citly for component types known to be susceptible to proton-specific effects, such as optocouplers, Charge Coupled Devices (CCDs), and others. 2.3.1 Total Ionizing Dose: TID requirements for a given mission are usually based on the composite electron-proton dose based on the depth-dose relation for the given mission. TID evaluations are customarily made using Co-60 test facilities with the assumption that there is a linear superposition of dose from protons and electrons (this assumption will be examined in a section IVA.3). 2.3.2 Destructive SEE: Similarly, for the case of single events effects resulting in hard failure, requirements for proton-related failure modes are rarely specified separately from heavy ion induced failure, though they sometimes should be. In practice however, extreme measures are usually taken to avoid hard failure, including the requirement that hard failures (e.g., latch-up) may not occur below the iron cutoff (or some higher LET value) of the heavy ion LET spectrum. If such measures are taken, then proton-induced hard failure will also be avoided, since proton sensitivity to SEEs is not expected where such high LET threshold values apply. Unless such assurances are in place, we suggest that requirements should be written to address the possibility of hard failures due to protons. In LEO applications of commercial power MOSFETs, for example, flight data has demonstrated that burnout is much more probable from protons than from heavy ions, even though the orbit inclination is 70° [Bart-98]. Expression of a requirement in terms of only LET would therefore be inadequate. Associated issues will be addressed in section 4.3.2 on Single Event Burnout (SEB). 2.3.3 Nondestructive SEE: It is more common for requirements to address proton-induced soft errors, at least indirectly, through the expression of requirements for average and peak error rates. Historically, this issue arose due to soft errors in memories, but in recent years the IV-13 literature (and unpublished flight data) provides many c