Effectiveness of Nuclear Weapons in Space.

[JGregory32]

There have been many space weaponry threads which boil down to Lazer's vs. Nukes. While I don't wish to debate this again I am wondering about some of the assumptions inherit to this argument.

I wonder about just how effective a nuclear detonation would be in a space enviroment.

Becasue of the lack of atmosphere there would be no blast wave, or fireball effect. Going by this link most of the imediate damage is from the blast effect. That just leaves the thermal pulse effect and radiation.

Thermal damage would drop off with distance but does anybody know how quickly that would be? This link seems to state that a one megaton explosion causes third degree burns up to five miles on exposed skin, which would not be happening in space combat. Also on the page is data saying that after five miles the damage drops considerably.

A greater concern would be 'flash blindness' which can occur up to 53 miles in atmosphere on a clear night. However flash blindness supposedly only lasts for a few minutes in most cases, and permanent damage only occurs in cases where people directly viewed the flash.

As for radiation here's a quote:

The level of initial nuclear radiation decreases rapidly with distance from the fireball to where less than one roentgen may be received five miles from ground zero.

Source

I know these examples are from a one megaton weapon and that larger weapons should scale to have larger damage areas but does anybody know HOW it scales? It a simple arithmatic scale or is it geometric?

Can anybody help me out with this? Am I missing something or does it seem like the only (realistic) damage from a nuclear weapon detonation in space would be from the thermal pulse and the radiation effects. These effects seem to have a (revativly) rapid drop off rate.

[Coyote]

A nuclear blast in space, even if only "close enough" can wipe a ship clean of its exposed, external sensors, overload its optics (if any), and create an EMP. It's be more of a 'soft kill', as opposed to destroying the vessel, but it would effectively render the target ship useless and open to terms.

[Sea Skimmer]

Becasue of the lack of atmosphere there would be no blast wave, or fireball effect. Going by this link most of the imediate damage is from the blast effect. That just leaves the thermal pulse effect and radiation.

The blast effect comes FROM the thermal pulse and hard radiation being rapidly absorbed by the atmosphere, which then expands to form the blast wave. You have no blast in space, but the radiation is then left totally unchecked and has vastly greater power. This becomes even more apparent when you build the space nuke as a neutron bomb (nothing else makes sense), for the absolute maximum possible intensity of the neutron flux. Neutrons will be the main kill mechanism, and they can not only kill a man through 20 inches of steel (while also making the steel its self lethally radioactive for several days), they can also totally destroy electronics.

[Hawkwings]

As always, Atomic Rocket has a lot of good info on the subject.

[phongn]

A nuclear blast in space, even if only "close enough" can wipe a ship clean of its exposed, external sensors, overload its optics (if any), and create an EMP. It's be more of a 'soft kill', as opposed to destroying the vessel, but it would effectively render the target ship useless and open to terms.

HEMP won't be generated in a space blast, though there may be some localized effects (SREE/SREMP).

[JGregory32]

based on quick read through of Atomic Rocket it looks like what you really want its a one megaton Enhanced-Radiation warhead that kills humans out to 300 km from detonation.

Does anybody have data on how large a lazer would have to be to kill a one megaton warhead at 300km?

[phongn]

Does anybody have data on how large a lazer would have to be to kill a one megaton warhead at 300km?

1. It's spelled "laser."
2. It depends on the characteristics of the weapon in question. Is the incoming missile armored? Is it maneuvering?

[JGregory32]

It's spelled "laser."

Terribly sorry, I thought laZer was the proper term but I stand corrected.

As for the characteristics of the weapon I not quite sure what you mean by armored. The warhead would have a casing but would it not be as thin as possible to save on mass?

Again according to Atomic Rocket the mass of the warhead itself would be 1/2 a metric ton, so 500 kilograms. That's not counting the casing or fuel needed.

As for maneuvering I would imagine that they would spin the warhead like a bullet as a anti-laser technique. If the warhead is spinning then doesn't that decrease the amount of damage a laser can do because it increases the surface areas the laser needs to affect?

[GrandMasterTerwynn]

It's spelled "laser."

Terribly sorry, I thought laZer was the proper term but I stand corrected.

As for the characteristics of the weapon I not quite sure what you mean by armored. The warhead would have a casing but would it not be as thin as possible to save on mass?

The warhead may employ some ablative material of sufficient thickness to harden it against missile-defense lasers/railguns long enough to get it through the engagement window of your target's PD. After all, a missile probably isn't going to be cheap. (After all, you're building what amounts to a miniature spaceship.)

As for maneuvering I would imagine that they would spin the warhead like a bullet as a anti-laser technique. If the warhead is spinning then doesn't that decrease the amount of damage a laser can do because it increases the surface areas the laser needs to affect?

Spinning up the warhead will make it difficult to maneuver, as it will now be gyroscopically stabilized. This may be a tactic that you employ as the missile enters its terminal phase, as by that point, it's very nearly out of delta-V and only needs to survive long enough to get to its preplanned, or proximity-fused initiation point.

[JGregory32]

when discussing advances in nuclear weapons does an increase in damage rating i.e. from one to two gigatons mean the explosion will release more radation or more energenic radation?

Would a two megaton bomb release twice as much radiation as a one megaton bomb or would it's radation have twice the radius of effect?

[phongn]

when discussing advances in nuclear weapons does an increase in damage rating i.e. from one to two gigatons mean the explosion will release more radiation or more energetic radiation?

The yield of the weapon refers to how much energy is released.

Would a two megaton bomb release twice as much radiation as a one megaton bomb or would it's radiation have twice the radius of effect?

A 2MT device would release twice as much energy as a 1MT device. As energy is being spread in all three directions, to get double the destructive radius you need to cube the difference: in this case ~ 2³ = 8 times as much energy.

[Venator]

Another question on the topic - if a ship had heavy armour for a "hard" sci-fi vessel (including, for example, a lead armour belt), as well as EMP hardened electronics, would that not negate most of the nuke's effectiveness?

I'm aware that some forms of radiation invalidate anything but an unrealistically thick armour layer, but it'd certainly reduce the efficiency of a radiation bomb.

[phongn]

Another question on the topic - if a ship had heavy armour for a "hard" sci-fi vessel (including, for example, a lead armour belt), as well as EMP hardened electronics, would that not negate most of the nuke's effectiveness?

Yes. However, that's a lot of mass to haul around, and dense material are very bad for defending against charged particles. Of course, if the device initiates close in, then it might just melt your armor anyways. EMP is not going to be an issue, but injecting enormous amounts of energy into the waveguides will be.

[K. A. Pital]

Depends on the proximity of detonation and the yield.

Personally I find it dubious to think that small nuclear devices could seriously harm sufficiently large starships, but they would be killing to hard sci fi (meaning current level or a little more advanced) space stations and ships (Shuttles, Burans, ISS type objects) if detonated in immediate proximity.

Without the VA belts to accumulate radiation and no HEMP in deep space, you're looking only at direct ionizing radiation. To kill with that would require a rather powerful device. The killing ability of the rays declines pretty fast, so detonations will have to be close.

Perhaps rockets with 100 kt or more yields, neutron bomb type preferred, could serve as a good enough weapon.

[Junghalli]

I'll just point out that for ship to ship combat there's probably no real reason to use nukes anyway. Just make the missile a hollow can of fuel with a rocket and a guidance system and slam it into the enemy ship: at 3 km/s it packs the equivalent of its own mass in TNT. If you want an area effect weapon fill its warhead with ball bearings and disperse them explosively in a shotgun pattern.

[JGregory32]

I'll just point out that for ship to ship combat there's probably no real reason to use nukes anyway. Just make the missile a hollow can of fuel with a rocket and a guidance system and slam it into the enemy ship: at 3 km/s it packs the equivalent of its own mass in TNT. If you want an area effect weapon fill its warhead with ball bearings and disperse them explosively in a shotgun pattern.

Actually because radiation is a speed of light effect (or so close that it doesn't matter) and the effective radius of a one megaton neutron bomb is 300km then battle between two ships with widly divergent delta V's becomes possible. Also becasue of the area affected what would be a clean miss by a shotgun ballbearing bomb turns into certain death.

Also becasue a neutron bomb would kill the crew WITHOUT doing major damage to the ship then you can acquire the ship for yourself.

[Junghalli]

Does anybody have data on how large a lazer would have to be to kill a one megaton warhead at 300km?

It's not a question of size so much as intensity. This will be a factor of two things:

1) Power. It needs to be able to apply sufficient energy to the target to damage it.

2) Wavelength. Lasers are subject to diffusion: like flashlight beams they have the form of spreading cones getting steadily wider and hence weaker the farther you get from the source. The higher the wavelength the less the beam will spread out. Also mirror size, which likewise has to do with how tightly collimated the beam will be.

It's complicated to figure out, I suggest you read the Atomic Rocket section on lasers. But the short version is that a laser's intensity can be calculated as follows.

RT = 0.61 * D * L / RL

RT = beam radius at target (meters)
D = distance from laser emitter to target (meters)
L = laser wavelength (meters)
RL = radius of the lens (meters)

To calculate the beam intensity figure out the surface area of the circle the beam forms using RT and then divide the beam power by that. Then calculate how much energy is required to melt through the surface and divide that by the beam intensity to figure out how long it'll take to burn the missile. A flimsy modern missile might require 10 kilojoules per cm^2 (100 MJ/M^2) to kill. A missile designed with PD lasers in mind might be three or four times "tougher", and you could double or triple that again by spinning the missile. So call it 90 KJ/cm^2.

Now I did some sample calculations for a 400 nanometer wavelength laser with a mirror 10 meters across and a power level of 100 MW a while back

At 10,000 km -- 4 seconds for thermal kill
At 20,000 km -- 17 seconds
At 30,000 km -- 40 seconds
At 40,000 km -- 71 seconds
At 50,000 km -- 113 seconds

This is a rather high wavelength laser but generally yes, 300 km will be eating the gun muzzle range for a high-energy point defense laser. Your nuke will be very hard-pressed to survive long enough to get that close, so you'll probably have to spam the enemy with lots and lots of missiles and hope they keep his PD lasers busy enough that one makes it through.

This is why I tend to favor KE missiles over nuclear. They'd be lighter so you could carry more of them, which is definitely desirable in this sort of battlefield.

[JGregory32]

What if you fired mixed loads? Sort of like a MIRNV (multiple independant reentry nuclear vehicle) carrying a half-nuke half-grapshot load.
Of course this puts the PD in the position of trying to guess which is the nuke which will kill at 300km and which is the grapshot which will kill at contact. Of course you will be firing in multiples of two (for mass balance) and if each missle carried 10 warheads then the PD has to deal with at least 20 warheads and if you paint them black them optics will have a hard time tracking them until they get close enough for Radar to reliably target.

[Sarevok]

Regarding spacecraft vulnerability to nuclear weapon it seems it always boils down to the crew. Even 20 inches of steel can't keep out enough neutrons to save a person as Sea Skimmer mentioned. While a spacecraft massing more than a few thousand tons would be impossible vaporize via a kiloton level nuke without a direct hit it would be left a derelict.

This raises an interesting question. How would a fully automated heavy armored spacecraft with vital components shielded against radiation do if a nuclear weapon is detonated within a few hundred meters ?

[JGregory32]

How big a nuclear weapon and what kind of shielding? At a few hundred meters there is going to be hull plates ripped in half if not shredded. Not to mention that sometimes material that gets irradiated seems to..well... change.

I'm not sure of the science behind it, the section on atomic rocket that mentioned it was way over my head but apparently when you get a high enough radiation dose to most kinds of metals they either become isotopes of those metals or possibly bumped up the periodic table into different kinds of materials with different properties.
If someone could explain how that works in a manner that a non-physcist could understand I would really appreciate it.

[JGregory32]

http://www.5596.org/cgi-bin/nuke.php
It's a good calculator for nukes in space.

[Junghalli]

What if you fired mixed loads? Sort of like a MIRNV (multiple independant reentry nuclear vehicle) carrying a half-nuke half-grapshot load.

Could work, but you'd have to make the warheads of both missiles the same mass, otherwise the enemy will be able to tell which is which by how hard the missiles' engines are thrusting to accelerate them and prioritize the more dangerous ones. And if they have the same mass and are equally likely to get through why not just use whichever system turns out to be the most effective?

and if you paint them black them optics will have a hard time tracking them until they get close enough for Radar to reliably target.

Not true. They'll be extremely visible however you paint them, because they're rockets. To accelerate toward the enemy ship they have to blow hot gas out of their nozzles and that's going to stand out very clearly in the IR. If they stop accelerating determining their position is a simple matter of math. There is no stealth in space.

[Sea Skimmer]

This is why I tend to favor KE missiles over nuclear. They'd be lighter so you could carry more of them, which is definitely desirable in this sort of battlefield.

They might be lighter but they have to get all the way to a direct hit to do anything… if the enemy has lasers that can destroy a nuclear missile at 300km then they’ll be able to destroy the guidance system on a kinetic missile even further away. Without guidance a kentic missile is very easily evaded.

Also remember a KE missile has to be way more energetic then a nuke at the end of its flight to be able to actually score a hit on a warship that can maneuver. This isn’t an atmosphere, a missile can’t just coast to the target at super high speed and use fins to maneuver to hit it, it has to remain under power and be able to compete with the sustained boost from a warships much larger engines over the whole missile time of flight, which could be many minutes. That demands a big ass missile with lots of fuel, compact it will not be. A spread of nuclear weapons meanwhile, can realistically expect to fill a large area of the projected enemy path with bursts reducing the need for accuracy and mid course maneuvers. A 250kt nuclear warhead is only 300lb, the lightest possible nuke with subkiloton yield would be about 40lb, that’s not a particularly terrible penalty to pay for a vastly increased kill envelope. I’d expect either type of missile to be multistaged.

[phongn]

How big a nuclear weapon and what kind of shielding? At a few hundred meters there is going to be hull plates ripped in half if not shredded. Not to mention that sometimes material that gets irradiated seems to..well... change.

Why would they be ripped in half or shredded? There's no blast wave in space to do mechanical work like that.

I'm not sure of the science behind it, the section on atomic rocket that mentioned it was way over my head but apparently when you get a high enough radiation dose to most kinds of metals they either become isotopes of those metals or possibly bumped up the periodic table into different kinds of materials with different properties. If someone could explain how that works in a manner that a non-physicist could understand I would really appreciate it.

How much about physics do you understand? The description is basic high-school physics, really, but if you don't have that you're going to be in trouble if you want to seriously discuss this.

[Crayz9000]

Probably the best method of protecting a spacecraft (realistically) against nuclear weapons would be this:

1. A magnetic shielding system that has an effect over the entire spacecraft, or most of it anyway.
2. Assuming the spacecraft is driven by an engine powered by D-D or D-T fusion, one of the fuels can be stored in the form of heavy water. The crew compartment can be suspended inside the heavy water storage, and lined with a layer of depleted uranium and secondary layer of neutron absorber material.