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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Radiometry of satellites and of the rings of Saturn

Brightness temperatures at wavelengths between 8 microns and 3.7 cm are tabulated for satellites of known size; except for Titan, they are consistent with blackbody emission values. For Titan a more complex thermal radiation spectrum with three separate regimes is identified. Radiometric brightness measurements, when used in conjunction with photometry, are shown to determine satellite sizes and albedos; this technique is calibrated by using satellites and asteroids with radii evaluated from other methods. Eclipse radiometry indicates the thermophysical properties of surface layers; such observations show that the uppermost coverings of Phobos, Callisto, and Ganymede have remarkably low thermal conductivities. Infrared and radar detections of the rings of Saturn are surveyed; the important constraints that they provide on ring particle sizes and bulk composition are outlined.

Morrison, D.↗
NASA NTRS1977

Dual-polarized ring lasers

Simultaneous laser oscillation of four nondegenerate polarization and propagation direction eigenstates of a single TEM-00 mode was observed in a ring laser cavity. The observed polarization and frequency properties of the ring laser were analyzed in terms of the Jones matrix calculus.

Sanders, V. E.↗
NASA NTRS1978

Effect of hydraulic fluid (MIL-H-83282) on selected commercial O-ring compounds

Acrylonitrile and fluorocarbon compounds were evaluated at various temperatures and time intervals in samples of the fluid obtained from three qualified suppliers. It was concluded that both polymers can function in hydraulic fluids within the conditions defined by this study. Hydraulic fluid from each manufacturer was similar in its effect upon each given O-ring material, with one exception. Similarly, there were no striking differences in the resistance of O-rings of the same generic rubber type when provided by the different manufacturers.

Wood, T. E.↗
NASA NTRS1977

Stiffness and damping of elastomeric O-ring bearing mounts

A test rig to measure the dynamic stiffness and damping of elastomer O rings was described. Test results for stiffness and loss coefficient in the frequency range from 50 Hz to 1000 Hz are presented. Results are given for three different materials, for five temperatures, for three amplitudes, for five values of squeeze for three values of stretch for three values of cross-section diameter and for three values of groove width. All test data points were plotted. In addition, trend summary plots were presented which compare the effect of material, temperature, amplitude, squeeze, stretch, cross-section diameter, and groove width. O ring deflections under a static load for different material were presented; and effective static stiffness values were compared with dynamic values.

Smalley, A. J.↗
NASA NTRS1978

Lectures on algebraic system theory: Linear systems over rings

The presentation centers on four classes of systems that can be treated as linear systems over a ring. These are: (1) discrete-time systems over a ring of scalars such as the integers; (2) continuous-time systems containing time delays; (3) large-scale discrete-time systems; and (4) time-varying discrete-time systems.

Kamen, E. W.↗
NASA NTRS1978

Photometric confirmation of the Encke division in Saturn's ring A

A physical model of the behavior of Saturn's satellite Iapetus passing through the shadow of the rings is discussed. The model is examined via computer simulation to give photometric confirmation of the Encke division in ring A. The actual event was observed with a two-channel sky-chopping photometer. Simultaneous pulse-counter output from the red and blue channels was integrated for 10-ms intervals alternately on the sky and on Iapetus. In the computer simulation a solar limb-darkening coefficient was used in the blue region and Iapetus was considered two limb-darkened hemispheres of radii 800 km with the trailing hemisphere brighter than the preceding hemisphere by a factor of seven.

Reitsema, H. J.↗
NASA NTRS1978

The velocity dispersion in Saturn's rings

The collisional dynamics of a differentially rotating disk of particles are considered. The investigation is to some extent an analytic counterpart of the numerical studies of Brahic (1977). Following Brahic, it is assumed that the particles are identical, indestructible, imperfectly elastic, smooth spheres. Gravitational interactions between the particles are neglected. The main result of the reported analysis is the derivation of the relation between the coefficient of restitution and the optical depth for a differentially rotating disk of identical, inelastic, smooth spheres. Questions concerning the applicability of the obtained results to Saturn's rings are studied. It is felt that the calculations should give accurate quantitative results if the rings' filling factor is small. If this assumption is not justified, the calculations should be at least qualitatively correct.

Goldreich, P.↗
NASA NTRS1978

Ring current electron trajectories associated with VLF emissions

The reported investigation had the objective to explain features of the ring current electron enhancements which are associated with the simultaneously observed VLF emissions during geomagnetic storms and substorms. Two examples of the electron intensity enhancements observed by Explorer 45 are presented, and the calculations of the electron trajectories injected from the geomagnetic tail into the nightside of the plasmasphere are discussed. These calculations are performed by modifying the computer program developed by Ejiri (1978) to explain the so-called nose events of the ring current protons. The presented calculation demonstrates the soundness of the models of the convective electric field and the static magnetic field.

Maeda, K.↗
NASA NTRS1978

The discovery of the rings of Uranus - An astronomy adventure personally experienced

The paper describes how observation of Uranus at far-red wavelengths during the planet's occultation of a star 3.5 magnitudes fainter led to the discovery of five rings surrounding the planet. Decreases in brightness occurring before the scheduled occultation were detected at the Perth Observatory near Bickley, Western Australia, and these decreases remained inexplicable until a study of the records showed a symmetric pattern before and after occultation by the planet. The Perth records support the planetary ring interpretation even though the planet's shadow could not be observed at Perth.

Millis, R. L.↗
NASA NTRS1979

Fabrication and testing of composite ring specimens

The tooling and techniques used in the fabrication of composite laminate tubes of any desired ply orientation and stacking sequence are described along with techniques for cutting ring specimens under internal pressure. The method consists of laying up the tube on a central circular mandrel, and by means of internal pressure, expanding the prepreg tube against the cavity wall of an external mold tool, which forms the geometric curing envelope for the tube. Tube quality is assessed by laminate wall thickness measurement, by hoop strength measurement on rings cut from the ends of the tube, and by ultrasonic inspection.

Liber, T.↗
NASA NTRS1979

Detection of Jupiter's ring at 2.2 microns

Reflected sunlight from the Jovian ring discovered by the Voyager spacecraft was detected at 2.2 microns. A chopping secondary photometric system and an indium antimonide photovoltaic apparatus were used in the detection. The search for the ring was conducted at 2.2 microns because at this wavelength scattered radiation from the planetary disk is reduced by the strong molecular absorption features in Jupiter's atmosphere.

Becklin, E. E.↗
NASA NTRS1979

Feedback invariants for linear systems defined over rings

A coefficient-assignability theorem is presented for systems defined over a commutative ring with 1. The conditions examined include all the general results on coefficient-assignability available in the literature. It is concluded that the proposed techniques are not effective for the case of the weaker property of pole placement when it is assumed that the commutative ring is a PID. Morse's well-known theorem seems to be the best result available for this situation.

Byrnes, C. I.↗
NASA NTRS1980

Analysis and design of a uniform-clearance, pumping-ring rod seal for the Stirling engine

A uniform clearance pumping ring, as opposed to the conventional taper clearance one, is described. The uniform clearance concept eliminates complex elastohydrodynamic problems and enables a simple analytical treatment to be made. An analytical expression is derived for the pumping rate showing the effect of various design parameters on the pumping ring's performance. An optimum clearance is found by which the pumping rate is maximized and a numerical example is presented to demonstrate the potential of the uniform clearance design.

Etsion, I.↗
NASA NTRS1979

Two-dimensional finite-element analyses of simulated rotor-fragment impacts against rings and beams compared with experiments

Finite element modeling alternatives as well as the utility and limitations of the two dimensional structural response computer code CIVM-JET 4B for predicting the transient, large deflection, elastic plastic, structural responses of two dimensional beam and/or ring structures which are subjected to rigid fragment impact were investigated. The applicability of the CIVM-JET 4B analysis and code for the prediction of steel containment ring response to impact by complex deformable fragments from a trihub burst of a T58 turbine rotor was studied. Dimensional analysis considerations were used in a parametric examination of data from engine rotor burst containment experiments and data from sphere beam impact experiments. The use of the CIVM-JET 4B computer code for making parametric structural response studies on both fragment-containment structure and fragment-deflector structure was illustrated. Modifications to the analysis/computation procedure were developed to alleviate restrictions.

Stagliano, T. R.↗
NASA NTRS1979

Fiber Ring Optical Gyroscope (FROG)

The design, construction, and testing of a one meter diameter fiber ring optical gyro, using 1.57 kilometers of single mode fiber, are described. The various noise components: electronic, thermal, mechanical, and optical, were evaluated. Both dc and ac methods were used. An attempt was made to measure the Earth rotation rate; however, the results were questionable because of the optical and electronic noise present. It was concluded that fiber ring optical gyroscopes using all discrete components have many serious problems that can only be overcome by discarding the discrete approach and adapting an all integrated optic technique that has the laser source, modulator, detector, beamsplitters, and bias element on a single chip.

Source record↗
NASA NTRS1980

Uncertainty in ring current parameters due to the quiet magnetic field variability at mid-latitudes

At midlatitudes the presence of Sq variation is a problem, as variability of Sq currents may produce magnetic perturbations comparable to the magnetic effects of the partial ring current on comparable time scales. The paper reports the results of an empirical determination of the quiet magnetic field, which includes the Sq variation and secular variation at 27 midlatitude magnetic observatories for the 1967-1968 period. The main concern is with the consequences of the quiet field uncertainty in terms of using midlatitude magnetic data to quantify the size and location of the magnetic disturbances caused by substorms and the ring current. Attention is given to investigating the error associated with the empirical model used. It is shown how the uncertainty can be reduced by examining the changes occurring in some interval of time.

Clauer, C. R.↗
NASA NTRS1980

Rings of Uranus - Proposed model is unworkable

A model of Uranus's rings proposed by Van Flandern (1979) is discussed. According to the proposed model, Uranus's rings are the gaseous tails of unobserved small satellites. The hypothesis raises a number of objections, e.g., a gaseous torus must have a minor diameter of thousands, not tens, of kilometers; very large densities are required to produce the postulated angles of refraction; and making up the mass losses, even with a generous lifetime, would use up quite a large body in a few million years.

Hunten, D. M.↗