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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Volatility and Wear Characteristics of a Variety of Liquid Lubricants for Space Applications

The vapor pressures and near characteristics are critical properties for liquid lubricants to assure long-term reliability and performance in space applications. Vapor pressures, obtained using a Knudsen cell technique, and near properties, obtained using a vacuum four-ball apparatus, were measured for a series of unformulated liquid lubricants. These include: two multiple alkylated cyclopentanes (MACs) (X-1000 and X-2000), two linear perfluoropolyalkylethers (PFPAEs) (Z-25 and 815Z), and four silahydrocarbons (a tri-, a tetra-, and two pentas). Vapor pressures were measured at three elevated temperatures (423, 448, and 498 K) and extrapolated to room temperature 298 K. The lowest 298 K vapor pressure of 5.7 x 10(exp -14) Pa, was obtained with the PFPAE fluid (815Z) and the highest value with the low molecular weight MAC (X-1000) at 3.6 x 10(exp -7) Pa. In addition, vacuum near rates were determined for some of the lubricants. The lowest wear rates (approximately 3 x 10(exp -11) cubic mm/mm) were observed for three of the silahydrocarbons while the highest wear rate (approximately 2 x 10(exp-9) cubic mm/mm) were observed with the two PFPAE fluids (Z-25 and 815Z). The MAC (X-2000) yielded a wear rate of about 10(exp -10) cubic mm/mm. The results indicated that the silahydrocarbon class of liquid lubricants offers the better potential for space applications.

Nguyen, Quynhgiao N.↗
NASA NTRS2008

Thermal Performance of Aged and Weathered Spray-On Foam Insulation (SOFI) Materials Under Cryogenic Vacuum Conditions (Cryostat-4)

The NASA Cryogenics Test Laboratory at Kennedy Space Center conducted long-term testing of SOFI materials under actual-use cryogenic conditions with Cryostat-4. The materials included in the testing were NCFI 24-124 (acreage foam), BX-265 (close-out foam, including intertank flange and bipod areas), and a potential alternate material, NCFI 27-68, (acreage foam with the flame retardant removed). Specimens of these materials were placed at two locations: a site that simulated aging (the Vehicle Assembly Building [VAB]) and a site that simulated weathering (the Atmospheric Exposure Test Site [beach site]). After aging/weathering intervals of 3, 6, and 12 months, the samples were retrieved and tested for their thermal performance under cryogenic vacuum conditions with test apparatus Cryostat-4.

Source record↗
NASA NTRSDate not supplied

Laser Beam Welding for in-Space Joining Demonstrated Under Vacuum on the Ground and By Parabolic Flight Experiments

High energy density electron beam welding enabled the first and, to date, only American weld performed in space during the M551 experiment on Skylab in 1973. Though welding is critical to 90% of durable goods manufacturing in America, there is not yet regular and reliable application of welding processes to the In-space Servicing, Assembly, and Manufacturing (ISAM) sector. Fundamental studies are needed to develop basic capabilities and to enhance fundamental process knowledge, which will support follow-on efforts to mature in-space welding for use in commercial, defense, and other aerospace applications. The current work seeks to build on past flights and improve understanding and quantification of materials joining in space conditions using laser beam welding (LBW). LBW offers several advantages over the electron beam welding of Skylab, amongst others: reduced electromagnetic interference, less exposure of operators to ionizing radiation, and flexible delivery through optical fibers supporting unique workpieces and joints. Since there is no orbital laboratory to mature laser beam welding for space, the current effort addresses maturation of laser beam welding through parabolic flights augmented with data collection to enable numerical modeling efforts that capture the physical effects of the space environment. This team has retrofitted an LBW experimental apparatus that can simulate the vacuum and, during a parabolic flight, the reduced gravity & microgravity conditions of in-space welding. A team of Capstone students modified the setup, originally developed by NASA Langley Research Center for electron beam free-form fabrication, to replace its electron gun with a 1 kW, 1070 nm Yb fiber laser. The apparatus was further instrumented with temperature sensing and high-speed welding cameras to monitor and record changes in the thermal state of the workpiece, the melt pool, the laser penetration level, and the development and orientation of spatter & plumes. The system will operate autonomously, demonstrating its utility to uncrewed missions. During upcoming parabolic flight campaigns expected summer 2024, this LBW equipment will weld common aerospace alloys of aluminum, stainless steel, and titanium under conditions representative of the space environment. This data will guide future computational modeling efforts of laser welding in space and help to qualify in-space welding as a viable ISAM technique.

laser beam welding↗
NASA NTRS1980

Safely splicing glass optical fibers

Field-repair technique fuses glass fibers in flammable environment. Apparatus consists of v-groove vacuum chucks on manipulators, high-voltage dc power supply and tungsten electrodes, microscope to observe joint alignment and fusion, means of test transmission through joint. Apparatus is enclosed in gas tight bos filled with inert gas during fusion. About 2 feet of fiber end are necessary for splicing.

Korbelak, K.↗
NASA NTRS1979

Splicing single-mode optical fibers

Approach used to weld multimode fibers has been adapted for more exacting splicing of single-mode fibers. Precision cleaver with tungsten carbide knife edge cuts single-mode optical fibers for welding. Welding apparatus includes micromanipulator, microscopes, and vacuum chucks.

Goldstein, R.↗
NASA NTRS1986

Etching Silicon Films With Xenon Difluoride

Microscopic circuit structures prepared for probing. Xenon difluoride removes relatively large amounts of silicon from integratedcircuit or solar-cell structures while leaving SiO2, Si3N4, Al2O3, and other compounds intact. In Etching Apparatus, solid XeF2 sublimated in vacuum, then allowed to flow over sample at controlled rate and pressure. Wafer etched from back to expose SiO2 and Al layers for spectroscopic analysis of SiO2/Al interface. Using XeF2 technique, silicon wafer with oxide layer reduced in thickness from standard 300 micrometer to as little as 10 nanometer without adversely affecting oxide.

Hecht, M. H.↗
NASA NTRS1990

The effects of the space environment on two aramid materials

Two aramid fibers having closely related chemical structures were chosen for important roles in the first tether to be used to connect pairs of orbiting vehicles. The protective outer jackets of the tethers will consist of woven fibers of poly(m-phenylene isophthalamide), commercially available from du Pont as Nomex. A cylindrical sheath of woven Kevlar 29, whose principal constituent is poly(p-phenylene terephthalamide), will be the load-bearing component for the tethers. Orbiting tethers will be in a hostile environment in which short wavelength electromagnetic radiation and energetic charged particles degrade exposed organic materials. At lower orbiting altitudes atomic oxygen is an especially serious hazard. Studies on the effects of ultraviolet radiation and atomic oxygen on fibers and films of Kevlar and Nomex are in progress. In an experiment to simulate the effects of atomic oxygen in space, small tows of Kevlar and Nomex were mounted in a commercial ashing device filled with oxygen at low pressure. An RF discharge in the instrument dissociated the molecular oxygen producing a strongly oxidizing atmosphere containing O(3P)(sup 4). Erosion was measured in terms of mass loss. Kevlar films were exposed to UV radiation in an apparatus consisting of a small vacuum chamber, 23 cm in diameter, into which a mass spectrometer and a quartz window were incorporated. Samples were exposed under vacuum with a 1000 watt xenon-arc lamp. Volatile products could be monitored with the mass spectrometer during the exposures. Transmission infrared spectra were taken before and after exposure to monitor chemical changes in the films.

Kiefer, Richard L.↗
NASA NTRS1993

XPS analysis of the effect of fillers on PTFE transfer film development in sliding contacts

The development of transfer films atop steel counterfaces in contact with unfilled and bronze-filled PTFE has been studied using X-ray photoelectron spectroscopy. The sliding apparatus was contained within the vacuum of the analytical system, so the effects of the native oxide, hydrocarbon, and adsorbed gaseous surface layers of the steel upon the PTFE transfer behavior could be studied in situ. For both the filled and the unfilled PTFE, cleaner surfaces promoted greater amounts of transfer. Metal fluorides, which formed at the transfer film/counterface interface, were found solely in cases where the native oxide had been removed to expose the metallic surface prior to sliding. These fluorides also were found at clean metal/PTFE interfaces formed in the absence of frictional contact. A fraction of these fluorides resulted from irradiation damage inherent in XPS analysis. PTFE transfer films were found to build up with repeated sliding passes, by a process in which strands of transfer filled in the remaining counterface area. Under these reported test conditions, the transfer process is not expected to continue atop previously deposited transfer films. The bronze-filled composite generated greater amounts of transfer than the unfilled PTFE. The results are discussed relative to the observed increase in wear resistance imparted to PTFE by a broad range of inorganic fillers.

Blanchet, T. A.↗
NASA NTRS2004

The Effect of Martian Dust on Radiator Performance

Experiments were performed in which the effective emittance of three types of radiator Coatings was measured as Martian dust simulant was added to the radiator face. The apparatus consisted of multiple radiator coupons on which Carbondale Red Clay dust was deposited. The coupons were powered by electric heaters, using a guard-heating configuration to achieve the accuracy required for acceptable emittance calculations. The apparatus was containing in a vacuum chamber that featured a liquid-nitrogen cooled shroud that simulated the Martian sky temperature. Radiator temperatures ranged from 250 to 350 K with sky temperatures from 185 to 248 K. Results show that as dust was added to the radiator surfaces, the effective emittance of the high - emittance coatings decreased from near 0.9 to a value of about 0.5. A low-emittance control surface, polished aluminum, demonstrated a rise in effective emittance for thin dust layers, and then a decline as the dust layer thickened. This behavior is attributed to the conductive resistance caused by the dust layer.

Hollingsworth, D. Keith↗
NASA NTRS2010

Pressure Decay Testing Methodology for Quantifying Leak Rates of Full-Scale Docking System Seals

NASA is developing a new docking system to support future space exploration missions to low-Earth orbit and the Moon. This system, called the Low Impact Docking System, is a mechanism designed to connect the Orion Crew Exploration Vehicle to the International Space Station, the lunar lander (Altair), and other future Constellation Project vehicles. NASA Glenn Research Center is playing a key role in developing the main interface seal for this docking system. This seal will be relatively large with an outside diameter in the range of 54 to 58 in. (137 to 147 cm). As part of this effort, a new test apparatus has been designed, fabricated, and installed to measure leak rates of candidate full-scale seals under simulated thermal, vacuum, and engagement conditions. Using this test apparatus, a pressure decay testing and data processing methodology has been developed to quantify full-scale seal leak rates. Tests performed on untreated 54 in. diameter seals at room temperature in a fully compressed state resulted in leak rates lower than the requirement of less than 0.0025 lbm, air per day (0.0011 kg/day).

Dunlap, Patrick H., Jr.↗
NASA NTRS1993

Tribological characteristics of perfluoropolyether liquid lubricants under sliding conditions in high vacuum

Tribological characteristics of three PFPE's (Fomblin Z, Demnum, and Krytox) were studied under high vacuum using a four-ball apparatus with 440C steel specimens. Fomblin Z and Demnum exhibited initial scuffing-like high friction whereas Krytox did not. Steady state friction with Fomblin Z was the lowest among the three oils. Frictional values for Demnum and Krytox were almost the same. The lowest wear rate in air was provided by Krytox regardless of load, and low wear rates in vacuum at high load were achieved with Krytox and Demnum. Results are explained by reactivity and pressure-viscosity characteristics of the oils.

Masuko, Masabumi↗
NASA NTRS1970

The Varestraint test for refractory metals, task 2

The principles of the Varestraint test were applied to the evaluation of refractory metal alloys. This required development of a special test apparatus employing a modest specimen size for improved economy and compatible with the high purity inert atmosphere required for welding these alloys. Minimum specimen size is desirable because of the high cost of these alloys and also to permit timely testing of limited production developmental alloys. The Varestraint apparatus satisfies these requirements by providing a timely and economic test for hot crack sensitivity. This test can be used both for alloy development and production surveillance. The test apparatus was designed for use in vacuum purged dry boxes and is completely compatible with high purity inert atmosphere. Augmented strain can be varied continuously from 1/4% thru 4%. In addition to varying the augmented strain, the primary Varestraint variable, the effect on hot cracking of varying other weld parameters such as unit weld length heat input have also been studied. Test reproducibility, in terms of bending or strain rate, was demonstrated using high speed photography.

Lessmann, G. G.↗
NASA NTRS1993

Diffusion in liquid state and solidification of binary system (M-7)

Diffusion is one of the most fundamental physical phenomena. It relates to the manufacturing of almost all materials. Therefore, the precise knowledge of diffusivities of relevant materials is necessary for the optimization of these processes. On the other hand, such knowledge is indispensable to understanding the diffusion mechanism and structure of liquid metal in the field of physical metallurgy. Many diffusion experiments on solid metal were undertaken and a lot of data were accumulated. But on liquid metals there are few measurements because of experimental difficulties, such as thermal convection, induced by very slight temperature gradients in the specimen. Under microgravity conditions, the movement of liquid metal due to density differences and thermal convection must be suppressed markedly. Therefore, the transportation process will be controlled only by the diffusion of constituent atoms. These conditions offer the optimum environments for the diffusion experiment. The experiments are briefly described. Diffusion couples are prepared by attaching end to end two rods of different pure metals using hot press equipment. These couples are inserted into a graphite crucible and then doubly enclosed by two silica ampoules, respectively. The specimen is inserted into a tantalum cartridge, which is welded in a vacuum using an electron-beam apparatus. These cartridges are charged in the continuous heating furnace in space and held at a given temperature for a predetermined time and then solidified. The concentration distribution of elements in these specimens will be measured along the rod axis by means of an electron probe microanalyzer. The counterdiffusivity of the liquid metal binary system is determined on the basis of the compensated concentration distribution profile for thermal contraction.

Dan, T.↗
NASA NTRS1994

Apparatus for performing high-temperature fiber push-out testing

The apparatus disclosed in the present invention measures the force at which a fiber resist the motion of an indenter driven at constant speed. This apparatus conducts these test in a vacuum of about 10(exp -6) tort and at temperatures up to 1100 C. Temperature and vacuum environment are maintained while controlling indenter motion, sample position, and providing magnified visual inspection during the test.

Eldridge, Jeffrey I.↗