aurorae. Note that the operating location of SPS on the nightside is the key region where the auroral process takes place in response to solar wind disturbances (Figure A2). As one moves earthward of GEO, the geomagnetic field configuration becomes increasingly less distorted by the solar wind and more dipole-like. At a radial equatorial distance of about 4RE, one encounters a distinct plasma boundary, the plasmapause, which marks the surface of the plasmasphere. The plasmasphere is a dipole-like volume inside of which the thermal plasma density is several orders of magnitude higher than magnetospheric regions outside. Indeed, there is increasing evidence that the plasmasphere is just a continuation of the topside ionosphere which is trapped by the geometry of magnetic and electric fields. The processes of particle trapping and diffusion in the dipole-like magnetic field of this region are conducive to long- lived accumulation of injected matter and energy. We consider some of these processes in this report. Aside from the cold plasma of ionospheric origin and hot plasma of solar wind origin, solar and galactic cosmic ray processes and magnetospheric energization give rise to a trapped component of energetic particles (electrons, protons and alpha particles) which undergo trapped adiabatic motion in the plasmasphere. These particles are primarily concentrated in two torus-like shells known as the Van Allen radiation belts (Figure A1). Since the natural radiation dosage in these belts are hazardous to humans and to space-borne equipment, radiation belt dosages represent design limits for space systems which operate in this region. For example, for manned lunar missions the thrusting schedule has to be carefully designed to avoid excessive dosage in traversing the radiation belts. Thus, any magnetospheric modification by SPS injectants must be considered in the light of their possible effects upon the A-2
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