 are stopped by 50 mils Al shielding. Also note that some protons above 400 MeV are present, in contrast to the trapped belt models. ISSA Cosmic Ray Environment 1.0E+06 50 MILS AL 1.0E+03 500 MILS AL 1.0E+00 1.0E-03 1.0E-06 1.0E-09 1.E-01 1.E+00 1.E+01 1.E+02 LET (MeVcm2/mg) Figure 5. Proton contributions to the cosmic ray environment at 500 km and 51.6 degrees are included in the heavy ion LET spectrum. They account for 87% of all particles at an LET of 0.001 MeVcm2/mg, but only .002% at the lowest LET shown in the chart. IV-12 high-density sector calculations. Additional discussion and a list of references are provided in the 1998 Short Course notes from this conference in section V part 3.1 [Kinn-98]. These tools play an important role in determining the dose or associated proton spectra at the box and component level. Usually, after surrounding boxes and satellite structural elements are considered, the resulting exposure at the subsystem and device level is less than that for a 100 mil Al spherical shield. However, the protection offered by structural shielding is of much less benefit than in the case of electron exposure because of the penetrating nature of protons. 2.3 Requirements: Proton Specific Issues Expressions of requirements vary greatly from program to program. Top level requirements usually address performance of a system in a specified environment in terms of system lifetime, availability to perform mission objectives, and accuracy in meeting those objectives. At this level proton effects, along with other radiation effects, are only part of the reliability picture. From this level, system engineers usually arrive at a set of derived requirements that are applied to individual subsystems. These will likely address destructive failures, TID failure levels, and possibly soft error rates. Most often proton effects are lumped together with associated effects from other radiation sources. More recently, with the increasingly important role of displacement effects, proton levels may be specified expli