liquid mirror telescopes

[ving (David)]

liquid mirror! now thats weirding me out!

if they made it out of coffee, you would have to top it up all the time.
how the heck does it work anyhow. zero gravity wouldnt be any good would it? it would just float around?

[bojan]

Originally Posted by Dooghan

One problem I can see with it is the sun is going to heat up the tube. That heats up the gas inside the tube and changes the shape of your mirror. Then when the tube goes into the earth shadow you've got the reverse happening. I also wonder if you air turbulence in the tube would be a problem?

Oh yes, everything you mentioned would be an issue.. but not necessarily the un-solvable problem... today we have ground-based telescopes with adaptive optics that have better resolution than Hubble... So, I am sure there is a way to compensate for all that :-) .
The beauty of this may be that virtually there is no limit to a size.. Also, if longer wavelengths are used (far IR or even /u-waves) then the distortion of optics is not an issue that much, but the size is, definitely.

[TheCrazedLog]

Bummer if you accidentally turned your scope upside down....

[g__day (Matthew)]

Some interesting links:

http://www.abc.net.au/science/k2/moments/s64751.htm

http://www.math.iupui.edu/m261vis/LMirror/LMirror.html

http://www.astro.ubc.ca/LMT/lm/index.html

What you need is a liquid spinning mirror you can snap freeze without shattering or changing the shape of the material - hard asks. Imagine if you could spin say silver this way at say 400 degrees Kelvin (or whatever) - then span freeze it whilst its still rotating without loosing its perfect surface. If it was bonded to its spinning base - which itself was structurally extremely rigid - you could simply lift this entire structure and mount it like any normal large telescope - hey presto - large perfect mirror very, cheaply formed.

If the mirror device was inside a bessel oven - and continued to rotate at say 3 turns a minute whilst the parabolic arc formed, and could be instantly snap frozen (there is the trick) without rippling the surface - way to go. You might be able to do this if the film of liquid metal was very, very thin - e.g, < 100 microns thick. If you heated and spun say 600 grams of silver in a 3 metre wide circular block that transfered heat very well (e.g. copper) and was already roughly parabolic in shape - you might be able to run collant liquid through the block and instantly snap freeze the silver.

Be really tricky but if you find a way to do it that works - be fantastic!

[citivolus (Ric)]

I wonder if there are any high viscosity, highly reflectivity fluids that would allow a tilt without shifting.

This brings up a question I have had for a while, and that is are metal mirrors practical at low thicknesses if backed with a supportive substrate? In other words, could you create a metal mirror using this method and then silver it, say using immersion, to overcome the problems associated with crystallisation? Or will using a metal introduce thermal expansion/contraction issues?

[wasyoungonce (Brendan)]

Yeah but spinning a liquid will create an inverted truncus (-1/x^2) shape not a parabola.

I think?