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Re: starship-design: We need to get on the same (pellet) track first

Timothy van der Linden wrote:
>>>I suppose a black hole as stardrive does comply with the rocket equation?

>>Well, it would be bizarre, but you could theoretically build a
>>"rocket" around a black hole.  For instance, it could be a large
>>sphere with a hole.  It absorbs Hawking radiation from the black
>>hole, except for that hole (which is where thrust comes from).
>>A really bizzare starship, considering how much better it would be
>>to just use the black hole as a highly effective anti-matter producer
>>(in a fixed anti-matter factory).

>Hmmm yes, I guess as long as you are a selfsufficient ship, you will comply
>with the rocket equation.
>I doubt though that you can get enough antimatter for these high exhaust
>velocities. Likely you have to feed much more matter to the blackhole than
>that you will get antimatter in return.

Hold it.  I think you're confusing what I'm talking about.  The first
idea, the black hole powered rocket, doesn't need antimatter
production at all.  All it cares about is that the spherical shell
blocks Hawking radiation in all directions except the desired thrust
direction, and that the Hawking radiation in the desired thrust
direction has momentum.  The fact that a significant fraction of
that radiation will happen to be antimatter particles is of no

The second, and more plausible idea, is that of using a black hole
to produce usable antimatter.  With sufficiently massive construction
efforts, near 100% efficiency is acheivable.  Assuming you can build
a massive spherical shell around it, you can get a very efficient
antimatter factory simply by throwing all your waste products back
into the black hole (including most waste heat).  Only a fraction of
Hawking radiation is antimatter, and only a very small fraction of
that could probably be captured into usable antimatter.  But all the
waste products except for a certain amount of waste heat radiation
(that which escapes into space) can be recycled in the black hole.

A black hole is quite indiscriminate about what it swallows up.

But anyway, these speculations are far beyond the scope of this mailing
list's purpose.

>>I should recalculate things and type them up on my web page.
>>Anyway, the important factor to keep in mind is that for any
>>useful muzzle velocity, the acceleration occurs essentially
>>instantly for purposes of rejecting waste heat.
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^(note this for later)
>>For a pellet launcher meant to fire frozen DT pellets, this
>>would seem to be disastrous.  The solution, as I see it, is
>>to use a "pusher plate" of plasma pushing a frozen DT sabot
>>which sacrificially melts, leaving a core frozen pellet which
>>leaves the muzzle.  Beyond the muzzle is a cylinder which
>>looks a little like a large gun silencer.  It is rotating
>>quickly and has a series of conical baffles; its only openning
>>is through the center, which the frozen pellet passes through.
>>Gas pressure expansion forces most of the waste gas into the
>>conical baffles, where centrifugal "force" funnels the gas to
>>reclaimation pumps along the outer surface of the cylinder.
>>Thus, most of the pusher plate and plasma material can be

>You say the gun silencer has series of conical baffles, but you don't
>mention how these baffles are attached to the "silencer".

In its simplest form, imagine the "silencer" is simply a cylinder
with two holes in the center of both ends.  The objective of this
cylinder is to capture gases escaping the muzzle, but it needs
these two holes to allow the "bullet" through.  Gas escaping
through the rear hole isn't a problem because the "gun barrel"
can seal this potential leak.  Gas escaping through the forward
hole is a problem, so some fraction of gas will escape through
this hole despite the best efforts of vacuum pumps trying to
reclaim the captured gases.

The solution?  How about another cylinder attached in front of
this cylinder?  It will succeed in capturing some fraction of
the gas escaping from the first one.  And how about another?
And another?  Pretty soon, you've got what looks like a long
cylinder with a bunch of circular baffles inside.

An extra refinement is to shape those baffles in a conical
shape, pointing rearward, thus using the forward velocity of
the gas to push it outward toward the rim mounted vacuum pumps.

Oh, another refinement is to cool the baffles with frozen
hydrogen to make the gas hitting them condense into liquid
form.  If you can do that, then the centrifugal "force"
from spinning up the "silencer" will force the liquid against
the outer surface.

>You suggest the acceleration of a pellet happens almost instantaniously by
>some plasma expansion. I wonder, won't the launcer blow apart?

I didn't specify, but the plasma pusher is pushed forward using
a rail gun design.  Easier to get high muzzle velocities this way
than with other methods.  Compared to a TNT detonation, this is
a gentle push.

However, for purposes of heat rejection, it is going to be
basically instantaneous (without a _very_ long barrel).  Heat
rejection is via radiation (it can't conduct away heat to the
barrel because friction would cause much more heat if they
were touching).  And radiating away heat when you're only a
few degrees Kelvin just doesn't happen very quickly.

>>>True, but I wonder, is a ramjet of the size that we need physically

>>This ramjet isn't supposed to scrounge around for interstellar
>>hydrogen, so its diameter is determined by how accurate the
>>pellet tracks can be laid and followed.

>To Kelly you wrote "TV tubes don't have to be many times longer than they
>are wide", you already noted that protons need 1000 times more energy.
>I think that the amount of protons/electrons will make a difference too.

You're right, it does, because the curved paths of the affected
particles are essentially induced currents which induce a magnetic
field opposing the original one.  However, it's not as simple as
requiring twice as much field to handle twice as many particles.
In a TV tube, the induced magnetic fields from the moving electrons
are, of course, negligible.  I confess I haven't done the math
to come up with how strong the induced magnetic fields are for
a DT pellet.

>A TV has to move around less than picograms of matter, compared to the
>kilograms that we need. That's a difference of rougly 15 magnitudes.
>Luckely, we won't have to supply that power since the particles will give
>back their energy as soon as they leave the magnet. The fieldstrength should
>not alter too much when the particles fly through the field of the
>superconducting magnets.

Unfortunately, the fieldstrength can alter--and just where it matters.
The field immediately around the superconductors won't change due to
the properties of superconductors, but that's not where the particles
are (however this does help in that the induced magnetic fields won't
heat up the ship at all).  The particles are near other particles from
the same pellet, just where the induced magnetic fields of those other
particles are strongest!

This is an area where I confess I haven't thought things through
with the real numbers.

>>>It may be so inefficient that the power losses melt it away the
>>>instant that it starts to produce 1E16 Watt of power.

>>The coolest thing about ramjets is that using superconducting
>>coils and an aneutronic fusion reaction _no_ waste heat is
>>absorbed by the starship.  Superconductors aren't just almost
>>lossless, they are _entirely_ lossless.

>OK, the magnets aren't giving losses, but isn't there still a lot of
>uncontrolable heat from the thermal radiation from the hot particles?

True, the hot plasma will glow with a lot of thermal radiation.
However, highly reflective surfaces can prevent the ship from
absorbing a significant amount, and since the magnetic fields
prevent any particles from actually hitting the surfaces, they
won't lose their flawless surfaces quickly.

>A more practical question: How are the superconducting magnets kept from
>blowing up? The charged particles that fly trough the magnets will create a
>magnetic flux. Normally as long as the particle flies trough without
>velocity gain, the superconducting magnets will have the same current before
>and after the particle flew trough. But in the ramjet design the particles
>will exit faster than they arived and thus will leave a non-zero flux.
>I do know little about how superconductors are given a current and a
>magnetic field, so the above question is more likely a result of not knowing
>then of doubting the design.

The superconductors resist any change in the magnetic field, which
is one of the ways they are so different from normal conductors.

What you point out would indeed be a serious concern if normal
magnetic coils were used.
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
/___________\ "Mari-san...  Yokatta...
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