Diffraction-limited performance of 30-m class telescopes requires the integration of structural, optical and control systems to sense and counteract real time disturbances to the telescope. Accurate simulation of an integrated telescope model is essential for optical performance estimation and design validation. Our approach to integrated time domain modeling of large telescopes is to interface commercially available structural, optical and control modeling software packages. The model architecture, data structures, and the interfacing tools of the simulation environment are presented. Preliminary simulation results of a 30-m class telescope subject to wind load and a ground layer phase screen are presented.
Ground-based telescopes operate in a turbulent atmosphere that affects the optical path across the aperture by changing both the mirror positions (wind seeing) and the air refraction index in the light path (atmospheric seeing). In wide field observations, when adaptive optics is not feasible, active optics are the only means of minimizing the effects of wind buffeting. An integrated, dynamic model of wind buffeting, telescope structure, and optical performance was developed to investigate wind energy propagation into primary mirror modes and secondary mirror rigid body motion. Although the results showed that the current level ofwind modeling was not appropriate to decisively settle the need for optical feedback loops in active optics, the simulations strongly indicated the capability of a limited bandwidth edge sensor loop to maintain the continuity of the primary mirror inside the preliminary error budget. It was also found that the largest contributor to the wind seeing is image jitter, i.e. OPD tip/tilt.
A sound system engineering approach and the appropriate tools to support it are essential in achieving the scientific and financial objectives of the Thirty Meter Telescope project. Major elements of the required tool set are those providing estimates for the performance of the telescope. During the last couple of years, the partners in the consortium developed a wide range of modeling and simulation tools with various levels of fidelity and flexibility. There are models available for time domain and frequency domain simulations and analysis, as well as for lower fidelity, parametric investigations of design trade-offs and for high fidelity, integrated modeling of structure, optics and control. Presented are characteristic simulation results using the existing preliminary point designs of the TMT, with emphasis on the telescope performance degradation due to wind buffeting. Under the conditions modeled, the wind induced image jitter and image quality degradation was found comparable to good atmospheric seeing.
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