nfiguration (altitude and inclination), location (latitude and longitude), local time, season within the year, and interval within the solar cycle. Although often considered a near perfect vacuum, the presence of these factors presents challenging design requirements which are unique to space systems. Energetic Charged Particle Environments [Barth97][Dyer98] The energetic charged particle environment is quite complex; it is not homogeneous, isotropic, nor static. The primary sources of energetic particles present in the environment of earth orbiting telecommunications satellites are the geomagnetically trapped particles, protons and electrons, the transient population of cosmic ray protons and heavy ions, and solar event generated protons and heavy ions. Flux levels of these particles vary with solar activity, and models of the environment reflect the changes in the population of these particles over the approximate eleven-year solar cycle. Modeling of the environment usually divides the solar cycle into a seven-year interval of solar maximum and a four-year interval of solar minimum. 3.1.1 Trapped Particles: Protons, Electrons, and Heavy Ions Particles trapped in the earth's geomagnetic field present the most significant contribution to the environment for low-Earth orbit, medium-Earth orbit, and highly elliptical orbit spacecraft. Ionization effects due to trapped protons contribute the majority of total ionizing dose effects, non-ionizing energy loss processes result in displacement damage dose effects, and reactions with atoms in the device structure result in single event effects in more sensitive devices and technologies. Particles trapped in the earth's geomagnetic field present the most significant contribution to the environment for low-Earth orbit, medium-Earth orbit, and highly elliptical orbit spacecraft. Ionization effects due to trapped protons contribute the majority of total ionizing dose effects, non-ionizing energy loss processes result in displacement damage dose effects, and reactions with ato