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starship-design: Fusion Cone Scoop

The accelerators we are familiar with, produce a concentrated linear beam, a
ray. If we could spread out our beam of accelerated particles, in a surface
of conical shape, each particle trajectory deflected by the same angle, we
could build a cone of accelerated particles. Made with light ions, this
cone, open forward, traverses space with the ship. Diffuse nuclear fusion
reactions occur, as the accelerated particles collide with particles of the
interstellar medium. Fusion pushes, as do all energy-releasing processes.

The cone of fusion traversing forward establishes a shock front, which
pushes progressively inward on both neutral gas and plasma, to serve as an
effective ram scoop. Though drag forces may occur on the ship, in its own
interaction with the medium, this drag is proportional to the ship's cross
sectional area, straight hydrodynamics. No back pressure is felt by the
accelerator, from remote fusion events many kilometers down its beam. So no
drag forces are due to the compression event, but all retarding forces are
from direct interactions of the ship with the onrushing column of gas.
Producing the cone by sending out light ions forward gives a decelerating
force, but (hopefully) this may be negligible compared to the chemical
energy released.

I think I'm on the trail of a straightforward ram scoop design. It hinges on
a lot of presumptive physics, though. My guesses, about might happen in
physics under exotic circumstances, should be treated as such, and carefully
examined by anyone who knows better.

1) A high energy beam, of light ions, will produce diffuse, energy-releasing
fusion reactions as it traverses the sparse interstellar hydrogen gas.

2) The ion beam sheet, formed into a cone, will, by remote induced nuclear
fusion, mechanically compress the interstellar gas into a jet, directed at
the bow of the starship.

3) The approaching column of gas, in laminar flow, is yet too sparse to
recombine chemically, until its periphery is further ionized, by electron
beam (or whatever's handy.)

4) This sheath of plasma, surrounding the neutral gas jet, is further
compressed magnetically, compressing its contained neutral gas.

5) In this final compression, the local atomic hydrogen achieves chemical
recombination. It burns.

So a fusion scoop can power a chemical rocket! That's the basic plan. At
least the following bolt-on accessories should be considered:

6) A magnetic field, transverse to the flame, gives mass spectroscopic
separation of ions heavier than helium. The other way, deflected electrons
give MHD power for the ship.

7) Metals scavenged, an adjustment field of opposite polarity realigns
hydrogen and helium ions. These tend to diverge in the mass spectroscopy
field, from the neutral jet, so are turned back to it between these poles.

8) These "sideways" pole pairs are followed by a magnetic coil which
actually loops the flame, making a virtual nozzle throat, with field lines
on-axis to the flame, for increased collimation.

9) The fusion booster is just your plain old chemical rocket, 1 through 5
above, with a power package in a long pipe, which surrounds your rocket
flame. Inside the ship is a cyclotron, which boosts lithium ions and ships
them down through the pipe. A certain fraction of them collide with protons
and produce fusion within the pipe. The heat captured by the pipe is used in
a heat engine, to provide power to the ship.

10) The top of the line version, uses all of the above just as a power
source. Pure "cold" protons (those with thermal energies, not having been
involved in fusion reactions) are diverted out into the tuned linac. This
machine is made of metal and kept cold, to provide the main reaction engine
in relativistic regimes.

11) Rotating steel ring magnets, "zero-pole" because their magnetic circuits
are complete, may store energy by spinning within cryogenic magnet coils.
The coil is a torus, helix-wound of high field Type II superconductor like
magnesium boride http://superconductors.org/39K.htm or niobium silicide. The
winding form may be of glass or ceramic, evacuated. Standing wave
modulations imposed on the DC magnet current will rotate the ring when their
phase is advanced, storing energy, or decelerate it when their phase is
retarded. The current induced in the winding when the ring is slowed, may be
tapped off to provide ship's power. (Talk about trouble getting turned
around, these you just won't get turned. They are far too good as
gyroscopes. That's a complication.)

The advanced machinery items, of suggestions 6-11, are not essential
components of the fusion ramscoop chemical rocket, which is described in
1-5. I put them in because I couldn't help it.

Johnny Thunderbird