Hybrid ball-hinged secondary mirror assembly for high-precision surface shape maintenance.

ABSTRACT

As an essential part of optical telescope, the secondary mirror is subject to the influence of ambient temperature, which leads to temperature-induced distortion on the surface shape. A hybrid ball-hinged secondary mirror assembly (HSMA) is proposed to achieve thermal adaptation over a wide range of temperature. Simulation investigation on the temperature-induced surface shape distortion of the HSMA were carried out by using the finite element model. Simulation results show that the change of secondary mirror surface distortions over a wide range of temperature are minimal and negligible. For the wide ambient temperature range from -30°C to 70°C, the PV and RMS values of the maximum residual distortions can reach as small as 16.31 nm and 3.005 nm, respectively. Furthermore, the influence of gravity-induced distortion on the surface shape is also carried out. Both simulation and experiment results show that the HSMA is able to maintain high-precision surface shape of the secondary mirror over a wide range of temperature and at different attitudes from 0 to 90 ∘.