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Re: starship-design: Fusion Cone Scoop

In-System Scoops?

Chemical boost, using the local gas medium, does not have to show it can
achieve lightspeed, to make it worth while. It only has to show it can
produce a 1 g sustained acceleration, in some range of velocities, to fit
with my schedule of preferred star flight techniques, to make it eligible as
a phase or stage in the propulsion of the starship. The spin off of this, is
possibly a very good way to build interplanetary vehicles, for the solar
wind is probably much denser than interstellar winds. Before we routinely
use particle beams in our system, however, we must firmly establish the
principle that you have to be careful where you aim that thing. You might
put somebody's eye out.

Though we might normally think a ram scoop would be useless in the solar
system, that it scarcely has room to get up to speed, reflection shows that
Hohmann least-energy transfer orbits, which take months, years or decades to
get from planet "Hither" to planet "Yon", are not very appealing as a way to
travel. If we can show the principle, that the interplanetary gas can also
be concentrated to the point at which it will yield its chemical energy of
recombination, to produce sustained thrust, this will lubricate the Solar
System economy enough that starship building becomes a feasible project.
Ease of fast transportation around this system, will increase available
resources by many orders of magnitude, making us a much wealthier species.

So can the ram scoop be useful in the system? The gas is roughly the same
stuff. Since the solar wind is denser than the interstellar medium, the
principle of inward compression by circumferential fusion, should apply to
it. A cone shaped particle beam traversing through it should produce the
desired concentration, assuming the beam does indeed ignite diffuse fusion
reactions of the order needed for bulk movement of the gas and plasma. Since
we know that particle beams in the lab do give fusion, at precisely
predictable energies, we can directly extrapolate these experimental results
to free space conditions.

It is calculable how intense a cone beam would need to be, to produce fusion
in the medium which will gather in our gas. (Speeds needed are in KeV's, not
MeV's. Electrons go that fast in your monitor's picture tube.) So the ram
scoop can be run in simulation with current software. Even I can do this, if
I can get my mind wrapped around learning it. Somebody else can if I can't,
for we are dealing with known phenomona, according to firmly established
physical laws. The fusion scoop, as a virtual machine model, can be realized
immediately, so if it works in the simulation, a test prototype can be built
and flown. This becomes science, for it is subject to Karl Popper's
falsifiability criterion for experimental science.

It's a long way out to the Kuiper Belt. Beyond that, it's a long, long, way
to the Oort Cloud, and lots of room above the ecliptic to shake out our
space legs. There is good new science to be learned, up those gravitational
hills, and there are some very collectible comets and asteroids, which might
be worth a pretty penny back home. A one-gravity acceleration is too much
for use within the system, we can settle for less. But sustained
acceleration, and sustained deceleration, are concepts which will cause a
sea change in our ideas of space travel. These are only practicable if
locally resident energy and mass are harvested for a reaction engine, rather
than the ship carrying its own fuel.

That space gas is explosive on compression, has evidently been overlooked
before. The hottest rocket engine we have now, gives but a small fraction of
the energy available, by simply squeezing the gas of space. The energy we
must use to form our collection beam is in the nature of a catalyst. The
beam is all consumed in fusion production. I expect practically none of its
constituent particles to be slowed in elastic collisions and thermalized.
The total fusion production will release excess energy, in an amount to
vastly outweigh the beam projection energy.

The potential chemical energy, in the cloud gathered for us by our fusion
ram, is our bonus. It is not directly related to the energy expended to
gather it, for the same ram scoop energy could be used to compress an inert
gas. Instead, we are collecting atomic hydrogen, the most powerful rocket
fuel which may be. There is only a gross and indirect proportionality of the
chemical energy which moves the ship, to the electrical energy first spent
to generate the scoop. The fusion itself dwarfs our beam energy, giving us
the chemical energy, an amount much greater than either our beam or its
fusion, for free. Nature didn't have to fill space with rocket fuel. Since
She did, we would do well to use it.

Johnny Thunderbird