IMPROVEMENT OF SUN ANGLE ACCURACY FROM IN-ORBIT DATA OF A QUADRANT PHOTODIODE SUN SENSOR

The sun vector is commonly used for defining a satellite attitude and many types of sensors exist for its determination. A fine pinhole sun sensor type was chosen and designed for HORYU-IV nanosatellite of Kyushu Institute of Technology. This sensor has a round-shaped hole and uses commercial off-the-shelf silicon photodiode, which consists of four small sensitive elements arranged close to each other. This type of sensors commonly uses look-up tables for providing high accuracy, which requires a large amount of data to be saved. Polynomial methods for sun vector determination were considered instead of look-up tables to avoid having a large amount of data to be saved. The influence of dead spaces between photodiodes on sensor accuracy was also investigated. The sensor was tested in space environment. It was found that its output signals went to saturation point. A method for the compensation of signals truncated by saturation was proposed. It was found that: 1) polynomial method provided 0.1deg accuracy for a sensor with ±5deg field of view; 2) accounting for gaps between photodiodes decreases the average error of the angle determined by 15%; 3) a method for compensation of truncated signals saves full sensor FOV with decreasing accuracy till 0.11deg.