To mix, grind and polish a mirror for a major telescope often takes years, judging by cases like the GMT project. Are there any emerging technologies that would reduce the time, cost and effort to make large aperture mirrors?
I think having such a long period of time between commissioning and first light is the cause of most of the problems that plague big telescope projects. While the mirrors are slowly settling in the blanks, funding can dry up, competing projects emerge etc. I think only the first of the Giant Magellan Telescope's eight mirrors has been cast. At this rate, it probably won't see first light within the decade, if ever. Added to that it now has to compete with the Thirty Meter Telescope (which has major funding and scheduling problems of it's own) and the EELT (which has been whittled down from its grand 100-meter original OWL concept to 39 meters last I checked). I wouldn't be surprised if the EELT, which is relying on several European governments for funding, doesn't get built at all due to the financial mess of the Eurozone. Even if it did, the time it would take to fabricate all those mirror segments puts first light depressingly far away.
I'd be interested to know if there are any new technologies being explored to shorten the time and reduce the cost of this process.