Research On Key Technology Of Focal Plane For Wide-range Space Cameras

With the rapid development of space technology,demands for large-scale and high-speed target acquisition have become increasingly intense.Space cameras are being developed for high-resolution and wide-range directions.Time delay and integration charge coupled Devices(TDICCDs)are widely used in the push-broom mode in space cameras.Defocus will happen when the focal plane position changes out of the permitted range because of some harsh conditions,such as shock and vibration during the launching process,changes in altitude,temperature,and atmospheric pressure on orbit.Additionally,the earth's rotation,orbital motion,satellite attitude change,and other factors will create a drift angle,that is,the angle between the push-broom direction and the target motion direction on the image plane.The drift angle produces a lateral image shift perpendicular to the push-broom direction,which results in modulation transfer function(MTF)drop and degrades the imaging quality.Wide-range cameras have large focal-plane sizes,resulting in large drift angle differences between positions on the focal planes.High resolution leads to high TDICCD integration levels,and low tolerances for drift angles.So it is more difficult for high-resolution and wide-range camera to compensate the drift angle.Aiming at the above requirements for wide-range cameras,this paper has carried out researches from following aspects:1.The image motion theory has been simplified by algebraic method,based on which a wide-range space camera has been used as an example for drift angle calculation,and the drift angle at different positions on the focal plane were obtained in condition of different satellite orbit positon and satellite alltitudes.The variation law of angle difference between different positions on the focal plane has been summarized.Specifically,the on-orbit drift angle compensation strategy was proposed,which solves the problem of the drift angle compensation for high-resolution,wide-range aerospace optical camera in the large attitude imaging mode.2.Considering of the drift angle error analysis results,the specific method was proposed that the yaw attitude adjustment will be adopted for average compensation,in combination with the focal plane mechanism adjustment in the camera to eliminate the angle difference between different positions,to meet the imaging quality requirement of TDICCD.3.Considering of large focal plane size of wide-range space cameras,the sensor splicing process and the grouping scheme for large size focal planes were analyzed.The imaging geometric model of the camera was established,based on which the existence reasons and variation law of the ground width differences corresponding to the splicing sensors were analyzed.So the calculation method of the splicing area sizes at different positions on the focal plane were introduced,along with different factors on these area sizes accordingly.4.Combining the drift angle compensation strategy of wide-range space cameras and the on-orbit focusing requirement of large scale off-axis three-reverse cameras,a set of focal plane comprehensive adjustment mechanism with high precision and high functional integration has been designed.The mechanism can both meet the on-orbit focusing and drift angle compensation requirements of the focal plane in time-sharing.What is more,the theoretical satisfaction and design rationality of the focal plane adjustment mechanism have been verified through theoretical analysis and finite element simulation analysis.5.The theoretical analysis of the motion curve and the result accuracy analysis for the drift angle compensation mechanism were carried out and the high linearity of the transmission was verified.Using the engineering prototype,the transmission linearity test of the drift angle compensation module was carried out,by which the theoretical analysis results were verified.6.The engineering prototype of the focal plane adjustment mechanism was used to carry out the transmission curve test of the focusing movement and the drift angle compensation movement,and the coupling test between the two movements.The environment tests were carried out to verify repeat accuracy of the transmission curve and for design results verification.Finally,the working heat effect of the focal plane electric box on the transmission accuracy of the drift angle compensation mechanism was tested,which further proves the motion accuracy stability and environmental adaptability of the drift angle compensation mechanism.