Extending multi-aperture geometric alignment with ELASTICS to an 18 sub-aperture system
Abstract
Large diffraction-limited telescopes are required to combine high-angular resolution and large collecting aperture, enabling the observation of distant galaxies, exoplanets or even our own solar system. Given the need for these increasingly large telescope diameters, segmented apertures are a possible solution to overcome manufacturing limitations as well as launch constraints for space-based telescopes. In consequence, the individual segments of such telescopes must be aligned and phased to a fraction of the observed wavelength to enable diffraction-limited imaging. The first step in such an alignment process is typically to stack all sub-point spread functions (sub-PSFs) stemming from each individual segment on top of each other, a problem which can be reduced to the correction of large amplitude tip and tilt aberrations. This adjustment must be precise enough to bring the residual tip/tilt aberrations within the capture range of fine phasing algorithms, which can in consequence correct for small amplitude piston/tip/tilt and higher order aberrations. The Estimation of Large Amplitude Sub-aperture Tip/tilt from Image Correlation and projections on orthogonal Subspace (ELASTICS) algorithm was developed to perform the PSF stacking (geometric alignment) using only two near-focus images and a low cost computing calculation. Its performance has been demonstrated on numerical simulations and with a closed-loop alignment of a six sub-aperture system in a laboratory setting. The residuals were shown to be within the capture range of the Linearized Analytic Phase Diversity (LAPD) algorithm, a real-time algorithm for fine- phasing of the sub-apertures. We present the results of simulation and implementation of these geometric and fine alignments on the James Webb Space Telescope Optical Simulation Testbed (JOST), extending the used-case of ELASTICS to 18 sub-apertures.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23315721L