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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

A study of the solar wind angular momentum including proton thermal anisotropy

The solution to the steady state magnetohydrodynamic equations governing the supersonic expansion of the solar corona into interplanetary space is obtained for various assumptions regarding the form in which proton thermal energy is carried away from the sun. The one-fluid, inviscid, formulation of the MHD equations is considered assuming that thermal energy is carried away by conduction from a heat source located at the base of the corona. Angular motion of the solar wind led to the existence of three critical points through which the numerical solutions must pass to extend from the sun's surface to large heliocentric distances. The results show that the amount of magnetic field energy converted into kinetic energy in the solar wind is only a small fraction of the total expansion energy flux and has little effect upon the final radial expansion velocity.

Acuna, M. H.↗
NASA NTRS1994

Superfluid helium sloshing dynamics induced oscillations and fluctuations of angular momentum, force and moment actuated on spacecraft driven by gravity gradient or jitter acceleration associated with slew motion

The generalized mathematical formulation of sloshing dynamics for partially filled liquid of cryogenic superfluid helium II in dewar containers driven by the gravity gradient and jitter accelerations associated with slew motion for the purpose to perform scientific observation during the normal spacecraft operation are investigated. An example is given with the Advanced X-Ray Astrophysics Facility-Spectroscopy (AXAF-S) for slew motion which is responsible for the sloshing dynamics. The jitter accelerations include slew motion, spinning motion, atmospheric drag on the spacecraft, spacecraft attitude motions arising from machinery vibrations, thruster firing, pointing control of spacecraft, crew motion, etc. Explicit mathematical expressions to cover these forces acting on the spacecraft fluid systems are derived. The numerical computation of sloshing dynamics is based on the non-inertia frame spacecraft bound coordinate, and solve time-dependent, three-dimensional formulations of partial differential equations subject to initial and boundary conditions. The explicit mathematical expressions of boundary conditions to cover capillary force effect on the liquid-vapor interface in microgravity environments are also derived. The formulations of fluid moment and angular moment fluctuations in fluid profiles induced by the sloshing dynamics, together with fluid stress and moment fluctuations exerted on the spacecraft dewar containers have also been derived. Examples are also given for cases applicable to the AXAF-S spacecraft sloshing dynamics associated with slew motion.

Hung, R. J.↗
NASA NTRS1970

How did Venus lose its angular momentum

Venus low retrograde spin rate explained as result of capture of moonlike object from retrograde orbit, transforming planet rotational energy into heat

Singer, S. F.↗
NASA NTRS1977

Computational tests of angular momentum decoupling approximations for pressure broadening cross sections

The utility of several approximate scattering methods for predicting collision induced spectral pressure broadening has been tested by comparison with accurate close coupling results. In particular, broadening of the pure rotational spectra of HD, HCl, CO, and HCN - all perturbed by low energy collisions with He atoms - has been computed using the effective potential formalism of Rabitz, the decoupled l-dominant approximation of DePristo and Alexander, and the j(2)-conserving coupled states method of McGuire and Kouri. For this last method, pressure broadening cross sections have been obtained with the new, correct expression recently derived by Goldflam and Kouri as well as with an earlier formalism based on an incorrect labeling of the scattering matrices. These methods were found to be generally diasppointing for predicting pressure broadening with the exception of the new, correctly formulated j(2)-conserving coupled states method which was found to agree quantitatively (better than 5%) with close coupling values for all cases studied.

Green, S.↗
NASA NTRS1981

Atmospheric angular momentum and the length of day - A common fluctuation with a period near 50 days

Four astronomical measures of changes in the length of day obtained in 1979 have been shown to exhibit the same, approximately 50-day fluctuation. To find whether this fluctuation was persistent, and of meteorological origin, lunar laser ranging observations and wind data deduced from sources distributed over the globe were analyzed. A high degree of correlation was found between the two sets of data. It is implied that the 50-day period fluctuations in length of day are real and related to meteorological effects. Observed changes in length of day can provide a constraint for models for atmospheric flow, and a partial check for global analyses of such motions.

Langley, R. B.↗
NASA NTRS1985

Contribution of stratospheric winds to annual and semiannual fluctuations in atmospheric angular momentum and the length of day

It is pointed out that modern data sets pertaining to the motions of the solid earth and the atmosphere have begun to achieve an accuracy sufficient to justify renewed interest in the classic problem of explaining variations in the rotation rate of the earth. The possibility exists that deficiencies in the current meteorological data sets account for most of the discrepancies in the annual and semiannual earth-atmosphere momentum budgets. On the basis of composite stratospheric wind analyses produced by Belmont et al. (1974), it has been demonstrated that the seasonal components of the stratosphere's momentum could contribute significantly to a reduction of the seasonal discrepancies thought to exist in the earth-atmosphere momentum budget. The present investigation is further concerned with this subject. A newly available stratospheric wind data set is utilized in conjunction with concurrent U.S. National Meteorological Center data and data of the European Centre for Medium Range Weather Forecasts.

Rosen, R. D.↗
NASA NTRS1985

Zonal winds and the angular momentum balance of Venus' atmosphere within and above the clouds

Temperatures and pressures inferred from radio occultation data acquired by the Pioneer Venus orbiter between September 1982 and November 1983 are used to derive cyclostrophic zonal winds in the middle atmosphere of Venus (1350 to 2.1 mb, 10 deg to 70 deg latitude). The main feature of the wind field is a jet positioned just above the cloud tops at 70 km and approximately 48 deg latitude. The maximum speed of the jet is about 130 m/s. A comparison with results of similar analyses on Pioneer Venus radio occultation data obtained between December 1978 and October 1981 suggests an equatorward shift of the jet and a decrease in jet speed during this five-year time interval. It is proposed that the poleward transport of westward zonal momentum by the upper branch of the cloud level Hadley cell supplies the excess momentum of the jet and maintains it against dissipation. The location of the jet thereby provides a minimum estimate of the latitudinal extent of the Hadley cell. Cyclostrophic zonal wind velocities decrease with height above about 70-75 km. It is suggested that this deceleration of the superrotation in equatorial latitudes is due to the dissipation of vertically propagating thermal tides forced primarily at altitudes around 65 km.

Walterscheid, R. L.↗
NASA NTRS1987

Compact X-ray binaries in hierarchical triples. I - Tidal angular momentum loss and GX 17 + 2

A general formalism is developed for the enhanced mass transfer rate expected in a close binary with a (distant) third companion star. Such a hierarchical triple model is applied to the X-ray burster and QPO source GX 17 + 2, consisting of an inner mass-transferring binary comprising a main-sequence secondary and an accreting neutron star, and a more distant companion. The model is shown to account for the anomalously high mass transfer rate for this burster and other systems with short orbital periods. A G star, which does not appear to be the binary companion of the neutron star but is consistent with the sub-arc second radio error box for GX 17 + 2, may be the triple companion. A predicted velocity curve for the triple companion is presented.

Bailyn, Charles D.↗
NASA NTRS1988

Angular-Momentum-Compensating Actuator

Reactionless actuator developed for instrument-pointing platforms on flexible spacecraft; by eliminating reactions, actuator changes aiming angle of platform without inducing vibrations in spacecraft, eliminateing vibrations in point angle of instrument platform. Actuator used on Earth in such systems as helicopter platforms for television cameras in law enforcement and news telecasts.

Wiktor, Peter J.↗
NASA NTRS1988

Observations of the 30-60 day oscillation in zonal mean atmospheric angular momentum and high cloud cover

Zonally averaged momentum and high-cloud data were analyzed for the periods of April-October 1979 and November 1982-October 1983 periods. The analysis yielded belt correlation fields implying a symmetry and propagation of momentum out of the tropics in the momentum data and an asymmetrical oscillation across the equatorial zone in the high-cloud data. The 30-60 day oscillation was found to be the dominant periodicity in tropical and subtropical belts in both the momentum and cloud fields, with variation of time spectra evident between 1979 and 1983. The lag correlations between high cloud belts and momentum belts showed strong correlations with the 30-60 day oscillation present. Anomalously high/low zonal mean high cloudiness in the tropics was accompanied by anomalously high/low zonal mean momentum in the tropics, with the latter anomalies subsequently propagating into midlatitudes.

Risbey, James S.↗
NASA NTRS1991

Extratropical aspects of the 40-50 day oscillation in length-of-day and atmospheric angular momentum

The 40-50-d oscillation in length-of-day (LOD) and AAM is investigated using the 12-yr overlap between two records: AAM data, compiled from the NMC, and LOD variation from the JPL Kalman-filtered earth rotation series. The NMC records are analyzed by latitude belts, in the light of the UCLA GCM results, in order to identify possibly distinct sources of the AAM oscillation in the midlatitudes and the tropics. Results suggest that two intraseasonal oscillations exist in the earth-atmosphere system: a tropical 50-d oscillation associated with the convectively driven waves of the type first described by Madden and Julian (1971) and a midlatitude 40-d oscillation associated with the interaction of nonzonal flow with topography.

Dickey, J. O.↗
NASA NTRS1991

Adaptive filtering and maximum entropy spectra with application to changes in atmospheric angular momentum

The spectral resolution and statistical significance of a harmonic analysis obtained by low-order MEM can be improved by subjecting the data to an adaptive filter. This adaptive filter consists of projecting the data onto the leading temporal empirical orthogonal functions obtained from singular spectrum analysis (SSA). The combined SSA-MEM method is applied both to a synthetic time series and a time series of AAM data. The procedure is very effective when the background noise is white and less so when the background noise is red. The latter case obtains in the AAM data. Nevertheless, reliable evidence for intraseasonal and interannual oscillations in AAM is detected. The interannual periods include a quasi-biennial one and an LF one, of 5 years, both related to the El Nino/Southern Oscillation. In the intraseasonal band, separate oscillations of about 48.5 and 51 days are ascertained.

Penland, Cecile↗