Results of the solar cell experiment of the first Brazilian satellite

Abstract

The first satellite of the Brazilian Complete Space Mission, launched on 9 February 1993, hosts a solar cell experiment (SCE). The objective of the SCE is to qualify in mission and real time the silicon solar cells for space use developed and manufactured in Brazil. The solar cells have the following characteristics: 4 cm 2 of area, base resistivity of 10 Ωcm and efficiency over 11% under AMO condition. The SCE is a small solar module composed by a single array of six silicon solar cells connected in series, laid down in an aluminium mechanical structure. The signal generated by the array is sent to a peak detector circuit located inside the mechanical structure. Three telemetry signals are available for the SCE behavior analysis, which are the peak detector output, the temperature sensor output, located inside the SCE mechanical structure under the solar array, and the attitude sensor signal, which gives the sunlight incidence angle with respect to the SCE plane. The SCE signal versus temperature curve is used to obtain the solar cell current versus voltage characteristic parameters values, based on the double exponential model, using a computational method developed to accomplish this task in real time, during the satellite lifetime. This work describes the solar cell experiment, the numerical methods and the analysis of the telemetry data received during the first two years in orbit. For this period, considering the standard deviation obtained in the output parameters, we can say that the radiation damage in the SCE solar cells is lower than expected when compared with data presented in the literature (1.7%) and those calculated from simulation in laboratory (1.0%). The analysis of the data indicates a degradation of the SCE solar cells around 0.5%.