Study On The Alignment Technique Of Large Aperture Reflecting Telescope On-line

Telescopes are influenced by alignment errors, the major factors of the ground-based telescopes are gravity, wind loads and heat exchange, while those are vibration and temperature gradient for the space telescopes. A larger telescope is more sensitive to these error sources, which becomes the concerns of researchers. In this thesis, the analysis, simulation and experiments, with image-quality merit, are proposed for two-mirror coaxial and three-mirror off-axis telescopes. The contents are as follows:Firstly, the vector aberration theory is used to analyze a two-mirror coaxial telescope system, the relationship between the misalignment of mirrors and the wavefront errors is obtained. The situation is further analyzed for a three-mirror off-axis optical system using this theory, especially for an off-axis Three Mirror Anastigmatic(TMA) telescope.Secondly, the theory and simulation of the influence of noise is investigated. The formula of calculating the optimal threshold to minimize the residual error is proposed and confirmed through analysis and simulation.Finally, methods based on Stochastic Parallel Gradient Descent(SPGD)algorithm are proposed to correct the alignment errors. The correcting process starts using on-axis image, but spots of multi-field must be adopted to optimize the position vector of the misaligning mirrors, this is because that the solve does not convergence if only on-axis field image is used. Then two simulations are researched based on the methods. One is for a two-mirror coaxial telescope, another for an off-axis TMA telescope. The influence of sampling error and light intensity is thoroughly analyzed with the off-axis TMA telescope design. Two experiments, the parameters are coincidence with those of our simulation, are carried out: the result of the one shows that efficient solution can be acquired but with certain boundary conditions and more than one solution exist. That of the other one indicates that a reasonable and only solution is obtained using multi-field images for the off-axis TMA telescope. Besides,the relationship between system quality after correcting and images’ Signal-to-Noise Ratio(SNR) is modeled with the experimental data.