Research On Digital Sun Sensor For Micro-satellite Based On CMOS Camera

Sun sensor is an important component of artificial satellite attitude determination system, which is a kind of widely used sensors in the aerospace science field. Lower power consumption, lighter mass and higher measure accuracy is the elementary requirement for sun sensor. Traditional sun sensor, using CCD as its image sensor, needs complicated timing circuit and DC/DC module. So it is hard to reduce power consumption and mass further. With the trend of satellite minimization, many researchers study on how to use advanced CMOS active pixel image sensor instead of CCD in sun sensor.A digital sun sensor based on CMOS camera is presented. The system mainly consists of Panoramic Annular Len (PAL), CMOS camera module and FPGA. PAL made by Zhejiang University can form an annular image circling the axis and has far depth of field.The attitude determination principle of the sun sensor system is as follows. Firstly, transform an image into a binary image according to the gray threshold, and then find boundary points of the binary image. Secondly, use an improved algorithm based on 8-connected boundary tracking to obtain the outline of the sun. At last, determine satellite's relative angle to the sun by the farthest and closest points from the center of sensor plane. The algorithm can effectively restrain noise and unclosed curves. Therefore, it has some application value.The paper detailedly introduces the implementation of the design and the architectonic method based on special FPGA. Xilinx Virtex-II Pro FPGA embedded PowerPC 405 core is used to verify the system. The most attitude determination principle is realized in PowerPC, and number calculation, data store and so on in FPGA logic structure. Matlab and Verilog HDL mixed simulation is also applied. Results show that the system satisfies the requirement of minimization and low power consumption for micro-satellite.