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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

The structure of Io's thermal corona and implications for atmospheric escape

A steady-state model of Io's exospheric corona and its interaction with the Io plasma torus is used to study the escape of species from Io's atmosphere. It is found that atmospheric sputtering is the major escape mechanism for models in which the plasma flow reaches the critical level, and that such models produce total mass-loading rates an order of magnitude larger than values inferred from observations. The results suggest the presence of an extended Na coronal component in the thermal exosphere, and are consistent with an O-dominated corona, an exospheric temperature of about 1000 K, an Na critical level mixing ratio of 0.001, and a critical level radius of about 1.5 Io radii.

Summers, M. E.↗
NASA NTRS2000

Internal and External reconnection in a Series of Homologous Solar Flares

Using data from the Extreme Ultraviolet Telescope (EIT) on SOHO and the Soft X-ray Telescope (SXT) on Yohkoh, we examine a series of morphologically homologous solar flares occurring in NOAA AR 8210 over May 1-2, 1998. An emerging flux region (EFR) impacted against a sunspot to the west and next to a coronal hole to the east is the source of the repeated flaring. An SXT sigmoid parallels the EFR's neutral line at the site of the initial flaring in soft X-rays. In EIT, each flaring episode begins with the formation of a crinkle pattern external to the EFR. These EIT crinkles move out from, and then in toward, the EFR with velocities approximately 20 km/s. A shrinking and expansion of the width of the coronal hole coincides with the crinkle activity, and generation and evolution of a postflare loop system begins near the. time of crinkle formation. Using a schematic based on magnetograms of the region, we suggest that these observations are consistent with the standard reconnection-based model for solar eruptions, but modified by the presence of the additional magnetic fields of the sunspot and coronal hole. In the schematic, internal reconnection begins inside of the EFR-associated fields, unleashing a flare, postflare loops, and a CME. External reconnection, first occurring between the escaping CME and the coronal hole field, and second occurring between fields formed as a result of the first external reconnection, results in the EIT crinkles and changes in the coronal hole boundary. By the end of the second external reconnection, the initial setup is reinstated; thus the sequence can repeat, resulting in morphologically homologous eruptions. Our inferred magnetic topology is similar to that suggested in the "breakout model" of eruptions [Antiochos, 1998], although we cannot determine if our eruptions are released primarily by the breakout mechanism (external reconnection) or, alternatively, are released primarily by the internal reconnection.

Sterling, Alphonse C.↗
NASA NTRSDate not supplied

Ground Testing of the MISSE-16 Materials

The harsh space environment imposes very stringent requirements upon spacecraft materials, especially those located on exterior surfaces of space objects in low Earth orbit (LEO). As humankind moves from space exploration to space commercialization, these materials may have to last for 15–20 years without considerable degradation of their optical, electrical, mechanical, and thermal properties. Operational requirements dictate that these materials continue to function according to expectations. Hence, we must understand the effects of the space environment on materials currently in use as well as on untested materials. For the years, the Materials International Space Station Experiment Flight Facility (MISSE-FF) have flown many different materials to investigate the effect of LEO space weather exposure on the performance and durability of materials and devices. The MISSE-16 scientific team members plan to launch fifteen different novel and well-characterized spacecraft-relevant materials to the LEO environment for a duration of six months during the MISSE-16 mission. Changes in spectral reflectivity will be measured throughout the mission as the samples are exposed to the space environment. The same chemical damage the produces changes in optical reflectance also causes changes in numerous other physical properties such as electrical conductivity, mechanical strength, and chemical reactivity. Correlation of the changes in each of these properties as a function of radiation type, flux, and fluence allows various material properties to be inferred from one experimentally tractable measurement: color change. Flying identical test fixtures on the ram, zenith, and wake positions of the MISSE-FF, collecting spectrally resolved images of the materials, and concomitantly measuring the ambient space environment allows deconvolution of the material effects which occur as a result of exposure to neutral atomic oxygen (AO), unfiltered solar ultraviolet (UV) radiation, and electrons. The flight experiment will function as a ground truth reference for our team’s ongoing laboratory-based space weather-material interactions experiments. Comparison of the MISSE-16 data with extensive testing of “flight-duplicate” samples under simulated space weather conditions will enable development of chemical models for prediction of material degradation. This paper discusses preliminary results from the ground test campaign including measurements of UV/VIS/IR reflectance spectra, bidirectional reflectance distribution function (BRDF), surface potential decay, and surface morphology under electron and AO exposure.

Elena A. Plis↗
NASA NTRS1973

Mechanisms for Mars dust storms.

Characteristics of the Mars global dust storm are reviewed. At the Mariner 9 encounter, the dust consisted of highly absorbing particles distributed rather uniformly up to great height (about 50 km). These observations together with temperature distributions inferred from the Mariner 9 IRIS by Hanel et al. (1972) are used to estimate global wind systems during the dust storm. The global distribution and direction of light surface streaks indicate that the axisymmetric circulation was a dominant part of flow during the dust storm. The axisymmetric winds may become strong enough to raise dust over wide areas of Mars' tropics under unusual conditions: the incoming solar radiation must be near its seasonal maximum, the static stability must be low, and the atmosphere must be able to absorb and re-emit a sizeable fraction of the incoming radiation. Strong winds around the periphery of the retreating south polar cap would be driven by the temperature gradient at the cap edge and by the mass outflow due to subliming CO2. These polar winds could generate local dust storms, raising the general level of dustiness, and providing the conditions necessary for onset of a global dust storm.

Leovy, C. B.↗
NASA NTRS1973

Mechanisms of inert gas narcosis

Experiments describing the mechanism of inert gas narcosis are reported. A strain of mice, genetically altered to increase susceptibility to botulin poisoning (synaptic response) appears to increase metabolic rates while breathing argon; this infers a genetically altered synaptic response to both botulin toxin and narcotic gases. Studies of metabolic depression in human subjects breathing either air or a 30% mixture of nitrous oxide indicate that nitrous oxide narcosis does not produce pronounced metabolic depression. Tests on mice for relative susceptibilities to narcosis and oxygen poisoning as a function of fatty membrane composition show that alteration of the fatty acid composition of phospholipids increases resistance to metabolically depressant effects of argon but bas no effect on nitrous oxide narcosis. Another study suggests that acclimatization to low tension prior to high pressure oxygen treatment enhances susceptibility of mice to convulsions and death; developing biochemical lesions cause CNS metabolite reductions and pulmonary damage.

Source record↗
NASA NTRS1997

Premixed Flame-Vortex Interactions Imaged in Microgravity

A unique experiment makes it now possible to obtain detailed images in microgravity showing how an individual vortex causes the wrinkling, stretching, area increase, and eventual extinction of a premixed flame. The repeatable, controllable flame-vortex interaction represents the fundamental building block of turbulent combustion concepts. New information is provided that is central to turbulent flame models, including measurements of all components of flame stretch, strain, and vorticity. Simultaneous measurements of all components of these quantities are not possible in fully turbulent flames but are possible in the present axisymmetric, repeatable experiment. Advanced PIV diagnostics have been used at one-g and have been developed for microgravity. Numerical simulations of the interaction are being performed at NRL. It is found that microgravity conditions greatly augment the flame wrinkling process. Flame area and the amplitude of wrinkles at zero-g are typically twice that observed at one-g. It is inferred that turbulent flames in microgravity could have larger surface area and thus propagate significantly faster than those in one-g, which is a potential safety hazard. A new mechanism is identified by PIV images that shows how buoyancy retards flame wrinkling at one-g; buoyancy produces new vorticity (due to baroclinic torques) that oppose the wrinkling and the stretch imposed by the original vortex. Microgravity conditions remove this stabilizing mechanism and the amplitude of flame wrinkling typically is found to double. Microgravity also increases the flame speed by a factor of 1.8 to 2.2. Both methane and propane-air flames were studied at the NASA Lewis drop tower. Results indicate that it is important to add buoyancy to models of turbulent flames to simulate the correct flame wrinkling, stretch and burning velocity.

Driscoll, J. F.↗
NASA NTRS1999

The Thermal Structure of Triton's Middle Atmosphere

The atmospheric structure of Triton in the altitude range 25-150 kilometers shows an unexpectedly steep thermal gradient of 0.26 K per kilometer above 50 kilometer altitude, with a nearly isothermal profile below. The upper part of the profile can be explained by downward conduction of heat deposited by magnetospheric electrons and solar UV. However, the atmospheric temperature below 50 kilometers is too cold for identified radiative processes to dispose of the inferred heat flux (0.0012 erg per square centimeter per second) from the upper atmosphere. This implies that either the atmosphere is not in a steady state and/or an unidentified cooling mechanism is at work in the altitude range 25-50 kilometers. When extrapolated to the surface, the inversion results yield a pressure of 19.0 sup (+1.8) sub (-1.5), mubar, about 5mubar greater than that observed by Voyager.

Elliot, J. L.↗
NASA NTRS1990

CLIPS enhanced with objects, backward chaining and explanation facilities

In this project we extend C Language Production System (CLIPS), an existing Expert System shell, by creating three new options. Specifically, first we create a compatible with CLIPS environment that allows for defining objects and object hierarchies, second we provide means to implement backward chaining in a pure forward chaining environment, and finally we give some simple explanation facilities for the derivations the system has made. Objects and object hierarchies are extended so that facts can be automatically inferred, and placed in the fact base. Backward chaining is implemented by creating run time data structures which hold the derivation process allowing for a depth first search. The backward chaining mechanism works not only with ground facts, but also creates bindings for every query that involves variables, and returns the truth value of such a query as well as the relevant variable bindings. Finally, the WHY and HOW explanation facilities allow for a complete examination of the derivation process, the rules triggered, and the bindings created. The entire system is integrated with the original CLIPS code, and all of its routines can be invoked as CLIPS commands.

Aldrobi, M.↗
NASA NTRS2000

Antarctic Rebound and the Time-Dependence of the Earth's Shape

Great strides have been made during the past 30 years in refining models of the last global glaciation. The refinements draw upon a vastly expanded relative sea level and sedimentary core record. Furthermore, we now possess a sharpened understanding of the mechanisms that drive climate changes associated with deglaciation. Some 15 years ago, using only 5.5 years of ranging data, analyses of the drift in LAGEOS I node acceleration was used to infer that postglacial rebound was responsible for a secular change in the Earth's ellipsoidal shape (Yoder et al., .1983]. Today there exists a wealth of geodynamics satellite orbit data that constrain the secular time-dependence of the Earth's shape and low order gravity field, which includes mass redistribution from present-day glacier and great ice sheet imbalance and from postglacial rebound. We have shown that an unambiguous determination of the secular variation in the Earth's pear shaped harmonic (l = 3, m = 0) might provide information that bears on the present-day mass balance of Antarctica. This issue is revisited in light of new constraints on glacial loading during the late-Pleistocene and Holocene. An especially critical issue for the interpretation of secular odd degree zonal harmonics, l = 3 to 7, is the timing and magnitude of the deglaciation of Antarctica from Last Glacial Maximum. We explore ways in which the recovery of secular variation in both zonal and non-zonal harmonics for l = 2 through 7 can improve constraints on both rebound and present-day ice sheet balance.

Ivins, Erik R.↗
NASA NTRS2016

Magnetic-Island Contraction and Particle Acceleration in Simulated Eruptive Solar Flares

The mechanism that accelerates particles to the energies required to produce the observed high-energy impulsive emission in solar flares is not well understood. Drake et al. proposed a mechanism for accelerating electrons in contracting magnetic islands formed by kinetic reconnection in multi-layered current sheets (CSs). We apply these ideas to sunward-moving flux ropes (2.5D magnetic islands) formed during fast reconnection in a simulated eruptive flare. A simple analytic model is used to calculate the energy gain of particles orbiting the field lines of the contracting magnetic islands in our ultrahigh-resolution 2.5D numerical simulation. We find that the estimated energy gains in a single island range up to a factor of five. This is higher than that found by Drake et al. for islands in the terrestrial magnetosphere and at the heliopause, due to strong plasma compression that occurs at the flare CS. In order to increase their energy by two orders of magnitude and plausibly account for the observed high-energy flare emission, the electrons must visit multiple contracting islands. This mechanism should produce sporadic emission because island formation is intermittent. Moreover, a large number of particles could be accelerated in each magneto hydro dynamic-scale island, which may explain the inferred rates of energetic-electron production in flares. We conclude that island contraction in the flare CS is a promising candidate for electron acceleration in solar eruptions.

Guidoni, S. E.↗
NASA NTRS1978

Sodium D-line emission from Io - Comparison of observed and theoretical line profiles

High-resolution spectra of the D-line profiles have been obtained for Io's sodium emission cloud. These lines, which are produced through resonance scattering of sunlight, are broad and asymmetric and can be used to infer source and dynamical properties of the sodium cloud. In this paper we compare line profile data with theoretical line shapes computed for several assumed initial velocity distributions corresponding to various source mechanisms. We also examine the consequences of source distributions which are nonuniform over the surface of Io. It is found that the experimental data are compatible with escape of sodium atoms from the leading hemisphere of Io and with velocity distributions characteristic of sputtering processes. Thermal escape and simple models of plasma sweeping are found to be incompatible with the observations.

Carlson, R. W.↗
NASA NTRS1981

Information theory lateral density distribution for Earth inferred from global gravity field

Information Theory Inference, better known as the Maximum Entropy Method, was used to infer the lateral density distribution inside the Earth. The approach assumed that the Earth consists of indistinguishable Maxwell-Boltzmann particles populating infinitesimal volume elements, and followed the standard methods of statistical mechanics (maximizing the entropy function). The GEM 10B spherical harmonic gravity field coefficients, complete to degree and order 36, were used as constraints on the lateral density distribution. The spherically symmetric part of the density distribution was assumed to be known. The lateral density variation was assumed to be small compared to the spherically symmetric part. The resulting information theory density distribution for the cases of no crust removed, 30 km of compensated crust removed, and 30 km of uncompensated crust removed all gave broad density anomalies extending deep into the mantle, but with the density contrasts being the greatest towards the surface (typically + or 0.004 g cm 3 in the first two cases and + or - 0.04 g cm 3 in the third). None of the density distributions resemble classical organized convection cells. The information theory approach may have use in choosing Standard Earth Models, but, the inclusion of seismic data into the approach appears difficult.

Rubincam, D. P.↗
NASA NTRS1983

Entwined and parallel bundled orbits as alternative models for narrow planetary ringlets

Particle orbits can be bundled in two different ways to produce narrow, Uranus-type ringlets. The usual assumption is that they are packed in a parallel manner in a structure that is essentially only two-dimensional, but it is then difficult to explain the large numbers of particles per unit area of the ring plane that are inferred from the observations. The alternative of a bundle of entwined orbits produces a three-dimensional structure of potentially large projected areal density. A start has been made in identifying possible mechanisms for stabilizing these structures, but much remains to be done, particularly for the less-studied model of entwined orbits. The two models might be discriminated observationally by differences in the motion of the line of intersection of the orbital and equatorial planes, and by the predicted radial reversal (entwined) or nonreversal (parallel) of features in occultation signatures taken at certain longitudes.

Eshleman, V. R.↗
NASA NTRS1984

The nonaxisymmetric baroclinic instability in thin accretion disks

The instability of linear, nonaxisymmetric baroclinic waves in the radiative regions of a thin accretion disk is investigated with simplifying assumptions used in the representation of the structure of the basic state. As in stars with rotation laws deviating from rotation on cylinders, the departure from barotropy ('baroclinicity') resulting from such rotation feeds potential energy from the basic state into the kinetic energy of the baroclinic motions. The baroclinic instability is considered as a possible mechanism for driving turbulence in disks. Estimations of the Reynolds stress from baroclinic waves indicate that the degree of baroclinicity in stationary disk models is insufficient to account for the large viscosity inferred from observations of, e.g., cataclysmic variables.

Cabot, W.↗
NASA NTRS1988

An expert system approach to turbopump health monitoring

A preliminary report is presented on the development of a system for monitoring the High Pressure Oxidizer Turbopump of the SSME. System development will proceed by defining the degradation mechanism of the turbopump, identifying those conventional and advanced sensor measurements that can monitor these mechanisms, and determining the digital processing requirements for these measurements. Once the failures and associated measurements have been defined, an expert system will be developed that can make both diagnostic and prognostic inferences about the condition and performance of the turbopump.

Perry, John G.↗
NASA NTRS1993

Oxygen ionization rates at Mars and Venus - Relative contributions of impact ionization and charge exchange

Oxygen ion production rates above the ionopauses of Venus and Mars are calculated for photoionization, charge exchange, and solar wind electron impact ionization processes. The latter two require the use of the Spreiter and Stahara (1980) gas dynamic model to estimate magnetosheath velocities, densities, and temperatures. The results indicate that impact ionization is the dominant mechanism for the production of O(+) ions at both Venus and Mars. This finding might explain both the high ion escape rates measured by Phobos 2 and the greater mass loading rate inferred for Venus from the bow shock positions.

Zhang, M. H. G.↗
NASA NTRS1993

Microstructural analysis of the 2195 aluminum-lithium alloy welds

The principal objective of this research was to explain a tendency of 2195 Al-Li alloy to crack at elevated temperature during welding. Therefore, a study was made on the effect of welding and thermal treatment on the microstructure of Al-Li Alloy 2195. The critical roles of precipitates, boundaries, phases, and other features of the microstructure were inferred from the crack propagation paths and the morphology of fracture surface of the alloy with different microstructures. Particular emphasis was placed on the microstructures generated by the welding process and the mechanisms of crack propagation in such structures. Variation of the welding parameters and thermal treatments were used to alter the micro/macro structures, and they were characterized by optical and scanning electron microscopy. A theoretical model is proposed to explain changes in the microstructure of welded material. This model proposes a chemical reaction in which gases from the air (i.e., nitrogen) release hydrogen inside the alloy. Such a reaction could generate large internal stresses capable to induce porosity and crack-like delamination in the material.

Talia, George E.↗