axis is offset from the earth’s spin axis and because proposed SPS launch site at Florida would necessitate a 28.5° orbit inclination change during transfer orbit to GEO. The exact orientation of the argon plasma beam with respect to the local magnetic field depends entirely on the above factors and on the details of the planned thrusting schedule, which are not available. Considerations of particle motion in the Appendix section indicate that this exact orientation is not of great significance for global scale environmental assessment except at the vicinity of LEO where direct precipitation of a dense beam of 3.5 keV Ar+ would cause airglow (artificial aurora) emissions and atmospheric heating far exceeding that of the natural aurorae. These effects will be discussed more fully in Section IV.A. For consideration of argon plasma emission parameters, Figure 3 (taken from Chiu et al., 1979a) shows the relationship between payload mass and argon propellant mass needed to transport the payload from LEO (~ 400 km altitude) to synchronous altitude with an accompanying orbital plane change of 28.5°. Obviously, the amount of propellant required for a given payload depends on the ion-beam streaming speed. For an SPS payload of ~ 107 kg, it will be necessary to expend ~ 106 kg of argon propellants for option 1 in Table I. This is ~ 1031 Ar ions, roughly comparable to the total content of the natural plasmasphere and ionosphere above 500 km. The exhaust deposition rate in terms of the time fraction of LE0-GE0 transfer orbit, which is nominally ~ 130 days, is shown as a function of geocentric radius R on Figure 4 (Chiu et al., 1979a). Thus, 80 percent of the total propellant content is released in the plasmasphere, R <= 4 Rg (Figure 2). The number of Ar+ released at a given geocentric distance for a payload mass of ~ 107 kg is shown on Figure 5 (Chiu et al., 1979c); for comparison, the number of ambient electrons lying within a flux shell of thickness equal to twice the argon gyroradius at a 7
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