steve@nuchat.UUCP (Steve Nuchia) (12/19/89)
In article <25145@cup.portal.com> hkhenson@cup.portal.com (H Keith Henson): >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. Hey, what's a major engineering hurdle or two when you're talking about launching a ten year mission complete with at least several megatons of nuclear demolition charges? :-) I hadn't looked at that too closely, but: The energy density on the primaries is low, staying close to that at the earth, so crud reduces your collection efficiency but won't destroy the reflectors. Any secondaries will be close enough to clean. Any escaping crud is potentially valuable reaction mass, it may pay to collect it all carefully and feed it to the thrusters, which of course aren't pointed at the mirrors. Some of the crud will be oxygen, which you may as well process and tank -- it will be darned near as valuable as the steel. One could design the primaries with several layers of removable transparent film over them, to be peeled off as required (and fed to the thrusters, wouldn't want to litter :-) Good question though, thank you! Another good question: How to stop when you get there. It would not be a real popular move to use another nuke so close to the nest, and I bet a lot of people would be real nervous about an aerobraking manoeuver (gotta learn to spell) ... I guess I'll just have to keep a certain amount of slag and ease into the parking spot real gentle-like. Or have an outgoing mission bring a jumper cable and trade a bunch of momentum. Can't plan on that though. -- Steve Nuchia South Coast Computing Services (713) 964-2462 "If the conjecture `You would rather I had not disturbed you by sending you this.' is correct, you may add it to the list of uncomfortable truths." - Edsgar Dijkstra
davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) (12/19/89)
In article <25145@cup.portal.com> hkhenson@cup.portal.com (H Keith Henson) 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? -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) "The world is filled with fools. They blindly follow their so-called 'reason' in the face of the church and common sense. Any fool can see that the world is flat!" - anon
lfa@VIELLE.CRAY.COM (Lou Adornato) (12/19/89)
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)
hkhenson@cup.portal.com (H Keith Henson) (12/20/89)
davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) in responding to a question I posted, suggested a design for a melting furnace cylinder which would keep metal/rock vapor from messing up the mirrors. The original posting was about using heat from solar colectors directly to melt astroid metal, no containers were implied. Keith Henson