Southwood (1979, private communications) for the Jupiter-Io momentum transfer problem. The main effect of the neutral exhaust cloud is that it acts as an artificial source that can charge-exchange with ring-current ions, thereby- reducing the lifetime of these energetic particles and modifying auroral activity. Natural charge-exchange lifetimes for ring current ions are ~ IO"1 sec, as can be seen from the duration of the recovery phase of a geomagnetic storm. If the ring-current particle lifetimes are significantly shortened by charge exchange interaction with the neutral cloud, auroral activity would be significantly reduced by the following sequence of effects: (a) charge- exchange reaction converts an energetic charged particle into an energetic neutral which immediately escapes geomagnetic confinement; (b) ring current precipitation and trapped fluxes are reduced, leading to (c) reduction of strength and duration of geomagnetic storms and ionospheric disturbances. 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 LOz/ LHz comprise 830 tons. The major part of the chemical exhaust, in the form of HzO 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 particular "burns" of the vehicle (private communication by Dr. C. Park of NASA/Ames who constructed a typical scenario of POTV burns). These 140 tons of H and O atoms (~ 2.4 x lO^ neutral atoms) form a spherical shell of charge exchange centers between 3000 km altitude and 30, 000 km altitude, precisely in the vicinities of the ring current and the radiation belts. The trapped neutral cloud (gravity vs. centrifugal force) 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 15, 000 km altitude. The accumulative effects of this "neutral" belt is not presently known and will be investigated in our research program.
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