lux at high inclination angle is shown. INTEGRAL FLUX FOR LET = 20 1E-03 1E-04 1E-05 1E-06 1E-07 1E-08 1E-09 1E-10 1E-11 1E-12 1E-13- INCLINATION (deg) ALTITUDE (km) Figure 6-1. Galactic Cosmic Ray Flux [Petersen97] The dependence of the proton population having energy greater than 30 MeV as a function of altitude and inclination is indicated in Figure 6-2. The geographic location of the trapped proton population in the South Atlantic Anomaly (SAA) region was indicated for orbit altitudes of 500 kilometers and 1000 kilometers in Figures 3-2 and 3-3 respectively. PROTON FLUENCES FOR CIRCULAR ORBITS 1E+10 Inclination 1,000 10,000 100,000 ALTITUDE (km) Figure 6-2. Trapped Proton Flux (>30 MeV) [Petersen97] From these figures the severity of the environment in regard to the propensity to experience charged particle induced single event upsets is indicated. As a fault avoidance provision, systems engineering trades regarding orbit architecture and the establishment of operating constraints in which critical operations must be performed during low SEU rate segment of the orbit may be established. 6.3.2 Effectiveness of Shielding [Smith94] [Petersen97] Depending upon the location of critical single-event-upset susceptible devices within the spacecraft, various levels of shielding are provided by the structure and other materials. Consideration of the shielding present, the potential to position sensitive devices in more highly shielded locations within the spacecraft, and the benefits available through utilization of localized additional shielding for sensitive devices may be addressed. Figure 6-3 indicates the attenuation provided by various levels of shielding for the solar minimum galactic cosmic ray heavy ion integral LET spectrum. Very limited attenuation of the GCR spectrum is provided over a significant range of shielding values presented in this figure. Moving of sensitive components and the use of additional shielding materials as a provision to reduce GCR single event upset rate in sensitive devices affords li