Abstract

At Steward Observatory, we are developing a process which will create honeycomb telescope mirror blanks of borosilicate glass. These castings which weigh approximately 25 percent of the solid alternative and have deep, up to f/1, curvature in the front faceplate are formed by spinning molten glass in an open mold. We have undertaken a development program to make a giant 8-meter diameter telescope mirror with this process. Three mirrors at 1.8-meters have been cast using a prototype furnace.¹ We are nearly ready to cast the first 3.5-meter mirror using this method. Two years of activity in preparation have built a new facility including much of the casting furnace for the large 8-meter mirrors, Figure 1. The turntable, bearing, rotation drive system, slip ring, and electrical power supply are sized and completed for 8-meter mirrors. The furnace, refractories and electrical heaters are a subset in which up to 5-meter mirrors can be cast. The furnace hearth will be expanded later to reach the circular 10-meter diameter walkway shown. The furnace lid shown hanging on the wall and the mirror castings are moved within the facility using a built-in 40-ton bridge crane. Systems testing of the furnace and assembly of the mold required to shape the mirror will continue during the summer and then casting of the 3.5 mirror in October.

© 1987 Optical Society of America