On-Orbit Response Analysis of Silicon Photodetectors in 4-Pi Sun Sensor of Aditya-L1 Mission

Silicon photodetectors indigenously developed by Laboratory for Electro-Optics Systems (LEOS) have been used in 4-pi sun sensors (4piSS) for space craft attitude determination. A performance analysis of these detectors during their latest flight in the Aditya-L1 mission was carried out, wherein an unprecedented fall in sensor output was observed during the first seven days of flight. The possibility of variation in sensor output due to effects of ionizing radiation in the inner Van Allen beltsduring orbit raising is explored. The radiation environment encountered by the spacecraft during different stages of orbit raising is studied and it is seen that the spacecraft orbit was completely inside the high intensity radiation zone during the first seven days. Moreover, stabilization of the sensor output coincides with the third orbit-raising maneuver, during which the spacecraft orbit was moved outside the high intensity region of the radiation belt. The cumulative proton fluence experienced by the satellite during the initial stages was computed to be 2.6×1011 cm-2. This matches well with the proton fluence required to cause the observed variation in photo response, as estimated using data from previous irradiation lab experiments conducted on these photodetectors.