I just had a [genius | crackpot] (DELETE ONE) idea. Maybe someone's already thought of it, but as far as I can tell there's no mention of it anywhere. Maybe just maybe I had an original idea for once, or maybe it's old and everybody's got that T-shirt, because it doesn't work.
Anyway. Liquid mirrors have been done already - you get a big round dish, with a roughly paraboloid bottom, put some mercury in it, and spin it. Luckily, liquids form perfect paraboloid surfaces when you spin them. Here's the 4 metre International Liquid Mirror Telescope, for instance.
The trouble is, you can only point the damned thing straight up. Not so useful, but compared to forging, polishing and silvering giant slabs of glass, you can get a large mirror for drastically less money.
So, here I am on one of my Wikipedia trails reading about Fusible alloys, which are eutectic metal alloys with very low melting points, usually some mixture of low melting point metals such as bismuth, lead, tin, gallium and indium. One of them is called Field's metal, which melts at a very pedestrian 60°C.
Get to the point already
Take one liquid mirror container, fit some hot water plumbing to it, heat it up to 60°C and spin it up using one of these molten solder alloys. Then slowly cool it to room temperature until it solidifies. Voilà, one solid metal paraboloid mirror.
- All the cheap production benefits of LMTs
- Less toxic, no mercury
- Solid mirror, can point it where you like
- Easy and cheap maintainance and repair - just re-spin it, or add to or replace the alloy.
Perhaps one might need to experiment with the temperature cooling profile and monitor the metal as it solidifies so that it maintains its surface shape, crystallographic properties and reflective surface.
Perhaps one may need to prevent oxidation of the surface, depending on the alloy. Perhaps seal it in a glass chamber and evacuate or fill with argon, periodically re-spin the surface, or periodically refresh the metal alloy.
Anyway, you read it here first. I can't be bothered patenting it, because I need a prototype, and thousands of dollars =)