Effects of realistic satellite shielding on SEE rates

Abstract

Realistic models of satellite shielding have been used to calculate SEE rates for Galactic Cosmic Rays (GCR) and solar flare protons. The results are compared with those obtained with a nominal 0.1 inch spherical shield. The rates for GCR (solar minimum) are systematically lower than those calculated with the nominal shield. The ratio of rates is greater than 75% for lightly shielded devices, but may be as high as a factor of two where there is shielding by other circuit boards. A more nearly realistic estimate of the rates would be obtained with a spherical shield with a thickness of at least 0.4 inches (3 gm/cm/sup 2/) for the typical satellites considered. The calculation of the SEE rate due to protons was reformulated to expedite shielding calculations. When the method was applied to the 93L422 RAM for various flare spectra, it was apparent that shielding has a first order effect on rate predictions. The calculated flare upset rates for the TDRS satellite were within 20% of the observed rates. A spherical shield of thickness 0.3 inches (2 gm/cm/sup 2/) would reproduce the rates. The method was also applied to a trapped proton environment predicted from standard models for CRRES. The predicted rate was consistent with the uncertainties of the environment. >