Research On Deformable Mirrors Applied To Space-borne Camera

It is important to maintain the high image quality of space-borne cameras in orbit, though the environments of space are very risking and the image quality may be degraded because of force and heat reasons. Traditional thermal and misfocus control techniques are very complex with large source reqirements and limited effect.In order to improve the environment adaptive ability of space cameras, an active deformable mirror technique is proposed to be applied to space optical systems in this dissertation. The wavefront error can be corrected and the difficulties of thermal control may be reduced through applying the active deformable mirror.There are mainly four contents in this dissertation:1. Parameter design of active deformable mirrorThe wavefront variation of a space camaera under gravity release and heat is analysed. The analysis results shows that defocus, astigmatism and coma are the main wavefront error. So defocus, astigmatism and coma are the wavefront errors should be corrected by the designed deformable mirror. Some requests of deformable mirror are analysed in order to apply in space and the basic design principle are determined. Two different support topologies are compared and analysed, and a new topology based on outer effective apteure supporting is proposed. The polynomial fit methods used in modal control are investigated. 2. Simulation and design of deformable mirror using finite element methodThe main content is how to simulate the deformable mirror by finite element method(FEM). First the finite element principle and basic rules of modeling are introduced; the method of transferring the results of FEM are discussed and programmed; the law of correction accuracy vary with the postions of actuators is studied by simulation, and the scheme of actuator pattern is determined which the coma correction ablity is improved.3. Structure design and test of active deformable mirrorThe design, analysis, manufacture and test are discussed. Step motor with spring is used as the actuator. The actuators have high force accuracy and linearity. The MPC elements are used to model the jointing of structure and the deoformable mirror is analysed by FEM. The surface of deformable mirror is processed by magnetortheological polishing mehod, and the RMS of surface error is0.023A. The milbond glue is used to bond the actuator to the mirror, and it is proved that the surface quality error because of bonding is neglectable. The static, dymatic characters of deformable mirror is tested by4D interfereomter, and the response frequency is up to28HZ. Astigmatism, defocus and coma can be generated by the deformable mirror with the accuracy of λ/30. The results of comparison with OKO37channel deformable mirror shows that the designed deformable mirror improved the accuracy of coma.4. Research on application of active deformable mirror in off-axis TMA systemThe feasibility of deformable mirror in off-axis TMA system is simulated and discussed, and the system aberration can be corrected by the secondary mirror is proved. The designed mirror is inserted to the TMA system as a folded mirror, and the experiments shows that the deformable mirror can correct the wave front error of system, and the MTF is advanced to0.428from0.364The dissertation focuses on the deformable mirror techniques applying to space-borne cameras. The type of deformable mirror is initially determined according to aberration characters of space optical system, and the parameter design method, integrated modeling and optimization, structure design and analysis are developed. The correction ability of coma is improved by a new outer effective aperture actuator pattern. The charaters and application to TMA systems of deformable mirror are experimentally studied, which shows the aberration correction ablity of the deformable mirror.