EFFECTS OF ROCKET EXHAUST PRODUCTS IN THE THERMOSPHERE AND IONOSPHERE JOHN ZINN and C. DEXTER SUTHERLAND Los Alamos Scientific Laboratory Los Alamos, New Mexico 87545 Abstract — This paper reviews the current state of our understanding of the problem of ionospheric F-layer depletions produced by chemical effects of the exhaust gases from large rockets, with particular emphasis on the “Heavy Lift Launch Vehicles” (HLLV) proposed for use in the construction of solar power satellites. The currently planned HLLV flight profile calls for main second-stage propulsion confined to altitudes below 124 km, and a brief orbit circularization maneuver at apogee. The second stage engines deposit 9x 1031 H2O and H2 molecules between 74 and 124 km. Model computations show that they diffuse gradually into the ionospheric F region, where they lead to weak but widespread and persistent depletions of ionization and continuous production of H atoms. The orbit circularization bum deposits 9x 1029 exhaust molecules at about 480-km altitude. These react rapidly with the F2 region O+ ions, leading to a substantial (factor-of-three) reduction in plasma density, which extends over a 1000- by 2000-km region and persists for four to five hours. For purposes of computer model verification, we include a computation representing the Skylab I launch, for which observational data exist. The computations and data are compared, and the computer model is described. 1. INTRODUCTION Present understanding of ionospheric F-layer depletions caused by exhaust products from large rockets began with the observations by Mendillo et al. (1) of an abrupt decrease in vertical electron column density along the trajectory of the launch of Skylab I, 14 May, 1973. The effect was attributed (1-4) to the chemical reaction of rocket exhaust molecules, primarily H2O and H2, with O+, the dominant F2-layer ion. These reactions produce molecular ions H2O+ and OH+, which recombine rapidly with electrons, causing a reduction in electron-ion concentrations. Practical interest in these ionospheric depletions (“holes”) has increased with the advent of proposals to build large space structures in earth orbit, such as the solar power satellite (SPS). Current SPS system studies call for space transportation activities on a far larger scale than any carried out heretofore. The proposed primary cargo vehicle, called the “heavy lift launch vehicle” (HLLV), is approximately six times larger than the NASA space shuttle vehicle (see, for example, the NASA SPS Concept Evaluation document (5)), and HLLV launches would occur with a frequency of several per day. The present paper is concerned with prediction of the ionospheric and environmental effects of HLLV launches. According to current design studies (5), the HLLV will be a two-stage vehicle with the capability of second-stage flyback. It is to be used for transportation between the surface and a low-earth orbit (LEO) at 450- to 500-km altitude. The second-stage engines are to be fueled with 300 t of liquid hydrogen and 2000 t of liquid oxygen. Hence, the exhaust gases will consist primarily of H2O and H2 in the molar ratio 3:1, about 9x 1031 molecules in all.
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