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Pomphrey, R. B.

Publications and source records attributed to Pomphrey, R. B..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Standard data systems architecture for the Space Station

Attention is given to an end-to-end Space Station Data System (SSDS) architecture which is based on internationally-recommended standards developed by the Consultative Committee for Space Data Systems (CCSDS). The proposed system uses simple modular building blocks that are recursively replicated and linked to construct essentially any desired data system configuration. The SSDS concept provides for a user-transparent data transport system which is entirely independent of the characteristics of the user data being transported, and in addition, has the flexibility to accommodate mission-induced changes in data traffic. SSDS physical elements include the following: (1) on-orbit local area networks, (2) space-to-ground, ground-to-space, and space-to-space data links, and (3) ground mission support facilities containing telemetry and telecommand data handling termini and preprocessing services.

Greenberg, E.↗
NASA NTRS1983

Voyager photopolarimeter stellar occultation of Saturn's rings

On Aug. 25, 1981, the Voyager 2 photopolarimeter system observed a stellar occultation by Saturn's rings. A brief description of this experiment along with details of the data reduction are presented. The occultation results are given in tabular and graphical form at a resolution of 60 km. Histograms of the frequency of optical depth show dominantly unimodal distributions in each of the classical ring elements. The frequency distribution of the entire ring system shows three modes at tau values of about 0.08, 0.5, and more than 2.5.

Esposito, L. W.↗
NASA NTRS1983

Photometry and polarimetry of Saturn at 2640 and 7500 A

Voyager 2 photometric and polarimetric data are reduced and tabulated, with spatially resolved limb-to-terminator scans across Saturn's equatorial zone providing information on the altitude distribution of UV-absorbing hazes, together with the phase function and polarizing properties of stratospheric and tropospheric aerosols. It is found that the UV photometry and polarimetry are best fit by Rayleigh's phase matrix. A stratospheric haze of small particles is allowed as long as the optical depth is near unity or less, and the center of the haze layer is in the 30 to 70 mbar region. The altitudes presently derived for three latitudes agree with those obtained by ground-based methane band studies and analyses from Pioneer 11. A high altitude absorber is abundant in the polar regions.

West, R. A.↗
NASA NTRS1983

Voyager 2 photopolarimeter observations of Titan

Observations of Titan's whole-disk polarization at 2460 and 7500 A are presented and analyzed in terms of model scattering atmospheres. If the Titan aerosols are spherical or nearly spherical, no single combination of refractive index and size distribution is able to fit data at both wavelengths. However, a vertically inhomogeneous distribution suggested by Tomasko and Smith (1980), characterized by a size gradient with altitude, fits the data at 2640 A moderately well but must be modified at intermediate and large optical depths to fit the 7500-A data. Results for synthetic phase functions indicate that the single-scattering polarization must be 70 percent or larger in the UV and 78 percent or larger in the near-IR at 90-deg phase angle, depending on the phase function. If the correct phase function is similar to that for 0.5-micron-radius spheres, the UV single-scattered polarization must be 84 percent and the near-IR single-scattered polarization must be over 90 percent. Such large polarizations are impossible for 0.5-micron-radius spheres but may be possible for nonspherical particles with effective radii near 0.5 micron, although the existence of nonspherical particles with the scattering properties required by these and other observations has not been demonstrated.

West, R. A.↗
NASA NTRS1983

Eccentric ringlet in the Maxwell gap at 1.45 Saturn radii Multi-instrument Voyager observations

The results of Voyager experiments to characterize the eccentric ringlet at 1.45 Saturn radius are discussed. The Voyager I carried out microwave occultation trials with a dual-frequency transmitter, while Voyager 2 observed the occultation of delta Scorpii using an UV spectrometer and a photopolarimeter. The ringlet was associated with a basically empty region next to an edge of the C ring which decreased to a few hundred meters thickness. The width of the ringlet in the gap was estimated to vary from 38-88 km, and it maintains an elliptical shape. It precesses within the 265 km gap it occupies, and has a double-peaked core 15 km wide. The bulk of the ringlet is particles of less than 1 cm radius.

Esposito, L. W.↗
NASA NTRS1983

Voyager photopolarimeter observations of Saturn and Titan

The Voyager 2 photopolarimeter experiment observed the intensity and polarization of scattered sunlight from the atmospheres of Saturn and Titan in the near-UV at 2640 A and in the near-IR at 7500 A. Measurements of Saturn's limb brightening and polarization at several phase angles up to 70 deg indicate that a significant optical depth of UV absorbers are present in the top 100 mbar of Saturn's atmosphere in the equatorial zone and north polar region, and possibly at other latitudes as well. UV absorbers are prominent in polar regions, suggesting that charged particle precipitation from the magnetosphere may be important in their formation. The whole-body polarization of Titan is strongly positive in both the UV and near IR. If spherical particles are responsible for the polarization, no single size distribution or refractive index can account for the polarization at both wavelengths. The model atmosphere proposed by Tomasko and Smith (1982), characterized by a gradient in particle size with altitude, seems capable of explaining the Voyager observations.

West, R. A.↗
NASA NTRS1982

Photopolarimetry from Voyager 2 - Preliminary results on Saturn, Titan, and the rings

The Voyager 2 photopolarimeter was reprogrammed prior to the August 1981 Saturn encounter to perform orthogonal-polarization, two-color measurements on Saturn, Titan, and the rings. Saturn's atmosphere has ultraviolet limb brightening in the mid-latitudes and pronounced polar darkening north of 65 deg N. Titan's opaque atmosphere shows strong positive polarization at all phase angles (2.7 deg to 154 deg), and no single-size spherical particle model appears to fit the data. A single radial stellar occultation of the darkened, shadowed rings indicated a ring thickness of less than 200 meters at several locations and clear evidence for density waves caused by satellite resonances. Multiple, very narrow strands of material were found in the Encke division and within the brightest single strand of the F ring.

Lane, A. L.↗
NASA NTRS1982

Extreme ultraviolet observations from the Voyager 2 encounter with Saturn

Combined analysis of helium (584 A) airglow and the atmospheric occultations of the star delta Scorpii imply a vertical mixing parameter in Saturn's upper atmosphere of K (eddy diffusion coefficient) of approximately 8 x 10 to the 7th sq cm per second, an order of magnitude more vigorous than mixing in Jupiter's upper atmosphere. Atmospheric H2 band absorption of starlight yields a preliminary temperature of 400 K in the exosphere and a temperature near the homopause of 200 K. Certain auroral emissions can be fully explained in terms of electron impact on H2, and auroral morphology suggests a link between the aurora and the Saturn kilometric radiation. Absolute optical depths have been determined for the entire C ring and parts of the A and B rings. A new eccentric ringlet has been detected in the C ring. The extreme ultraviolet reflectance of the rings is fairly uniform at 3.5 to 5 percent. Collisions may control the distribution of H in Titan's H torus, which has a total vertical extent of about 14 Saturn radii normal to the orbit plane.

Sandel, B. R.↗
NASA NTRS1981

Extreme ultraviolet observations from Voyager 1 encounter with Saturn

Hydrogen Lyman-alpha, helium and molecular hydrogen band ultraviolet emissions from Saturn and the Titan atmosphere are considered. The Saturn H2 band excitation mechanism, while qualitatively similar to that of Jupiter, is closely related to the solar flux. The occurrence of auroras at 80 deg latitude suggests an earth-like magnetotail activity. No ion emissions have been detected from the Saturn magnetosphere. Although nitrogen emissions excited by particles have been detected in the Titan dayglow and bright limb scans, no such emission has been detected from its dark atmosphere. Enhancement of the nitrogen emission is observed in the region of interaction between Saturn's corotating plasmasphere and the Titan atmosphere.

Broadfoot, A. L.↗
NASA NTRS1979

NGC 1275 /3C 84/ - Similar structure in the optical and 3-mm radio variations

Optical and 3.3-mm data for the Seyfert galaxy NGC 1275 (3C 84) are compared. Similarities exist between the variations at the two wavelengths with regard to amplitude, time scale, and interval between events. The question is raised whether these similarities may be the result of a common triggering mechanism.

Epstein, E. E.↗
NASA NTRS1977

IPL Processing of the Viking Orbiter Images of Mars

The Viking orbiter cameras returned over 9000 images of Mars during the 6-month nominal mission. Digital image processing was required to produce products suitable for quantitative and qualitative scientific interpretation. Processing included the production of surface elevation data using computer stereophotogrammetric techniques, crater classification based on geomorphological characteristics, and the generation of color products using multiple black-and-white images recorded through spectral filters. The Image Processing Laboratory of the Jet Propulsion Laboratory was responsible for the design, development, and application of the software required to produce these 'second-order' products.

Ruiz, R. M.↗
NASA NTRS1976

Search for correlated radio and optical events in long-term studies of extragalactic sources

For the first time, long-term records of radio and optical fluxes of a large sample of variable extragalactic sources have been assembled and compared, with linear cross-correlation analysis being used to reinforce the visual comparisons. Only in the case of the BL Lac object OJ 287 is the correlation between radio and optical records strong. In the majority of cases there is no evidence of significant correlation, although nine sources show limited or weak evidence of correlation. The results do not support naive extrapolation of the expanding source model. The general absence of strong correlation between the radio and optical regions has important implications for the energetics of events occurring in such sources.

Pomphrey, R. B.↗