Re: [gundam] Civilian Space Travel

Mark Simmons (
Wed, 31 Mar 1999 11:00:59 -0800

Matt Hanyok writes,

>What about nuclear engines? I know people made a big fuss about a rocket that
>was launched a year or so back because it had a nuclear power source...
>couldn't some kind of reactor work, or do I just have a misunderstanding of
>the way those things work?

  Yep, you'll get much further with a nuclear rocket engine; in a nutshell,
these give you a higher exhaust velocity and hence greater "fuel
efficiency." Better engines enable more aggressive flight patterns, which
is why we presume that in emergencies Gundam warships might be able to get
about the Earth sphere faster than the propellant-conserving spacecraft of

Lim Jyue writes,

> I'm not qualified to say much, but a nuclear REACTOR can only
>provide power, not thrust.. current tech require a propellant, using
>action-reaction to push the vehicle forward, but nuclear reactors generate
>power by heating water/medium (as far as I know..=) to drive a turbine.

  But by the same token, the heated water (or whatever) can simply be
sprayed out of the back end of the spacecraft to create a working rocket.
This is the technique used in Gundam, and it's significantly more efficient
than chemical rockets.

  When modern-day researchers talk about nuclear rockets, they typically
mean "leaky reactor" designs where the plasma within the reactor is allowed
to spray out though the back of the ship. For obvious reasons, this can
only give you a pretty small amount of thrust, but the fuel efficiency is
much higher dues to the plasma's high temperature (and hence high exhaust

  You can combine both approaches by mixing in water or some other bulk
medium with the escaping plasma, trading off raw thrust versus fuel
efficiency. In this sense, Gundam's non-leaky designs are at the extreme
end of the scale, giving plenty of thrust but only modest gains in

>But there was this idea to detonate _nukes_ to propel a spacecraft...

  Yep, and this "nuclear pulse propulsion" is used in Gundam as well. In
essence, you spit teeny fusion fuel pellets out of the back of the vessel,
then use lasers to crush the pellets and trigger a brief fusion reaction.
Conventionally, a metal "pusher plate" protects the ship and directs the
blast backwards, but since Gundam's helium-3 fusion yields no neutral
particles, you should be able to do most of this with magnetic fields.

  When you perform this operation a couple of hundred times a second, you
get a continuous and highly efficient source of thrust. In Gundam, the
system is used to move asteroids, Jupiter energy fleet vessels, and other
large, slow-moving objects for which rapid acceleration is less important
than fuel efficiency.

>Anyway, the hoo-haa about the spacecraft you mention was because pple
>were afraid a leak will contaminate the atmosphere.. not an unwarranted
>fear, but still..

  Actually, I saw a news item the other day about Russian scientists who
warn that chemical rocket engines are destroying the ozone layer (what with
all these satellite launches), so space travel may be ecologically unsound
any way you look at it.

  In other downer space news, a recent Sunday paper feature described local
researchers who plan to beam energy _up_ to satellites - apparently, solar
panel arrays are too fragile and vulnerable to damage from orbiting junk.
If this is really the wave of the future, it's the death knell to Gerard
O'Neill's dream, in which orbiting satellites would beam cheap solar power
down to an energy-starved Earth, rather than vice versa...

  By the way, these researchers plan to use lasers rather than microwaves
for energy transmission. The idea is to set up a huge Solar System-style
grid on the ground, and focus the transmission on the satellite; in
between, the beam would be too diffused to hurt anyone. This mechanism too
is the opposite of O'Neill's, which had a small microwave transmitter on
the satellite and a huge receiving array on the ground.

-- Mark

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