Research On Compensation Method Of Aberration For Large Aperture Off-axis Three-mirror Telescope

Large-aperture space reflection telescope is widely used in many scientific research fields such as astronomical exploration and earth observation.In order to improve the resolution and light collecting ability of space telescope,its main development direction is lightweight and large aperture.The off-axis triple inverse structure is widely used in space telescopes because of its wide field of view and no shielding.When a large aperture space telescope is launched,the surface precision of the mirror will degenerate relative to the surface machining precision due to the change of gravity environment.In order to ensure the imaging quality of the large off-axis three-mirror space telescope,the aberration distribution of the system mirrors with surface error should be proved.For the need to analyze the optical aberration compensation mechanism,the nodal aberration theory is used as the theoretical framework to build the aberration compensation model for the aperture and non-aperture position errors of large off-axis three-mirror system.1.The form of vector is used to describe the surface profile error of the off-axis tri-inverse system.The non-aperture beam locus expression is introduced into the aberration expression to quantitatively describe the non-aperture aberration in off-axis system.It is necessary to add that the trajectories of the non-aperture aberrations are different from those of the apertures.Therefore,it is necessary to consider the specific situation of each field of view when analyzing the distribution law of aberration field in non-aperture position,and other aberrations will be derived from non-aperture position aberration due to pupil coordinate transformation.2.The aberration distribution of misaligned off-axis system is analyzed by using the nodal aberration theory of third order and fifth order,and the vector analytical expression of aberration of fifth order and third order aberration in off-axis system is derived.Based on the third-order vector aberration field,a model for adjusting the position and orientation of off-axis system is established and verified by simulation experiments.Simulation results show that the proposed model can accurately calculate the pose adjustment of secondary mirror in off-axis system,which lays a foundation for aberration compensation model.3.Combining the analytical expression of aberration of off-axis three-mirror space telescope at the position of aperture and non-aperture with the solution model of position and attitude adjustment of off-axis system,a compensation model for mirror aberration of off-axis space telescope with large aperture is proposed based on the imaging quality evaluation standard of root square value of out-of-pupil aberration,and its effectiveness is verified by simulation.The experimental results show that the aberration compensation model can effectively compensate the aberration quality degradation caused by the aberration position errors of the off-axis system.After compensation,the RMS value of the system outgoing pupil aberration is close to 0.1 .Based on the experimental results,the aberration field distribution and the compensation method are discussed.