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Re: starship-design: Fusion Cone Scoop
> it's questionable whether a ramscoop can really collect enough fuel to
You just don't like ramscoops, do you Steve? The fact is, a ramscoop does
take energy to operate. It has to be a very large construct, far too large
to be feasibly constructed wirh matter. It must be built of less substantial
fabric, fields or shock waves or other dynamic extensions of the ship, and
these require a continuous energy expenditure to maintain. A magnetic funnel
doesn't necessarily need sustained energy input to maintain its structure,
but because it only works for plasma, and the medium is mostly atomic,
ionization energy must be added. Also, if the magnetic current loop solenoid
forming the scoop field is physically detatched from the ship structure,
because of being big, further energy must be expended to hold it in place,
in front of (perceptually "above") the ship. But the magnitude of these
energy debits is not determined yet.
I suggested a different type of ramscoop, to gather gas which was not
ionized, and also to gather plasma, indiscriminately. This would use a
hollow bow shock, formed of a continuous conical explosion front from
thermonuclear reactions. Fusion would be engendered by a fast particle beam
of cone shape. Once again, the energy cost cannot even be estimated until
the system is further specified. But it should be noted, that the fusion
energy which actually produces the bulk movement of the gas does not come
from the ship's energy reserves, but from the nuclei of the space gas. It is
disproportionate to the amount of energy used to project the particle beam.
With either version of the ram scoop, the energy spent to gather in gas is
proportional to the volume of space swept by the scoop. The lower the
density of the space gas encountered, the larger the scooped region must be,
so the scoop becomes energetically costlier at lower gas densities. This is
a scaling problem with the electromagnetic scoop, which deals with an
inverse square law on the propagation of its effectiveness. The fusion scoop
has no inherent size limits.
Yet we can't firm up any specifications for ram scoop designs, until we have
a good idea how thick the gas is in local interstellar space. A few years
ago, people thought it must be a bit less than the gas in our system, which
has 2 or 3 particles per cc when the sun's quiet. More recently, evidence
has been found that we may have just entered a gas cloud, which could make
the gas density in local interstellar space actually higher than it is in
our solar system. I believe next year, Voyager 1 will cross the heliopause
at 100 AU, with Voyager 2 following the next year, so we can find out then.
Ram scoop proposals are meant to get energy and reaction mass from the
ambient medium. They are machines which will work, if there is enough fuel
for them to collect, otherwise not. I think the particle beam type scoop may
have a better shot at success, for it can be made arbitrarily large. Without
hardware changes, you can fire a more narrow cone of particles a greater
distance ahead of the ship, as speed increases. A magnet, which is only
effective to a fixed distance, has less time to move material at high
velocity of traverse.
I can understand your reservations about the concept of remotely induced
fusion. It takes a high energy beam, so you want me to prove it will pay off
the inertial costs, and the sheer energy costs, of producing that beam. I
found some high energy physics programs which might help me do that.While
I'm working on that, here's another type of scoop for you to hate.
It has a similar approach, of conical excitation remotely producing a
centralizing compression. Instead of using local fusion to power the
compression, it uses local chemical recombination for the purpose. Thermal
excitation of the gas medium, produced by a cone of laser illumination,
gives a shock front of increased pressure which travels at the ship's speed.
Local atoms recombine chemically, as they pile up against that shock front.
That traveling explosion gives leverage to the laser's thermal excitation,
resulting in a compressive force much greater than that exerted by the laser
Though this seems similar in concept to the fusion cone, it's actually much
more complex than the other, and will be lots harder to demonstrate. It
illustrates using the heating laser for a triggering energy input, like the
particle beam which incites fusion in this thread, to release locally
resident potential energy from afar. In both cases, the triggering energy is
considerable, but is far less than is needed to do the actual work.
Your doubts are your own, and certainly they are sensible, but some think
scoops may work.