Extreme Environment Solar Power (EESP)

The Extreme Environments Solar Power (EESP) Project is developing advanced photovoltaic technologies to provide reliable power for NASA missions in the general vicinity of Jupiter. These advanced concepts, which address radiation damage and Low sunlight Intensity, Low Temperature (LILT) degradation effects, will extend NASA's use of solar array technology for exploration of the depths of our solar system. The majority of NASA missions utilize solar cells that are designed and qualified for long-term operation within an Earth-orbit environment. Deep space NASA missions, however, subject solar-powered arrays to stresses well beyond those experienced by commercial space and military satellites. Spacecraft sent to explore planets and other bodies farther from the Sun will encounter reduced light intensity levels and very low temperatures. A subset of these missions may encounter low-intensity low temperature (LILT) environments that can cause performance degradation in the power output of the solar cell. This LILT effect has been noted and verified through ground-based testing. The effect is variable from cell to cell, affecting the reliability of accurately predicting solar array performance throughout the life of a mission. The issue becomes more pronounced when one cell with this degradation characteristic is added in a series string with well behaved, predictable cells. Under LILT conditions, the entire string will be current-limited by the output of the bad cell and the performance of the entire string will be degraded. Current methods of minimizing LILT effects involve screening all solar cells for the mission, adding considerable cost and schedule to the spacecraft power system.