High-precision centering measurement of large-aperture aspheric mirror

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.