Ground‐based video photography of firings of Space Shuttle Primary Reaction Control System (PRCS) engines show optical emissions extending nearly 4 km from the vehicle after steady state is reached. The total intensity and spatial distribution of these emissions depend on the angle between the spacecraft velocity vector and the engine exhaust axis. Candidate sources for this radiation are reviewed and the conclusion is reached that it is most likely due to vibrationally excited OH, formed by the reaction of fast ambient O atoms and H2O molecules in the exhaust.

SECUMIT .LASS1FS ATION OF THV, PAr.rI'I,w , ij)ta I.ntrfd) 20. Abstract (continued) "4;.-was applied to determine three-dimensional coordinates of the trail. Highly accurate camera orientations were obtained for input to the triangulation procedure by digitizing images of known stars. Time sequences of positions of points on the trail centerline were then processed to determine the horizontal wind field and its vertical shears. 4 4. <1I,

A wide spectral range transmissometor has been developed at the Phillips Laboratory for long path atmospheric measurements. It was designed to provide narrow band spectral coverage in three bands between 0.4 and 14 micrometers by programmed scanning with circular variable filters. The system uses three detectors so that three spectral regions can be sampled simultaneously. Two sources, a black body and a ribbon filament lamp are combined in a single beam. A two way path is provided by use of cat's-eye retro-reflectors. Transmitter and receiver are combined in the same unit and by using multiple retroreflectors located at different positions the path length can be readily changed by realignment of the unit. This increases the dynamic range of the system and makes possible measurement of rapidly changing atmospheric conditions. The transmissometer was recently used to provide transmission measurements as part of the FLAPIR (Forward looking infrared and Lidar Atmospheric Propagation in the InfraRed) field measurement program at Brunswick Naval Air Station, which had the purpose of determining the feasibility ofusing lidars to predict the effectiveness ofinfrared imaging devices. Measurements were made primarily in fog and rain conditions.

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A D --266 9 '1 kG I0MSNyo, 0704-0 188iii c G ~the lime for rqv,*t.g ifftuuuvorn. searchmf esiIMnq data I0 =7gg a n manc l IIlIIIIIII Swll rend fll falmmitili egrding thi ,rden estimate of any~ Othtr asetOf hi 0-% "K&V 9nOm lllili .i 11111II111li l souner $r,.Oi r ota Ic lot inflion 00 oraoris and Repoili. 9 i AGENCY USE ONLY (Ledvi 93-14691Analysis of intensified video photographs of a twilight venting Of excess water from space shuttle showed that the -1 mm diameter stream cavitasionally fragments within about 1 =. forming two discrete-Particle components and vaOor. The images from nearby cameras are domitiated by irregular, polydisverse water/ice droplets with sizes comparable with the venting orifice and outward velocity indistiguishable from that of the initially coherent Liquid. In contrs-st the 2VA lzz-loog quasconical mril imaged from a distant ground station consists of 1cc opaflyifl submicroO ice spberules that were produc-Ed by partial recoodensation of the overexpanded vacuum-evaporatted water gas, which are sublimating at rates that we calculated from the measured faloff of aial sunlight-scatter radiance and the energy balance of progressively roughening ice at 329 Ian altiude-, at low latitudes they cool to 180K in < 1 s. 2nd their radii transition to the Rayleigh-SCa2tttrilg range in LMi The very much larger fragmentation particles come to a slightly higher equiLibrium temperature within -2 min, and persist for a few earth orbits. Thes three components of the vented water (and other high vapor pressure liquids) radiate and scatter earthshine and solar photons. and tne orbital-velocity molecules are also excited by collisions with the residual atmlospheric gas, overlaying wide-angle conaminating foregrounds On remotc Optical sensing from onboard. The particle sizes, diensities, and tEmpes-anres derived from the visible data are applied in eswtin~fg ultraviolet and iafrared radiances of the icei'vapor-containing volumes near Shuttle Orbiter. SUBJECT TERMS NUMBER OF PAGES Optical properties Orbital-velocity molecules 12Low Rarth orbit Solar photons PL-TR-93-2134Optical properties of water released in low earth orbit ABSTR-CrAnalysis of intensified video photographs of a twilight venting of excess water from space shuttle showed that the -1 mm diameter stream cavitationally fragments within about I m, forming two discrete-particle components and vapor. The images from nearby cameras are dominated by irregular, polydisperse water/ice droplets with sizes comparable with the venting orifice and outward velocity indistinguishable from that of the initially coherent liquid. In contrast the 2'h ki-long quasiconical trail imaged from a distant ground station consists of accompanying submicron ice spherules that were produced by partial recondensation of the overexpanded vacuum-evaporated water gas, which are sublimating at rates that we calculated from the measured falloff of axial sunlight-scatter radiance and the energy balance of progressively roughening ice at 329 kim altitude; at low latitudes they co...