-Z- (Z@Gundam.Com)
Sat, 27 May 2000 15:55:07 -0700


At 09:32 5/27/2000, you wrote:
> Assuming there's still an atmosphere in it, will the change in heat,
>and hence pressure, blow the windows out? Stress along the weak lines of the
>structure might also give way due to this, hence breaking the cylinder out.

The cylinder was designed to contain a circulating atmosphere with
Earth-normal pressures from an all-encompassing vacuum. It has to have
some "give" for both expansion and contraction. By the time the internal
atmosphere has heated up to the point where it becomes problematic, you'll
already have had structural failures from other causes. As with the
Titanic, there'll be all manner of interesting breakups before the thing
finally comes apart.

>I guess a good number of colony parts must have either ended up decorating
>the ocean floors of either the Pacific or the Indian Ocean. Did the event
>happen along the East-West axis, or the North-South? Or.. straight down? =)

When I first started thinking about this, I envisioned it was having been
pushed into a polar orbit, travelling north as the Earth turned east, so
that it's course toward Jaburu was extended over North America, over the
top of the world and thence southward to Sydney.

But now I have all these reprints of original Gundam fan and professional
books and that's not what happened at all. Instead, the space colony
Island Iffish is pushed out of Side 2 (L4) into a slingshot orbit around
the Moon (see also Island Ease in 0083 -- did these guys do *anything*
original?) and into a decaying west-to-east orbit that will intersect the
Earth's surface near Jaburu. The plan goes awry when the Federation fires
on it as it passes over the Persian Gulf. It splits into four parts, the
largest of which hits Sydney, while the other three rain down across North
America.

> Won't the spin contribute to stresses, especially along the mirrors?

Spin might contribute to the torque force if the spin were being applied or
opposed by an external force, but the colony is either spinning as it
always has or not spinning, having already been spun down preparatory to
the drop. The only forces at work are those of atmospheric friction and
momentum and the different between a spinning or non-spinning colony are
negligible.

The mirrors are toast in any case, I think. It's doubtful that they can
remain attached. If somehow they do, they'll act as rotary drogues, at
which point you'll see the kind of torque and shear forces that you
suggest. But that torque and shear will be to the attachment points, not
to the cylinder as a whole.

>Although the colony is designed to spin at a constant rate, it isn't exactly
>designed to reenter atmosphere; dozens of things can increase or decrease
>the rotation of the colony during reentry.

Consider the inertia of a 32 km (20 mile) by 6.4 km (4 mile) cylinder. You
don't just rev it up and down like a lathe.

> Actually, in 0083, they were talking about a Critical Interception
>Point. (IIRC, of course) I don't think this point refers to a point where
>the colony could still be stopped; the masses involved and speeds may be too
>great for the Albion to do much about.
>
> I've always been of the impression that this CIP is the last
>possible location where the Albion could nudge the colony so that it either
>miss Earth or skim the atmosphere rather than crash. Where the colony will
>end up in this case is anybody's guess..

You are correct. The Critical Intercept Point (or, as I prefer, the Point
of No Return) is the orbital altitude below which it's no longer possible
to apply enough acceleration to deflect the colony from intersection with
the Earth's surface. As it is, the colony does a long transit through the
atmosphere, passing over Jaburu low enough to be clearly discernable by the
man in the street.

This, by the way, MUST be a northerly transit of a polar orbit, from
central Brazil to central United States -- unless the colony went west,
completely around the world, before coming down in Kansas.

-Z-

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