The physical dimensions of the cells used in the reference design are typically 4 cm x 4 cm. However, the physical dimensions which will be ultimately available are relatively unimportant. The major determinant will be 1) what size cell can be conveniently produced in the still to be developed continuous process and 2) what size is less susceptible to mechanical damage in the SPS application. Solar Cell Covers The covers to be used in this application serve two primary purposes. 1) They provide protection from charged particle radiation and 2) they provide a selective band pass filter to minimize incidence on the solar cell of light at wavelengths to which the solar cell is less sensitive from a power generation standpoint. The covers in this reference system are thin (^25 PM) since the radiation environment is not a severe one. In the reference system, a plastic cover is desired which can be heat sealed or otherwise attached to the cell without the addition of an adhesive layer. Interconnect Material Several choices are available for interconnect material. Major among these are silver, copper, and aluminum. The lightest weight system would be aluminum; however, copper offers distinct advantages. The interconnect system in this application will be designed to withstand the severe thermal cycling environment imposed by a geostationary orbit, without imposing major stresses on the solar cells and the welds themselves. This will be accomplished by designing a pattern of stress loops in the pattern. The use of stress loops adds to the effective conductor length within the blanket and thus adds weight. This could be avoided only if the entire blanket assembly, including substrate, interconnect, and solar cells could be fabricated of materials with a good (nearly perfect) match of thermal expansion characteristics. The interconnect pattern will be generated via photo repeat techniques and will be mechanically or chemically formed. Substrate Materials The basic substrate to be used will be a plastic membrane system probably thin (12.5 uM) Kapton laminate with a material like FEP Teflon as the adhesive layer bounding the interconnect. Reinforcing can be provided by framing each module section with fiberglass in the outer edge of the laminate. This type of construction is currently being used in all advanced, flexible solar array work. Much long term testing has been performed to characterize these materials at elevated temperatures under mechanical stress.
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