&lt;title&gt;W. M. Keck Telescope segmented primary mirror active control system&lt;/title&gt;

Jared, R. C.; Arthur, A. A.; Andreae, S.; Biocca, A. K.; Cohen, Richard W.; Fuertes, Josep M.; Franck, J.; Gábor, G; Llacer, J.; Mast, Terry S.; Meng, John D.; Merrick, T.; Minor, R.H.; Nelson, James T.; Orayani, M.; Salz, P.; Schaefer, Barbara A.; Witebsky, C.

doi:10.1117/12.19266

Cited by 43 publications

(35 citation statements)

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“…For existing and future optical telescopes with segmented primary (or other) mirrors, the segments are typically nearly hexagonal, with three actuators behind each segment to control the piston, tip, and tilt of the segment [4]. (The analytical results in Section 3 do not depend on the segmentation geometry, only the quantitative results in Section 4 do.)…”

Section: A Segmented-mirror Controlmentioning

confidence: 94%

“…This matrix is ill conditioned, and thus the estimate of the segment displacement is highly sensitive to certain types of uncertainty in the interaction matrix. The same sensing and control approach is used successfully at existing telescopes [4]. However, the condition number of the interaction matrix increases as the number of segments increases, and hence robustness to uncertainty decreases.…”

Section: Introductionmentioning

confidence: 99%

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Interaction matrix uncertainty in active (and adaptive) optics

MacMynowski

2009

Appl. Opt.

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Uncertainty in the interaction matrix between sensors and actuators can lead to performance degradation or instability in control of segmented mirrors (typically the telescope primary). The interaction matrix is ill conditioned, and thus the position estimate required for control can be highly sensitive to small errors in knowledge of the matrix, due to uncertainty or temporal variations. The robustness to different types of uncertainty is bounded here using the small gain theorem and structured singular values. The control is quite robust to moderate uncertainty in actuator gain, sensor gain, or the ratio of sensor dihedral and height sensitivity. However, the control is extremely sensitive to small errors in geometry, with the maximum error that can be tolerated scaling inversely with the number of segments. The same tools can be applied to adaptive optics; however, the interaction matrix here is better conditioned and so uncertainty is less of an issue, with the tolerable error scaling inversely with the square root of the number of actuators.

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Section: A Segmented-mirror Controlmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Interaction matrix uncertainty in active (and adaptive) optics

MacMynowski

2009

Appl. Opt.

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“…Two sensors are also needed on each edge to measure the relative motion between segments, as on ground-based segmented-mirror telescopes [17], where differential height between segments can be measured with a resolution of a few nanometers using either differential capacitive [18] or differential inductive sensors [19]. Unless a manufacturing approach is used that ensures sensor installation errors of nanometers, an initial phasing approach using star light would be needed after the mirror was assembled in order to determine the correct set point for each sensor; these techniques are well established on the ground, but some modifications to the approach would be required to handle many thousands of segments [6].…”

Section: Modelmentioning

confidence: 99%

Control of a Hypersegmented Space Telescope

MacMynowski

2012

Journal of Guidance, Control, and Dynamics

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The primary mirror diameter of affordable space telescopes is limited by mass and manufacturing cost. Currently planned optical/near-infrared space telescopes use a segmented primary mirror with relatively few segments and make limited use of real-time position control. However, control can be used as an enabler for a fundamentally different, very highly segmented architecture, leading to a significant reduction in areal density, and hence a significant increase in the realistically achievable diameter of a space telescope. Weight can be reduced by minimizing the structure that supports mirror segments and instead relying on control for overall stiffness. Furthermore, smaller segments can be thinner (hence, lighter) while still providing sufficient internal rigidity. However, with these architectural changes, the control problem involves not only thousands of actuators and sensors but also many lightly damped modes within the control bandwidth. The objective here is to demonstrate that this control problem is solvable by applying a local control approach. This is illustrated for a 30-m-diam primary mirror composed of 12,000 0.3-m-diam segments.

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“…This requires a total of 108 actuators, compensating for gravity and thermal deformations by feeding back information from 168 edge sensors at a 2 Hz update rate 3,4 . The initial design concept for CELT has 1080 hexagonal segments, 3240 actuators, and 6204 edge sensors 1 .…”

Section: Introductionmentioning

confidence: 99%

Active control issues for the California Extremely Large Telescope

MacMartin

Mast

Cruz

et al. 2001

AIAA Guidance, Navigation, and Control Conference and Exhibit

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A team of researchers from the University of California and Caltech are investigating the feasibility of building a 30 meter diameter segmented mirror telescope, following the design approach pioneered by the 36-segment Keck telescopes. The current design concept for the California Extremely Large Telescope (CELT) has 1080 segments forming the primary mirror, with the piston, tip, and tilt of each segment controlled by three actuators. The control approach must correct for gravity-and temperature-induced deformations of the mirror support structure, and potentially wind and seismic disturbances, with a cost effective design. We discuss some of the active control issues, including requirements (optical and cost), estimates of the disturbances, actuator options, and control analysis. Several candidate actuator technologies appear capable of meeting the technical and cost requirements, and preliminary error propagation analyses indicate that the optical error budget can likely be met. Additional issues being addressed are identified.

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<title>W. M. Keck Telescope segmented primary mirror active control system</title>

Cited by 43 publications

References 0 publications

Interaction matrix uncertainty in active (and adaptive) optics

Interaction matrix uncertainty in active (and adaptive) optics

Control of a Hypersegmented Space Telescope

Active control issues for the California Extremely Large Telescope

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