Wavefront Control Strategies for Large Active Thin Shell Primaries with Unimorph Actuators

This paper presents various aspects of the wavefront control strategies for an ultra-lightweight composite reflector made of polymers for the large primary of a space telescope, and the shape control is made by a set of patterned unimorph strain actuators attached to the reflector. It starts with an analytical investigation of the mechanical behaviors of a strain-actuated curved shell, resulting in the accurate prediction of typical features, such as the damped wave deformation at the transition between electrodes and the limited morphing amplitude of a print-through actuation, which indicates that the curvature-induced rigidity deteriorates the performances of the forming accuracy of the active reflector and the morphing stroke of the actuators. The morphing capabilities are evaluated with both petal-like segmented and monolithic configured reflectors by numerical tests on forming target shapes of Zernike modes with various patternings of electrodes, and the structural dynamics are examined. Finally, a compound control strategy is proposed, which uses a deformable relay mirror to compensate for the residual surface error corrected partially by the active unimorph primary mirror, showing a great relaxation of the shape error budget of the thin-shell primary, especially for on-axis observation.

Automated summary

This paper presents wavefront control strategies for an ultra-lightweight composite reflector made of polymers for the large primary of a space telescope. The shape control is achieved using patterned unimorph strain actuators attached to the reflector. The mechanical behaviors and limitations of the actuators are analyzed, and the morphing capabilities of segmented and monolithic reflectors are evaluated. A compound control strategy involving a deformable relay mirror is proposed to compensate for residual surface errors.