Re: USA urges scientists to block out sun

On Jan 31, 9:51 pm, "steve" <stephen.colbou...@xxxxxxxxxxxxxxx> wrote:
Just for those who do not know

GBO = giant birefringent optics

http://www.3m.com/about3m/technologies/lightmgmt/learn/overview.html

I feel that it would be possible to reduce the weight of the film down
to about 1 tonne per/sqkm

We can also build much larger mirrors.
All we need is one mirror 1000km by 1000km and at 1 tonne per/sqkm
this is going to be 1 million tonnes.
This would probably not be practical and any damage could ruin the
whole of our shield.
I would aim for mirrors of 100km diameter requiring approx 130
mirrors to be built.

The size of the mirror is a function of how it is to be controlled.

The real mass driver is the thickness of the mirror material - 1 tonne
- 1,000 kg - per sq km, implies a mass of 1 milligram per square
meter.

GBO material is on aveage 1.2 tonnes per cubic meter.

This implies a little less than 1 micron thickness - TOTAL - - so, in
my design,which is quite specific and on its way to the patent office,
is a lenticular structure, consisting of two sheets stabilized and
erected by gas pressure.

One film is transparent, the other film by dint of its birefringent
structure, quite reflective.

The wavelength of visible light ranges from about 800 nm to 300 nm.
GBO to be highly reflective requires dozens if not hundreds of
birefringent layers be sandwiched together.

Therefore, if the structure be solid, (which it need not be) you need
at least 25 microns per layer - there are also issues of porosity and
so forth - and stability in the space environment.

These are all open issues,

But I believe there is a strong reason to believe that 50 um - at
least for 1st generation mirrors - is the practical design limit. And
any practical system that seeks to make a buck in this arena should
look at that as a good target.

This doesn't stop a portion of one's activity, around 10% of the total
activity, from being directed at extending this limit since it is a
critical cost driver.

And what to get below 100 mg per sq m this entails is some sort of
space structure on the scale of light. A structured material on the
nano-scale much like a butterfly wing, with space rather than solid
between the optically active layers. This would reduce teh total
mass. A fresnel plate in 3D so to speak.

Relative to these sorts of structures, its quite easy to make thin
film GBO. And 100 mg per sq meter is quite GOOD! haha.. 1 tonne per
hectare! Wow.

The investment in rockets, in lift capacity to ship this much material
to L1 in 3 km diameter mirrors (which is quite unweildy, in its own
right) is well worth the effort.

But, yes, if we're talking about spending trillions of dollars on
infrastructure to loft a planet sized mirror to L1 - it is well worth
spending billions if not hundreds of billions of dollars - on research
to make stable, long lasting structures that might be 10% or even as
you suggest 1% of the mass of the GBO technology I am proposing. It
has a huge payoff if successful, and we can get by with 8 ships,
instead of 750! lol.

I don't know that such research will bear fruit. I am only saying
that with 100 mg per square meter, money can be made, and a private
operation can be contemplated that has a reasonable expectation of
making significant money.

At 10 mg per square meter, or less, profits are beyond the dreams of
avarice, since very little must be invested in rocket fleets - so
ABSOLUTELY - 3d nanostructures that implement highly reflective
surfaces made of diamondoid type structures - might be worth doing.

Whether diamondoid structures of this type can be made cheaply as
trash bags, is another question. But once we know how to do a thing,
automation typically reduces things to the cost of its components -
and here we're talking carbon. Which is pretty damn cheap on Earth.

So, yeah, reduce the mass of highly reflective mirrors to 1 mg per sq
meter, this means a solid film of about 1,000 micron -total- which
implies a diamondoid nano-structure - not a solid - that is very
lightweight, and not able to be structured by gas pressure, since its
a open as chicken wire on the atomic scale - but quite reflective due
to its 3D structure

http://micro.magnet.fsu.edu/optics/olympusmicd/galleries/butterfly/blackandwhiteheleno1.html

Of course, in lieu of gas pressure there is the potential of
electrostatic pressure - electrets - so, a transparent nanostructured
'film' might hold a similar charge as a reflective nanostructured film
- which in zero gee would give us the desired shapes when bound
together mechanically.


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