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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 NTRS1973

Design of various fixed-geometry water-lubricated hydrodynamic journal bearings for maximum stability

This publication is the result of over 260 fractional-frequency-whirl stability tests on a variety of fixed-geometry journal bearings. It is intended principally as a guide in the selection and design of antiwhirl bearings that must operate at high speeds and low loads in low-viscosity fluids such as water or liquid metals. However, the various fixed-geometry configurations can be employed as well in applications where other lubricants, such as oil, are used and fractional-frequency whirl is a problem. The important parameters that effect stability are discussed for each bearing type, and design curves to facilitate the design of optimum-geometry bearings are included. A comparison of the stability of the different bearing configurations tested is also given.

Schuller, F. T.↗
NASA NTRS1974

Development of fine diameter mullite fiber

Results are presented of a program to develop and evaluate mullite fiber with a mean diameter under two microns. The two micron fiber is produced by a blowing process at room temperature from a low viscosity (10-25 poise) solution. The blown fiber was evaluated for dimensional stability in thermal cycling to 1371 C, and was equivalent to the 5 micron spun B and W mullite fiber. An additive study was conducted to evaluate substitutes for the boron. Three levels of chromium, lithium fluoride, and magnesium were added to the standard composition in place of boron and the fiber produced was evaluated for chemical and dimensional stability in thermal cycling to 1371 C. The magnesium was the most chemically stable, but the chrome additive imparted the best dimensional stability.

Long, W. G.↗
NASA NTRS1973

Lava flows in Mare Imbrium - Geologic evaluation from Apollo orbital photography

A study of Apollo photographs indicates that all Eratosthenian age mare deposits in the Imbrium basin consist of extensive lava flows from a single eruptive source region bounded by 18 to 23 N and 28 to 32 W in the south-southwest corner of the basin. It is suggested that three major eruptive periods occurred between 3.0 plus or minus 0.4 and 2.5 plus or minus 0.3 b.y. Lavas assigned to these three phases extended for 1200, 600, and 400 km, respectively, over slopes approaching 1:1000. These materials cover an area of 200,000 sq km and have a volume of perhaps 40,000 cu km. The vent source of the youngest lava phase appears to be a 20 km long, structurally controlled fissure at 22 deg 50 min N and 31 deg 20 min W. The flow heights and lengths are consistent with the lunar gravity and imply extremely high rates of lava extrusion with low viscosity of the basalt melt playing a secondary role. The location of the volcanic source region on the intersection of major ring faults from two large basins suggests a basin structural control.

Schaber, G. G.↗
NASA NTRS1974

In situ polymerization of monomers for polyphenylquinoxaline/graphite fiber composites

Methods currently used to prepare fiber reinforced, high temperature resistant polyphenylquinoxaline (PPQ) composites employ extremely viscous, low solids content solutions of high molecular weight PPQ polymers. An improved approach, described in this report, consists of impregnating the fiber with a solution of the appropriate monomers instead of a solution of previously synthesized high molecular weight polymer. Polymerization of the monomers occurs in situ on the fiber during the solvent removal and curing stages. The in situ polymerization approach greatly simplifies the fabrication of PPQ graphite fiber composites. The use of low viscosity monomeric type solutions facilitates fiber wetting, permits a high solids content, and eliminates the need for prior polymer synthesis.

Serafini, T. T.↗
NASA NTRS1974

The thermal state and internal structure of Mars

The evolution and state of the interior of Mars are studied through the use of theoretically calculated thermal history and density models. Invoking melting of an Fe-FeS mixture permits initial core formation within the first billion years. At the present time the core radius ranges from about 1300 to 1800 km, depending on composition, and the core is liquid even if the composition is varied from the eutectic. Large-scale differentiation of the silicates occurs in the last 2 b.y. When the mean density is 3.96 g/cu cm, the radius is 3389 km, and the moment of inertia factor is 0.377, the density models indicate high mantle densities near 3.74 g/cu cm. Thus an FeO content of about 29% is implied, consistent with the production of a low-viscosity magma. Chemical models of the Martian mantle indicate a composition primarily of olivine with about 56% forsterite.

Johnston, D. H.↗
NASA NTRS1975

Study of diffusion coefficients of glasses under zero-G

Diffusion studies of the glass forming ion are examined in zero-g environments and diffusion data obtained from these experiments are unique because of earth based experimental problems. The choice of system for diffusion studies is discussed along with the lab processing. The space processing is described consisting of a heating cycle designed to maximize time exposed to the diffusion temperature without exposing the low viscosity melt to gravitational forces.

Kinser, D. L.↗
NASA NTRS1974

Lunar deposits of possible pyroclastic origin

Orange glass droplets sampled from the Apollo 17 site were found to be both chemically and texturally homogeneous. None of these droplets, which are of possible pyroclastic origin, contained shock-damaged crystals which are common in glass produced by meteorite impacts. Black droplets are apparently the partially crystallized equivalents of the orange glass. Since chemically and texturally homogeneous glass droplets are known to form in terrestrial lava fountains of basaltic melt, the orange glasses from Apollo 11 and 17 sites and the green glasses from the Apollo 15 site may have formed in lava fountains of low-viscosity lunar basaltic magmas.

Heiken, G. H.↗
NASA NTRS1975

Tidal friction and the early history of the moon's orbit

The present work investigates the consequences implied by various rheological models of the early earth for the orbital history of the moon subsequent to its formation. Models of the earth that yield small tidal angles, such as low-viscosity models, imply that the moon never orbited in the earth's equatorial plane, thereby ruling out an equatorial origin for the moon. A high-viscosity model is shown to permit the moon to originate in the equatorial plane and still account for the present-day characteristics of the moon's orbit.

Rubincam, D. P.↗
NASA NTRS1974

Stabilization of lunar core samples

Processing of lunar cores includes: (1) careful dissection for study of loose fines, and (2) stabilization of the residue by peeling and impregnation. The newly developed technique for preparing thin peels of lunar cores requires application of the methacrylate adhesive to a backing strip, before taking the peel. To ensure complete impregnation of the very fine, dry lunar soil, the low-viscosity epoxy, Araldite 506, is gently flowed onto the core, under vacuum.

Nagle, J. S.↗
NASA NTRS1975

Numerical simulation of interacting, three-dimensional vortex filaments

Unsteady three-dimensional fluid flows which are characterized by low viscosity and the presence of distinct regions of high vorticity embedded in an otherwise irrotational flow are considered, taking into account the case in which an intermingling of vortex filaments appears. Incompressible flows of the considered type are simulated with the aid of an approach in which the vorticity distribution is modeled in terms of continuous closed filaments. It is attempted to track these filaments in a Lagrangian reference frame.

Leonard, A.↗
NASA NTRS1978

Improved epoxy adhesive with radiographic tracer

Addition of tungsten powder (4 percent by weight) to commercially available low viscosity epoxy adhesive, yields nonmetal composite repair material with enhanced radiographic contrast for radiographic and ultrasonic inspection techniques.

Campbell, R. G.↗
NASA NTRS1977

A possible explanation of the mechanism of formation of the equatorial jet on the surface of Jupiter

Formation of the equatorial jet of the Jovian surface was explained as a consequence of the Taylor-Proudman theorem. The asymptotic theory of motion of low viscosity fluids in a rotating spherical shear layer was included. The model shows the straited structure of the Jovian surface as the outflow of convective cells having the shape of axisymmetric rolls extended along the axis of rotation in the meridional direction. Depth of the layer was found to be of the order of 1000 kilometers.

Yavorskaya, I. M.↗
NASA NTRS1977

A model for eruption behavior of a volcanic vent in eastern Mare Serenitatis

The origin is considered of droplets of ultramafic composition which are present in all soils collected from the mare surface at the Apollo 17 landing site. The droplets consist of homogeneous orange glass or their partially crystallized equivalent, the black droplets. These clastic deposits have a mean grain size of 40 micrometers. The droplet formation ages range from 3.5 to 3.83 b.y. It has been proposed that the droplets formed as a spray of low viscosity melt during lava fountaining. Based upon the thermal history as determined by studying olivine and particle shapes, two models for the formation of the sequence of droplets represented by samples 74001 and 74220 are presented. Both models assume, as proposed by Heiken et al. (1974), that the droplets were formed as a spray from a lava fountain and the compound forms were evidence for 'recycling' of solid, cooler droplets back into the fountain, encountering molten droplets before being deposited.

Heiken, G.↗
NASA NTRS1978

Primitive atmosphere and implications for the formation of channels on Mars

It is suggested that, if primitive Mars had a reducing atmosphere composed mainly of methane, this atmosphere could be polymerized by solar ultraviolet radiation to produce higher hydrocarbons. These compounds, which would be low-viscosity liquids at present temperatures on Mars, could have contributed to the formation of channels. The Martian atmosphere model used in the analysis is similar to Sagan's (1977), except that ammonia is omitted. Major reactions in this early Martian atmosphere are examined, and the number densities of the lighter alkanes in the lower atmosphere of Mars are determined. Since the photochemical mechanism investigated here would provide only a modest amount of fluid for a comparatively brief period of time (10-100 million years), liquid alkanes would not be the major factor in the formation of the channels, although their derivatives could contribute to the greenhouse effect or depress the freezing point of water.

Yung, Y. L.↗
NASA NTRS1979

Isentropic decompression of fluids from crustal and mantle pressures

Criteria are derived according to which the flow of single-phase magmatic fluids and the rarefaction expansion of low-viscosity liquids and gases may be considered approximately isentropic. Graphs of entropy vs. density with contours of constant pressure and mass fraction are used to examine the possible thermodynamic histories of H2O and CO2 decompressing isentropically from crustal and upper mantle pressures; these graphs offer a simple visual representation of a number of thermodynamic variables involved in isentropic processes. It is shown how the graphs can be used to examine the behavior of volatiles that (1) ascend in volcanic systems originating at different depths within the earth, and (2) decompress from a shock Hugoniot state. Entropy-density graphs are presented separately for H2O and CO2.

Kieffer, S. W.↗
NASA NTRS1979

A global geochemical model for the evolution of the mantle

It is proposed that the upper mantle transition region, 220 to 670 km, is composed of eclogite which has been derived from primitive mantle by about 20 percent partial melting and that this is the source and sink of oceanic crust. The remainder of the upper mantle is garnet peridotite which is the source of continental basalts and hotspot magmas. This region is enriched in incompatible elements by hydrous and CO2 rich metasomatic fluids which have depleted the underlying layers in the L.I.L. elements and L.R.E.E. The volatiles make this a low-velocity, high attenuation, low viscosity region. The eclogite layer is internally heated and its controls the convection pattern in the upper mantle. Plate tectonics is intermittent. The continental thermal anomaly at a depth of 150-220 km triggers kimberlite and carbonatite activity, alkali and flood basalt volcanism, vertical tectonics and continental breakup. Hot spots remain active after the continents leave and build the oceanic islands. Mantle plumes rise from a depth of about 220 km. Midocean ridge basalts rise from the depleted layer below this depth. Material from this layer can also be displaced upwards by subducted oceanic lithosphere to form back-arc basins.

Anderson, D. L.↗
NASA NTRS1979

Topography and tectonics of mid-oceanic ridge axes

Numerical fluid dynamic models of mid-oceanic ridge axes were constructed using distributions of material properties constrained by seismic studies and thermal calculations. The calculations indicate that spreading is passive except for forces caused by density differences due to thermal expansion and partial melt. Except for geometric differences due to temperature distribution, one set of mechanical properties can adequately explain central rifts of slow ridges and central peaks of fast ridges. Viscous head loss in the upwelling material dominates at low spreading rates where material ascends through a narrow conduit. Thermal expansion and partial melting dominate at high spreading rates where a wide low viscosity crustal magma chamber is present. The preferred rheology is 10 to the 20th poise for the upwelling lithosphere; less than 5 x 10 to the 17th for the crustal magma chamber and axial intrusion zone at fast ridges, and a yield stress of 200 bars for the lithosphere. The calculation correctly predicts the existence of central peaks at 'hot-spot' ridges, where seismic evidence indicates a large magma chamber.

Sleep, N. H.↗
NASA NTRS1983

Two classes of volcanic plumes on Io

Results of an analysis of the properties, source regions and deposits of volcanic plumes on Io are presented which suggest the presence of two plume types. Eruptions at the Aten Patera caldera in the south polar region and the Surt caldera in the far north, which were deduced to have taken place between the times of the Voyager 1 and Voyager 2 encounters from evidence of surface changes, are similar to the Pele eruption. These Pele-type eruptions are characterized by durations of from a few days to a few weeks, dark-red annular deposits of about 1400 km in diameter, temperatures of about 650 K and locations restricted to areas with large, silicate landforms. Smaller, more numerous eruptions of the Prometheus type were observed on both encounters, being characterized by durations in excess of several years, bright ringed deposits about 250 km in diameter, restriction to an equatorial location high in SO2 and temperatures less than 400 K. In addition, an intermediate type of feature was noted at either end of the linear feature Loki. Two separate mechanisms, involving SO2 and sulfur as driving sources, are proposed to account for the Pele- and Prometheus-type eruptions, respectively, and the discrete temperatures of the plumes are suggested to reflect the temperatures at which sulfur is a low-viscosity fluid.

Mcewen, A. S.↗