Due to the large size of large-aperture aspheric mirrors and the long optical path each of them needs to inspect, the deviation of the optical axis from the structural reference cannot be accurately measured by conventional inspection means. However, as the aperture of the optical lens increases, alignment puts higher requirements on the concentricity of the optical axis of the mirror with the axis of the structure. Excessive eccentricity leads to severe consequences, including interference of the lens’ optomechanical structure, and non-adjustable misalignment. In this study, the accurate measurements of all the optical parameters of the mirror were realized by building an inspection optical path with mirror, measuring the spatial position of the apex of each optical component structure using a laser tracker, and testing the mirror through rotations. The conventional inspection methods and the inspection method of this study were simultaneously applied to the aspherical mirror with a diameter of 448 mm. Through the test results, it has been proven that the method proposed in this study is feasible.
With the increasing demand for high resolution earth observation and the development of deep space exploration and scientific research activities, the focal length of space camera is getting longer and longer, and the aperture of space camera keeps increasing. When a large-aperture space camera is mounted on the ground, the figure and position of the mirror will change due to the gravity effect on the mirror and its supporting structure. The three-mirror coaxial (TMC) space camera has certain structural symmetry. In order to improve the reliability and efficiency, the optical axis vertical alignment technology is widely used in the world. The main content of this paper is to elaborate the design process of optical axis vertical alignment scheme for Φ1.3m TMC space camera, as well as the test verification process and results. The on-orbit wavefront of the central field of view is 0.050 λ, and the on-orbit wavefront of the edge field of view is 0.064 λ and 0.059 λ. The camera wavefront meets the design requirements, and the setting factor is better than 0.94. The optical axis vertical alignment scheme of optical axis of Φ1.3m TMC space camera is verified.
For a three-mirror coaxial (TMC) space camera, the centralization of the primary mirror is an important measurement link in the process of optical processing and alignment. The centering of aspheric mirrors is generally divided into contact measurement and non-contact measurement. For contact measurement, the mirror is scanned in the mechanical reference coordinate system by using a three-coordinate instrument or a laser tracker. After fitting the mirror equation, the deviation data between the optical axis and the mechanical axis are obtained. For non-contact measurement, there are two ways of centering: using centralizer or using interferometer. The main content of this paper is to introduce the centering of the 1.3m primary mirror of a space camera. Firstly, the realizability and accuracy of different methods are analyzed. Centering of aspheric mirror with large aperture by centralizer is of low precision and difficult to realize. For contact method, the accuracy of centering with laser tracker is only 0.15 degree. However, the accuracy of the CMM centering method and the interferometric centering method can reach 0.005 degrees. Secondly, for the 1.3m primary mirror, the centering of the primary mirror is accomplished by using the above two methods. The results of the two measurement methods are compared. The maximum deviation of the two eccentricities is only 0.023 mm and 0.002 degree. For the centering of large aperture aspheric mirror, the CMM centering method and interferometric centering method have their own advantages. The interferometry method can realize in-situ measurement in optical processing.