previously unimportant aspects of the environment, are continually identified. From the radiation effects perspective, it's hard to overdo the level of detail in the environment description called out in a requirement. 2.2 Example Proton Environment Description As an example of the proton environment description in a program currently under way, the interested reader may examine the document SSP 30512 Rev. C entitled "Space Station Ionizing Radiation Design Environment" [SSP-30512]. This document, released in June of 1994, describes the ionizing radiation environment as calculated for the International Space Station Alpha (ISSA) at an altitude of 500 kilometers and inclination of 51.6 degrees. Five years later, it remains the reference environment description for hardware currently being designed for ISSA, and it has general applicability to the multi-national and multi-agency effort. We include this example because this program is of general interest and also because the proton environment description is unusually thorough. The descriptions of various proton environments for ISSA are contained in table 1. The first item accounts for most of the protons encountered in the low-Earth orbit. Though not indicated explicitly in any of the ten items, most of these protons will be encountered during passes through the South Atlantic Anomaly (SAA). The average daily proton flux predicted in this table is calculated by using the AP-8 model for solar maximum conditions and shown below in integral form as figure 2. In table 1 the second and third listings address the depth-dose relation and are included here since protons account for a portion of the total ionizing dose. Figure 3 shows the relative annual dose contributions for electrons and protons at the center of a solid aluminum sphere. The chart indicates how protons dominate the TID for shield thicknesses greater than about 200 mils Al, and this result is typical of most orbits that encounter the trapped proton belts. Careful inspection of the proton curve illustrates