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Robustness of the Thirty Meter Telescope Primary Mirror Control System

MacMynowski, Douglas G. and Thompson, Peter M. and Shelton, Chris and Roberts, Lewis C. (2010) Robustness of the Thirty Meter Telescope Primary Mirror Control System. In: Ground-based and airborne telescopes III. Proceedings of SPIE. No.7733. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 77332J . ISBN 978-0-81948-223-5 . http://resolver.caltech.edu/CaltechAUTHORS:20110314-154329232

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Abstract

The primary mirror control system for the Thirty Meter Telescope (TMT) maintains the alignment of the 492 segments in the presence of both quasi-static (gravity and thermal) and dynamic disturbances due to unsteady wind loads. The latter results in a desired control bandwidth of 1Hz at high spatial frequencies. The achievable bandwidth is limited by robustness to (i) uncertain telescope structural dynamics (control-structure interaction) and (ii) small perturbations in the ill-conditioned influence matrix that relates segment edge sensor response to actuator commands. Both of these effects are considered herein using models of TMT. The former is explored through multivariable sensitivity analysis on a reduced-order Zernike-basis representation of the structural dynamics. The interaction matrix ("A-matrix") uncertainty has been analyzed theoretically elsewhere, and is examined here for realistic amplitude perturbations due to segment and sensor installation errors, and gravity and thermal induced segment motion. The primary influence of A-matrix uncertainty is on the control of "focusmode"; this is the least observable mode, measurable only through the edge-sensor (gap-dependent) sensitivity to the dihedral angle between segments. Accurately estimating focus-mode will require updating the A-matrix as a function of the measured gap. A-matrix uncertainty also results in a higher gain-margin requirement for focus-mode, and hence the A-matrix and CSI robustness need to be understood simultaneously. Based on the robustness analysis, the desired 1 Hz bandwidth is achievable in the presence of uncertainty for all except the lowest spatial-frequency response patterns of the primary mirror.


Item Type:Book Section
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1117/12.857380DOIArticle
http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=750374PublisherArticle
ORCID:
AuthorORCID
MacMynowski, Douglas G.0000-0003-1987-9417
Roberts, Lewis C.0000-0003-3892-2900
Additional Information:© 2010 SPIE. The finite element models used herein for the telescope structure and the primary segment assembly were developed by DSL and by HYTEC Inc., respectively. The soft actuator parameters used here are based on a design and prototype from Marjan Research. The contributions of all of these organizations are gratefully acknowledged. The TMT Project gratefully acknowledges the support of the TMT partner institutions. They are the Association of Canadian Universities for Research in Astronomy (ACURA), the California Institute of Technology and the University of California. This work was supported as well by the Gordon and Betty Moore Foundation, the Canada Foundation for Innovation, the Ontario Ministry of Research and Innovation, the National Research Council of Canada, the Natural Sciences and Engineering Research Council of Canada, the British Columbia Knowledge Development Fund, the Association of Universities for Research in Astronomy (AURA) and the U.S. National Science Foundation. A portion of the research in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Group:Thirty Meter Telescope
Funders:
Funding AgencyGrant Number
Association of Canadian Universities for Research in Astronomy (ACURA)UNSPECIFIED
CaltechUNSPECIFIED
University of CaliforniaUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Canada Foundation for InnovationUNSPECIFIED
Ontario Ministry of Research and InnovationUNSPECIFIED
National Research Council of CanadaUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
British Columbia Knowledge Development FundUNSPECIFIED
Association of Universities for Research in Astronomy (AURA)UNSPECIFIED
NSFUNSPECIFIED
NASA/JPL/CaltechUNSPECIFIED
Subject Keywords:Extremely Large Telescopes; Control Systems; Uncertainty
Record Number:CaltechAUTHORS:20110314-154329232
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20110314-154329232
Official Citation:Douglas G. MacMynowski, Peter M. Thompson, Chris Shelton and Lewis C. Roberts, Jr., "Robustness of Thirty Meter Telescope primary mirror control", Proc. SPIE 7733, 77332J (2010); doi:10.1117/12.857380
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22875
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:16 Mar 2011 22:56
Last Modified:24 Apr 2017 21:24

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