Abstract
The Naval Postgraduate School’s segmented mirror telescope (SMT) was developed using prototype silicon carbide active hybrid mirror technology to demonstrate lower cost and rapid manufacture of primary mirror segments for a space telescope. The developmental mirror segments used too few actuators limiting the ability to adequately correct the surface figure error. To address the unintended shortfall of the developmental mirrors, a deformable mirror is added to the SMT and control techniques are developed. The control techniques are similar to woofer-tweeter adaptive optics, where the SMT segment represents the woofer and the deformable mirror represents the tweeter. The optical design of an SMT woofer-tweeter system is presented, and the impacts of field angle magnification on the placement and size of the deformable mirror are analyzed. A space telescope woofer-tweeter wavefront control technique is proposed using a global influence matrix and closed-loop constrained minimization controller. The control technique simultaneously manipulates the woofer and tweeter mirrors. Simulation and experimental results demonstrate a significant improvement in wavefront error of the primary mirror and the control technique shows significant wavefront error improvement compared to sequentially controlling the woofer and tweeter mirrors.
Highlights
Current earth-imaging satellites operate in low Earth orbit (LEO) and use large monolithic primary mirrors to achieve high-resolution images
The results show that a space telescope woofer-tweeter system is viable and can improve the wavefront error attributed to a primary mirror segment
A space telescope woofer-tweeter design concept was developed to compensate for surface error of a telescope using a segmented active primary mirror
Summary
Current earth-imaging satellites operate in low Earth orbit (LEO) and use large monolithic primary mirrors to achieve high-resolution images. The launch vehicle volume and mass constraints impact the space telescope primary mirror design. The James Webb Space Telescope (JWST) overcomes the mass and volume constraints using a lightweight segmented mirror design with an active wavefront sensing and control system. An Earth imaging satellite woofer-tweeter system does not have to correct atmospheric high temporal frequency disturbances, but rather static errors and low frequency disturbances caused by a thermally dynamic environment.[6,7] The SMT active segment represents the woofer since the resonant frequency is lower than the deformable mirror, and the additional deformable mirror represents the tweeter. The simulation and experimental results show the feasibility of using adaptive optics to improve the optical performance of a large aperture imagery satellite and the ability to trade optical surface requirements between the primary mirror segments and a deformable mirror
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