15 meter multiple mirror telescope design study

Taking as a starting point the existing Multiple Mirror Telescope (MMT), a concept for a large and more advanced instrument has been developed. It makes use of four 7.5 m diameter paraboloidal glass primaries of the honeycomb-sandwich type being developed by the University of Arizona. These are mounted quite close together in a square configuration, with their axes coaligned. Two distinct optical configurations are provided. Wide fields of view in the optical and near-infrared are achieved at four separate fast Cassegrain foci (f/4.5). Secondaries of 3 m diameter are used with three-element refractive correctors designed by Epps to give flat 1° fields. When it is necessary to work at a combined focus an alternate set of small Cassegrain secondaries is used. The light is relayed to a coherent central focus, that is made available at several Nasmyth and other instrument stations via steering mirrors. The mechanical and thermal design of the mirrors and the optical designs are aimed at an overall telescope image quality of 0arcsec.25. The use of advanced detectors and instruments now being designed to operate with this telescope is also outlined.