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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

An Io thermal model with intermittent volcanism

Observations have indicated that heat flow out of Io at present may be several times greater than the heat input from enhanced tidal heating; this may indicate that the observed heat flow is intermittent, rather than continuous. A two-dimensional time-dependent thermal model of Io was constructed to examine the relationship between enhanced tidal heating, heat flow within the body, and surface volcanism. From the models one can conclude that (1) a simple homogeneous body cannot maintain enhanced tidal heating in a thin crust, but such heating is possible if the crust contains an insulating layer, as of sulfur; (2) this sulfur layer will be subject to melting by heat from the interior, resulting in hotspots which can expel heat much more rapidly than tidal heating inputs it; and (3) the location of these hotspots will vary in time and space; they can appear anywhere on the surface, even if tidal heating is concentrated at the poles, and they seem to occur roughly 10% of the time.

Consolmagno, G. J.↗
NASA NTRS1985

Sintered Lining for Heat-Pipe Evaporator

Hotspots eliminated by lining inner wall. Distribution of heat transfer liquid in heat-pipe evaporator improved by lining inner wall with layer of sintered metal. Sintered layer takes place of layer of screen wick formerly sintered or bonded to wall. Since sintered layer always full of liquid, no hotspot of type that previously arose where former screen wick did not fit properly against wall.

Ernst, D. M.↗
NASA NTRS1985

High-speed photometry of Z Chamaeleontis covering the 1983 March normal outburst

High-speed photometry over a three-week period covering the Mar. 13, 1983 normal outburst of Z Cha is presented. Multicolor observations revealed significant reddening during eclipse in both the quiescent and outburst states. Quiescent primary eclipse timings remained consistent with an increasing orbital period. Hotspot eclipse timings revealed that the accretion disk had physically expanded in radius after the outburst. The duration of the eclipse during outburst, however, limited the optical emission to a region bounded by the radius of the preoutburst accretion disk. In the final stages of decline this emission region had shrunk in size by a factor of approximately 4. The postoutburst observations showed the hotspot eclipse to be less stable in structure compared to before the outburst.

Cook, M. C.↗
NASA NTRS1986

High-Performance Heat Pipe With Screen Mesh

Liquid distributed more evenly in evaporator section. Improved heat pipe contains an artery and wick rolled from stainless-steel screen of 180 mesh (openings about 80 micrometers). Screen material helps to prevent dryout in evaporator section by conducting liquid through hotspots and to vaporchannel wall. Insert reduces incidence of dryout at hotspots or during intervals of general thermal overload.

Alario, J. P.↗
NASA NTRS1988

Deccan volcanism at the Cretaceous-Tertiary boundary

The accuracy with which one can claim that Deccan trap volcanism occurred at the Cretaceous-Tertiary boundary (KTB) over a very short time interval is of key importance in deciding whether a volcanic origin of the KTB events should be taken seriously. In the two years since paleomagnetic, paleontological and geodynamic evidence was published, further data have become available and the case now appears to be well constrained. The Ar-40/Ar-39 results from six labs have yielded some 24 reliable plateau ages that narrow the age range to 65 to 69 Ma. Moreover, it appears that a significant part of this range results from inter-lab spread and possible minor alteration. Paleontology demonstrates that volcanism started in the Maestrichtian, more precisely in the A. mayaroensis zone. Paleomagnetism shows that volcanism spanned only 3 chrons and only one correlation remains possible, that of the main central reversed chron with 29R. Therefore, whereas Ar-40/Ar-39 is able only to restrict the duration of volcanism to some 4 Ma, paleomagnetism restricts it to 0.5 Ma. Using some geochemical indicators such as C-13 as proxy, it is suggested that volcanism actually consists of a few shorter events of unequal magnitude. Extrusion rates may be as high as 100 cu km/yr and fissure lengths as long as several 100 km. Such a scenario appears to be at least as successful as others in accounting for most anomalies observed at the KTB. Particularly important are Iridium and other platinum group elements (PGE) profiles, Sr-87/Sr-86, C-13, 0-18, other exotic geochemical signatures, spherules, soot, shocked minerals, selective and stepwise extinctions. The environmental impact of CO2 possibly released during explosive phases of volcanism, and SO2 released during effusive phases, and the ability of volcanism to ensure worldwide distribution of KTB products are now all addressed. In conclusion, the case for a causal link between internal hotspot activity, birth of the Reunion hotspot itself as the Deccan and KTB events appears to rest on an increasingly stronger basis.

Courtillot, V.↗
NASA NTRS1988

Flood basalts and mass extinctions

There appears to be a correlation between the times of flood basalts and mass-extinction events. There is a correlation of flood basalts and hotspot tracks--flood basalts appear to mark the beginning of a new hotspot. Perhaps there is an initial instability in the mantle that bursts forth as a flood basalt but then becomes a steady trickle that persists for many tens of millions of years. Suppose that flood basalts and not impacts cause the environmental changes that lead to mass-extinctions. This is a very testable hypothesis: it predicts that the ages of the flows should agree exactly with the times of extinctions. The Deccan and K-T ages agree with this hypothesis; An iridium anomaly at extinction boundaries apparently can be explained by a scaled-up eruption of the Hawaiian type; the occurrence of shocked-quartz is more of a problem. However if the flood basalts are all well dated and their ages indeed agree with extinction times, then surely some mechanism to appropriately produce shocked-quartz will be found.

Morgan, W. Jason↗
NASA NTRS1988

Flood basalt eruptions, comet showers, and mass extinction events

A chronology of initiation dates of the major continental flood basalt episodes has been established from compilation of published K-Ar and Ar-Ar ages of basaltic flows and related basic intrusions. The dating is therefore independent of the biostratigraphic and paleomagnetic time scales, and the estimated errors of the inititation dates are approximately + or - 4 pct. There are 11 distinct episodes of continental flood basalts known during the past 250 Myr. The data show that flood basalt episodes are generally relatively brief geologic events, with intermittent eruptions during peak output periods lasting ony 2 to 3 Myr or less. Statistical analyses suggest that these episodes may have occurred quasi-periodically with a mean cycle time of 32 + or - 1 Myr. The initiation dates of the flood basalts are close to the estimated dates of marine mass extinctions and impact-crater clusters. Although a purely internal forcing might be argued for the flood basalt volcanism, quasi-periodic comet impacts may be the trigger for both the flood basalts and the extinctions. Impact cratering models suggest that large-body impactors lead to deep initial cratering, and therefore may cause mantle disturbances and initiate mantle plume activity. The flood basalt episodes commonly mark the initiation or jump of a mantle hotspot, and are often followed by continental rifting and separation. Evidence from dynamical studies of impacts, occurrences of craters and hotspots, and the geochemistry of boundary layers is synthesized to provide a possible model of impact-generated volcanism. Flood basalt eruptions may themselves have severe effects on climate, and possibly on life. Impacts might, as a result, have led to mass extinctions through direct atmospheric disturbances, and/or indirectly through prolonged flood basalt volcanism.

Rampino, Michael R.↗
NASA NTRS1990

Evidence for age and evolution of Corner seamounts and Great Meteor seamount chain from multibeam bathymetry

The morphology of the Corner and Cruiser seamounts is discussed and the apparent age of seamount geomorphic features that are thought to have formed at sea level is derived. High-resolution, multibeam bathymetry of the seamounts shows geomorphic features such as guyots and terraces. The pattern of volcanism is consistent with the sequential formation of the New England, Corner, and Great Meteor chain seamounts above the New England hotspot. However, Late Cretaceous and Cenozoic absolute motion of the African plate over the hotspot differs significantly from predictions of the existing models. The derived age pattern of volcanism indicates formation of the Corner seamounts at ca. 80 Ma to 76 Ma.

Tucholke, Brian E.↗
NASA NTRS1991

SO2-rich equatorial basins and epeirogeny of Io

Comparison of Io's large scale topography with an SO2 abundance map shows that SO2 is concentrated in equatorial topographic basins. In these basins, about 30 pct. of the surface is covered by SO2 at all elevations above the mean triaxial figure, and SO2 coverage increases with decreasing elevation to as much as 56 pct. at elevations below -1.5 km. The correlation is not good from long 240 to 360 degs where bright areas are covered by red, Pele type plume fallout, and in the polar regions where the topography is poorly known. The histogram of SO2 abundance binned by elevation appears bimodal, with a secondary concentration of SO2 at high elevations, but it is not certain that this is significant. Additional observations suggest that the basins have relatively little higher frequency topographic relief. The distribution of active plumes and hotspots show no obvious correlation with the topography. However, the Pele type plume all erupted from regions higher than the mean figure, and five of the eight Prometheus type plumes are more energetic and are associated with high temperature hotspots, whereas Prometheus type plumes are long lived and require large volatile reservoirs.

Mcewen, Alfred S.↗
NASA NTRS1992

Global distribution and characteristics of coronae and related features on Venus - Implications for origin and relation to mantle processes

The increased coverage and resolution of Magellan images and altimetry data have resulted in significant new identifications of coronae and coronalike features and more detailed information on corona morphology, topography, and distribution. The distribution of coronae and coronalike features in Magellan data are assessed in the light of the proposed hotspot origin of these features. The basic characteristics of coronae are then compared with other possible hotspot features on Venus (e.g., major volcanic shields and domelike highlands) in a first-order assessment of the implications of mantle plume-related features on Venus for interior convective processes.

Stofan, Ellen R.↗
NASA NTRS1993

Structure of axisymmetric mantle plumes

The structure of axisymmetric subsolidus thermal plumes in the earth's lower mantle is inferred from calculations of axisymmetric thermal plumes in an infinite Prandtl number fluid with thermally activated viscosity. The velocity and temperature distribution is determined for axisymmetric convection above a heated disk in an incompressible fluid cylinder 2,400 km in height and 1,200 km in diameter. Several calculations of plumes with heat transport in the range 100-400 GW, similar to the advective heat transport at the Hawaiian hotspot, are presented. Hotspot formation by plumes originating at the base of the mantle requires both large viscosity variations and a minimum heat transport.

Olson, Peter↗
NASA NTRS1993

Helium-3 from the mantle - Primordial signal or cosmic dust?

Helium-3 in hotspot magmas has been used as unambiguous evidence for the existence of a primordial, undegassed reservoir deep in the Earth's mantle. However, a large amount of helium-3 is delivered to the Earth's surface by interplanetary dust particles (IDPs). Recycling of deep-sea sediments containing these particles to the mantle, and eventual incorporation in magma, can explain the high helium-3/helium-4 ratios of hotspot magmas. Basalts with high helium-3/helium-4 ratios may represent degassing of helium introduced by ancient (probably 1.5 to 2.0 billion years old) pelagic sediments rather than degassing of primordial lower mantle material brought to the surface in plumes. Influx of IDPs can also explain the neon and siderophile compositions of mantle samples.

Anderson, Don L.↗
NASA NTRS1994

Venus' center of figure-center of mass offset

Magellan altimetry data reveal that the center of figure (CF) of Venus is displaced approximately 280 m from its center of mass (CM) toward 4.4 deg S, 135.8 deg E, a location in Aphrodite Terra. This offset is smaller than those of other terrestrial planets but larger than the estimated error, which is no more than a few tens of meters. We examine the possibility that the CF-CM offset is related to specific geologic provinces on Venus by deriving three simple models for the offset: a thick-crust model, a hotspot model, and a thick-lithosphere model. The offset caused by a region of thick crust depends upon the region's extent, the crust-mantle density contrast, and the thickness of excess crust. A hotspot-related offset depends on the extent of the thermally anomalous region and the magnitude of the thermal anomaly. Offset due to a region of thick lithosphere depends upon the extent of the region, the average temperature contrast across the lithosphere, and the amount of excess lithosphere. We apply the three models to Venus plateau-shaped highlands, volcanic rises, and lowlands, respectively, in an attempt to match the observed CF-CM offset location and magnitude. The influence of most volcanic rises and of Ishtar Terra on the CF-CM offset must be quite small if we are to explain the direction of the observed offset. The lack of influence of volcanic rises can be explained if the related thermal anomalies are limited to a few hundred degrees or less and are plume-shaped (i.e., characterized by a flattened sublithospheric `head' with a narrow cylindrical feeder `tail'). The unimportance of Ishtar Terra is most easily explained if it lies atop a significant mantle downwelling.

Bindschadler, Duane L.↗
NASA NTRS1995

Large Topographic Rises on Venus: Implications for Mantle Upwelling

Topographic rises on Venus have been identified that are interpreted to be the surface manifestation of mantle upwellings. These features are classified into groups based on their dominant morphology. Atla and Beta Regiones are classified as rift-dominated, Dione, western Eistla, Bell, and Imdr Regiones as volcano-dominated, and Themis, eastern Eistla, and central Eistla Regiones as corona-dominated. At several topographic rises, geologic indicators were identified that may provide evidence of uplifted topography (e.g., volcanic flow features trending upslope). We assessed the minimum contribution of volcanic construction to the topography of each rise, which in general represents less than 5% of the volume of the rise, similar to the volumes of edifices at terrestrial hotspot swells. The total melt volume at each rise is approximated to be 10(exp 4) - 10(exp 6) cu km. The variations in morphology, topography, and gravity signatures at topographic rises are not interpreted to indicate variations in stage of evolution of a mantle upwelling. Instead, the morphologic variations between the three classes of topographic rises are interpreted to indicate the varying influences of lithospheric structure, plume characteristics, and regional tectonic environment. Within each class, variations in topography, gravity, and amount of volcanism may be indicative of differing stages of evolution. The similarity between swell and volcanic volumes for terrestrial and Venusian hotspots implies comparable time-integrated plume strengths for individual upwellings on the two planets.

Stofan, Ellen R.↗
NASA NTRS2000

Constraints on Particles and Fields from X-Ray Data

We review emission processes for the handful of extragalactic radio sources which produce X-rays from hotspots and knots in radio jets. In almost all cases, the emitting feature shows a large gradient in radio brightness, indicative of the presence of a strong shock. Since both thermal and synchrotron self Compton models face severe difficulties (except for the hotspots of Cygnus A and 3C 295), the most likely explanation is the presence of gamma = 10(exp 7) electrons producing X-ray synchrotron emission. The major problems remaining are why so few features have been detected so far and why has no optical emission been detected in some cases. While a somewhat unique situation exists for 3C 390.3, serious problems remain for Pictor A, 3C 120, and the quasar jets in 3C 273 and PKS 0637.

Harris, D. E.↗
NASA NTRS2002

Recent Results from Galileo PPR at Io: Orbits I31 and I32

Recent Galileo PPR (Photo-Polarimeter Radiometer) results will be shown, including global day and nighttime maps, high latitude regional maps, and high-resolution scans across hotspots and from pole to pole. SO2 vapor pressure, global heatflow, and hotspot power outputs are estimated. Additional information is contained in the original extended abstract.

Rathbun, J. A.↗
NASA NTRS2002

Insights into Corona Formation through Statistical Analyses

Statistical analysis of an expanded database of coronae on Venus indicates that the populations of Type 1 (with fracture annuli) and 2 (without fracture annuli) corona diameters are statistically indistinguishable, and therefore we have no basis for assuming different formation mechanisms. Analysis of the topography and diameters of coronae shows that coronae that are depressions, rimmed depressions, and domes tend to be significantly smaller than those that are plateaus, rimmed plateaus, or domes with surrounding rims. This is consistent with the model of Smrekar and Stofan and inconsistent with predictions of the spreading drop model of Koch and Manga. The diameter range for domes, the initial stage of corona formation, provides a broad constraint on the buoyancy of corona-forming plumes. Coronae are only slightly more likely to be topographically raised than depressions, with Type 1 coronae most frequently occurring as rimmed depressions and Type 2 coronae most frequently occuring with flat interiors and raised rims. Most Type 1 coronae are located along chasmata systems or fracture belts, while Type 2 coronas are found predominantly as isolated features in the plains. Coronae at hotspot rises tend to be significantly larger than coronae in other settings, consistent with a hotter upper mantle at hotspot rises and their active state.

Glaze, L. S.↗
NASA NTRS2007

Compact and Integrated Liquid Bismuth Propellant Feed System

Operation of Hall thrusters with bismuth propellant has been shown to be a promising path toward high-power, high-performance, long-lifetime electric propulsion for spaceflight missions [1]. There has been considerable effort in the past three years aimed at resuscitating this promising technology and validating earlier experimental results indicating the advantages of a bismuth-fed Hall thruster. A critical element of the present effort is the precise metering of propellant to the thruster, since performance cannot be accurately assessed without an accurate accounting of mass flow rate. Earlier work used a pre./post-test propellant weighing scheme that did not provide any real-time measurement of mass flow rate while the thruster was firing, and makes subsequent performance calculations difficult. The motivation of the present work is to develop a precision liquid bismuth Propellant Management System (PMS) that provides hot, molten bismuth to the thruster while simultaneously monitoring in real-time the propellant mass flow rate. The system is a derivative of our previous propellant feed system [2], but the present system represents a more compact design. In addition, all control electronics are integrated into a single unit and designed to reside on a thrust stand and operate in the relevant vacuum environment where the thruster is operating, significantly increasing the present technology readiness level of liquid metal propellant feed systems. The design of various critical components in a bismuth PMS are described. These include the bismuth reservoir and pressurization system, 'hotspot' flow sensor, power system and integrated control system. Particular emphasis is given to selection of the electronics employed in this system and the methods that were used to isolate the power and control systems from the high-temperature portions of the feed system and thruster. Open loop calibration test results from the 'hotspot' flow sensor are reported, and results of integrated thruster/PMS tests demonstrate operation of the feed system in the relevant environment.

Polzin, Kurt A.↗