A Study In Alignment Method Of Coaxial Three Mirror Optical System On Space Camera

With the rapidly increasing requirements for remote sensing technology coverage in field of the surface of the earth for both civil and military uses, like national and survey, natural disaster prevention and mitigation, prediction of strategic posture and national defense and safety, etc. Space optical system has been developed towards longer focal length, larger aperture and wider field, the optical and mechanical structure of the system has become more complicated. Higher imaging quality put forward higher requirements to system alignment, which is now the key link in the optical system development process.Based on a space camera optical system alignment, The paper introduces respectively the main mirror, the second mirror, the thind mirror and the folded mirror of the optical system. And this paper analyzes the key technical problems in the development process, using the theory calculation, Respectively introduces the micro stess of the main mirror,the primary and secondary mirror,the adjustment of the third mirror and the mirror, Strictly in accordance with the requirements of indicators, and finally summarizes a set of effective methods for the system alignment; With the aid of a computer-aided alignment technology, the image information is quantified and managed, which can guide the alignment process, and significantly Improve the alignment efficiency. At the same time, with some modification, the above methods carry on a comprehensive consummation for a certain off-axis optical system alignment.The main research contents of this thesis are as follows:1. The paper introduces the development of space camera at home and abroad, as well as the computer-aided alignment technology;2. The paper introduces the different optical style of large diameter space camera and analyzes the advantages or disadvantages of each optical system, and points out the coaxial three mirror system in large aperture optical system superiority in application, finally concludes the There-Mirror Anastigmat(TMA) optical system is more suitable for the agile satellite with increasing mirror size because of its coaxial design and low moment of inertia. Then, the method of measuring optical system aberration in space camera is introduced, a more practical and accurate method of interference inspection is selected for the surface inspection of optical components. Finally the way of using Zernike polynomial to describe the result of wavefront aberration in the interference test is detailedly explained. Then for building the aberration model of misalignment component, the vector theory is introduced based on the wavefront aberration theory, and mathematical model for the relationship among the three-order wavefront aberration of the system, optical field coordinate and Fringe Zernike coefficients is set up. All of these provide the basis for the three mirror alignment of the camera.3. The requirements of the space camera on the optical system and optical components' imaging quality are theoretically analyzed. The method of detecting the two curved surface mirror and the optical system is summarized. Combined with the actual alignment, the optical components and the system for interference testing are applied. Finally, the micro stress alignment of the main aspheric mirror is introduced in detail. In view of the changes of the main mirror surface, the supporting structure is analyzed, and the compensation measures are put forward to achieve the expected results.4. The relationship between the relative position and attitude of the primary and secondary mirrors and the primary aberration is analyzed. And the traditional adjustment method is introduced. Then, the high precision centering method is put forward. Finally, through the use of special equipment, the problems of the method of interference inspection appearing in large aperture camera detection are solved. It makes the primary and secondary mirrors achieve a high degree of coaxial.5. The method of three mirror initial positioning in the system is introduced. Then, the relationship between the three mirror offset, the wave aberration of the field of view and the Zernike coefficient is set up by the computer-aided alignment technology, and the precise positioning of the three mirror is accomplished. At last, the special function of the folded mirror in the optical system is analyzed, the interference image is analyzed and summarized, the variation law of the system is obtained, and the accuracy and efficiency of the testing results is improved.6. The principle and method of coaxial optical system can also be applied to the off-axis optical system. Firstly, the limitation of the existing off-axis aspheric mirror processing and detection for optical alignment is introduced. Then, the principle of self collimation and precision measurement is proposed, and the variation law of the off-axis quantity and off-axis angle is summarized, which can provide a guarantee for the initial positioning of the optical element in a certain off-axis optical system, and the accurate positioning of the computer-aided alignment.