Control of the California Extremely Large Telescope primary mirror

MacMartin, Douglas G.; Chanan, G. A.

doi:10.1117/12.458150

Cited by 17 publications

(13 citation statements)

References 7 publications

(5 reference statements)

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“…We considered this question in detail elsewhere 19,20 and concluded that a supplementary wave-front sensor is not likely to be needed for stabilization purposes. Here we just summarize the argument.…”

Section: Error Multipliers From Singular-value Decompositionmentioning

confidence: 99%

Control and alignment of segmented-mirror telescopes: matrices, modes, and error propagation

Chanan¹,

MacMartin²,

Nelson³

et al. 2004

Appl. Opt.

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Starting from the successful Keck telescope design, we construct and analyze the control matrix for the active control system of the primary mirror of a generalized segmented-mirror telescope, with up to 1000 segments and including an alternative sensor geometry to the one used at Keck. In particular we examine the noise propagation of the matrix and its consequences for both seeing-limited and diffractionlimited observations. The associated problem of optical alignment of such a primary mirror is also analyzed in terms of the distinct but related matrices that govern this latter problem.

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Section: Error Multipliers From Singular-value Decompositionmentioning

confidence: 99%

Control and alignment of segmented-mirror telescopes: matrices, modes, and error propagation

Chanan¹,

MacMartin²,

Nelson³

et al. 2004

Appl. Opt.

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“…If additional sensors are also used ͑such as wave-front information͒, then y can be expanded to include both sets of measurements. The baseline disturbance rejection control algorithm 5,12 can be divided into two steps, shown in Fig. 2.…”

Section: Control Analysismentioning

confidence: 99%

“…The average over these data sets of the estimated residual surface error at Keck due to uncontrolled low-frequency vibration is 50 -75 nm. 14 The low-frequency spectrum is of primary interest for assessment of control system noise, and the sensor noise level is estimated with the approach outlined above. Figure 6 shows the correlation between the low-frequency energy in the physical and unphysical components for Keck 1, averaged over 0 -2.5 Hz and from 2.5 to 5 Hz.…”

Section: Analysis Of Keck Sensor Datamentioning

confidence: 99%

Measurement accuracy in control of segmented-mirror telescopes

MacMartin¹,

Chanan²

2004

Appl. Opt.

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Design concepts for future large optical telescopes have highly segmented primary mirrors, with the out-of-plane degrees of freedom actively controlled. We estimate the contribution to errors in controlling the primary mirror that results from sensor noise and, in particular, compare mechanical measurements of relative segment motion with optical wave-front information. Data from the Keck telescopes are used to obtain realistic estimates of the achievable noise due to mechanical sensors. On the basis of these estimates, mechanical sensors will be more accurate than wave-front information for any of the telescope design concepts currently under consideration, and therefore supplemental wave-front sensors are not required for real-time figure control. Furthermore, control system errors due to sensor noise will not significantly degrade either seeing-limited or diffraction-limited observations.

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“…MacMartin [52]. The wind disturbance, shown here as an input to the plant, is represented as frequency based disturbance spectra.…”

Section: Tmt Model and Fidelitymentioning

confidence: 99%

Spatial Nyquist fidelity method for structural models of opto-mechanical systems

2008

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As technology employed in complex multidisciplinary systems such as high performance telescope systems becomes ever more sophisticated, simulation is becoming more important during the initial design phases. The method of building these simulation models is often based on engineering experience with older, potentially dissimilar systems. A method is needed to measure the fidelity of simulation models so early design decisions are made based on appropriate modeling techniques.Previously, fidelity was a qualitative concept used to indicate a model's validity or accuracy. Here it is defined as the ability of a model to accurately predict chosen output figures of merit. In this thesis, a quantitative measure of fidelity, termed the Nyquist fidelity metric, is defined for commonly used structural model components. It expresses the ability of a finite element model to accurately predict structural eigenvalues based on the mesh size required by the spatial Nyquist criterion. The Nyquist fidelity method is developed which uses the fidelity metric to both assess the fidelity of existing complex models and to synthesize new multi-component models starting from architectural considerations such as geometric and material properties of the system. This method also estimates the error bound on the output figures of merit based on the fidelity levels and sensitivity analysis.The Nyquist fidelity method is applied to simple sample problems to first demonstrate the methodology and it is then applied to complex telescope models to show the accuracy and computational benefits of this method compared to current methods such as model reduction. The three high performance telescope case studies are the Modular Optical Space Telescope (MOST), the Thirty Meter Telescope, and the Stratospheric Observatory for Infrared Astronomy. It is shown in the MOST example that the Nyquist fidelity method provides a 40% improvement in computational time while assuring less than 5% modal frequency error, and less than 2.2% error in the output figure of merit.

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Control of the California Extremely Large Telescope primary mirror

Cited by 17 publications

References 7 publications

Control and alignment of segmented-mirror telescopes: matrices, modes, and error propagation

Control and alignment of segmented-mirror telescopes: matrices, modes, and error propagation

Measurement accuracy in control of segmented-mirror telescopes

Spatial Nyquist fidelity method for structural models of opto-mechanical systems

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