Study on the sensitivity of temperature gradient for large aperture SiC lightweight mirror based on active optics

With the aperture of large ground-based telescopes increasing, thermal issues appear more evidently. As a relatively large thermal expansion coefficient SiC (about 2.510-6/C), it makes large aperture SiC lightweight primary mirror more sensitive to temperature gradient. Firstly, discuss thermal issue of the mirror seeing induced by the temperature difference between the mirror surface and ambient theoretically. Then analyze the mirror surface deformation under seven different steady-state temperature fields with a unit temperature load. A uniform axial gradient can cause a mirror surface deflection RMS which can reach 438.4 nm. According to the simulation results, it shows that the primary is most sensitive to a uniform axial gradient and least to uniform change. Lastly, the parameter of thermal control is determined through the above analysis with the error budget to get a better image quality. 2014 SPIE.