Research And Design Of Star Sensor For Pico-satellite

Star Tracker(ST)is a three-axis attitude detector referring to stars,which has high-precision in aerospace mission and is an import part of space vehicle.Limited by the size and power of Pico-satellites,the size of ST needs to be minimized as well.The ST for Pico-satellites is studied from several aspects in this thesis.The main purpose of this thesis is to analyze the key technology during the design process,and to verify the measurement accuracy of the whole system.Based on the exist prototype of Micro-Satellite Research Center of Zhejiang University,the work was completed:The main problems of the existing ST prototype are analyzed,and the qualification and structure of are introducted.To image accurately,the basic observation model is studied.The accuracy of single star measurement in the whole frame is analyzed,which provides an evaluation method for measurement,and determines the main error source.Aiming at the problem that the model parameter estimation error affects the measurement accuracy,the star calibration algorithm is adopted to improve the parameter precision.To imporve the accuracy of attitude measurement,the algorithm based on topological recognition is designed which can identify all stars in the whole frame,and the threshold determination,navigation table and simulation work are completed.To improve the speed,stability and maintainability of the prototype,the DSP program flow and the basic driver are optimized,and the CPLD software is designed by the finite state machine.To read image from CMOS stably,the reading timing of CMOS image sensor is analyzed.To verify the ability of Star-Identification(Star-ID)without complete experimental environment,semi-physical experiments were carried out using a simulated star map.Then based on the field star map,the Star-ID is verified,and the result shows that the Star-ID is reliable and effective.In order to determine the accuracy of the attitude,a field experiment based on the rotation of the earth is designed.The samples show that 1? precision of the Euler angle is 30",and the precision of single star is between 5" to 20".In summary,there are three aspects including the optimization design,the engineering realization and experimental test of the ST prototype are introduced in this thisis.And it is improved that the ST prototype can be effectively applied to Pico-satellites.