With the increasing requirement on spatial resolution to achieve ideal performance in space-based optical imaging
system, there is a need to enlarge primary apertures. However, primary mirrors of such systems cannot maintain its
optical tolerances across the mirror surface after sending to space, because of gravity change and varying ambient
temperature. It necessitates active optics technology of primary mirror surface correction. Since mass-to-orbit is
expensive and limited, lightweight primary mirror is needed. The paper investigates a lightweight, active primary mirror.
This primary mirror structure includes lightweight face sheet and substrate with surface-parallel actuators embedded in
the recess of web support ribs. Finite element models of lightweight, active primary mirror structures with different
structural parameters are established and simulated. Using the response function matrixes acquired from finite element
analysis, the fitting errors for Zernike polynomials are computed by MATLAB. Correctability comparisons of
lightweight, active primary mirror structures with different parameters are carried out. To get best correctability, the
mirrors should have small recess depth, high and thin ribs, thick face sheets and long actuators. The structural analysis
result will be valuable for the design of lightweight, active primary mirror.