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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 NTRS1973

Unusual chemical compositions of noctilucent-cloud particle nuclei

Two sounding rocket payloads were launched from the ESRO range in Sweden during a noctilucent cloud display. Large numbers of submicron particles were collected, most of which appear to be made up of a high density material coated with a low density material. Typical electron micrographs are shown. Particle chemical compositions have been measured by use of dispersive X-ray analysis equipment attached to an electron microscope and have revealed that most of the high density particle nuclei have atomic weights greater than iron.

Hemenway, C. L.↗
NASA NTRS1973

Origin and characteristics of excess Fe metal in lunar glass welded aggregates

We show that the characteristic features of lunar glass welded aggregates including their irregular shapes, vesicularity, and content of submicron Fe metal in the welding glass can be explained by a model in which they are predominantly formed by micrometeorite impacts into the solar wind saturated topmost surface of the regolith. The Fe metal is reduced from silicates by the solar wind gases. Other possible mechanisms of Fe metal formation are discussed and shown to play at most minor roles. It is shown that surface tension forces control vesicularity and that the low gravity and high vacuum conditions prevailing on the moon are unimportant. Consequences of this surface tension control to possible lunar eruptive volcanism and to the Ar-40/Ar-39 dating of impact events are discussed.

Housley, R. M.↗
NASA NTRS1974

Vacuum ultraviolet holography

We report the first demonstration of holographic techniques in the vacuum ultraviolet spectral region. Holograms were produced with coherent 1182-A radiation. The holograms were recorded in polymethyl methacrylate and examined with an electron microscope. A holographic grating with a fringe spacing of 386 A was produced and far-field Fraunhofer holograms of submicron particles were recorded.

Bjorklund, G. C.↗
NASA NTRS1975

Internal optical losses in very thin CW heterojunction laser diodes

Theoretical calculations are presented showing the relationship between the internal laser absorption and structural parameters appropriate for CW room-temperature lasers. These diodes have submicron-thick recombination regions, and very small spacings between the heat sink and the recombination region to minimize the thermal resistance. The optical loss is shown to be strongly dependent on the degree of radiation confinement to the active region. In particular, absorption in the surface GaAs layer providing the ohmic contact becomes very significant when the intermediate (AlGa)As layer is reduced below about 1 micron. It is further shown that excessive penetration into the GaAs regions gives rise to anomalies in the far-field radiation profiles in the direction perpendicular to the junction plane.

Butler, J. K.↗
NASA NTRS1974

Lunar surface phenomena - Solar flare track gradients, microcraters, and accretionary particles

Data are presented concerning the energy spectra of solar flare particles and the distribution of particles producing submicron diameter craters. Processes which alter the albedo and possibly the chemistry of exposed lunar surfaces are also considered. Measurements are reported of solar flare track gradients in rock 64455 which is sufficiently young to have uneroded surfaces on its sides. Attention is also given to accretionary particles adhering to host surfaces, microcraters on soil particles, and microcraters on the oriented surfaces of sample 76015 from a boulder at Station 6 of the Apollo 17 site.

Blanford, G. E.↗
NASA NTRS1975

Heavy element affinities in Apollo 17 samples

Pb-204, Bi, Tl, and Zn in samples from the Apollo 17 site exhibit relationships not found in samples from other sites. Pb-204, Tl, and Zn in residues remaining after dilute acid leaching are correlated with one another. Orange soil 74220, which is enriched in Pb-204, Tl, and Zn, is included in these relationships. In addition, the submicron metallic phase generally associated with agglutinate formation is correlated with all three of these elements; this relationship has already been reported for Pb-204 in other samples. Thus, orange soil and agglutinates appear to be involved in concentrating heavy volatile metals. A process other than mixing is required to account for this. As a consequence of the isolation of the landing site by the surrounding massifs, local supply and recycling of volatile trace elements in soils may account for some of the interelement relations.

Allen, R. O., Jr.↗
NASA NTRS1975

Hyperbolic cosmic dust - Its origin and its astrophysical significance

The heliocentric radial distribution of the flux of hyperbolic cosmic dust particles, as measured by the Pioneer 8 and 9 spacecraft, is closely related to the radial variation of the spatial density of source or parent meteoroids. Within the limits of the experimental and theoretical uncertainties the spatial density of parent meteoroids, as deduced from the hyperbolic cosmic dust data, is found to be increasing with increasing heliocentric distance in the neighborhood of one AU. Other recent experimental evidence confirms this result. The new results also suggest that the ratio of the areal density of submicron-sized craters to the areal density of millimeter-sized craters will be less on the north-south faces of lunar rocks than on the east-west faces of the same rocks. The change in ratio is not as large as previously thought. It is noted that the solar system is not presently contributing significant amounts of dust to the interstellar medium though it may once have done so.

Zook, H. A.↗
NASA NTRS1976

Laser Doppler spectrometer method of particle sizing

A spectrometer for the detection of airborne particulate pollution in the submicron size range is described. In this device, airborne particles are accelerated through a supersonic nozzle, with different sizes achieving different velocities in the gas flow. Information about the velocities of the accelerated particles is obtained with a laser-heterodyne optical system through the Doppler shift of light scattered from the particles. Detection is accomplished by means of a photomultiplier. Nozzle design and signal processing techniques are also discussed.

Weber, F. N.↗
NASA NTRS1976

Investigation of shock-induced separation of a turbulent boundary layer using laser velocimetry

Boundary-layer measurements realized by laser velocimetry are presented for a Mach 2.9, two-dimensional, shock-wave/turbulent boundary-layer interaction containing an extensive region of separated flow. Mean velocity and turbulent intensity profiles were obtained from upstream of the interaction zone to downstream of the mean reattachment point. The superiority of the laser velocimeter technique over pressure sensors in turbulent separated flows is demonstrated by a comparison of the laser velocimeter data with results obtained from local pitot and static pressure measurements for the same flow conditions. The locations of the mean separation and reattachment points as deduced from the mean velocity measurements are compared to oil-flow visualization results. Representative, velocity probability density functions obtained in the separated flow region are also presented. Critical to the success of this investigation were: (1) the use of Bragg cell frequency shifting and (2) artificial seeding of the flow with submicron light-scattering particles.

Modarress, D.↗
NASA NTRS1976

Electrostatic disruption of lunar dust particles

The possibility that dust particles might explode catastrophically on the lunar surface due to electrostatic charging is examined. For the dark side along the terminator zone, dust balls and compact stony particles of micron and submicron sizes will be blown up if their surface potential is as low as a kilovolt negative. This mechanism does not operate on the sunlit side because the surface potential is only 3.5-20 volts positive.

Rhee, J. W.↗
NASA NTRS1976

Stratospheric aerosols and climatic change

Generated primarily by volcanic explosions, a layer of submicron silicate particles and particles made of concentrated sulfuric acids solution is present in the stratosphere. Flights through the stratosphere may be a future source of stratospheric aerosols, since the effluent from supersonic transports contains sulfurous gases (which will be converted to H2SO4) while the exhaust from Space Shuttles contains tiny aluminum oxide particles. Global heat balance calculations have shown that the stratospheric aerosols have made important contributions to some climatic changes. In the present paper, accurate radiative transfer calculations of the globally-averaged surface temperature (T) are carried out to estimate the sensitivity of the climate to changes in the number of stratospheric aerosols. The results obtained for a specified model atmosphere, including a vertical profile of the aerosols, indicate that the climate is unlikely to be affected by supersonic transports and Space Shuttles, during the next decades.

Baldwin, B.↗
NASA NTRS1976

Some modifications of the theory of colloidal plasmas

Two effects leading to significant modifications of the theory of colloidal plasmas are discussed. The first concerns the fact that depending on the sign of the electric potential on a droplet in a colloidal plasma, the electrons or the ions impact on the droplet with a much higher effective temperature than their background plasma temperature. The analytical expression for this temperature is derived in the first part of the paper. In the second part, it is shown that the electron-droplet collision rate in a wet alkali-metal vapor plasma may be substantially modified by the effect of the attractive potential between a droplet and an electron because of the image of the electron in the droplet. This effect is found to be important when the droplet sizes are in the submicron range.

De, B. R.↗
NASA NTRS1976

Image intensifier tube observations of the OH airglow during the Space Shuttle simulation

The OH airglow studies discussed have evolved from a lead-sulfide-cell scanning photometer to photographic techniques to, currently, image-tube photography. During the Space Shuttle Simulation, photography (35-mm and 16-mm) and filter-wheel photometry of submicron OH airglow were performed aboard the NASA CV990 Airborne Laboratory. Examples of ground-based and airborne photographs are presented for comparison. Analysis of the aircraft data is described.

Peterson, A. W.↗
NASA NTRS1977

Distribution and flux of micrometeoroids

The mass distribution, flux, and distribution in space of the micrometeoroid complex at 1 AU are estimated on the basis of data from Apollo 17 rocks and recent calibrations of solar-flare track-production rates. It is found that the size frequency distribution of microcraters on lunar rocks suggests a bimodal mass distribution of micrometeoroids, but the precise form of the curve requires further definition, particularly insofar as the degree of depletion of particles producing craters 10 to 100 microns in diameter is concerned. Variations in slope with crater-diameter or particle-mass increments are shown to indicate that different processes affect one or more particle populations. Fluxes corresponding to varied lunar surface orientation and residence time are calculated, but no striking difference is observed between the flux of submicron-diameter particles with orbits in the plane of the ecliptic and fluxes of particles with orbits normal to the plane in the solar apex direction.

Morrison, D. A.↗
NASA NTRS1976

Microcraters and solar flare tracks in crystals from carbonaceous chondrites and lunar breccias

Results of microcrater and solar-flare track studies of grains from the interiors of five carbonaceous chondrites and one lunar 'soil breccia' are combined to investigate variations in solar flare intensity, variations in micrometeorite particle flux, characteristics of interplanetary submicron particles, and the probable region in space where the precompaction irradiation occurred. The thickness turnover rate, material loss rate, and other parameters of the regolith-like surface where the meteorites must have formed are determined to a certain extent by considering published data on solar-wind and spallogenic species in the meteorites in conjunction with the present data. It is found that: (1) most irradiation features are most plausibly explained in terms of a regolith origin; (2) the shape of the solar-flare energy spectrum has not changed over the last 4.2 billion years; (3) the flux of small micrometeoroids about 4.2 billion years ago cannot have been more than 4 to 20 times higher than the flux today; and (4) parent-body regolith turnover rates were not extremely high.

Goswami, J. N.↗
NASA NTRS1976

Photometric studies of light scattering above the lunar terminator from Apollo solar corona photography

Excess brightness is found in 70-mm photographs of the solar corona above the lunar terminator during Apollo 15 and 17. Maximum brightness of this scattered light is determined from calibration of image density. The observed excess brightness displays circular symmetry above the lunar-horizon subsolar point, characteristic of forward diffraction scattering from micron or submicron size (solid) grains, and decays rapidly in intensity with altitude and distance from the lunar terminator. The observed brightness cannot be accounted for by a co-orbiting cloud of spacecraft contaminants, but requires a variable lunar dust 'atmosphere' over the terminator regions extending to altitudes in excess of 100 km. To maintain such large masses of lunar fines above the terminator requires either local mass-churning rates in excess of 2 by 10 to the -11th power g/sq cm sec or the assumption of some degree of high-altitude electrostatic suspension to increase the dwell time of individual grains at the altitudes observed. Such a model would reduce mass-churning rates while causing selective erosion/deposition and potential for escape of significant mass from the moon

Mccoy, J. E.↗
NASA NTRS1978

High resolution masks for ion milling pores through substrates of biological interest

The feasibility was investigated of electrochemically oxidizing vapor deposited aluminum coatings to produce porous aluminum oxide coatings with submicron pore diameters and with straight channels normal to the substrate surface. Porous aluminum oxide coatings were produced from vapor deposited aluminum coatings on thin stainless steel (304), copper, Teflon (FEP) and Kapton substrates and also on pure aluminum substrates. Scanning electron microscope examination indicated that porous oxide coatings can be produced with straight channels, appropriate pore diameters and none or minimal intervening residual aluminum. The oxide coatings on the copper and Kapton substrates had the straightest channels and in general were superior to those fabricated on the other substrate materials. For oxide coatings fabricated at 600 V and 300 V, pore diameters were 0.4-0.6, and 0.3 micron with center-to-center spacing of 0.7-0.8, and 0.4 micron, respectively. Estimated direct labor and materials costs to prepare an oxide mask is anticipated to be about $4-$6 per square foot.

Donovan, S. S.↗
NASA NTRS1977

Comparison of predicted and observed solar radiation in an urban area

Measurements of the downward solar radiant flux in the St. Louis area are compared with predictions from an approximate solution to the radiative transfer equation. The atmospheric aerosols were assumed to have a power size distribution and the refractive indices suggested by Fischer (1973) for an urban area. On a relatively clean day, the predictions compared well with observations. On a hazy day, the comparison was poor with the a priori choice of aerosol properties. The particles on the hazy day apparently had more submicron particles than those found in the assumed size distribution, and the particles were considerably less absorbing than those observed by Fischer. These changes could represent the effects of relative humidity and different air mass characteristics.

Bergstrom, R. W.↗