Nukes in Space

[Steel]

It seems to be that whenever nuclear weapons are mentioned in scifi, somebody says that nukes are not very effective in space because there is no blast/thermal effects as there is no air, and so 60% of the energy cant do anything.

Isnt that shit? Doesnt that just mean that you get hit my a masive ammount of powerfully ionising radiation (or whatever it is that makes the blast effect) directly, as opposed to it affecting the air first. The bomb releases the same ammount of energy wherever it is detonated, and so at the same distance there should be the same intensity on the target.

Or is there a flaw in this logic?

[Elheru Aran]

Yes. Inverse square law. The further you are from the radiation source, the less radiation reaches you.

At least that's how it works, IIRC... it's been a while since I had a science course.

[Adrian Laguna]

At point-blank it will hurt like hell, but the farther you get the less damage it does. IIRC at a distance that will severly damage a building on the ground, a nuke detonated in space will singe the paint job on the hull and maybe give the crew radiation poisoning.

[phongn]

You have to get really, really close otherwise not enough energy will arrive on target and be wasted (ignoring exotic weapons like bomb-pumped X-ray lasers)

[Azazal]

Check out Atomic Rocket, has a really nice listing for nukes in space

[Solauren]

Nukes in space make a nice weapon if they where to hit the enemies hull (or shields) or armor.

However, if they were to blow up prematurely, the seriously lose effectiveness

[Adrian Laguna]

Like I said, point-blank detonation. It really isn't that unrealistic, real air-to-air missles also detonate at point-blank range (no, they do not detonate on contact).

[Sea Skimmer]

It seems to be that whenever nuclear weapons are mentioned in scifi, somebody says that nukes are not very effective in space because there is no blast/thermal effects as there is no air, and so 60% of the energy cant do anything.

Isnt that shit? Doesnt that just mean that you get hit my a masive ammount of powerfully ionising radiation (or whatever it is that makes the blast effect) directly, as opposed to it affecting the air first. The bomb releases the same ammount of energy wherever it is detonated, and so at the same distance there should be the same intensity on the target.

Or is there a flaw in this logic?

This is correct, 60% of the energy release can't simply cease to exist. The exact types and ratios of energy released can also be adjusted through warhead design to some extent. However while an intense pulse of radiation would damage or destroy any realistic spacecraft (save a ship built inside an asteroid or something) it might not do much against sci fi warships where using mass for armor is an option. But since no weapon is going to work any better then a proximity hit, and a direct hit with a nuke will always be a bad thing, there isn’t much reason not to use them. Nothing can offer better bang for the mass except anti matter weapons, which would be horrendously expensive and unsafe.

[Darth Wong]

It seems to be that whenever nuclear weapons are mentioned in scifi, somebody says that nukes are not very effective in space because there is no blast/thermal effects as there is no air, and so 60% of the energy cant do anything.

You're strawmandering. People aren't saying that nukes will be ineffective; we're just saying that they won't produce the sort of spectacular visual effects that we expect from them because those effects are caused by interaction with atmosphere.

[Steel]

Im trying to see the mechanism by which the same ammount of energy released is so much more devastating in an atmosphere. Alright the intensity decreases with inverse square in space, but so too in the atmosphere.

How is it that the big fireball (which i would assume would decrease by up to the cube of distance, as it affects a volume out to a certain distance) is more effective at a certain distance than just dumping the energy that created it into the target?

[SirNitram]

Im trying to see the mechanism by which the same ammount of energy released is so much more devastating in an atmosphere. Alright the intensity decreases with inverse square in space, but so too in the atmosphere.

How is it that the big fireball (which i would assume would decrease by up to the cube of distance, as it affects a volume out to a certain distance) is more effective at a certain distance than just dumping the energy that created it into the target?

Atmospheric shockwave and a medium for the fireball. Otherwise it's just a flash of hard radiation and plasma.

[Darth Wong]

Im trying to see the mechanism by which the same ammount of energy released is so much more devastating in an atmosphere. Alright the intensity decreases with inverse square in space, but so too in the atmosphere.

How is it that the big fireball (which i would assume would decrease by up to the cube of distance, as it affects a volume out to a certain distance) is more effective at a certain distance than just dumping the energy that created it into the target?

Did you not bother reading my post at all, asstard? No one's saying that nukes are useless in space. However, one could argue that the combination of several different damage modes is harder to defend against than a single damage mode.

[Adrian Laguna]

Steel may have been refering to this comment:

IIRC at a distance that will severly damage a building on the ground, a nuke detonated in space will singe the paint job on the hull and maybe give the crew radiation poisoning.

He is asking how a nuke at x distance might brake the space shuttle in half if its on the ground, but in space the same nuke at the same distance would probably only damage the paint job and give the crew premature deaths.[/code]

[GrandMasterTerwynn]

Im trying to see the mechanism by which the same ammount of energy released is so much more devastating in an atmosphere. Alright the intensity decreases with inverse square in space, but so too in the atmosphere.

How is it that the big fireball (which i would assume would decrease by up to the cube of distance, as it affects a volume out to a certain distance) is more effective at a certain distance than just dumping the energy that created it into the target?

A one megaton nuclear device in the atmosphere will produce the same 4.184E+15 joules of energy that a one megaton nuclear device in space will. One does not magically produce more energy than the other. However, what differs is where that energy goes.

On Earth, a one megaton nuclear device will cause third-degree burns at 11,700 meters out. (Main site nuclear calculator.) Human skin begins to burn rapidly at temperatures of 134 degrees Farenheit or better. It takes something like 83 joules of energy per gram of skin to accomplish this feat (As skin is almost all water, we use the specific heat equations and assume water's specific heat.) To generate burns over 50% of the human body (the fifty percent facing the blast) you need just ~351 kilojoules of energy per square meter (the surface area of human skin is roughly 2 square meters and skin accounts for 12-15% of the mass of the human body.) This energy, spread out over the mass of the entire body (assumed to be 70 kilograms in this case) would be enough to raise its temperature by one degree (centigrade). (This is an upper end. One is likely not to suffer burns to such a severe extent, so the radiant energy at this distance is likely to be lower.)

In vacuum, that same person can expect to absorb just over two megajoules of energy per square meter, in the form of high-energy photons. This is enough to raise the person's entire body temperature by seven degrees (centigrade.) Rather than suffering third-degree burns, the person in this case is baked to death.

What happened to the rest of the energy?

Answer: In the atmosphere, the rest of the energy was absorbed by the atmosphere. What causes the third-degree burns 11,700 meters away is the electromagnetic radiation that the atmosphere is transparent to. Much closer to the point of detonation, the atmosphere absorbs the high-energy photons generated by the nuclear blast, and converts it to mechanical energy (read: extremely high winds, and a shockwave.) This produces dramatic looking damage to anything above-ground that is within the blast-zone. However the energy needed to do this damage would likely add up to a number that is significantly less than the total radiant energy the structures would have absorbed if they'd been in vacuum.

Example: A controlled demolition of an arbitrary three story building with dimensions of 30.7x30.7x10.2 meters massing 164,500 kilograms would take just 80 megajoules of energy (this is a hopelessly idealized minimum, as this is just the potential energy of the entire mass of the building dropped from three stories or 10.2 meters up) plus the explosive yield of 23 kilograms of TNT.) For purposes of this post, we assume this building is at the maximum radius for widespread destruction (7200 meters.) However, these radii aren't magic numbers. A building at 7201 meters away from ground-zero isn't going to emerge unscathed any more than a building 7199 meters from ground-zero is going to be razed to ground. At 7,200 meters from ground-zero our three-story building may well survive as something that is still recognizeable as a building. When we transport this same building onto the Moon and set off a nuclear device at the same 7,200 meters distance . . . this same building, whose surface area facing the blast is 1256 square meters (the surface area of a roof and one wall,) will absorb 8067 megajoules worth of high-energy photons in vacuum.

The point is that most of the energy in an atmospheric nuclear burst goes into heating the surrounding atmosphere. The abrupt thermal expansion of the atmosphere is what causes the spectacular mechanical destruction seen in a nuclear blast. However, in terms of direct-energy transfer it is actually fairly inefficient. While a space-ship on the ground will expect to experience some heating and a lot of blasting by the wind and flying debris . . . it can expect to experience significant heating in vacuum, certainly not just to the extent that it'd "only damage the paint job."

[Darth Wong]

Steel may have been refering to this comment:

How is it possible that he started this thread to talk about a comment that would be made later in the thread? He obviously thinks this is a widespread belief.

[Sriad]

-If you set off a nuke near the ground, at ground zero the inverse square law applies, but as you get further out the ground will reflect more energy, extending the range of devestation.

-The hard radiation of the nuke passes through lots of air which absorbs those frequencies, translating them to heat and pressure. In space, the only materials that translate the radiation into heat are whatever is present in the target. This may be just a couple meters of metal and air; it is reasonable to expect a ship to absorb less energy from the bomb than it would on a planet at the same distance.

Mind you, nukes are still the most cost effective way of fucking up a spaceship in a reasonably firm SFverse, they're just less effective than they'd be on the ground.

[Sriad]

Steel may have been refering to this comment:

How is it possible that he started this thread to talk about a comment that would be made later in the thread? He obviously thinks this is a widespread belief.

I think the OP was about some attitude he's seen in SF works and other internet boards? He seems to me to be seeking edification of some sort more than trolling.

[Steel]

Steel may have been refering to this comment:

How is it possible that he started this thread to talk about a comment that would be made later in the thread? He obviously thinks this is a widespread belief.

I think the OP was about some attitude he's seen in SF works and other internet boards? He seems to me to be seeking edification of some sort more than trolling.

Just to clarify, i was in fact referring to the opinions of people in other places, rather than specific people here when i made this thread. Apologies to anyone who thought i was misrepresenting them, as presenting some crap argument can be seen as trivialising or strawmanning a decent argument

[Winston Blake]

While a space-ship on the ground will expect to experience some heating and a lot of blasting by the wind and flying debris . . . it can expect to experience significant heating in vacuum, certainly not just to the extent that it'd "only damage the paint job."

The 'paint job' comment is likely based on Atomic Rocket's calcs (linked to above):

Nuclear weapons will destroy a ship if they detonate exceedingly close to it. But if it is further away than about a kilometer, it won't do much more than singe the paintjob and blind a few sensors. And in space a kilometer is pretty close range.

[...]

A one kiloton nuclear detonation produces 4.19e12 joules of energy. One kilometer away from the detonation point defines a sphere with a surface area of about 12,600,000 square meters (the increase in surface area with the radius of the sphere is another way of stating the Inverse Square law). Dividing reveals that at this range the energy density is approximately 300 kilojoule per square meter. Under ideal conditions this would be enough energy to vaporize 25 grams or 10 cubic centimeters of aluminum (in reality it won't be this much due to conduction and other factors).

1e8 watts per square centimeter for about a microsecond will melt part of the surface of a sheet of aluminum. 1e9 W/cm2 for a microsecond will vaporize the surface, and 1e11 W/cm2 for a microsecond will cause enough vaporization to create impulsive shock damage (i.e., the surface layer of the material is vaporized at a rate exceeding the speed of sound). The one kiloton bomb at one kilometer only does about 3.3e7 W/cm2 for a microsecond.

[GrandMasterTerwynn]

While a space-ship on the ground will expect to experience some heating and a lot of blasting by the wind and flying debris . . . it can expect to experience significant heating in vacuum, certainly not just to the extent that it'd "only damage the paint job."

The 'paint job' comment is likely based on Atomic Rocket's calcs (linked to above):

Nuclear weapons will destroy a ship if they detonate exceedingly close to it. But if it is further away than about a kilometer, it won't do much more than singe the paintjob and blind a few sensors. And in space a kilometer is pretty close range.

[...]

A one kiloton nuclear detonation produces 4.19e12 joules of energy. One kilometer away from the detonation point defines a sphere with a surface area of about 12,600,000 square meters (the increase in surface area with the radius of the sphere is another way of stating the Inverse Square law). Dividing reveals that at this range the energy density is approximately 300 kilojoule per square meter. Under ideal conditions this would be enough energy to vaporize 25 grams or 10 cubic centimeters of aluminum (in reality it won't be this much due to conduction and other factors).

1e8 watts per square centimeter for about a microsecond will melt part of the surface of a sheet of aluminum. 1e9 W/cm2 for a microsecond will vaporize the surface, and 1e11 W/cm2 for a microsecond will cause enough vaporization to create impulsive shock damage (i.e., the surface layer of the material is vaporized at a rate exceeding the speed of sound). The one kiloton bomb at one kilometer only does about 3.3e7 W/cm2 for a microsecond.

That would be for a one kiloton bomb. A one megaton bomb would produce 332,000 kilojoules per square meter at that distance. Which would produce about 3.3E+10 W/cm^2 for a microsecond. This is approximately 33 times the energy needed to cause vaporization, and a third of the energy needed to cause structural damage-inducing explosive vaporization. A one kiloton bomb might not do much damage, but a one megaton bomb will fuck our hypothetical target up pretty good. A three to five megaton nuclear device at that distance would probably ruin their day.

Essentially, what this says is that with nukes in space, their effectiveness is dependent on how much bomb you're willing to throw at the problem. Sure a tiny, tiny bomb will only singe the paint of a ship that's too far away; however, you don't automatically assume that all bombs won't work in this scenario because of that. You would simply get a bigger bomb and try again.

[Plushie]

A one kiloton bomb is horribly underpowered. The average strategic nuclear weapon is somewhere in the area of 300 kilotons, and even then the devices themselves tend to travel in MIRVs with about 7 other, similar devices. We can make 1 Mt devices only a little larger than a man.