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M. Lloyd-Hart, J.R.P. Angel (Steward Observatory, The University of Arizona)
The 20/20 telescope is a new concept for the GSMT with two 21 m filled-aperture elements. It has the light collecting power of a single 30 m telescope, but by moving the two elements apart and combining their images coherently, it will be capable of higher resolution. To obtain a wide field of view at the combined focus, the two apertures must be maintained perpendicular to the source. This is achieved by their continuous motions about a 100 circular track.
Both the individual and combined foci will take advantage of multi-conjugate adaptive optics (MCAO) to obtain diffraction limited fields of ~1 arcminute. At the coherent, combined focus, the PSF is the Airy pattern of the individual telescope multiplied by Young's fringes. Adaptive correction of path length for one star in the MCAO field ensures a PSF with a stable, centered fringe for all stars in the field. Images are reconstructed using generalized Lucy-Richardson methods from exposures with different baseline angles and separations. The highest resolution is 4 times that of a 30 m telescope and the images, with the same number of resolution elements as a Palomar Schmidt plate, will be rich in detail. The combination of MCAO stabilized wavefronts and long baseline should result in astrometric accuracy of better than 10 \muarcsec. The double aperture telescope is also ideal for Bracewell nulling interferometry for direct detection of extra-solar planets.
Wavefront measurements for MCAO will be made from 5 sodium and 5 Rayleigh laser guide stars and 1 natural star at each telescope. Models which reconstruct tomographically the turbulence and make correction at DMs conjugated to just 0 and 6 km, show 50% Strehl over more than an arcmin field. The tomographic method can be tested at 1/3 scale at the 6.5 m MMT telescope with just the 5 Rayleigh laser guide stars at 30 km. A similar level of correction is predicted.