atisfactorily simulate proton dose for most purposes. Many different single event phenomena arise from protons including soft errors from nuclear inelastic reaction events, nuclear scattering events, and even direct ionization in several types of more sensitive devices. Special considerations are needed for SEU testing of high speed devices and for evaluations of devices with low soft error cross sections relative to their TID failure levels. In addition, both destructive and nondestructive hard errors may result from proton-induced reactions. In many cases, the concern for hard errors will be greater for cosmic rays, but in geomagnetically shielded (e.g., low-Earth orbits) the greater risk can be proton-related. Satellite subsystem design efforts benefit from proper expression of the anticipated proton environments in thorough requirements aimed at describing realistic typical and worst case proton flux and fluence levels. We have discussed many aspects of the environment models and their associated uncertainties as they affect the requirement definition. 6.0 ACKNOWLEDGMENTS We gratefully acknowledge partial support, technical suggestions, and complete encouragement from our colleagues and friends in the Radiation Effects and Analysis Group and Radiation Physics Office at NASA Goddard Space Flight Center. We also appreciate the helpful interactions with the Radiation Effects Branch members at the Naval Research Laboratory and throughout the radiation effects community. IV-43 REFERENCES FOR INTRODUCTION AND PART A (All references are unclassified.) [Adam-92] L. Adams, E.J. Daly, R. Harboe-Sorensen, R. Nickson, J. Haines, W. Schafer, M. Conrad, H. Griech, J. Merkel, T. Schwall, and R. Henneck, "A Verified Proton-Induced Latch-up in Space," IEEE Trans. Nucl. Sci., Vol. 39, No. 6, pp. 1804-1808, 1992. [Adol-96] John W. Adolphsen, Janet L. Barth, and George B. Gee, "First Observation of Proton- Induced Power MOSFET Burnout in Space: The CRUX Experiment on APEX," IEEE Trans. Nucl. Sci., NS-43, No. 6, pp. 2921-2926, 19