rty of interest (e.g., current transfer ratio of an optocoupler or the maximum power of a solar cell) behaves nonlinearly with proton fluence. In both cases, the energy dependence of the property in question may be assumed to follow the calculated NIEL, and the concept of displacement damage dose in units of MeV/g is employed. (Note that, as discussed above, the NIEL may be replaced by a damage function constructed to provide a worst case performance analysis.) This predictive tool was first used to predict on-orbit CTE in Si CCDs [Dale91, Dale93], but the interested reader can refer to the literature to learn more about this approach as applied to other applications (e.g., InGaAs detector dark current and responsivity predictions [Mars94] and solar cell characterization in space [Sum94, Mess97, Walt99]). We will first illustrate the basic method for performing space predictions for the case where a damage factor can be defined, by calculating the yearly on-orbit CTE degradation for CCDs. Although the present section focuses on the predictive tool itself, we note that some of the issues raised will be explored in more depth in section 3.2.2, which concentrates on displacement damage in CCDs. IV-70 The first step is to define the relevant damage factor, and determine the most appropriate damage function to describe the energy dependence of this damage factor. In the present case, we consider the CTE damage factor, K(E), defined as the change in CTE per unit proton fluence, (E) as shown: ACTE(E)=K(E).P(E). The change in CTE is dominated by bulk displacement damage and therefore linear with proton fluence. The experimental CTE damage factors are shown in figure 10, together with the NIEL calculated in Si. The data from each CCD type exhibit a similar energy dependence, and each data set has been independently scaled to NIEL using a constant, C, which has units of CTE change per unit of non-ionizing energy deposited. Hence, we K(E)=CNEL(E). Recall that a scale factor is necessary because it is not presently possible 