Re: starship-design: Fusion Cone Scoop

["bugzapper" <bugzappr@bellsouth.net>]

Lee sure got my attention with:

> First, drag on an electromagnetic scoop: Not an issue, since the scoop is
> _attracting_ the ionized atoms, it is generating a net pull against a
> (relatively) stationary object. There IS NO drag, you realize acceleration
> out of the scoop process instead.

Way cool! This meditation calls for some thought. Steve slowed my enthusiasm
for an EM scoop with his comments on drag, which I'd never even considered.
Your contribution does seem sensible, as did his at first, but we need
details to resolve the matter. Further comments? Anybody?

> Second, ionization of the interstellar medium:  Requires only lasers, and
> relatively low powered ones at that. See Forward et. al., too many
> references to  list here.

Listen: if you ionize only the outer sheath of the volume of gas you scoop
in, it may serve as an envelope to compress its enclosed column of neutral
gas. This gives an electromagnetic "handle" by which you can manipulate
non-ionized gas in bulk, using the ionized plasma layer to transmit the
pressure to it. This way you need less energy expended in ionization at
first. Lasers couple energy well to the task of ionizing gas, particularly
at short wavelengths, in the UV. Free electron lasers are very promising;
also frequency multiplying substances may be used. Urea is a frequency
tripler.

Since I figured a week or two ago, that free gas in space has enormous
potential chemical energy, I have looked for a way to make use of this
resource. That's why I'm interested in a method of scoop compression which
doesn't require extensive ionization of the bulk of the gas. I feel that a
real ship design will use a mixture of techniques, rather than one
all-encompassing approach to traverse space. To reject anything out of hand,
such as chemical recombination, which produces a net gain of energy, is an
error.

> Third, ignition of fusion burn: No outside ignition source required, the
> magnetic fields generated by the scoop and the velocity of the accelerated
> ionized atoms create a stellerator type fusion engine

That's also a very appealing observation. I think that another stage of
magnetic squeezing, after the ram scoop field, might be called for to induce
fusion. This makes the plasma more controllable. Also, it gives an
opportunity for a spectroscopy field prior to the fusion region. Pulling
heavy elements out of thin "air", as it were, allows the ship to actually
gain useful matter in transit. Building things en route could be very handy,
especially if the ship didn't boost all the mass used for the new
construction.

> The only catch is getting the thing up to a velocity where it will work at
> all, very much like an air breathing ramjet. And yes, the density of the
> interstellar medium is still an issue. The lower the density, the greater
> the velocity required for ignition.
>
> Lee

Your picture of a magnetic scoop with fusion burn is elegant. We ought to
get beyond fussing with theories, and progress into physical modeling.
Looking into simulation software on the fuzzy fringes of physics, I have
been able to find real treasures for free, at the big accelerator sites. Now
I'm dreaming of proving out some of my wild proposals, and yours, and
others. Lots of work, and it won't happen tomorrow. Steve brought up Rex
Finke's review, of this list's earlier results, at just the right time.
Those Fortran programs look good to build on, or to convert and build with,
and we're on our way.

Johnny Thunderbird