On Mon, 22 Apr 1996, Chi Ming Hung wrote:
> On Apr 22, 3:55am, Walter Amos wrote:
> > Subject: Iserlohn specs?
> > By now I think a number of you have seen the subtitled episodes of the 2nd
> > series showing the big battle between Fortresses Iserlohn and Geiersburg.
> This
> > battle contains the neato physics component of the 2 fortresses getting close
> > together so their mutual gravity causes their liquid metal outer armor to
> flow
> > tidally more toward their facing sides, leaving the rear side with thinner
> > armor leaving it vulnerable to fleet attack.
>
> Seems like we should consider a more basic problem: Is it possible to hold
> a liquid metal sphere together in space?
>
> If we assume the liquid metal is mercury (not reasonable because even mercury
> (and almost everything else) freezes in the near absolute-zero temperature in
> space), and assuming the radius of the fortresses are 50km, the total mass of
> each of them will be 7x10^18 kg, which will imply a surface g of 0.19m/s^2.
> The surface escape velocity will then be 138m/s, or 500kph, which is pretty
> slow. So any major splashing in the surface will cause the splashed liquid
> metal to escape into space instead of returning to the surface.
>
> Another problem is whether under the zero pressure of space, the liquid metal
> will all vaporize into space in no time. To answer this, we need the phase
> diagram for the liquid metal, which isn't provided in the novel I suppose :)
In space there's no temperature because there's no medium. So how
is the temperature in space absolute zero?
> Yet another problem is the cohesive power of the liquid metal surface. Due
> to the very small gravitational attraction, we can't expect gravity to be
> able to hold the liquid metal together when the fortresses undergo even mild
> accelerations (anything larger than 0.19m/s^2), so we must assume tremendous
> surface tension if the liquid metal is to be held together.
>
> After all these questions are answered, *then* we can start worrying about
> the tidal effects :) I tend to think it won't be enough to produce
> significant distortion in the shape of the surfaces, not enough to defend
> against Thor's Hammer anyway, but that's another physics problem... :)
>
Talking about these physics are fun but I think it's futile to do
those calculation. If the technology is advanced enough to have space
travel, it is possible that the fortress is made of materials that we
haven't discovered yet. The point is, this is a fiction :) I am not
discouraging the discussion though. Personally, I like these discussion.
Gotto Kiichi
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