he amount of charge deposited by a single ionization track from a proton traversal, then the event cross sections may be greatly increased, by up to four orders of magnitude over the indirect mechanism. Such devices will therefore be very likely to exhibit SEEs with high rates in proton environments. 4.2.1 CCDs: In order for a device to be sensitive to direct ionization from protons, it is likely designed for an application requiring high sensitivity. In the case of the charge coupled device imaging array, the sensitivity is required to register faint signals from distant objects. For some applications, the signal may literally be only a few electrons integrated into the imager's depletion volume prior to readout. Not surprisingly, when a proton traverses the same depletion region or nearby material from which the deposited charge can diffuse, the CCD pixel registers a false signal. These false signals from proton SEEs can affect science instruments and star tracker based navigational equipment as well. An excellent reference exists which examines the rates and charge signatures for carefully controlled test conditions and provides orbital predictions for a LEO application in the proton belts [Lomh-90]. There are two techniques to minimize the effects from unwanted proton strikes. Imaging arrays on the NASA HST mission are troubled with these stray signals when in the South Atlantic Anomaly SO much that they curtail the science operations when passing IV-29 through this high flux region. When stopping operation is not practical, such as with a star tracker, transient events are usually rejected by using a Kalman filter approach to average over several frames of imagery and reject signals which are not repeated in subsequent frames taken in view of the same region. In figure 12, the four images have been acquired by a 1024 pixel by 1024 pixel CCD incorporated into one of the chronograph instruments on board the Solar and Heliospheric Observarory (SOHO) satellite. SOHO occupies an orbit around the L1 libration poin