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.
