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
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.
D. G., and H. Thompson, “A vibration budget for observatory equipment”,
SPIE J. Astronomical Telescopes, Instruments, and Systems, 1 (3), 034005
(September 16, 2015). doi:
MacMartin, D. G., Thompson, P., Colavita, M. M., Sirota, M. J., “Dynamic
analysis of the active-controlled segmented mirror of the Thirty Meter
Telescope”, IEEE Transactions, Control Systems Technology,
D. G., “Control of a hypersegmented space
telescope”, AIAA J. Guidance, Control and Dynamics,
Heimsten, R., MacMynowski, D. G, Andersen, T. and Owner-Peterson, M.,
“Concept, modeling, and performance prediction of a low-cost large
deformable mirror”, submitted, Applied Optics, 2011
R. Owner-Peterson, M., Andersen, T., and MacMynowski, D. G., “Suppressing
low-order eigenmodes with local control for deformable mirrors”,
accepted, Optical Engineering, 2011.
D. G., Heimsten, R., and Andersen, T. “Distributed force control of
deformable mirrors”, Vol 17(3):249-260, European J. Control, 2010.
MacMynowski, D.G. and Andersen, T. "Wind buffeting of large telescopes",
Applied Optics, Vol. 49(4):625-636, 2010.
MacMynowski, D.G., "Interaction matrix
uncertainty in active (and adaptive) optics", Applied Optics,
Vol. 48, No. 11, pp. 2105-2114, 2009
Lessard, L. A., D. G. MacMynowski, M. West, A. Bouchard and S. Lall, “Experimental
validation of single-iteration multigrid
wavefront reconstruction at the Palomar Observatory”, Optics
Letters, Vol. 33, No. 18, pp. 2047-2049, 2008.
Lessard, L. A., M. West, D. G. MacMynowski and S. Lall, “Warm-started
wavefront reconstruction for adaptive optics”, J. Optical
Society of America (A), Vol. 25, No. 5, pp. 1147-1155, 2008.
MacMynowski, D. G., K. Vogiatzis, G. Z. Angeli, J. Fitzsimmons,
and J. E. Nelson, "Wind Loads on
Ground-Based Telescopes", Applied Optics, Vol. 45, No. 30, pp.
7912-7923, Oct. 2006.
Pottebaum, T. and MacMynowski, D. G., "Wind
Tunnel Testing of a Vented and Unvented Hemispherical Telescope Enclosure", J. Fluids and Structures, Vol. 22, 2006,
MacMynowski, D. G.,
"Hierarchic Estimation for Control of Segmented-Mirror Telescopes'',
AIAA J. Guidance, Control and Dynamics, Vol. 28, No. 5, Sept-Oct 2005.
Chanan, G., MacMartin, D.G., Nelson, J., and Mast, T., "Control
and Alignment of Segmented-Mirror Telescopes: Matrices, Modes and Error
Vol 43, No. 6,
pp. 1223-1232, 2004.
and Chanan, G. "Measurement
Accuracy in Control of Segmented-Mirror Telescopes",
Applied Optics, Vol. 43, No. 3, pp. 608-615, 2004.
MacMartin, D.G., "Local,
Hierarchic, and Iterative Reconstructors for Adaptive Optics",
J. of the Optical Society of America (A), Vol. 20, No. 6, pp. 1084-1093, 2003.