Vacuum Ultraviolet Radiation in the Expansion Tube
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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The findings are presented of an optical survey of vacuum ultraviolet VUV radiation emitted from the shock layer of a 1-12 in. diameter sphere in hypersonic flows of air, argon, nitrogen and argon-nitrogen mixtures. Free stream velocities of 17,000-20,000 ftsec and densities corresponding to altitudes of about 90,000 ft. were obtained in the BRL expansion tube facility steady flow conditions prevailed over the model for about 75 microsec. The radiation was recorded on sensitized film down to a lower limit of 1100A. The purpose of the survey was to explore the feasibility of using this facility to measure time and space resolved radiation of the nonequilibrium, vibrationally- excited N2 in the shock layer part of this radiation is conjectured to ionize O2 ahead of the shock around a hypersonic vehicle, thus enhancing its radar signature. Methods and problems of measuring VUV from this shock layer are discussed.
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