Active control issues for the California Extremely Large Telescope

Abstract

A team of researchers from the University of California and Caltech are investigating the feasibility of building a 30 meter diameter segmented mirror telescope, following the design approach pioneered by the 36-segment Keck telescopes. The current design concept for the California Extremely Large Telescope (CELT) has 1080 segments forming the primary mirror, with the piston, tip, and tilt of each segment controlled by three actuators. The control approach must correct for gravity-and temperature-induced deformations of the mirror support structure, and potentially wind and seismic disturbances, with a cost effective design. We discuss some of the active control issues, including requirements (optical and cost), estimates of the disturbances, actuator options, and control analysis. Several candidate actuator technologies appear capable of meeting the technical and cost requirements, and preliminary error propagation analyses indicate that the optical error budget can likely be met. Additional issues being addressed are identified.