SF rocket propulsion?

Be it resolved that currently feasible rocket propulsion systems
are too pathetically weak for an action-packed pulp-style SF novel,
what is the *minimum* handwaving we can do to rectify the situation?

As always the danger is that handwaving a scientific breakthrough
that is too large, one will quickly run afoul of the law of unintended
consequences.

Rockets work on the principle of Newton's third law, that is,
you throw junk backwards in order for the reaction to propel
the ship forwards.

Thermal rockets do this by heating the propellant. For reasons
that I do not fully understand, this works best with low mass
propellant, like hydrogen (better with Heinlein's "single-H",
or "handwavingly stabilized monoatomic hydrogen).

But the limit is that at some point enough waste heat will
leak through the thermal control system to vaporize the rocket engine.
This leads one from solid-core nuclear thermal rockets,
up through liquid and gas core, ending with Orion style
engines where the "engines" are allowed to vaporize in
the nuclear explosion.

Ion drives use Newton by electrostatic particle acceleration.
Unlike thermal rockets, these work better with more massive
propellant (I read about one design that used Buckyballs for
propellant).

The limit here is on propellant mass flow, which translates
into low thrust.

John Schilling says:
And it suffers from the same critical thrust-limiting problem as any
other ion engine: since you are accelerating ions, the acceleration
region is chock full of ions. Which means that it has a net space
charge which repels any additional ions trying to get in until the
ones already under acceleration manage to get out, thus choking the
propellant flow through the thruster.

The upper limit on thrust is proportional to the cross-sectional area
of the acceleration region and the square root of the voltage
gradient across the acceleration region, and even the most optimistic
plausible values (i.e. voltage gradients just shy of causing vacuum
arcs across the grids) do not allow for anything remotely resembling
high thrust.

Erik Max Francis says:

You can only increase particle energy so much; you then start to get
vacuum arcing across the acceleration chamber due to the enormous
potential difference involved. So you can't keep pumping up the
voltage indefinitely.

To get higher thrust, you need to throw more particles into the mix.
The more you do this, the more it will reduce the energy delivered to
each particle.

It is a physical limit. Ion drives cannot have high thrusts.

So just to start brain storming, what if we handwave some
sort of rocket drive where the propellant is accelerated,
say, by some very limited form of artificial gravity?

What kinds of limits can be piled on that would hopefully
prevent unintended consequences but still allow a viable
drive? (maybe if the range of the artificial gravity
was limited to a few millimeters or something similarly absurd)

Would such a drive be just a fancy version of an electromagnetic
mass driver, with the same limits?
.

Relevant Pages

  • Re: SF rocket propulsion?
    ... As always the danger is that handwaving a scientific breakthrough ... Thermal rockets do this by heating the propellant. ... Ion drives use Newton by electrostatic particle acceleration. ... The upper limit on thrust is proportional to the cross-sectional area ...
    (rec.arts.sf.science)
  • Re: A small rocket-science brain teaser
    ... > This occurred to me during a recent argument over rockets and I ... It depends on the burn time, the thrust and the mass. ... The smaller the mass the greater the terminal velocity. ... The problem you run into is that the propellant is part ...
    (sci.physics.relativity)
  • Re: BELLS PARADOX FOR DUMMIES
    ... Yet the string between the rockets ... discretizes the acceleration by talking about firecrackers exploding ... (as measured in their current rest frame). ...
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  • Re: Electrogravitics is Reality!
    ... was launched by a rail gun type device, ... The fact that SSTO is regarded as impossible is the fact that none have ... What worked for rockets that rose a couple of hundred feet in the air ... an F-15 can take off like a shot out of a gun with a 1 to 1 thrust to ...
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  • Re: height of my rocket - help!!!
    ... I really like rockets and drivers that develop their thrust so quickly. ... I had previously dried my strontium nitrate and crushed it to a fine ... I make the nozzle 7/8" thick. ...
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