Design and analysis of support structure of small and medium-sized common optical path system

Primary and secondary mirror support technology is one of the key technologies of common optical path system. For the airborne optical system operating within the temperature change range of ±60 ℃, the pairing of invar steel and ULE, titanium alloy and K9 were selected as the materials of primary and secondary mirrors as well as supporting structures according to the matching principle of thermal expansion coefficient, and the athermalization flexible support structure with high stiffness was designed. Finally, the imaging quality of the primary and secondary mirror types as well as the whole optical system was analyzed by using a self-developed opto-mechanical co-simulation program. The results show that when invar steel and ULE are paired, under uniform temperature difference of ±60 ℃ and 10 ℃ axial and radial temperature gradient, the surface shape is better than (1/100) λ after the primary and secondary mirror removing defocus, and the root-mean-square (RMS) radius of spot diagram of the whole optical system is smaller than Airy spot radius. The central wavefront of the phase surface is better than (1/50) λ, the MTF@63 lp/mm is better than 0.45, and the first-order natural frequency with athermalization flexible support is up to 263 Hz. When titanium alloy and K9 are paired, the imaging index of the system under uniform temperature difference of 60 ℃ meets the requirements, and the imaging quality at 10 ℃ axial and radial temperature cannot meet the requirements. The resolution of invar steel and ULE paired opto-mechanical system was tested at low temperature, and there is no obvious change in resolution, which indicates that the design and analysis are feasible.