As the caliber of a Spatial Optical Remote Sensor increases constantly, it is an inevitable trend to design a highly lightweight mirror. In the testing process of the mirror surface with a large caliber and higher lightweight level, the supportive distortion caused by gravity is a crucial factor that influences its testing precision. Aiming at this problem, we studied a testing method on the rail surface of the tested mirror that was detached from the gravity field. Deviations of the mirror wave surface were expressed by Zernike polynomial functions, so that wave surface data from different angles could be calculated by superposition. The optical axis vertical approach is adopted to test the wavefront of the aspherical mirror. By rotating the measured mirror, the surface shape data in different directions is tested. Through superposition calculation of the Zernike coefficients, the cumulative error of the test optical path is eliminated. In the same approach, the wavefront data of the surface of the reflecting mirror after rotating 180 degrees is measured . By using the finite element analysis, it is known that the deformation directions of the reflecting mirror in the two states are opposite caused by gravity during the test. And the orbital surface deformation data of the mirror can be obtained by calculation.
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.
The large-caliber light-weight reflector assembly is the core optical component of the large-size space camera. It needs to be highly light-weight to meet the constraint of emission weight. At the same time, the on-orbit reflector assembly needs to have extremely high force and thermal stability, be able to withstand the changes in the in-orbit temperature environment and the resulting stress changes and maintain the profile quality. This paper introduces the development of 1.3m caliber space mirror module. The reflector adopts the uniform thickness back arc design and the positioning support adopts the six-bar Bipod support technology. The simulation analysis verifies that the reflector component has good force and heat stability. The optical axis vertical test is carried out on the surface of the reflector assembly which has been processed and adjusted. The test results are consistent with the mechanical analysis results of the reflector assembly under the condition of gravity field, which meets the technical requirements of the spatial reflector.
The boresight of the aerial remote sensing camera (ARSC) need to be elicited to the reference coordinate system of the
satellite after the assemblage of the whole satellite. Because it is difficult to aim the boresight after finish fixing the
camera to the satellite, the boresight must be elicited by a cube before the fixing. So the cube coordinate system can be transited to the reference coordinate system.
The boresight of the camera is measured by a theodolite. The orientation of the boresight can be solved through
measuring four angles of the CCD, the top left corner, the bottom left corner, the top right corner, and the bottom right corner, and then the spatial angle of the boresight can be solved.
According to the traditional methods of the data processing after boresight measuring, the limitation has been analyzed by using the Mat lab software. The trace of motion of the theodolite is provided, while it is rotating horizontally with a vertical angle around the vertical axis and rotating vertically with a horizontal angle around the horizontal axis. Based on the vector combination theory, the normalized vector of the boresight can be obtained, so the spatial angle of the boresight can also be calculated. At last, this paper shows two applications in factual measuring.