starship-design: Starship-design: Plasma power

["Johnny Thunderbird" <jthunderbird@nternet.com>]

----- Original Message -----
From: "L. Parker" <lparker@cacaphony.net>
To: "Starship-Design (E-mail)" <starship-design@lists.uoregon.edu>
Sent: Friday, June 16, 2000 5:51 PM
Subject: starship-design: Plasma power could usher in human travel to Mars

I can't remember whether I posted my latest and greatest launch vehicle
combo here, but I agree with this post that for inner-system work, the MPD
(magnetoplasmadynamic) arcjet is certainly the way to go. The citation
brings in an intermediate stage in the engine, of RF excitation between the
arc and the clamping magnetic field which forms the "nozzle" of the MPD
arcjet. I have to express my preliminary approval of this addition; in fact,
I was just looking for a way to allow a greater degree of electrical
excitation of the plasma before its expulsion. For real legs, working in the
outer system and beyond, I lean toward using a linac as main propulsion, so
you can really show your exhaust particles which way to the back door and
boot the bastards out.

Here is a wrap of my launch scheme, which I have held stable for nearly a
year, so I must have have said it here sometime. Oh well, maybe not
everybody took it seriously. Pardon the past tense, due to a hopeful
fictionalization.

Propulsion in space was no longer a matter of the amount of fuel and
oxidizer carried, but the amount of electricity available to boost the
reaction mass, since the vehicle did not rely on chemical rocket engines to
provide acceleration in space. Instead, the fuel for space maneuvering was
entirely hydrogen, without an oxidant. The fuel was energized by a steady
electric arc, and squirted out through a coil providing an intense magnetic
field to collimate the exhaust plasma. The acceleration was determined not
so much by the amount of fuel exhausted, but by its velocity, which was a
function of the electrical energy it gained in the arc, not by chemical
recombination. The hydrogen of the jet was highly ionized, so was tightly
constrained to spiral the magnetic lines of force supplied by the coil, so
tended to go straight back, rather than expanding in a cloud like ordinary
escaping gas.

The space drive was called a magnetoplasmadynamic arcjet, MPD arcjet for
short, and was many times more efficient than rocket propulsion. That meant
very little hydrogen need be released at a time, to maintain thrust, so fuel
was conserved to allow space journeys on constant thrust, rather than
periodic episodes of acceleration, punctuating long weightless periods of
drifting in gravitational fields. Zero-G, or microgravity, was thereby
avoided, with its manifold detrimental health effects on all organisms. A
further benefit was that space travel took less time than it might have
using chemical rocketry. In space, as in computation, speed was of the
essence.

The power rings were of overstressed, defect-free steel, rotating at speeds
well past their normal bursting point. These rings rotated within toroidal
superconducting coils which produced extremely strong magnetic fields. The
fields produced within these coils clamped implacably down on the granular
structure of the steel, simply not permitting the metal to burst and fly
apart, even far over the stress which would normally snap it under tension.
Such overstressed steel rings had but one failure mode, namely a planar
explosion of iron vapor, expanding outward from the center of rotation at
extreme velocity. So long as the field windings held the crystalline
structure of the steel tightly in compression, this failure could not occur,
so the flywheel formed by the spinning steel ring could store
electromechanical energy. Energy could be tapped at will, in the form of
electric direct current, and used to maintain the arc of the drive. As power
was drawn from a ring, the magnetic field strength was reduced as rotation
slowed. When the speed went below the normal bursting point for
non-magnetized steel, the flywheel was declared to be operating in safe
mode, though its rotation still stored a great amount of energy. Then the
rupture of the coil would no longer produce the fearful slicing explosion of
instantly vaporized steel which so worried any neighbors, but the more
normal type of flywheel explosion was still a factor to be considered, until
the ring's rotation was stilled. The overstressed steel ring flywheels
provided a greater energy density than any other form of battery, enough to
power space flight.

The launch sequence was totally unlike any space launch visualized in
earlier centuries. Informally, the launch vehicle was considered to be shot
out of a hypervelocity gun at twelve miles altitude, but that concept was
only a very inaccurate portrayal of a small part of the launch. The launch
vessel was sealed within a long sleeve, of nitrocellulose fabric and film,
inflated with hydrogen. The sleeve was within a tube which runs the length
of the launch airship, also hydrogen filled. At launch time, air enriched
with ozone was driven in through the rear of the tube, igniting the hydrogen
within the tube and driving the sleeve forward, with its contained launch
vehicle. Overpressure in advance of the moving sleeve burst the front seal
of the tube, and the pressurized sleeve with the launch vehicle within it
left the tube in the launch airship in a puff of hydrogen, followed by
burning hydrogen.

Only outside the airship does the flame catch up to the back of the inflated
nitrocellulose sleeve, initiating the detonation of the guncotton material.
Starting from the rear, the sleeve implodes on the hydrogen it contains,
squeezing it to the center and forward. This creates a hypersonic shock
tube, which drives a bolus of hydrogen forward, containing the launch
vehicle, at high speed. The jet of the launch vehicle is now burning, and it
ignites any free hydrogen mixed with air in its wake. When the vehicle
attains hypersonic speed, its bow shock wave contributes this ignition
function.

But in synchrony with this space launch, other shock tubes of hydrogen had
burst along the projected path of the launch vehicle, so its flight path was
enriched in unburned hydrogen. The launch vehicle engine was adaptive to
rapid variations in oxidizing and reducing ambient, so when it encountered a
patch of hydrogen, it expelled mainly oxygen, but in plain oxidizing air it
threw off a hydrogen-rich jet. In this way, the maximum chemical
recombination was assured in the exhaust jet, and all this burning
contributed to acceleration of the launch vehicle, by overpressure on the
shock cone.
____________________

As I have said before, I like fusion to occur, not within the structure of a
starship, but within the exhaust jet. Also, I like the proton-boron reaction
because no neutrons are produced, which makes it clean, the kind of fusion
reaction you might want to have in your neighborhood. Boron furthermore is
cheaper than deuterium, much less tritium, and protons are a dime a dozen.
In other words, a boron enrichment of the exhaust gas, perhaps by making
boron a component of your anode to strike your arc for the arcjet, would
make fine fat targets (measured in barns) for the beam of your proton linac.
Smite the boron nuclei which hang around lazily in your exhaust jet with
some really energetic protons out of the proton linac, and you obtain clean
fusion. This may or may not catalyze proton-proton reactions, but either way
it's an energy bonus.

I have figured that fusion in the exhaust jet will indeed contribute to the
acceleration of the starship. The analogy is of the hypersonic shock cone
which forms the outer boundary of an external combustion SCRAMJET
(supersonic combustion ramjet), which I also calculated that reactions in
the exhaust jet will accelerate the vehicle. For the external combustion
SCRAMJET to work, basically all you have to do is dump the fuel overboard,
and it will burn sho' nuff, and it will push you forward sho' nuff. In both
cases, the vehicle at the apex of the cone will be accelerated by any
explosive reactions in its wake, because of overpressure acting on the
surface of the cone. In the case of a relativistic starship, the cone is not
an acoustic discontinuity, but the cone of causation caused by the limited
velocity of light. Fusion in your jet, although it may be furlongs behind
your actual solid starship, will emit photons to impinge upon this cone of
causation, and there's got to be a push. Sure, go ahead with the quibbles,
I'll be glad to argue that, because it's gonna happen.

See ya,
Johnny Thunderbird
Climate Catastrophe: http://personal.msy.bellsouth.net/~bugzappr
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