 the on-orbit performance expected for a device or subsystem. Case Studies 3.3.1 Bipolar Transistors As discussed earlier, discrete bipolar transistors have served as important test vehicles to study displacement damage effects, but this should not be construed to imply that such devices would be primarily degraded by displacement damage effects on-orbit. Quite the opposite is true. (In order to isolate displacement damage induced effects, the devices in these studies are pre-irradiated to multi-megarad levels with Co-60 to saturate the ionization damage prior to the proton, neutron and heavy ion exposures [Summ86]. Also, such studies may choose not to operate devices with low current bias SO as to minimize surface currents.) Much of the early displacement damage work on bipolar transistors focussed on neutron induced degradation and provides the basis for the current understanding the proton effects [e.g., Mess86]. Neutron induced degradation of the DC gain, drive current and VCE were explored and mitigation approaches derived. Although radiation effects research has resulted in hardened discrete bipolar devices, there continue to be displacement damage concerns, particularly for analog bipolar IC applications. IV-77 The susceptibility of linear bipolar ICs varies over a wide range because significant variations in processing, device design and specific performance requirements [Gaut83, Gove84, Mess86, Raym87, John87, Rax97, Rax98]. In general, it has been found that devices that contain substrate or lateral pnp transistors are most sensitive to displacement damage as a result of degradation of the minority carrier lifetime in the wide base regions (i.e., low fT, or gain-bandwidth product). Circuit level design also plays a large role. For example, the use of a lateral pnp transistor as a primary input transistor operating at low current levels would be expected to increase the device vulnerability to degradation from displacement damage. A recent study by Rax et al. provides another example of a design practice