tion point was reached at all heights. Such a remnant contrail might produce a spectacular noctilucent cloud display at first dusk or dawn after an HLLV launch. 5. CONCLUSION Through detailed model calculations, we have found that the water vapor emissions of SPS rockets would not cause a significant increase in global high-altitude cloud coverage, nor trigger a noticeable change in the climate. Simulations of HLLV rocket plumes in the midlatitude mesosphere indicate that dense contrails could be formed, and might persist for several hours, depending on local meteorological conditions. However, each contrail would only expand to cover a small geographical region, and would have little significance for local microclimates. Except for the possibility of impressive noctilucent cloud displays in the launch corridor, we have uncovered no evidence to suggest that sustained, widespread clouds can be produced by liquid propellant rockets such as the HLLV. It must be stressed, however, that these conclusions are based on limited scientific data and approximate computer models, and are therefore preliminary. Acknowledgement — Helpful discussions with C. Park of the NASA Ames Research Center, and K. Brubaker and D. Rote of the Argonne National Laboratory are gratefully acknowledged. This work was supported by Interagency Agreement A1-01-79ER-10035 from the Department of Energy. The editor wishes to thank Michael Mendillo and John Zinn for reviewing this paper. REFERENCES 1. Satellite Power System Concept Development and Evaluation Program, Reference System Report, U.S. Department of Energy/NASA Report DOE/ER-0023, Washington, DC, 1978. 2. R.C. Whitten, W.J. Borucki, C. Park, L. Pfister, H.T. Woodward, R.P. Turco, L.A. Capone, C.A. Riegel, and T. Kropp, The Satellite Power System: Assessment of the Environmental Impact on Middle Atmosphere Composition and on Climate, Space Solar Power Rev. 3, 195-221, 1982. 3. J.M. Forbes, Upper Atmosphere Modifications Due to Chronic Discharges of Water Vapor from Space Launch Vehicle Exhausts, in Space Systems and Their Interactions with Earth's Space Environment, H.B. Garrett and C.P. Pike, eds., Progr. Astronaut. Aeronaut. 71, 78-98, 1979. 4. G. Witt, The Nature of Noctilucent Clouds, Space Res. 9, 157-169, 1969. 5. R.P. Turco, O.B. Toon, R.C. Whitten. R.G. Keesee, and D. Hollenbach, Noctilucent Clouds: Simulation Studies of Their Genesis, Properties, and Global Influences, Planet. Space Sci. (to be published). 6. G. Grams and G. Fiocco, Equilibrium Temperatures of Spherical Ice Particles in the Upper Atmosphere and Implications for Noctilucent Cloud Formation, J. Geophys. Res. 82, 961-966, 1977. 7. D.M. Hunten, R.P. Turco, and O.B. Toon, Smoke and Dust Particles of Meteoric Origin in the Mesosphere and Stratosphere, J. Atmos. Sci. 37, 1342-1357, 1980. 8. J.S. Theon, W. Nordberg, and W.S. Smith, Temperature Measurements in Noctilucent Clouds, Science 157, 419-421, 1967. 9. U.S. Standard Atmosphere Supplements, U.S. Government Printing Office, 1966. 10. W.F. Tozer and D.E. Beeson, Optical Model of Noctilucent Clouds Based on Polarimetric Measurements from Two Sounding Rocket Campaigns, J. Geophys. Res. 79, 5607-5612, 1974. 11. A.B. Meinel, B. Middlehurst, and E. Whitaker, Low-Latitude Noctilucent Cloud of 15 June 1963, Science 141, 1176-1178, 1963. 12. J.E. McDonald, Stratospheric Cloud Over Northern Arizona, Science 140, 292-294, 1963. 13. B. Benech and J. Dessens, Mid-Latitude Artificial Noctilucent Clouds Initiated by High-Altitude Rockets, J. Geophys. Res. 79, 1299-1301, 1974. 14. A.E. Potter, Proceedings of the Space Shuttle Environmental Assessment Workshop on Stratospheric Effects, NASA TM X-58198, 1977. 15. B. Fogle and B. Haurwitz, Noctilucent Clouds, Space Sci. Rev. 6, 278-340, 1966. 16. E. Bauer, ed., Proceedings of the Workshop on the Modification of the Upper Atmosphere by Satellite Power System (SPS) Propulsion Effluents, La Jolla Institute Report CONF-7906180, La Jolla, CA, 1979.
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