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?

Heck, they are seriously looking at doing this on the ground, including
exactly the studies you describe:

http://www.eso.org/projects/owl/publ..._Messenger.htm

Several times larger, at the very least, should be possible in space.

As for radio telescopes, what are the limits are baseline
inferometry?
what would a few telescopes, each say 3km across, in solar orbit, say
1
billion km apart be able to achieve?

Good question. We know from pulsar studies that coherence is
maintained at the microsecond level all the way around the earth's
orbit. We can't measure any better now, but there is no obvious reason
why a humongous interferometer would not give resolution roughly equal
to wavelength/spacing (in radians).

We have done correlation from high orbit to earth, and it works as
expected, so single dishes up to 36,000 km diameter (!) would work.
Two of these on opposite sides of the sun would be a rather powerful
facility.

Lou Scheffer