Simulating Large Area, High Intensity AM0 Illumination - Test Results from Bepicolombo and Solar Orbiter Qualification

Abstract

Two ESA high temperature missions, BepiColombo and Solar Orbiter, are planned to start in 2018. Severe environmental conditions with sun intensities up to 10.6 resp. 12.8 solar constants will be encountered during both missions. Different tests have been performed to qualify the main component for the solar array, the solar cell. The key qualification test for these high temperature, high intensity missions is a combined test which exposes a large number of cells simultaneously to the complete AM0 spectrum at the required irradiance and temperature. During the last European Space Power Conference in 2014, the development and performance of the appropriate test setup in the VTC1.5 chamber located at ESTEC was presented. In the meanwhile, the BepiColombo 4000 hour qualification test is successfully finished. This paper summarizes the results of the qualification test and highlights the main findings. Specifically, the following topics will be treated. Different methods like electrical performance, thermo-optical and external quantum efficiency measurements have been used to characterize the behaviour of the solar cells after illumination under these conditions. A special focus has been put on the electrical performance. A comparison to other solar cell qualification tests under solely UV radiation has been undertaken. The results have also been compared to a theoretical model. However, the paper will not cover only characterization results but will also give some insight in challenges experienced during the test execution itself. Deviating from other solar cell qualification tests, a representatively equipped photovoltaic assembly on carbon fibre reinforced cyanate has also been included. On these coupon segments, solar cell assemblies connected to shunt diodes and placed next to optical surface reflectors have been exposed to AM0 illumination to qualify the solar cells including their surroundings which therefore covers also contamination effects. Last but not least, first results from the Solar Orbiter qualification are presented. This test with additional 1000 hours and increased intensity has been completed recently.