Study On Key Technique Of APS Star Sensor

Star tracker is a high precision attitude measurement instrument which takes sky as the working object and star as the frame of reference; it's now the most precise attitude measurement instrument. Many more shortcomings of CCD have been discovered in many application projects for a long time. APS (active pixel sensor) is now becoming increasingly competitive with respect to their CCD counterparts, while adding advantages such as simpler driving requirements, small volume, low power dissipation, wide dynamic range, anti-radiation capability and the potential of on-chip integration of sensor, analogue circuitry, and digital processing functions. It has great potential in star tracker application and now is being investigated in many countries. But its disadvantages, such as high noise signal and small fill factor, might influence star tracker characteristics, special on detection capacity and detection accuracy. So it is a important issue in this paper. The main purpose of this thesis is to study detection capacity and detection accuracy applying APS on star tracker, and how to improve detection capacity and detection accuracy of APS star tracker. Main study in the paper is following: First of all, APS characteristics are discussed in the paper in detail, such as the main working principle, structure scheme, technical parameters. Second, APS star tracker system design considerations are analyzed and the conceptions and relations of main technology parameters are described and analyzed. Based on star energy to focus plane array, star image energy math model is founded, and sub-pixel accuracy centriod estimation is analyzed on detail. Analyzes relation of detection sensitivity and detection probability, founds model of star detecting sensitivity, and discusses star energy focus degree and star spot position might influence detection sensitivity. Few ways of improve detection sensitivity are analyzed. Detection accuracy and issue of effect on detection accuracy of APS star tracker are analyzed. Moreover, various infections on the detection accuracy are discussed. And based on APS characteristics, all effects on centiod accuracy, such as APS fill factor, size of image window, and so on, are discussed. Based on found APS star tracker system hardware and thesis analysis, the experiments of star images collection and centroid estimation are done. Conclusion is given at the end of the thesis based on the discussion and analysis of the principle and experimental results.