[extropy-chat] Space elevator numbers III

[Keith Henson]

At 08:11 PM 2/17/2007 +0100, you wrote:

>On Sat, Feb 17, 2007 at 12:30:24PM -0500, Keith Henson wrote:
>
> > If you are at the pole, you can't leave them on the ground.  And how are
>
>It seems to be just the rim (assuming, it is there at all). I presume
>the rim has an inclination.

You don't get a flat surface from gravity on an incline.

>If it doesn't, one has to lift off the sheet
>glass product from the regolith.

snip

> > you going to collect the current from the PV surface?
>
>Just like it's being done in commercial amorphous Si cells.
>I recall you mentioned the difficulties about gathering current
>from very thin silicon surfaces -- it is not a problem with a
>fractalish, dendrite type of surface electrode.

Then you have to bring the conductor materials along or make them from 
local materials.

> > If you want to make metals, you need to sort out the oxides before you
>
>Not really. Though it *is* possible to do a lot of separation of fine-grained
>material. Just melting everything and electrolysing the mess will give you
>oxygen and a number of alloys and pure metals/elements, most of which are
>not miscible, so you separate them at this stage.

I have news for you.  Silicon, iron, aluminum and magnesium all alloy in 
just about any proportions.  If you reduced the mess to powder, you could 
probably get the iron out with the low temperature carbonal process.  It 
might be possible to get the Al out with using chlorine, but I suspect you 
would have to sort out the SiCl4.  Whole thing is possible, but we are 
talking oil refinery level complexity.  And you are going to be losing 
irreplaceable gases in all the leaks.

> > reduce the metals.  There is lot of aluminum in lunar rock, but getting it
> > out as Al2O3 is going to be a major effort.  The Hall process to reduce
> > aluminum not only requires 99% aluminum oxide, but uses huge amounts of
> > carbon, which is burned up at the anodes.
>
>Most terrestrial processes are not applicable to the lunar environment,
>and vice versa. For instance, nobody would consider fractional destillation
>with solar ovens on Earth. On the Moon, it's a potentially very useful
>and workable process.

Drexler and I did considerable work on this subject, though in space rather 
than on the moon.  Vaporization up in the range where iron or aluminum 
boils is a very tricky business due to wall corrosion.  See "Vapor-phase 
Fabrication of Massive Structures in Space, Space Manufacturing AIAA 
1977."  What do you propose to use for the oven?

snip

> > Off hand I don't think there is much in regolith that hydrogen is going to
> > reduce.  Please list for my edification.
>
>Iron, titanium, oxygen.

Since "reduction" means removal of oxygen, that does not count,

>http://www.nas.nasa.gov/About/Education/SpaceSettlement/Contest/Results/2002/Aether/Construction.htm

"II.D.2.b Ilmenite Reduction

"Iron, oxygen, and titanium can readily be extracted from lunar ores 
through the hydrogen reduction of ilmenite.  The reaction is: FeTiO3 + H2 
--> Fe + TiO2 +H2O. "

Note that the titanium is *not* reduced.  While they are right about 
getting iron out of this process, there is much in that report that is just 
nonsense or was so condensed that it no longer makes any sense.

snip

> > http://en.wikipedia.org/wiki/Calutron
>
>I know about that, of course. But what I meant was something much simpler,
>like http://en.wikipedia.org/wiki/Quadrupole_mass_analyzer

It doesn't matter what hardware you use.  The problem is the ratio of 
coulombs (6.24×10**18) or amp-seconds to Avogadro number 6.02 x 
10**23.  For single ionized beam currents, you need 100,000 amp-seconds (or 
27 amp hours) plus a huge magnet to sort out a mole of some element.  Since 
the voltage is at least a kV, we are talking 27 kwh to get (say) 23 gms of 
Al.  That's about a hundred times worse than the energy to reduce aluminum, 
and does not count the efficiency which is very poor.

>A tennis court or a square mile of these

Gak.

> > They are closely related.  See the paper Eric Drexler and I wrote on vapor
> > phase fabrication.  In that case the apparatus was able to deposit its own
> > mass in metal every 8 hours.
>
>That's one heck of a productivity. Initial bootstrap can be slow, e.g.
>transfer time Earth-Moon with an ion drive takes about 6 months. It can
>take a decade or two to achieve a closure of over unity. But since this
>is a positive autofeed process, things can and will explosive later.
>
> > To this day I have a chunk of sheet metal I made in a high vacuum chamber
> > by vaporizing aluminum with a 10 kw electron beam.  I might add that
> > getting rid of waste heat is often more of a problem than energy.
>
>I'm really impressed. You certainly know about this stuff far more than
>I do. I wonder where you see the difficulties so high you would propose
>a tether, which is a far more demanding design space than a lunar
>bootstrap, objectively so.

Given the current state of the art, I don't see a space elevator as nearly 
as hard to do as a lunar bootstrap.  Further, a relatively short term 
payback in power sats possible.  If I thought bootstrap projects of this 
kind were worth the effort, I would be going after asteroids as Giorgio 
suggests rather than the moon.

> > >How many launches into high Earth orbit would it take to get to get your
> > >material (counterweight and the carbon nanotube cloth belt) up?
> >
> > The counterweight is salvaged space junk.  Brad Edwards thinks you can
> > start with an 18 ton seed cable.  The cable is not cloth and not a
> > belt.  There are no climbers, just elevator cars going up a moving cable.

>I've probably missed the URL you posted. Can you repost the link?

It's been right here in 5 parts so far.

You might also look at the Wikipedia pages for Space elevator and solar 
power satellite.

> > I am writing a novel where 99% of the population has uploaded so in the
> > long run I too see a computronium future.  This project is a stop gap
> > measure to bridge between now and full scale nanotechnology.  You can't
> > quit farming now because people will be living on electricity some time in
> > the future.
>
>There are considerable disruptions in our future short-term. There's
>already unrest brewing in Mexico over rising corn prices because the
>gringos decided to move on to bioethanol destilled from corn syrup
>melasse.

And the diversion of food into fuels is a direct result of the end of cheep oil

> > If discussing space elevators and power sats is too low tech and too near
> > term to hold on this group I will move it.
>
>No, it is interesting. Please continue here. I'm particularly interesting
>on how to improve on phased-array radiator targetting the terrestrial rectenna
>approach. There must be publications about this problem I'm unfamiliar with.
>They probably predate the world wide web, so online sources will be scarce.

They do, this material is over 30 years old and the physics is dirt 
simple.  See the section "Spacecraft sizing" in 
http://en.wikipedia.org/wiki/Solar_power_satellite

The only way you can improve the phased array antenna is to make it bigger.

Keith