Re: [ATM] Metallic Mirrors Vol 9, Issue 20

[Andy Saulietis <iss@pvtnetworks.net>]

rE:

>In the past I thought what it might be like,  making a parabolic
>mirror out of molten glass, using centrifugal force to generate
>the curve.
>
>Pour the lava like stuff on a rotating platen and let the
>centrifugal force "stretch" the glass into a concave meniscus. I
>have not a clue if anyone has ever made a mirror that way.

The Arizons Mirror Lab has been spin casting up to 8.4m
murrors for years now..the curve is within a few mm and still has to
be ground, polished, and figured the usual way.

>Then I saw these posts on metallic mirrors and wondered what it
>would be like to spin a quart of room temp mercury into a
>parabolic shape. Change the f stop by speeding up or slowing down
>the "dish"! I wonder if mercury would be reflective enough.

We had a 3m rotating mercury telescope here in Cloudcroft for a
few years..it was a NASA project to get info on orbital debris.
The Hg layer was onliu a mm or so thick, the epoxy dish was
spin cast to be approximately parabolic shape. The obsevers
were in an environmentally isolated room both to protect
them and not add to air motion on the mirror. A large CCD
with a coma corrector was exposed/read out continuously in synch with
the earth rate to reacs ~23rd mag in a few minutes effective exposure.

The debris project was successfully concluded and the scope mothballed
AFAIK.

There have been proposals to have a network of such scopes, each with about
a 1 deg fov to get more coverage by spacing the multiple telescopes a degree
apart in latitude for survey work at large aperture.




Andy Saulietis
ISS Enterprises
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