Telescope Research

Research topics:

  • Developing the control algorithm, understanding robustness, and understanding the dynamic analysis for the 1476 actuators that control the primary mirror segments.  The ability of the control system to ensure that the 492 hexagonal segments behave collectively as a single monolithic mirror is one of the key enabling technologies that allows TMT to be conceived and built.  The relative motion between neighbouring segments must be controlled to ~10nm.  (A nanometer is the distance your fingernail grows in a second.)  We believe that we will be able to achieve a 1Hz control bandwidth for the TMT primary mirror; a factor of ten higher than the bandwidth used in controlling the segmented primary mirrors for the Keck Observatories, despite the larger structure and therefore lower resonant frequencies.

  • Understanding the dynamic performance of the telescope through integrated modeling.  Much of the focus has been on understanding wind turbulence inside telescope enclosures, and the response of the structure to wind - this requires the development of modeling tools that integrate the structure, the wind model, the control system, and the optical response.  Early in the design process there was a significant concern that scaling of the wind response would make a telescope of this size infeasible. Understanding narrowband equipment vibration is also critical; this is clearly measurable at existing observatories such as Keck, and in addition to having 9-times the collecting area, TMT is also seeking to achieve better optical performance!

  • Developing and testing computationally efficient algorithms for adaptive optics (AO) with many actuators and sensors, as future AO systems may involve as many as 50000 actuators to compensate for looking through atmospheric turbulence.  Both hierarchic algorithms based on local control, and computationally simpler multigrid algorithms have been tested on the sky at Palomar Observatory.  A key contribution is the demonstration that a single-iteration of the simplest possible multigrid reconstruction algorithm (which is order n scaling with the number of actuators) cannot be distinguished from the O(n2) full least-squares reconstructor in closed-loop performance.  (This is not true in open-loop, for which previous analyses were typically conducted.)

  • Distributed control for future highly-flexible mirrors; this collaboration with Lund University is in its early stages but shows significant promise for enabling future low-cost but large (>1m diameter) deformable mirrors; the ideas are also relevant for enabling lightweight space telescopes.

Relevant Publications: