injection burn. The illumination was presumably caused by sunlight scattered from ice crystals in the exhaust cloud (see also Aviation Week, 6 January 1969). It is not known how large the ice crystals formed in a liquid fuel (H2” □2) rocket are, but they are probably smaller than those observed in aluminized solid propellant rocket, i.e., submicron. Note also that various components of rocket exhausts such as atomic and molecular ions, small ice crystals and various contaminants may induce the condensation of supercooled water vapor in the ambient atmosphere to form a contrail. Such phenomena are thought to be responsible for the "noctilucent cloudlike" formation observed in some past rocket launches (see Benech and Dessens, 1974). Note also the observations of Meinel et al., 1963 of several contrails (seven over six months) observed at an altitude of order 70 km from Arizona following launches of Scout solid propellant rockets from Vandenberg Air Force Base. B. Summary of Water-Dump Experiments Several water-dump experiments have been decribed that address the condensation issues raised by rocket exhausts. These are: (1) Wallops Island High Water Test. On 2 March 1962, a Nike-Cajun rocket released 18 kg of water at an altitude of approximately 100 km over Wallops Island, Virginia. The time of the release was 05:47 E.S.T., corresponding to dawn twilight. The main objective of the experiment was to provide background data for a proposed release of water from the second and third stage of a vehicle designed to test the Saturn booster (the Saturn High Water Experiments described below). The ground-based optical diagnostics led to three main conclusions (Edwards, 1962): (a) Upon release of the water from the canister a small portion (2 kg) was perhaps vaporized and the remainder formed ice particles that continued to follow the ballistic trajectory established by the Nike-Cajun rocket. (b) The ice crystals probably had a random size distribution with diameters from a few to several hundred microns. (c) The vaporized water, if present, was too faint to be seen or photographed, whereas the ice crystal cloud was visible by means of scattered sunlight and could be photographed (e.g., at t = 60 seconds after the release, the diameter of the cloud was aproximately 6 km). (2) Saturn High Water Experiments. The largest known "chemical release" experiments yet performed were the Saturn water dumps of April and November 1962. These experiments were a secondary objective of the Saturn test flight program (Debus et al., 1964). • On two occasions, over 86,000 kg of water, carried as ballast in the upper stages of the Saturn vehicle, were
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