On-orbit Calibration Technology Research And Simulation Test Evaluation For Aerospace Optical Mapping Camera

For aerospace optical mapping satellites,the accuracy of geometric orientation elements have a large impact on the reliability of ground positioning.Due to the influence of environmental factors during satellite launching and orbital operation such as vibration,air pressure,temperature and humidity,the internal parameters of aerospace optical cameras and the angles between the principal optical axes of cameras will change unpredictably.Although these deviations may be small,they have an inevitable disturbance to positioning and mapping accuracy.At present,most domestic and foreign research scholars adopt the on-orbit calibration method based on the ground calibration field to solve the above problems.This method has a long calibration cycle,low timeliness and high cost.With the increasing requirements of satellite resolution and positioning accuracy,a large number of processing work relying on the ground needs to be completed intelligently and in real time on the satellite.Current solutions are getting farther from meeting the demands.On the basis of analyzing the on-orbit geometric principle of aerospace optical single camera,this paper presents the on-orbit calibration model of the angles between the principal optical axes of the star-ground cameras and between the principal optical axes of the ground-ground cameras,then perfects the theory of on-orbit geometric calibration.In addition,this paper also designs the on-orbit calibration simulation scheme and hardware system,and carries out error calculation and accuracy evaluation to verify the feasibility and superiority of the proposed method.The innovative work of this paper is as follows:(1)Based on the analysis of the formation factors and elimination methods of the star sensor self-error and the error of angles between the principal optical axes of the star-ground cameras,aiming at the problems of low attitude stability and long calibration period of the current star-ground cameras,a real-time on-orbit calibration method for the angles between the star-ground cameras based on the principle of self-collimation is proposed.This method can realize the real-time on-orbit self-calibration for the angles between the star-ground cameras and between the ground-ground cameras.(2)The physical simulation scheme of on-orbit calibration is designed in this paper.The simulation scheme can truly reflect the on-orbit geometric calibration and simulate the changes of on-orbit geometric orientation elements,including the focal length of cameras and the rotation of the principal optical axes in the X,Y and Z directions.A hardware simulation system based on off-axis three-mirror design is developed for the scheme,which contains the optical design of calibration detection and recording,the selection of the key components and the hardware system structure design.By calculating the calibration target position change of the calibration detectors,we can decompose the changes of the focal length,the principal point coordinates and the intersection angles of cameras.(3)According to the proposed on-orbit geometric calibration simulation scheme,the positioning error of spot images and the measurement error of parameters can be analyzed and calculated,after which the calibration accuracies under ground and on-orbit conditions can be obtained respectively.Finally,the accuracy of ground positioning is derived using the space forward rendezvous method.The experimental results showed that the measurement accuracy of the angle between the star-ground cameras reaches 0.33?,and that of the angle between the forward-view camera and the rear-view camera reaches 0.22''.It can be estimated that under the condition of weightlessness,the measurement accuracy of the angle between the star-ground cameras is better than 0.15'',and that of the angle between the forward-view camera and the rear-view camera is better than 0.1''.Compared with the traditional calibration methods,the on-orbit calibration method proposed in this paper can not only perform calibration in real time,but also improve the accuracy significantly.