substantially larger than the density estimated by Farley and Walt for L = 2.5). However, the density model used by Tinsley yields densities of 300 cm -3 (L = 4), 210 cm-3 (l = 4.5), 150 cm-3 (L = 5), and 120 cm-3 (L = 5.5) at ringcurrent altitudes. Thus, a single POTV flight would reduce the chargeexchange lifetime of 10-keV protons from 37 hours to 20 hours at L = 5 and the lifetime of a 10-keV oxygen ion (O+) or a 50-keV hydrogen ion (H+) from 148 hours to 80 hours there. The cumulative effect of several POTV flights would be to reduce the lifetime of the storm-time ring current even further. Thus, we conclude that routine operation of chemical engines for the POTV would drastically reduce the level of geomagnetic activity associated with natural magnetospheric plasmas, i.e. auroral activity. Whether the additional plasma injected by ion engines can offset this reduction is a question that requires further study (see Section IV.E). B. Intensification of Geocorona Gravitationally trapped hydrogen at high altitudes is the source of the geocorona since neutral hydrogen atoms absorb solar radiation and re-radiate it in the Ly-[[spi:math]] wavelength region. The geocorona is, in turn, important to human activities in at least two aspects. First, it is the main optical background against which optical astronomical observations in space must discriminate. Second, Ly-[[spi:math]] radiation from the geocorona is the primary source of D-region ionization. Therefore, our concern is to estimate the intensification of the geocoronal Ly-[[spi:math]] radiation due to the belt of gravitationally trapped H-atoms resulting from bum 2 of a single POTV flight. Based on data provided by Dr. A. B. Christensen of Aerospace, the singlescattered intensity of Ly-[[spi:math]] radiation produced by solar flux [[spi:math]] impinging on a distribution HN of hydrogen atoms over optical path lengths can be written as 70
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