Modeling, simulation and implementation of primary mirror control system for the prototype segmented mirror telescope

Abstract

The next generation large astronomical telescopes are primarily made of segmented mirrors and construction of such a telescope is a big challenge. It require enormous amount of works to conceptualize various sub-systems, design, analysis, planning and execution. It also demands to prototype various critical subsystems like actuators, edge sensors, segment support, drive and control system, etc. To build a 10m class Segmented Mirror Telescope in India, several activities have been initiated at the Indian Institute of Astrophysics. As a first step towards realizing bigger telescope, development of a Prototype Segmented Mirror Telescope (PSMT) has been proposed. Design and development of the few critical subsystems linked with the control of segmented primary mirror of the PSMT are part of this Ph.D. thesis. The focus of the thesis is primary mirror control system, which comprises local and global control systems. The first task undertaken was, design and development of a soft actuator based on a voice coil motor. Before realizing it, detailed modeling and simulation have been conducted to make sure that the concept is feasible. Then after a prototype actuator was built. A customized precision controller has also been developed to control the actuator in closed loop mode. Varieties of experimentation show that indeed the prototype actuator meets most of stringent requirements. Further to check the performance under dynamically varying disturbances such as wind force, novel test equipment named Dynamic Loading Assembly has been developed. Through the tests conducted with DLA we ensured that the actuator is capable to reject wind induced disturbances. To understand working of global control system of the PSMT and any other segmented mirror telescopes, we have developed a simulation tool called as the codeSMT. Creating the control matrix for any telescope made of many segment rings is cumbersome task. We have proposed a new numbering technique which is generic and can be used for any size SMT’s. As a case study, the codeSMT is successfully tested in the PSMT active control simulation and error multiplier analysis. Finally, an integrated local and global control system of the PSMT has been designed, implemented and tested in the laboratory.