Phasing a segmented telescope

Paykin, Irina; Yacobi, Lee; Adler, Joan; Ribak, Erez N.

doi:10.1103/physreve.91.023302

Cited by 22 publications

(11 citation statements)

References 35 publications

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“…In fact, for different wavelengths, the position coordinates of the MTF sidelobes are different. However, the coordinate difference introduced by different wavelengths is very small when the bandwidth is much smaller than the central wavelength [ 26 ], so the position coordinate

with different wavelengths can be approximated as

. The effect of different wavelengths is mainly reflected in the e-index part.…”

Section: Theoretical Relation Between the Piston Error And Amplitudes Of Mtf Sidelobesmentioning

confidence: 99%

Piston Error Measurement for Segmented Telescopes with an Artificial Neural Network

Yue

2021

Sensors

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A piston error detection method is proposed based on the broadband intensity distribution on the image plane using a back-propagation (BP) artificial neural network. By setting a mask with a sparse circular clear multi-subaperture configuration in the exit pupil plane of a segmented telescope to fragment the pupil, the relation between the piston error of segments and amplitude of the modulation transfer function (MTF) sidelobes is strictly derived according to the Fourier optics principle. Then the BP artificial neural network is utilized to establish the mapping relation between them, where the amplitudes of the MTF sidelobes directly calculated from theoretical relationship and the introduced piston errors are used as inputs and outputs respectively to train the network. With the well trained-network, the piston errors are measured to a good precision using one in-focused broadband image without defocus division as input, and the capture range achieving the coherence length of the broadband light is available. Adequate simulations demonstrate the effectiveness and accuracy of the proposed method; the results show that the trained network has high measurement accuracy, wide detection range, quite good noise immunity and generalization ability. This method provides a feasible and easily implemented way to measure piston error and can simultaneously detect the multiple piston errors of the entire aperture of the segmented telescope.

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with different wavelengths can be approximated as

. The effect of different wavelengths is mainly reflected in the e-index part.…”

Section: Theoretical Relation Between the Piston Error And Amplitudes Of Mtf Sidelobesmentioning

confidence: 99%

Piston Error Measurement for Segmented Telescopes with an Artificial Neural Network

Yue

2021

Sensors

View full text Add to dashboard Cite

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“…A wavefront-sensorless approach was also considered for the phasing the telescope segments, similar to the method described by Paykin et al [6]. In this method, the position of the mirror segments is optimized such that the sharpness observed at the image plane is optimized.…”

Section: Overview Of Existing Technologiesmentioning

confidence: 99%

“…Since the telescope is looking at polychromatic sources, the optical performance at the points where these maxima occur is significantly lower than when the global maxima has been found. To avoid these local maxima, nondeterministic algorithms can be used, such as Simulated Annealing [6].…”

Section: Overview Of Existing Technologiesmentioning

confidence: 99%

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Active correction system of a deployable telescope for Earth observation

Dolkens

Marrewijk

Kuiper

2019

International Conference on Space Optics — ICSO 2018

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Deployable optics can bring major cost reductions to the field of Earth Observation. One of the key challenges in the development of a deployable optical system, however, is making sure that it can meet its performance targets following its deployment. In this paper, a novel active correction system for a deployable telescope is described. The correction system co-aligns and phases the primary mirror segments and subsequently corrects remaining aberrations using a deformable mirror. A novel phasing sensor called PistonCam can bring telescope segments into phase while the telescope is staring at extended scenes. By only sampling segment boundaries, PistonCam is able to isolate piston and tip/tilt errors which allows the errors to be corrected more effectively. After phasing process has been completed, a moving scene sharpness optimization technique is used to correct the remaining aberrations with a deformable mirror, The technique does not require a constant scene, unlike existing sharpness optimization techniques. As such, the telescope does not need to track a ground scene during the correction process. The technique can also be used for continuous correction of telescope deformations. The active optics system offers robust aberration correction, is computationally inexpensive and requires limited additional optical hardware.

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“…To optimize the sharpness criterion, several non-systematic optimization methods can be used, such as the Stochastic Gradient Descent method, the Nelder and Mead Simplex method [6] and the Simulated Annealing method [7]. Each of these methods has been simulated using FORTA.…”

Section: A Calibration Based On the Sharpness Criterionmentioning

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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Phasing a segmented telescope

Cited by 22 publications

References 35 publications

Piston Error Measurement for Segmented Telescopes with an Artificial Neural Network

Piston Error Measurement for Segmented Telescopes with an Artificial Neural Network

Active correction system of a deployable telescope for Earth observation

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

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