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re: fuel chat

From: Sid Jones <sjones@n...>
Date: Fri, 27 Nov 1998 17:44:17 -0500
Subject: re: fuel chat

On Fri, 27 Nov 1998, Tom Anderson wrote:

>oooh, *that* kind of fusion drive. right. there are two types of fusion
>drive, which for want of a better term i will call internal combustion
>external combustion.

[snipped for brevity]

Right.	The problem is that the internal-style combustion and NERVA
rockets son't produce the thrust needed to get anything anywhere.  Their
Isps are down around 10-20 thousand km/sec.  At that low an efficiency,
like 80% of the rocket has to be fuel just to get from Earth to Mars- 
not exactly the ship design described in the FT rules.	Ion engines put
out (note-  I'm still going by the sources mentioned last time) around
160 km/sec, while an He(3)-D fusion pulse engine puts out on the order
of 8,000 km/sec, an efficiency good enough to push around those NAC
carriers and not worry about pushing around a bunch of liquid hydrogen. 
These engines have already been designed (in theory at least) and work
off principles that don't change as your technology improves since
they're based on basic chemistry and the energy levels contained in the
atoms used (at least until you start getting into the grav-drive realm,
but then you discard the inefficient old reaction drives in favor of
something a little faster).

I guess what got me about the whole photon-drive thing is that if I
could focus enough photonic energy to drive a battleship around, I think
I'd rather sit in one place and spend my time pointing my drive at
soon-to-be-extinct enemy ships in my general neighborhood....



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