A control system using mirror displacement sensors and position actuators to maintain proper surface control of a segmented mirror is summarized. The system is composed of three major components; a figure control computer, displacement sensors and displacement actuators. Desired positioning accuracy is 50 nm. Several methods for achieving the needed sensor sensitivity and stability are discussed. A capacitive hridge detector was chosen and its expected and measured behavior is described. Two mechanisms for positioning a mirror segment to optical tolerances, yet having a large dynamic range to compensate for mirror cell deformation are reviewed. Test results for a roller screw are given with an outline of the servo loop design.
George Gabor, George Gabor,
"Position Sensors And Actuators For Figure Control Of A Segmented Mirror Telescope", Proc. SPIE 0172, Instrumentation in Astronomy III, (3 May 1979); doi: 10.1117/12.957065; https://doi.org/10.1117/12.957065