Dave S:
Henry S:

A factor of 100 improvement would bring it down within reach of reason,
but a 1km mirror is beyond what's reasonably practical in the near future.
Eventually, yes.

Is there any indication of how big a bubble could be blown in
microgravity to create an Al or Au sphere, that could be sectioned to
provide several spherical mirrors (yes, I know, there's another conic
section that is better for focusing; ignore the man behind the
curtain for the moment) ?

Surface tension vs expansion rates and cooling issues are the obvious
factors; using a chemical rocket for the blowing (and maybe for
heating the melt) might give some ability to sustain an elastic
temperature, though, by filling the bubble with hot exhaust.


Personally I don't see a problem manufacturing a 1 or 2km conic section
using an inflatable structure. Accuracy is less a problem for focusing
power. A ten-meter spot size seems about right. Using a more accurate
semi-ridged mirror to focus down to a 20 cm spot. Rather a nozzle-bell
shape with a spherical clear end, much like a flashlight reflector.

One-half mill Kapton with a sputtered silver/gold reflector layer and
the end with a UV stabilized PET with a selective filter coating under
an anti-reflective coating. After the main area is inflated a grid of
tubes would be inflated on the mirror section and then the whole mirror
section plasma-sprayed with aluminum. Once completed the structure
should have the pressure reduced to a minimum to avoid the risk of
overpressure.

Current Vacuum sputter coating technology limit the width of gores to a
two-meter width and length to ~8km. Dupont's large width for Kapton is
54" but 2 meters should be negotiable with a very large order.
Fabrication would have to be planet side.
--
Anvil*

Personally I'd rather see such a structure used as a solar furnace to
scrap space junk into useable forms.