THE LOW-EARTH-ORBIT RADIATION ENVIRONMENT AND ITS EVOLUTION FROM MEASUREMENTS USING THE CREAM AND CREDO EXPERIMENTS

Data obtained from Cosmic Radiation Environment Monitors carried on Sh uttle missions during 1991/92, as well as on the polar orbiting micros atellite UOSAT-3 since April 1990, show the long term trends in the co smic-ray and trapped proton environments responsible for single event phenomena. Cosmic-ray fluxes have increased by a factor of two since J une 1991, while the solar flare event of March 1991 created an additio nal region of trapped radiation which intersects high inclination Shut tle and polar orbits and, although decaying, was still present in Dece mber 1992. Deployment at a variety of shielding depths on Shuttle enab les the influence of shielding to be explored and shows the influence of secondaries.