Nukes

[chulbert]

I'm sorry, I didn't mean to imply that nukes do nothing in space. They, in fact, release the same amount of energy as you stated. However, instead of creating a shockwave and fireball, nukes in space shower everything in radiation directly. This changes the scenario in several ways.

While the radiation does travel further in the vacuum of space, it also follows the inverse square rule. In other words, if you double your distance from the detonation, you cut your exposure by a factor of 4. This means that the energy density drops off VERY rapidly, so you need to get the nuke almost impossibly close while also staying far enough away that you're not damaged. It's fantastic to blow up your enemy but not if your own weapon strips off 10% of your plated hull.

Also, the capcity of a material like iron to absorb energy is MUCH greater than air. While you'll certainly vaporize a layer off the surface of the ship, it's not as much as you might think. For example, a 20 mega-ton detonation at 1 kilometer away will vaporize a layer of iron off the hull of a ship only 13 centi-meters thick under ideal circumstances. Most large ships probably have far, far thicker shielding.

Now, the vaporization of the iron may or may not be enough to cause a shockwave through the rest of the ship. It depends on the strength of the weapon, the thickness of the shielding and the sturdiness of the ship.

In other words, nukes are REALLY hard to use in space.

 

[James McMurray]

For example, a 20 mega-ton detonation at 1 kilometer away will vaporize a layer of iron off the hull of a ship only 13 centi-meters thick under ideal circumstances.

Source?

 

[Chernobyl]

yeah, I'm wondering how you got those numbers as well.

Chernobyl

 

[Aramanthus]

The numbers do sound very reasonable that Chulbert posted.

 

[Slightly Norse John]

Presumably, useful energy on target- everything below X-rays, more penetrative radiation would pass through rather than transfer it's energy- divided by the specific heat capacity of the material.
A 20- megatonne weapon is going to release, roughly, one hundred and ten quadrillion joules. I might have rounded up too drastically, that could be a hundred and four. Now, that does obey the inverse square law. At a thousand metres, it's a million times less intense- a hundred and ten billion joules per square meter. The actual size of the ship doesn't matter; what's happening to each of it's square metres is the same.
Four hundred and fifty joules to raise one kilo of steel by one kelvin, 7900 kilos in a cubic metre of steel, so using those as ballpark numbers, that cubic metre is going to get hotter by a shade over 309,000 degrees.
I don't know about you, but I'd call that a kill.

 

[James McMurray]

So we've got one person stating uncategorically that it would only destroy 13 inches, and another saying total kill. Gotta love the internet.

 

[chulbert]

Source?

First, some physical and mathematical constants and formulas that you can look up anywhere.

a) 1 megaton releases 4.184 x 10^15 joules of energy.
b) Specific heat of iron is 0.44 joules per gram degree Kelvin.
c) Atomic volume of iron is 7.1 cubic centimeters per mole.
d) Surface area of a sphere is 4 x pi x r^2.
f) Heat of vaporization of iron is 350 kilo-joules per mole.
g) Boiling point of iron is 3000K.
h) Density of iron is 7.86 grams per cubic centimeter.

Now some basic calculations based on the above.

- 20 megatons releases 8.368 x 10^16 joules of energy.

- The surface area of a sphere of radius 1,000 meters is 1.3 x 10^6 square meters.

- We divide the first by the second and get 6.4 x 10^9 joules per square meter.

So now we've got to heat up the extremely cold metal. Given that we're out in the middle of space, I'm going to say the metal would be 100K, so we need to heat it up 2900K then vaporize it. I'm going to use moles of iron as the base amount of iron.

- Multiplying the atomic volume by density, a mole of iron has a mass of 55g.

- To raise 55g by 2900K requires 7.0 x 10^4 joules.

- To then vaporize that same mole requires an additional 3.5 x 10^5 joules. (This is a critical step Slightly Norse John missed.)

- In total, it requires 4.2 x 10^5 joules to heat and vaporize a mole of iron.

- By dividing, we have enough energy to heat and vaporize 15,000 moles.

But how much is that? Simply multiply.

- 100,000 cubic centimeters, which is a 10 cm layer off the side of a cubic meter.

(Note, the actual thickness varies a bit depending on how much I round and when.)

 

[frobisher]

Energy densities (energy/unit area) area fall off with the inverse square law regardless of their source.

The atmospheric explosion does exactly the same (on average).

You cannae change the laws of physics...

 

[frobisher]

So now we've got to heat up the extremely cold metal. Given that we're out in the middle of space, I'm going to say the metal would be 100K, so we need to heat it up 2900K then vaporize it. I'm going to use moles of iron as the base amount of iron.

It's probably a lot hotter than you've estimated.

You've got an active fusion power plant on the vessel, plus you're maintaining the interior of the ship at 293K or there about. Space craft belch heat like there's no tomorrow (which is why stealth in spacecraft is really not that viable if the ship is under power...).

 

[tenabrae]

If i'm not wrong, and my research indicates some semblance of accuracy, b5 is a TV show If ships move at the speed of plot, I suspect nukes do damage equal to plot, as the following formula demonstrates:

energy = ship armour - (ship armour/plot importance)

where plot importance is expressed with a percentage

thus a ship with 1000 armour and an importance of zero, in fact takes 1000 damage units, while a ship with an importance of 100% takes none.

 

[sigma957]

re the thridspace device that was placed inside a confined area in direct contact with the mechanism thus, whatever its in contact with (obviously something critical lyta told him about) is going to be vapourised by the nuke when it does a mini sun impersonation and the total energy of the bomb that dosnt go directly into it will be absorbed by the interior of the thirdspace gate as its inside, as for the landmine trick inthe beginning and at corianna i think the trick is red hot hyperaccelerated chunks of asteroid from where they were blown up

 

[chulbert]

Energy densities (energy/unit area) area fall off with the inverse square law regardless of their source.

The atmospheric explosion does exactly the same (on average).

You cannae change the laws of physics...

I'm not sure what you're trying to say here. I don't think I've ever tried to change the laws of physics.

 

[chulbert]

It's probably a lot hotter than you've estimated.

Sure, we can haggle over the temperature of the metal, but in the end it doesn't matter very much. The energy absorbed heating the metal is peanuts compared to the energy absorbed vaporizing it.

 

[frobisher]

Energy densities (energy/unit area) area fall off with the inverse square law regardless of their source.

The atmospheric explosion does exactly the same (on average).

You cannae change the laws of physics...

I'm not sure what you're trying to say here. I don't think I've ever tried to change the laws of physics.

The energy density of the shockwave of an atmospheric detonation will fall off with the inverse square law as well, and in fact will be (barring secondary detonations) less than the energy density of the radiant energy in a vacuum detonation as there is no attenuation due to the medium...

The quote was retorical

 

[frobisher]

It's probably a lot hotter than you've estimated.

Sure, we can haggle over the temperature of the metal, but in the end it doesn't matter very much. The energy absorbed heating the metal is peanuts compared to the energy absorbed vaporizing it.

The thing is, solids don't vapourise neatly like that either. If you have say a vein of metal that is very slightly impure and has a slightly higher thermal condutivity than the surrounding "pure" medium, then that will in fact vapourise more quickly and in preference, and in doing so will in fact blast the surrounding (unvapourised) metal apart. Joins and welds will undergo a similiar experience.

As it stands, the effect you describe would probably be sufficent to blow most starships apart.

 

[chulbert]

The thing is, solids don't vapourise neatly like that either. If you have say a vein of metal that is very slightly impure and has a slightly higher thermal condutivity than the surrounding "pure" medium, then that will in fact vapourise more quickly and in preference, and in doing so will in fact blast the surrounding (unvapourised) metal apart. Joins and welds will undergo a similiar experience.

Yes and no. You're right that things aren't so simple. It's not as if the outer 10 cm are peeled off and the 11th cm looks like nothing happens and remains cool to the touch. Some of the heat will be conducted by the metal to greater depts. However, the radiation only lasts about a microsecond so most of the damage really will be localized to the outer most layers.

The rapid vaporization will indeed cause some impulsive shock. It will cause some damage but whethe or not it will tear apart a ship depends on its construction. At this size and distance, probably not. Remember, there's lots of radiation out in space and ships have means to do deal with it.

 

[Chernobyl]

I think Chulbert's done his homework on this one... :wink: the math is fairly accurate as far as energy conversion is considered, but the types of energy released is what I'm not sure about (I doubt its as clean as all one type of energy, ie gammas of varying energy level) but then bombs aren't my nuclear specialty :lol:

Chern

 

[Greg Smith]

... but then bombs aren't my nuclear specialty :lol:

Chern

With a name like 'Chernobyl'?

 

[Chernobyl]

yes, its reactors, not bombs...!

Chern

 

[sigma957]

in a fusion type warhead the balance of the blast is from deuterium deuterium or deuterium tritium fusion into helium, which occurs at 10Million Kelvin and is the core reaction that keeps the stars burning,

this reaction is a broadspectrum emmiter of energy (like the sun) covering the entire spectrum from Radiowaves all the way down to Gamma, the gamma will punch through everything except sufficiant lead, Bleach, water or other shielding material, because of this uneven penetration the ships is unlikly to have its hull vapourised but instead have the entire hull heated very rapidly

heated materials expand, different materials have different coefficiants of expansion and expand differently ergo the hull literaly pops open as the first microscopic breach in integrity will allow air to escape and cause explosive decompression which will rip the ship into bits, mostly this gap will occur along the joins as the welds will be expanding differently to the hull plates and BOOM

As for radiation in space, the ambient background is substantially less than having a nuke go bang within a kilometer (which the uses look like) this is infact the same effect that would happen if a ship got too close to a star,