Tons of Molten Glass Go Into Making Mirror for Giant Telescope : The Two-Way : NPR
Technicians on Saturday are set to cast 20 tons of glass for the third of seven ultra-precise primary mirrors that will make up the 72-foot , scheduled for completion in northern Chile’s arid Atacama Desert in 2020.
The parabolic mirror will be cast at the University of Arizona’s . The molten borosilicate glass, made by the Ohara Corporation, will be spun cast at 2140 degrees Fahrenheit.
Describing the production of the first such mirror in 2005, the Lab explained the process:
The glass was “… melted in a rotating furnace until it flowed into a honeycomb mold. Once the glass had cooled and the mold material was removed, scientists at the lab used a series of fine abrasives to polish the mirror, checking its figure regularly using a number of precision optical tests.”
How precise?
Once the mirror cools, and the polishing complete — a process that is expected to take a year — it will be accurate to within 1/20 the wavelength of light, or put another way, “one part in 10 billion in terms of precision manufacturing,” according to Patrick McCarthy, the project’s director.
More: Tons of Molten Glass Go Into Making Mirror for Giant Telescope : The Two-Way : NPR