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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 991 records · Page 55
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NASA NTRS1984

Hyperion - 13-day rotation from Voyager data

The rotation period of Hyperion is determined here on the basis of a light-curve derived from low-resolution Voyager images taken over a two-month span. The data indicate a coherent 13-day spin period over 61 days, with the spin axis nearly parallel to the orbital plane. Since Hyperion is not in synchronous rotation, it cannot be used to test the hypothesis that dark dust spiralling inward on retrograde orbits causes the pronounced leading side/trailing side albedo asymmetry observed on the surface of Iapetus.

Thomas, P.↗
NASA NTRS1984

A statistical study of active regions 1967-1981

A study is conducted of 15 years of active region data based on the Mount Wilson daily magnetograms in the interval 1967-1981. The analysis revealed the following: (1) The integral number of regions decreases exponentially with increasing region sizes, or N(A) = 4788 exp(-A/175) for the 15 years of data, where A is the area in square degrees and N(A) is the number of active regions with area equal to or greater than A; (2) the average area of active regions varies with the phase of the solar cycle. There are more larger regions during maximum than during minimum. (3) Regions in the north are 10 percent larger on average than those in the south during this interval. This coincides with a similar asymmetry in the total magnetic flux between the hemispheres. (4) Regions of all sizes and magnetic complexities show the same characteristic latitude variation with phase in the solar cycle. The largest regions, however, show a narrower latitude range.

Tang, F.↗
NASA NTRS1984

Effects of the motions of a platform-mounted payload on the nutational stability of a dual-spin spacecraft - A Galileo case study

In the presence of spacecraft nutation, tracking of an inertially fixed target by the Galileo scan platform requires the use of two control loops to move the scan platform and the stator in such a way as to compensate for spacecraft motion. The effect of these control loops on spacecraft nutational stability is examined using an eigenvalue analysis approach as well as several computer analysis packages. It was found that the actions of these control loops tend to drive nutation to the point of neutralizing, and even overpowering the damping actions of the spacecraft nutation damper, for pointing directions close to the spacecraft's poles. Stable and unstable zones are mapped out for two sets of spacecraft mass properties, and contributions of rotor asymmetry and stator flexibility are also discussed.

Man, G. K.↗
NASA NTRS1984

Distribution of upflowing ionospheric ions in the high-altitude polar cap and auroral ionosphere

The frequency of occurrence and characteristics of upflowing ions (UFI) in the polar cap and auroral ionosphere are examined statistically using data from the Atmospheric Dynamics Explorer I. A total of 43,000 measurements of the UFI were made from 1981-83, and covered both masses and energies of the ions. The data indicated that many UFI observed at high altitudes originated as low altitude conical or perpendicular ions. The peak source of the ions was below 23,000 km and was latitude and time dependent. The frequency of O+ conics decreased with altitude relative to the H+ conics. The O+ and H+ conics distributions both, however, displayed dawn-dusk asymmetries that favored the dusk sector.

Yau, A. W.↗
NASA NTRS1984

On the '3 kiloparsec arm' - Resonance excitation of linear and nonlinear waves by an oval distortion in the central region

The mechanism responsible for the massive rapidly expanding Galactic feature known as the 3-kpc arm (Rougoor and Oort, 1960) is investigated theoretically in the framework of a density-wave model of the Galaxy. The arm is attributed to outgoing waves excited at the outer Lindblad resonance (OLR) of a small rotating oval distortion near the Galactic center. Linear and nonlinear models are developed, and it is shown that a density crest at 3.5 kpc with expansion velocity 53 km/s can be generated by a distortion turning at 118 km/s kpc with a 10-percent perturbation of the main gravitational field at the OLR (located at 3 kpc). The wave character of the nonlinear solution is found to be the same as that of the linear solution and to give good agreement with the observations in terms of expansion velocity, size, shape, and mass; only the observed asymmetry of the arm is not reproduced.

Yuan, C.↗
NASA NTRS1984

The spatial and seasonal distribution of Martian clouds and some meteorological implications

All Mariner 9 and Viking Orbiter images of Martian atmospheric clouds were analyzed to obtain temporal meteorological characteristics of Mars. The data comprised over 57,000 images which were separated into seven categories of surface obscuration. The classes included: lee waves, waves, plumes, streak clouds, cloud streets, localized fogs and hazes and were associated with particular formation mechanisms, probabilities of wind shear, static stability and surface shear stress and composition. Near surface winds followed the cap edges except in summer. Hemispheric asymmetries were attributed to the hydration state and global dust storm effects. Static stability was regionally and seasonally variable. Finally, clouds formed more easily in the northern than in the southern hemisphere in all corresponding seasons.

Kahn, R.↗
NASA NTRS1985

An investigation of vortex-induced aerodynamic characteristics of supersonic cruise configurations

The linear lifting surface theory which predicts the life in supersonic flow, even though the drag is usually underpredicted, is described. A method for calculating the nonlinear wave drag was developed to remedy this deficiency. The calculated sectional drag is modified by adding the difference between the exact two dimensional (2-D) and the linear 2-D wave drag at the calculated sectional lift coefficient. Improvement in the supersonic drag prediction is shown. The VORCAM code was modified for the FORTRAN 77 language and its input stream was rearranged. The Boeing code was adapted to the computer system. All CDC special features in the code are replaced with standard FORTRAN algorithms. It is suggested that because of the nonlinearity the solution appears to be nonunique crowding of two vortices, a mechanism of vortex asymmetry, is investigated.

Lan, C. E.↗
NASA NTRS1985

Effect of aerodynamic and angle-of-attack uncertainties on the May 1979 entry flight control system of the Space Shuttle from Mach 8 to 1.5

A six degree of freedom simulation analysis was performed for the space shuttle orbiter during entry from Mach 8 to Mach 1.5 with realistic off nominal conditions by using the flight control systems defined by the shuttle contractor. The off nominal conditions included aerodynamic uncertainties in extrapolating from wind tunnel derived characteristics to full scale flight characteristics, uncertainties in the estimates of the reaction control system interaction with the orbiter aerodynamics, an error in deriving the angle of attack from onboard instrumentation, the failure of two of the four reaction control system thrusters on each side, and a lateral center of gravity offset coupled with vehicle and flow asymmetries. With combinations of these off nominal conditions, the flight control system performed satisfactorily. At low hypersonic speeds, a few cases exhibited unacceptable performances when errors in deriving the angle of attack from the onboard instrumentation were modeled. The orbiter was unable to maintain lateral trim for some cases between Mach 5 and Mach 2 and exhibited limit cycle tendencies or residual roll oscillations between Mach 3 and Mach 1. Piloting techniques and changes in some gains and switching times in the flight control system are suggested to help alleviate these problems.

Stone, H. W.↗
NASA NTRS1984

The galactic gamma-ray distribution: Implications for galactic structure and the radial cosmic ray gradient

The radial distribution of gamma ray emissivity in the Galaxy was derived from flux longitude profiles, using both the final SAS-2 results and the recently corrected COS-B results and analyzing the northern and southern galactic regions separately. The recent CO surveys of the Southern Hemisphere, were used in conjunction with the Northern Hemisphere data, to derive the radial distribution of cosmic rays on both sides of the galactic plane. In addition to the 5 kpc ring, there is evidence from the radial asymmetry for spiral features which are consistent with those derived from the distribution of bright HII regions. Positive evidence was also found for a strong increase in the cosmic ray flux in the inner Galaxy, particularly in the 5 kpc region in both halves of the plane.

Harding, A. K.↗
NASA NTRS1984

Comparative effects of auxin and abscisic acid on growth, hydrogen ion efflux and gravitropism in primary roots of maize

In order to test the idea that auxin action on root growth may be mediated by H(+) movement, the correlation of auxin action on growth and H(+) movement in roots was examined along with changes in H(+) efflux patterns associated with the asymmetric growth which occurs during gravitropism. The effects of indoleacetic acid (IAA) and abscisic acid (AbA) on growth, H(+) secretion, and gravitropism in roots were compared. Results show a close correlation existent between H(+) efflux and growth in maize roots. In intact roots there is strong H(+) efflux from the elongation zone. Growth-promoting concentrations of IAA stimulate H(+) efflux. During gravitropism the H(+) efflux from the elongation zone becomes asymmetric; the evidence indicates that auxin redistribution contributes to the development of acid efflux asymmetry. That AbA stimulates root growth is reflected in its ability to stimulate H(+) efflux from apical root segments.

Evans, M. L.↗
NASA NTRS1985

Phase function, backscatter, extinction, and absorption for standard radiation atmosphere and El Chichon aerosol models at visible and near-infrared wavelengths

Tabular values of phase function, Legendre polynominal coefficients, 180 deg backscatter, and extinction cross section are given for eight wavelengths in the atmospheric windows between 0.4 and 2.2 microns. Also included are single scattering albedo, asymmetry factor, and refractive indices. These values are based on Mie theory calculations for the standard rediation atmospheres (continental, maritime, urban, unperturbed stratospheric, volcanic, upper atmospheric, soot, oceanic, dust, and water-soluble) assest measured volcanic aerosols at several time intervals following the El Chichon eruption. Comparisons of extinction to 180 deg backscatter for different aerosol models are presented and related to lidar data.

Whitlock, C. H.↗
NASA NTRS1982

Infrared observations of the Uranian rings

Maps of the Uranian rings at 2.2 microns and spectrophotometric observations covering 2.0 to 2.4 and 2.9 to 3.9 microns are discussed. The maps reveal a 2:1 azimuthal brightness variation whose amplitude and phase are consistent with the width variation and apsidal precession of the epsilon ring. Comparison with models based on stellar occultation data leads to an upper limit of 0.01 on the normal optical depth of any broad (5000 km wide), diffuse component of the ring system. A significant east-west asymmetry, corresponding to a brightening of the near side of the rings relative to the far side, is unexplained. The spectrum of the rings is flat over the range 2.1 to 3.9 microns. There is no spectroscopic evidence for the presence of H2O.

Nicholson, P. D.↗
NASA NTRS1985

A modeling analysis program for the JPL table mountain Io sodium cloud

Progress and achievements in the first year are discussed in three main areas: (1) review and assessment of the massive JPL Table Mountain Io sodium cloud data set, (2) formulation and execution of a plan to perform further processing of this data set, and (3) initiation of modeling activities. The complete 1976-79 and 1981 data sets are reviewed. Particular emphasis is placed on the superior 1981 Region B/C images which provide a rich base of information for studying the structure and escape of gases from Io as well as possible east-west and magnetic longitudinal asymmetries in the plasma torus. A data processing plan is developed and is undertaken by the Multimission Image Processing Laboratory of JPL for the purpose of providing a more refined and complete data set for our modeling studies in the second year. Modeling priorities are formulated and initial progress in achieving these goals is reported.

Smyth, W. H.↗
NASA NTRS1985

The study of the physics of cometary nuclei

The development and utilization of an optimized computer program to analyze orbital stabilization by repeated calculations is presented. The stability of comets in the Opik-Oort Cloud about the Sun against perturbations by the Galactic center involve the same basic type of calculation. The supposed persistence of these bodies in orbits over the life of the solar system, depends upon the stability of bodies of negligible mass in orbits around a body whose mass is small compared to the central mass about which they revolve. The question remains of preferential orientation of extremely eccentric comet orbits, possibly to explain the asymmetry observed among new comet motions. A third application of the computing programs is suited to meteoroids that may exist in orbits about asteroids and that may endanger science spacecraft making flybys too near to asteroids. As in the double-comet case, solar activity and solar gravitational perturbations limit the attendance to an asteroid by small meteroids in their orbits. It is found that the mass distances planned for asteroid fly-bys are adequate.

Whipple, F. L.↗
NASA NTRS1985

Large-Eddy Simulation in Planetary Boundary-Layer Research

The structure and dynamics of the convective boundary layer are discussed. The vertical transport of a conservative, passive scalar was simulated. Also studied were the statistics by top-down and bottom-up scalar fields. Substantial differences were found between them due, presumably, to the asymmetry in the convective boundary layer. A generalization of mixed-layer scaling was developed which allows one to include the effects of top-down diffusion.

Wyngaard, J. C.↗
NASA NTRS1985

Dynamic models of flux tubes in the interpretation of polarization measurements

Recent observations of Stokes parameter profiles indicate the presence of mass motions with large velocity gradients associated with small-scale magnetic elements. Dynamic models of flux tubes were used in order to interpret observations of unresolved elements. It is clear that the physical picture of the dynamic models will be quite different from the hydrostatic ones since there is a strong coupling between the magnetic and the velocity field. Polarization measurements have to be interpreted in terms of dynamic models. Two-D steady flow solutions in slender magnetic tubes have been worked out. It was found that the main properties of the intensity line profiles as well as the asymmetries of the V Stokes profiles can be explained best in terms of magnetic elements with moderate field strength.

Ribes-Nesme, E.↗
NASA NTRS1985

An observation of cosmic ray positrons from 10-20 GeV

A balloon flight of the University of Chicago electron telescope was performed. Making use of the east-west asymmetry in the geomagnetic cut off rigidity, the cosmic ray positrons and negatrons were separated over the range 10 GeV to 20 GeV. The positron to electron ratio, e+/(e++e-), was measured to be 17% + or - 5%, significantly higher than the ratio measured in the 1 GeV to 10 GeV range by other experiments. This increase appears to suggest that either a primary component of positrons become significant above 10 GeV, or that the spectrum of primary negatrons decreases above 10 GeV more sharply than that of secondary positrons.

Mueller, D.↗