Research on the effects and alignment of in-plane motion in a segmented solar telescope

For ground-based segmented telescopes, the active control system primarily adjusts three out-of-plane DOFs: tip, tilt, and piston. In contrast, in-plane DOFs rely on high-precision mechanical alignment. A systematic analysis of the effects of in-plane motion on the optical performance of ring segmented mirror systems is presented, and an analytical relationship between in-plane motion and the higher-order residual aberrations after tilt compensation is derived. Conventional alignment techniques based on three-dimensional metrology do not provide the necessary in-plane motion detection accuracy required for the CGST, which operates in the visible spectrum and demands higher surface precision than infrared telescopes. Previous measurements using laser trackers indicate that the achievable accuracy is insufficient for CGST alignment. A method based on wavefront aberration has been proposed to enhance the accuracy of in-plane motion measurements and alignments. This approach establishes a correlation between wavefront aberrations and in-plane motion. Wavefronts are obtained through phase retrieval and fitted using orthogonal Zernike polynomials to develop the mapping model. During the alignment process, the effect induced by Clocking is compensated by adjusting DX. Simulations using parameters from the CGST show that, with a point spread function image SNR above 20 dB, the residual wavefront aberration after compensation meets the diffraction-limited requirements in the visible range. The results confirm the potential of this method for achieving high-precision in-plane DOFs alignment in segmented solar telescopes.