condensed water from the localized point(s) of injection. Since the size of the crystals is probably in the 0.1 pm range, with perhaps 10 -ICr molecules, current estimates point to relatively rapid fall (speeds on the order of kilometers per second above several hundred kilometer altitude). In the lower atmosphere (Domain A) winds would be the main source of ice cloud transport. Theoretical studies of condensation usually assume that the ice crystals can be replaced by equivalent spheres. This assumption may be too restrictive for the present application. For example, in trying to infer the degree of condensation from optical measurements, as was done in LAGOPEDO for instance, the conclusions may have a strong dependence on the shape as well as size of the ice crystals, especially if the longest dimension essentially determines the scattering properties. An important aspect of the water injection problem deals with the subsequent sublimation of the ice crystals. In Domain A, collisions with the neutral atmosphere are probably the main source of sublimation; at higher altitudes collisional heating is no longer effective. The role of sunlight in the sublimation process is not fully understood at this time. Estimates of a half-life of ice crystals in the 2-10 minute range (see e.g., Molander and Wolfhard, 1969) may be too short (Zinn and Bernhardt, private communication; also Sharma and Buffalano, 1971, Table 1, who estimate from 20 minutes near 640 km and over a day in cislunar space). Additional areas that need to be investigated are: (1) The role of multi-constituent exhaust clouds in which the individual species may influence each other's tendency to condense (e.g., the Space Shuttle OMS engines, used in its circularization burn, emit 1^0, CO2, H2, N2, and other minor species). In addition, any particulates or ionic species in the exhaust may enhance the condensation procss. (2) The possible chemical interaction between ice and a plasma need to be examined. (3) Past and current studies of comets should be examined in the context of the sublimation and plasma chemistry questions. (4) Any archived data on rocket exhaust condensation and subsequent sublimation should be reviewed. (5) The feeling that possible laboratory experiments (with the possible exception of Castleman's work on condensation on ions) are probably not directly relevant to rocket exhaust effects suggests that only rocket observations (via experiments of opportunity) should be planned. (6) The use of LIDAR to address the condensation/sublimation question needs to be examined, as well as any nonvisual optical detection technique.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==