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# Re: Vector Rules

From: Samuel Penn <sam@b...>
Date: Thu, 09 Oct 1997 18:56:35 +0100
Subject: Re: Vector Rules
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Status: RO

In message
<Pine.OSF.3.96.971008065731.2299B-100000@zeorymer.alf.dec.com>
Alexander Williams <thantos@alf.dec.com> wrote:

> On Wed, 8 Oct 1997, Imre A. Szabo wrote:
>
> > If you ignore friction, I'll take you on; but I want someone ten
times
> > taller then you to turn my log.  You are using same size engines to
turn
> > different size objects.  Get real.	If I have a ship 10 times
bigger,
> > I'll have 10 times bigger manuevering thrusters...
>
> You're changing the grounds of the argument /and/ introducing a new
> fallacy at the same time.  To address both:
>
> a) The whole point is that the larger vehicle /requires more thrust to
> turn at the same rate/.  First and foremost.	Secondarily,
>
> b) You assume a linear increase in engine efficency with engine mass.
If
> the drive is based on conventional technology, this will /definitely/
not
> hold, in fact, efficency will probably fall off fairly sharply with
size
> if conventional means of acceleration are used, whether that be
> reaction-mass throwers or ion drives.

My understanding is that bigger drives are actually more
efficient, though that comes from many similar discussions
over in rec.arts.sf.science, rather than from personal
experience.

Anyway, for the sake of argument, let's say that a mass 10
engine gives a thrust of X, and a mass 30 engine gives a
thrust of 2X. Obviously with this sort of relationship
between engine size and mass, big ships are going to be
slow.

Wrong!

The big ship does not mount a mass 30 engine. Instead, it
mounts 3 mass 10 engines, giving it a thrust of 3X - just
as efficient as the smaller ship.

If big engines are inefficient, you mount lots of smaller
ones. There is added complexity, which leads to less
efficiency, but such disadvantages are probably far
outweighed by the advantages of big designs.

If ships carry armour (I don't like magical shield technology),
then a big ship has _far_ less surface area to armour than
a small ship does, proportional to their volumes.

A ship eight times as big, has only four times as much
armour mass, but has eight times as much drive space.
So if armour is non-negligable, big ships can easily
be faster.

--
Be seeing you,
Sam.
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