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From: lfa@VIELLE.CRAY.COM (Lou Adornato)
Newsgroups: sci.space
Subject: Re: Space industry projects: dismantling moons and asteroids
Message-ID: <8912191558.AA01690@aldrin.cray.com>
Date: 19 Dec 89 15:58:18 GMT
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zaphod.mps.ohio-state.edu!rpi!crdgw1!crdos1!davidsen@tut.cis.ohio-state.edu  (Wm E Davidsen Jr) writes:

>| About 10 years ago Eric Drexler and I wrote a paper on furnaces to 
>| process metals in space.  I would be interested if Steve has any new 
>| ideas on how to get heat to the metal *without* curding up the mirrors
>| with various rock and metal vapors.  Keith Henson
 > I had assumed that if there were a problem in this area it would be
>transporting the furnace. If the material to be melted were placed in a
>cylinder of, say, ceramic, heating the cylinder would cause the
>outgassing to come from the ends with some reasonable velocity. If the
>mirror were on the side of the cylinder it would be at right angles to
>the outgassing as should get minimal depositing.
>
>  This is so simple and obvious that I must be missing something. What
>is it, please?

Ummm...ok

1)The original idea was to dismantle an asteroid by positioning a mondo
  mirror and melting it down.  Now you need to dismantle the asteroid, put the
  pieces into a ceramic cylinder (composition unknown), and _then_ melt it.  Why
  bother with the melting if you've already powdered it enough to put it in a 
  can?

2)There is also a problem of a localized hot spot on the cylinder (pretty 
  similar to one of the SDI concepts), partially solveable by putting a spin 
  on the cylinder, better solved if you sweep the focus along the cylinder's 
  axis of spin (kind of like a fishing reel).

3)The heat transfer mechanism (from cylinder wall to material inside) is going
  to be pretty strange, with no predictable convection and conduction more or
  less proportional to how finely you've pulverized the sample.  Not only that, 
  but any outgassing at "sufficient velocity" will probably throw out large 
  amounts of the melt.  Again, a spin would help, allowing the melt to cling to
  the cylinder walls (and be drawn off into some kind of baffle arrangement),
  and for the gasses to head for the spin axis.  Problem is, any imbalance in 
  the outgassing is going to cause the spinning, hot cylinder to precess, and
  I can't imagine an active attitude control system operating at those 
  temperatures for long. 

One big advantage of the spinning cauldron is that you could separate metals
by density, and, just like on Earth (and in corporate life), all the scum will
rise to the top.  But the precession problem might be more trouble to fix than
it's worth.

I think a better solution would be to use a larger mirror farther out, and 
possibly place a grid next to the path between the mirror and the rock.  
Charge both the mirror and the rock positively in respect to the grid, and 
hope that the crud heads for the grid and not the mirror.

Lou Adornato    |  Statements herein do not represent the opinions or attitudes 
Cray Research   |  of Cray Research, Inc. or its subsidiaries.
lfa@cray.com    |       (...yet)