Manufacture of segments for extremely large telescopes: a new perspective

We consider the production-route for aspheric segments for extremely large telescopes. The classical stressed-miffor polishing route followed by ion-figuring is introduced, leading to consideration of a new route combining precision aspheric grinding with computer-controlled polishing. We present estimates of process times in the polishing and grinding phases, based on scaling previous experimental results, and outline the next stage of the process development project. We are optimistic that the new route will be capable of faster processing with reduced risk, and will free the telescope and enclosure designers from the dimensional constraints imposed by segment asphericity.