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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

The hollow cathode in the quasi-steady MPD discharge

A large hollow cathode has been operated in a quasi-steady MPD discharge over a range of current from 7 to 30 kA and argon mass flow from 0.04 to 6.0 g/sec. The 1.3-cm-i.d. cathode cavity attains steady emission characteristics in some tens of microseconds without the assistance of auxiliary heating, low work function inserts, or external keeper electrodes. Measured current and potential distributions within the cavity reveal that the current attaches in a zone 1 to 2 cm long with a surface current density greater than 1000 A/sq cm and a local axial electric field less than 10 V/cm. Electron densities within the cavity, estimated from spectroscopic records, are above 10 to the 17th power per cu cm, at least one order of magnitude greater than has been reported for either ion engine hollow cathodes or conventional solid cathodes in similar arc discharges.

Von Jaskowsky, W. F.↗
NASA NTRS1974

Physical and dynamical studies of meteors

Distribution of meteors in streams detected in the synoptic-year meteor sample plus a study of the fragmentation characteristics of the synoptic-year meteor sample are presented. Population coefficients and dispersion coefficients were determined for each meteor stream. These two parameters serve to determine the number of definite members of the stream in the sample used, and to estimate the actual space density of meteor streams. From results of the fragmentation study, it appears that the main body of most radar meteors does not ablate fragments layer by layer, but collapses rather suddenly under dynamic pressures on the order of 0,0002 dynes/cm. Furthermore, it is believed that fragmentation does not cause a serious selection effect in the radar meteor data.

Southworth, R. B.↗
NASA NTRS1975

Hot-cold plasma interactions in the earth's magnetosphere

The paper gives a synopsis of observations and results obtained from the Explorer-45 satellite which pertain directly to the interaction of the magnetospheric hot and cold plasma populations. The specific case discussed is the interaction of the hot ring current plasma with the cold plasmaspheric plasma in the evening to early morning local time sector during magnetic storm recovery phase. It was found that above the plasmapause region, the hot ring current plasma is stable with negligible losses due to pitch angle diffusion; the hot ring current plasma enters a moderate pitch angle regime in the plasmapause region, whereby the addition of cold plasma destabilizes the hot plasma. Analysis of the energy, spatial, and temporal dependence of the above destabilization along with the ion-cyclotron resonant energy equation, and comparison of this analysis with an in situ estimate of the plasma density strongly indicate that the mechanism responsible for destabilization of the hot plasma is the amplification of ion-cyclotron waves due to the interaction of the cold plasmaspheric plasma with the hot ring current plasma in a manner similar to that discussed by Cornwall et al. (1970).

Williams, D. J.↗
NASA NTRS1975

Application of multivariate autoregressive spectrum estimation to ULF waves

The estimation of the power spectrum of a time series by fitting a finite autoregressive model to the data has recently found widespread application in the physical sciences. The extension of this method to the analysis of vector time series is presented here through its application to ULF waves observed in the magnetosphere by the ATS 6 synchronous satellite. Autoregressive spectral estimates of the power and cross-power spectra of these waves are computed with computer programs developed by the author and are compared with the corresponding Blackman-Tukey spectral estimates. The resulting spectral density matrices are then analyzed to determine the direction of propagation and polarization of the observed waves.

Ioannidis, G. A.↗
NASA NTRS1975

Molecular hydrogen in the galaxy and galactic gamma rays

Estimates made of column densities of H2 at galactic longitude equals 0 deg indicate that H2 is far more abundant than HI in the inner galaxy and is the key to an explanation of the gamma-ray observations. This is also reflected in the correlation of galactic longitude and latitude distributions of gamma-rays and molecular clouds. Particularly strong evidence is found from the galactic survey of CO emission at 2.64 mm. The cosmic-ray distribution inferred from the calculations is not uniform but only weakly dependent on the total gas distribution in the inner galaxy.

Stecker, F. W.↗
NASA NTRS1976

Turbulence measurements in a transonic boundary layer and free-shear flow using laser velocimetry and hot-wire anemometry techniques

Quantitative measurements of the turbulence fluctuations in velocity and mass flux have been obtained in Mach 0.6 and 0.8 turbulent boundary layer and free-shear layer flows by laser velocimetry and hot-wire anemometry techniques. To evaluate the effects of compressibility, these transonic data are compared to available incompressible and supersonic results. Based on some simplifying assumptions, estimates of the rms density fluctuations are made for which error bounds are given. In addition to these fluctuation data, the compressible mean velocity data obtained with the laser velocimeter are presented and compared to pitot tube results. The investigation was conducted in the Ames 6- by 6-Foot Supersonic Wind Tunnel at free-stream Mach numbers of 0.6 and 0.8 for a unit Reynolds number of about 10,000,000 per meter.

Johnson, D. A.↗
NASA NTRS1978

Observations of five moderate-luminosity far-infrared sources in Orion and Monoceros

Far-infrared and submillimeter observations of Orion Molecular Cloud-2 (OMC-2), OMC-1, OMC-3, NGC 2024 and Monoceros R2 are reported. The areas surveyed include far-infrared sources with luminosities between 100 and 250,000 solar luminosities. The data are employed to estimate masses and column densities for the radiating clouds, the radial dependence of the density in the clouds, and the masses of the stellar clusters. Brightness temperatures of both the extended and compact far-infrared sources in OMC-2 are found to be lower than the brightness temperature of the extended (C-12)O emission, indicating an important role in (C-12)O heating for stars external to the compact center.

Thronson, H. A., Jr.↗
NASA NTRS1978

Europa - Ultraviolet emissions and the possibility of atomic oxygen and hydrogen clouds

Emission signals from Europa with wavelength below 800 A were detected by the Pioneer 10 ultraviolet photometer. In the present paper, improved procedures for data reduction are used to determine the spatial region as well as the intensity of the suggested emission sources. The observations indicate a cloud with a radius of about 1.5 Jupiter radii and an apparent brightness of approximately 10 rayleighs for a wavelength of 500 A. It is argued that neutral oxygen atoms, along with neutral hydrogen, are produced through dissociation of water ice on the surface of Europa by particle impact. Electron impact ionization excitation of oxygen atoms in the resulting cloud then gives rise to the observed emission. The present source brightness and cloud radius results are used to estimate an oxygen column density of the order of 10 trillion per sq cm, while the density of atomic hydrogen is at most 100 billion per sq cm and 1 trillion per sq cm for molecular hydrogen.

Wu, F.-M.↗
NASA NTRS1979

Quantitative Analysis of Radar Returns from Insects

When a number of flying insects is low enough to permit their resolution as individual radar targets, quantitative estimates of their aerial density are developed. Accurate measurements of heading distribution using a rotating polarization radar to enhance the wingbeat frequency method of identification are presented.

Riley, J. R.↗
NASA NTRS1978

Molecular clouds in the vicinity of W3, W4, and W5

An extensive and well-sampled map of CO emission over the entire complex consisting of the H II regions W3 (IC 1795), W4 (IC 1805), and W5 (IC 1848) is presented which was obtained at an angular resolution of 8 arcmin. A contour map of integrated (C-12)O emission overlaid on the corresponding fields of the Palomar Sky Survey is provided along with a map of the peak (C-12)O brightness temperature for the W3-W4 region. Two large cloud complexes are found within the area surveyed, and three bright CO condensations are resolved in the peak-temperature map. Column densities and masses are estimated for the cloud complex in the W3-W4 region, and it is suggested that the ionization front of W4 and the molecular cloud are interacting physically. Two condensations associated, respectively, with W3 and W3 (OH) are shown to contain unmistakable evidence for recent OB star formation.

Lada, C. J.↗
NASA NTRS1979

Possible detection of energetic Jovian heavy ions at Skylab orbit

Evidence for the presence of sodium ions at a concentration about 10% that of oxygen among the particles with energies 10 to 20 MeV/nucleon seen with a detector on Skylab suggests that Jupiter is a significant source of energetic heavy particles inside the earth's magnetosphere. A numerical estimate based on the density of energetic sodium ions at 50 Jupiter radii measured on Voyager 1 indicates that the source strength is adequate.

Price, P. B.↗
NASA NTRS1979

Oxides of nitrogen and the clouds of Venus

Nitric oxide may be produced in the atmosphere of Venus by lightning storms in the clouds. The paper suggests that the odd nitrogen thus formed may play an important part in the chemistry of the clouds. Specifically, production rates for NO2 in the limiting case of high NO concentrations are estimated. If the NO density is high, it is suggested that NO2 may catalyse the production of sulfuric acid aerosol from sulfur dioxide and water vapor, and may also form nitrogen-sulfur compounds such as nitrosyl sulfuric acid, NOHSO4. The large partricles seen by the Pioneer Venus sounder probe may contain considerable quantities of NOHSO4. If this is the case, odd nitrogen must be present in the atmosphere in at least a parts-per-million mixing ratio.

Watson, A. J.↗
NASA NTRS1982

Gravity and geoid anomalies of the Philippine Sea: Evidence on the depth of compensation for the negative residual water depth anomaly

A negative free-air gravity anomaly which occurs in the central part of the Philippine Sea was examined to determine the distribution and nature of possible regional mass excesses or deficiencies. Geoid anomalies from GEOS-3 observation were positive. A negative residual geoid anomaly consistent with the area of negative free-air gravity anomalies were found. Theoretical gravity-topography and geoid-topography admittance functions indicated that high density mantle at about 60 km dept could account for the magnitudes of the gravity and residual geoid anomaly and the 1 km residual water depth anomaly in the Philippine Sea. The negative residual depth anomaly may be compensated for by excess density in the uppermost mantle, but the residual geoid and regional free-air gravity anomalies and a slow surface wave velocity structure might result from low-density warm upper mantle material lying beneath the zone of high-density uppermost mantle. From a horizontal disk approximation, the depth of the low-density warm mantle was estimated to be on the order of 200 km.

Bowin, C.↗
NASA NTRS1982

Langley Atmospheric Information Retrieval System (LAIRS): System description and user's guide

This document presents the user's guide, system description, and mathematical specifications for the Langley Atmospheric Information Retrieval System (LAIRS). It also includes a description of an optimal procedure for operational use of LAIRS. The primary objective of the LAIRS Program is to make it possible to obtain accurate estimates of atmospheric pressure, density, temperature, and winds along Shuttle reentry trajectories for use in postflight data reduction.

Boland, D. E., Jr.↗
NASA NTRS1982

Random walks with the 6420- and 6825-A features of methane: Lost in the wilderness

A feature near 6420 A which appears in the spectra of Uranus and Neptune, and was recently detected in the spectrum of Titan is investigated. When originally identified, it was assigned to the pressure induced 4 to 0 band of molecular hydrogen. Not only did the wavelength agree--a small apparent shift was arm waved away, but when the feature was reduced using a dipole-induced strength, it gave results for H2 column densities consistent with best estimates for the sharp quadrupole lines. In studying the long path spectra of methane, that same feature was also present. A second similar problem exists with a Uranian feature--indeed, a general planetary feature centered near 6825 A.

Lutz, B. L.↗
NASA NTRS1983

Preliminary rotor wake measurements with a laser velocimeter

A laser velocimeter (LV) was used to determine rotor wake characteristics. The effect of various fuselage widths and rotor-fuselage spacings on time averaged and detailed time dependent rotor wake velocity characteristics was defined. Definition of time dependent velocity characteristics was attempted with the LV by associating a rotor azimuth position with each velocity measurement. Results were discouraging in that no apparent time dependent velocity characteristics could be discerned from the LV measurements. Since the LV is a relatively new instrument in the rotor wake measurement field, the cause of this lack of periodicity is as important as the basic research objectives. An attempt was made to identify the problem by simulated acquisition of LV-type data for a predicted rotor wake velocity time history. Power spectral density and autocorrelation function estimation techniques were used to substantiate the conclusion that the primary cause of the lack of time dependent velocity characteristics was the nonstationary flow condition generated by the periodic turbulence level that currently exists in the open throat configuration of the wind tunnel.

Hoad, D. R.↗
NASA NTRS1982

Diameters and albedos of satellites of Uranus

Products of the masses of the five known satellites of Uranus, and estimates of their bulk densities and surface albedos, are used to infer their probable dimensions. Spectrophotometry has established the presence of water ice on the surfaces of all save Rhea, and the brightnesses of the satellites have been measured photoelectrically. The diameter measurements presented were made using a photometric/radiometric technique, whose recent recalibration, using independent solar system object measurements, has yielded absolute accuracies better than 5 per cent. The new albedo measurements show that Umbriel, Titania and Oberon are similar to the Jupiter moon Callisto, while Ariel resembles the Saturn moon Hyperion. The diameters of all four are similar to those of the large, icy Saturn satellites Rhea and Iapetus.

Brown, R. H.↗
NASA NTRS1982

The origins of the plasma in the distant plasma sheet

It is pointed out that ion mass spectrometers operating in the keV range have recently begun to provide a new class of information on magnetospheric processes. One of the principal motivations for the development of energetic ion mass spectrometers has been to investigate the origins of the hot plasma populations of the magnetosphere. Peterson et al. (1981) were able to estimate the fractional ion density of ionospheric origin in five intervals by intercomparing the He(++) and H(+) spectra and assuming the excess low-energy H(+) ions were from the ionosphere. They obtained values in the range from 0.1 to 0.65. The present investigation is concerned with an expansion of the previous study. A substantially larger data base is utilized, and a different set of assumptions is considered to infer the relative fractions of solar and ionospheric H(+) and to look for systematic changes in the relative source strengths with magnetic activity.

Sharp, R. D.↗