d location of well-separated signals produced in the CCD via illumination with X-rays which produce well defined charge packets. X-ray CTE measurements can reproducibly detect very small changes in CTE, but they may considerably over-estimate the CTE degradation that would be observed on-orbit for several reasons. During many missions, CCDs will be viewing scenes that provide significant background radiation charge and larger signal sizes. As seen in figure 15, the CTE in proton irradiated CCDs can be strongly dependent on both signal size and background radiation charge. Also, sophisticated readout algorithms and signal processing software on board the satellite may decrease the impact of CTE loss for a given application. As a simple example, an application may call for the signal in neighboring pixels to averaged together, SO that the charge lost to trailing pixels as a result of CTE degradation is less significant. In the case of star tracker applications, the results of X-ray CTE measurements (along with dark current results, etc.), may be input to detailed system level radiation effects models to predict the performance impact. In addition, the irradiated CCDs themselves may be placed in elaborate simulation stations complete with calibrated star fields for a detailed evaluation. However, many satellite applications involve a range of performance requirements, and less sophisticated laboratory radiation tests must be designed to provide the most reasonable worst case assessment. IV-84 + 12 MeV p+ 22 MeV p+ + 63 MeV p+ FISSION n° FLUENCE (x1011 cm-2) Figure 18 The linear dependence of the change in dark current on particle fluence permits the definition of the dark current damage factor (given by the slopes of the lines). After [Dale89b]. The second major effect of proton induced displacement damage on CCDs is the increase in dark current as a result of carrier generation in the bulk depletion region of the pixel. (This assumes that the CCD or CID has a hardened oxide and/or else is run in inversion SO that t