metal or ceramic foam

>>>That makes sense, although it seems like the energy to escape the gravity
well of the Moon might still be worthwhile when compared to the energy
required to escape the Earth's gravity well, plus you still gain the
benefit of Jay's atmosphere-less manufacturing ability. I'd have to see
numbers.>>>

The problem with manufacturing on the moon, is not simply a problem of
exporting. Many of the feedstocks and a great deal of heavy manufacturing
equipment (or at least the more complex mechanical parts required to make that
equipment) would have to be imported from Earth or Near Earth space.
I think this argument comes back to what O'Neill said, 'Why go to so much
effort crawling out of one gravity well, only to crawl into another?' One of the
advantages of being in orbit, is that you are half way to anywhere else in the
solar system, in terms of D-v. You will also never again require high-thrust
propulsion systems. In my mind, it makes sense to keep the amount of materials
that are sent to the moon, to an absolute minimum.

Tony