High-performance chopping secondary mirror for infrared astronomy

The paper describes the electromechanical design of the drive system for the actively controlled chopping secondary mirror of the W.M. Keck Ten Meter Telescope, which performs two-axis spatial chopping. Also described are the reaction cancellation system, the special packaging and cooling features, and the operation of the adaptive drive system. Laboratory test data are presented showing the performance of the drive and control system for chop amplitudes up to 54 arcmin (mirror motion), duty cycles of up to 98 percent, and frequencies from 1 to 50 Hz.