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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 325 records · Page 18
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NASA NTRS1976

Ignition Transients of Large Segmented Solid Rocket Boosters

A model is described which provides a means for analyzing the complexities of ignition transients and pressure peaks of large, high performance, segmented solid rocket boosters. The method accounts for: (1) temporal and spatial development of the flow field set up by the head end igniter discharge, (2) ignition and flame spreading coupled to chamber flow, (3) the steep velocity, pressure, and temperature gradients that occur during the early phases of ignition, and (4) the interactions that produce ignition spikes (i.e., compression of chamber gases during pressurization, erosive burning, and mass added effect of igniter discharge). The technique differs from earlier models in that the flow interactions between the slots and main chamber are accounted for, and the original computer program for monolithic motors is improved. The procedures were used to predict the ignition transients of the current design for the space shuttle booster.

Caveny, L. H.↗
NASA NTRS1976

Metal-insulator-semi-conductor studies of lead telluride

The capacitance and conductance-voltage characteristics were measured on metal-insulator-semiconductor capacitors fabricated with zirconium dioxide films on single-crystal lead telluride. At 77 K, on both n- and p-type substrates, evidence of surface potential control was obtained. Comparison of the measured capacitance-voltage characteristics with those calculated from the equilibrium solution of the one-dimensional Poisson equation indicated qualitative agreement, although the slope of the measured capacitance in the region near the capacitance minimum was less steep than calculated.

Lilly, D. A.↗
NASA NTRS1977

Boundary layer separation on isolated boattail nozzles

The phenomenon of separated flow on a series of circular-arc afterbodies was investigated using the Langley 16-foot transonic tunnel at free-stream Mach numbers from 0.40 to 0.95 at 0 deg angle of attack. Both high-pressure air and solid circular cylinders with a diameter equal to the nozzle exit diameter were used to simulate jet exhausts. A detailed data base of boundary layer separation locations was obtained using oil-flow techniques. The results indicate that boundary layer separation is most extensive on steep boattails at high Mach numbers.

Abeyounis, W. K.↗
NASA NTRS1977

Application of LANDSAT data to delimitation of avalanche hazards in Montane Colorado

The author has identified the following significant results. Many avalanche hazard zones can be identified on LANDSAT imagery, but not consistently over a large region. Therefore, regional avalanche hazard mapping, using LANDSAT imagery, must draw on additional sources of information. A method was devised that depicts three levels of avalanche hazards according to three corresponding levels of certainty that active avalanches occur. The lowest level, potential avalanche hazards, was defined by delineating slopes steep enough to support avalanches at elevations where snowfall was likely to be sufficient to produce a thick snowpack. The intermediate level of avalanche hazard was interpreted as avalanche hazard zones. These zones have direct and indirect indicators of active avalanche activity and were interpreted from LANDSAT imagery. The highest level of known or active avalanche hazards was compiled from existing maps. Some landslides in Colorado were identified and, to a degree, delimited on LANDSAT imagery, but the conditions of their identification were highly variable. Because of local topographic, geologic, structural, and vegetational variations, there was no unique landslide spectral appearance.

Knepper, D. H., Jr.↗
NASA NTRS1976

Superconducting critical fields of alkali and alkaline-earth intercalates of MoS2

Results are reported for measurements of the critical-field anisotropy and temperature dependence of group-VIB semiconductor MoS2 intercalated with the alkali and alkaline-earth metals Na, K, Rb, Cs, and Sr. The temperature dependences are compared with present theories on the relation between critical field and transition temperature in the clean and dirty limits over the reduced-temperature range from 1 to 0.1. The critical-field anisotropy data are compared with predictions based on coupled-layers and thin-film ('independent-layers') models. It is found that the critical-field boundaries are steep in all cases, that the fields are greater than theoretical predictions at low temperatures, and that an unusual positive curvature in the temperature dependence appears which may be related to the high anisotropy of the layer structure. The results show that materials with the largest ionic intercalate atom diameters and hexagonal structures (K, Rb, and Cs compounds) have the highest critical temperatures, critical fields, and critical-boundary slopes; the critical fields of these materials are observed to exceed the paramagnetic limiting fields.

Woollam, J. A.↗
NASA NTRS1976

Effects of atomic oxygen on graphite ablation

It is shown that a previously derived semiempirical equation for describing observed ablation rates of isotropic graphites cannot be applied to low-density flows containing dissociated oxygen. Experimentally determined reaction probabilities of isotropic graphites to molecular and atomic oxygen are used to calculate heat-transfer rates and stagnation-point ablation rates for typical conditions. Integrated mass losses are computed for a group of flight trajectories which start from geosynchronous orbit and enter earth's atmosphere in a skipping motion following near-elliptic decaying orbits. A comparison of the results with those obtained by the equation under question shows excellent agreement for steep trajectories, but large discrepancies for shallow trajectories. The differences are attributed to surface oxidation by atomic oxygen.

Park, C.↗
NASA NTRS1976

Airborne testing of three antimotion sickness preparations

Thirteen human volunteers were exposed to weekly flights in which standardized, steep turns were used to produce motion sickness. A combination of promethazine hydrochloride (25 mg) plus ephedrine sulphate (25 mg) was found to be equally as effective as the combination of 1-scopolamine hydrobromide (0.35 mg) plus d-amphetamine sulphate (5 mg). Droperidol (2.5 mg) was indistinguishable from the placebo. It was concluded that the treatment of choice for motion sickness is promethazine plus ephedrine.

Johnson, W. H.↗
NASA NTRS1977

Experimental investigation of subsonic turbulent separated boundary layers on an airfoil

Detailed measurements of flow fields associated with low-speed turbulent boundary layers have been made for the 17% thick GA(W)-1 airfoil section at nominal angles of attack of 10, 14, and 18 deg; Reynolds number 2.2 million; and Mach number 0.13. The data include extensive pressure and velocity surveys of the pre- and post-separated regions on the airfoil and the associated wake. Integrated boundary-layer characteristics, including regions of separation on the airfoil, are also presented. The results indicate steep gradients of displacement thickness, momentum thickness, shape factor, and the separation streamline from the point of separation to the trailing edge of the airfoil. The present tests reveal that the region of flow reversal terminates within a suprisingly short distance of less than 20% chord downstream from the trailing edge for the test range of angle of attack.

Seetharam, H. C.↗
NASA NTRS1976

Electrons in a closed galaxy model of cosmic rays

The paper considers the consistency of positrons and electrons with a propagation model in which the cosmic rays are stopped by nuclear collisions or energy losses before they can escape from the Galaxy (the closed-galaxy model). The fact that no inconsistency is found between the predictions and the data implies that the protons which produce the positrons by nuclear reactions could have their origin in a large number of distant sources, as opposed to the heavier nuclei which in this model come from a more limited set of sources. The closed-galaxy model predicts steep electron and positron spectra at high energies. None of these are inconsistent with present measurements; but future measurements of the spectrum of high-energy positrons could provide a definite test for the model. The closed-galaxy model also predicts that the interstellar electron intensity below a few GeV is larger than that implied by other models. The consequence of this result is that electron bremsstrahlung is responsible for about 50% of the galactic gamma-ray emission at photon energies greater than 100 MeV

Ramaty, R.↗
NASA NTRS1977

Celestial diffuse gamma-ray emission observed by SAS-2 and its interpretation

A clearly established diffuse celestial gamma-ray component was seen by SAS-2 above 35 MeV, after examining several regions of the sky at different latitudes, including the north celestial pole. For energies above 100 MeV the gamma ray results are consistent with an equation of the form I(b)=C1+C2/sin b with the second term being dominant, suggesting that the radiation above 100 MeV comes largely from the local regions of the galactic disk. Between 35 and 100 MeV, a similar equation is also a reasonable representation of the data, but here the two terms are comparable, with the first, or isotropic term, actually being the larger one. In addition to indicating that the diffuse radiation is partially galactic, these results imply a steepness for the energy spectrum of the diffuse isotropic component which places significant constraints on possible theoretical models of this radiation.

Fichtel, C. E.↗
NASA NTRS1977

Spin-tunnel investigation of the spinning characteristics of typical single-engine general aviation airplane designs. 2: Low-wing model A; tail parachute diameter and canopy distance for emergency spin recovery

A spin tunnel study is reported on a scale model of a research airplane typical of low-wing, single-engine, light general aviation airplanes to determine the tail parachute diameter and canopy distance (riser length plus suspension-line length) required for energency spin recovery. Nine tail configurations were tested, resulting in a wide range of developed spin conditions, including steep spins and flat spins. The results indicate that the full-scale parachute diameter required for satisfactory recovery from the most critical conditions investigated is about 3.2 m and that the canopy distance, which was found to be critical for flat spins, should be between 4.6 and 6.1 m.

Burk, S. M., Jr.↗
NASA NTRS1977

Diffuse gamma radiation

An examination of the intensity, energy spectrum, and spatial distribution of the diffuse gamma-radiation observed by SAS-2 satellite away from the galactic plane in the energy range above 35 MeV has shown that it consists of two components. One component is generally correlated with galactic latitudes, the atomic hydrogen column density was deduced from 21 cm measurements, and the continuum radio emission, believed to be synchrotron emission. It has an energy spectrum similar to that in the plane and joins smoothly to the intense radiation from the plane. It is therefore presumed to be of galactic origin. The other component is apparently isotropic, at least on a coarse scale, and has a steep energy spectrum. No evidence is found for a cosmic ray halo surrounding the galaxy in the shape of a sphere or oblate spheroid with galactic dimensions. Constraints for a halo model with significantly larger dimensions are set on the basis of an upper limit to the gamma-ray anisotropy.

Fichtel, C. E.↗
NASA NTRS1978

Development of systems and techniques for landing an aircraft using onboard television

A flight program was conducted to develop a landing technique with which a pilot could consistently and safely land a remotely piloted research vehicle (RPRV) without outside visual reference except through television. Otherwise, instrumentation was standard. Such factors as the selection of video parameters, the pilot's understanding of the television presentation, the pilot's ground cockpit environment, and the operational procedures for landing were considered. About 30 landings were necessary for a pilot to become sufficiently familiar and competent with the test aircraft to make powered approaches and landings with outside visual references only through television. When steep approaches and landings were made by remote control, the pilot's workload was extremely high. The test aircraft was used as a simulator for the F-15 RPRV, and as such was considered to be essential to the success of landing the F-15 RPRV.

Gee, S. W.↗
NASA NTRS1978

Boundary-layer separation on isolated boattail nozzles

An angle of attack of 0 deg was investigated in the Langley 16 foot transonic tunnel at free-stream Mach numbers from 0.40 to 0.95 to study the phenomenon of separated flow on a series of circular-arc afterbodies. Both high-pressure air and solid circular cylinders with the cylinder diameter equal to the nozzle-exit diameter were used to simulate jet exhausts. The results indicate that boundary-layer separation is most extensive on steep boattails at high Mach numbers. The jet total-pressure ratio changes (jet total pressure to free-stream static pressure) affected the extent of separation very little; however, comparison of the separation data obtained by using the two jet-simulation techniques indicate that entrainment associated with the presence of a jet had a significant effect on the extent of separation. The solid-simulator separation data were also used to evaluate the predictions of eight separation criteria.

Abeyounis, W. K.↗
NASA NTRS1977

Preliminary geologic evaluation of L-band radar imagery: Arkansas test site

The relatively small angles of incidence (steep depression angles) of the L-band system provide minimal shadowing on terrain back-slopes and considerable foreshortening on terrain fore-slopes which sacrifice much of the topographic enhancement afforded by a more oblique angle of illumination. In addition, the dynamic range of the return from vegetated surfaces is substantially less for the L-band system, and many surface features defined primarily by subtle changes in vegetation are lost. In areas having terrain conditions similar to those of northern Arkansas, and where LANDSAT and shorter wavelength aircraft radar data are available, the value of the JPL L-band imagery as either a complimentary or supplementary geologic data source is not obvious.

Macdonald, H.↗
NASA NTRS1977

Geology of the Valles Marineris - First Analysis of Imaging from the Viking 1 Orbiter Primary Mission

The Valles Marineris on the planet Mars constitute an enormous group of steep-walled equatorial canyons extending over an area more than 4000 km long and up to 700 km wide. An overview of Valles Marineris is provided, taking into account canyon system subdivisions, imaging and topographic data, Noctis Labyrinthus, western troughs, central troughs, east central troughs, and eastern canyons. Aspects of canyon wall and canyon floor morphology are discussed, giving attention to erosional features, layered rocks in canyon walls, tectonic features, plains, landslide deposits, hilly terrain, fractured floor, and floor plateaus and ridges. Upland pits and closed depressions in the canyons are considered along with regional tectonics and regional erosional styles.

Blasius, K. R.↗
NASA NTRS1977

Experimental determination of sound and high-speed flow interaction

An experimental facility for measuring the attenuation of sound at various frequencies and modes in a finite duct with high-speed flow (with or without an axial pressure gradient) is described. The facility consists of an anechoic chamber transonic compressor with inlets of different area variations (or axial gradients); sound of selected frequencies and modes is produced with eight circumferential acoustic drivers. The experimental results indicate that high Mach number inlets can increase noise propagation. In addition, an inlet with a constant axial gradient is found to have a better acoustic and aerodynamic performance than inlets of the same area ratio with steep gradients near the throat or exit.

Lumsdaine, E.↗
NASA NTRS1977

Copernicus studies of interstellar material in the Perseus II complex. III - The line of sight to Zeta Persei

Ultraviolet spectrophotometric data obtained with Copernicus are used to analyze the distribution, composition, density, temperature, and kinematics of the interstellar material along the line of sight to Zeta Persei. The far-UV extinction curve for the star is evaluated along with the kinematics of the interstellar gas, observations of atomic and molecular hydrogen, curves of growth for neutral and ionized species, atomic abundances and depletions, ionization equilibria, and observations of CO and OH lines. The results show that there are apparently three clouds along the line of sight to Zeta Persei: a main cloud at approximately +13 km/s which contains most of the material and forms all the neutral and molecular lines as well as most of the ionic lines, a second component at +22 km/s which must contribute to the strong UV lines of most ions, and a third component at roughly +2 km/s which gives rise to a strong Si III line at 1206 A. It is also found that the UV extinction curve has a somewhat steep far-UV rise, indicating the presence of a substantial number of small grains, and that about 30% of the hydrogen nuclei over the entire line of sight are in molecular form.

Snow, T. P., Jr.↗