factors indicating needs for large design margins can be minimized. However, for now, many proton effects are only beginning to work their way into the concerns of the typical design effort. Proton testing is still viewed as an expensive alternative to be used sparingly. In many cases the details of defining proton test approaches and deciding on acceptable margins falls within the scope of "nonstandard parts evaluation" efforts. Resolution of these issues can present a significant set of interesting challenges. 2.4 Recent Updates to the Proton Environment Models The preceding discussions have identified many of the proton environment models now being used, and indicated references for additional information. There are however a few key points to make regarding the dynamic status of the environment models. Janet Barth, in the 1997 Short Course notes [Bart-97], includes a section entitled "Problems with the AP-8 and AE-8 Models," and she follows this with a section entitled "Dynamic Models, A Beginning." These notes are well worth reading to see the path toward revisions to the existing NASA models. Last year, at this conference, Houston and Pfitzer presented a paper entitled "A New Model for the Low Altitude Trapped Proton Environment," [Hous-98]. This "new model" is based on data acquired by instruments on the TIROS/NOAA spacecraft from 1978 through 1995. The key finding, from the satellite designer's perspective, is that the predicted fluxes are about twice as high as those from the AP-8 model, as indicated in figure 6. This finding seems to hold for proton energies of interest to satellite designers (> 16 MeV). The data cover the altitude range from 250-850 km. In conjunction with the CRESSPRO model [Meff-94], this significantly improves the empirical basis for major revision to the AP-8 model. The probabilistic model for SPE peak fluxes presented at the 1998 NSREC has already been mentioned [Xaps-98]. Environment specialists also rely on a probabilistic modeling tool for predicting solar proton fluences durin