[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

starship-design: Blackhole, Railgun and superconductor

Hi Isaac,

>>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.
>Actually, black holes produce _more_ energy the smaller they are.
>In fact, if you don't keep feeding it, it will explosively evaporate
>away.  Playing around with small black holes makes letting Calvin
>play with a flame thrower indoors look positively safe.

Are you sure about black holes producing more energy the smaller they are?
I've heard that they evaporate faster and faster, but that's only because
the surface:volume ratio gets bigger. I'd guess the total evaporated energy
gets less if the surface gets less.
But indeed if you would have 1000 small holes instead of 1 big with the same
total mass, you'd probably be better of with the 1000 small holes.

>>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?
>Very small.  Anyway, I'm no expert on electromagnetic railgun designs,
>but plenty of real scientists doing real research on actual railguns
>are, and some of them even have web pages.  Search Yahoo! with
>"electromagnetic railgun".  There are a lot of cool things out there.

I will do so...

>Particularly pertinent to this discussion is research into hydrogen
>pellet accelerators for magnetic fusion reactor fueling, since these
>same pellets would be ideal for the fusion ramjet I'm proposing.
>Muzzle velocities of over 3km/s have been demonstrated, but I
>suggest thinking in terms of only 1km/s or so because the fuel packets
>will ideally have a lightweight railgun with a limited power supply
>(on board fission and/or collection panels for ship based beamed

Like Kelly mentioned, these velocities of 0.00001c are not near to what we
like. Especially not near to the velocities we need for the deceleration track.
I'm afraid that you/we need to work hard on the pellet beaming part.

>>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).
>Your analysis is flawed because the electrons would travel along with
>the ions.  It would be very nice if we could somehow convince the
>electrons and nuclei to somehow part from each other, because then
>electric fields could be used to manipulate them as well as magnetic
>However, they're rather stuck on each other because of their
>opposing electric charge.

True, I forgot that.

>Anyway, the sort of pulsed fusion I'm proposing is similar to
>magnetic target fusion, which requires starting densities of
>10^18 nuclei per cm^3.  The specifics of the plasmatizing of
>the pellet would determine what mass of pellet is needed.
>I'm not familiar enough with the factors involved to make a
>good assessment of that part.

Knowing that our engine will be several magnitudes larger than any magnetic
fusion proposal you've heard of; Can you estimate what the change in
magnetic fieldstrength would need to be?

>>>>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.
>Yes, but since the magnetic field they are resisting is only momentary,
>so is the opposing electric current.  It doesn't build up.

Momentarily? Having a pulsed engine doesn't change things. Instead of
increasing constantly, the current in the superconductor will increase with
If it has nothing to do with a pulsed engine, then you have to explain to me
why it is momentarily.