Influence of solar cycle on SPOT-1,-2,-3 upset rates

The French SPOT Earth observation system has now been used for more than eight years. A former study had presented results obtained during the first years of service which took place in solar minimum activity conditions. This paper presents the evolution of the upset rate measured on the 1088 1-kbit memories (CMOS SRAMs) of the on-board computer (OBC) throughout minimum and maximum solar activity. Upset rate is well correlated with solar cycle. Little influence of solar flares was observed. Most critical periods are transitions between phases of the solar cycle. Comparison is made with model predictions.