• Increase collection efficiency (small effort) • Decrease base resistivity • Attain higher doping in p and n regions • Develop improved production processes while at the same time reducing cell thickness to control the solar array weight. (3) Reduced Solar Array Weight The array weight for the SSPS is a direct function of the thickness of the silicon solar cells. Single-crystal silicon solar cells are presently 500 to 1000 microns thick, although thicknesses on the order of 200 microns are routinely fabricated and cells of 50 microns have been built and tested in the laboratory. The importance of reducing solar cell thickness derives from the fact that the solar array represents 67 percent of the satellite mass and the solar cells contribute nearly two-thirds of the solar array mass. The specific mass of the 2 2 array blankets is projected to be 0.0576 Ib/ft (0.282 kg/m ) for a total blanket mass of 17.2 million pounds (7.83 million kilograms). If 100 micron cells were used rather than the projected 50 micron cells, blanket mass increases to approximately 22 million pounds (10 million kilograms). The SSPS will utilize very large area solar cell arrays that can be effectively handled only if large integrated submodules or blankets of cells are developed. Presently solar cell arrays are made much like an art mosaic where individual cells are fitted, interconnected, and bonded to substrates. Power to weight ratios of about 60 W/lb (132 W/kg) could presently be achieved, but ultra lightweight blankets of over 400 W/lb (880 W/kg) are required for the SSPS. This will require, in addition to the reduced thickness of the solar cells: • New blanket fabrication techniques • Inproved radiation resistant materials • New thermal control coatings (4) Improved Solar Array Lifetime The goal of the SSPS is to produce power at high voltage in a relatively stable thermal environment (except during predictable
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