针对高分辨率、宽覆盖面积、全天时海洋目标的红外侦察与搜索需求，设计了一种大口径、长焦距的同轴折反射式中波红外光学系统。其工作轨道高度为1200 km，波段为3.7~4.8 μm，星下点地面像元分辨率优于10 m。通过分析计算确定系统焦距为3000 mm，相对孔径为14。采用镜头前组摆扫方式实现了视场角14.203°，地面覆盖宽度为300 km。利用调焦机构在10 ℃~30 ℃温度范围内主动消热差，在奈奎斯特频率21 lp/mm处全视场调制传递函数(MTF)大于0.39，接近衍射极限。实现了100%冷光阑匹配以抑制系统自身的杂散辐射。设计结果表明，该系统各项性能指标和结构的可实现性均满足要求。

According to the requirements on high-resolution, wide-field-of-view, all-time reconnaissance and search for maritime targets, a coaxial catadioptric optical system with medium wave infrared (MWIR) is designed. It operates at the orbit altitude of 1200 km with the wavelength spanning from 3.7 μm to 4.8 μm, and it presents the ground resolution of 10 m at nadir. After detailed analysis and calculation, the focal length of this system is 3000 mm, and the relative aperture is 14. The angle of field reaches 14.203°, and the earth area coverage can reach 300 km with scanning former lens group. A focusing mechanism is developed to correct thermal aberrations of the system from 10 ℃ to 30 ℃. The modulation transfer function (MTF) corresponding to the whole field of view (FOV) is larger than 0.39, which can approach diffraction limit at Nyquist frequency of 21 lp/mm. In order to suppress stray radiations, the optical system is optimized to realize 100% cold-shield-match efficiency. The above results show that the properties and structure feasibility of this optical system closely meet the requirements.