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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Phase coherent effects in a collisional turbulent plasma

The presence of mode-mode coupling in turbulent fluctuations in the positive column of a glow discharge in argon is studied experimentally and analytically. The auto-power spectra, the cross power spectra, the phase spectra, the cross correlation functions and the bispectrum are determined. The results are relevant to the theoretical speculations of Grabec and Mikac (1974) and it is shown that ionization instability is the primary cause of the turbulence. The phase spectra indicate that the system is nearly linear at low frequency and the bispectrum plots show that nonlinear wave-wave interactions play a role in the development of the fluctuation components in the turbulent spectrum. Distinctions are made between the azimuthal and axial behaviors of the fluctuations and the results imply a trend toward longer azimuthal scales and shorter axial scales for characterizing fluctuation wave-packets as the density of the turbulent environment increases.

Johnson, J. A., III↗
NASA NTRS1985

Electrostatic wave observation during a space simulation beam-plasma discharge

ELF waves which were observed during beam-plasma discharge in the large vacuum chamber at Johnson Space Center are studied. Phase delays as a function of radius (obtained from cross-correlation measurements of density fluctuations) along with measurements of frequency and plasma potential, density, and temperature have been compared to a zero-order slab model of nonlocal azimuthal drift wave propagation. The inferred wave phase velocity in the plasma frame after Doppler correction is found to be near one half the electron diamagnetic drift velocity. Although the measurements presented do not uniquely define a propagation mode, a model of azimuthal drift wave propagation is found to be consistent with observations.

Walker, D. N.↗
NASA NTRS1985

Simple equation to approximate the bidirectional reflectance from vegetative canopies and bare soil surfaces

A simple equation has been developed for describing the bidirectional reflectance of some vegetative canopies and bare soil surfaces. The equation describes directional reflectance as a function of zenith and azimuth view angles and solar azimuth angle. The equation works for simulated and field measured red and IR reflectance under clear sky conditions. Hemispherical reflectance can be calculated as a function of the simple equation coefficients by integrating the equation over the hemisphere of view angles. A single equation for estimating soil bidirectional reflectance was obtained using the relationships between solar zenith angles and the simple equation coefficients for medium and rough soil distributions. The equation has many useful applications such as providing a lower level boundary condition in complex plant canopy models and providing an additional tool for studying bidirectional effects on pointable sensors.

Walthall, C. L.↗
NASA NTRS1985

Orbit on demand - Will cost determine best design?

Eleven design concepts for vertical (V) and horizontal (H) take-off launch-on-demand manned orbital vehicles are discussed. Attention is given to up to three stages, Mach numbers (sub-, 2, or 3), expendable boosters, drop tanks (DT), and storable (S) or cryogenic fuels. All the concepts feature lifting bodies with circular cross-section and most have a 7 ft diam, 15 ft long payload bay as well as a crew compartment. Expendable elements impose higher costs and in some cases reduce all-azimuth launch capabilities. Single-stage vehicles simplify the logistics whether in H or V configuration. A two-stage H vehicle offers launch offset for the desired orbital plane before firing the rocket engines after take-off and subsonic acceleration. A two-stage fully reusable V form has the second lowest weight of the vehicles studied and an all-azimuth launch capability. Better definition of the prospective mission requirements is needed before choosing among the alternatives.

Macconochie, J. O.↗
NASA NTRS1983

Spaceborne multifunction imaging radar antenna development

Past and present studies of Multifunction Synthetic Aperture Radar Technology at NASA's Johnson Space Center have given attention to the design of lens antennas, planar arrays, and continuous apertures, such as reflectors. Current emphasis is on an interleaved, open ended waveguide array and microstrip antenna, with design work proceeding for multifrequency operation L, C, and X-band antennas, all of which possess multipolarization. In order to meet ground swath and azimuth resolution requirements, the antennas are designed to provide a beamwidth of 6.2 deg in elevation and 1 deg in azimuth.

Schaeper, H. R. A.↗
NASA NTRS1985

Theoretical interpretation of the observed interplanetary magnetic field radial variation in the outer solar system

Observations of the azimuthal component of the IMF are evaluated through the use of an MHD model which shows the effect of magnetic flux tubes opening in the outer solar system. It is demonstrated that the inferred meridional transport of magnetic flux is consistent with predictions by the MHD model. The computed azimuthal and radial magnetic flux deficits are almost identical to the observations. It is suggested that the simplest interpretation of the observations is that meridional flows are created by a direct body force on the plasma. This is consistent with the analytic model of Nerney and Suess (1975), in which such flux deficits in the IMF arise naturally from the meridional gradient in the spiralling field.

Suess, S. T.↗
NASA NTRS1985

Performance degradation of helicopter rotor in forward flight due to ice

This study addresses the analytical assessment of the degradation in the forward flight performance of the front rotor Boeing Vertol CH47D helicopter in a rime ice natural icing encounter. The front rotor disk was divided into 24 15-deg sections and the local Mach number and angle of attack were evaluated as a function of azimuthal and radial location for a specified flight condition. Profile drag increments were then calculated as a function of azimuthal and radial position for different times of exposure to icing, and the rotor performance was re-evaluated including these drag increments. The results of the analytical prediction method, such as horsepower required to maintain a specific flight condition, as a function of icing time have been generated. The method to illustrate the value of such an approach in assessing performance changes experienced by a helicopter rotor as a result of rime ice accretion is described.

Korkan, K. D.↗
NASA NTRS1985

ISEE 1 and 2 observation of the spatial structure of a compressional Pc5 wave

A compressional Pc5 was observed on an ISEE 1 and 2 outbound path on September 28, 1981 at L = 5.6-7.3 near the magnetic equator at about 10 hr local time during the recovery phase of a geomagnetic storm. The wave propagated westward with a large azimuthal wave number of about 30 and exhibited in-phase oscillations of plasma density and magnetic field magnitude. During this event, component-dependent variations in phase and amplitude were observed for the magnetic field oscillations. The radial and compressional components had a constant phase and their amplitude was finite. In contrast, the azimuthal component changed its phase by 180 deg and its amplitude became zero during the middle of the wave event. The observation as indicating the spatial structure of the Pc5 wave is interpreted. The polarization reversal is likely to be caused by a crossing of a node of a standing wave located 4 deg above the geomagnetic equator.

Takahashi, K.↗
NASA NTRS1986

Vortex conception of rotor and mutual effect of screw/propellers

A vortex theory of screw/propellers with variable circulation according to the blade and its azimuth is proposed, the problem is formulated and circulation is expanded in a Fourier series. Equations are given for inductive velocities in space for crews, including those with an infinitely large number of blades and expansion of the inductive velocity by blade azimuth of a second screw. Multiparameter improper integrals are given as a combination of elliptical integrals and elementary functions, and it is shown how to reduce elliptical integrals of the third kind with a complex parameter to integrals with a real parameter.

Lepilkin, A. M.↗
NASA NTRS1986

A study of a collision avoidance system mounted on a curved ground plane

Research conducted on a traffic advisory and collision avoidance system (TCAS 2) mounted on a curved ground plane is described. It is found that a curved finite ground plane can be used as a good simulation model for the fuselage of an aircraft but may not be good enough to model a whole aircraft due to the shadowing of the vertical stabilizer, wings, etc. The surface curvature of this curved disc significantly affects the monopulse characteristics in the azimuth plane but not as much in the elevation plane. These variations of the monopulse characteristics verify the need of a lookup table for the 64 azimuth beam positions. The best location of a TCAS 2 array on a Boeing 737 is to move it as far from the vertical stabilizer as possible.

Law, P. H.↗
NASA NTRS1986

The new 34-meter antenna

The new 34-m high efficiency Azimuth - Elevation antenna configuration, including its features, dynamic characteristics and performance at 8.4-GHz frequencies is described. The current-technology features of this antenna produce a highly reliable configuration by incorporation of a main wheel and track azimuth support, central pintle pivot bearing, close tolerance surface panels and all-welded construction. Also described are basic drive controls that, as slaved to three automatic microprocessors, provide accurate and safe control of the antenna's steering tasks. At this time antenna installations are completed at Goldstone and Canberra and have operationally supported the Voyager - Uranus encounter. A third installation is being constructed currently in Madrid and is scheduled for completion in late 1986.

Pompa, M. F.↗
NASA NTRS1986

Bilateral symmetry of circular impact structures of astroblemes

The relief of the true crater-bottom and the distribution of impactites and allogenic breccias for the Popigay and Kara astroblemes is examined. It is shown that the crater morphology and the distribution of ejecta of fragmented and melted masses has a series of features of symmetry in common with lunar analogs of large astroblemes, formed as a result of an oblique impact, as well as with impact and impact-explosive craters. This leads to the conclusion that both structures were formed as a result of oblique impact of meteoroid bodies; the trajectory projection of the body which formed the Popigay crater had an azimuth of 200 + or - 10 deg., while this azimuth for the Kara crater was 50 + or - 10 deg.

Masaytis, V. L.↗
NASA NTRS1986

Corotation of the Kronian magnetosphere

Observations of the radial variation of azimuthal plasma velocity in the inner part of the magnetosphere of Saturn show deviations from corotation occur as far in as L = 4. Major deviations from rigid corotation occur near the orbits of Rhea and Dione. Voyager-derived neutral and plasma density and temperature vs. altitude profiles in the upper atmosphere to verify that the atmospheric torque needed to drive corotation through neutral-ion coupling is available are used. It is found that the observed azimuthal velocities and calculated Pedersen conductance are consistent with one another, but that the conductance is much less than previous values estimated for Saturn and Jupiter. The lower than anticipated conductivity is attributed to the large heliocentric distance, to the absence of an active satellite (such as Jovian Io) and to a possible role of ring material in depleting the ionosphere.

Eviatar, A.↗
NASA NTRS1986

Effects of anisotropy on the frequency spectrum of gravity waves observed by MST radar

In the investigation of gravity waves using mesosphere-stratosphere-troposphere radar data, model gravity-wave spectra have been used. In these model spectra, one usually assumes azimuthal symmetry. The effect of spectral anisotropy on the observed spectrum is studied here. It is shown that for a general Garrett-Munk-type spectrum, the anisotropy does not affect the frequency spectrum observed by the vertically beamed radar. For the oblique beam, however, the observed frequency spectrum is changed. A general gravity wave spectrum including azimuthal anisotropy is considered.

Liu, C. H.↗
NASA NTRS1986

Pioneer 10 and 11 (Jupiter and Saturn) magnetic field experiments

Magnet field data obtained by the vector helium magnetometer (VHM) during the encounters of Jupiter (Pioneer 10 and 11) and Saturn (Pioneer 11) was analyzed and interpreted. The puzzling characteristics of the Jovian and Saturnian magnetospheric magnetic fields were studied. An apparent substorm (including thinning of the dayside tail current sheet) was observed at Jupiter, as well as evidence suggesting that at the magnetopause the cusp is at an abnormally low latitude. The characteristics of Saturn's ring current as observed by Pioneer 11 were dramatically different from those suggested by the Voyager observations. Most importantly, very strong perturbations in the azimuthal ring current magnetic field suggest that the plane of the ring was not in the dipole equatorial plane, being tilted 5 to 10 deg. relative to the dipole and undergoing significant changes during the encounter. When these changing currents were corrected for, an improved planetary field determination was obtained. In addition, the ring and azimuthal currents at Saturn displayed significantly different time dependences.

Jones, D. E.↗
NASA NTRS1986

Spatially growing disturbances in a two-stream, coplanar jet

The influence of the outer stream on the instability of a two-stream, coplanar jet with only the primary (central) stream heated for a nominal outer-to-primary velocity ratio of 0.3 was investigated by means of inviscid linearized stability theory. The instability properties of spatially growing axisymmetric and first order azimuthal disturbances were studied. It was found that the instability characteristics of the two stream jet are very different from those of a single stream jet. The presence of the outer stream enhanced the instability of the jet and increased the unstable frequency range for the first order azimuthal mode.

Miles, Jeffrey H.↗
NASA NTRS1986

Operational wave forecasting with spaceborne SAR: Prospects and pitfalls

Measurements collected in the Shuttle Imaging Radar (SIR-B) Extreme Waves Experiment confirm the ability of Synthetic Aperture Radar (SAR) to yield useful estimates of wave directional energy spectra over global scales, at least for shuttle altitudes. However, azimuth fall-off effects tend to become severe for wavelengths shorter than about 100 m in most sea states. Moreover, the azimuth fall-off problem becomes increasingly severe as the platform altitude increases beyond 300 km. The most viable solution to the global wave measurements problem may be a low altitude spacecraft containing a combination of both the SAR and the Radar Ocean Wave Spectrometry (ROWS). Such a combination could have a synergy which yield global spectral estimates superior to those of either instrument singly employed.

Beal, R. C.↗
NASA NTRS1987

Statistical analysis of secondary particle distributions in relativistic nucleus-nucleus collisions

The use is described of several statistical techniques to characterize structure in the angular distributions of secondary particles from nucleus-nucleus collisions in the energy range 24 to 61 GeV/nucleon. The objective of this work was to determine whether there are correlations between emitted particle intensity and angle that may be used to support the existence of the quark gluon plasma. The techniques include chi-square null hypothesis tests, the method of discrete Fourier transform analysis, and fluctuation analysis. We have also used the method of composite unit vectors to test for azimuthal asymmetry in a data set of 63 JACEE-3 events. Each method is presented in a manner that provides the reader with some practical detail regarding its application. Of those events with relatively high statistics, Fe approaches 0 at 55 GeV/nucleon was found to possess an azimuthal distribution with a highly non-random structure. No evidence of non-statistical fluctuations was found in the pseudo-rapidity distributions of the events studied. It is seen that the most effective application of these methods relies upon the availability of many events or single events that possess very high multiplicities.

Mcguire, Stephen C.↗