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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Technology Validation of Optical Fiber Cables for Space Flight Environments

Periodically, commercially available (COTS) optical fiber cable assemblies are characterized for space flight usage under the NASA Electronic Parts and Packaging Program (NEPP). The purpose of this is to provide a family of optical fiber cable options to a variety of different harsh environments typical to space flight missions. The optical fiber cables under test are evaluated to bring out known failure mechanisms that are expected to occur during a typical mission. The tests used to characterize COTS cables include: (1) vacuum exposure, (2) thermal cycling, and (3) radiation exposure. Presented here are the results of the testing conducted at NASA Goddard Space Flight Center on COTS optical fiber cables over this past year. Several optical fiber cables were characterized for their thermal stability both during and after thermal cycling. The results show how much preconditioning is necessary for a variety of available cables to remain thermally stable in a space flight environment. Several optical fibers of dimensions 100/140/172 microns were characterized for their radiation effects at -125 C using the dose rate requirements of International Space Station. One optical fiber cable in particular was tested for outgassing to verify whether an acrylate coated fiber could be used in a space flight optical cable configuration.

Ott, Melanie N.↗
NASA NTRS2000

Thermal and Evolved Gas Analysis of Hydromagnesite and Nesquehonite: Implications for Remote Thermal Analysis on Mars

Volatile-bearing minerals (e.g., Fe-oxyhydroxides, phyllosilicates, carbonates, and sulfates) may be important phases on the surface of Mars. In order to characterize these potential phases the Thermal Evolved-Gas Analyzer (TEGA), which was onboard the Mars Polar Lander, was to have performed differential scanning calorimetry (DSC) and evolved-gas analysis of soil samples collected from the surface. The sample chamber in TEGA operates at about 100 mbar (approximately 76 torr) with a N2, carrier gas flow of 0.4 seem. Essentially, no information exists on the effects of reduced pressure on the thermal properties of volatile-bearing minerals. In support of TEGA, we have constructed a laboratory analog for TEGA from commercial instrumentation. We connected together a commercial differential scanning calorimeter, a quadruple mass spectrometer, a vacuum pump, digital pressure gauge, electronic mass flow meter, gas "K" bottles, gas dryers, and high and low pressure regulators using a collection of shut off and needle valves. Our arrangement allows us to vary and control the pressure and carrier gas flow rate inside the calorimeter oven chamber.

Lauer, H. V., Jr.↗
NASA NTRS1980

A study of the Jovian forbidden line S II nebula at high spectral resolution

Observations of forbidden line S II 6716-6731 A emissions from the Jovian magnetosphere have been carried out with a PEPSIOS spectrometer at the Hale 5 m telescope. Spectral resolving power was sufficient to resolve the forbidden line S II line widths. From measured 6716-6731 A doublet ratios and spectral line widths a thermal plasma is found characterized by temperatures about 2 x 10 to the 4th K and electron densities about 2000 cu cm. The source of forbidden line S II emissions was centered within a toroidal region of radius 5 Jupiter radii (inside the orbit of Io), with tight latitudinal confinement near the equilibrium equator for ions in the tilted corotating Jovian magnetic field, and significant long-lived longitudinal structure.

Trauger, J. T.↗
NASA NTRS1982

Synthesis and characterization of a melt processable polyimide

A melt processable polyimide which contains sulfur and oxygen bridges between the aromatic rings (BDSDA/APB) was synthesized and characterized. Its physical, mechanical, thermal and flow properties were determined as was its resistance to some of the more commonly used solvents. The melt flow properties were measured for the temperature range 250 C - 350 C and under the conditions (stress/strain) encountered in commercial processes.

Burks, H. D.↗
NASA NTRS1984

Synthesis and characterization of a melt processable polyimide

A melt processable polyimide which contains sulfur and oxygen bridges between the aromatic rings (BDSDA/APB) was synthesized and characterized. Its physical, mechanical, thermal and flow properties were determined as was its resistance to some of the more commonly used solvents. The melt flow properties were measured for the temperature range 250 C - 350 C and under the conditions (stress/strain) encountered in commercial processes.

Burks, H. D.↗
NASA NTRS1986

Synthesis of diamino terminated poly(arylene ether sulfone) oligomers as reactive intermediates in copolymer systems

Reactive diamino terminated oligomers of pre-determined molecular weights can be prepared by either of two synthetic routes depending upon the compound used to introduce the amine functionality. After characterization by spectroscopic and thermal methods, these oligomers can be used in several post-reactions to yield novel block and segmented copolymer systems. A potential application for these poly(arylene ether sulfone) oligomers exists in the curing or co-curing of epoxy resins for improving toughness. They can also be used to prepare toughened bismaleimide systems as well as producing copolymers with improved solvent resistance, especially with respect to chlorinated solvents.

Jurek, M. J.↗
NASA NTRS1988

Recent advances at NASA in calculating the electronic spectra of diatomic molecules

Advanced entry vehicles, such as the proposed Aero-assisted Orbital Transfer Vehicle, provide new and challenging problems for spectroscopy. Large portions of the flow field about such vehicles will be characterized by chemical and thermal nonequilibrium. Only by considering the actual overlap of the atomic and rotational lines emitted by the species present can the impact of radiative transport within the flow field be assessed correctly. To help make such an assessment, a new computer program is described that can generate high-resolution, line-by-line spectra for any spin-allowed transitions in diatomic molecules. The program includes the matrix elements for the rotational energy and distortion to the fourth order; the spin-orbit, spin-spin, and spin-rotation interactions to first order; and the lambda splitting by a perturbation calculation. An overview of the Computational Chemistry Branch at Ames Research Center is also presented.

Whiting, Ellis E.↗
NASA NTRS1990

Far-infrared observations of Circinus and NGC 4945 galaxies

Circinus and NGC 4945 are two galaxies luminous in the infrared and are characterized by compact non thermal radio nuclei, deep silicate absorption features and unusually strong water vapor maser luminosities. Moorwood and Glass (1984) have observed these galaxies extensively in the 1 to 20 micron range. In the far-infrared, observations up to 100 microns are available from the Infrared Astronomy Satellite (IRAS). In order to study the cool dust component of these galaxies, researchers observed them at 150 microns using the Tata Institute of Fundamental Research (TIFR) 100 cm balloon-borne telescope. Here, they report observations along with deconvolved maps at 50 and 100 microns obtained from the Chopped Photometric Channel (CPC) on board IRAS.

Bisht, R. S.↗
NASA NTRS1991

UV spectroscopy of Titan's atmosphere, planetary organic chemistry and prebiological synthesis. II - Interpretation of new IUE observations in the 220-335 nm range

The theoretical model developed by McKay et al. (1989) to characterize the size distribution, thermal structure, and chemical composition of the stratospheric haze of Titan is applied to new 220-335-nm albedo measurements obtained with the long-wavelength prime camera of the IUE during August 1987. Data and model predictions are presented in extensive graphs and discussed in detail. It is shown that a simple model with particles of one size at a given altitude does not accurately reproduce the observed features in all spectral regions, but that good general agreement is obtained using a model with a uniformly mixed layer at 150-600 km and a bimodal distribution of small 'polymer' haze particles (radius less than 20 nm) and larger haze particles (radius 100-500 nm). The number densities implied by this model require, however, a mechanism such as electrostatic charging or reaction kinetics to inhibit coagulation of the smaller particles.

Courtin, Regis↗
NASA NTRS1993

The nanosphere iron mineral(s) in Mars soil

A series of surface-modified clays containing nanophase (np) iron/oxyhydroxides of extremely small particle sizes, with total iron contents as high as found in Mars soil, were prepared by iron deposition on the clay surface from ferrous chloride solution. Comprehensive studies of the iron mineralogy in these 'Mars-soil analogs' were conducted using chemical extractions, solubility analyses, pH and redox, x ray and electron diffractometry, electron microscopic imaging specific surface area and particle size determinations, differential thermal analyses, magnetic properties characterization, spectral reflectance, and Viking biology simulation experiments. The clay matrix and the procedure used for synthesis produced nanophase iron oxides containing a certain proportion of divalent iron, which slowly converts to more stable, fully oxidized iron minerals. The noncrystalline nature of the iron compounds precipitated on the surface of the clay was verified by their complete extractability in oxalate. Lepidocrocite (gamma-FeOOH) was detected by selected area electron diffraction. It is formed from a double iron Fe(II)/Fe(III) hydroxyl mineral such as 'green rust', or ferrosic hydroxide. Magnetic measurements suggested that lepidocrocite converted to the more stable meaghemite (gamma-Fe203) by mild heat treatment and then to nanophase hematite (aplha-Fe203) by extensive heat treatment. Their chemical reactivity offers a plausible mechanism for the somewhat puzzling observations of the Viking biology experiments. Their unique chemical reactivities are attributed to the combined catalytic effects of the iron oxide/oxyhydroxide and silicate phase surfaces. The mode of formation of these (nanophase) iron oxides on Mars is still unknown.

Banin, A.↗
NASA NTRS1997

Chemical Characterization and Reactivity of Fuel-Oxidizer Reaction Product

Fuel-oxidizer reaction product (FORP), the product of incomplete reaction of monomethylhydrazine and nitrogen tetroxide propellants prepared under laboratory conditions and from firings of Shuttle Reaction Control System thrusters, has been characterized by chemical and thermal analysis. The composition of FORP is variable but falls within a limited range of compositions that depend on three factors: the fuel-oxidizer ratio at the time of formation; whether the composition of the post-formation atmosphere is reducing or oxidizing; and the reaction or post-reaction temperature. A typical composition contains methylhydrazinium nitrate, ammonium nitrate, methylammonium nitrate, and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. Thermal decomposition reactions of the FORP compositions used in this study were unremarkable. Neither the various compositions of FORP, the pure major components of FORP, nor mixtures of FORP with propellant system corrosion products showed any unusual thermal activity when decomposed under laboratory conditions. Off-limit thruster operations were simulated by rapid mixing of liquid monomethylhydrazine and liquid nitrogen tetroxide in a confined space. These tests demonstrated that monomethylhydrazine, methylhydrazinium nitrate, ammonium nitrate, or Inconel corrosion products can induce a mixture of monomethylhydrazine and nitrogen tetroxide to produce component-damaging energies. Damaging events required FORP or metal salts to be present at the initial mixing of monomethylhydrazine and nitrogen tetroxide.

David, Dennis D.↗
NASA NTRS1998

Synthesis and Characterization of Polyimides with Ether Linkages

A series of polyimides derived from a newly synthesized diamine, namely, 4,4-bis(4-aminophenoxy)-2,2-dimethylbiphenyl (BAPD), were developed and characterized. Their physical and thermal properties were compared to polyimides based on'commercially available 2,2-bis(4-(4-aminophenoxy)phenyl)propane (BAPP).

Chuang, Kathy C.↗
NASA NTRS1999

Can Kelvin-Helmholtz Instabilites of Jet-Like Structures and Plumes Cause Solar Wind Fluctuations at 1 AU?

The long high-latitude sampling of Ulysses provides the opportunity to study fine structures. At latitudes poleward of about -60 degrees the solar wind had fluctuations in velocity gradients which were attributed to "microstreams." The data also suggested fluctuations characterized by magnetic plus thermal pressure balance structures ('PBS'). At higher frequencies, MHD turbulence was observed and found to be less evolved than it is in the ecliptic but essentially independent of heliographic latitude. It is argued here that microstreams, PBS, and MHD turbulence could all be the remnants of mixing due to shear instabilities associated with plumes and other filamentary structures ("jets") in coronal holes. To show this, we simulate a plume-like jet in the presence of an ambient magnetic field. We find that the presence of the ambient field reduces the growth rate of the instability, but the shear between a jet and its ambient still becomes unstable to the MHD Kelvin-Helmholtz instability when the shear speed is larger than the largest local magnetosonic speed, a condition probably satisfied for plumes.

Parhi, S.↗
NASA NTRS1998

Can Kelvin-Helmholtz Instabilities of Jet-Like Structures and Plumes Cause Solar Wind Fluctuations at 1 AU?

The long high latitude sampling of Ulysses provides the opportunity to study fine structures. At latitudes poleward of approx. -60 deg, the solar wind had fluctuations in velocity gradients which were attributed to "microstreams". The data also suggested fluctuations characterized by magnetic plus thermal pressure balance structures ("PBS"). At higher frequencies, MHD turbulence was observed and found to be less evolved than in the ecliptic, but essentially independent of heliographic latitude. It is argued here that microstreams, PBS, and MHD turbulence could all be the remnants of mixing due to shear instabilities associated with plumes and other filamentarystructures ("jets") in coronal holes. To show this we simulate a plume-like jet in the presence of an ambient magnetic field. We find the presence of the ambient field reduces the growth rate of the instability, but the shear between a jet and its ambient still becomes unstable to the MHD Kelvin-Helmholtz ("KH") instability when the shear speed is larger than the largest local magnetosonic speed - a condition probably satisfied for plumes.

Shyamsundar, Parhi↗
NASA NTRS2000

Deconstructing the Spectrum of the Soft X-ray Background

The soft X-ray background in the 0.1-1.0 keV band is known to be produced by at least three sources; the Local Hot Bubble (LHB), the extragalactic power law (EPL), and a seemingly galactic component that lies outside the bulk of the absorption that is due to the ISM of the galactic disk. This last component, which we call the Trans-Absorption Emission (TAE), has been modeled by a number of groups who have derived disparate measures of its temperature. The differences have arisen from differing assumptions about the structure of the emitting gas and unrecognized methodological difficulties. In particular, spectral fitting methods do not uniquely separate the TAE from the foreground emission that is due the LHB. This "degeneracy" can be resolved using the angular variation of the absorption of the TAE. We show that the TAE cannot be characterized by a single thermal component; no single-component model can be consistent with both the spectral energy distribution of the TAE emission and the angular variation due to absorption by the galactic disk. We use the angular anticorrelation of the ROSAT All-Sky Survey with the galactic absorption to separate local from distant emission components, and to fit the spectral energy distribution of the resulting distant emission. We find that the emission is best described by a two-thermal-component model with logT(sub S) = 6.06(sup +0.14, sub -0.12) and log T(sub H) = 6.42(sup +0.14, sub -0.12). This two-thermal-component TAE fits the ROSAT spectral energy distribution significantly better than single-component models, and is consistent with both angular variation and spectral constraints.

Kuntz, K. D.↗
NASA NTRS1999

Differential Scanning Calorimetry and Evolved Gas Analysis of Hydromagnesite

Volatile-bearing minerals (e.g., Fe-oxyhydroxides, phyllosilicates, carbonates and sulfates) may be important phases on the surface of Mars. In order to characterize these phases the Thermal and Evolved Gas Analyzer (TEGA) flying on the Mars'98 lander will perform analyses on surface samples from Mars. Hydromagnesite [Mg5(CO3)4(OH)2.4H2O] is considered a good standard mineral to examine as a Mars soil analog component because it evolves both H2O and CO2 at temperatures between 0 and 600 C. Our aim here is to interpret the DSC signature of hydromagnesite under ambient pressure and 20 sccm N2 flow in the range 25 to 600 C. The DSC curve for hydromagnesite under the above conditions consists of three endothermic peaks at temperatures 296, 426, and 548 and one sharp exotherm at 511 C. X-ray analysis of the sample at different stop temperatures suggested that the exotherm corresponded with the formation of crystalline magnesite. The first endotherm was due to dehydration of hydromagnesite, and then the second one was due to the decomposition of carbonate, immediately followed by the formation of magnesite (exotherm) and its decomposition to periclase (last endotherm). Evolution of water and CO2 were consistent with the observed enthalpy changes. A library of such DSC-evolved gas curves for putative Martian minerals are currently being acquired in order to facilitate the interpretation of results obtained by a robotic lander.

Lauer, H. V., Jr.↗
NASA NTRS2002

Mullite+CAS Bond Coat for Environmental Barrier Coatings for Si-Based Ceramics

Current environmental barrier coatings (EBCs) for silicon-based ceramics consist of a bond coat and a top coat. Mullite bond coat modified by adding low CTE glass ceramics, such as BSAS (xBaO.1xSrO.Al2O3.2SiO2) or CAS (CaO.Al2O3.2SiO2), was developed in the NASA Enabling Propulsion Materials (EPM) Program. EBCs based on mullite+CAS bond coat were characterized using high steam thermal cycling test and high steam isothermal thermogravemitry (TGA) at 1225 C - 13,000 C. The Mullite+CAS bond coat showed far superior durability compared to mullite bond coat, due to enhanced crack resistance. A BSAS top coat provided further improved durability compared to EBCs with a yttria-stabilized zirconia (YSZ) top coat. Still further improvement in the durability was achieved by adding a silicon bond coat between the mullite and the substrate. However, the silicon/mullite+CAS/BSAS EBC showed inferior long-term durability compared to the current state-of-the art EBC (silicon/mullite+BSAS/BSAS EBC), presumably due to the higher CAS-silica chemical reactivity.

Lee, Kang N.↗