initial longitudes relative to that of the gas cloud). Moreover, if the "burn” were to occur in a short burst rather than continuing for a full drift period, the gas cloud might have escaped from the magnetosphere before a certain charged particle had encountered it. Next, we consider the interaction of ring current particles with gravitationally trapped neutrals. According to the DOE/NASA baseline concept of July 1978, the POTV will have ignition weight at LEO of 890 tons, of which the propellants LO2/LH2 comprise 830 tons. The major part of the chemical exhaust, in the form of H2O initially and in the form of dissociated H and O neutrals, will eventually escape the earth’s gravitational field except for some 140 tons emitted by burn 2 of Figure 6. These 140 tons of H and 0 atoms (~ 2.4 x 1031 neutral atoms) form a spherical shell of charge-exchange centers between 3000 km altitude and 30000 km altitude, so as to overlap the ring current and the radiation belts. The gravitationally trapped neutral cloud will have a very long lifetime because its density is not sufficient to change the collisionless character of the medium. Thus, aside from prompt and transient effects of charge exchange caused by the neutral exhaust cloud immediately after release, about 1/5 of the propellants of each POTV flight would be trapped in orbits centered at about 15000 km altitude. The cumulative effects of this "neutral" belt is not presently known and will be investigated in our future research program. As a first estimate we consider that the 2.4 x 1031 neutral atoms are distributed uniformly throughout a geocentric spherical shell of inner radius 9370 km and outer radius 36370 km, i.e., spanning the 3000-30000 km altitude range. The spherical shell has a volume of 1.89 x 1029 cm3 and thus contains neutral gas at a density of 127 atoms/cm3. This would be the density experienced by equatorially mirroring ring-current ions for 68
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