Sci-fi balistics

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tomandlu
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Sci-fi balistics

Postby tomandlu » Sun Aug 21, 2011 5:43 am UTC

Hi,

Anyone got a rough idea about what would happen if you shot a marble-sized* bit of white dwarf matter at very high speed through a tank?

* R = 0.8cm, M = 4,000kg
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Re: Sci-fi balistics

Postby yurell » Sun Aug 21, 2011 5:50 am UTC

Define 'very high speed'. Also, do you have a magical means of keeping the matter degenerate / hot?
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Re: Sci-fi balistics

Postby tomandlu » Sun Aug 21, 2011 6:19 am UTC

Well, we're in a very odd bit of universe, so we'll just assume that makes the dwarf star matter stable. Speed - hard to say (see previous answer), but let's give it something silly like 20,000 miles / second...

I guess it's primarily a choice between:

  1. Small hole, little bigger than the marble, with slightly deformed edges
  2. Humongous great hole, with very deformed edges
  3. Something between 1 and 2
  4. Something far more catastrophic

Hmm, what about shock-waves and secondary effects? Would the steep gradient of the thing's gravity well have any interesting effects, or is it still just too light for that to have any impact? (sic)

Basically, I'm after a serious but not totally destructive impact - a biggish hole but not too much damage beyond the area that was hit, although some interesting side-effects are always nice...
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Re: Sci-fi balistics

Postby Cobramaster » Sun Aug 21, 2011 6:36 am UTC

Well the marble sized piece of Dwarf star would weigh a few hundred thousand tons and if it was moving at 20,000 miles/second it would utterly destroy the tank in much the same fashion as a modern "silver arrow" tankbuster round from an Abrams tank though even more so and it would keep going not stopping until it hits something very substantial, like the bulk of the earth or the moon, even a mountain would be torn apart by something with that amount of force. Essentially you have a very small, relativistic kill weapon.

Oh and this should probably get moved to the Science fiction forum.
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Re: Sci-fi balistics

Postby tomandlu » Sun Aug 21, 2011 6:57 am UTC

Cobramaster wrote:Well the marble sized piece of Dwarf star would weigh a few hundred thousand tons and if it was moving at 20,000 miles/second it would utterly destroy the tank in much the same fashion as a modern "silver arrow" tankbuster round from an Abrams tank though even more so and it would keep going not stopping until it hits something very substantial, like the bulk of the earth or the moon, even a mountain would be torn apart by something with that amount of force. Essentially you have a very small, relativistic kill weapon.


Would relativistic effects have much impact at that speed? I make it that 4,000kg at 20,000/second = 4025kg (in any event, I'm basically ignoring relativity my odd bit o' universe)

Also, as far as I can tell, and based on a mass of 2*1030kg and a radius of 6000km for the source white dwarf, a 0.8cm radius bit of it would have a mass of 3946kg

I guess another way of phrasing the question is "why would a small, very heavy, fast moving thing not just punch straight through?" (assuming it hadn't been specifically designed to shatter)

Oh and this should probably get moved to the Science fiction forum.


Ah - sorry. Mods?
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Re: Sci-fi balistics

Postby yurell » Sun Aug 21, 2011 7:15 am UTC

I'm no material scientist, but I don't think anything that the ball hits will deform it (presuming you can keep it magically together I don't think the external pressure of the tank will be much compared to the internal degeneracy pressure trying to blast it apart) — I'd imagine that it would punch a clean hole straight through the tank, since nothing it hits would have time to transfer energy to any other part of the tank. That said, you're travelling at 10% the speed of light, so you'd get a nice burst of gamma rays as anything it hits immediately fuses.
Basically, you've made a relativistic bullet that will shoot a small hole through anything. 'Bullets' should be soft so that they deform on impact, enabling them to transfer more energy to their target.

This is just me working off my gut feeling, though ... I certainly wouldn't defend this should someone with more authoritative knowledge of the subject come along.
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Re: Sci-fi balistics

Postby Soralin » Sun Aug 21, 2011 8:50 am UTC

This thing would have insane recoil. Let's see, 4000kg, at 32,186,000 m/s or so. The most massive battleships constructed on earth were the Yamato class battleships, which masses in at about 73,000,000 kg fully loaded. The battleship is about 18250x more massive than the projectile, so on firing it, the entire ship would recoil backwards at a speed of about 1764 m/s, or about 3950 miles/hour.

So, upon the largest battleship ever built on earth firing this single projectile, the recoil would send the supersonic battleship flying backwards at over 5x the speed of sound. If it was evenly accelerated along a gun barrel the entire length of the ship (263m), this would happen over a span of time of about 16 microseconds, giving a brief acceleration of the ship of a bit over 10 million g's. If you used a lighter ship, say the Los Angeles class nuclear submarine at about 6927 tonnes, the recoil of the projectile would be enough to blast it off the Earth at greater than the escape velocity of the planet. A bit lighter than that and it would be enough to leave the solar system entirely. Something like say an M1 Abrams firing this, at a mere 61 tonnes, wouldn't stand a chance, being thrown backwards by the recoil at a speed of about 4.7 million miles/hour.

This thing has a kinetic energy of about 2*1018 J. That's about 10x larger than Tsar Bomba, the largest thermonuclear bomb ever detonated. It has about the same energy as a 9.0 earthquake, or about 3x as powerful as the Krakatoa volcanic eruption, and that thing took out the whole volcano and 2/3 of the island itself. So yeah, this projectile could blow up mountains. As for a tank, the projectile itself might pass cleanly through, but everything that it runs into, like the armor, it would accelerate up to speeds nearly as fast as itself, which would fly out and do massive damage itself. Not to mention, even passing through the air, it would knock air molecules out of the way at very high speeds, which would fly off and hit more air molecules and so on and so forth, and possibly create a large shockwave which could do damage itself. And heck, this thing is going over .1c, it might end up fissioning or fusing elements that it hits in it's path. I'm not sure what exactly it would do, but it would be absurdly destructive in any case. :)

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Re: Sci-fi balistics

Postby gmalivuk » Sun Aug 21, 2011 3:49 pm UTC

Soralin wrote:This thing has a kinetic energy of about 2*1018 J. That's about 10x larger than Tsar Bomba, the largest thermonuclear bomb ever detonated. It has about the same energy as a 9.0 earthquake, or about 3x as powerful as the Krakatoa volcanic eruption, and that thing took out the whole volcano and 2/3 of the island itself. So yeah, this projectile could blow up mountains.
Only if you have some way for it to release all of that energy in one place. Which, if you're magically preventing it from exploding in the first place, such a small mostly rigid body wouldn't do.

As for a tank, the projectile itself might pass cleanly through, but everything that it runs into, like the armor, it would accelerate up to speeds nearly as fast as itself, which would fly out and do massive damage itself.
No, because it's like if you shoot an armor-piercing round through something soft: it barely slows down the bullet, and barely speeds up the something soft. At the speeds and energies we're talking, a tank is pretty soft.
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Re: Sci-fi balistics

Postby Ibid » Sun Aug 21, 2011 4:53 pm UTC

gmalivuk wrote:
As for a tank, the projectile itself might pass cleanly through, but everything that it runs into, like the armor, it would accelerate up to speeds nearly as fast as itself, which would fly out and do massive damage itself.
No, because it's like if you shoot an armor-piercing round through something soft: it barely slows down the bullet, and barely speeds up the something soft. At the speeds and energies we're talking, a tank is pretty soft.


At the speeds and energies we're talking, anything is pretty soft.

Well, except for other white dwarf matter/neutron star/exotic material.

Point is, wha you've got is essentially going to take out a small cross-section and carry on having imparted little to no energy o what it goes through. It is similar to how against a soft-unprotected target one does not use armour piercing rounds.
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Re: Sci-fi balistics

Postby Yakk » Tue Aug 23, 2011 7:53 pm UTC

514 KJ/mol to turn titanium into a gas.
4.5 g/cm^3
47.867 g/mol
0.094 mol/cm^3
48 KJ/cm^3

Assume the tank is pure titanium and 2 meters thick. Then a mere 9600 KJ (9.6E6J).

The projectile has 2E18 J of energy

20,000 miles/second goes through 2 meters in 6.21371192 × 10^-8 seconds.

1.6E14 Watts of power to vaporize the titanium.

We also want to look into the rate that titanium would spread heat. We'd end up with a really hot, possibly plasma. That will produce a lot of pressure.

I'm not sure the heat would have time to spread and evaporate stuff "beside" the projectile, or the stuff in front to move out of the way. The density of stuff that comes along the front ends up being pretty high (which might require phase changes more energetic than mere gas).

An elastic collision might be interesting.
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