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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Electrode performance parameters for a radioisotope-powered AMTEC for space power applications

The alkali metal thermoelastic converter (AMTEC) is a device for the direct conversion of heat to electricity. Recently a design of an AMTEC using a radioisotope heat source was described, but the optimum condenser temperature was hotter than the temperatures used in the laboratory to develop the electrode performance model. Now laboratory experiments have confirmed the dependence of two model parameters over a broader range of condenser and electrode temperatures for two candidate electrode compositions. One parameter, the electrochemical exchange current density at the reaction interface, is independent of the condenser temperature, and depends only upon the collision rate of sodium at the reaction zone. The second parameter, a morphological parameter, which measures the mass transport resistance through the electrode, is independent of condenser and electrode temperatures for molybdenum electrodes. For rhodium-tungsten electrodes, however, this parameter increases for decreasing electrode temperature, indicating an activated mass transport mechanism such as surface diffusion.

Underwood, M. L.↗
NASA NTRS2003

Application of Core Dynamics Modeling to Core-Mantle Interactions

Observations have demonstrated that length of day (LOD) variation on decadal time scales results from exchange of axial angular momentum between the solid mantle and the core. There are in general four core-mantle interaction mechanisms that couple the core and the mantle. Of which, three have been suggested likely the dominant coupling mechanism for the decadal core-mantle angular momentum exchange, namely, gravitational core-mantle coupling arising from density anomalies in the mantle and in the core (including the inner core), the electromagnetic coupling arising from Lorentz force in the electrically conducting lower mantle (e.g. D-layer), and the topographic coupling arising from non-hydrostatic pressure acting on the core-mantle boundary (CMB) topography. In the past decades, most effort has been on estimating the coupling torques from surface geomagnetic observations (kinematic approach), which has provided insights on the core dynamical processes. In the meantime, it also creates questions and concerns on approximations in the studies that may invalidate the corresponding conclusions. The most serious problem is perhaps the approximations that are inconsistent with dynamical processes in the core, such as inconsistencies between the core surface flow beneath the CMB and the CMB topography, and that between the D-layer electric conductivity and the approximations on toroidal field at the CMB. These inconsistencies can only be addressed with numerical core dynamics modeling. In the past few years, we applied our MoSST (Modular, Scalable, Self-consistent and Three-dimensional) core dynamics model to study core-mantle interactions together with geodynamo simulation, aiming at assessing the effect of the dynamical inconsistencies in the kinematic studies on core-mantle coupling torques. We focus on topographic and electromagnetic core-mantle couplings and find that, for the topographic coupling, the consistency between the core flow and the CMB topography is critical for correct evaluation of the coupling torque.

Kuang, Weijia↗
NASA NTRS2014

Spring Hydrology Determines Summer Net Carbon Uptake in Northern Ecosystems

Increased photosynthetic activity and enhanced seasonal CO2 exchange of northern ecosystems have been observed from a variety of sources including satellite vegetation indices (such as the Normalized Difference Vegetation Index; NDVI) and atmospheric CO2 measurements. Most of these changes have been attributed to strong warming trends in the northern high latitudes (greater than or equal to 50N). Here we analyze the interannual variation of summer net carbon uptake derived from atmospheric CO2 measurements and satellite NDVI in relation to surface meteorology from regional observational records. We find that increases in spring precipitation and snow pack promote summer net carbon uptake of northern ecosystems independent of air temperature effects. However, satellite NDVI measurements still show an overall benefit of summer photosynthetic activity from regional warming and limited impact of spring precipitation. This discrepancy is attributed to a similar response of photosynthesis and respiration to warming and thus reduced sensitivity of net ecosystem carbon uptake to temperature. Further analysis of boreal tower eddy covariance CO2 flux measurements indicates that summer net carbon uptake is positively correlated with early growing-season surface soil moisture, which is also strongly affected by spring precipitation and snow pack based on analysis of satellite soil moisture retrievals. This is attributed to strong regulation of spring hydrology on soil respiration in relatively wet boreal and arctic ecosystems. These results document the important role of spring hydrology in determining summer net carbon uptake and contrast with prevailing assumptions of dominant cold temperature limitations to high-latitude ecosystems. Our results indicate potentially stronger coupling of boreal/arctic water and carbon cycles with continued regional warming trends.

Carbon Uptake↗
NASA NTRS2012

The Influence of Internal Model Variability in GEOS-5 on Interhemispheric CO2 Exchange

An ensemble of eight atmospheric CO2 simulations was completed employing the National Aeronautics and Space Administration (NASA) Goddard Earth Observation System, Version 5 (GEOS-5) for the years 2000-2001, each with initial meteorological conditions corresponding to different days in January 2000 to examine internal model variability. Globally, the model runs show similar concentrations of CO2 for the two years, but in regions of high CO2 concentrations due to fossil fuel emissions, large differences among different model simulations appear. The phasing and amplitude of the CO2 cycle at Northern Hemisphere locations in all of the ensemble members is similar to that of surface observations. In several southern hemisphere locations, however, some of the GEOS-5 model CO2 cycles are out of phase by as much as four months, and large variations occur between the ensemble members. This result indicates that there is large sensitivity to transport in these regions. The differences vary by latitude-the most extreme differences in the Tropics and the least at the South Pole. Examples of these differences among the ensemble members with regard to CO2 uptake and respiration of the terrestrial biosphere and CO2 emissions due to fossil fuel emissions are shown at Cape Grim, Tasmania. Integration-based flow analysis of the atmospheric circulation in the model runs shows widely varying paths of flow into the Tasmania region among the models including sources from North America, South America, South Africa, South Asia and Indonesia. These results suggest that interhemispheric transport can be strongly influenced by internal model variability.

Allen, Melissa↗
NASA NTRS2006

Miniature Distillation Column for Producing LOX From Air

The figure shows components of a distillation column intended for use as part of a system that produces high-purity liquid oxygen (LOX) from air by distillation. (The column could be easily modified to produce high-purity liquid nitrogen.) Whereas typical industrial distillation columns for producing high-purity liquid oxygen and/or nitrogen are hundreds of feet tall, this distillation column is less than 3 ft (less than about 0.9 m) tall. This column was developed to trickle-charge a LOX-based emergency oxygen system (EOS) for a large commercial aircraft. A description of the industrial production of liquid oxygen and liquid nitrogen by distillation is prerequisite to a meaningful description of the present miniaturized distillation column. Typically, such industrial production takes place in a chemical processing plant in which large quantities of high-pressure air are expanded in a turboexpander to (1) recover a portion of the electrical power required to compress the air and (2) partially liquefy the air. The resulting two-phase flow of air is sent to the middle of a distillation column. The liquid phase is oxygen-rich, and its oxygen purity increases as it flows down the column. The vapor phase is nitrogen-rich and its nitrogen purity increases as it flows up the column. A heater or heat exchanger, commonly denoted a reboiler, is at the bottom of the column. The reboiler is so named because its role is to reboil some of the liquid oxygen collected at the bottom of the column to provide a flow of oxygen-rich vapor. As the oxygen-rich vapor flows up the column, it absorbs the nitrogen in the down-flowing liquid by mass transfer. Once the vapor leaves the lower portion of the column, it interacts with down-flowing nitrogen liquid that has been condensed in a heat exchanger, commonly denoted a condenser, at the top of the column. Liquid oxygen and liquid nitrogen products are obtained by draining some of the purified product at the bottom and top of the column, respectively. Because distillation is a mass-transfer process, the purity of the product(s) can be increased by increasing the effectiveness of the mass-transfer process (increasing the mass-transfer coefficient) and/or by increasing the available surface area for mass transfer through increased column height. The diameter of a distillation column is fixed by pressure-drop and mass-flow requirements. The approach taken in designing the present distillation column to be short yet capable of yielding a product of acceptably high purity was to pay careful attention to design details that affect mass-transfer processes.

Rozzi, Jay C.↗
NASA NTRS2019

Liquid Nitrogen Testing of ISRU Liquefaction Methods in Unsteady Applications

To enable NASA’s planned long duration missions, the agency is putting emphasis on reusable cryogenic systems. Such systems will require replenishing of cryogens on-orbit via a cryogenic tanker or refueling depot, and potentially on the lunar or Martian surfaces with the utilization of in-situ resources. Surface replenishing requires the in-situ production of gaseous oxygen (and hydrogen if on the lunar surface), followed by liquefaction and storage. Funded by NASA’s Advanced Exploration Systems, and managed under the Advanced Cis-Lunar Space Capability Project, the Cryogenic Fluid In-Situ Liquefaction for Landers (CryoFILL) multi center team was formed to develop a liquefaction and storage system that is efficient, reliable and scalable. This presentation will demonstrate the liquefaction and storage of “In-Situ like” propellant via a Tube-On-Tank Heat Exchanger integrated with Active Cooling (cryocooler) (verify proof of concept and obtain relevant data for model validation) and gather lessons learned from “brassboard” testing which will be applied to future liquefaction system prototype testing, then eventually to an end-to-end demonstration.

Stephens, J. R.↗
NASA NTRS1985

On the Origin of Triton and Pluto

Lyttleton's (1936) hypothesis that Triton and Pluto originated as adjacent prograde satellites of Neptune is evaluated, and it is shown that with the presently accepted masses of Triton and Pluto-Charon, the momentum and energy exchange required to sell Triton on a retrograde orbit is impossible. The Pluto-Charon system could not have acquired its present angular momentum state during an ejection event unless a physical collision was involved, which is quite unlikely. The simplest hypothesis is that Triton and Pluto are independent representatives of large outer solar system planetesimals. Triton is simply captured, with spectacular consequences that include runaway melting of interior ices and release to the surface of clathrated CH4, CO, and N2. Condensed remnants of this protoatmosphere could account for features in Triton's unique spectrum.

Mckinnon, W. B.↗
NASA NTRS1984

On the origin of Triton and Pluto

Lyttleton's (1936) hypothesis that Triton and Pluto originated as adjacent prograde satellites of Neptune is evaluated, and it is shown that with the presently accepted masses of Triton and Pluto-Charon, the momentum and energy exchange required to set Triton on a retrograde orbit is impossible. The Pluto-Charon system could not have acquired its present angular momentum state during an ejection event unless a physical collision was involved, which is quite unlikely. The simplest hypothesis is that Triton and Pluto are independent representatives of large outer solar system planetesimals. Triton is simply captured, with spectacular consequences that include runaway melting of interior ices and release to the surface of clathrated CH4, CO, and N2. Condensed remnants of this protoatmosphere could account for features in Triton's unique spectrum.

Mckinnon, W. B.↗
NASA NTRS1993

The Sub-bureau for Atmospheric Angular Momentum of the International Earth Rotation Service - A meteorological data center with geodetic applications

By exchanging angular momentum with the solid portion of the earth, the atmosphere plays a vital role in exciting small but measurable changes in the rotation of our planet. Recognizing this relationship, the International Earth Rotation Service invited the U.S. National Meteorological Center to organize a Sub-bureau for Atmospheric Angular Momentum (SBAAM) for the purpose of collecting, distributing, archiving, and analyzing atmospheric parameters relevant to earth rotation/polar motion. These functions of wind and surface pressure are being computed with data from several of the world's weather services, and they are being widely applied to the research and operations of the geodetic community. The SBAAM began operating formally in October 1989, and this article highlights its development, operations, and significance.

Salstein, David A.↗
NASA NTRS2002

Direct-Drive Gas-Cooled Reactor Power System: Concept and Preliminary Testing

This paper describes the concept and preliminary component testing of a gas-cooled, UN-fueled, pin-type reactor which uses He/Xe gas that goes directly into a recuperated Brayton system to produce electricity for nuclear electric propulsion. This Direct-Drive Gas-Cooled Reactor (DDG) is designed to be subcritical under water or wet- sand immersion in case of a launch accident. Because the gas-cooled reactor can directly drive the Brayton turbomachinery, it is possible to configure the system such that there are no external surfaces or pressure boundaries that are refractory metal, even though the gas delivered to the turbine is 1144 K. The He/Xe gas mixture is a good heat transport medium when flowing, and a good insulator when stagnant. Judicious use of stagnant cavities as insulating regions allows transport of the 1144-K gas while keeping all external surfaces below 900 K. At this temperature super-alloys (Hastelloy or Inconel) can be used instead of refractory metals. Super-alloys reduce the technology risk because they are easier to fabricate than refractory metals, we have a much more extensive knowledge base on their characteristics, and, because they have a greater resistance to oxidation, system testing is eased. The system is also relatively simple in its design: no additional coolant pumps, heat exchanger, or freeze-thaw systems are required. Key to success of this concept is a good knowledge of the heat transfer between the fuel pins and the gas, as well as the pressure drop through the system. This paper describes preliminary testing to obtain this key information, as well as experience in demonstrating electrically heated testing of simulated reactor components.

Wright, S. A.↗
NASA NTRS2003

Thermally Simulated Testing of a Direct-Drive Gas-Cooled Nuclear Reactor

This paper describes the concept and preliminary component testing of a gas-cooled, UN-fueled, pin-type reactor which uses He/Xe gas that goes directly into a recuperated Brayton system to produce electricity for nuclear electric propulsion. This Direct-Drive Gas-Cooled Reactor (DDG) is designed to be subcritical under water or wet-sand immersion in case of a launch accident. Because the gas-cooled reactor can directly drive the Brayton turbomachinery, it is possible to configure the system such that there are no external surfaces or pressure boundaries that are refractory metal, even though the gas delivered to the turbine is 1144 K. The He/Xe gas mixture is a good heat transport medium when flowing, and a good insulator when stagnant. Judicious use of stagnant cavities as insulating regions allows transport of the 1144-K gas while keeping all external surfaces below 900 K. At this temperature super-alloys (Hastelloy or Inconel) can be used instead of refractory metals. Super-alloys reduce the technology risk because they are easier to fabricate than refractory metals, we have a much more extensive knowledge base on their characteristics, and, because they have a greater resistance to oxidation, system testing is eased. The system is also relatively simple in its design: no additional coolant pumps, heat exchanger, or freeze-thaw systems are required. Key to success of this concept is a good knowledge of the heat transfer between the fuel pins and the gas, as well as the pressure drop through the system. This paper describes preliminary testing to obtain this key information, as well as experience in demonstrating electrical thermal simulation of reactor components and concepts.

Godfroy, Thomas↗
NASA NTRS2016

Active Flow Control (AFC) and Insect Accretion and Mitigation (IAM) System Design and Integration on the Boeing 757 ecoDemonstrator

This paper presents a systems overview of how the Boeing and NASA team designed, analyzed, fabricated, and integrated the Active Flow Control (AFC) technology and Insect Accretion Mitigation (IAM) systems on the Boeing 757 ecoDemonstrator. The NASA Environmentally Responsible Aviation (ERA) project partnered with Boeing to demonstrate these two technology systems on a specially outfitted Boeing 757 ecoDemonstrator during the spring of 2015. The AFC system demonstrated attenuation of flow separation on a highly deflected rudder and increased the side force generated. This AFC system may enable a smaller vertical tail to provide the control authority needed in the event of an engine failure during takeoff while still operating in a conventional manner over the rest of the flight envelope. The AFC system consisted of ducting to obtain air from the Auxiliary Power Unit (APU), a control valve to modulate the system mass flow, a heat exchanger to lower the APU air temperature, and additional ducting to deliver the air to the AFC actuators located on the vertical tail. The IAM system demonstrated how to mitigate insect residue adhesion on a wing's leading edge. Something as small as insect residue on a leading edge can cause turbulent wedges that interrupt laminar flow, resulting in an increase in drag and fuel use. The IAM system consisted of NASA developed Engineered Surfaces (ES) which were thin aluminum sheet substrate panels with coatings applied to the exterior. These ES were installed on slats 8 and 9 on the right wing of the 757 ecoDemonstrator. They were designed to support panel removal and installation in one crew shift. Each slat accommodated 4 panels. Both the AFC and IAM flight test were the culmination of several years of development and produced valuable data for the advancement of modern aircraft designs.

Alexander, Michael G.↗
NASA NTRSDate not supplied

GeoNEX-ML: A Machine Learning System for Earth Observations

Improved capabilities of earth monitoring satellites are enabling a wide range of studies on the environmental effects of climate change, often leveraging the recent advancements in machine learning. At the same time, the new capabilities, including higher spatial resolution and temporal frequency, are expanding the amount of data generated at exponential rates. At the NASA Earth eXchange (NEX), we build deep learning methods to learn from cross sensor satellite-based Earth observations for generating new datasets with efficient processing techniques. Using current generation geostationary satellites on NEX, we present an interchangeable set of machine models to perform spectral adjustment, physical model emulation, LEO-GEO emulation, and optical flow. These tools are used to generate consistent virtual observations across sensors, perform atmospheric correction and cloud detection, and estimate land surface temperature and atmospheric winds. This approach aims to improve the robustness of remotely sensed data processing by learning from diverse sets of observations while enabling near real-time and on-demand capabilities.

Geostationary↗
NASA NTRSDate not supplied

Atmospheric winds with deep optical flow

Improved capabilities of earth monitoring satellites are enabling a wide range of studies on the environmental effects of climate change, often leveraging the recent advancements in machine learning. At the same time, the new capabilities, including higher spatial resolution and temporal frequency, are expanding the amount of data generated at exponential rates. At the NASA Earth eXchange (NEX), we build deep learning methods to learn from cross sensor satellite-based Earth observations for generating new datasets with efficient processing techniques. Using current generation geostationary satellites on NEX, we present an interchangeable set of machine models to perform spectral adjustment, physical model emulation, LEO-GEO emulation, and optical flow. These tools are used to generate consistent virtual observations across sensors, perform atmospheric correction and cloud detection, and estimate land surface temperature and atmospheric winds. This approach aims to improve the robustness of remotely sensed data processing by learning from diverse sets of observations while enabling near real-time and on-demand capabilities.

Atmospheric winds↗
NASA NTRS1972

The aluminum electrode in AlCl3-alkali-halide melts.

Passivation phenomena have been observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and omega to the minus 1/2 power. Upon cathodic polarization, dendrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/sq cm at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/sq cm were measured.

Holleck, G. L.↗
NASA NTRS1987

Impact of thermal energy storage properties on solar dynamic space power conversion system mass

A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overalll system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1880 kg/cu m.

Juhasz, Albert J.↗
NASA NTRS1987

Impact of thermal energy storage properties on solar dynamic space power conversion system mass

A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overall system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1800 kg/cu m).

Juhasz, Albert J.↗
NASA NTRS1990

Theoretical characterization of the potential energy surface for H + N2 yields HN2. II - Computed points to define a global potential

A previous calculation for H + N2 (Walch et al., 1989) focused on the minimum energy path (MEP) region of the potential energy surface and on estimates of the lifetime of the HN2 species. In this paper, energies computed at geometries selected to permit a global representation of the potential energy surface (PES) are reported. As in the previous work, the calculations were performed using the complete active space self-consistent field/externally contracted configuration interaction method. The surface was characterized using the same basis set as in the previous paper except that an improved contraction of the H s-basis is used. Calculations with a larger basis set were carried out along an approximate MEP obtained with the smaller basis set. The new PES exhibits a sharp curvature, which was not present in the previous calculations, and has a slightly narrower and smaller barrier to dissociation. Saddle points for H atom exchange via collinear and T shaped HN2 complexes are also reported.

Walch, Stephen P.↗