随着航天遥感需求的不断提高，光学遥感器的口径越来越大，光学元件的支撑和重力变形对光学系统的影响难以消除，因此需要在轨调整光学元件位置变量，来补偿主镜面形误差引起的系统光学性能的下降。以一个大口径同轴三反射式光学系统为例，在理论上分析了次镜的倾斜、偏心和轴向位置引起的初级像差的变化，得出次镜的在轨补偿能力。利用Zernike多项式模拟主镜面形误差，通过调整次镜的位置自由度，分别补偿主镜的球差、彗差和像散，给出了仿真结果，并进行了工程可实现性分析。结果表明，次镜的位置自由度调整能够补偿主镜的彗差，并能够补偿一定量的像散，但是只能补偿小量球差。

With the uprating requirements of space remote sensing, the aperture of the remote sensor is getting larger and larger. The influences of both the support of optical elements and gravity deformation on the optical system are difficult to conquer. Therefore, it is necessary to compensate the descending optical performance which is caused by the surface error of the primary mirror by means of adjusting the position parameters of the optical elements on-orbit. A large aperture coaxial three-mirror optical system is introduced. The variation of primary aberrations caused by tilting, off-centering and varying of axial position of the secondary mirror are theoretically analysed. The on-orbit compensation ability of the secondary mirror is deduced consequently. Zernike polynomials are used to simulate the surface error of the primary mirror. The spherical aberration, coma and the astigmatism of the primary mirror are compensated respectively by adjusting the positional freedoms of the secondary mirror, which are proved by both simulation results and feasibility analysis. The results show that the adjustment of the positional freedoms of the secondary mirror can compensate both the coma and some astigmatism of the primary mirror, but a little spherical aberration.