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A novel method nicknamed ELASTIC is proposed for the alignment ofmultiple-aperture telescopes, in particular segmented telescopes. It only needsthe acquisition of two diversity images of an unresolved source, and is basedon the computation of a modified, frequency-shifted, cross-spectrum. Itprovides a polychromatic large range tip/tilt estimation with the existinghardware and an inexpensive noniterative unsupervised algorithm. Itsperformance is studied and optimized by means of simulations. They show thatwith 5000 photo-electrons/sub-aperture/frame and 1024x1024 pixel images,residues are within the capture range of interferometric phasing algorithmssuch as phase diversity. The closed-loop alignment of a 6 sub-aperture mirrorprovides an experimental demonstration of the effectiveness of the method.  Author accepted version. Final version is Copyright 2017 Optical Society ofAmerica. One print or electronic copy may be made for personal use only.Systematic reproduction and distribution, duplication of any material in thispaper for a fee or for commercial purposes, or modifications of the content ofthis paper are prohibited.

Large amplitude tip/tilt estimation by geometric diversity for multiple-aperture telescopes