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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 199 records · Page 11
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NASA NTRS1980

Ring formation in rotating protostellar clouds

The formation of a ring during the dynamic collapse of a rotating gas cloud is shown to be an understandable physical phenomenon. By analytically integrating the equation of motion for particles in the equatorial plane of a rotating cloud which collapses in a gravitational potential well defined by a (1 - r-squared) mass density distribution the mechanism which initiates the growth of the toroidal structure is demonstrated. An analysis of the ring formation process indicates that the ring should develop in rotating, self-gravitating gas clouds which collapse from a wide range of axisymmetric intial conditions; the degree of central condensation and the initial distribution of angular momentum in a cloud should affect only the position and size of the developing ring. Ring formation, being a dynamic process in collapsing gas clouds, cannot be explained in terms of the classical ring instability that arises in rapidly rotating, equilibrium spheroids. Conditions in a cloud which should inhibit ring formation are also discussed.

Tohline, J. E.↗
NASA NTRS1981

Performance of jet- and inner-ring-lubricated 35 millimeter bore ball bearings operating to 2.5 million DN

Parametric tests were conducted with a 35 millimeter bore, angular contact ball bearing having a single outer land guided cage. Lubrication was achieved by flowing oil through axial grooves and radial holes machined in the inner ring of the bearing. Test conditions were a thrust load of 667 N (150 lb), shaft speeds from 48,000 to 72,000 rpm, and an oil inlet temperature of 394 K (250 F). Data from tests where the distribution of the total oil supplied to the inner ring was 50 percent for bearing lubrication and 50 percent for bearing inner ring cooling were compared with those where the distribution pattern was 25 percent lubrication and 75 percent cooling. Successful operation was experienced with both the 50-50 and 25-75 percent flow distribution patterns to 2.5 million DN. The 50-50 percent flow pattern provided the cooler bearing operation of the two inner ring lubricated bearings. The jet lubricated bearing had lower outer ring and higher inner ring temperatures than the inner ring lubricated bearings. Maximum power loss of 2.8 kW (3.7 hp) was experienced with the 25-75 percent flow distribution, and maximum percent cage slip of 7.0 occurred at 72,300 rpm with the 50-50 percent flow distribution.

Schuller, F., T.↗
NASA NTRS1981

A search for cold water rings

SAR imagery obtained by Seasat in the Sargasso Sea during 1978 is examined for cold ring signatures. One orbit on August 26 is thought to have imaged the edge of a cold ring, although the ring's position was not well known at the time. During another orbit on September 23, drifting buoy and expendable bathythermography data furnished conclusive evidence that the ring was centered directly in the SAR swath. Although some suggestive patterns are visible in the images, it is not clear that cold rings can be identified by SAR, even though dynamically similar features, such as the Gulf Stream and warm rings, can be accurately detected. The suggestion is made that cold rings may be imaged inadequately because of their lack of surface temperature gradient.

Cheney, R. E.↗
NASA NTRS1981

Rings in the solar system

The structure and composition of the rings of Jupiter, Saturn, and Uranus are discussed, with special attention given to the rings of Saturn. Processes that are known to shape the rings are then described. Alternative explanations for the origin of the rings are proposed. It is pointed out that the architecture of a ring system results from the interplay of a number of forces, among them gravitational forces due to moons outside the rings and the moonlets embedded in them, electromagnetic forces due to the planet's rotating magnetic field, and even the gentle forces exerted by the dilute gaseous medium in which the rings rotate.

Pollack, J. B.↗
NASA NTRS1980

Modified spiral wound retaining ring

A spiral wound retaining ring with angled ends is described. The ring is crimped at the same angle as the ring ends to maintain a constant thickness dimension. The angling of the ends of the ring and crimp allow the ends to be positioned closer together while maintaining enough clearance to enable insertion and removal of the ring. By reducing the separation distance between the ends a stronger ring results since the double layer area of the ring is maximized.

Lawson, A. G.↗
NASA NTRS1983

Planetary ring systems

It is pointed out that in the last several years planetary ring studies have evolved from observations of a single example, related to Saturn, to studies of a class of objects. The rings of Uranus were discovered in 1977 by their unexpected occultations of a star. Observations of planetary rings during the time from 1979 to 1982 are largely related to space missions involving the Pioneer 11 Saturn encounter (1979), and Voyager Jupiter (1979) and Saturn (1980-81) encounters. However, ground-based observations he also played and will continue to play a major role. The rings of Saturn are discussed, taking into account structural details, particle properties, and questions concerning an existence of embedded moonlets. Details regarding Jupiter's ring and Uranus' rings are also investigated. Theoretical developments of general interest are considered, giving attention to gravitational torques, internal collective effects, and electromagnetic and erosive processes acting on ring particles.

Cuzzi, J.↗
NASA NTRS1983

Ring and plasma - The enigmae of Enceladus

The E ring associated with the Kronian moon Enceladus has a lifetime of only a few thousand years against sputtering by slow corotating O ions. The existence of the ring implies the necessity for a continuous supply of matter. Possible particle source mechanisms on Enceladus include meteoroidal impact ejection and geysering. Estimates of ejection rates of particulate debris following small meteoroid impact are on the order of 3 x 10 to the -18th g/(sq cm sec), more than an order of magnitude too small to sustain the ring. A geyser source would need to generate a droplet supply at a rate of approximately 10 to the -16th g/(sq cm sec) in order to account for a stable ring. Enceladus and the ring particles also directly supply both plasma and vapor to space via sputtering. The absence of a 60 eV plasma at the Voyager 2 Enceladus L-shell crossing, such as might have been expected from sputtering, cannot be explained by absorption and moderation of plasma ions by ring particles, because the ring is too diffuse. Evidently, the effective sputtering yield in the vicinity of Enceladus is on the order of, or smaller than, 0.4, about an order of magnitude less than te calculated value. Small scale surface roughness may account for some of this discrepancy.

Haff, P. K.↗
NASA NTRS1983

The structure of Saturn's rings - Implications from the Voyager stellar occultation

A 100-m resolution has been obtained in the radial direction, across the entire Saturn ring system, in Voyager 2 photopolarimeter observations of Delta Scorpii as it was occulted by the rings. An automatic search with finite Fourier transforms located 13 density waves excited by resonances with Saturn's satellites. Although strong density waves can be easily located, no waves have been identified which have predicted torques/surface mass density values lower than 4 x 10 to the 16th cu cm/sec-squared. This suggests a limit of less than 100 waves to be found in the Saturn rings. Total ring mass is estimated as 5 x 10 to the -8th of the mass of Saturn. The power spectrum for the rings shows no dominant individual wavelengths. The majority of ring structures and most variance in ring optical depth are not explainable by currently entertained physical mechanisms.

Esposito, L. W.↗
NASA NTRS1985

Ringed planets - Still mysterious. II

The morphology of the rings of Saturn and the mechanisms proposed to explain their fluctuations and origin are discussed and illustrated with photographs and diagrams in a general review. The kinks and braids of the F ring are attributed to the gravitational effects of the known shepherding satellites and/or a number of as yet unseen moonlets; the irregular gaps in the B and inner A rings, to particle interactions (diffusion-instability processes); and the flickering spokes of the central B ring, to the rotation of the Saturn magnetic field. It is pointed out that the composition of the single Jovian ring and of the Jovian satellites can be explained if both are remnants of the planet's primordial disk, but that the rock-ice compositions of the rings and inner satellites of Saturn require a more sophisticated model, perhaps involving meteoroid erosion. The rings of Uranus and Neptune are briefly considered.

Cuzzi, J. N.↗
NASA NTRS1984

Electrodynamic processes in the ring system of Saturn

A number of recently observed Saturn ring phenomena are discussed in terms of their electrodynamic implications. Voyager 1 and 2 observations of the rotating near-radial spokes in the B Ring, waves and braids of the F Ring, and discrete episodic bursts of broadband radio emission, claimed by some to originate in a ring, are addressed. Several other phenomena are considered, including the origin and evolution of the diffuse E Ring and G Ring (which appear to be composed of fine dust), as well as the existence of a number of sharp discontinuities in the main ring system, within the context of gravitoelectrodynamics of charged dust in the magnetosphere.

Mendis, D. A.↗
NASA NTRS1984

Dynamics of narrow rings

The ring models described here were developed to account for the dynamical problems posed by the narrow rings of Uranus. Some of these rings are now known to be eccentric, inclined, nonuniform in width, optically thick, and narrow, with very sharp edges. The eccentric rings have common pericenters and large, positive eccentricity gradients. The theory of shepherding satellites successfully accounts for most of these features and can also account for some features of the narrow Saturnian rings, in particular, waves, kinks, and periodic variations in brightness. Outstanding problems include the putative relation between eccentricity and inclination displayed by eight of the nine Uranian rings, and the magnitudes of the tidal torques acting on the shepherding satellites. The horseshoe-orbit model, although viable, probably has more application to the narrow rings from which the Saturnian coorbital satellites formed. The angular momentum flow rate due to particle collisions is a minimum at the Lagrangian equilibrium points L(4) and L(5), and one can expect accretion to be rapid at these points.

Dermott, S. F.↗
NASA NTRS1985

Are Uranus' rings black because they are in the solar wind?

It is shown that the rings of Uranus are mostly immersed in the solar wind if Uranus lacks an intrinsic magnetic field. Except for geologically active moons like Io, the rings and moons of Jupiter and Saturn have either high albedos in a low radiation environment or low albedos in a high radiation environment. It is suggested that the moons of Uranus have a significantly lower albedo than those in the low radiation environment of Saturn, and that the rings of Uranus are black because the rings and moons of that planet are relatively depleted in their surface stores of ices. In this scenario, immersion of the Uranus rings in the solar wind provides a loss mechanism for ring ices. The black rings may thus imply the lack of an intrinsic Uranus magnetic field.

Curtis, S. A.↗
NASA NTRS1986

Aperture synthesis observations of the molecular ring in the galactic center

Reported are 88 GHz aperture synthesis observations of HCN J=1 yields 0 emission and absorption in the central 5 pc of the Galaxy. The data, taken by the Hat Creek mm-interferometer at 5" to 10" spatial and 4 km/s spectral resolution, show a complete, clumpy ring of molecular gas surrounding the ionized central 2 pc of the Galaxy. The ring is the inner edge of a larger disk extending to about 5 pc. Comparison with sub-mm line data suggests that the HCN 1-0 line is slightly optically thick and originates in subthermally populated gas. The clumpy line emission distribution reflects a combination of hydrogen volume and column density variations. The new data clearly show a close physical relation between the molecular and the ionized gas in the central cavity. The western arc appears to be the ionized inner surface of the molecular ring, and the northern arm and bar may be streamers of ionized gas falling from the ring toward the center. The dominant large scale velocity pattern of the majority of the molecular gas in the inner 5 pc is rotation. No overall radial motion of the ring greater than about 20 km/s is apparent. The rotation is perturbed in several ways; (1) there is a very large local velocity dispersion, (2) the ring shows changes in position angle and inclination (warps), (3) there is a bright, redshifted cloud which appears to be located in the western part of the ring but does not participate in the rotation. These characteristics and the high degree of clumpiness indicate a non-equilibrium configuration of short (less than or approx. 10 to the 4th power to 10 to the 5th power y) dynamical lifetime. The warping and tilting of the structure and the short dynamical lifetime make an accurate determination of equilibrium rotation velocity uncertain.

Guesten, R.↗
NASA NTRS1987

Jupiter's ring system - New results on structure and particle properties

Jupiter's diffuse ring system is upon reexamination of Voyager images noted to be composed of a relatively bright narrow ring and an inner toroidal halo as well as the 'gossamer' exterior ring, while the previously suspected inner disk is missing. Several narrow, bright features are visible in the main ring, and are suggested to be related in some way to Adrastea and Metis. The smallest ring particles and the dark, rough, red largest bodies both have total optical depths of 1-6 x 10 to the -6th. After arising at the bright ring's inner boundary, the halo rapidly expands inward to a 20,000-km thickness, and disappears at a radius of 90,000 km halfway between the main ring and the planet's cloudtops.

Showalter, Mark R.↗
NASA NTRS1987

Hot piston ring tests

As part of the DOE/NASA Automotive Stirling Engine Project, tests were made at NASA Lewis Research Center to determine whether appendix gap losses could be reduced and Stirling engine performance increased by installing an additional piston ring near the top of each piston dome. An MTI-designed upgraded Mod I Automotive Stirling Engine was used. Unlike the conventional rings at the bottom of the piston, these hot rings operated in a high temperature environment (700 C). They were made of a high temperature alloy (Stellite 6B) and a high temperature solid lubricant coating (NASA Lewis-developed PS-200) was applied to the cylinder walls. Engine tests were run at 5, 10, and 15 MPa operating pressure over a range of operating speeds. Tests were run both with hot rings and without to provide a baseline for comparison. Minimum data to assess the potential of both the hot rings and high temperature low friction coating was obtained. Results indicated a slight increase in power and efficiency, an increase over and above the friction loss introduced by the hot rings. Seal leakage measurements showed a significant reduction. Wear on both rings and coating was low.

Allen, David J.↗
NASA NTRS1988

A multiple-vortex-ring model of the DFW microburst

A multiple-vortex-ring model of the winds associated with a microburst is verified by matching the model-generated winds to those encountered at the Dallas-Ft. Worth (DFW) microburst. The basis of the model consists of time-invariant vortex ring filaments embedded in irrotational flow. Each ring's viscous core is modeled by distributing the vorticity over a small distance (relative to the ring diameter) radially from the filaments. Parameters such as the size and strength of the vortex rings are identified using a modified Newton-Raphson technique. The parameters identified from the analysis of the DFW microburst encounter indicate a large ring with a radius of 8500 ft and a smaller ring with a radius of 1700 ft.

Schultz, Thomas A.↗
NASA NTRS1989

Voyager radio occultation by Uranus' rings. I - Observational results

The January 24, 1986 radio occultation of Voyager 2 by the Uranian rings yielded fine-resolution, 50- and 200-m optical depth profiles at a 3.6 cm wavelength for the nine pre-Voyager rings; these are found to be opaque, reaching optical depths as great as 6-8 in rings gamma and epsilon, which are the only two rings possessing extremely sharp inner and outer edges. Rings 6, 5, 4, and delta share a morphology characterized by a sharp outer-edge transition and a quasi-exponential inner edge one. In ring eta, this behavior is reversed, and ring beta exhibits both diffuse edges and the smallest of the observed opacities.

Gresh, Donna L.↗
NASA NTRS1989

Simulations of light scattering in planetary rings

The current status of efforts to model light scattering in the Uranian and Saturnian rings is briefly reviewed, with an emphasis on the treatment of thin, vertically warped, or clumpy rings. Consideration is given to observations of an opposition surge in the rings (indicating that they are physically thick) and possible reasons for the failure of classical models to predict the forward-scattering characteristics of the B and inner A rings of Saturn, the quadrupole brightness variations in the A ring, the increase in reflectivity with optical depth in the A and B rings, the increase in brightness with solar and observer angle in the B ring, and systematic brightness variations in images of the inner Cassini division. It is pointed out that some of these discrepancies are eliminated by the use of a ray-tracing simulation code which determines the singly scattered light from a layer one or many particles thick.

Dones, L.↗