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Pyrolytic graphite thin film deposition with liquid metal substrate
An analysis of structural failures that have occurred in NASA programs was conducted. Reports of 231 examples of structural failure were reviewed. Attempts were made to identify those factors which contributed to the failures, and recommendations were formulated for actions which would minimize their effects on future NASA programs. Two classes of factors were identified: (1) those associated with deficiencies in existing materials and structures technology and (2) those attributable to inadequate documentation or communication of that technology.
Two definitive spectra of strongly differentiated meteors are discussed. The meteors entered the earth's atmosphere at velocities greater than 40 km/sec from high-inclination and retrograde orbits. Both were magnesium-calcium particles, and their spectra show them to be highly deficient in iron and sodium. The moon and the asteroids have been discussed as sources of such calcium-rich achondrites, but these sources give low or intermediate geocentric velocities. Long-period comets and meteoroids of probable cometary origin are the only objects now known to have orbits similar to the orbits of these two meteors.
A series of 2024 type aluminum alloys modified by additions of 1 to 2% Li were studied to determine the role of the Cu:Li and the (Cu + Mg):Li ratios on resultant strength, ductility, notch-tensile behavior, and crack propagation rates. Ultrasonically gas atomized powders with quench rates of 10 to 100 thousand degrees/s were atomized in an argon atmosphere, producing yields of powder such that almost 100% was finer than 250 microns. The powders are free of gases and porosity, are quite spherical, have few satellites (adhering fine powder particles) and are of uniform microstructure. Strength properties are such that yield strength is 20% greater than for lithium-free 2024 ingot alloy, tensile strength is 10% greater than that of 2024 ingot material, and ductilities are comparable. In terms of specific strength and specific modulus, these RS 2024-Li alloys are significantly better than IM 2024.
Molten bubbles of metal or plastic coalesce into strong, lightweight materials that look like solidified foam. Bubbles formed in compartment that receives molten material and compressed gas that fills bubbles. Compartment has matrix of nozzles. Leaving nozzles, bubbles fall into acoustic chamber and coalesce; then drop through funnel and are cast into desired shape by extrusion or molding. Materials used for construction, extruded into molds, sawed, nailed, and generally handled as wood.
Results are presented of shock modeling of the H2, CO, and OH infrared emission lines in the Becklin-Neugebauer-Kleinmann-Low region of the Orion Molecular Cloud-1. The strength of the preshock magnetic field is estimated to be approximately 1 mGs, which indicates that magnetic pressure may help support the gas in this region. Determinations of the shock speed and the preshock density, along with the measured extent of the gas, show that the momentum and energy in the swept-up shocked material is rather high compared with the usual estimates of the available momentum and energy from the embedded sources. The abundance of shock-heated CO is found to be close to the solar abundance of carbon, and the extinction to the 2-micron region of H2 is approximately 2-2.5 mag. In addition, it is determined that the high-velocity wings of the H2 emission lines are most likely produced either behind fast dissociative shock waves or behind slower nondissociative shock waves traversing high-speed material.
Experimental values of acoustic wave propagation constant and characteristic impedance in fibrous materials, and normal absorption for two plastic foams, were compared to theoretical predictions obtained with Biot's theory. The best agreement was observed for fibrous materials between Biot's theory and Delany and Bazley experiments for a nearly zero mass coupling parameter. For foams, the lambda/4 structure resonance effect on absorption was calculated by using four-pole modelling of the medium. A significant mass coupling parameter is then necessary for obtaining agreement between the behavior of the measured absorption coefficients and the theoretical predictions. It is shown how the formalism used for predicting foams absorption coefficients may be used for studying the acoustic behavior of multi-layered media.
A method is provided to bond strain gauges to various materials. First, a tape with an adhesive backing is placed across the inside of the fixture frame. The strain gauge is flatly placed against the adhesive backing and coated with a thin, uniform layer of adhesive. The tape is then removed from the fixture frame and placed, strain gauge side down, on the material to be tested. If the material is a high reluctance material, the induction heating source is placed on the tape. If the material is a low reluctance material, a plate with a ferric side and a rubber side is placed, ferric side down, onto the tape. The induction heating source is then placed upon the rubber side. If the material is an insulator material, a ferric plate is placed on the tape. The induction heating source is then placed on the ferric plate. The inductive heating source then generates frequenty from 60 to 70 kilocycles to inductively heat either low reluctance material, ferric side, of ferric plate and provides incidental pressure of approximately five pounds per square inch to the tape for two minutes, thoroughly curing the adhesive. The induction heating source, and, if necessary, the plate or ferric plate, are then removed from the tape after one minute. The tape is then removed from the bonded strain gauge.
Aircraft dynamic analyses are demanding of computer simulation capabilities. The modeling complexities of semi-monocoque construction, irregular geometry, high-performance materials, and high-accuracy analysis are present. At issue are the safety of the passengers and the integrity of the structure for a wide variety of flight-operating and emergency conditions. The technology which supports engineering of aircraft structures using computer simulation is examined. Available computer support is briefly described and improvement of accuracy and efficiency are recommended. Improved accuracy of simulation will lead to a more economical structure. Improved efficiency will result in lowering development time and expense.
Before large power systems for manned exploration of the Martian surface can be put into place, it must be determined how their performance will be affected by the Martian environment. A program was started to assess the impact of these environmental factors on power system performance, and to find ways to mitigate the degradative effects. The effects of blowing dust on photovoltaic (PV) and radiator surfaces is studied. Extensive use was made of the Martian Surface Wind Tunnel (MARSWIT) located at NASA-Ames to simulate Martian winds. Two basic types of experiment sets were run. In the first, the threshold clearing velocity of dust deposited on PV coverslip material and high emissivity radiator materials in clear Martian-like winds was examined. In the second, dust was dropped near the inlet of the wind tunnel and the winds were allowed to carry the dust past the samples, simulating a dust storm. A summary of results is given.
This paper discusses the factors that control the flexibility of fabric space suit elements by examining a bending model of a pressurized fabric tube. Results from the model are used to evaluate the current direction in highly mobile EVA glove research and suggest that changes are necessary in the glove fabric selection methodology.
A brief review of state-of-the-art thermoelectric materials both for cooling and power generation is given.
This document represents a presentation offered by the Jet Propulsion Laboratory, with assistance from researchers from Brown University and Northrop Grumman. The presentation took place in Seoul, Korea in July 2003 and attempted to demonstrate the fabrication approach regarding the development of high quality factor (high-Q) mechanical oscillators (in the forms of a tunable nanotube resonator and a nanotube array radio frequency [RF] filter) aimed at signal processing and based on carbon nanotubes. The presentation also addressed parallel efforts to develop both in-plane single nanotube resonators as well as vertical array power devices.
The field emission characteristics of niobium electrodes were compared to those of stainless steel electrodes using a DC high voltage field emission test apparatus. A total of eight electrodes were evaluated: two 304 stainless steel electrodes polished to mirror-like finish with diamond grit and six niobium electrodes (two single-crystal, two large-grain, and two fine-grain) that were chemically polished using a buffered-chemical acid solution. Upon the first application of high voltage, the best large-grain and single-crystal niobium electrodes performed better than the best stainless steel electrodes, exhibiting less field emission at comparable voltage and field strength. In all cases, field emission from electrodes (stainless steel and/or niobium) could be significantly reduced and sometimes completely eliminated, by introducing krypton gas into the vacuum chamber while the electrode was biased at high voltage. Of all the electrodes tested, a large-grain niobium electrode performed the best, exhibiting no measurable field emission (< 10 pA) at 225 kV with 20 mm cathode/anode gap, corresponding to a field strength of 18:7 MV/m.
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