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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Low speed aerodynamic characteristics of a large scale model with a thin, highly swept, 2.67 aspect ratio wing having a cranked leading edge

The low speed aerodynamic characteristics of a large-scale model intended to represent advanced fixed-wing fighters have been investigated in the Ames 40 by 80 foot wind tunnel. The model possessed positive static longitudinal stability to nearly 28 deg angle of attack, the maximum tested, both with and without leading-edge flaps deflected. Lateral control with differentially deflected ailerons and a right wing spoiler simultaneously deployed as combined controls was only slightly greater than that with the differentially deflected ailerons deployed as a separate control without the spoiler. Measured lift and drag were in close agreement with that predicted by theory to about 14 deg angle of attack, including the prediction of lift due to 30 deg of trailing edge flap deflection. Estimated takeoff performance of an aircraft 4/3 the scale of the test model showed takeoff distances of less than 2000 ft.

Giulianetti, D. J.↗
NASA NTRS1973

Statistical analysis of catalogs of extragalactic objects. II - The Abell catalog of rich clusters

The results of a power-spectrum analysis are presented for the distribution of clusters in the Abell catalog. Clear and direct evidence is found for superclusters with small angular scale, in agreement with the recent study of Bogart and Wagoner (1973). It is also found that the degree and angular scale of the apparent superclustering varies with distance in the manner expected if the clustering is intrinsic to the spatial distribution rather than a consequence of patchy local obscuration.

Hauser, M. G.↗
NASA NTRS1977

The Venus bow shock - Detached or attached

Examination of the locations of the bow shock encounters of Mariner 5 and 10 and Venera 4, 6, and 9 suggests that the bow shock of Venus is on the average detached from the ionosphere. However, the standoff distance of the nose of the shock is closer to the planet than the distance that one would obtain by simply scaling the solar wind Venus interaction under the assumption that Venus completely deflects the solar wind. This fact implies that there is a significant influx of solar wind plasma into the Venus ionosphere. If the absorption of the solar wind by Venus is great enough, the shock may become attached to the ionosphere. The Mariner 10 bow shock encounter may have occurred during such a period. A rough estimate of the average fraction of the solar wind incident on the cross section of the planet that is absorbed is 29%.

Russell, C. T.↗
NASA NTRS1979

Uniform color space analysis of LACIE image products

The author has identified the following significant results. Analysis and comparison of image products generated by different algorithms show that the scaling and biasing of data channels for control of PFC primaries lead to loss of information (in a probability-of misclassification sense) by two major processes. In order of importance they are: neglecting the input of one channel of data in any one image, and failing to provide sufficient color resolution of the data. The scaling and biasing approach tends to distort distance relationships in data space and provides less than desirable resolution when the data variation is typical of a developed, nonhazy agricultural scene.

Nalepka, R. F.↗
NASA NTRS1979

Interstellar polarization in an irregularly fluctuating medium

The interstellar polarization of starlight for an irregularly fluctuating medium is analyzed statistically. A general formulation is presented for the case in which the propagation distance s is larger than the coherence scale of the fluctuations. One specific result for randomly changing field direction is that the linear polarization saturates at a value which can be much less than unity, in agreement with observations.

Nee, S. F.↗
NASA NTRS1982

The hard X-ray flux from gamma Cassiopeiae during 1970-73

X-ray observations are presented of the Be star Gamma Cas obtained with the Uhuru satellite between December 27, 1970, and February 15, 1973. Though variable, the X-ray source (MX 0053+60) persisted throughout the life-time of the Uhuru satellite, with an average daily flux (2-6 keV) of 4.1 counts/s or 4.0 x 10 to the 32nd ergs/s if the star is at a distance of 220 pc. Variations on time scales of months, days, and hours were observed, but a pulsation period was not found. An analysis is made of the continuous X-ray spectrum, and the X-ray flux and its behavior during the early 1970s are compared with more recent observations from the SAS-3, Copernicus, HEAO-1, and Einstein satellites.

Peters, G.↗
NASA NTRS1983

A large molecular cloud toward the SNR W50 and SS 433

The CO 1 yields 0 transition at 115 GHz has been mapped over an area of more than 6 deg sq toward W50, the extended SNR surrounding the peculiar object SS 433. W50 is found to lie at the end of a filamentary molecular cloud 4 deg long and 1 deg wide that closely matches a conspicuous dust lane on the Palomar Sky Survey; the cloud's kinematic distance is within 0.7 of 2.2 kpc, in agreement with the distance 2-3.3 kpc estimated for the SNR, and its mass is about 120,000 solar masses. Though there is little evidence of star formation in the molecular filament, or evidence of an interaction between the filament and W50 (or SS 433), the positional coincidence of the two, their similar distance, and their displacement nearly two molecular scale heights from the plane all suggest a physical relationship or common origin. One possibility is that both the molecular filament and the stellar progenitor of W50 were ejected from a large active molecular complex lying in the plane at l = 40 deg.

Huang, Y.-L.↗
NASA NTRS1986

Effect of an upstream wake on a pusher propeller

An analytical/computational study has been conducted to predict the effect of an upstream wake on an operating propeller. The upstream wing/pylon was modeled by a constant chord wing of NACA 0012 sections and was placed at a variable distance (0.1 - 0.3 chord) upstream of a scaled model propeller (SR-2). The wake model was a similarity formulation. The periodic behavior ofthe flow during the passage through the wake was formulated in terms of time-dependent variation of each blade section's angle of attack. It was found that the final expressions for the unsteady pressure distribution on each blade section are periodic and that the unsteady circulation and lift coefficieents exhibit a hysteresis loop.

Takallu, M. A.↗
NASA NTRS1987

Correlating east-west asymmetries in the Jovian magnetosphere and the Io sodium cloud

Three east-west intensity asymmetries in the Jupiter system that would appear to an earth observer in optical S+, extreme ultraviolet S++ and optical Na emissions are reviewed. The three asymmetries imply that some combination of the plasma torus number densities and electron temperature is, on the long-term average, larger west of Jupiter than east of Jupiter. A small east-to-west electric field, previously proposed to explain the ion intensity asymmetries, is also shown to provide a natural explanation for the sodium intensity asymmetry. A long-term average east-to-west electric field of about 3 mV/m and a corresponding west-to-east offset of about 0.16 Jupiter radii for the plasma torus at Io's orbital distance are implied. On a shorter time scale, the east-west electric field appears to be time variable and may be readily monitored from earth by observations of the sodium cloud.

Smyth, William H.↗
NASA NTRS1988

Rapid formation of Jupiter by diffuse redistribution of water vapor in the solar nebula

In the present, water-vapor diffusive redistribution and condensation model of solid material abundance enhancement in the solar nebula's Jupiter-formation region, the assumed turbulent nebula temperatures decrease inversely with radial distance from the center, and time-scales are set by turbulent viscosities. The length scale for condensation of diffusively-transported water vapor is about 0.4 AU, and the surface density of ice in the Jupiter-formation zone undergoes enhancement by a factor of as much as 75; this surface density enhancement is enough to precipitate the rapid accretion of planetesimals into a solid core.

Stevenson, David J.↗
NASA NTRS1988

The isotopic and chemical evolution of planets: Mars as a missing link

The study of planetary bodies has advanced to a stage where it is possible to contemplate general models for the chemical and physical evolution of planetary interiors, which might be referred to as UMPES (Unified Models of Planetary Evolution and Structure). UMPES would be able to predict the internal evolution and structure of a planet given certain input parameters such as mass, distance from the sun, and a time scale for accretion. Such models are highly dependent on natural observations because the basic material properties of planetary interiors, and the processes that take place during the evolution of planets are imperfectly understood. The idea of UMPES was particularly unrealistic when the only information available was from the earth. However, advances have been made in the understanding of the general aspects of planetary evolution now that there is geochemical and petrological data available for the moon and for meteorites.

Depaolo, D. J.↗
NASA NTRS2002

Stars and Planets: A New Set of Middle School Activities

A set of lesson plans for grades 6-8 which deal with the sizes and distances of stars and planets using a scale factor of 1 to 10 billion, the life cycle of stars, and the search for planets beyond the solar system. Additional information is contained in the original extended abstract.

Urquhart, M. L.↗
NASA NTRS2008

Plasmaspheric Plumes Observed by the CLUSTER and IMAGE Spacecraft

Global IMAGE/EUV observations have revealed complex changes in plasmaspheric structures as the plasmasphere responds to geomagnetic activity while remaining under varying degrees of influence by co-rotation, depending on the radial distance. The complex plasmaspheric dynamics, with different scales of variability, is clearly far from being well understood. There is now renewed interest in the plasmasphere due to its apparent connections with the development of the ring current and radiation belt, and loss of ionospheric plasmas. Early in the mission, the Cluster spacecraft only crossed the plasmapause (L - 4) occasionally and made measurements of the outer plasmasphere and plasmaspheric drainage plumes. The study by Darrouzet et al. [2006] provided detailed analyses of in situ Cluster observations and IMAGE EUV observations of three plasmaspheric plumes detected in April-June, 2002. Within the next couple of years, Cluster orbit will change, causing perigee to migrate to lower altitudes, and thus providing excellent opportunities to obtain more detailed measurements of the plasmasphere. In this paper, we report our analyses of the earlier Cluster-IMAGE events by incorporating the different perspectives provided by the IMAGE Radio Plasma Imager (RPI) observations. We will discuss our new understanding of the structure and dynamics of the Cluster-IMAGE events.

Fung, S. F.↗
NASA NTRS1995

The influence of intermediate-scale variations in the heliospheric magnetic field on the transport of galactic cosmic rays

Variations in the heliospheric magnetic field occur on most scales including those lying intermediate between the gyro-radii of galactic cosmic rays and heliocentric radial distance. It is demonstrated that a correlation exists between these intermediate-scale variations in the magnetic field and the variations in the cosmic ray distribution function that result from the field variations. This correlation will affect the average transport of galactic cosmic rays by significantly altering the patterns of gradient and curvature drifts in the heliosphere. During the current solar cycle, the altered drift patterns can lead to larger radial gradients of the galactic cosmic rays and significantly smaller latitude gradients than is expected only from drifts in the mean magnetic field.

Fisk, L. A.↗
NASA NTRS2016

Observation of Chorus Waves by the Van Allen Probes: Dependence on Solar Wind Parameters and Scale Size

Highly energetic electrons in the Earths Van Allen radiation belts can cause serious damage to spacecraft electronic systems and affect the atmospheric composition if they precipitate into the upper atmosphere. Whistler mode chorus waves have attracted significant attention in recent decades for their crucial role in the acceleration and loss of energetic electrons that ultimately change the dynamics of the radiation belts. The distribution of these waves in the inner magnetosphere is commonly presented as a function of geomagnetic activity. However, geomagnetic indices are nonspecific parameters that are compiled from imperfectly covered ground based measurements. The present study uses wave data from the two Van Allen Probes to present the distribution of lower band chorus waves not only as functions of single geomagnetic index and solar wind parameters but also as functions of combined parameters. Also the current study takes advantage of the unique equatorial orbit of the Van Allen Probes to estimate the average scale size of chorus wave packets, during close separations between the two spacecraft, as a function of radial distance, magnetic latitude, and geomagnetic activity, respectively. Results show that the average scale size of chorus wave packets is approximately 13002300 km. The results also show that the inclusion of combined parameters can provide better representation of the chorus wave distributions in the inner magnetosphere and therefore can further improve our knowledge of the acceleration and loss of radiation belt electrons.

Aryan, Homayon↗
NASA NTRS1987

Prediction of added noise due to the effect of unsteady flow on pusher propellers

An analytical/computational study has been conducted to predict the effect of an upstream wing or pylon on the noise of an operating propeller. The wing trailing edge was placed at variable distances (0.1 and 0.3 chord) upstream of a scaled model propeller (SR-2). The wake was modeled using a similarity formulation. The instantaneous pressure distribution on the propeller blades during the passage through the wake was formulated in terms of a time-dependent variation of each blade section's angle of attack and in terms of the shed vortices from the blade trailing edge. It was found that the final expressions for the unsteady loads considerably altered the radiated noise pattern. Predicted noise for various observer positions, rotational speeds and propeller/pylon distances were computed and are presented in terms of the pressure time history. It has been shown that the positioning of a pylon upstream of a propeller indeed increases the noise. Some comparisons with experimental results are also given.

Takallu, M. A.↗
NASA NTRS1987

Added noise due to the effect of an upstream wake on a propeller

An analytical/computational study has been conducted to predict the effect of an upstream wing or pylon on the noise of an operating propeller. The wing trailing edge was placed at variable distances (0.1 and 0.3 chord) upstream of a scaled model propeller (SR-2). The wake was modeled using a similarity formulation. The instantaneous pressure distribution on the propeller blades during the passage through the wake was formulated in terms of a time-dependent variation of each blade section's angle of attack and in terms of the shed vortices from the blade trailing edge. It was found that the final expressions for the unsteady loads considerably altered the radiated noise pattern. Predicted noise for various observer positions, rotational speeds, and propeller/pylon distances were computed and are presented in terms of the pressure time history, harmonics of the Fourier analysis, and overall sound pressure levels (OASPL). The addition of the tangential stress due to skin friction was found to have a damping effect on the acoustic pressure time history and the resulting spectrum of the generated noise. It is shown that the positioning of a pylon upstream of a propeller indeed increases the overall noise.

Takallu, M. A.↗
NASA NTRS1981

Accretion disk models for QSOs and active galactic nuclei - The role of magnetic viscosity

The inner regions of standard accretion disk models are known to be thermally unstable, and when scaled to quasar black hole masses, optically thin. Alternative accretion disk models are constructed under the assumption of a purely magnetic viscosity in the limiting cases of equipartition of gas and magnetic pressures and global flux conservation. The inner regions of these models are considerably denser than the standard model and therefore remain optically thick in all regions. The equipartition model is thermally stable throughout, while flux conservation leads to a localized thermal instability at the gas pressure/radiation pressure boundary and marginal stability as the radial distance approaches zero. The outer regions of quasar scaled accretion disks are strongly self-gravitating, leading to a vertical scale height which is smaller than that found in the inner region. Most of the outer region is gravitationally unstable, implying that the outer parts of galactic nuclei accretion disks are populated by dense self-gravitating gas clouds or possibly by stars.

Sakimoto, P. J.↗