of these elements. The discussion which follows pertains to both silicon (Si) and gallium-aluminum-arsenide (GaAlAs) cells. If the electrical connectors are soldered, they are the most vulnerable element of the cell, as typical aerospace solders melt at about 180° C. The assumption is made here that the connectors are welded or otherwise fastened to eliminate this low failure temperature. The next temperature of interest is about 350° C. Here, typical adhesives begin to bubble, lose their adhesiveness, and lose their transparency. In addition, the GaAlAs cells begin to experience contact metalization. As the temperature increases to about 450° C, both cell types experience significant metalization or diffusion of dopants and contact material into the cell body. A reasonable estimate for the upper limit of commercial cell operation for both cell types is about 600° C. The temperature range for failure for either the silicon or the GaAlAs cells is therefore estimated to be 350 to 600° C. Figure C.3-5 and C.3-6 show equilibration temperatures and times as a function of the incident irradiance E. As indicated, the 600° C failure irradiances of 3.1 2 and 8.6 W/cm are reached by the GaAlAs and Si cells, respectively, in about 4 and 2 seconds. As with the antenna, the solar cell arrays could be expected to withstand a nominal Earth-based laser attack but could easily be vulnerable to a spacebased laser attack. C.3.5 Implementation A long lead time is required for the optics and primary mirror system. The polishing of the mirror to the required accuracy may take several years, particularly for the shorter wavelengths. The segmented array concept must be defined, along with the activation method. Most of the technology areas require a concerted effort to significantly advance the state-of-the-art in order to achieve the capabilities in the "nominal" projections by the year 2000. For instance, power must be increased by at least two orders of magnitude, and primary mirror area by a similar factor. The HEL system development cost is estimated to be less than one billion dollars, with unit cost on the order of one hundred million dollars. C. 3.6 Safeguards Safeguards to nullify an HEL's effectiveness include reflective paints or coatings and increased mass to moderate thermal effects. Neither of these
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