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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Vapor Growth and Characterization of Cr-Doped ZnSe Crystals

Cr-doped ZnSe single crystals were grown by self-seeded physical vapor transport technique under both vertical (stabilized) and horizontal configurations. The source materials were mixtures of ZnSe and CrSe. The growth temperatures were in the range of 1140 to 1150C and the furnace translation rates were 1.9 to 2.2 mm/day. The surface morphology of the as-grown crystals was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The different features on the as-grown surface of the vertically and horizontally grown crystals suggests that different growth mechanisms were involved for the two growth configurations. The [Cr] doping levels were determined to be in the range of 1.8 to 8.3 x 10(exp 19)/cubic centimeter from optical absorption measurements. The crystalline quality of the grown crystals were examined by high resolution triple crystal X-ray diffraction (HRTXD) analysis.

Su, Ching-Hua↗
NASA NTRS2005

Light shift measurements in a Cesium Fountain without the use of mechanical shutters

We present measurements confirming operation of a cesium fountain frequency standard with light shift below 10^-15 (and with evidence suggesting it is several orders of magnitude below this level) but without the use of mechanical shutters. Suppression of the light shift is realized using a master-slave laser configuration by reducing the overall optical power delivered to the physics package as well as spoiling the injection of the slave, causing it to lase far off resonance (1-2 nm) as proposed by the authors several years ago [l]. In the absence of any mitigation, this (AC Stark) shift, due to near-resonant laser light reaching the atoms during their microwave interrogation period, is the largest shift in such frequency standards (2x10^-11 for Our fountain). Mechanical shutters provided adequate light attenuation but have been prone to failure.

light shift measurements↗
NASA NTRS1971

Research and investigation of gas dynamic lasers

Chemical mixing laser investigations were conducted (1) to investigate the properties of a bimolecular exchange laser system pumped by the H + Cl2 yields HCl(v) + Cl reaction, initiated by arc-dissociated H2, with lasing occurring between wavelengths of 3.4 and 4.0 microns, and (2) to establish the feasibility of an atom recombination-transfer laser employing recombination of arc-dissociated nitrogen with subsequent transfer of vibrational energy to CO2 for lasing at 10.6 microns. One-dimensional analytical results indicate higher results should be obtained with up to v = 3 to 2 transitions participating. Diagnostic and analytical results show that the reaction mechanism during mixing, a back reaction of HCl(v) with H atoms, reaction of Cl with H2(v), moderately fast V-V, V-T processes, and possible HCl(o) initial contaminant level may explain the low performance. N2-CO2 thermal mixing laser studies were extended to measure the efficiency of transfer of recombination energy in such a nonequilibrium N2 source to 10.6 microns optical energy. The low level of efficiency suggests that V-T decay processes may prevent vibrational energy freezing until much lower temperatures are achieved and that trapping of energy in long-lived electronic excitation of N2 may be a factor.

Boedeker, L. R.↗
NASA NTRS1972

Petrology of basaltic and monomineralic soil fragments from the Sea of Fertility.

Basaltic and monomineralic fragments from the 150-425 micron size fractions of the Luna 16 core obtained from the Sea of Fertility were studied by optical petrographic, electron microprobe, and single-crystal X-ray diffraction techniques. Three textural varieties were identified in the basalts (intersertal, subophitic, and recrystallized). These textures, the assemblages, and individual mineral compositions (especially pyroxenes) indicate that these basalts crystallized under conditions very similar to those from Apollo 11. The pyroxenes have slightly lower Ti/Al (atomic) ratios than the Apollo 11 pyroxenes. We interpret the presence of octahedral Al as being due to the low TiO2/Al2O3 (weight %) ratio in the bulk rock. All observations made on the fine-grained basalt fragments are consistent with a rapid, near-surface, one-stage crystallization history.

Bence, A. E.↗
NASA NTRS1975

A search for chemical laser action in low pressure metal vapor flames

Optical emissions were studied from low pressure (approximately 1 torr) dilute diffusion flames of Ca and Mg vapor with O2, N2O and mixtures of CCl4 and O2. The Ca flames with O2 and N2O revealed high vibrational excitation of the product CaO molecule (up to v=30). The flames with CCl4 revealed extreme nonequilibrium metal atom electronic excitation, up to the metal atom ionization limit (6.1 eV for Ca, 7.6 eV for Mg). The metal atom excited electronic state populations did not follow a Boltzmann distribution, but the excitation rates ('pumping rate') were found to obey an Arrhenius-type expression, with the electronic excitation energy playing the role of activation energy and a temperature of about 5000 K for triplet excited states and 2500 K for singlets (vs. approximately 500 K translational temperature).

Zwillenberg, M. L.↗
NASA NTRS1979

Extreme ultraviolet observations from Voyager 1 encounter with Jupiter

Observations of the optical extreme ultraviolet spectrum of the Jupiter planetary system during the Voyager 1 encounter have revealed previously undetected physical processes of significant proportions. Bright emission lines of S(+2), S(+3), O(+2) indicating an electron temperature of 100,000 K have been identified in preliminary analyses of the Io plasma torus spectrum. Strong auroral atomic and molecular hydrogen emissions have been observed in the polar regions of Jupiter near magnetic field lines that map the torus into the atmosphere of Jupiter. The observed resonance scattering of solar hydrogen Lyman alpha by the atmosphere of Jupiter and the solar occultation experiment suggest a hot thermosphere (greater than or equal to 1000 K) with a large atomic hydrogen abundance. A stellar occultation by Ganymede indicates that its atmosphere is at most an exosphere.

Broadfoot, A. L.↗
NASA NTRS1989

Type of silicate feature in oxygen rich stellar envelopes

In many astronomical studies, the emissivity function derived from the Trapezium emission feature has been used. A statistical study of a large sample of objects is described that deals with the applicability of this function (hereafter TR). For comparison, another emissivity function derived for lunar silicate (LS) sample 14321 was used which has a maximum at 10.2 microns instead of at 9.7 microns as for TR. The IRAS low resolution spectra sources classified as 7n was used which has a silicate absorption feature without any atomic line emission. Most of these sources are likely to be oxygen rich stellar envelopes or hotspots in molecular clouds. The central source as assumed to emit a Plankian spectrum characterized by a temperature (t) and an absorbing envelope with an emissivity dependence of type TR or LS. Values of t and tau, the absorption optical depth were obtained by minimizing chi(exp 2) between the observed and fitted spectra in the 7 to 13 micron range. Values of reduced chi(exp 2) were obtained by taking the noise listed in the LRS Catalog as standard deviation. The tau values obtained correspond to 9.7 microns for TR and 10.2 for LS.

Iyengar, K. V. K.↗
NASA NTRS1986

On the direct and dissociative excitation of the O(3s 3S0) state by electron impact on atomic and molecular oxygen

The ratio of the cross sections for the direct and dissociative excitation of the OI(3s 3S0-2p 3P; 1304 A wavelength) transition, sigma A/sigma D, are accurately determined, and the sigma A/sigma D ratio is directly normalized to the ratio of the O(+) and O2(+) ionization cross sections using a high-density diffuse gas source, an electrostatically focused electron gun, a vacuum-ultraviolet monochromater, and a quadrupole mass spectrometer for simultaneous optical and composition measurements. Using revised sigma A(1304 A) values calculated with new calibration standards, the shape of the cross section for the excitation of the O(3s 3S0) state agrees well with previous results, though the absolute magnitude of sigma A(1304 A) is smaller than the results of Stone and Zipf (1974) by a factor of 2.8. The revised cross sections agree well with recent quantum calculations when cascade excitation of the 3s 3S0 state is taken into account.

Zipf, E. C.↗
NASA NTRS2014

Atomic Layer Deposition of Chemical Passivation Layers and High Performance Anti-Reflection Coatings on Back-Illuminated Detectors

A back-illuminated silicon photodetector has a layer of Al2O3 deposited on a silicon oxide surface that receives electromagnetic radiation to be detected. The Al2O3 layer has an antireflection coating deposited thereon. The Al2O3 layer provides a chemically resistant separation layer between the silicon oxide surface and the antireflection coating. The Al2O3 layer is thin enough that it is optically innocuous. Under deep ultraviolet radiation, the silicon oxide layer and the antireflection coating do not interact chemically. In one embodiment, the silicon photodetector has a delta-doped layer near (within a few nanometers of) the silicon oxide surface. The Al2O3 layer is expected to provide similar protection for doped layers fabricated using other methods, such as MBE, ion implantation and CVD deposition.

Hoenk, Michael E.↗
NASA NTRS1973

Optical study of charge exchange collisions between He+ and CO2.

Helium ions were produced in an electron bombardment ion source and directed into a gas cell containing carbon dioxide. A Wien filter placed between the ion source and the gas cell insured that only singly charged helium ions reached the cell. The spectrum obtained for the bombardment of carbon dioxide with the helium ions at 1200 eV is shown in a graph. Prominent features of the lower spectrum are two atomic lines at 3889 and 4471 A.

Coplan, M. A.↗
NASA NTRS1980

Discovery of optical molecular emission from the bipolar nebula surrounding HD 44179

Spectrophotometry and spectropolarimetry with HD 44179 are presented. These measurements reveal that the very broad bump evident in previous low-resolution spectra possesses a large amount of structure, including groups of narrow emission lines and several diffuse features. A reduction in polarization, but constant position angle, through the bump indicates that this emission originates within the nebula itself and merely dilutes the polarized scattered starlight. A few very weak atomic emission lines are detected, but the overall feature, which strongly resembles the emission spectra of some molecules, remains unidentified. Constraints on the excitation mechanism are discussed.

Schmidt, G. D.↗
NASA NTRS1992

LDEF results for polymer matrix composite experiment AO 180

This report represents a summary of the results obtained to-date on a polymer matrix composite experiment (AO 180) located at station D-12, about 82 deg off the 'ram' direction. Different material systems comprised of graphite, boron, and aramid (Kevlar) fiber reinforcements were studied. Although previous results were presented on in-situ thermal-vacuum cycling effects, particularly dimensional changes associated with outgassing, additional comparative data will be shown from ground-based tests on control and flight samples. The system employed was fully automated for thermal-vacuum cycling using a laser interferometer for monitoring displacements. Erosion of all three classes of materials due to atomic oxygen (AO) will also be discussed, including angle of incidence effects. Data from this experiment will be compared to published results for similar materials in other LDEF experiments. Composite materials' erosion yields will be presented on an AO design nomogram useful for estimating total material loss for given exposure conditions in low Earth orbit (LEO). Optical properties of these materials will also be compared with control samples. A survey of the damage caused by micrometeoroids/debris impacts will be addressed as they relate to polymer matrix composites. Correlations between hole size and damage pattern will be given. Reference to a new nomogram for estimating the number distribution of micrometeoroid/debris impacts for a given space structure as a function of time in LEO will be addressed based on LDEF data.

Tennyson, R. C.↗
NASA NTRS1993

Optical constants from mirror reflectivities measured at synchrotrons

Improved mirror reflectivity measurement techniques have been introduced to permit more accurate determinations of optical constants delta and beta in the complex index of refraction n = 1 - delta - i(beta) over the energy range 50 to 5000 eV. When the density has been determined by X-ray or other means, one can calculate the real and imaginary parts, f-prime and f-double prime, of the complex atomic scattering factor f = f(o) + f-prime + if-double prime from delta and beta. Preliminary results are given for the Ni LIII edge around 852 eV, and the Au M edge region from 2150 to 3500 eV. Since these are the first experimental evaluations of delta for these element edges, they are compared with appropriate reservations to semiempirical tabulations. There is much potential for this technique applied to synchrotron sources.

Blake, R. L.↗
NASA NTRS1981

Structure of the solar chromosphere. III - Models of the EUV brightness components of the quiet-sun

The described investigation is concerned with the solution of the non-LTE optically thick transfer equations for hydrogen, carbon, and other constituents to determine semiempirical models for six components of the quiet solar chromosphere. For a given temperature-height distribution, the solution is obtained of the equations of statistical equilibrium, radiative transfer for lines and continua, and hydrostatic equilibrium to find the ionization and excitation conditions for each atomic constituent. The emergent spectrum is calculated, and a trial and error approach is used to adjust the temperature distribution so that the emergent spectrum is in best agreement with the observed one. The relationship between semiempirical models determined in this way and theoretical models based on radiative equilibrium is discussed by Avrett (1977). Harvard Skylab EUV observations are used to determine models for a number of quiet-sun regions.

Vernazza, J. E.↗
NASA NTRS1991

Evolution of optical coatings in earth orbit

High-resolution medium-energy backscattering analyses have been performed on SiO and SiO2 optical coatings that were exposed to the space environment aboard the NASA long-duration experiment module flight. The data show an increase in areal density of 1 percent (resolved at the 10 sigma level) in the SiO film as a result of this exposure. It appears that this effect has been produced by the incorporation of atomic oxygen from the ambient environment. Data on the SiO2 film are less compelling but are consistent with some loss of material from the surface. These analyses set a new standard for profiling film thicknesses by ion backscattering.

Mendelhall, Marcus H.↗
NASA NTRS2011

A Debris Disk Case Study: 49 Ceti with Herschel

Gas-poor debris disks represent a fundamentally different class of circumstellar disk than gas-rich protoplanetary disks. Their gas probably originates from the same source as the dust, i.e. planetesimal destruction, but the low gas densities make it difficult to detect. So far, Herschel has detected far-IR gas emission from one debris disk, Beta Pictoris. Here I discuss a well-known debris disk system in the GASPS survey, 49 Ceti. It serves as a case study for modeling low-density gas in optically thin disks. The dust disk appears to be spatially resolved at 70 um. Most interestingly, there appears to be a hint of ClI 158 urn emission at the roughly 2 sigma level. Preliminary modeling suggests that reconciling the sub-mm CO emission from this system with the weak or non-existent far-IR atomic lines may require an unusual chemical composition in the gas of this disk.

Roberge, Aki↗
NASA NTRSDate not supplied

Development of Radioluminescent Tritium Polymeric Material for High Visibility Applications

The Development of Radioluminescent Tritium Polymeric Material for High Visibility Applications effort investigates the nature and properties of materials consisting of tritium lights combined with various silicone adhesives. Physical, mechanical, and optical properties will be observed/measured, including their durability in the low earth orbit environment. Tritium or hydrogen-three is a radioactive isotope of hydrogen that emits beta particles as it undergoes a process called beta decay. A beta particle is a high-energy, high-speed electron (or positron) emitted from radioactive decay of an atomic nucleus. Because it is a gas, tritium must be bound to a material or encapsulated in a sealed glass container. The gaseous tritium can then be combined with a phosphor source which when struck with beta particles, fluoresces and emits light. Such a light source is referred to as a gaseous tritium light source (GTLS). A self-powered, radioluminescent tritium material capable of surviving multiple space environments has the potential to fulfill visibility requirements levied on space flight hardware and facilitate additional long term internal and external lighting needs such as for imaging, docking, tracking, and xEMU suits for lunar exploration on the moon.

Lauren Fisher↗
NASA NTRSDate not supplied

Extending ISS Life Beyond 2030

The United States On-orbit Segment (USOS) of the International Space Station (ISS) was designed to meet a 15-year on-orbit life. Since the first hardware was launched in late 1998, the ISS would have reached its end of life in 2013. With the realization that the ISS would be needed well into the next decade, and beyond, a multi-disciplinary effort was undertaken to extend the ISS’ life through 2028 and to show that further extension to 2040 and beyond is not only feasible but achievable. Currently, NASA and the ISS international partners have agreed to extend its operations through 2030. This collaborative effort ensures that the ISS will continue to serve as a hub for scientific research, international cooperation, and educational endeavors for the next decade. Maintaining a continuous human presence in Low Earth Orbit (LEO) is desirable for testing new LEO, lunar, and deep-space technologies; conducting scientific research in micro-gravity for the benefit of life on Earth; and enabling a seamless transition of capabilities to one or more commercially owned and operated destinations. This paper provides an overview of the ISS life extension project with a particular focus on the analytical approach used to assess the primary structure. This analytical approach includes future operations planning, critical location screening, on-orbit dynamic load simulation, on-orbit optical property degradation studies, on-orbit thermal analyses, spectra generation, crack model idealization, fracture analyses, and post processing. Structural life results and identification of the most critical on-orbit events are presented. Also addressed are life extension approaches for other affected sub-systems, including: 1. Secondary Structure. 2. Materials. Evaluations consider environmental exposure to atomic oxygen, ionizing and gamma radiation, fluids, etc. Life limited materials, wear, and usage effects are also considered. 3. Environmental Control and Life Support Systems, including oxygen supply and generation, water recovery and management, and regenerative hardware. Evaluations are performed to determine which hardware can be run to failure and which are assessed for life extension. 4. Electrical power system. ISS is powered by eight channels of solar arrays and an electrical energy storage system providing 357 kWh power. Power generation and balance analyses are performed considering hardware degradation and increasing power demand. 5. Logistics and maintenance. Analyses are performed to determine critical spares required to maintain functionality. Consideration is given to supply chain health, obsolescence issues, onboard stowage availability, and up-mass capability. The successful life extension results have built confidence to safely operate, maintain and enhance the ISS well beyond the current decade. Extending the operational life of the ISS maintains an international presence in LEO and serves to avoid a gap in capability necessary to fulfill the exploration and research needs of NASA, international partners, and industry without interruption until a commercial space station is operational.

design life↗