The Research On High-Precision Pointing Control Technology With Reflected Point Light

The modulation transfer function(MTF)can be used to comprehensively evaluate the contrast and sharpness of an image qualitatively.For optical satellite images,there are various methods for on-orbit MTF modulation of optical satellite sensors,such as knife-edge targets,periodic target-based,reflection-point-based on-orbit MTF detection methods,etc.For reflection-point-based on-orbit MTF detection method,the diffusion characteristics of the system can be judged more intuitively.There are active and passive point light sources.Regardless of the point light source,in order to achieve on-orbit MTF detection,it is necessary to accurately irradiate the light into the entrance pupil of the optical satellite sensor and then carry out subsequent tests.In order to improve the pointing accuracy of the point light source system,a convex mirror can be used to diverge the reflected light spot to form a large-area light spot,which can be easily captured and imaged by an optical satellite sensor.However,due to the spread of the light spot,the luminous flux will be reduced,making it difficult to perform on-orbit MTF detection for the medium-to-high orbit optical satellites.In order to achieve MTF detection based on a reflective point light source medium-to-high orbit optical satellite sensor,the convex mirror needs to be replaced with a plane mirror,and the integrated pointing accuracy of the existing equipment should be improved,and its high-precision pointing is key to ensure the reflection of sunlight to the entrance pupil of the remote sensor.The improvement of pointing accuracy can reduce the volume and weight of the existing point light source,and has important engineering significance.The key to high-precision pointing is the normal direction of the plane mirror.In order to calibrate its normal direction,a solar sensor is designed in conjunction with a solar observer and a CCD camera.With the sun sensor directing the sun,the relationship between camera coordinates and the mirror coordinate system can be confirmed.Analyze the source of error of the mirror-type reflective point light source system,mainly including rotation error,fabrication and installation error,placement error and so on.These geometric errors are calibrated using the sun vector in the CCD camera coordinate system and the sun vector in the northeast upper coordinate system.The vector of the sun in the camera coordinate system is calculated using the centroid algorithm,and this vector is passed to the pitch axis coordinate system,azimuth axis coordinate system,local northeast upper coordinate system,and then combined with the sun position vector calculated by the solar position algorithm in the local northeast upper coordinate system to construct a point light source system geometric error model.After redefining the rotation sequence of each rotation matrix in the geometric error model,the correlation of parameters in the model is removed,and the system model is simplified.Using the damping Gauss-Newton method to iteratively solve the parameters of the calibration model.A pointing accuracy of more than 0.1° is obtained.The technology the pointing accuracy of the plane mirror reflective point light source better than 0.1 degree is achieved.This technology will lay the foundation for high accuracy,high frequency,and full dynamic range calibration of optical instrument.