During the final approach phase of the on-orbit service, high accuracy positional measurement of the non-cooperative target is critical to the success of the mission. In this paper, a convergent trinocular stereo vision measurement model is studied. First, trinocular stereo vision non-linear solving methods were investigated; then, the relationship between the structural parameter configuration of the stereo vision measurement model and the 3D coordinate measurement accuracy, as well as the relationship between the stereo vision camera position placement structure and the effective detection field of view of the measurement system is studied, providing a theoretical basis for the system configuration and optimal configuration design of the trinocular stereo vision camera; afterwards, the three cameras were designed with a baseline distance of 1.3m and the optical axis of each camera was tilted 18° towards the centre of the "Y" bracket, which could meet the continuous position measurement of large non-cooperative targets at close range with high accuracy. Finally, the simulation result of the motion of the non-cooperative target from 15.0 to 1.8m validates that the model has high accuracy and strong robustness in positional solution.
During the capture operation, the hand-eye camera measures the spatial position of the center of the docking ring. However, the center can’t be used as a direct capture point, so we need to find a suitable capture point on the docking ring. This point can be connected with the center of the docking ring while satisfying the capture of the manipulator. This paper presents a method to find the capture point based on the intersection of the circle and a straight line, consisting of the image main point and the center of the circle. Furthermore, an algorithm for calculating the spatial position of the capture point is proposed. The digital and semi-physical simulation experiments verify the effectiveness of the method. The results show the position error of the capture point is within 0.8mm, and the capture angle error is within 0.4°.
The docking ring is a typical structure on space targets, and the spatial circle feature extracted from it is an important reference mark for non-cooperative space target vision measurement. However, there are two problems in the pose calculation process: the docking ring pose calculation result of the monocular camera is ambiguous, and the roll angle information cannot be obtained when the pose is solved. In this paper, a non-cooperative space target binocular vision 6- DOF pose measurement method based on docking ring feature is proposed. The binocular vision measurement system is used to solve the ambiguity problem of the docking ring calculation result, and the target coordinate system is constructed by selecting reference feature point outside the docking ring to realize 6-DOF pose measurement. The accuracy and stability of the method are verified by digital simulation experiments, and the results indicate that the method still can calculate stable pose when the pixel position error is 4 pixels. In the scene simulation experiments, the absolute error of vertical optical axis position measurement is less than 1.6 mm, the relative error of parallel optical axis position measurement is less than 0.7%, and the absolute error of attitude measurement is less than 0.2 deg, which can meet the requirements of space navigation mission.
The metal-semiconductor-metal (MSM) structured ZnO photodetectors with same electrode spacings are made by radio frequency magnetron sputtering. A study of the thermal annealing effects on photodetectors with sequential annealing temperature (300, 400, 500 and 600 ℃).The responsivity of the photodetector was enlarged greatly after annealing the MSM device. Meanwhile, the enhancement in the dark current that resulted from the experiment was accompanied by the increasing annealing temperature. These results demonstrate that a simple route to improve the responsivities of photodetectors can be realized easily by annealing the devices.
A space-based infrared camera was launched to collect atmospheric radiation data. In order to investigate its performance quantitatively both under pre-launch and post-launch conditions, a practical estimation model of radiometric calibration precision was proposed that only depended on the measured image data from ground and on-orbit blackbody-based calibration tests. The model treated the calibration error as a consequence of two independent factors. One was introduced by using the calibration equation to represent the relationship between the object apparent radiance and the camera digital response, and the other was the measurement uncertainty when imaging a target with known constant emission. Distribution maps of the errors for the focal plane array were constructed by means of estimating the calibration error pixel-wisely. Results show that the camera’s performance after launch is slightly worse than that before launch. The pixels with calibration errors more than 10% only account for about 5% for this camera, and they generally locate in the edge of the focal plane. The maps will be helpful in weighing the validity of sampled data at the pixel level.
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