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Applied Optics

Applied Optics


  • Vol. 51, Iss. 12 — Apr. 20, 2012
  • pp: 1929–1938

In-plane effects on segmented-mirror control

Douglas G. MacMynowski, Lewis C. Roberts, Jr., J. Chris Shelton, Gary Chanan, and Henri Bonnet  »View Author Affiliations

Applied Optics, Vol. 51, Issue 12, pp. 1929-1938 (2012)

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Extremely large optical telescopes are being designed with primary mirrors composed of hundreds of segments. The “out-of-plane” piston, tip, and tilt degrees of freedom of each segment are actively controlled using feedback from relative height measurements between neighboring segments. The “in-plane” segment translations and clocking (rotation) are not actively controlled; however, in-plane motions affect the active control problem in several important ways, and thus need to be considered. We extend earlier analyses by constructing the “full” interaction matrix that relates the height, gap, and shear motion at sensor locations to all six degrees of freedom of segment motion, and use this to consider three effects. First, in-plane segment clocking results in height discontinuities between neighboring segments that can lead to a global control system response. Second, knowledge of the in-plane motion is required both to compensate for this effect and to compensate for sensor installation errors, and thus, we next consider the estimation of in-plane motion and the associated noise propagation characteristics. In-plane motion can be accurately estimated using measurements of the gap between segments, but with one unobservable mode in which every segment clocks by an equal amount. Finally, we examine whether in-plane measurements (gap and/or shear) can be used to estimate out-of-plane segment motion; these measurements can improve the noise multiplier for the “focus-mode” of the segmented-mirror array, which involves pure dihedral angle changes between segments and is not observable with only height measurements.

© 2012 Optical Society of America

OCIS Codes
(110.6770) Imaging systems : Telescopes
(110.1080) Imaging systems : Active or adaptive optics

ToC Category:
Imaging Systems

Original Manuscript: December 14, 2011
Revised Manuscript: January 26, 2012
Manuscript Accepted: January 27, 2012
Published: April 11, 2012

Douglas G. MacMynowski, Lewis C. Roberts, J. Chris Shelton, Gary Chanan, and Henri Bonnet, "In-plane effects on segmented-mirror control," Appl. Opt. 51, 1929-1938 (2012)

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