Model-Based Wavefront Control for CCAT
2011
The 25-m aperture CCAT submillimeter-wave telescope will have a primary mirror that is divided into 162 individual
segments, each of which is provided with 3 positioning actuators. CCAT will be equipped with innovative Imaging
Displacement Sensors (IDS) - inexpensive optical edge sensors - capable of accurately measuring all segment relative
motions. These measurements are used in a Kalman-filter-based Optical State Estimator to estimate wavefront errors,
permitting use of a minimum-wavefront controller without direct wavefront measurement. This controller corrects the
optical impact of errors in 6 degrees of freedom per segment, including lateral translations of the segments, using only
the 3 actuated degrees of freedom per segment. The edge sensors do not measure the global motions of the Primary and
Secondary Mirrors. These are controlled using a gravity-sag look-up table. Predicted performance is illustrated by
simulated response to errors such as gravity sag.
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