earth's atmosphere. It is a more serious matter that the increased hydrogen loss due to SPS activities would be at the expense of fossil hydrocarbon fuels rather than water alone. If the rate of escape of hydrogen atoms were not to increase, the concentration of hydrogen atoms in the upper atmosphere would tend to build up, possibly with a factor of 2 as an upper bound. A factor of 2 buildup would probably be serious as it could lead to changes in thermospheric wind patterns, changed in the stability of the radiation belts, changes in nighttime ionization by scattered Lyman-a and Lyman-0 radiation from the expanded geocorona (see Section 3.1.4), along with the possibility of significant increases in satellite drag. Possible effects on F-region ionization are discussed in Section 3.2. 3.1.3 Some Details of the Distribution of Propulsion Effluents (Park) A. Mass Budget. In Table 8 some assumptions are made about the distribution of propulsion effluents of different elements of the SPS transportation system. Here we present the logic underlying that partition. It is clear that the HLLV circularization and deorbit burns occur at or very close to LEO. Regarding the POTV, which uses chemical propulsion to go from LEO to GEO and return, evidently much of the burn will occur at or close to LEO, with the remainder (30%, see below) taking place at or very near GEO. In any case, the POTV emissions near LEO should be combined with the HLLV circularization and deorbit burns to provide a source of H2O/H2 at or near LEO. There is a certain ambiguity in the relative source strengths of HLLV and POTV, with the latter providing perhaps 80% or 30% of HLLV, depending on whether one uses the figures in Table 2 (from RSR, 1978, silicon reference system listed in the text) or in Table 4, which comes from the Boeing study (RSR, 1978, p. B-100). (While not critical, this should be resolved.) We shall take a figure of 1.5 times the HLLV circularization and deorbit burns as the hypothesized injection near LEO, ^.nd shall assume that 30% of POTV injections of 103 kg hydrogen, or 6 x 10° H-atoms are emitted near GEO. For the electric propulsion COTV, things are somewhat different, as chemical rockets are used only for attitude control. Thus we shall assume that the use of the chemical rockets is proportional to the main propulsion, so that the emission of H2O/H2 as a function of altitude or time is proportional to the corresponding emission of argon. An additional problem that has been raised deals with ambient heating due to exothermal chemical reactions involving propulsion effluents. If we hypothesize a net exothermicity of 3 eV per H-atom, then the total COTV and POTV emission of 1.3 x 1033 H-atoms per year corresponds to an energy dissipation rate of 6.3 x 101 J/yr of 1% of the kinetic energy of the argon ions. B. Condensation of Water Vapor in Rocket Exhausts Expanding in Vacuum. The exhaust effluents from an H2-O2 rocket engine leave the exit plane of the rocket motor at about 4.0 km/sec, while those of a CH4-O2 engine move at around 3.0 km/sec. The effluents accelerate outside the rocket motor in the first ten meters or so to attain the "limiting velocity," which can be taken to be approximately 4.5 km/sec for the ^“02 system and about 3.5 km/sec
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