| The demand for high resolution and visible earth observation satellite has increased greatly in and out of board, which is due to frequent occurences of disasters such as fire, earthquake and tsunami, resulting from rapid changes in international environment. The analysis and design of high resolution image motion compensation model is the most critical technology among the factors that influence high resolution satellite imaging quality. But until now image motion compensation model design theory was immature. And there was not enough research on the influence on high resolution TDI CCD imaging generated by spacecraft attitude, orbital parameters and actuator’s high-speed rotation. Since spacecraft orbit design and attitude control is essential to TDI CCD image, it is necessary to investigate the image motion compensation deeply.This paper deals with image motion compensation technology based upon day- regressive sun-synchronous orbit design. The effect of image motion error which induced by spacecraft attitude and orbit control on TDI CCD camera imaging is evaluated. First, a 561km Day-regressive Sun-synchronous orbit which suited for high resolution reconnaissance satellite is designed. Then based on the satellite orbital parameters act as inputs, a high precision image motion compensation system is designed. And simultaneously based on TDI CCD image principle, Monte Carlo method is used to analyze the influence of deviant angle error on TDI CCD camera imaging. Next, the technique of back-sway to compensate ground velocity is proposed under the analysis of the effect of satellite orbit attenuation on high resolution camera readout frequency increase and on the influence of TDI CCD imaging. Finally, the analysis and simulation results of the affection on high resolution camera image introduced by satellite’s actuator Single Gimbal Control Moment Gyro (SGCMG in short) of pyramid configuration in high rotating speed are performed.As a prerequisite condition for satellite design, satellite orbit design is also input for image motion mode design and analysis. In this paper, Sun-synchronous circular orbit is initially determined, for the reasons that enough sunlight illumination is needed to obtain better resolution when payload scouting ground target and beneficial illumination angle is necessary for power system. Simultaneously, in order to satisfy rapid response to large scale sudden events, satellite orbit design should mix up high time resolution. Therefore a 561km Day-regressive Sun-synchronous orbit is adopted. Finally, the characteristics of orbit trajectory, illumination, attenuation, track and measurement and control data transmission arc segment are analyzed to this orbit model.Based on previous analysis of orbit characteristics, how to find a reasonable and high efficiency method to carry out image motion compensation model design and analysis become the most important task of this paper. First, image motion velocity vector compensation model is designed and orbital parameters variation, satellite attitude parameters transformation and earth rotation are introduced to the vector. Then the effect of attitude and orbital parameters on image motion velocity mismatching is analyzed by means of Monte Carlo method. Next, the problem of TDI CCD splice leakage produced by deviant structure adjustment and deviant structure rotating center are designed and analyzed. After that, a method of adjusting deviant angle through satellite platform is raised to regulate image velocity. According to the influence of image motion velocity mismatching on camera image, the TDI CCD camera one-to-one model of image points and object points is established. Finally, the effect and simulation of deviant angle error on TDI CCD camera image is calculated.Satellite orbit is always attenuating because of spatical environment. And high resolution camera data readout frequency would increase obviously with orbit reducing. Sequently, high frequency disturbance arises, which would affect image quality. So satellite orbit is very necessary to be maintenaned to guarantee constant readout frequency. But one question is that orbit maintenance is limited by quatities of fuels on satellite. To conquer the two problems, a proposal that back-sway compensates ground velocity while imaging is introduced. That means, after lowing orbit, utilizing satellite pitch angular velocity to compensate ground velocity, which caused high readout frequency. Of course, the prerequisite is to guarantee camera data readout frequency under certain limitation. Finally, the result of analyzing image motion velocity mismatch and error produced by back-sway through the simulation system, formulated by means of TDI CCD camera image points and object points, is performed. It demonstrates that the program satisfies image demand well if imaging time is not longer and pitch angle is smaller.High resolution satellite needs high time resolution. But the distance between two adjacent tracks is large. So on-orbit satellite is requested to have ability of quick maneuvering to take picture sensitive areas in large region. Meanwhile, high spatial resolution mission raises high requirements for satellite orientation precision and attitude stability. Here a kind of actuator named SGCMG which is to be used in spacecraft field in China is presented. The major advantage is its torque amplification ability. It can provide greater control torque. First, SGCMG’s working principle is given. Then SGCMGs of pyramid configuration and its pseudo-inverse steering law with null-motion are to be listed. Finally, through homogeneous coordinate transformation, rotator dynamic disequilibrium torque is tranformed into satellite body coordinate. Then how does SGCMGs’rotator dynamic inequilibrium affect remote sensing image is simulated and analyzed, which would be valuable proof and method for SGCMGs to be used on high resolution satellite.This paper copes with projects needs and presents design methods and simulation procedures of day-regressive sun-synchronous orbit and high precision image motion compensation system. Meanwhile, deviant angle error, and satellite back-sway compensating ground velocity to improve image resolution while orbit attenuating, the effect of attitude actuator SGCMGs vibration on high resolution camera imaging are included in this paper with respect to projects practical needs. By experiment simulating, the method proposed here is proved to be practical and effective and still of great value in theory and project. Key words: sun-synchronous; high resolution camera; image motion compensation;... |
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