For Sampling Volatile Materials In Containers

Fixture based on T-connector enables mass-spectrometric analysis of volatile contents of cylindrical containers without exposing contents to ambient conditions. Used to sample volatile contents of pressurized containers, contents of such enclosed processing systems as gas-phase reactors, gases in automotive emission systems, and gas in hostile environments.

Melton, Donald↗
NASA NTRS1996

Workshop on Evolution of Martian Volatiles

Different aspects of martian science are discussed. Topics covered include: early Mars volatile inventory, evolution through time, geological influences, present atmospheric properties, soils, exobiology, polar volatiles, and seasonal and diurnal cycles

Jakosky, B.↗
NASA NTRS1998

Vertical Profiles of Cloud Condensation Nuclei, Condensation Nuclei, Optical Aerosol, Aerosol Optical Properties, and Aerosol Volatility Measured from Balloons

Under the support of this grant a balloon-borne gondola containing a variety of aerosol instruments was developed and flown from Laramie, Wyoming, (41 deg N, 105 deg W) and from Lauder, New Zealand (45 deg S, 170 deg E). The gondola includes instruments to measure the concentrations of condensation nuclei (CN), cloud condensation nuclei (CCN), optically detectable aerosol (OA.) (r greater than or equal to 0.15 - 2.0 microns), and optical scattering properties using a nephelometer (lambda = 530 microns). All instruments sampled from a common inlet which was heated to 40 C on ascent and to 160 C on descent. Flights with the CN counter, OA counter, and nephelometer began in July 1994. The CCN counter was added in November 1994, and the engineering problems were solved by June 1995. Since then the flights have included all four instruments, and were completed in January 1998. Altogether there were 20 flights from Laramie, approximately 5 per year, and 2 from Lauder. Of these there were one or more engineering problems on 6 of the flights from Laramie, hence the data are somewhat limited on those 6 flights, while a complete data set was obtained from the other 14 flights. Good CCN data are available from 12 of the Laramie flights. The two flights from Lauder in January 1998 were successful for all measurements. The results from these flights, and the development of the balloon-bome CCN counter have formed the basis for five conference presentations. The heated and unheated CN and OA measurements have been used to estimate the mass fraction of the aerosol volatile, while comparisons of the nephelometer measurements were used to estimate the light scattering, associated with the volatile aerosol. These estimates were calculated for 0.5 km averages of the ascent and descent data between 2.5 km and the tropopause, near 11.5 km.

Deshler, T.↗
NASA NTRS1999

Characterization of Regolith Volatile Transport and Storage Properties by The MECA MSP 2001 Lander Payload

The diffusive and adsorptive properties of the Martian regolith influence the exchange of volatiles between the atmosphere and subsurface. Our quantitative knowledge of these properties is extremely poor -introducing substantial uncertainties in efforts to model long-term evolution of ground ice and diurnal, seasonal, and climatic cycles of CO2 and H20. This situation should significantly improve upon arrival of the 2001 Mars Surveyor Lander in 2002. In support of the Human Exploration and Development of Space (HEDS) enterprise, the 2001 mission will include a suite of instruments to characterize the nature of the Martian environment and assess whether it contains hazards that may threaten future human exploration. A major element of this effort is the Mars Environmental Compatibility Assessment (MECA) payload, which consists an optical microscopy system incorporating electrostatic, magnetic, and scratch-hardness materials testing palets, an atomic force microscope with imaging capabilities comparable to an SEM, a wet chemistry laboratory with four independent test cells, an electrometer on the robotic arm, material test patches, a camera also mounted on the arm, and a soil scoop for excavating down to about 50 cm into the soil. Although conceived to address the needs of HEDS, MECA payload is a sophisticated soil science laboratory that should provide a wealth of new data relevant to the volatile transport and storage properties of the regolith. Additional information os contained in the original.

Clifford, S. M.↗
NASA NTRS2000

Differential Scanning Calorimetry of Volatile-Bearing Iron Minerals Under Mars-Like Pressures: New Insights Into Energetics and Mechanisms of Thermal Decomposition

In this study, we have examined the thermal decomposition of two volatile-bearing iron minerals, in particular, lepidocrocite (gamma-FeOOH) and siderite (FeCO3), under Mars-like pressures. Both minerals exhibit different enthalpic events during their decomposition at reduced atmospheric pressures when compared to those at ambient pressure. These differences in energetics are related to the mechanisms of thermal decomposition at Mars-like pressures. Such knowledge regarding the thermal stability of volatile-bearing minerals on Mars will provide useful information for planetary surface processes.

Lin, I.-C.↗
NASA NTRS1999

A Second-Generation Volatile Organic Analyzer for the International Space Station

Early in the development of the Crew Health Care System (CHECS) for the International Space Station (ISS), it was recognized that detection of target volatile organic compounds would be a key component of the air monitoring strategy. Experiences during the NASA/Mir program supported the decision to include a real-time volatile organic analyzer (VOA) aboard ISS to help assess the impact of air quality events on crew health and determine the effectiveness of decontamination efforts. Toward this end, a joint development by the Toxicology Laboratory at Johnson Space Center and Graseby Dynamics produced a VOA that has been delivered and is ready for the first 5 years of ISS operation. The first-generation VOA selection criteria included minimizing size, weight, and power consumption while maintaining analytical performance. Measuring available technologies against these criteria, a VOA system based upon gas chromatography/ion mobility spectrometry (GC/IMS) was selected in the mid-90's. However, as NASA looks forward to later-stage ISS operations and to new frontiers such as human exploration of Mars, the ISS VOA (weighing 43 kg and consuming 160 watts) must be replaced by a smaller, less resource-intensive device. This paper will present a possible second-gene ration VOA based upon the same technology as the first-generation unit. Utilizing GC/IMS technology again will permit the instrumental data and experience gained during the initial phase of ISS to be applied to later ISS phases and advanced spacecraft missions. During the past 3 years, efforts to reduce the size of ion mobility spectrometers have been pursued by Graseby Dynamics, the manufacturer of the first-generation VOA. The concept of operation, expected analytical performance, and estimated size of a fully functional second-generation VOA based upon GC/mini-IMS technology will be presented. Furthermore, results of initial laboratory evaluations will be shown.

Limero, Thomas↗
NASA NTRS2001

An FPGA-Based Test-Bed for Reliability and Endurance Characterization of Non-Volatile Memory

Memory technologies are divided into two categories. The first category, nonvolatile memories, are traditionally used in read-only or read-mostly applications because of limited write endurance and slow write speed. These memories are derivatives of read only memory (ROM) technology, which includes erasable programmable ROM (EPROM), electrically-erasable programmable ROM (EEPROM), Flash, and more recent ferroelectric non-volatile memory technology. Nonvolatile memories are able to retain data in the absence of power. The second category, volatile memories, are random access memory (RAM) devices including SRAM and DRAM. Writing to these memories is fast and write endurance is unlimited, so they are most often used to store data that change frequently, but they cannot store data in the absence of power. Nonvolatile memory technologies with better future potential are FRAM, Chalcogenide, GMRAM, Tunneling MRAM, and Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) EEPROM.

Rao, Vikram↗
NASA NTRS2002

Oxidation and Volatilization of Silica-Formers in Water Vapor

At high temperatures SiC and Si3N4 react with water vapor to form a silica scale. Silica scales also react with water vapor to form a volatile Si(OH)4 species. These simultaneous reactions, one forming silica and the other removing silica, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved, After steady state is achieved, the oxide found on the surface is a constant thickness and recession of the underlying material occurs at a linear rate. The steady state oxide thickness, the time to achieve steady state, and the steady state recession rate can all be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate can also be determined from parameters that describe a water vapor-containing environment. Accordingly, maps have been developed to show these steady state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of silica formers in water-vapor containing environments such as combustion environments. Finally, these maps are used to explore the limits of the paralinear oxidation model for SiC and Si3N4

Opila, E. J.↗
NASA NTRS2002

Modeling the Stability of Volatile Deposits in Lunar Cold Traps

There are several mechanisms acting at the cold traps that can alter the inventory of volatiles there. Primarily, the lunar surface is bombarded by meteoroids which impact, melt, process, and redistribute the regolith. Further, solar wind and magnetospheric ion fluxes are allowed limited access onto the regions in permanent shadow. Also, although cold traps are in the permanent shadow of the Sun, there is a small flux of radiation incident on the regions from interstellar sources. We investigate the effects of these space weathering processes on a deposit of volatiles in a lunar cold trap through simulations. We simulate the development of a column of material near the surface of the Moon resulting from space weathering. This simulation treats a column of material at a lunar cold trap and focuses on the hydrogen content of the column. We model space weathering processes on several time and spatial scales to simulate the constant rain of micrometeoroids as well as sporadic larger impactors occurring near the cold traps to determine the retention efficiency of the cold traps. We perform the Monte Carlo simulation over many columns of material to determine the expectation value for hydrogen content of the top few meters of soil for comparison with Lunar Prospector neutron data.

Crider, D. H.↗
NASA NTRS2004

Volatile Element Geochemistry in the Lower Atmosphere of Venus

We computed equilibrium abundances of volatile element compounds as a function of altitude in Venus lower atmosphere. The elements included are generally found in volcanic gases and sublimates on Earth and may be emitted in volcanic gases on Venus or volatilized from its hot surface. We predict: 1) PbS, Bi2S3, or possibly a Pb-Bi sulfosalt are the radar bright heavy metal frost in the Venusian highlands; 2) It should be possible to determine Venus' age by Pb-Pb dating of PbS condensed in the Venusian highlands, which should be a representative sample of Venusian lead; 3) The gases HBr, PbCl2, PbBr2, As4O6, As4S4, Sb4O6, BiSe, InBr, InCl, Hg, TlCl, TlBr, SeS, Se2-7, HI, I, I2, ZnCl2, and S2O have abundances greater than 0.1 ppbv in our nominal model and may be spectroscopically observable; 4) Cu, Ag, Au, Zn, Cd, Ge, and Sn are approx. 100 % condensed at the 740 K (0 km) level on Venus.

Schaefer, L.↗
NASA NTRS2004

Volatility of Common Protective Oxides in High-Temperature Water Vapor: Current Understanding and Unanswered Questions

Many structural materials rely on the formation of chromia, silica or alumina as a protective layer when exposed in high temperature oxidizing environments. The presence of these oxide layers provides a protective diffusion barrier which slows down further oxidation. In atmospheres containing water vapor, however, reactions to form volatile hydroxide species occur which remove the surface oxide, thus, lowering the protective capability of the oxide scale. This paper summarizes the current understanding of volatility of chromia, silica and alumina in water vapor containing combustion environments. In addition unanswered questions in each system are discussed. Th current paper represents an update on the considerable information learned in the past five years for these systems.

Opila, Elizabeth J.↗
NASA NTRS2004

From Dust to Planets: The Tale Told by Moderately Volatile Element Depletion (MOVED)

The pronounced depletion of moderately volatile elements (MOVE, that condense or evaporate at temperatures in the range 1350-650K) relative to the average solar composition is a characteristic feature in most primitive chondrites and bulk terrestrial planets. It differs from the composition of the Sun and from the materials further away from the Sun (CI chondrites). None of the remaining planets or even meteorites shows an enrichment of volatile elements that would balance the depletion in the inner Solar System. Whether this depletion occurred in solar nebular stage or in planetary formation stage has been the subject of long lasting debate. The search for mysterite initiated in 1973 continues today in search of lost planets. Here I show that the MOVED patterns demonstrate a clear connection between the rocky materials of the inner solar system and the interstellar dust. The inheritance of interstellar materials by the solar system is not only documented by the presence of presolar grains, various isotopic anomalies, but also expressed in the chemical element distribution in the inner solar system.

Yin, Qing-Zhu↗
NASA NTRS2005

Experiment to Characterize Aircraft Volatile Aerosol and Trace-Species Emissions (EXCAVATE)

The Experiment to Characterize Aircraft Volatile and Trace Species Emissions (EXCAVATE) was conducted at Langley Research Center (LaRC) in January 2002 and focused upon assaying the production of aerosols and aerosol precursors by a modern commercial aircraft, the Langley B757, during ground-based operation. Remaining uncertainty in the postcombustion fate of jet fuel sulfur contaminants, the need for data to test new theories of particle formation and growth within engine exhaust plumes, and the need for observations to develop air quality models for predicting pollution levels in airport terminal areas were the primary factors motivating the experiment. NASA's Atmospheric Effects of Aviation Project (AEAP) and the Ultra Effect Engine Technology (UEET) Program sponsored the experiment which had the specific objectives of determining ion densities; the fraction of fuel S converted from S(IV) to S(VI); the concentration and speciation of volatile aerosols and black carbon; and gas-phase concentrations of long-chain hydrocarbon and PAH species, all as functions of engine power, fuel composition, and plume age.

Anderson, B. E.↗
NASA NTRS2005

A Theoretical Investigation of Oxidation Efficiency of a Volatile Removal Assembly Reactor Under Microgravity Conditions

Volatile Removal Assembly (VRA) is a subsystem of the Closed Environment Life Support System (CELSS) installed in the International Space Station. It is used for removing contaminants (volatile organics) in the wastewater produced by the space station crews. The major contaminants are formic acid, ethanol, and propylene glycol. The VRA contains a slim packbed reactor (3.5 cm diameter and four 28 cm long tubes in series) to perform catalyst oxidation of wastewater at elevated pressure and temperature under microgravity conditions. In the reactor, the contaminants are burned with oxygen gas (O2) to form water and carbon dioxide (CO2) that dissolves in the water stream. Optimal design of the reactor requires a thorough understanding about how the reactor performs under microgravity conditions. The objective of this study was to develop a mathematical model to interpret experimental data obtained from normal and microgravity conditions, and to predict the performance of VRA reactor under microgravity conditions. Catalyst oxidation kinetics and the total oxygen-water contact area control the efficiency of catalyst oxidation for mass transfer, which depends on oxygen gas holdup and distribution in the reactor. The process involves bubbly flow in porous media with chemical reactions in microgravity environment. This presents a unique problem in fluid dynamics that has not been studied. Guo et al. (2004) developed a mathematical model that predicts oxygen holdup in the VRA reactor. No mathematical model has been found in the literature that can be used to predict the efficiency of catalyst oxidation under microgravity conditions.

Guo, Boyun↗
NASA NTRS2007

Revalidation of the Volatile Organic Analyzer Following a Major On-Orbit Maintenance Activity

The Volatile Organic Analyzer (VOA) contributes to the assessment of air quality aboard the International Space Station (ISS) by identifying and quantifying target airborne volatile organic contaminants in the module air. This on-orbit contaminant monitoring capability becomes particularly important during an air quality degradation event such as a system leak. During several ISS air quality degradations, the VOA has generated near real-time data that was used to make decisions or to better understand the contingency. The VOA was operational from January 2002 through June 2003, during which time it was validated by comparing VOA data to simultaneously acquired grab sample containers (GSCs). In January 2003, one of the two analytical channels of the VOA was shutdown because of a component failure, but a redundant channel continued to supply the necessary analytical data. In June 2003, the sole remaining channel was deactivated. Initial assessments of the channel shutdowns pointed to failed fuses or heaters, but neither was considered repairable on orbit. In 2005, it was determined that failed fuses could be replaced on orbit and the crew conducted a diagnostic procedure to identify the failed component. The crew discovered that both channels incurred failed fuses, which lead to a subsequent on orbit maintenance activity and return of the VOA to operational status in December 2005. The VOA has been providing data on the ISS atmosphere since its reactivation in 2005 and this paper will present the VOA data collected during 2006. Special emphasis will be placed upon the revalidation of the repaired VOA using GSCs as well as a summary of the diagnostic and repair procedures.

Limero, Thomas↗
NASA NTRS2007

Volatile Organic Analyzer (VOA) in 2006: Repair, Revalidation, and Restart of Elektron Event

The Volatile Organic Analyzer (VOA) was launched to the International Space Station (ISS) in August 2001 and was the first instrument to provide near real-time measurement of volatile organic compounds in a spacecraft atmosphere. The VOA performed an analysis of the ISS air approximately twice a month for most of its operation through May 2003. This intermittent operation, caused by a software interface issue with the ISS communication bus, slowed the validation of the VOA. However, operational validation was completed in 2003 when analysis of air samples collected in grab sample containers (GSCs) compared favorably with simultaneous VOA runs (1). The VOA has two channels that provide redundant function, albeit at slightly reduced performance, when only one channel is operating (2). Most target compounds can be detected on both channels. In January 2003, the VOA identified a malfunction in the channel 2 preconcentrator and it shut down that channel. The anomaly profile suggested that a fuse might have failed, but the root cause could not be determined. In May 2003, channel 1 was shut down when the detector s elevated temperature could not longer be maintained. Since both VOA channels were now deactivated, VOA operations ended until an in-flight repair could be planned and executed. This paper describes the process to repair the VOA and to revalidate it for operations, and then an account is given of the VOA s contribution following a contingency event on ISS.

Limero, Thomas↗