&lt;title&gt;Gran Telescopio Canarias: current status of its optical design and optomechanical support system&lt;/title&gt;

Jochum, Lotti; Castro, Jordi; Devaney, Nicholas

doi:10.1117/12.319300

Cited by 7 publications

(4 citation statements)

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“…As will be shown in this study, this approximation also lacks accuracy, and it has been found that a better estimation may be made using CIR fl CIR n (2) The procedure used to estimate the image quality of the GTC is numerical simulation of the expected wavefront errors. This method is much more complicated, but avoids the inaccuracies of accumulating individual contributions of error sources using approximate methods.…”

Section: Optical Performancementioning

confidence: 98%

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<title>Image quality and active optics for the Gran Telescopio Canarias</title>

et al. 1998

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The conceptual design of the Gran Telescopio Canarias (GTC) has been completed. One of the challenges facing the GTC Project is to obtain excellent image quality using a segmented primary mirror. The segmentation will introduce a physical effect that contributes to significant degradation of image quality.The image quality requirement imposes the use of an active optical system to correct figure instabilities of the optical surfaces and part of the unavoidable fabrication figure errors. The active correction includes the capability of 5-axis motion of the secondary mirror, 3-axis motion of each primary mirror segment, and 6 active degrees of freedom to deform each segment. A mixed strategy of closed-and open-loop control of the active correction will be implemented. This paper discusses the expected wavefront errors of the GTC, how they are corrected by active optics, and the expected image quality performance in FWHM, 080 and Central Intensity ratio.

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Section: Optical Performancementioning

confidence: 98%

“…In the first simulated case, the total Cifi of 0.767 is found from the simulated data would be estimated as 0.708 using equation (1) and 0.739 using equation (2). In the second simulated case the CW is 0.796, while the estimates are 0.748 and 0.77 1 respectively.…”

Section: Optical Quality Of the Gtcmentioning

confidence: 99%

<title>Image quality and active optics for the Gran Telescopio Canarias</title>

et al. 1998

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“…In addition, other telescopes such as the W M Keck, Very Large Telescope, Subaru, and Gemini have primary and secondary mirror sizes * Authors to whom any correspondence should be addressed. of 8 and 10 m and 1 and 1.4 m, respectively [1][2][3][4][5]. However, as the mirror size increases, it becomes more challenging to fabricate and test the diffraction-limited optical performance of the mirror.…”

Section: Introductionmentioning

confidence: 99%

Astigmatism correction of convex aspheres using the subaperture stitching hindle test

Kim¹,

Song²,

Kihm³

et al. 2022

Meas. Sci. Technol.

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We propose an astigmatism correction method for the subaperture stitching Hindle test to measure hyperbolic convex aspheres. Astigmatic wavefront errors arise from misaligned Hindle setups, mechanical runout errors of the rotational motion for stitching, and the surface error of the target itself. Because these errors are combined, they cannot be separated in the conventional subaperture stitching Hindle tests. We exploited the rotational periodicity of each error to distinguish the surface figure error from other astigmatic error sources and rectified the Hindle test results with a third-order astigmatism. Using the subaperture stitching Hindle test, we averaged two sets of measurement data with a 180° rotational phase difference between them to calculate the astigmatic surface error. The proposed method was verified experimentally by comparing it with the results from a commercial stitching interferometer from QED Technologies; only subnanometer differences in the root-mean-square values were obtained. Therefore, the proposed method calibrated the system errors from the test surface wedge and the rotational decenter easily, thereby reducing the mechanical costs and alignment efforts and making it more accessible than a sophisticated mechanism.

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“…As an example, a wavefront map, PSF and MTF curve for the Gran Telescopio Canarias (GTC) are shown in Fig. 5, which are based on the design prescription given in [4].…”

Section: A Optical Raytracing and Fourier Modelmentioning

confidence: 99%

Design and end-to-end modelling of a deployable telescope

Dolkens

Kuiper

2017

International Conference on Space Optics — ICSO 2016

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Deployable optics have the potential of revolutionizing the field of high resolution Earth Observation. By offering the same resolutions as a conventional telescope, while using a much smaller launch volume and mass, the costs of high resolution image data can be brought down drastically. In addition, the technology will ultimately enable resolutions that are currently unattainable due to limitations imposed by the size of launcher fairings.To explore the possibilities and system complexities of a deployable telescope, a concept study was done to design a competitive deployable imager. A deployable telescope was designed for a ground sampling distance of 25 cm from an orbital altitude of 550 km. It offers an angular field of view of 0.6° and has a panchromatic channel as well as four multispectral bands in the visible and near infrared spectrum.The optical design of the telescope is based on an off-axis Korsch Three Mirror Anastigmat. A freeform tertiary mirror is used to ensure a diffraction limited image quality for all channels, while maintaining a compact design. The segmented primary mirror consists of four tapered aperture segments, which can be folded down during launch, while the secondary mirror is mounted on a deployable boom. In its stowed configuration, the telescope fits within a quarter of the volume of a conventional telescope reaching the same resolution.To reach a diffraction limited performance while operating in orbit, the relative position of each individual mirror segment must be controlled to a fraction of a wavelength. Reaching such tolerances with deployable telescope challenging, due to inherent uncertainties in the deployment mechanisms. Adding to the complexity is the fact that the telescope will be operating in a Low Earth Orbit (LEO) where it will be exposed to very dynamic thermal conditions. Therefore, the telescope will be equipped with a robust calibration system. Actuators underneath the primary mirror will be controlled using a closed-loop system based on measurements of the image sharpness as well as measurements obtained with edge sensors placed between the mirror segments. In addition, a phase diversity system will be used to recover residual wavefront aberrations.To aid the design of the deployable telescope, an end-to-end performance model was developed. The model is built around a dedicated ray-trace program written in Matlab. This program was built from the ground up for the purpose of modelling segmented telescope systems and allows for surface data computed with Finite Element Models (FEM) to be imported in the model. The program also contains modules which can simulate the closedloop calibration of the telescope and it can use simulated images as an input for phase diversity and image processing algorithms. For a given thermo-mechanical state, the end-to-end model can predict the image quality that will be obtained after the calibration has been completed and the image has been processed. As such, the model is a powerful systems engineering tool, which can be ...

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<title>Gran Telescopio Canarias: current status of its optical design and optomechanical support system</title>

Cited by 7 publications

References 0 publications

<title>Image quality and active optics for the Gran Telescopio Canarias</title>

<title>Image quality and active optics for the Gran Telescopio Canarias</title>

Astigmatism correction of convex aspheres using the subaperture stitching hindle test

Design and end-to-end modelling of a deployable telescope

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