Design Of Telescope Focal Plane Structure And Research On The Re-orientation Accuracy Based On On-orbit Replacement

The focal plane structure of telescope is an important part to provide support for the orbital replaceable optical device.In order to ensure the imaging quality of optical device,the focal plane structure should provide stable support for the optical device.At the same time,the application requirement of on orbit replaceable requires the optical device to have good re-orientation position accuracy after replacement,which is very important for the imaging effect of telescope.In this paper,based on a national major project,the focal plane structure in a large telescope is studied from the aspects of theoretical analysis,structural design,simulation analysis and experimental verification.The research contents mainly include the design of the focal plane structure,the research on the re-orientation positioning angle accuracy of the optical device,and the research on the re-orientation positioning accuracy of the device focal plane.The detailed research contents are described as follows:The focal plane structure consists of supporting device frame structure,positioning mechanisms that guarantee the position of the optical device,locking mechanisms that resist the mechanical impact in the transport and launch stages,and guiding mechanisms that guide direction for the optical device during replacement.In this paper,the structures of these parts are designed.The positioning mechanisms adopt the "3-2-1" kinematic positioning method and support the astronauts to change quickly in orbit.The locking mechanisms can automatically lock and unlock,and support the astronauts to manually unlock.The re-orientation positioning angle accuracy of optical device is studied.According to the vectoriality of the infinitesimal angular displacement,the mathematical models of the rotation angles of the optical device around the coordinate axes are deduced by using the synthesis and decomposition of the vector,and the mathematical relationship between the rotation angles and the fit clearances of the positioning mechanisms and the relative position of the positioning mechanisms are obtained.A method for measuring the re-orientation positioning angle accuracy of the optical device is proposed,and a set of test device is set up for testing.The results show that when the envelope size of the optical device is 350×860×1120mm,the angles of the optical device around the three-axis are not more than ±8.5?.According to the principle of coordinate system transformation,the accuracy of re-orientation translation and rotation of focal plane around focal plane coordinate system in optical device is studied.The mathematical models of the displacement of the focal plane edge points and the rotation angle of the focal plane are established respectively.The range of the displacement and the rotation angle are solved using Mathematica,and the re-orientation positioning accuracy is determined.When the envelope size of the optical device is 980×860×1120mm,the translation accuracy of the focal plane is not less than ±0.041 mm in the x direction,not less than ±0.029 mm in the y direction and not less than ±0.033 mm in the z direction;the rotation accuracy is not less than ±11.05? for the focal plane around the x axis,not less than ±10.57? around the y axis and not less than ±10.77? around the z axis.Using the finite element simulation software,the dynamic and static simulation of focal plane structure is carried out.The stiffness of the device frame structure,locking mechanisms and focal plane structure are checked by modal analysis,and the stress and strain state of claws in the locking mechanisms under the 7g acceleration launching state are checked by static analysis.The analysis results are all in ideal state.A set of test device is built to verify whether the positioning mechanisms can effectively release internal stress and realize kinematic positioning when the temperature changes.In order to highlight the experiment effect and facilitate the measurement of deformation,the aluminum sheet with large thermal expansion coefficient is used to simulate the optical device,and the laser tracker is used to track the position change of the points on the aluminum sheet.The experimental results effectively prove that the positioning mechanisms meet the positioning principle of "3-2-1" and can effectively release the thermal stress.