latter approach requires some degree of ongoing monitoring of production devices, since the total dose sensitivity is very sensitive to manufacturing process changes in some devices. Several device manufacturers are beginning to introduce lines of radiation-hardened devices that should reduce this concern in the future. Collateral Nuclear Effects The baseline environment defined for the nuclear radiation levels arising from a nuclear weapons test by another power, or from an attack on another satellite, is the JCS guidelines level defined in SAMSO Exhibit 69-13 (secret). For a synchronous satellite over the continental United States, the probability of seeing these levels resulting from an actual test is very small. Radiation levels resulting from an attack on another satellite will vary depending on the distance from the nuclear event, except for the electron and electromagnetic pulse (EMF) environments which are relatively independent of distance. The following discussion will be based on the distance specified in 69-13, and the levels, and the effects will vary as the distance varies. The principal impact of nuclear radiation on the Satellite Power System will be in the solar array itself and in the seminconductor devices that implement the vehicle electronics. The potential radiation failure modes are: • Catastrophic failure, arising from the burnout of semiconductors from X-ray induced photocurrents, or from electrical currents resulting from X-ray illumination of the vehicle cables or structure. X-ray illumination of the solar array itself at 69-13 levels will not result in catastrophic failure of the array, but couild result in surges in the primary power lines which could damage equipment connected to those lines. Such surges can be eliminated by a combination of mitigation of the X-ray environment by the use of shielding by material of high atomic number and by limiting the devices response by the addition of limiting impedances in series with the power supply lines to the affected devices. The efficacy of these protective approaches will be valid for increases in the environmental level of 3 to 4 times in most cases. The effects of electrical currents resulting from X- ray illumination of the cables or structure may be eliminated by the use of terminal protection devices (e.g., surge limiters, voltage clamps) at component input/output circuits. • Degradation, which is the same effect considered in the discussion of the natural radiation environment, except that the environments of concern are the weapon electron and neutron environments. The weapon electron environment will be larger than the natural environment, but otherwise may be treated in the same way. The neutron environment may not be shielded, but at the 69-13 level is too low to be of concern to the large majority of parts. Degradation which does exist must be characterized on the basis of tests on specimen devices in a simulated neutron environment, and then allowed for in the design.
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