of the SAA region is indicated. Also present in these figures are the populations of electrons in the high latitude extensions of the outer belt structure forming the horn regions. Electrons are not as penetrating as protons, and shielding is significantly more effective at attenuating Dipole Shell Parameter . L their effects on microelectronic devices. Figure 3-4. Variation of Electron Flux Levels Electrons contribute to mission integrated [Barth97] ionizing dose effects, caused by primary electrons and secondary photons which are produced when the incident electrons are stopped or slowed by the shielding materials. Integral Electron Flux Contours for E > 0.5 MeV (#/cm2/s) Integral Electron Flux Contours for E > 0.5 MeV (#/cm2/s) Altitude = 500 km, Solar Maximum Altitude = 1000 km, Solar Maximum 100000000 100000 100000 Geographic Longitude (deg) Geographic Longitude (deg) Figure 3-5. Electron Flux Contours at 500 km. Figure 3-6. Electron Flux Contours at 1000 km. [Barth97] [Barth97] It is known from particle spectrometer measurements of the environment that anomalous cosmic rays become trapped in the magnetosphere. These trapped heavy ions lack sufficient energy to penetrate typical spacecraft shielding and therefore do not contribute significantly to mission-integrated dose or single event effects in microelectronic devices. 3.1.2 Galactic Cosmic Ray Heavy Ions Flux levels of Galactic Cosmic Ray (GCR) heavy ions are low compared to the population of geomagnetically trapped particles. They are extremely penetrating and result in single event effects in microelectronics devices; however, their contribution to mission integrated dose effects is minimal. The population of galactic particles varies with solar cycle; their population is highest during solar minimum and lowest during solar maximum, due to interaction with the solar wind. The ability of GCR heavy ions to penetrate the geomagnetic field results in the exposure to this particle population varying with spacecraft orbit. Increases in orbit altitude and inc