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

[TLG.van.der.Linden@tip.nl (Timothy van der Linden)]

Hello Isaac,

You replied:
>>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
>consequence.

Oh, sorry, I indeed misread.

>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.

I wonder though what momentum per unit of mass both designs would give you.
The problem with using a blackhole is likely has to be too heavy to produce
a usable amount of energy. As a result the "engine" would be much heavier
than the fuel.

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

True, but ocassionally the list is used to exchange a bit of knowledge.

>>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....
<More explanation removed>

OK, the design is much clearer now.

>>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.

True, but even if it is a gentle push compared to a TNT detonation, it
likely is still a big bang. What do you suggest is the mass of the pellet
you want to accelerate?

>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.

Do you have any guess what the energy waste per pelletmass will be?

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

It might be interesting to do some rough calculations. If we'd catch 1 kg of
hydrogen ions that means 6.2E26 ions and a current of 1E8 Ampere.
That current alone would generate non trivial magnetic fields. On the other
hand we would have a similar amount of electrons that go the same direction
(however likely along the outside of the ship).

>>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 arrived 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.

If I understand correctly, the way that they resist that change in magnetic
field is by changing the current inside the superconductor.
In the situation explained above, the current would rise more and more until
the current would become too high and break down the special properties of
the superconductor.

Timothy