Development of Low-Cost Sun Sensor for Small Satellite Based on Photodiode Sensor

Sun sensor is one of the attitude determination sensors used on satellite. In the previous generation of LAPAN satellites, sun sensor was built using solar cells. For LAPAN-A4, a new idea of low-cost sun sensor using COTS photodiode is suggested. The type of photodiode proposed to be used is OSRAM BPW 21 with consideration of its maximum sensitivity wavelength and radiant sensitive area specifications. Moreover, the method used in designing this low-cost sun sensor using BPW 21 photodiode only requires inexpensive instrumentations. This method also offers simple and flexible observation steps. In this sun sensor design, BPW 21 photodiode is connected in series with a resistor. 10-bit ADC feature of Atmel ATmega128 is used to convert the photodiode voltage into DN value. The value of the resistor used can affect the result of the DN value, so determining the right resistor value is important. Several observation steps were performed to ensure that the photodiode is sufficient for use in space and to determine the right resistor value that has to be used to avoid saturation condition when BPW 21 photodiode faces the sun directly in space. The results of the observation steps show that BPW 21 photodiode is sufficient for use in space and the configuration of BPW 21 photodiode in series with a 1.8 kΩ resistor is the best to avoid such saturation state. The use of this resistor value also allows the sun sensor to optimally respond to a wide range of angles of incidence of sunlight.