The levels of nuclear radiation rates and of trapped electron fluxes necessary to produce upset and/or degradation were estimated from radiation transport calculations for typical satellite materials and configurations. The resulting estimates of vulnerability appear in Table C.l-1, although there is substantial uncertainty in any vulnerability guidelines such as shown in this table. Any vulnerability assessments which are sensitive to parameters quoted in this table should be used with caution pending detailed analysis of specific designs. The x-rays and gamma-rays incident on the solar cells also shorten the minority carrier lifetimes, lowering the capabilities of the solar cell both in short circuit current and in open circuit voltage. Simultaneously, high transient rates of ionizing radiation induce enormous transient currents in the solar cells, as shown in Figure C.l-1. Note that 10^10 rads/sec in silicon produces transient short circuit currents of order 2 amperes/cm^2 in typical solar cells. Under normal operating conditions for the power satellites and COTVs, the solar cells will produce about 0.02 watts/cm^2 for the silicon option and about 0.04 watts/cm^2 for the gallium option, with a potential drop of order 1 volt across each cell. These transient currents would thus be about 100 times normal operating currents for warhead ranges of up to 80 or 100 km, and higher yet for shorter ranges. Currents generated by x-rays and gamma rays in the power collection and distribution cable networks by EMP effects or by SGEMP would further aggravate the problems with transient currents, since conductors have intrinsic conductivities many orders of magnitude higher than do semiconductors. The lethality range for a one-megaton warhead could thus be multiplied to several hundred kilometers. (These EMP and SGEMP effects cannot be estimated without detailed calculations for specific power satellite or COTV designs.) The Reference Design system includes no provision for current-limiting devices to protect its power collection and conversion circuits from such enormous transient currents. If unimpeded, such transient currents could severely damage the electrical brushes and slip rings at the rotary joint, the power conversion and conditioning equipment at the microwave transmitter antenna, the klystrons which generate the microwave power beam, and the phase control system for the power beam.
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