0191 -9067/82/030223-12$03.00/0 Copyright © 1982 SUNSAT Energy Council A STUDY OF MESOSPHERIC ROCKET CONTRAILS AND CLOUDS PRODUCED BY LIQUID-FUELED ROCKETS R. P. TURCO R&D Associates Marina del Rey, California 90291, USA O. B. TOON, R. C. WHITTEN, R. G. KEESEE, and D. HOLLENBACH NASA Ames Research Center Moffett Field, California 94035, USA Abstract — We investigate the formation of mesospheric contrails and clouds following the launch of large satellite power system (SPS) rockets. Specifically, we study the condensation of water vapor emitted by the booster motors of the liquid-fueled heavy-lift launch vehicle (HLLV). A one-dimensional model is described which treats the photochemistry and vertical transport of water vapor, its nucleation into an ice cloud, and the microphysical development of the ice cloud. Simulations of naturally-occurring noctilucent clouds, of widespread cloud perturbations associated with SPS rocketry, and of local HLLV rocket contrails are discussed. It is shown that regular HLLV activity (1 launch per day for a decade or more), which could increase the water vapor concentration in the upper mesosphere by 10%-20%, would enhance the size and opacity of natural noctilucent clouds by no more than —50%. This change has little climatic significance. Water vapor condensation trails are almost certain to form behind the HLLV engines. Rough simulations of these contrails indicate that they could persist for several hours and eventually spread over several hundred square kilometers. While these artificial clouds are unimportant climatologically, they might occasionally create spectacular night-luminous cloud displays otherwise rarely seen at midlatitudes. 1. INTRODUCTION The proposed satellite power system (SPS) will demand extremely large rockets (heavy lift launch vehicles, or HLLVs) to carry construction workers and materials into space. Engineering concepts for the HLLV are described in numerous planning documents (e.g., 1). Basically, each second-stage liquid-fueled rocket booster will operate between 60 and 120 km (36 and 72 mi) above Earth in a narrow latitude corridor centered at —30 °N, depositing more than 1200 tonnes (1320 tons) (1 tonne = 106 g) of water vapor in this region. It happens that the ambient water vapor burden of the mesosphere (50-90 km) (30-54 mi) is —106 tonnes. Thus, the projected 400 HLLV launches per year represent a substantial perturbation of the natural water vapor budget of the upper atmosphere. In an accompanying paper, we analyze the changes in atmospheric composition that might be caused by HLLV launches (2). In this paper, we emphasize the condensation properties of the water vapor exhaust. With the deposition of large quantities of water vapor in the mesosphere by SPS rockets, extensive exhaust contrails might be formed. Forbes (3) has estimated that HLLV contrails would be confined to regions «200 km2 (—80 mi2). Whether these
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