this topic. The eighth table entry (combined integral flux LET spectra (weather index=4) no solar flare flux) describes the cosmic ray design environment for ISSA in terms of the LET spectrum from heavy ions. We acknowledge that for orbits encountering the trapped proton belts there are relatively few cosmic ray protons. However, for devices (e.g., detectors) sensitive to single events from proton ionization, cosmic ray protons may be a concern. Hydrogen ions (protons) are after all the most abundant constituent of the composite cosmic ray spectrum, and they account for 83% of all cosmic rays outside the effects of the Earth's magnetic field. Figure 5 indicates the composite LET spectrum with two shield thicknesses for ISSA. In terms of LET, protons account for only about 1 in 105 incident particles at the lowest LET value shown in the figure (0.1 MeVcm2/mg). Though not shown, at LET values of 0.01 MeVcm2/mg and 0.001 MeVcm2/mg proton contributions increase to 0.5% and 88% respectively. If lower LET values are important, then the proton component of cosmic rays may dominate. Most cosmic ray protons are very energetic and shielding has little effect. For the ISSA environment definitions, proton spectra are provided with various shield thicknesses. Not all design efforts provide this level of detail, and it is often necessary to modify the provided spectra to evaluate the detailed effects of additional shielding. Several transport code based routines are available to provide spectra and sometimes dose behind additional shielding. The capability and complexity of these tools cover a broad range from transport through relatively simple spherical or slab single thickness to full-up ray tracing and IV-11 Maximum Solar Proton Flux for ISSA 1.E+11 0 MILS AL 1.E+10 50 MILS AL 500 MILS AL 1.E+09 1.E+08 1.E+07 1.E+06 Proton Energy (MeV) Figure 4. Peak solar proton flux from the October 1989 event, as propagated into the 500 km X 51.6 degree Space Station orbit, shows that less than a third of the protons reaching that orbit