In sci.space.policy wrote:
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?
what would it see?

Hmm.
100 light years = 3*10^8m/s * 3*10^7s * 100 = 9*10^17m.
For 1m resolution at that range, in the visible you're looking at about a
diameter of 10^12m, or an area of around 10^24m^2.

For an average thickness of 100nm, this is 10^17m^3, or for aluminium,
or a cube of about a thousand kilometers across.
I'd guess this to be about the aluminium content of the moon, plus a few
other bodies.

This would take a fairly reasonable space industry.