The Hinode Solar Optical Telescope (SOT) is the first space-borne visible-light telescope that enables us to observe magnetic-field dynamics in the solar lower atmosphere with 0.2 -0.3 arcsec spatial resolution under extremely stable (seeing-free) conditions. To achieve precise measurements of the polarization with diffraction-limited images, stable pointing of the telescope (< 0.09 arcsec, 3σ ) is required for solar images exposed on the focal plane CCD detectors. SOT has an image stabilization system that uses image displacements calculated from correlation tracking of solar granules to control a piezo-driven tiptilt mirror. The system minimizes the motions of images for frequencies lower than 14 Hz while the satellite and telescope structural design damps microvibration in higher frequency ranges. It has been confirmed from the data taken on orbit that the remaining jitter is less than 0.03 arcsec (3σ ) on the Sun. This excellent performance makes a major contribution to successful precise polarimetric measurements with 0.2 -0.3 arcsec resolution.K. Kobayashi now at

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Feasibility of active shape formation or correction of a deployable space antenna reflector under the conditions of limited number of actuators and limited information of its surface shape is investigated to aim to suppress its deformations mainly due to thermal loads. Those conditions are practical for actual development of large space antennas. A reflector surface control scheme through checking electrical radiation patterns, instead of measuring structural surface, is also proposed, and its performance is evaluated through numerical simulations.

A shape control algorithm for a large flexible structure is proposed: (a) a reduced order model, which represents the precise shape of a structure; (b) a shape esti mation filter, which reduces the estimation error caused not only by the white noises of sensor measurements but also by the variation of the D.C. offsets of sensors; (c) a simple and robust controller to regulate many state variables by using many sensors and actuators. The controller is realized by a zero proportional, integral, derivative controller (zero P-ID controller) with the concept of low authority control/high authority control (LAC/HAC). The proposed shape control algorithm is illustrated through applications to a numerical model of an experimental setup.

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