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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 253 records · Page 14

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NASA NTRS1981

Optimal air-breathing launch vehicle design

A generalized two-point boundary problem methodology, similar to techniques used in deterministic optimal control studies, is applied to the design and flight analysis of a two-stage air-breathing launch vehicle. Simultaneous consideration is given to configuration and trajectory by treating geometry, dynamic discontinuities, and time-dependent flight variables all as controls to be optimized with respect to a single mathematical performance measure. While minimizing fuel consumption, inequality constraints are applied to dynamic pressure and specific force. The optimal system fuel consumption and staging Mach number are found to vary little with changes in the inequality constraints due to substantial geometry and trajectory adjustments. Staging, from an air-breathing first stage to a rocket-powered second stage, consistently occurs near Mach 3.5. The dynamic pressure bound has its most pronounced effects on vehicle geometry, particularly the air-breathing propulsion inlet area, and on the first-stage altitude profile. The specific force has its greatest influence on the second-stage thrust history.

Hattis, P. D.↗

NASA NTRS1981

Ceramics for the AGT101 automotive gas turbine

An advanced gas turbine powertrain for automotive application is being developed. Objectives of the program include a fuel consumption of 42.8 mpg on No. 2 diesel fuel in a 3000 pound car, same overall vehicle performance as obtained with a conventional spark ignition internal combustion engine, low emission, multiple fuel capacity, reliability, and competitive cost. The AGT101 powertrain consists of a power section, gearbox and transmission, and the design and analysis conducted thus far support the initial engine concept, as no significant design changes have been required. The ceramic rotor design approach and component materials are discussed, and it is projected that the AGT powertrain will be competitive with any other alternative powertrain in meeting the design objectives.

Kreiner, D. M.↗

NASA NTRS1982

Observation of gamma-ray bursts with the SMM gamma-ray spectrometer

The gamma-ray spectrometer on SMM is sensitive to bursts within its field of view with intensities greater than 0.000005 erg/sq cm above 100 keV. It has detected 17 events between February 1980 and March 1981 with the characteristics of cosmic gamma-ray bursts. The most intense burst, on 19 April 1980, had a photon spectrum consistent with a power law with spectral index - 2.5 from 300 keV to approximately 7 MeV. It is not possible at present to exclude the sun as the source of this burst. Spectra of 11 of the bursts have been studied for line features with no clear evidence for line emission greater than 300 keV. The continuum radiation from about half of these events have hard emission extending to approximately equal to or greater than 2 MeV.

Share, G. H.↗

NASA NTRS1982

Further measurements of high energy cosmic ray electrons

The University of Chicago balloon telescope for cosmic ray electrons has been substantially modified and improved, and has been exposed in another successful balloon flight in 1980. Preliminary results from this flight, over the energy range 5 to 200 GeV, are presented. Data indicate an electron flux of 0.27 plus or minus 0.04/(sq m sec sr GeV) at 10 GeV, and a spectral shape consistent with a power law E to the -3.0 power at low energies, but steepening further, probably due to radiative energy losses, with increasing energy.

Mueller, D.↗

NASA NTRS1982

An X-ray study of two Crablike supernova remnants - 3C 58 and CTB 80

The instruments on the Einstein Observatory have been used to study the X-ray properties of two Crablike SNRs: 3C 58 and CTB 80. Images of the objects are similar, showing an extended plateau of emission surrounding a pronounced central maximum consistent with the presence of a point source. The X-ray spectrum of 3C 58 is consistent with a power law of spectral index 0.5 + 0.5 or -0.2 modified by absorption in a hydrogen column density N sub H of (2 + or - 0.5) x 10 to the 21st/sq cm. These data suggest an analogy with the Crab Nebula, where the extended X-ray emission is nonthermal and the pointlike emission emanates from a central neutron star. Quantitative comparisons of the X-ray and radio properties for six Crablike remnants indicate significant differences which may reflect an evolutionary sequence.

Becker, R. H.↗

NASA NTRS1982

Fracture of directionally solidified multicrystalline silicon

Fracture toughness data is given for multicrystalline silicon which has been prepared by directional solidification. Results indicated a plane-strain fracture toughness of 0.8 to 0.87 MN/m to the 3/2 power, which is consistent with data for single-crystal silicon.

Chen, C. P.↗

NASA NTRS1985

Improved Ellipsoidal Radiation Furnace

Spherical reflector around heat source increases efficiency and minimizes power requirements. Furnace consists of ellipsoid with point heat source, at one focus and sample heated at other focus. Spherical reflector with circular slit surrounds heat source. All radiation not passing through circular slit in spherical reflector reflected back to lamp. Radiation passing through spherical slit focused by ellipsoid surface onto sample. Arrangement uses heat efficiently, reduces waste heat generation and permits full view of specimen.

Ethridge, E. C.↗

NASA NTRS1985

Implications of the experimental results on high energy cosmic rays with regard to their origin

It was shown in an earlier report that current cosmic ray evidence supports a change in the cosmic ray composition in the region between 10 to the 6th power and 10 to the 8th power GeV total energy in the direction of a smaller average value of A. Compared to normal celestial abundances, the heavy nuclei are much less abundant, and, in fact, the composition measurements above 10 to the 8th power GeV are consistent with there being only protons. Here, these results combined with those of the energy spectrum and anisotropy of the comsic rays and other astrophysical information will be examined to try to determine their implications for the origin of the cosmic rays. In this paper, consideration is given to the implications of one or more than one type of source in the galaxy to see which are consistent with the interpretation of current measurements. The nature of the source types that would be required are discussed.

Fichtel, C. E.↗

NASA NTRS1985

Particle distributions in approximately 10(13) - 10(16) eV air shower cores at mountain altitude and comparison with Monte Carlo simulations

Photographs of 521 shower cores in an array of current-limited spark (discharge) chambers at Sacramento Peak (2900m above sea level, 730 g /sq cm.), New Mexico, U.S.A., have been analyzed and the results compared with similar data from Leeds (80m above sea level, 1020 g sq cm.). It was found that the central density differential spectrum is consistent with a power law index of -2 up to approx. 1500/sq m where it steepens, and that shower cores become flatter on average with increasing size. Scaling model predictions for proton primaries with a approx E sup -2.71 energy spectrum account well for the altitude dependence of the data at lower densities. However, deviations at higher densities indicate a change in hadron interaction characteristics between approx few x 10 to the 14th power and 10 to the 15th power eV primary energy causing particles close to the shower axis to be spread further out.

Ash, A. G.↗

NASA NTRS1985

Soft X-ray spectral observations of low-luminosity active galaxies

The X-ray spectra of a sample of 12 low-luminosity AGNs observed using the solid state spectrometer on the HEAO 2 satellite are investigated. The AGNs discussed here have X-ray luminosities below about 10 to the 44th erg/s, and thus form a sample complementary to the higher luminosity sample discussed by Petre et al. (1984). The spectra are well described by a simple model consisting of a power law, with photon spectral index about 1.7, plus absorption by cold gas. The objects in the sample can be separated into three groups: (1) those whose spectra show no significant absorption; (2) those for which the X-ray source is totally covered by a spatially uniform absorbing medium; and (3) those for which partial covering by 'patchy' absorbers is indicated. Column densities and covered fractions do not correlate systematically with X-ray luminosity. Implications regarding physical conditions in AGNs are discussed.

Reichert, G. A.↗

NASA NTRS1986

The nearby Abell clusters. I - Abell 168

As part of a large program to study the spatial and luminosity distributions of galaxies in the nearby Abell clusters, the results of a photometric study of Abell 168 are presented and compared to the previous results of Dressler (1978). The previous result is confirmed that the faint end of the luminosity function for the galaxies in the central 0.2 sq deg of this cluster is quite flat (alpha = -1.0 in the Schechter formalism). The slope of the faint end appears to be fairly normal if galaxies from a larger region (1 sq deg) are included, but this may be due to a larger than expected contribution of background galaxies. Consequently, the faint end of the luminosity function of galaxies in a 0.2 sq deg region (and possibly also in a 1 sq deg region) centered on A168 is flatter than the 'universal' luminosity function (a Schechter function with alpha = -1.25). Nevertheless, the luminosity functions for both these regions are well fit by Schechter functions. A study of the spatial distribution of galaxies indicates that the radial dependence of the projected surface density is consistent with a power law of slope - 1.01 + or - 0.09.

Oegerle, W. R.↗

NASA NTRS1986

Ignition of metals and alloys in gaseous oxygen by frictional heating

The ignition of metals and alloys have been investigated by rotating the end of a hollow cylinder against an identical stationary cylinder on a common axis (frictional heating) in gaseous oxygen. A ranking criterion that measures the resistance of metals and alloys to ignition is discussed. It consists of the power per unit area required for ignition conveniently expressed as the product of contact pressure P and average linear velocity ALV. Data are presented that demonstrate that materials that are high in nickel and copper require greater P-ALV products for ignition (more resistant to ignition) than materials that are high in iron. Aluminum and titanium alloys are shown to require the lowest P-ALV products for ignition. The effects of varying surface velocity, contact pressure, coefficient of friction, and oxygen pressure on P-ALV products required for ignition are discussed. The results indicate that P-ALV product required for ignition increases as surface velocity increases, as contact pressure decreases, and as the coefficient of friction decreases. Increasing oxygen pressure will cause the P-ALV product required for ignition to decrease at low pressures and increase at high pressures. In some cases, the relative ranking of materials based on P-ALV products will also change as conditions are varied. The data presented in this paper are from a development program to determine the merits of using such a dynamic test method for ranking materials for oxygen service. The results to date have indicated that more testing is required before this method can be made into a standard test. The data presented do show some of the major parameters affecting the ignition of materials when exposed to frictional heating. The repeatability of the data at any set of conditions have not been thoroughly investigated.

Benz, F. J.↗

NASA NTRS1988

Development of experimental systems for material sciences under microgravity

As part of the Space Experiment Program of the Society of Japanese Aerospace Companies, three experimental systems (G452, G453, G454) have been developed for materials science studies under microgravity by the NEC Corporation. These systems are to be flown as Get Away Special payloads for studying the feasibility of producing new materials. Together with the experimental modules carrying the hardware specific to the experiment, the three systems all comprise standard subsystems consisting of a power supply, sequence controller, temperature controller, data recorder, and video recorder.

Tanii, Jun↗

NASA NTRS1989

The effects of nonlinear loading upon the Space Station Freedom 20 kHz power system

The Space Station Freedom power distribution system, which consists of dual redundant 20-kHz, 440-V RMS, single-phase power systems, is discussed. The effect of a typical space station nonlinear load on the measurement of RMS current and voltage at various points in the space station power system has been investigated using the Electromagnetic Transients Program (EMTP). The load current distortion at the user interface, its effect on the distribution system, and its relationship to power factor have been studied. Modeling results are compared to test data. The differences under nonlinear loading are evaluated and presented as a measure of distribution voltage distortion and current measurement accuracy.

Leskovich, R. Thomas↗

NASA NTRS1990

Hypervelocity, minimum-radii, coordinated turns

An analytic solution is presented for the most basic powered-flight maneuver, consisting of a constant-altitude coordinated turn and expressions for minimum-turn radii; associated flight conditions are derived. It is shown that the formulation for hypervelocity turns differs from that for subsonic and hypersonic speeds. Illustrative calculations using approximate aerodynamics based on Newtonian theory are presented, and these demonstrate the differences of hypersonic flight conditions and their associated turning radii from those at lower speeds.

Tauber, Michael E.↗

NASA NTRS1991

On the origin of the diffuse x ray background

The first measurement is reported of the intensity and spectrum of the diffuse x ray background in the 0.16 to 3.5 keV band which is free from contamination by sources with fluxes greater than approx. 6 x 10(exp -14) erg/sq cm/s. This result was made possible by the development of a number of techniques for reducing cosmic ray contamination and instrumental artifacts in the data collected by the Einstein Observatory imaging proportional counter. The analysis of the background data reveals a mean absolute intensity for the emission I sub x(0.16 to 3.5 keV) approx. = 5.6 x 10(exp -8) erg/sq cm/s/sr. The intensity is dependent on galactic longitude even when only high galactic data are used, allowing the setting of a lower limit of 20 pct. on the galactic contribution to the mean emission band. The spectrum of the total background is consistent with a power law of slope similar to 0.7 between 0.16 and 3.5 keV with evidence for a steep rise toward lower energies. Preliminary evidence is also reported for the association of faint radio sources with peaks in the arcminute scale fluctuations of the diffuse x ray surface brightness distribution and then some implications are considered of these results.

Helfand, David J.↗

NASA NTRS1995

Horizontal axis wind turbine post stall airfoil characteristics synthesization

Blade-element/momentum performance prediction codes are routinely used for wind turbine design and analysis. A weakness of these codes is their inability to consistently predict peak power upon which the machine structural design and cost are strongly dependent. The purpose of this study was to compare post-stall airfoil characteristics synthesization theory to a systematically acquired wind tunnel data set in which the effects of aspect ratio, airfoil thickness, and Reynolds number were investigated. The results of this comparison identified discrepancies between current theory and the wind tunnel data which could not be resolved. Other factors not previously investigated may account for these discrepancies and have a significant effect on peak power prediction.

Tangler, James L.↗

NASA NTRS1995

Photon-photon opacity constraints for relativistically expanding gamma-ray burst sources

Five bright gamma-ray bursts (GRBs) detected by the Burst and Transient Source Experiment (BATSE) have also been detected at higher energies by EGRET. Four are consistent with power-law spectra extending to energies as high as, in the case of GRB930131, 1 GeV. The fifth, and most recent, GRB940217, has a more complex spectrum, with one photon detected at 18 GeV, the most energetic GRB photon detection to date. The optical depth to photon-photon pair production in these sources is extremely large for distances more than about 10pc away if the radiation is emitted isotropically in the observer's frame. This optical depth can be dramatically reduced if the source is moving with a relativstic bulk Lorentz factor Gamma, and recent calculations for this situation have been limited to cases of a beam with opening angle 1 Gamma, or expansions of infinitely thin spherical shells. This paper presents our extension of the pair production otpical depth calculation in relativistically expanding sources to more general geometries, including shells of finite thickness and arbitrary opening angle. We find that the minimum bulk Lorentz factors for the Energy Gamma Ray Experiment Telescope (EGRET) sources to be optically thin, i.e. display no spectral attenuation, is only moderately dependent on the shell thickness and its opening solid angle; these new limits on required velocity for given geometries will aid in placing realistic constraints on GRB source models.

Baring, M. G.↗