A. COTV Ion Engine Exhaust The current technology of ion engines is still evolving (Kauffman, 1974; Byers and Rawlin, 1976); therefore, the parameters of argon-ion engine operations in space must largely be regarded as uncertain at present, although it is by now fairly firm that the most economical and environmentally safe propellant is argon. According to the Reference System Report of the Satellite Power System Concept Development and Evaluation Program (U.S. DOE, 1979) argon-ion engines of specific impulse 13000 sec. are projected for the COTV. Other considerations (Byers and Rawlin, 1976), with perhaps less stringent requirements on projected advances on the technology of ion engines, assumed 5000 sec. specific impulse as standard for comparison. Some projected characteristics of these two options of ion engine operation are listed in Table I, in which Option I (the official concept option) will be used as reference in this report. From Table I, it is seen that the ion beam exhaust is a very dense but fairly cool plasma whose streaming kinetic energy (3.5 keV) far exceeds the thermal energy. In order to propel the COTV to geosynchronous orbit, the argon plasma beam will be directed primarily perpendicular to the geomagnetic field at the equatorial plane in the azimuthal direction (Figure 1). The COTV transfer orbit will be a spiral in the equatorial plane (Figure 2). Plasma beams propagating perpendicular to the geomagnetic field entail very interesting dynamical interactions with the magnetosphere-ionosphere system; in this case, this interaction takes place not at a single location but at all equatorial altitudes from LEO and GEO (Figures 1 and 2). Although, for purposes of considering large-scale magnetospheric modification, the argon plasma beam can be regarded as being perpendicular to the magnetic field at the equatorial plane, it is technically not entirely correct because the magnetic 5
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