Search NASA⌕ Search

SEARCH · Search NASA

Results for “RINGS - STRESSES”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Saturn's microwave spectrum: Implications for the atmosphere and the rings

Measurements of Saturn's disk temperature are compiled to determine the planet's microwave spectrum from 1 mm to 100 cm wavelength. The data were adjusted to conform with a common flux density scale. A model of Saturn's rings is used to remove the effects of the rings from the atmospheric component at centimeter and decimeter wavelengths. Theoretical spectra for a number of convective atmospheric models were computed and compared with the observed spectrum. Radiative-convective models with approximately solar composition and with an effective temperature of approximately 89 K are in good agreement with the observations. The agreement between the observed and theoretical spectra is a strong indication that gaseous ammonia is present in Saturn's atmosphere. A good fit to the data is obtained with an ammonia mixing ratio of approximately 5 x 10,0001. A comparison of the millimeter wavelength data with the best-fitting atmospheric spectrum indicates that the thermal component of the ring brightness temperature near 1 mm wavelength is approximately 25 k.

Klein, M. J.↗
NASA NTRS1979

Propellant grain dynamics in aft attach ring of shuttle solid rocket booster

An analytical technique for implementing simultaneously the temperature, dynamic strain, real modulus, and frequency properties of solid propellant in an unsymmetrical vibrating ring mode is presented. All dynamic parameters and sources are defined for a free vibrating ring-grain structure with initial displacement and related to a forced vibrating system to determine the change in real modulus. Propellant test data application is discussed. The technique was developed to determine the aft attach ring stiffness of the shuttle booster at lift-off.

Verderaime, V.↗
NASA NTRS1979

Azimuthal brightness variations of Saturn's rings. III - Observations at tilt angle B approximately equal to 11.5 deg

The brightness variation in Saturn's ring A with orbital phase of the ring particles does not change significantly as the declination of the earth, B, decreases from about 16.5 to 11.5 deg and is noticeably more pronounced than when the rings are fully open. The present data are also not inconsistent with earlier results suggesting that the amplitude of this azimuthal effect diminishes near opposition.

Lumme, K.↗
NASA NTRS1979

Relationship between the growth of the ring current and the interplanetary quantity

Akasofu (1979) has reported that the interplanetary parameter epsilon correlates reasonably well with the magnetospheric substorm index AE; in the first approximation, epsilon represents the solar wind coupled to the magnetosphere. The correlation between the interplanetary parameter, the auroral electrojet index and the ring current index is examined for three magnetic storms. It is shown that when the interplanetary parameter exceeds the amount that can be dissipated by the ionosphere in terms of the Joule heat production, the excess energy is absorbed by the ring current belt, producing an abnormal growth of the ring current index.

Akasofu, S.-I.↗
NASA NTRS1979

Jupiter's rings

Voyager 2 observations of the jovian ring system discovered by Voyager 1 are presented. The rings were observed both above and below the jovian equatorial plane and at extremely low and high phase angles. This ring system seems to represent a steady state configuration for small particles that are slowly moving in toward Jupiter. It must be resupplied from sources well outside Roche's limit.

Owen, T.↗
NASA NTRS1981

Eliminating gaps in split rings

Simple installation method allows thinner, lighter tether rings than conventional procedures, saving expensive materials. Installer inverts ring with pliers before it is slid over cable, then returns it to its original position after installation. Ring is in correct orientation, and coils are tightly compressed for high reliability fastening.

Gould, R. W.↗
NASA NTRS1979

On the inference of properties of Saturn's Ring E from energetic charged particle observations

The paper demonstrates that information about Saturn's Ring E particle size is potentially obtainable from observations of Saturnian trapped radiation. It is shown that observations of the radial dependence of the intensities, energy spectra, electron-to-proton intensity ratio, and pitch angle distributions of energetic charged particles trapped outside of Ring A can potentially provide information (1) on the existence of Ring E, (2) on the effective size of the particulate matter therein, and (3) on the magnitude of the radial diffusion coefficient for energetic particles. A parametric study of these possibilities is specialized to the characteristics of the University of Iowa detectors on Pioneer 11 which was scheduled to make a close encounter with Saturn in 1979.

Thomsen, M. F.↗
NASA NTRS1979

A model for the azimuthal brightness variations in Saturn's rings

The paper presents a model to explain brightness variations in Saturn rings. These variations have been interpreted as implying the presence of large, synchronously rotating particles with elongated shapes or leading-trailing-edge differences although such synchronous rotation appears unlikely. The model given here assumes that the gravitational wakes or waves can be considered as elongated distributions of particles referred to as blobs, and the radiative transfer in the rings will involve both processes internal to the blobs and analogous processes among blobs. This model explains the existence of azimuthal variation in ring brightness, as well as the dependence of their amplitude on geometrical and photometric parameters. The probable photometric effects are outlined assuming the existence of density irregularities as a result of self-gravitation, and the results simplify the geometric discussion of Franklin and Colombo (1978).

Lumme, K.↗
NASA NTRS1980

New results from optical polarimetry of Saturn's rings

Linear polarimetry of Saturn's rings, obtained through the period of the 1979 opposition, is presented. The polarisation clearly correlates in direction with the plane containing the Sun, planet and Earth, but not the ring plane. The results are consistent with local scattering on the surface of individual ring bodies, covered with frost

Johnson, P. E.↗
NASA NTRS1980

Saturnian trapped radiation and its absorption by satellites and rings - The first results from Pioneer 11

Preliminary results from Pioneer 11 concerning the acceleration and trapping of charged particles in the magnetic field of Saturn are reported. The identification and measurement of the intensities and spectra of charged particle species was performed by an experiment including four charged particle sensor systems, within 20 Saturn radii of the planet. Increases in the intensity of 0.5- to 1.8-MeV protons within 15 Saturn radii indicate the trapping and acceleration of particles in the dipole field region, while a decrease in proton intensity between seven and four Saturn radii is attributed to absorption by Dione and Enceladus and possibly ring material as well. Proton and electron intensity distributions are found to be axially symmetric within four Saturn radii, indicating a centered dipole aligned with the planetary rotation axis. Trapped radiation absorption at the orbit of Mimas is analyzed to obtain an upper limit of 4 x 10 to the -8th Saturn radii-squared/sec to the inward diffusion coefficient; an absorption-like feature observed at L = 2.5 is attributed to a previously unidentified satellite of diameter less than 200 km and semimajor axis 2.51 Saturn radii. Radiation absorption by the newly discovered F ring was also observed, however beneath the A, B and C rings a low flux of high-energy electrons was detected.

Simpson, J. A.↗
NASA NTRS1980

Photo-sputtering of ice and hydrogen around Saturn's rings

It is noted that rocketborne UV spectroscopic measurements have shown that a dense cloud on atomic hydrogen surrounds Saturn which has been interpreted as being associated with the Saturn ring system. Several ring sources of atomic hydrogen have been proposed, but abundance and lifetime estimates require a source which is much more potent than those previously considered. An alternate mechanism is proposed which satisfies this source requirement and involves photodissociation of surface water molecules on the icy ring material. The source rate for this mechanism is within a factor of two of the required value and is within the experimental error of the measurement.

Carlson, R. W.↗
NASA NTRS1980

Dynamics of the AMCD ring

The derivation of the force-free equations of motion of a spinning flexible ring via Lagrange's equations is presented. Closed-form expressions for the natural frequencies are obtained for the most general motion of the ring. Numerical results for rings of different radii and spin rates are presented.

Oz, H.↗
NASA NTRS1980

The terminal Eocene event - Formation of a ring system around the earth

It is suggested that the formation of a ring system about the earth by particles and debris related to the North American strewn tektite field is responsible for the terminal Eocene event of 34 million years ago, in which severe climatic changes accompanied by widespread biological extinctions occurred. Botanical data is cited which implies a 20-C decrease in winter temperature with no change in summer temperature, and evidence of the correlation of the North American tektite fall, which is estimated to have a total mass of 10 to the 9th to 10 to the 10th tons, with the disappearance of five of the most abundant species of radiolaria is presented. The possible connection between the tektites and climatic change is argued to result from the screening of sunlight by an equatorial ring of trapped particles of extraterrestrial origin in geocentric orbit which would cut off sunlight only in the winter months. Such a ring, located at a distance of between 1.5 and 2.5 earth radii (the Roche limit) is estimated to have a lifetime of a few million years.

Okeefe, J. A.↗
NASA NTRS1980

Ganymede, Europa, Callisto, and Saturn's rings - Compositional analysis from reflectance spectroscopy

The reflectance spectra of Ganymede, Europa, Callisto, and the rings of Saturn are analyzed, using laboratory reflectance studies of water, frost, ice, and mineral mixtures. It is found that the spectra of the icy Galilean satellites are characteristic of water ice, or frost on ice, rather than pure water frost; and that the decrease in reflectance at visible wavelengths is caused by other mineral grains on the surface. The spectra of Saturn's rings are more characteristic of water frost, with other mineral grains mixed in the frost but not on the surface. It is also found that impurities of all these objects are not in isolated patches, but intimately mixed with the water. A new absorption feature at 1.15 microns has been identified in Ganymede, Callisto, and possibly Europa, which cannot be seen in Saturn's rings and whose cause is unknown.

Clark, R. N.↗
NASA NTRS1981

Near-infrared spectrophotometry of the satellites and rings of Uranus

New spectrophotometry from 1.5 to 2.5 microns is reported for the Uranian satellites Titania, Oberon, and Umbriel. A spectrum of the rings of Uranus from 2.0 to 2.4 microns is also reported. No evidence is found for frost covering the surface of the ring material, consistent with the low albedo of the rings previously reported by Nicholson and Jones (1980). The surfaces of the satellites are found to be covered by dirty water frost. Assuming albedos of the frost and gray components covering the Uranian satellites to be the same as the light and dark faces of Iapetus, radii are derived that are roughly twice those inferred from the assumption of a visual albedo of 0.5.

Soifer, B. T.↗
NASA NTRS1981

Thermal response of Saturn's ring particles during and after eclipse

The investigation is based on data which were obtained on May 18, 1978, at the 5-m Hale telescope on Palomar Mountain. A Ge:Ga bolometer was used at the f/70 Gregorian focus; a cold interference filter limited the wavelength response to between 16 and 26 micrometers. A brightness asymmetry is observed between the ansae of all three rings; the largest asymmetry occurs in the C ring. The simplest explanation of such asymmetries is just the eclipse cooling and subsequent heating of similar particles at different radial distances from Saturn, coupled with the different travel times from eclipse exit to east ansa. The observed eclipse cooling and subsequent heating in Saturn's B ring support the idea that the uppermost surface of the particles is of low-conductivity water frost, similar to the uppermost surface of the Galilean satellites (omitting Io).

Froidevaux, L.↗
NASA NTRS1981

Moonlets in Saturn's rings

The brightness structure within Cassini's division in Saturn's rings is explained in terms of perturbations produced by moonlets embedded within an optically thin disk of smaller ring particles. The moonlets exert gravitational torques on neighboring ring particles and create gaps; diffusion acts to fill the gaps. A new explanation is offered for the inner edge of the Cassini division being located at the 2:1 resonance with Mimas.

Lissauer, J. J.↗
NASA NTRS1981

Saturn's ring current and inner magnetosphere

The Voyager 1 magnetic field observations at Saturn are shown in a graph. The departure of the oberved magnetic field from the field of a dipole is considered. The observed field magnitude is appreciable less than that of the model dipole at small radial distances and greater than the model dipole in the more distant magnetosphere. These characteristics can be understood by introducing a model current system similar to a system originally applied to observations of the Jovian magnetic disk. Saturn's ring current has important implications for charged-particle motion in Saturn's magnetosphere, particularly the absorption of trapped radiation by its many satellites and rings. The absorption signature observed by the Voyager 1 cosmic ray experiment near the orbital position of Rhea illustrates well the effects of Saturn's ring current on charged particle trajectories.

Connerney, J. E. P.↗