e induced Single Hard Errors (SHE) requires testing to determine device susceptibility. The selection of alternative devices which do not exhibit such susceptibility is an obvious method for eliminating this potential failure mode. Application techniques such as the fault masking provisions discussed in Section 6, error detection and correction coding or spatial redundancy, enable proper device operation in the presence of failed circuit elements. Analysis of Single Event Upset Rates and System Effects The analysis of single event upset rates consists of characterizing component susceptibility, establishing particle flux models for the specific orbit (including the severity of the environment at specific times and locations), and folding the energy or linear energy transfer dependent device characteristic with the appropriate particle spectrum to produce an estimate of component level SEU rate. 5.3.1 Component Single Event Upset Characterization [Petersen97] [Stapor95] The first element in establishing an estimation of the rate of occurrence of single event effects is characterizing the susceptibility of devices which are utilized in implementation of the system. Ground based measurements using particle beam accelerators are used to produce energetic particles which travel through the device structure similar to particles in the space environment. In the case of heavy ions, the energy of particles used in ground based testing is significantly less than that of particles found in space. By utilizing particles of equivalent LET an approximation of the charge deposition characteristics is realized. Differences in the dimensions of track structure and the inability to utilize a wide diversity in the direction of propagation of the particle through the device structure are sometimes areas of concern in how ground based testing simulates the space environment. In the case of energetic protons, the energy available from test facilities approximates the energy of protons in the space environment. The single event upset c