Proceedings PaperProgress of the University of Texas 7.6m Telescope Design
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The University of Texas 7.6m telescope design has evolved through several stages, each bringing added strength and efficiency to a well-planned overall approach. The current design is based on an f/1.8-f/13.5 Nasmyth beam directed through either of the elevation bearings. Recent studies include consideration of a class of correctors defined for an f/4.0 internal Cassegrain focus by Charles F. W. Harmer, optical consultant. An implementation of a truss design suggested by Meinel and Meinel has the possibility of zero coma at the Nasmyth focus. In the area of primary mirror design and support, research toward a superlative design is still in progress, primarily to take advantage of the rapidly emerging techniques of high efficiency borosilicate spin casting developed at Steward Observatory. There exist designs of ribbed borosilicate mirrors of the 7.6m class which are very nearly passively supportable. The figure stability can be made considerably better than any mirror extant with a modest number of controlled supports in the axial support mechanism. Mirror support consists of a combination of pneumatic and counterweighted flotation systems with a low bandwidth tuning system added for figure improvement. Certain classes of external loads, to be expected in a realistic observatory environment, may be obviated by such a system. There are also designs for the ribbed mirror that lend themselves to laboratory-grade fabrication, where modern NC cutting machines are not common, but are somewhat more difficult, yet not impossible, to support. One such design is a candidate for the 7.6m mirror.