The time, T, to empty the inner belt of protons is Here N is the total number of protons between magnetospheric shell L = \ and 2. is the number of protons cm-3 at any energy, E, with velocity v(E). The volume, V, between/. = 1 and L = 2 is 3.1 x 1027 cm3 (9). Solution of equation (5) gives n = 6.6 x 10-4 cm-3 so that N = 2.0 x 1024 protons for the total proton population of the inner radiation belt. The total number of protons precipitated per second is given in equation (3) as p and can be expressed as p = FtA second-1 The total flux FT = F„Eocm-2sec-1 and the area into which protons are precipitated is A = 8 x 1017 cm2 representing 16% of the global surface area. Therefore, p is 2.0 x 1024 protons sec-1. Substitution of these values for p and N into equation (3) gives the time T required to empty the inner radiation belt of protons as about 1 second. In comparison with the hundreds of years required to replenish the belt through neutron decay the time to precipitate is very small indeed. Hence ion propulsion operations will empty the inner radiation belt in a short time producing an amount of NO which is much less than the normal production per day due to cosmic rays and nitrous oxide as demonstrated in Fig. 1. Once empty the radiation belts will be unable to refill fast enough to maintain the initial proton precipitation rate. As far as NO production in the middle atmosphere and its possible consequences for ozone are concerned, proton precipitation by ion propulsion does not pose any hazard. Acknowledgement — The editor wishes to thank Dr. Harold Liemohn and Dr. John Zinn for their assistance in reviewing this paper. REFERENCES 1. G. Hanley and C.H. Guttman, Satellite Power Systems Concept Definition Study: Final Report Executive Summary, Vol. I, Rockwell International, April 1978. 2. S.A. Curtis and J.M. Grebowsky, Changes in the terrestrial atmosphere-ionosphere-magnetosphere system due to ion propulsion for solar power satellite placement, submitted to Space Solar Power Review. 3. P.J. Crutzen, I.S.A. Isaksen and G.C. Reid, Solar proton events: Stratospheric sources of nitric oxide. Science, 189, 457, 1975. 4. J.E. Frederick, Solar corpuscular emission and natural chemistry in the earth’s middle atmosphere, J. Geophys. Res., 81, 3179, 1976. 5. J.I. Vette, Trapped radiation population, in The Trapped Radiation Handbook, J.B. Cladis, G.T. Davidson and L.L. Newkirk, Eds. Lockheed Palo Alto Research Laboratory, Palo Alto, CA, January 1977. 6. C.H. Jackman, J.E. Frederick and R.S. Stolarski, Production of odd nitrogen in the middle atmosphere: an intercomparison of source strengths, submitted to J. Geophys. Res., 1980. 7. P. Wameck, Cosmic radiation as a source of odd nitrogen in the stratosphere, J. Geophys. Res., 77, 6589, 1972. 8. M. Nicolet, On the production of nitric oxide by cosmic rays in the mesosphere and stratosphere, Planet. Space Sci., 23, 637, 1975. 9. W.N. Hess, The Radiation Belt and Magnetosphere, Blaisdell Publishing Company, Waltham, MA, 1968.
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