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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Random variations in the ultraviolet spectrum of Beta Lyrae

Spectrophotometric scans of Beta Lyrae over the wavelength range from 1100 to 3700 A are analyzed which were obtained at different times with different resolutions by the OAO 2 satellite and from the ground. A model atmosphere with normal H and He abundances, an electron temperature of 11,000 K, and log g of 3.0 is found to fit the visual region of the spectrum well but to be a poor representation in the Balmer continuum. It is shown that a large complex emission feature dominates the spectrum from about 1700 to 2200 A, that there is a very pronounced strengthening of the spectrum just shortward of the 1550-A C IV feature at phase 0.69, and that the overall level of the spectrum shortward of 1400 A is quite high in comparison with the broad emission feature. A model is discussed in which the light from a disk-shaped secondary is highly concentrated toward the polar regions.

Bless, R. C.↗
NASA NTRS1981

Boron and beryllium in Gamma Geminorum

Observations have been made of the B II resonance line at 1362 A in the A0 IV star Gamma Gem with the Princeton spectrometer on the Copernicus satellite at a spectral resolution of 0.05 A. Complementary ground-based observations of the Be II resonance lines at 3130 and 3131 A have been made at Mauna Kea Observatory with a comparable resolution. A model-atmosphere abundance analysis has been done which includes the effects of the lines that blend with the B II and Be II lines. Previous data on Alpha Lyr and Alpha CMa for B II (which blends with a V III feature) have been reanalyzed with the help of new photographic and Reticon data from Mauna Kea which enable the determination of the V abundance. The results show that Gamma Gem is depleted in B by a factor of 5-10 relative to Alpha Lyr and other normal B stars and depleted in Be by at least a factor of four. By comparison, the hot Am star Alpha CMa is B-deficient by about three orders of magnitude and Be-deficient by at least fifteen times. It is suggested that the abundance deficiencies are due to diffusion, and that Alpha CMa is intrinsically a slow rotator, and Gamma Gem is a slightly evolved slow rotator where some, but not all, of the B and Be has resurfaced.

Boesgaard, A. M.↗
NASA NTRS1987

Multiwavelength monitoring of the dwarf nova VW Hydri. IV - Voyager observations

Results from Voyager far-ultraviolet (500-1200 A) observations of the dwarf nova VW Hyi are presented as part of a coordinated, multiwavelength program. Data from one normal outburst and one superoutburst are discussed in detail. Far-ultraviolet (1050 A) light curves are produced showing a significant delay (0.5 day) in the rise to maximum at 1050 A with respect to optical wavelength, followed by a simultaneous decline. The superoutburst data show a distinct double-peaked light curve with the first rise and decline closely resembling that of a normal outburst. These data suggest that the rise to supermaximum in the far-ultraviolet is also delayed with respect to optical wavelengths. The spectral distribution of VW Hyi shows the steeply falling spectrum shortward of 1200 A, characteristic of dwarf novae in outburst and absorption features at 985 (N III, C III and Ly gamma) and 1030 (Ly beta and O VI). No flux shortward of 912 A was detected in VW Hyi.

Polidan, R. S.↗
NASA NTRS1987

An experimental investigation of the chopping of helicopter main rotor tip vortices by the tail rotor. Part 2: High speed photographic study

The interaction of a free vortex and a rotor was recorded photographically using oil smoke and stroboscopic illumination. The incident vortex is normal to the plane of the rotor and crosses the rotor plane. This idealized aerodynamic experiment most nearly corresponds to helicopter flight conditions in which a tip vortex from the main rotor is incident upon the tail rotor while hovering. The high speed photographs reveal important features not observed using conventional photography where the image is the time average of varying instantaneous images. Most prominent is the strong interaction between the rotor tip vortex system and the incident vortex, resulting in the roll-up of the incident vortex around the (stronger) tip vortices and the resulting rapid destabilization of the deformed incident vortex. The viscous interaction is clearly shown also. Other forms of instabilities or wave-like behavior may be apparent from further analysis of the photographs.

Cary, Charles M.↗
NASA NTRS1990

Welding arc plasma physics

The problems of weld quality control and weld process dependability continue to be relevant issues in modern metal welding technology. These become especially important for NASA missions which may require the assembly or repair of larger orbiting platforms using automatic welding techniques. To extend present welding technologies for such applications, NASA/MSFC's Materials and Processes Lab is developing physical models of the arc welding process with the goal of providing both a basis for improved design of weld control systems, and a better understanding of how arc welding variables influence final weld properties. The physics of the plasma arc discharge is reasonably well established in terms of transport processes occurring in the arc column itself, although recourse to sophisticated numerical treatments is normally required to obtain quantitative results. Unfortunately the rigor of these numerical computations often obscures the physics of the underlying model due to its inherent complexity. In contrast, this work has focused on a relatively simple physical model of the arc discharge to describe the gross features observed in welding arcs. Emphasis was placed of deriving analytic expressions for the voltage along the arc axis as a function of known or measurable arc parameters. The model retains the essential physics for a straight polarity, diffusion dominated free burning arc in argon, with major simplifications of collisionless sheaths and simple energy balances at the electrodes.

Cain, Bruce L.↗
NASA NTRS1993

Teaching high-performance skills using above-real-time training

The above real-time training (ARTT) concept is an approach to teaching high-performance skills. ARTT refers to a training paradigm that places the operator in a simulated environment that functions at faster than normal time. It represents a departure from the intuitive, but not often supported, feeling that the best practice is determined by the training environment with the highest fidelity. This approach is hypothesized to provide greater 'transfer value' per simulation trial, by incorporating training techniques and instructional features into the simulator. Two related experiments are discussed. In the first, 25 naive male subjects performed three tank gunnery tasks on a simulator under varying levels of time acceleration (i.e., 1.0x, 1.6x, 2.0x, sequential, and mixed). They were then transferred to a standard (1.0x) condition for testing. Every accelerated condition or combination of conditions produced better training and transfer than the standard condition. Most effective was the presentation of trials at 1.0x, 1.6x, and 2.0x in a random order during training. Overall, the best ARTT group scored about 50 percent higher and trained in 25 percent less time compared to the real-time control group. In the second experiment, 24 mission-capable F-16 pilots performed three tasks on a part-task F-16A flight simulator under varying levels of time compression (i.e., 1.0x, 1.5x, 2.0x, and random). All subjects were then tested in a real-time environment. The emergency procedure (EP) task results showed increased accuracy for the ARTT groups. In testing (transfer), the ARTT groups not only performed the EP more accurately, but dealt with a simultaneous enemy significantly better than a real-time control group. Although the findings on an air combat maneuvering task and stern conversion task were mixed, most measures indicated that the ARTT groups performed better and faster than a real-time control group. Other implications for ARTT are discussed along with future research directions.

Guckenberger, Dutch↗
NASA NTRS2011

Preliminary Examination of Particles Recovered from the Surface of the Asteroid Itokawa by the Hayabusa Mission

The Hayabusa spacecraft arrived at S-type Asteroid 25143 Itokawa in November 2006, and reveal astounding features of the small asteroid (535 x 294 x 209 m). Near-infrared spectral shape indicates that the surface of this body has an olivinerich mineral assemblage potentially similar to that of LL5 or LL6 chondrites with different degrees of space weathering. Based on the surface morphological features observed in high-resolution images of Itokawa s surface, two major types of boulders were distinguished: rounded and angular boulders. Rounded boulders seem to be breccias, while angular boulders seem to have severe impact origin. Although the sample collection did not be made by normal operations, it was considered that some amount of samples, probably small particles of regolith, was collected from MUSES-C regio on the Itokawa s surface. The sample capsule was successfully recovered on the earth on June 13, 2010, and was opened at curation facility of JAXA (Japan Aerospace Exploration Agency), Sagamihara, Japan. A large number of small particles were found in the sample container. Preliminary analysis with SEM/EDX at the curation facility showed that at least more than 1500 grains were identified as rocky particles, and most of them were judged to be of extraterrestrial origin, and definitely from Asteroid Itokawa. Minerals (olivine, low-Ca pyroxene, high-Ca pyroxene, plagioclase, Fe sulfide, Fe-Ni metal, chromite, Ca phosphate), roughly estimated mode the minerals and rough measurement of the chemical compositions of the silicates show that these particles are roughly similar to LL chondrites. Although their size are mostly less than 10 m, some larger particles of about 100 m or larger were also identified. A part of the sample (probably several tens particles) will be selected by Hayabusa sample curation team and examined preliminary in Japan within one year after the sample recovery in prior to detailed analysis phase. Hayabusa Asteroidal Sample Preliminary Examination Team (HASPET) has been preparing for the preliminary examination with close cooperation with the curation team.

Tsuchiyama, A.↗
NASA NTRS2018

Tetrahedral-Mesh Simulations of Shock-Turbulence Interaction

Despite decades of development of unstructured mesh methods, direct numerical simulations (DNS) of turbulent flows are still predominantly performed on structured or unstructured hexahedral meshes with high-order finite-difference methods, weighted essentially nonoscillatory (WENO) schemes, or hybrid schemes formed by their combinations. Tetrahedral meshes offer easy mesh generation and adaptation around complex geometries and the potential of an orientation-free grid that would benefit the isotropic nature of small-scale dissipation, as well as the solution accuracy of intermediate scales. To advance the state of the art of unstructured-mesh simulation capabilities for shock/turbulence interaction, DNS using pure tetrahedral meshes are carried out with the space-time conservation element, solution element (CESE) method in this research. By its design, the CESE method is constructed based on a non-dissipative scheme and is a genuinely multidimensional numerical framework that is free from the use of an approximate Riemann-solver. The numerical framework also provides the ability to add numerical dissipation (the nondissipative scheme acts as the reference state like that of the reversible state in thermodynamics) when needed (with justification from mathematics/physics). The above-mentioned features along with the CESE method's consistent shock-capturing approach and strong enforcement of flux conservation in spacetime offers a novel method to accurately simulate turbulent flows and their interaction with shocks using tetrahedral meshes. Two canonical problems, namely, isotropic turbulence interaction with a normal shock and a Mach 2.9 turbulent boundary layer flow over a 24deg compression corner are investigated in this study. Computational results show reasonably good agreement with experimental data and results from structured-mesh, high-order simulations available in the literature. Successful validation of these canonical problems demonstrated here paves the way for future high-fidelity supersonic flow simulations involving complex-geometries.

Venkatachari, Balaji Shankar↗
NASA NTRS1978

Interplanetary gas. XXII - Interaction of comet Kohoutek's ion tail with the compression region of a solar-wind corotating stream

An apparently successful identification of a comet-tail feature with a solar-wind event is presented. Photographs of comet Kohoutek 1973f show a large-scale disturbance in the middle and outer regions of the ion tail early on January 20 of 1974. On the previous and succeeding days the comet had, however, a 'normal' and less active appearance. The peculiar tail structure is linked to an encounter with rapidly changing solar-wind conditions on the forward edge of the high-velocity solar-wind stream which encountered the earth late on January 24. The stream produced a geomagnetic storm of the recurrent type. The high-speed stream appears to have been associated with a large near-equatorial coronal hole which underwent central meridian passage on January 22. It is proposed that the comet was in the compression region on the stream forward edge at the time of formation of the tail disturbance. The accuracy of the time delays is actually tested by an application of the wind shock theory of ionic tail orientations.

Niedner, M. B., Jr.↗
NASA NTRS1979

Power Extension Package (PEP) system definition extension, orbital service module systems analysis study. Volume 1: Executive summary

An array deployment assembly, power regulation and control assembly, the necessary interface, and display and control equipment comprise the power extension package (PEP) which is designed to provide increased power and duration, as well as reduce fuel cell cryogen consumption during Spacelab missions. Compatible with all currently defined missions and payloads, PEP imposes minimal weight and volume penalties on sortie missions, and can be installed and removed as needed at the launch site within the normal Orbiter turnaround cycle. The technology on which it is based consists of a modified solar electric propulsion array, standard design regulator and control equipment, and a minimally modified Orbiter design. The requirements from which PEP was derived, and the system and its performance capabilities are described. Features of the recommended project are presented.

Source record↗
NASA NTRS1989

Highly ionized species and circumstellar shells in B8-A1 stars

The nature of the C IV and Si IV absorption seen in the spectra of apparently normal late-type B and early-type A stars located within 200 pc of the sun was investigated by examining a total of 93 archival IUE spectra of 41 stars. In three of these objects, variable or asymmetric C IV profiles indicate that the absorption features have a stellar origin. One star, HD 119921, showed shortward-shifted discrete C IV and Si IV absorption components similar to those observed in Be stars. All of the stars with detected C IV in their spectra had large values of v sin i. Four of the stars showing C IV and Si IV also showed sharp absorption features in Si II, with two of these stars displaying variable Si II features. These results strongly suggest that these stars are unidentified Be/Ae and shell stars.

Bruhweiler, Frederick C.↗
NASA NTRS1994

Global shortwave energy budget at the earth's surface from ERBE observations

A method is proposed to compute the net solar (shortwave) irradiance at the earth's surface from Earth Radiation Budget Experiment (ERBE) data in the S4 format. The S4 data are monthly averaged broadband planetary albedo collected at selected times during the day. Net surface shortwave irradiance is obtained from the shortwave irradiance incident at the top of the atmosphere (known) by subtracting both the shortwave energy flux reflected by the earth-atmosphere system (measured) and the energy flux absorbed by the atmosphere (modeled). Precalculated atmospheric- and surface-dependent functions that characterize scattering and absorption in the atmosphere are used, which makes the method easily applicable and computationally efficient. Four surface types are distinguished, namely, ocean, vegetation, desert, and snow/ice. Over the tropical Pacific Ocean, the estimates based on ERBE data compare well with those obtained from International Satellite Cloud Climatology Project (ISCCP) B3 data. For the 9 months analyzed the linear correlation coefficient and the standard difference between the two datasets are 0.95 and 14 W/sq m (about 6% of the average shortwave irradiance), respectively, and the bias is 15 W/sq m (higher ERBE values). The bias, a strong function of ISCCP satellite viewing zenith angle, is mostly in the ISCCP-based estimates. Over snow/ice, vegetation, and desert no comparison is made with other satellite-based estimates, but theoretical calculations using the discrete ordinate method suggest that over highly reflective surfaces (snow/ice, desert) the model, which accounts crudely for multiple reflection between the surface and clouds, may substantially overestimate the absorbed solar energy flux at the surface, especially when clouds are optically thick. The monthly surface shortwave irradiance fields produced for 1986 exhibit the main features characteristic of the earth's climate. As found in other studies, our values are generally higher than Esbensen and Kushnir's by as much as 80 W/sq m in the tropical oceans. A cloud parameter, defined as the difference between clear-sky and actual irradiances normalized to top-of-atmosphere clear-sky irradiance, is also examined. This parameter, minimally affected by sun zenith angle, is higher in the midlatitude regions of storm tracks than in the intertropical convergence zone (ITCZ), suggesting that, on average, the higher cloud coverage in midlatitudes is more effective at reducing surface shortwave irradiance than opaque, convective, yet sparser clouds in the ITCZ. Surface albedo estimates are realistic, generally not exceeding 0.06 in the ocean, as high as 0.9 in polar regions, and reaching 0.5 in the Sahara and Arabian deserts.

Breon, Francois-Marie↗
NASA NTRS1979

Ionosphere scintillations associated with features of equatorial ionosphere

Amplitude scintillations of radio beacons aboard the ATS-6 satellite on 40 MHz, 140 MHz and 360 MHz recorded during the ATS-6 phase II at an equatorial station Ootacamund (dip 4 deg N) and the ionograms at a nearby station Kodaikanal (dip 3.5 deg N) are examined for scintillation activity. Only sporadic E events, other than Es-q, Es-c or normal E are found to be associated with intense daytime scintillations. Scintillations are also observed during night Es conditions. The amplitude spread is associated with strong scintillations on all frequencies while frequency spread causes weaker scintillations and that mainly at 40 MHz.

Chandra, H.↗
NASA NTRS1975

On a suspected ring external to the visible rings of Saturn

Reexamination of a photograph of Saturn taken on Nov. 15, 1966, when the earth was nearly in the ring plane, indicates that ring material may exist outside the visible rings, extending to more than 6 Saturnian radii. Although the suspected feature on the photograph appears to be real, the possibility of its being a developed pressure mark or a chance alignment of grains cannot be ruled out. The observed brightness in the blue light was estimated to be 19.5 plus or minus 0.5 per linear arcsecond, implying a normal optical thickness, .0000001 for ice-covered particles. For spacecraft passing through this region, the hazards are found to be minimal.

Smith, B. A.↗
NASA NTRS1983

W-shaped occultation signatures - Inference of entwined particle orbits in charged planetary ringlets

A model for the ringlets of Saturn is proposed where concentration of material near the inner and outer radial edges of the ringlets is a natural consequence of particles in entwined elliptical orbits, with the same particles alternately defining both edges. The existence of a collisionless state where particles fly along entwined paths in a compressed helical formation on and within a toroidal surface whose meridional cross section is a very thin ellipse is explained. The cancellation of strong oblateness perturbations by an extremely weak force normal to the orbit planes and directed primarily outward from the major axis of the meridional cross section of the torus is shown, and the possibility that electric repulsion of like-charged particles could provide the expansion force preventing cross-sectional collapse is examined. The model features a large stability domain within which orbital inclinations and arguments of periapse oscillate but do not progress. Features of the model that can be tested experimentally are mentioned.

Eshleman, V. R.↗
NASA NTRS1986

Objective analysis of tidal fields in the Atlantic and Indian Oceans

An objective analysis technique has been developed to extrapolate tidal amplitudes and phases over entire ocean basins using existing gauge data and the altimetric measurements which are now beginning to be provided by satellite oceanography. The technique was previously tested in the Lake Superior basin. The method has now been developed and applied in the Atlantic-Indian ocean basins using a 6 deg x 6 deg grid to test its essential features. The functions used in the interpolation are the eigenfunctions of the velocity potential (Proudman functions) which are computed numerically from a knowledge of the basin's bottom topography, the horizontal plan form and the necessary boundary conditions. These functions are characteristic of the particular basin. The gravitational normal modes of the basin are computed as part of the investigation, they are used to obtain the theoretical forced solutions for the tidal constituents, the latter provide the simulated data for the testing of the method and serve as a guide in choosing the most energetic modes for the objective analysis. The results of the objective analysis of the M2 and K1 tidal constituents indicate the possibility of recovering the tidal signal with a degree of accuracy well within the error bounds of present day satellite techniques.

Sanchez, B. V.↗
NASA NTRS1987

Second-overtone models of RR Lyrae stars

Linear models of RR Lyrae stars pulsating in the second overtone indicate that this mode is self-excited only for rather low luminosities if the masses are normal. An unstable second-overtone model has been selected from the linear survey and has been followed up to limiting amplitude by using a nonlinear hydrodynamical computer program. Deep splitting of the main light peak in the theoretical light curve occurs but does not resemble any observed feature. Moreover, the distribution of periods of RR Lyrae stars in globular clusters can be accounted for adequately by fundamental-mode and first-overtone pulsation. It is concluded that second-overtone pulsators probably do not exist among RR Lyrae stars.

Stothers, Richard B.↗
NASA NTRS1993

An atlas of ultraviolet spectra of star-forming galaxies

A systematic study is presented of the UV spectra of star-forming galaxies of different morphological type and activity class using a sample drawn from a uniformly reduced IUE data set. The spectra for a wide variety of galaxies, including normal spiral, LINER, starburst, blue compact, blue compact dwarf, and Seyfert 2 galaxies, are presented in the form of spectral energy distributions to demonstrate the overall characteristics according to morphology and activity class and in the form of absolute flux distributions to better show the absorption and emission features of individual objects. The data support the picture based on UV spectra of the Orbiting Astronomical Observatory and of the Astronautical Netherlands Satellite that spiral galaxies of later Hubble class have more flux at the shortest UV wavelengths than do spiral galaxies of earlier Hubble class.

Kinney, A. L.↗