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At least 829 records · Page 46
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NASA NTRS1979

Charged dust in the outer planetary magnetospheres. I - Physical and dynamical processes

Typical interplanetary grains (Brownlee types) and the physical and dynamical processes associated with their entry into the Jovian magnetosphere are discussed. The charging and subsequent distribution of interplanetary dust grains entering the magnetosphere as well as the basic aspects of orbital dynamics of charged grains are examined. Results showed that all negatively charged fragments are strongly attracted towards the planet by the radial corotational electric field, while some are stably trapped, suggesting that the sudden enhancement by about two orders of magnitude of the interplanetary dust flux, measured at 30 Jupiter radii by Pioneer 10, is a combination of these two results. The similarity in brightness asymmetries between the Jovian and Saturnian satellites leads to the expectation that Saturn's magnetic moment and spin are parallel with the limit of plasma corotational lying between satellites Rhea and Iapetus.

Hill, J. R.↗
NASA NTRS1979

Jovian cloud structure and velocity fields

A global view of Jovian small-scale morphologies and zonal velocity profiles has been discussed previously. In the present paper, a regional comparison is made of the structures and velocity fields (meridional and zonal velocities) in the Jovian atmosphere as observed by Voyager I imaging system. The cloud structures discussed are fairly independent of the visual wavelength. The analysis shows that although both Jovian hemispheres exhibit similar patterns of diminishing and alternating eastward and westward jets as one progresses polewards, there is a pronounced asymmetry in the structural appearance of the two hemispheres.

Mitchell, J. L.↗
NASA NTRS1979

Control of forebody three-dimensional flow separations

The development of the turbulent symmetric and asymmetric vortex flow about the lee side of a 5 deg semiangle conical forebody at high relative incidence was investigated. The cone was immersed in a Mach 0.6 airstream at a Reynolds number of 13.5 x 10 to the 6th power based on the 1.4 m axial length of the cone. Small amounts of air injected normally or tangentially to the cone surface, but on one side of the leeward meridian and beneath the vortex farthest from the wall, were effective in biasing the asymmetry. With this reorientation of the forebody vortices, the amplitude of the side force could be reduced to the point where its direction was reversed. This phenomenon was obtained either by changing the blowing rate at constant incidence or by changing incidence at constant blowing rate. Normal injection appeared more effective than tangential injection. The contrarotating vortices in the penetrating jet flow were of opposite hand to the rotational directions of the forebody vortices. A distinctively organized and stable flow structure emerged with the jet vortices positioned above the forebody vortices.

Peake, D. J.↗
NASA NTRS1980

Critique of a Hughes shuttle Ku-band data sampler/bit synchronizer

An alternative bit synchronizer proposed for shuttle was analyzed in a noise-free environment by considering the basic operation of the loop via timing diagrams and by linearizing the bit synchronizer as an equivalent, continuous, phased-lock loop (PLL). The loop is composed of a high-frequency phase-frequency detector which is capable of detecting both phase and frequency errors and is used to track the clock, and a bit transition detector which attempts to track the transitions of the data bits. It was determined that the basic approach was a good design which, with proper implementation of the accumulator, up/down counter and logic should provide accurate mid-bit sampling with symmetric bits. However, when bit asymmetry occurs, the bit synchronizer can lock up with a large timing error, yet be quasi-stable (timing will not change unless the clock and bit sequence drift). This will result in incorrectly detecting some bits.

Holmes, J. K.↗
NASA NTRS1980

Outer satellite atmospheres: Their extended nature and planetary interactions

Highly developed numerical models are applied to interpret extended-atmosphere data for the sodium cloud of Io and the hydrogen torus of Titan. Solar radiation pressure was identified and verified by model calculations as the mechanism to explain two different east-west asymmetries observed in the sodium cloud. Analysis of sodium line profile data, suggesting that a Jupiter magnetospheric wind may be responsible for high speed sodium atoms emitted from Io, and preliminary modeling of the interaction of the Io plasma torus and Io's sodium cloud are also reported. Models presented for Titan's hydrogen torus are consistent both with the recent Pioneer 11 measurements and earlier Earth-orbiting observations by the Copernicus satellite. Progress is reported on developing models for extended gas and dust atmospheres of comets.

Smyth, W. H.↗
NASA NTRS1979

The magnetospheric electric field and convective processes as diagnostics of the IMF and solar wind

Indirect measurements of the convection field as well as direct of the ionospheric electric field provide a means to at least monitor quanitatively solar wind processes. For instance, asymmetries in the ionospheric electric field and ionospheric Hall currents over the polar cap reflect the solar wind sector polarity. A stronger electric field, and thus convective flow, is found on the side of the polar cap where the y component of the IMF is parallel to the y component of the geomagnetic field. Additionally, the magnitude of the electric field and convective southward B sub Z and/or solar wind velocity, and thus may indicate the arrival at Earth of an interaction region in the solar wind. It is apparent that processes associated with the convention electric field may be used to predict large scale features in the solar wind; however, with present empirical knowledge it is not possible to make quantitative predictions of individual solar wind or IMF parameters.

Kaye, S. M.↗
NASA NTRS1980

Critique of the Hughes Aircraft shuttle Ku band leading edge bit synchronizer

A bit synchronizer is analyzed via timing diagrams in a noise-free environment. It is believed that this new bit synchronizer will track the rising edge of the data bits with 25% asymmetry and up to a 90 deg phase shift between the received clock and data bit timing. In addition, the data bits will be demodulated correctly. It is not true that phase shifts larger than 90 deg will necessarily be corrected by this bit synchronizer. However, the specifications currently require the loop to operate over only a + or - 75 deg phase shift between the received data stream leading edges and the bit synchronizer leading edges; consequently, there should be no problem.

Holmes, J. K.↗
NASA NTRS1980

Shuttle Ku-band and S-band communications implementation study

Various aspects of the shuttle orbiter S-band network communication system, the S-band payload communication system, and the Ku-band communication system are considered. A method is proposed for obtaining more accurate S-band antenna patterns of the actual shuttle orbiter vehicle during flight because the preliminary antenna patterns using mock-ups are not realistic that they do not include the effects of additional appendages such as wings and tail structures. The Ku-band communication system is discussed especially the TDRS antenna pointing accuracy with respect to the orbiter and the modifications required and resulting performance characteristics of the convolutionally encoded high data rate return link to maintain bit synchronizer lock on the ground. The TDRS user constraints on data bit clock jitter and data asymmetry on unbalanced QPSK with noisy phase references are included. The S-band payload communication system study is outlined including the advantages and experimental results of a peak regulator design built and evaluated by Axiomatrix for the bent-pipe link versus the existing RMS-type regulator. The nominal sweep rate for the deep-space transponder of 250 Hz/s, and effects of phase noise on the performance of a communication system are analyzed.

Dodds, J. G.↗
NASA NTRS1980

Results of the investigation of the otolith function in manned space flights

The effects of conditions of long term and short term space flights on the otolith function of cosmonauts were investigated via pre and post examinations. The results show that after long term flight, the intensity of the otolith reflex increased and asymmetry occurred in the indicators of the otolith function. Large changes in terms of expression and duration in the indicators of the otolith function after long term flight as compared with short term flight were also noted.

Kornilova, L. N.↗
NASA NTRS1979

Observations of emission lines in M supergiants

Copernicus observations of Mg 2 h and k emission lines from M giants and supergiants are described. Supergiants with extensive circumstellar gas shells show an asymmetric k line. The asymmetry is ascribed to superimposed lines of Fe 1 and Mn 1. The Mg 2 line width fit the Wilson-Bappu relation derived from observations of G and K Stars. Results of correlated ground-based observations include (1) the discovery of K 1 fluorescent emission from the Betelgeuse shell; (2) extimates of the mass-loss rates; and (3) the proposal that silicate dust grains must account for the major fraction of the Si atoms in the Betelgeuse shell.

Lambert, D. L.↗
NASA NTRS1980

The rate of mass loss and variations in the wind from the Be star delta Centauri

Copernicus ultraviolet scans of the Be star delta Centauri obtained in 1976 and 1979, show a significant variation in the Si III lambda 1206 profile, The strong asymmetry that was present in 1976 had disappeared by 1979. The Si IV lambda 1400 doublet was also asymmetric in 1976, but was not observed in 1979. A quantitative fit of the line shapes to theoretical wind profiles shows that the mass-loss rate in 1976 was 2 x 10 to the minus 8th power/yr, and that the rate of mass loss in Si III was at least one order of magnitude less in 1979. It is not possible to determine whether the variation represented an overall change in the lass-loss rate, or whether it was due to a change in the ionization balance. The profile fitting procedure resulted in the adoption of assumed underlying photospheric Si III and Si IV profiles, and the equivalent widths measured from these profiles are most consistent with T sub eff between 30,000 and 35,000 K, somewhat hotter than implied by the spectral classification normally assigned to this star. The ultraviolet photospheric line widths, coupled wit published theoretical analyses of rotational gravitational darkening, imply an intrinsic equatorial velocity of about 310 km/sec and an angle of inclination of the rotational axis to the line of sight of i is less than or equal to 44 deg.

Snow, T. P., Jr.↗
NASA NTRS1980

Space shuttle orbiter flow visualization study

The vortex flows generated at subsonic speed during the final portion of atmospheric reentry were defined using a 0.01 scale model of the orbiter in a diagnostic water tunnel. Flow visualization photographs were obtained over an angle-of-attack range to 40 deg and sideslip angles up to 10 deg. The vortex flow field development, vortex path, and vortex breakdown characteristics were determined as a function of angle-of-attack at zero sideslip. Vortex flows were found to develop on the highly swept glove, on the wing, and on the upper surface of the fuselage. No significant asymmetries were observed at zero sideslip in the water tunnel tests. The sensitivity of the upper surface vortex flow fields to variations in sideslip angle was also studied. The vortex formed on the glove remained very stable in position above the wing up through the 10 deg of sideslip tested. There was a change in the vortex lifts under sideslip due to effective change in leading-edge sweep angles. Asymmetric flow separation occurred on the upper surface of the fuselage at small sideslip angles. The influence of vortex flow fields in sideslip on the lateral/ directional characteristics of the orbiter is discussed.

Lorincz, D. J.↗
NASA NTRS1979

Equatorial electrojet control on the low latitude ionospheric total electron content

Faraday rotation measurements at 140 MHz were made at a number of locations (covering dip latitudes 3 deg N to 27 deg N) in India, during the period October 1975 to July 1976, when the geosynchronous satellite ATS-6 was positioned at 35 deg E. The ionospheric total electron content (TEC) derived from these measurements shows a semi-annual variation with maxima in equinoxes at all the stations. It is observed that the mean peak electron content is more in April than in October, for the stations situated to the north (poleward) of the crest of the equatorial anomaly whereas for the stations situated to the south (equatorward) of the crest of the equatorial anomaly, a peak larger in October than in April is observed. The equatorial electrojet in this period is found to be stronger in April than in October and can be considered as contributing to this asymmetry in the semi-annual variation of the ionospheric TEC.

Sethia, G.↗
NASA NTRS1979

Observational and theoretical evidence in support of a significant in-situ photochemical source of tropospheric ozone

The latitudinal and seasonal variation of ozone in the troposphere is discussed. Of particular interest is the asymmetrical behavior of this gas with respect to the two hemispheres. These asymmetries, when coupled with a diagnostic photochemical model of the troposphere, lends support to the view that ozone cannot be viewed as an inert tracer of stratospheric origin. In the calculations it is noted that it is likely that the budgets of carbon monoxide and tropospheric ozone may be quite dependent on each other and the calculations are discussed in light of the uncertainty which currently exists about representative global tropospheric background concentrations of the nitrogen oxides. In addition, the seasonal variation of excess (C-14)O2 (a stratospheric tracer) is examined and compared with the seasonal ozone variation during the same period of observations at the same location and altitudes. The distinct maxima for ozone found during the summer in the lower troposphere are not present for the (C-14)O2 data. This finding likewise suggests that photochemical processes taking place in the troposphere are an important source term for tropospheric ozone.

Fishman, J.↗
NASA NTRS1979

High time resolution spectrophotometry of nova DQ Herculis /1934/

Thirty-four spectra of DQ Her are analyzed which were obtained with a time resolution greater than 0.01 cycle. It is found that: (1) the 18th mag visual companion of DQ Her has an energy distribution similar to that of a late F star and is not likely to be a member of the system; (2) the time of minimum has no wavelength dependence and agrees better with the elements of Patterson et al. (1978) than with a linear ephemeris; (3) only very weak evidence exists for the detection of a late-type star, which is of spectral type M4 or later, even at mideclipse; (4) the spectrum of the residual light at mideclipse can be represented by optically thin free-free plus bound-free emission at a temperature of 35,000 K, an electron density of (1-10) trillion per cu cm, and a star contributing about 90% of the red flux; and (5) there is a definite asymmetry in the light curve, as well as strong evidence for a localized bright spot on the side of the disk eclipsed last.

Schneider, D. P.↗
NASA NTRS1979

Sunspots and the physics of magnetic flux tubes. VIII - Overstability in a magnetic field in a downdraft

The dynamical properties of convective overstability in a vertical magnetic field with a downdraft are considered. A variety of effects is illustrated. The overstability produces Alfven waves propagating both upward or downward along the magnetic field. The favored direction of emission may be upward or downward depending upon the magnitude of the heat transport coefficient. The largest asymmetry is produced by a difference in reflectivity between the upper and lower boundaries. It is shown that a very modest reflection coefficient of the upper boundary, with no reflection at the lower boundary, causes most of the waves to be emitted downward, and vice versa. Applying these results to the flux tubes extending up through the convective zone of the Sun, it follows that those flux tubes are dynamically active beneath the surface, as suggested earlier by ourselves and others, but there is no reason to expect any significant wave flux to appear in the field above the surface. The waves propagate downward into the Sun and are presumably dispersed there by the nonlinear interaction with the turbulent convection, etc.

Parker, E. N.↗
NASA NTRS1979

F layer positive response to a geomagnetic storm - June 1972

A circulation model of neutral thermosphere-ionosphere coupling is used to interpret in situ spacecraft measurements taken during a topside midlatitude ionospheric storm. The data are measurements of electron density taken along the circular polar orbit of Ariel 4 at 550 km during the geomagnetically disturbed period June 17-18, 1972. It is inferred that collisional momentum transfer from the disturbed neutral thermosphere to the ionosphere was the dominant midday process generating the positive F-layer storm phase in the summer hemisphere. In the winter hemisphere the positive storm phase drifted poleward in the apparent response to magnetospheric E x B drifts. A summer F-layer positive phase developed at the sudden commencement and again during the geomagnetic main phase; a winter F-layer positive phase developed only during the geomagnetic main phase. The observed seasonal differences in both the onsets and the magnitudes of the positive phases are attributed to the interhemispheric asymmetry in thermospheric dynamics.

Miller, N. J.↗
NASA NTRS1979

A comparison of Pioneer Venus and Venera bow shock observations - Evidence for a solar cycle variation

Observations by the Venera 9 and 10 orbiters in 1975-76 have been used in previous studies to determine the mean location and shape of the Cytherean bow shock. In addition it has also been reported that the shock is found to be more distant from the planet above regions of the ionosheath where draped IMF field lines are oriented perpendicular to the flow as opposed to parallel. An examination of the dependence of shock altitude in the terminator plane on upstream IMF direction using 86 Pioneer Venus orbiter bow shock crossings in 1978-79 sets an upper limit on this asymmetry of 12% or approximately half that derived earlier from the Venera data. More significantly, the mean distance to the bow shock observed by Pioneer Venus Orbiter is 35% greater than was the case in 1975-76 near solar minimum. As the growth in effective obstacle radius is an order of magnitude larger than can be accounted for in terms of varying ionopause altitude due to all causes, these results strongly suggest that Venus can absorb significantly more of the incident solar wind plasma during solar minimum when EUV flux is low than during the current epoch in which maximum is approaching.

Slavin, J. A.↗