Static and dynamic disturbance compensation for optical misalignment of large ground-based wide field survey telescope.

Abstract

For large ground-based telescopes, static and dynamic disturbances would greatly degrade the optical performance. This is especially true for wide field survey telescopes with prime focus optics. The estimation of disturbance effects on large telescopes is becoming increasingly important during the design phase. Therefore, a wide field survey telescope with 2.5 m aperture and 3.5 deg field of view is studied in this research. This telescope is under construction now, and its first light is expected at the beginning of 2023. The estimation method for the optical performance under static and dynamic disturbances in the temporal domain and the active compensation method to improve the optical alignment, are investigated, which is a supplement for the simulation in the frequency domain. First, based on the mechanical model, the optical misalignment is established, where the deviation of the primary mirror is obtained from the length gauges and the deviation of the corrector is computed using the fitting method. Second, a method for compensating the static and dynamic disturbances is proposed, improving the optical performance. This method uses the disturbed primary mirror as the reference, and the corrector is actively controlled to align with it. Finally, a series of experimental tests and numerical simulations is conducted. The results show that the mechanical modeling error is within 10% and the maximum optical misalignment is reduced from 12''/0.27 to 0.2''/0.006mm for static disturbance and from 1.3''/0.03 to 0.4''/0.01mm for dynamic disturbance. Through active compensation, the telescope optical property is greatly improved. The modeling method and the simulation process mentioned in this research can also be used in the other relevant fields.