On 20 Feb 2005 15:24:38 -0800, in a place far, far away,
made the phosphor on my monitor glow in such a
way as to indicate that:

Just seen some pictures of Hubble, and The "Very Large Telescope"
(original name) in Chile. It made me think.

With a reasonable space based industry, moon mining, metal working,
aluminium and glass production, precision engineering, how big an
optical telescope could be built in zero-g?

What are the limits? Could a 100m diameter optical telescope be built?

Possibly, but there'd be little point, since you can get equivalent
resolution with multiple-mirror systems.