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NASA NTRSDate not supplied

Small Particle Glovebox Experiments - Preliminary Results

A substantial portion of the asteroid samples returned by the HAYABUSA2 and OSIRIS-REx missions will consist of small (submm) components (due to the collection of those particles on the asteroid surface and due to the fragmenting of larger, friable material post-collection). In order to minimize the alteration/oxidation of asteroid regolith, the bulk collections will be stored and curated in nitrogen purged gloveboxes. The processing of small particles in an N2 glovebox will present challenges that are different from those experienced during lunar and meteorite sample processing. Particles in this size range are susceptible to unpredictable electrostatic charging that can result in sample loss during processing operations. Methods for the handling of sub-mm particles have been well developed for environments with ambient atmospheric conditions and relative humidity (RH) ranges between 40-70%. In such conditions, a number of factors can be successfully employed to minimize the effects of triboelectric charging, including the use of Po-210 sources that neutralize excess charge and the utilization of conductive manipulation tools and sample substrates. However, relative humidity levels above 40% also contribute significantly to dissipation of triboelectric effects. We had not previously investigated our charge mitigation methods in a completely dry, nitrogen-purged environment, or whether they would be sufficient in enabling the successful processing of sub-mm samples. Current glovebox configurations in use in our lunar and meteorite curation laboratories are optimized for the processing of macroscopic samples and tools; these glovebox designs are likely unsuitable for the processing of collections for which the bulk collection is comprised of sub-mm components. Small particle sample preparation requires the use of an optical magnification instrument – typically a stereo binocular microscope with at least 20x magnification. Current glovebox designs are not optimized for the utilization or integration of stereo microscopes; while many current cabinets include microscope viewports that enable the use of small, externally mounted stereo microscopes, the focusing methods (usually involving the use of a lab jack) lack the fidelity and precision required for small particle manipulation and imaging. Working distances of higher (>50x magnification) objective lenses may preclude the external use of a stereo microscope through a viewport; in order to successfully manipulate and image very small (< 20m) particles, stereo and digital microscope systems that are integrated within the glovebox should be investigated. Finally, ergonomic considerations for small particle work within a glovebox must be considered to minimize risk of injury to sample processors. In order to investigate some of the unknown parameters relating to small particle processing within an N2 glovebox, we conducted preliminary, qualitative experiments utilizing a small lunar cabinet that was originally used for film development.

C. J. Snead↗
NASA NTRS1997

Boron Abundances in A and B-type Stars

Boron abundances in A- and B-type stars may be a successful way to track evolutionary effects in these hot stars. The light elements - Li, Be, and B - are tracers of exposure to temperatures more moderate than those in which the H-burning CN-cycle operates. Thus, any exposure of surface stellar layers to deeper layers will affect these light element abundances. Li and Be are used in this role in investigations of evolutionary processes in cool stars, but are not observable in hotter stars. An investigation of boron, however, is possible through the B II 1362 A resonance line. We have gathered high resolution spectra from the IUE database of A- and B-type stars near 10 solar mass for which nitrogen abundances have been determined. The B II 1362 A line is blended throughout; the temperature range of this program, requiring spectrum syntheses to recover the boron abundances. For no star could we synthesize the 1362 A region using the meteoritic/solar boron abundance of log e (B) = 2.88; a lower boron abundance was necessary which may reflect evolutionary effects (e.g., mass loss or mixing near the main-sequence), the natal composition of the star forming regions, or a systematic error in the analyses (e.g., non-LTE effects). Regardless of the initial boron abundance, and despite the possibility of non-LTE effects, it seems clear that boron is severely depleted in some stars. It may be that the nitrogen and boron abundances are anticorrelated, as would be expected from mixing between the H-burning and outer stellar layers. If, as we suspect, a residue of boron is present in the A-type supergiants, we may exclude a scenario in which mixing occurs continuously between the surface and the deep layers operating the CN-cycle. Further exploitation of the B II 1362 A line as an indicator of the evolutionary status of A- and B-type stars will require a larger stellar sample to be observed with higher signal-to-noise as attainable with the Hubble Space Telescope.

Lambert, David L.↗
NASA NTRS2000

The relationship between dietary intake, exercise, energy balance and the space craft environment

Space flight is associated with the loss of skeletal muscle, principally from muscles with anti-gravity functions. Examination of data across different missions can permit a distinction to be made between true microgravity responses and what are mission-specific responses. Protein metabolism has been investigated on six missions, four short-term [Shuttle missions Space Life Sciences 1 (1991, SLSI), Space Life Sciences 2 (1993, SLS2), Deutsche-2 (1993, D2) and the Life and Microgravity Sciences (1996, LMS)] and two long-term missions (Skylab 1993 and NASA/MIR, 1996-1998). Measurements made include dietary intake (six missions), nitrogen balance (four missions), whole-body protein kinetics with [15N]glycine as the tracer (four missions) and cortisol excretion (three missions). Also available for comparison are bed rest studies with and without exercise. The purpose of this paper is to see what can be learnt about the muscle loss problem by comparing metabolic results across the six missions for which data are available and against bed rest. The analysis suggests that there is a linkage between the inability to maintain energy balance and exercise, and the connection is the decreased efficiency of removal of the metabolic by-products of exercise (heat, CO2) during space flight.

long duration↗
NASA NTRS1978

Nitrogen abundances and isotopic compositions in stony meteorites

Nitrogen contents range from a few parts per million in ordinary chondrites and achondrites to several hundred parts per million in enstatite chondrites and carbonaceous chondrites. Four major isotopic groups are recognized: (1) C1 and C2 carbonaceous chondrites, (2) enstatite chondrites, (3) C3 chondrites, and (4) ordinary chondrites. The major variations are primary, representing isotopic abundances established at the time of condensation and accretion. Secondary processes, such as spallation reactions, solar wind implantation and metamorphic loss may cause small but observable isotopic variations in particular cases. The large isotopic difference between enstatite chondrites and carbonaceous chondrites cannot be accounted for by equilibrium condensation from a homogeneous nebular gas, and requires either unusually large kinetic effects, or a temporal or spatial variation of isotopic composition of the nebula. Nitrogen isotopic heterogeneity in the nebula due to nuclear processes has not been firmly established, but may be required to account for the large variations found within the Allende and Leoville meteorites. The unique carbonaceous chondrite, Renazzo, also requires a special source. It is not yet possible, from the meteoritic data, to establish the mode of accretion of nitrogen onto the primitive earth.

Kung, C.-C.↗
NASA NTRS1983

Influence of peroxyacetyl nitrate (PAN) on odd nitrogen in the troposphere and lower stratosphere

Nonmethane hydrocarbon breakdown in the atmosphere produces aldehydes of which a fraction are transferred into peroxyacetyl nitrates (PAN) in the presence of NO and NO2. Since ethane is destroyed photochemically primarily above 1 km, PAN can be introduced into the upper troposphere and lower stratosphere without the need to be transported from the boundary layer where most hydrocarbons are destroyed and where PAN may be lost due to thermal decomposition and heterogeneous loss. Mixing ratios of ethane in the lower troposphere increase by a factor of 4-8 from equatorial to northern mid-latitudes. This difference is directly translatable into a PAN latitude gradient. At mid-latitudes the concentration of PAN below 20 km is 0.1 ppb comparable to and in some instances larger than predicted HO2NO2 mixing ratios. Like HO2NO2 and HNO3, PAN serves as a reservoir for odd nitrogen.

Aikin, A. C.↗
NASA NTRS1993

A global analysis of the ozone deficit in the upper stratosphere and lower mesosphere

The global measurements of temperature, ozone, water vapor, and nitrogen dioxide acquired by the Limb Infrared Monitor of the Stratosphere (LIMS), supplemented by a precomputed distribution of chlorine monoxide, are used to test the balance between odd oxygen production and loss in the upper stratosphere and lower mesosphere. An efficient photochemical equilibrium model, whose validity is ascertained by comparison with the results from a fully time-dependent one-dimensional model at selected latitudes, is used in the calculations. The computed ozone abundances are systematically lower than observations for May 1-7, 1979, which suggests, contrary to the conclusions of other recent studies, a real problem in model simulations of stratospheric ozone.

Eluszkiewicz, Janusz↗
NASA NTRS2004

Quantitative Relationships between Photosynthetic, Nitrogen Fixing, and Fermentative H2 Metabolism in a Photosynthetic Microbial Mat

The ultimate potential of any microbial ecosystem to contribute chemically to its environment - and therefore, to impact planetary biogeochemistry or to generate recognizable biosignatures - depends not only on the individual metabolic capabilities of constituent organisms, but also on how those capabilities are expressed through interactions with neighboring organisms. This is particularly important for microbial mats, which compress an extremely broad range of metabolic potential into a small and dynamic system. H2 participates in many of these metabolic processes, including the major elemental cycling processes of photosynthesis, nitrogen fixation, sulfate reduction, and fermentation, and may therefore serve as a mediator of microbial interactions within the mat system. Collectively, the requirements of energy, electron transfer, and biomass element stoichiometry suggest quantitative relationships among the major element cycling processes, as regards H2 metabolism We determined experimentally the major contributions to 32 cycling in hypersaline microbial mats from Baja California, Mexico, and compared them to predicted relationships. Fermentation under dark, anoxic conditions is quantitatively the most important mechanism of H2 production, consistent with expectations for non-heterocystous mats such as those under study. Up to 16% of reducing equivalents fixed by photosynthesis during the day may be released by this mechanism. The direct contribution of nitrogen fixation to H2 production is small in comparison, but this process may indirectly stimulate substantial H2 generation, by requiring higher rates of fermentation. Sulfate reduction, aerobic consumption, diffusive and ebulitive loss, and possibly H2-based photoreduction of CO2 serve as the principal H2 sinks. Collectively, these processes interact to create an orders-of-magnitude daily variation in H2 concentrations and fluxes, and thereby in the oxidation-reduction potential that is imposed on microbial processes occuring within the mat matrix.

Hoehler, Tori M.↗
NASA NTRS1996

Nitrogen Chemistry in Titan's Upper Atmosphere

In Titan's upper atmosphere N2 is dissociated to N by solar UV and high energy electrons. This flux of N provides for interesting organic chemistry in the lower atmosphere of Titan. Previously the main pathway for the loss of this N was thought to be the formation of HCN, followed by diffusion of this HCN to lower altitudes leading ultimately to condensation. However, recent laboratory simulations of organic chemistry in Titan's atmosphere suggest that formation of the organic haze may be an important sink for atmospheric N. Because estimates of the eddy diffusion profile on Titan have been based on the HCN profile, inclusion of this additional sink for N will affect estimates for all transport processes in Titan's atmosphere. This and other implications of this sink for the N balance on Titan are considered.

McKay, Christopher P.↗
NASA NTRS1981

Ozone photochemistry and OH - A two-dimensional model study

Recent measurements of key HO(x) reaction rates are presented which imply that OH concentrations at altitudes below 30 km are lower than those predicted by current photochemical models. The consequences of the lower OH abundances are examined with respect to calculated perturbations of ozone by added nitrogen oxides, chlorine, and water vapor. Consideration is also given to the perturbation of stratospheric ozone by continuing release of chlorofluoromethanes in light of the new HO(x) reaction rates. The ozone loss is found to be reduced by about 25% compared with earlier estimates, mainly because the reduced OH abundance below 30 km slows the reaction between OH and HCl.

Whitten, R. C.↗
NASA NTRS2018

The Geology of the Pluto System

NASA's New Horizons mission acquired a large set of images and other data making possible thorough geological analysis of landscapes in the Pluto System. Pluto and Charon exhibit strikingly different surface appearances, despite their similar densities and presumed bulk compositions. Systematic investigation, modelling and mapping revealed that much of Pluto's surface is attributed to surface-atmosphere interactions and the mobilization of volatile ices by insolation. Many mapped valley systems appear to be the consequence of glaciation involving nitrogen ice. Other geological activity requires or required long periods of internal heating, such as Pluto's extensive tectonic fabric. The convection and advection of volatile ices in Sputnik Planitia are thought to be powered by present-day radiogenic heat loss. The prominent mountains at the western margin of Sputnik Planitia, and the strange, multi-km-high mound features to the south, probably composed of H2O, are young geologically as inferred by light cratering and superposition relationships. These multi-km-high mound features might be cryo-volcanoes. Their origin, and what drove their formation so late in Solar System history, is under investigation. East of Sputnik Planitia are large fields of aligned ranks of sharp-crested ridges found only at high altitude that are apparently composed of massive deposits of CH4 ice, referred to as Bladed Terrain. New Horizons found evidence that Bladed Terrain may cover much of Pluto's low latitudes and may have originally formed there as a consequence of Pluto's very high obliquity. Currently Bladed Terrain is undergoing net erosion. This observation, along with evidence for formally more extensive nitrogen glaciation implies that Pluto undergoes significant climate evolution. The dynamic remolding of landscapes by volatile transport seen on Pluto is not unambiguously evident in the mapping of Charon. Charon does, however, display a large resurfaced plain and globally engirdling extensional tectonic network attesting to its early endogenic vigor.

Moore, J. M.↗
NASA NTRS1990

Triton - Topside ionosphere and nitrogen escape

The principal ion in the ionosphere of Triton is N(+). Energetic electrons of magnetospheric origin are the primary source of ionization, with a smaller contribution due to photoionization. To explain the topside plasma scale height, it is postulated that N(+) ions escape from Triton. The loss rate is 3.4 x 10 to the 7th/sq cm per sec or 7.9 x 10 to the 24th ions/sec. Dissociative recombination of N2(+) produces neutral exothermic fragments that can escape from Triton. The rate is estimated to be 8.6 x 10 to the 6th N/sq cm per sec or 2.0 x 10 to the 24th atoms/sec. Implications for the magnetosphere of Neptune and Triton's evolution are discussed.

Yung, Y. L.↗
NASA NTRS1973

Estimates of fluid and energy balances of Apollo 17

Fluid and caloric balance has been calculated for the Apollo 17 crew. This included measurement of nitrogen, water, and caloric value of the ingested food and the volume and nitrogen content of the excreted urine and feces. Body composition changes were determined from total body water and extracellular fluid volume differences. The body composition measurements made it possible to divide the weight loss into lean body mass and adipose tissue losses. From this division a caloric equivalent was calculated. These tissue losses indicated that the caloric requirements of the mission were considerably greater than the actual caloric intake. The 3.3 kilo mean loss of body weight represented 1 kilo of lean body mass and 2.3 kilos of adipose tissue. Calculated fluid balance was more positive during the mission than during the control period. These changes are unlike the body composition and fluid balance changes reported in bedrested subjects.

Johnson, P. C.↗
NASA NTRS1976

Denitrogenation interruptions with air

A 3-h denitrogenation period at ground-level pressure with 95% O2-5% N2, with an air interruption of 5 min or more and matched with additional denitrogenation time equal to the interruption, will later result occasionally in altitude decompression sickness ('bends') during a 2-h decompression exposure at 3.8 psia (10,058 m equivalent) with 92% O2- 8% N2. Thus the equal time or 'mirror-image' make-up time for loss of denitrogenation did not prevent bends 7 times in 17 subjects during 71 exposures with air interruptions; on the other hand, no case of bends was reported after uninterrupted denitrogenation periods. Nitrogen-loading during the interruptive period is believed to resupply the bends sites with additional nitrogen, which re-establishes conditions favoring a return to a high incidence of bends.

Cooke, J. P.↗
NASA NTRS1986

Earth's early atmosphere as seen from carbon and nitrogen isotopic analysis of Archean sediments

The origin and evolution of the Earth's early atmosphere has long been a topic of great interest but determination of actual compositions over geologic time is a difficult problem. However, recent systematic studies of stromatolite deposits (Precambrian Paleobiology Research Group) has extended our knowledge of Archean ecosystems. It has been shown that many stromatolite deposits have undergone negligible alteration since their time of formation. The discovery of primary fluid inclusions within unaltered 3.5 b.y. old Archiean sediments and the observation that the 3.3 b.y. old Barberton cherts have remained closed to argon loss and have not been subjected to thermal metamorphism suggests that an opportunity exists for the direct measurement of the volatile constituents present at their time of formation. Of primary interest to this study was the possibility that the stromatolites and other Archean sediments might retain a vestige of the atmosphere and thus afford an indication of the variations in carbon dioxide and nitrogen isotopic compositions with time. A suite of essentially unaltered Archean stromatolites and the cherts of different ages and geologic sites have been analyzed for their trapped carbon dioxide and nitrogen compositions by the stepped combustion extraction tech nique utilizing static mass spectrometers for the isotope measurements.

Gibson, E. K., Jr.↗
NASA NTRS1994

Light Weight Ceramic Ablators for Mars Follow-on Mission Vehicle Thermal Protection System

New Light Weight Ceramic Ablators (LCA) were produced by using ceramic and carbon fibrous substrates, impregnated with silicone and phenolic resins. The special infiltration techniques (patent pending) were developed to control the amount of organic resins in the highly porous fiber matrices so that the final densities of LCA's range from 0.22 to 0.24 g/cc. This paper presents the thermal and ablative performance of the Silicone Impregnated Reusable Ceramic Ablators (SIRCA) in simulated entry conditions for Mars-Pathfinder in the Ames 60 MW Interaction Heating Facility (I HF). Arc jet test results yielded no evidence of char erosion and mass loss at high stagnation pressures to 0.25 atm. Minimal silica melt was detected on surface char at a stagnation pressure of 0.31 atm. Four ceramic substrates were used in the production of SIRCA's to obtain the effective of boron oxide present in substrate so the thermal performance of SIRCA's. A sample of SIRCA was also exposed to the same heating condition for five cycles and no significant mass loss or recession was observed. Tensile testing established that the SIRCA tensile strength is about a factor of two higher than that of the virgin substrates. Thermogravimetric Analysis (TGA) of the char in nitrogen and air showed no evidence of free carbon in the char. Scanning Electron Microscopy of the post test sample showed that the char surface consists of a fibrous structure that was sealed with a thin layer of silicon oxide melt.

Tran, Huy K.↗
NASA NTRS1974

NaK-nitrogen liquid metal MHD converter tests at 30 kw

The feasibility of electrical power generation with an ambient temperature liquid-metal MHD separator cycle is demonstrated by tests in which a NaK-nitrogen LM-MHD converter was operated at nozzle inlet pressures ranging from 100 to 165 N/sq cm, NaK flow rates from 46 to 72 kg/sec, and nitrogen flow rates from 2.4 to 3.8 kg/sec. The generator was operated as an eight-phase linear induction generator, with two of the eight phases providing magnetic field compensation to minimized electrical end losses at the generator channel inlet and exit.

Cerini, D. J.↗
NASA NTRS1989

Inspecting our upper atmosphere

The Upper Atmosphere Research Satellite (UARS) has been proposed for intensive studies of the 15-100 km-altitude region of the earth's atmosphere, begining in 1991. This 14,000-lb satellite will carry a suite of 10 instruments able to study the energy input and loss, photochemistry, and circulation of the upper atmosphere, as well as the extensive web of interactions among these three processes. UARS's remote sensors will give attention to the atmospheric molecular species of the nitrogen, hydrogen, and chlorine families.

Reber, C. A.↗
NASA NTRS1984

Improved materials characterization for spacecraft applications

A material outgassing test consists of an effusion cell, mass spectrometer, and thermally controlled quartz crystal microbalance (TQCM). The material sample is placed in the effusion cell at a predetermined temperature, and the sample is outgassed in a vacuum of 0.000001 torr range. The total outgassing mass as a function of time is determined with the TQCM which is cooled to LN2 temperatures. Based on the view factor of the TQCM, the total outgassed mass can be determined. The technique can be verified by comparing the results to the actual mass loss of the sample which is determined by hanging the diffusion cell from the Cohn microbalance. The mass spectrometer can be used to determine if there are any low molecular weight components outgassing, such a nitrogen which does not condense on the TQCM. After the material outgasses to a point of saturation, the effusion cell is closed off, and the TQCM is slowly heated to allow the condensed film to be broken down into its components. As the temperature is increased, the components evaporate from the surface at a different rate and can be detected with the mass spectrometer. The relative amount of each component is found by the change in frequency of the TQCM as the component evaporates. Hence, from this test, not only is isothermal kinetic data obtained, but the primary components can also be identified in terms of their molecular weight.

Cull, R.↗