Optimization of a Sun Vector Determination for Pinhole Type Sun Sensor

The sun vector is commonly used for defining a satellite attitude and many types of sensors exist for its determination. An attitude determination system is designed for each satellite project based on missions’ requirements. 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. Linear and polynomial methods for sun vector determination were considered instead of look-up tables to avoid having a large amount of data to be saved. Moreover, the influence of dead spaces between photodiodes on sensor accuracy was also investigated. Six real sun sensors and their theoretical models with different configurations were designed for investigating the difference between various calculating methods. The comparison of accuracies between proposed methods for real sun sensor models leads to two main findings: 1) on average, a polynomial method decreases error level of determined angle by 70% when compared with linear method; 2) accounting for gaps between photodiodes further decreases the average error of the angle determined by 15 % for polynomial, and by 6% for linear method when compared with methods not accounting for gaps.