Dynamical aspects in control of E-ELT segmented primary mirror (M1)

Control of primary segmented mirror of an extremely large telescope with large number of actuators and sensors and multiple control loops is a complex problem. The designer of the M1 unit is confronted to the dilemma of trade-off between the relatively though performance requirements and the robust stability of the control loops. Another difficulty arises from the contradictory requirements of the stiffness of the segment support system and position actuators for wind rejection on one hand and vibration mitigation on other hand. The presence of low frequency mechanical modes of the back structure and possible interaction of the large number of control loops through such structure could be a limiting factor for achieving the required control bandwidths. To address these issues a better understanding of dynamical behavior of segmented mirror is necessary. This paper addresses the trade-offs on dynamical aspects of the M1 segmented mirror and the robust stability conditions of various control loops.