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During the opening salvos of the second Cylon war, the Battlestar Galatica was engaged by several Cylon basestars. During the engagement the Cylons launched an atomic weapon which struck the Galatica and detonated. My question is this: How could any ship survive being struck by a blast of an atomic weapon and not either be totally destroyed, or have its crew irradiated by the radiation given off by such a blast?

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Nuclear explosion damage comes in three flavours:

  1. Direct heat

  2. Blast overpressure

  3. Prompt (mostly gamma) radiation

Type 2 is only applicable in an atmosphere. There is no blast in space as there's no air to create the blast.

Type 3 is expected to be sustainable by a space worthy ship. Interstellar space is a very radiation rich environment, so we can assume the ship is radiation proof.

This leaves direct heating. In space this would consist mainly of radiative heat transfer. Large amounts of this would be directed away from the ship into empty space. A large amount would still be absorbed by the ship itself and would no doubt cause substantial damage to the ship, but not necessarily enough to destroy it by vapourising it. Most metal objects survived in Hiroshima for example. Given the advanced tech here, they no doubt have equally advanced materials technology resistant to this sort of damage (as we indeed see throughout the series).

Probably the greatest threat to the ship would be via electro-magnetic disruption of its sensors and communications, disruption of flight ops, and destruction of unarmoured critical weapons systems exposed on the ship's surface.

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    As an aside, nukes are a lame weapon in space fiction. If you want something really damaging, get a rock and accelerate it to near light speed and smash it into the target. The kinetic energy in that will make a mess of almost anything short of a planet. eg : 100kg rock and .99%c = .5*.99*100*(3x10^8)^2 = ten to the nineteenth power joules.... ouch. – WOPR Apr 4 '12 at 13:25
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    I chuckled to see a user named WOPR answering a question about nuclear weapons. – Simon Apr 4 '12 at 14:02
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    @WOPR: So basically what you're saying is, Sir Isaac Newton is the deadliest SOB in space? ;) – Mason Wheeler Apr 4 '12 at 22:03
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    @WOPR: Science, bitches, it works. – casperOne Apr 5 '12 at 16:08
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    @ChrisLutz I know, that's why I said it leads to bomb pumped lasers - after all, a laser is just a super focused expression of energy :). As long as you're in the future, why stop at boring shaped charges when you can have frakking nukes with frakking lasers attached to their frakking heads? – Tacroy Apr 5 '12 at 22:36
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Something important: the Galactica is big - in the 1.5 km range, if I remember correctly. That would allow for several meters of armor on its hull. Even with the materials in our disposal, that would make a rather tough nut to crack, even with nuclear weaponry. And that would be even harder considering the materials probably available in the BSG universe...

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I won't try to repeat the excellent answer of WOPR.

It is also not stated what range of yield of weapons used in Battlestar Galactica. Yields of weapons tested by the USA and USSR/Russia have ranged from the equivalent to 10 tons of TNT at the low end to 50 megatons of TNT. The largest weapons have tended to be air-dropped weapons rather than missiles due to the constraints placed upon the design of needing to be propelled.

A Trident II missile can carry a little under 6 megatons in total (12 x 500kt warheads) as a concrete example of a missile deployed weapon.

Perhaps to be effective as a weapon in space with moving targets a missile has to move relatively fast - leading to smaller warheads.

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Of course any direct hit with a nuclear weapon will vaporize any armor Galactica can have (if normal physics apply) - we are talking about a ball as hot as the center of the sun. See here for more about nuclear weapons than you ever wanted to know. And here is an online calculator for the effects of nuclear weapons on armor. Just try a range of 1 meter and check the armor thickness.

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    +1. So a 100kt weapon would (picking titanium as the material) - if the weapon detonates at 10m from the hull (not unrealistic, travelleling at speed, you would not want to hit the ship and risk damaging the weapon before it detonates) - the depth of hull vaporized is 7.5m - clearly a lot. But as you move from the epicenter of the explosion this reduces. By about 26m from the epicenter the vaporized depth reduces to 1m - not unrealistic for a battleship. So with a 1m depth of hull you would end up with a 50m hole - a bad but not necessarily a fatal blow to a huge ship. – iandotkelly Apr 11 '12 at 14:27
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    My argument is that 1m might be unrealistically close. For a missile travelling at some speed to hit a moving target and avoid countermeasures it would probably detonate some distance from the hull. A hit at speed against the hull might damage the equipment that starts the detonation. Why bother with hitting when you have a weapon that is powerful anyway. 100kt is relatively small however, but we don't know very much about how fast the missiles need to move, or how long their typical flight it, so don't know whether the payload could be more than that. – iandotkelly Apr 11 '12 at 14:32
  • @iandotkelly: And if the missile is a "bunker buster"? – Reinstate Monica - M. Schröder Apr 11 '12 at 16:47
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    Agreed! I'm just trying (desperately) to justify why a nuke might not obliterate Galactica. Keeping the weapon small and detonating far from the ship is the only way this works. Really it seems more likely that the Cylons would launch a few 10mt nukes at once and that would be the end of that! It gets even worse when you consider that the nukes might be designed to have a shaped explosion. – iandotkelly Apr 11 '12 at 21:27
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    That online calculator has some major issues. I simulated a 25 KT explosion (Hiroshima size) at a range of 0.001 meter (1mm, i.e. direct contact) against Tungsten armor. It gave a armor vaporization depth of over 100,000,000,000 mm. About 100000 km of solid Tungsten armor would be vaporized, per the calculator. Whereas in the real Hiroshima blast, even 20 km away there was no damage. – user35920 Nov 11 '14 at 3:08
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On top of the points made about the lessening of the effectiveness of a nuke in space, combined with not knowing what yield the missile carried - likely to be smaller, as it was fired from a raider, rather than ship-launched - I think it's worth mentioning that it hit one of the hangar pods (IIRC) rather than hitting the main hull.

The pod in question was shown to have major structural damage and fires inside the armoured layers; when you consider how a goodly portion of the hangar pods are empty space, I'd say that if the hit had been taken on the inner hull, Galactica would have been crippled or worse. But, taking the hit on the pod - which curves more radically than the main hull - meant that the damage was directed towards less critical areas, which presented less hull area to hit.

I think the fact Galactica was able to proceed with damage control unmolested leads us to underestimate how bad a hit she took. And let's not forget Tigh knowingly vented a bunch of people into space because the ship was very close to exploding from secondary damage.

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