1,721,009 research outputs found
An exploratory study of some liquid catalysts for use with hydrogen peroxide
No full textLiquid catalysts for decomposing hydrogen peroxide in rocket engines have certain advantages over solid catalysts. However, some liquid catalysts have a tendency to precipitate at the outlet to the injector, which militates against their use for multiple engine restarts. In the study reported here, experiments have been carried out with several liquid catalysts, from which the rate of reaction and the tendency to form precipitates are compared against the benchmark catalytic agent, sodium permanganate. The results to date suggest that, although exhibiting a reduced tendency to form precipitates, none of the candidate agents considered match the reaction rate of sodium permanganate. However, at least one of the agents (sodium iodide) was found to initiate a very high decomposition rate, albeit with an undesirable initial delay. It was found that ferrous chloride tetrahydrate had no such delay and was capable of producing useful decomposition temperatures
Screen printed carbon sensors for atomic oxygen measurement
No full textCarbon-based atomic oxygen actinometers sensors were produced by screen-printing high and low carbon inks onto an alumina substrate between thick film gold tracks and palladium contacts. The performance of the sensors was evaluated by exposure to atomic oxygen in a plasma asher and a pulsed laser facility (ATOX) and compared with that of evaporated and sputtered thin film carbon sensors. All three types of sensor exhibited linear resistance increase with fluence and demonstrated sensitivity to flux change. The lower erosion yield and greater thickness makes the screen-printed sensors more suitable for high fluence/long duration missions
Carbon-based atomic oxygen sensors
No full textCarbon-based sensors have been developed to measure the atmospheric neutral atomic oxygen (AO) flux experienced by spacecraft in low Earth orbit (LEO). Thick- and thin film carbon sensor elements were deposited on an alumina substrate between thick film gold tracks and silver palladium solder pads. AO flux is deduced by measuring resistance changes as the carbon film erodes, and applying a simple theory. Measured resistance increases during exposure in a ground-based AO facility compare favourably with theoretical predictions. These sensors appear to offer a number of advantages compared with similar silver-based sensors that have been flown previously, particularly for small satellite missions with significant mass/power constraints
High-speed flow with discontinuous surface catalysis
Full text linkIn a reacting gas flow both gas-phase chemical activity and surface catalysis can increase the rate of heat transfer from the gas to a solid surface. In particular, when there is a discontinuous change in the catalytic properties of the surface, there can be a very large increase in the local heat transfer rate. In this study numerical simulations have been performed for the laminar high-speed flow of a high-temperature, non-equilibrium reacting gas mixture over a flat plate. The surface of the plate is partly catalytic, with the leading region non-catalytic, and a discontinuous change in the catalytic properties of the surface at the catalytic junction. The surface is assumed to be isothermal, and cold relative to the free stream. The gas is assumed to be a mixture of molecular and atomic forms of a diatomic gas in an inert gas forming a thermal bath, giving a three-species mixture with dissociation and recombination of the reactive species. The calculations are performed for a gas with atomic and molecular oxygen in an argon bath, but a full range of gas-phase chemical and surface catalytic effects is considered. Kinetic schemes with frozen gas-phase chemistry, and partial or full recombination of atomic oxygen in the boundary layer are investigated. The catalytic nature of the surface material is given by a catalytic recombination rate coefficient, which varies from zero (non-catalytic) to one (fully catalytic), and the effects on the flow and the surface heat transfer of materials which are non-, partially, or fully catalytic are considered. A self-similar thin-layer analytical model of the change in the gas composition downstream of the catalytic junction is developed. For physically realistic (O(10-2)) values of the catalytic recombination rate coefficient, the predictions from this model of the surface values of the atomic oxygen mass fraction and the catalytic surface heat transfer rate are excellent when the only change in the composition of the gas comes from the surface catalysis, and reasonable when there is partial recombination of the gas in the boundary layer due to the gas-phase chemistry. In contrast, when the surface is fully catalytic, the streamwise diffusion terms play a significant role, and the model is not valid. These results should apply to other situations with an attached boundary layer with recombination reactions. A comparison is made between the calculated and experimental measurements of the heat transfer rate at the catalytic junction. With a kinetic scheme which allows partial recombination in the boundary layer, good agreement is found between the experimental and predicted values for surface materials which are essentially non-catalytic. For a catalytic material (platinum), the experimental and numerical heat transfer rates are matched to estimate the value of the catalytic recombination rate coefficient. The values obtained show a considerable amount of scatter, but are consistent with those found in the literature
Results from the Atomic Oxygen Experiment on the STRV-1a spacecraft
No full textAnexperiment to makein situ measurements of thermospheric atomicoxygen fluxes andtheir effect on some common spacecraft materials has been flown in orbit on board the SpaceTechnology Research Vehicle 1amicrosatellite. The results from active sensors were based on resistance measurements of silver films and were interpreted relative to space simulationsmade in a ground-based pulsed laser atomic oxygen source. It was concluded that silver
resistance sensors can be used to measure atomic oxygen fluxes but are best suited to low flux environments, e.g., <10(14) atoms cm-2 s-1. Some silver sensors were overlaid with thin coatings to measure the erosion resistance of the coating materials. It was found that erosion rates were affected by the structure of the materials; this structure must therefore be taken into account in experiment and spacecraft design
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