Figure 2.2-6. Solar Cell Efficiency (Figure 2.2-6), then a projected GaAlAs 1985-1990 technology curve was plotted for efficiency versus temperature as shown in Figure 2.2-6. The 20-percent AMO, 30°C data point is shown on the projected curve. The design temperature that was determined in the study to operate the array was 125°C and, from the curve, the cell output is seen to be the 17.6 percent which was used in the sizing calculations. Radiation Effects The radiation environment on the performance of a 4-mil Si cell is shown in Figure 2.2-7 for a 30-year mission life at GEO. The radiation environment is plotted as equivalent 1-Mev electron fluence (e/cm^), There are two radiation environmental models shown in the figure. The more conservative model having a fluence of 3.2 x 1016 e/cm2 is based on the NASA model, "Natural Space Environment Criteria for 1975-1985". The second model is based on a probablistic analysis of the solar flare events and the model is described in the "Solar Cell Radiation Handbook". Solar cells made from direct bandgap materials are usually more radiationresistance than cells made from indirect gap materials, especially for penetrating particles. The higher resistance results from the high absorption
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