-Z- (z@gundam.com)
Thu, 22 Feb 2001 18:29:40 -0800


> hmmm...i understand the propellant, but how can the
> gas not be used up? don't you burn gas to power the
> engine to run? or am i stuck in thinking about car
> engines?

The "engine" of an MS is a Minovsky-Ionescu compact fusion reactor -- about the
size of a refrigerator or washing machine -- that uses the fusion of hydrogen
and helium-3 to create a miniature star suspended in a magnetic bubble. It's
unbelievably hot but very tiny, so the heat doesn't extend very far from the
fusion point. It's also got a very powerful electromagnetic field that can be
tapped directly for electrical power through induction coils. It only takes
microscopic amounts of hydrogen and helium-3 fuel to create and maintain the
fusion reaction, so a couple of liters could last for years.

The propellant is run through the reactor, very close to the fusion reaction, so
that it is superheated to the point where it becomes a plasma -- the last state
of matter before it becomes energy. Essentially, it's more than vaporized, it's
disintegrated into subatomic particles. Propellant is thus expended beyond any
hope of recovery the instant it comes into proximity with the fusion reaction.

> what do you use as "propellant" for space mecha? you
> use air to propel you in atmospheric flight, and water
> for undersea motion. what about in space? you'd
> use rocket thrust, no? if it's rocket thrust, then
> won't you be using fuel? thus the extra fuel tanks?

A jet engine works by combining a combustible fuel with oxygen, usually in the
form of the ambient air, and burning it explosively in a tightly enclosed space
to that the force of the explosion is channeled in one direction and propels the
craft in the opposite direction. Continuous combustion creates a direction jet
of consumed fuel and air, hence the name jet propulsion. Although the fuel is
often referred to as the propellant, the words are not interchangeable.
"Propellant" is actually the combination of fuel and air -- both are needed to
create the jet that propels the craft.

A conventional chemical rocket is a jet with a self-contained oxygen supply,
usually called an oxidizer. Fuel and oxygen are both contained in tanks,
internally or externally, and combined in the combustion chamber, where they're
burned to create the same propulsive jet exhaust. Because it doesn't rely on
the ambient atmosphere for its oxidizer, a rocket can operate underwater (where
it's called a "subroc" or "submarine rocket") or in the vacuum of space.

The fusion powered rocket motors on the MS work a bit differently. Since any
fluid -- liquid or gas -- is converted to an explosively expanding cloud of ions
by the heat of the reaction, no oxidation is required. Air, water, petroleum,
maple syrup, milk, swamp gas, neon, freon, the blood of the Zeon -- it all
atomizes quite nicely, thank you. Whatever fluid you use is the propellant --
the material whose expansion in a directed jet propels the craft.

A ground unit like the MS-09 Dom can use the ambient air as propellant and an
amphibious unit like the MSM-07 Zugock can use the ambient water in the same
way -- draw it in, pump it through the reactor and spit it out as a jet of
plasma. In space, however, you need to carry that fluid with you, hence
propellant tanks.

The most common propellant is probably liquefied hydrogen gas -- the smaller the
atom, the faster it breaks down to plasma and the higher the speed of the
exhaust, and monatomic hydrogen is about as small as it gets. The next most
common propellant is probably good old distilled water -- readily available,
inexpensive, safe to handle and you can even drink some of it in a pinch. But
you can use any fluid, really, and, if you divert some of the heat of the
reaction to a preheater, you could probably melt just about any solid into a
fluid and use it, too -- uneconomical and impractical but certainly possible.
If you can burn something and use it as conventional fuel, you probably don't
want to throw it away in a fusion reaction -- burn something that's otherwise in
ert and useless, instead. Neon, xenon, helium, argon, Dr Pepper -- why, you
could even divert your waste disposal into the reactor and use, uh, stuff that
you'd otherwise be looking to drain out at your next pit stop as propellant.

> at least...i think they're fuel tanks (what else would
> you store in those tanks, if you're using air and
> water?) given that those big thingamajiggers are
> always attached on 'long-range' mecha or 'custom'
> officer's mecha like rick dom 2, gelgoog marine,
> gelgoog jaeger, cima's gelgoog, gerbera tetra, dra-c,
> aaaand....practically anything else katoki gets his
> hands on :P.

Short-range MS theoretically have all the propellant they need for their
assigned missions in external reservoirs. When you need to go farther or stay
longer, you need to add additional propellant, which means attaching external
tanks that can be tossed away when the propellant is used up.

-Z-

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