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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Preliminary estimates of nucleon fluxes in a water target exposed to solar-flare protons: BRYNTRN versus Monte Carlo code

A baryon transport code (BRYNTRN) has previously been verified using available Monte Carlo results for a solar-flare spectrum as the reference. Excellent results were obtained, but the comparisons were limited to the available data on dose and dose equivalent for moderate penetration studies that involve minor contributions from secondary neutrons. To further verify the code, the secondary energy spectra of protons and neutrons are calculated using BRYNTRN and LAHET (Los Alamos High-Energy Transport code, which is a Monte Carlo code). These calculations are compared for three locations within a water slab exposed to the February 1956 solar-proton spectrum. Reasonable agreement was obtained when various considerations related to the calculational techniques and their limitations were taken into account. Although the Monte Carlo results are preliminary, it appears that the neutron albedo, which is not currently treated in BRYNTRN, might be a cause for the large discrepancy seen at small penetration depths. It also appears that the nonelastic neutron production cross sections in BRYNTRN may underestimate the number of neutrons produced in proton collisions with energies below 200 MeV. The notion that the poor energy resolution in BRYNTRN may cause a large truncation error in neutron elastic scattering requires further study.

Shinn, Judy L.↗
NASA NTRS1994

Process for preparing an assembly of an article and a polyimide which resists dimensional change, delamination and debonding when exposed to changes in temperature

An assembly of an article and a polyimide composition is prepared. The assembly resists dimensional change, delamination, or debonding when exposed to changes in temperature. An article is provided. A polyamic acid solution which yields a polyimide having a low coefficient of thermal expansion (CTE) was prepared. Equimolar quantities of an aromatic diamine and an aromatic dianhydride were reacted in a solvent medium to form a polyamic acid solution. A metal ion-containing additive was added to the solution. Examples of this additive are: TbCl3, DyCl3, ErCl3, TmCl3, Al(C5H7O2)3, and Er2S3. The polyamic acid solution was imidized and is combined with the article to form the assembly.

Stoakley, Diane M.↗
NASA NTRS1993

Discrimination of poorly exposed lithologies in AVIRIS data

One of the advantages afforded by imaging spectrometers such as AVIRIS is the capability to detect target materials at a sub-pixel scale. This paper presents several examples of the identification of poorly exposed geologic materials - materials which are either subpixel in scale or which, while having some surface expression over several pixels, are partially covered by vegetation or other materials. Sabol et al. (1992) noted that a primary factor in the ability to distinguish sub-pixel targets is the spectral contrast between the target and its surroundings. In most cases, this contrast is best expressed as an absorption feature or features present in the target but absent in the surroundings. Under such circumstances, techniques such as band depth mapping (Clark et al., 1992) are feasible. However, the only difference between a target material and its surroundings is often expressed solely in the continuum. We define the 'continuum' as the reflectance or radiance spanning spectral space between spectral features. Differences in continuum slope and shape can only be determined by reduction techniques which considers the entire spectral range; i.e., techniques such as spectral mixture analysis (Adams et al., 1989) and recently developed techniques which utilize an orthogonal subspace projection operator (Harsanyi, 1993). Two of the three examples considered herein deal with cases where the target material differs from its surroundings only by such a subtle continuum change.

Farrand, William H.↗
NASA NTRS1995

The surface properties of fluorinated polyimides exposed to VUV and atomic oxygen

The effect of atomic oxygen flux and VUV radiation alone and in combination on the surface of fluorinated polyimide films was studied using XPS spectroscopy. Exposure of fluorinated polyimides to VUV radiation alone caused no observable damage to the polymer surface, while an atomic oxygen flux resulted in substantial oxidation of the surface. On the other hand, exposure to VUV radiation and atomic oxygen in combination caused extensive oxidation of the polymer surface after only 2 minutes of exposure. The amount of oxidized carbon on the polymer surface indicated that there is aromatic ring opening oxidation. The changes in the O1s/C1s, N1s/C1s, and F1s/C1s ratios suggested that an ablative degradation process is highly favorable. A synergistic effect of VUV radiation in the presence of atomic oxygen is clearly evidenced from the XPS study. The atomic oxygen could be considered as the main factor in the degradation process of fluorinated polyimide films exposed to a low earth orbit environment.

Forsythe, John S.↗
NASA NTRS1995

Hubble Space Telescope high resolution spectroscoy of the exposed white dwarf in the dwarf nova VW Hydri in quiescence: A rapidly rotating white dwarf

We obtained a far-ultraviolet spectrum of the dwarf nova VW Hyi in quiescence, with the Hubble Space Telescope Goddard High Resolution Spectrograph covering the region of the Si iv lambda(lambda)1393, 1402 resonance doublet. The broad, shallow Si iv doublet feature is fully resolved, has a total equivalent width of 2.8 A, and is the first metal absorption feature to be clearly detected in the exposed white dwarf. Our synthetic spectral analysis, using a model grid constructed with the code TLUSTY, resulted in a reasonable fit to a white dwarf photosphere with T(sub eff) = 22,000 +/- 2000 K, log g = 8.0 +/- 0.3, an approximately solar Si/H abundance, and a rotational velocity, v sin i approximately equal to 600 km/s. This rotation rate, while not definitive because it is based upon just one line transition, is 20% of the Keplerian (breakup) velocity of the white dwarf and hence does not account for the unexpectedly low boundary-layer luminosity inferred from the soft-X-ray/extreme ultra-violet bands where most of the boundary-layer luminosity should be radiated. The predicted boundary-layer luminosity for a 0.6 solar mass white dwarf accreting at the rate 10(exp -10) solar mass/yr and rotating at 600 km/s, corresponding to VW Hyi in quiescence, is 2 x 10(exp 32) ergs/s when proper account is taken of the rotational kinetic energy going into spinning up the white dwarf. If the boundary-layer area is equal to that of the white dwarf, then T(sub bl) = 24,000 K. This is essentially identical to the photspheric luminosity and temperature determined in far-ultraviolet photospheric analyses. If the boundary-layer area is 10(exp -3) of the white dwarf surface area, then T(sub bl) = 136,000 K.

Sion, Edward M.↗
NASA NTRS1995

Enhanced Boiling-Metal Cooling Of Vanes Exposed To Hot Gases

Incorporation of automatic, self-powered jet pumps proposed to enhance boiling-liquid-metal cooling of vanes exposed to hot gases. In original intended application, vanes and probes thrust-vector-control devices inserted in supersonic flows of hot gases in rocket-engine nozzles; this cooling concept also applicable to vanes and blades in high-performance turbine engines. In further improvement, additional axial and transverse slots added to coolant passages in vane or probe and to coolant reservoir. Slots reduce stresses caused by thermal expansion and contraction of solid coolant.

Osofsky, I. B.↗
NASA NTRS1995

Summary of GPC/DV results for space exposed poly(arylene ether phosphine oxide)s

Gel Permeation Chromatography (GPC) was used to analyze poly(arylene ether phosphine oxide)s whose backbones were identical except for the ketone content and placement. These samples were exposed to low Earth orbit environment (predominantly atomic oxygen) on space shuttle flights. The materials and their unexposed controls were then characterized by GPC to investigate the effect of atomic oxygen on the molecular weight distributions. Analysis of the soluble portion of the samples revealed that there was significant loss of high molecular weight species. The presence of insoluble material also suggested that crosslinking was induced by the atomic oxygen exposure and that this very likely occurred at the high molecular weight portion of the molecular weight distribution.

Siochi, Emilie↗
NASA NTRS1995

Evaluation of Thermal Control Coatings and Polymeric Materials Exposed to Ground Simulated Atomic Oxygen and Vacuum Ultraviolet Radiation

Numerous thermal control and polymeric samples with potential International Space Station applications were evaluated for atomic oxygen and vacuum ultraviolet radiation effects in the Princeton Plasma Physics Laboratory 5 eV Neutral Atomic Oxygen Facility and in the MSFC Atomic Oxygen Drift Tube System. Included in this study were samples of various anodized aluminum samples, ceramic paints, polymeric materials, and beta cloth, a Teflon-impregnated fiberglass cloth. Aluminum anodizations tested were black duranodic, chromic acid anodize, and sulfuric acid anodize. Paint samples consisted of an inorganic glassy black paint and Z-93 white paint made with the original PS7 binder and the new K2130 binder. Polymeric samples evaluated included bulk Halar, bulk PEEK, and silverized FEP Teflon. Aluminized and nonaluminized Chemfab 250 beta cloth were also exposed. Samples were evaluated for changes in mass, thickness, solar absorptance, and infrared emittance. In addition to material effects, an investigation was made comparing diffuse reflectance/solar absorptance measurements made using a Beckman DK2 spectroreflectometer and like measurements made using an AZ Technology-developed laboratory portable spectroreflectometer.

Kamenetzky, R. R.↗
NASA NTRS1996

Quantification of Bone Growth Rate Variability in Rats Exposed to Micro- (near zero G) and Macrogravity (2G)

Our stated primary objective is to quantify the growth rate variability of rat lamellar bone exposed to micro and macrogravity (2G). The primary significance of the proposed work is that an elegant method will be established that unequivocally characterizes the morphological consequences of gravitational factors on developing bone. The integrity of this objective depends upon our successful preparation of thin sections suitable for imaging individual bone lamellae, and our imaging and quantitation of growth rate variability in populations of lamellae from individual bone samples.

Bromage, Timothy G.↗
NASA NTRS1996

Calcium Balance in Mature Rats Exposed to a Space Flight Model

Negative calcium balances are seen in humans during spaceflight and bed rest, an analog of space flight. Due to the infrequency and costliness of space flight and the difficulties, cost, and restraints in using invasive procedures in bed rest studies, several ground based animal models of space flight have been employed. The most useful and well developed of these models is hind limb unloading in the rat. In this model the hind limbs are non-weight bearing (unloaded) but still mobile; there is a cephalad fluid shift similar to that seen in astronauts in flight; the animals are able to feed, groom and locomote using their front limbs; the procedure is reversible; and, importantly, the model has been validated by comparison to space flight. Several laboratories have studied calcium balance using rats in hind limb unweighting. Roer and Dillaman used young male rats to study calcium balance in this model for 25 days. They found no differences in dietary calcium intake, percent calcium absorption, urinary and fecal excretion, hence indicating no differences in calcium balance between control and unloaded rats. In another study, employing 120 day old females, rats' hind limbs were unloaded for 28 days. While negative calcium balances were observed during a 25 day recovery period no balance measurements were possible during unweighting since the researchers did not employ appropriate metabolic cages. In a recent study from this laboratory, using 200 g rats in the space flight model for two weeks, we found depressed intestinal calcium absorption and increased fecal calcium excretion (indicating less positive calcium balances) and lower circulating 1,25-dihydroxyvitamin D. The above studies indicate that there remains a dearth of information on calcium balance during the hind limb unloading rat space flight model, especially in mature rats, whose use is a better model for planned manned space flight than juvenile or growing animals. With the aid of a newly designed metabolic cage developed in our laboratory it is now possible to accurately measure urinary and fecal calcium excretions in this space flight model. The purpose of this study, then, was to extend and enlarge our previous findings viz: to measure calcium balances in mature rats exposed to a space flight model.

Wolinsky, Ira↗
NASA NTRS1993

X-Ray Photoelectron Spectroscopy Study of the Effect of Hydrocarbon Contamination on Poly(Tetrafluoroethylene) Exposed to a Nitrogen Plasma

It has been shown that unless the surface of poly(tetrafluoroethylene)(PTFE) is free of hydrocarbon contamination, anomalous changes in the oxygen and fluorine contents, as measured by X-ray photoelectron spectroscopy (XPS), and hence also the surface properties, may be improperly ascribed to a PTFE film exposed to a oxygen plasma.

Golub, Morton A.↗
NASA NTRS1997

Quantitation of Bone Growth Rate Variability in Rats Exposed to Micro-(near zero G) and Macrogravity (2G)

Our stated primary objective is to quantify the growth rate variability of rat lamellar bone exposed to micro- (near zero G: e.g., Cosmos 1887 & 2044; SLS-1 & SLS-2) and macrogravity (2G). The primary significance of the proposed work is that an elegant method will be established that unequivocally characterizes the morphological consequences of gravitational factors on developing bone. The integrity of this objective depends upon our successful preparation of thin sections suitable for imaging individual bone lamellae, and our imaging and quantitation of growth rate variability in populations of lamellae from individual bone samples.

Bromage, Timothy G.↗
NASA NTRS1961

Stability of Titanium Nitride and Titanium Carbide When Exposed to Hydrogen Atoms from 298 to 1950 K

Titanium nitride and titanium carbide deposited on tungsten wires were exposed to hydrogen atoms (10(exp -4) atm pressure) produced by the action of microwave radiation on molecular hydrogen. The results of these experiments in the temperature range 298 to 1950 K indicate that no appreciable reaction takes place between atomic hydrogen and TiN or TiC. The formation of reaction products (NH3, CH4, C2H2) should be favored at lower temperatures. However, because of the high catalytic activity of Ti for H atom recombination, the rate of such reactions with H atoms is controlled by the rate of evaporation of Ti from the surface, this rate being low at temperatures below 1200 K. In order to interpret the stability of TiN and TiC in H atoms more fully, the stability of TiN and TiC in vacuum and H2 gas was also studied. The thermodynamic computations conform in order of magnitude to the experimentally found rates of decomposition of TiN and TiC in vacuum and are also consistent with the fact that no appreciable reaction is found with these compounds in molecular H2 at a pressure of 10(exp -3) atmosphere in the temperature range 2980 to 2060 K. When TiN or TiC was heated in atomic H or molecular H2, no reaction products other than those obtained from the simple decomposition of the nitride and carbide were observed. The gaseous products were analyzed in a mass spectrometer.

Philipp, Warren H.↗
NASA NTRS1999

Investigation of Atomic Oxygen Erosion of Polyimide Kapton H Exposed to a Plasma Asher Environment

Experimental results are presented on the erosion characteristics of the polyimide Kapton H, which serves as a blanket material in solar arrays. This polymer has a number of characteristics that make it a suitable choice for both terrestrial and space applications. In this paper attention is focused on the durability of protected Kapton when exposed to atomic oxygen (AO) in a plasma asher. A strip of 0.025-mm thick Kapton film, coated on both sides with SiO2, was studied during a 1306 hour exposure. The erosion, located at defect sites in the protective coating and measured optically, is described in terms of volume loss as a function of AO fluence. Three simple geometric profiles are used to generate a useful array of cavity shapes to model erosion evolution. These models connect the volume erosion rate to the observed lateral expansion of the developing cavities via their diameters, measured adviacent to the upper and lower protective film, and fitted by least-squares regression to simple power law functions of fluence. The rationale for the choice of models is discussed. It was found that lateral growth in cavity size evolves less than linearly with fluence.

Snyder, Aaron↗
NASA NTRS1991

Thermal Modeling and Analysis of a Cryogenic Tank Design Exposed to Extreme Heating Profiles

A cryogenic test article, the Generic Research Cryogenic Tank, was designed to qualitatively simulate the thermal response of transatmospheric vehicle fuel tanks exposed to the environment of hypersonic flight. One-dimensional and two-dimensional finite-difference thermal models were developed to simulate the thermal response and assist in the design of the Generic Research Cryogenic Tank. The one-dimensional thermal analysis determined the required insulation thickness to meet the thermal design criteria and located the purge jacket to eliminate the liquefaction of air. The two-dimensional thermal analysis predicted the temperature gradients developed within the pressure-vessel wall, estimated the cryogen boiloff, and showed the effects the ullage condition has on pressure-vessel temperatures. The degree of ullage mixing, location of the applied high-temperature profile, and the purge gas influence on insulation thermal conductivity had significant effects on the thermal behavior of the Generic Research Cryogenic Tank. In addition to analysis results, a description of the Generic Research Cryogenic Tank and the role it will play in future thermal structures and transatmospheric vehicle research at the NASA Dryden Flight Research Facility is presented.

Stephens, Craig A.↗
NASA NTRS1999

A Laboratory Study of the Charging/Discharging Mechanisms of a Dust Particle Exposed to an Electron Beam

The interaction of micron sized particles or "dust particles" with different space and planetary environments has become an important area of research. One particular area of interest is how dust particles interact with plasmas. Studies have shown that charged dust particles immersed in plasmas can alter plasma characteristics, while ions and electrons in plasmas can affect a particle's potential and thereby, its interaction with other particles. The basis for understanding these phenomena is the charging mechanisms of the dust particle, specifically, how the particle's charge and characteristics are affected when exposed to ions and electrons. For example, when electrons collide with a dust particle, secondary electrons can be produced from the surface of a particle and can affect the surrounding plasma.

Venturini, C.C.↗
NASA NTRS2000

Effect of Air and Vacuum Storage on the Tensile Properties of X-Ray Exposed Aluminized-FEP

Metallized Teflon(Registered Trademark) FEP (fluorinated ethylene propylene), a common spacecraft thermal control material, from the exterior layer of the Hubble Space Telescope (HST) has become embrittled and suffers from extensive cracking. Teflon samples retrieved during Hubble servicing missions and from the Long Duration Exposure Facility (LDEF) indicate that there may be continued degradation in tensile properties over time. An investigation has been conducted to evaluate the effect of air and vacuum storage on the mechanical properties of x-ray exposed FEP. Aluminized-FEP (Al-FEP) tensile samples were irradiated with 15.3 kV Cu x-rays and stored in air or under vacuum for various time periods. Tensile data indicate that samples stored in air display larger decreases in tensile properties than for samples stored under vacuum. Air-stored samples developed a hazy appearance, which corresponded to a roughening of the aluminized surface. Optical property changes were also characterized. These findings indicate that air exposure plays a role in the degradation of irradiated FEP, therefore proper sample handling and storage is necessary with materials retrieved from space.

deGroh, Kim K.↗
NASA NTRS2000

Thermoelastic Analysis of Hyper-X Camera Windows Suddenly Exposed to Mach 7 Stagnation Aerothermal Shock

To visually record the initial free flight event of the Hyper-X research flight vehicle immediately after separation from the Pegasus(registered) booster rocket, a video camera was mounted on the bulkhead of the adapter through which Hyper-X rides on Pegasus. The video camera was shielded by a protecting camera window made of heat-resistant quartz material. When Hyper-X separates from Pegasus, this camera window will be suddenly exposed to Mach 7 stagnation thermal shock and dynamic pressure loading (aerothermal loading). To examine the structural integrity, thermoelastic analysis was performed, and the stress distributions in the camera windows were calculated. The critical stress point where the tensile stress reaches a maximum value for each camera window was identified, and the maximum tensile stress level at that critical point was found to be considerably lower than the tensile failure stress of the camera window material.

Ko, William L.↗