on-orbit device performance assessments based on laboratory radiation measurements at one (or at most a few) proton energies, and therefore must make an assumption concerning the energy dependence the measurements will follow. There are several possible approaches including use of: (1) a calculated NIEL curve, (2) an experimental displacement damage curve (if available), or (3) a piecewise "manufactured" worst case displacement damage function. All of these approaches have significant uncertainty associated with them that must be reflected in the design margin applied to a given application. 2.3.3 Calculation of Displacement Damage Equivalent Fluences It is very useful for the radiation design engineer to become comfortable with the calculation of damage equivalent fluences (and displacement damage dose). Data in the literature are collected using a variety of incident proton energies, and one needs to be able to convert to an equivalent fluence at a particular energy of interest. (The respective fluences are "equivalent" in the sense that they will produce the same amount of displacement damage in the device.) Likewise, it may be necessary to convert the proton spectrum for a particular mission to an equivalent fluence at a specific proton energy. To the extent that the proton energy dependence of the device degradation correlates with NIEL (or a relevant measured damage function), radiation testing can (in principle) be performed at only one proton energy. In practice, we have seen that there can be significant uncertainty in the energy dependence of the device radiation response. Nevertheless, program constraints often restrict proton testing to a single energy, and it is important to choose the test energy very carefully. We will see in section 2.4 that we can use our displacement damage analysis tools to select appropriate test energies, and that the choices will depend on the degree of device shielding in a particular application. Many of the space applications employing photonic devices (e.g., CCDs, etc.) 