Use of Nuclear Artillery in space combat

[GrandMasterTerwynn]

Also FYI unless your ship is moving in perfect strait line even tiny movements ( moving .005 inches to the right) is more than enough to cause a total miss because people always forget... Space is big, any hypothetical combat engagement would occur at huge ranges with lasers for the close up "IE inside a 250,000 km bubble" work were weapons will be instant hit. Where even a super agile craft simply won't be able to dodge.

One big problem. The only laser capable of doing ship-killing damage at 250,000 km, without requiring a giant aperture, would be a hard X-ray laser. To build an X-ray laser of the free-electron variety requires an electron accelerating ring a kilometer in diameter. Lasers of longer wavelength require much higher apertures and energy inputs to produce a beam tight enough and potent enough to poke holes in things at ranges one or two orders of magnitude less than a light-second.

So where can coilguns or railguns or other solid projectile weapons be useful? Hmmm considering they are not C, much less than what a Laser can give you, with extra mass savings because the Laser's only ammo is energy, which you need to produce anyway.

Higher efficiency, I suspect. If mass drivers can achieve 90%+ efficiency, they're doing much better than lasers which tend to achieve considerably worse efficiencies (I'm not sure what the maximum theoretical efficiency of a laser is. I think it's between 50% to 80%. Which means laser weapons have significant waste heat problems which require creative solutions.)

[Mr Bean]

Higher efficiency, I suspect. If mass drivers can achieve 90%+ efficiency, they're doing much better than lasers which tend to achieve considerably worse efficiencies (I'm not sure what the maximum theoretical efficiency of a laser is. I think it's between 50% to 80%. Which means laser weapons have significant waste heat problems which require creative solutions.)

Second point first
A mass driver, lets say it fires a .1 C projectile at a target 300,000km's away. So ten seconds to cross the distance assuming a stationary target. So lets say it's a ship going at a very slow space speed, escape velocity at 11.2 kilometers a second.

A mass driver would then be trying to hit a target that covers a volume of 90 kilometers across in the time it takes from firing to hitting the target. And we are assume a very... very slow spacecraft. Slowing down by even a small fraction will cause a near miss. The faster your going the slower the fraction gets. What about a 2,500 kps spacecraft? Even slowing down by .005 kps will cause a 100+ kilometer miss.

If your shell can't readjust for these tiny changes in speed it's going to miss and miss and miss. And the faster your target goes the bigger the target area. The more shells you have to throw. And the less and less argument you can make for efficiency.

[Sea Skimmer]

Higher efficiency, I suspect. If mass drivers can achieve 90%+ efficiency, they're doing much better than lasers which tend to achieve considerably worse efficiencies (I'm not sure what the maximum theoretical efficiency of a laser is. I think it's between 50% to 80%. Which means laser weapons have significant waste heat problems which require creative solutions.)

Waste heat isn't that crushing a deal really, you could dump it into the ships propellent supply (nuclear powered or not the ship must have some kind of propellent) and then radiate it into space over a long time latter. This is the current plan for cooling aircraft lasers. A laser also has the nice advantage that since it has very minimal recoil for its firepower, shooting it off in space won't require a major engine burn to avoid slowing down the firing ship like a railgun or coilgun would. However I am absurdly skeptical that a laser will ever be able to focus its power into a worthwhile area at anything like the ranges people are speculating. They may never work well past tens of thousands of kilometers or even much less then that. Current uses of very long range lasers like measuring the distance to the moon simply don't require a tightly focused beam.

[spartasman]

So, is nuclear artillery useful? I mean, in realistic space warfare, without "inertial compensators", Wouldn't you be able to hit your target? Even if it is still moving very fast, certainly a computer could calculate the difference.

[Starglider]

So, is nuclear artillery useful? I mean, in realistic space warfare, without "inertial compensators"

Did you actually read the answers? Short answer, no. Conventional guns have too low a muzzle velocity to be of any use. Very high velocity EM guns don't need a nuke, because their sheer velocity will already mission kill any plausible spacecraft, and a cloud of darts is more useful than the tiny nuke you could fit into the shell. Guidance in the shell is essential and it'd be nearly impossible to squeeze that and a nuke in, plus nukes are really expensive for negligible gain.

You might want to carry a few high-yield nuclear missiles for special purposes though, e.g. ground strikes, taking out dispersed space complexes in fewer shots etc. BSG got that part right.

[Ford Prefect]

(I'm not sure what the maximum theoretical efficiency of a laser is. I think it's between 50% to 80%. Which means laser weapons have significant waste heat problems which require creative solutions.)

I recall a paper mentioning 80% maximum theoretical efficiency, but I don't recall the exact type. I distinctly remember the 80% number, however.

[GrandMasterTerwynn]

So, is nuclear artillery useful? I mean, in realistic space warfare, without "inertial compensators", Wouldn't you be able to hit your target? Even if it is still moving very fast, certainly a computer could calculate the difference.

As has been stated numerous times in this thread . . . not really. Not unless you make it a miniature nuclear missile. The values I picked in my example were not accidental. You can have a 0.5 kiloton nuclear warhead in a 100 kg missile (the real-life example was the AIM-26 Falcon nuclear-tipped air-to-air missile. That had a 0.25 kiloton warhead onboard, but the device was a design that could be dialed clear up to a kiloton.)

Guidance would be very simple (guiding commands being issued from the firing ship,) due to the requirement that the electronics and RCS be capable of witshtanding the huge EM flux inside the mass driver and the huge acceleration of the 'shell' being fired.

Even then, ranges would be inside a few tens of thousands of kilometers against a limited combination of engagement trajectories where the relative velocities are much less than that of the shell.

Worse, the 20 billion joules of kinetic energy imparted on my putative 20 km/sec 100 kilogram nuclear shell requires that the firing ship absorb 20 billion joules worth of recoil energy. Enough to accelerate a 100,000 metric ton ship 20 meters/sec in the opposite direction (How's that for recoil kids? Can you say "ouch?" Good.) Yes, there are creative ways you can address this problem . . . except that none of this is really necessary.

A 0.5 kiloton nuclear device will impart over two trillion joules of energy on a target. The kinetic energy of its delivery vehicle will impart 20 billion. A reasonably-hard sci-fi ship, however, can be killed using enough shots in the megajoule range.

To whit, a 1 kilogram slug being accelerated to the same 20 km/sec as my nuclear shell from earlier carries 200 megajoules of kinetic energy. Being much smaller, it will be much harder to intercept. Of course, it will be completely unguided, so the firing ship will be required to apply some smarts in deciding where to shoot. However, for the energy expenditure in firing one guided nuclear shell, we can fire 100 of these 1 kilogram slugs, for the exact same mass penalty as the one nuclear shell. Even better, the 100,000 ton firing ship only gets accelerated to 4 m/s in the opposite direction. This is still nasty, but more manageable than shooting off the nuclear shell.

A 100 gram ball-bearing from hell accelerated to 20 km/sec has 20 megajoules of KE. Roughly the same kinetic energy carried by a box truck running into a brick wall at highway speed. A thousand of these can be fired for the price of one nuclear shell. The recoil velocity of the 100,000 ton ship? 0.63 m/sec.

[spartasman]

I had read the comments, but most of it seemed to be between regular railguns/coilguns. What about nuclear shells being used as a point defense weapon, or as some sort of tactical orbital bombardment device? Both of those rolls would not necessitate incredibly high speeds and could be useful.

[Simon_Jester]

If the enemy runs out of fuel trying to evade your salvos, well, that's just as good as actually blowing him up though.

True, but while he's dodging he's also shooting back. Which means you have to be dodging too, which means there's no guarantee he'll run out of fuel first.

Also FYI unless your ship is moving in perfect strait line even tiny movements ( moving .005 inches to the right) is more than enough to cause a total miss because people always forget... Space is big, any hypothetical combat engagement would occur at huge ranges with lasers for the close up "IE inside a 250,000 km bubble" work were weapons will be instant hit. Where even a super agile craft simply won't be able to dodge.

Well... for hard-SF standards of "agile," manned craft won't be able to dodge light speed or high-relativistic weapons at those ranges. Unmanned craft capable of something like ~10g lateral accelerations might, and it's theoretically possible to design such a beast, but I'm not sure they'd be good for much. They certainly wouldn't be easy to build.

So where can coilguns or railguns or other solid projectile weapons be useful? Hmmm considering they are not C, much less than what a Laser can give you, with extra mass savings because the Laser's only ammo is energy, which you need to produce anyway.

As a general rule, the paraphernalia for a high energy laser are pretty extreme (and massive), so I wouldn't count on that.

One big problem. The only laser capable of doing ship-killing damage at 250,000 km, without requiring a giant aperture, would be a hard X-ray laser. To build an X-ray laser of the free-electron variety requires an electron accelerating ring a kilometer in diameter.

Hmm... You might be able to do it with a linac; that's how they do it at the LCLS. Still going to be a big damn linac, but not necessarily a totally unmanageable one.

[GrandMasterTerwynn]

I had read the comments, but most of it seemed to be between regular railguns/coilguns. What about nuclear shells being used as a point defense weapon, or as some sort of tactical orbital bombardment device? Both of those rolls would not necessitate incredibly high speeds and could be useful.

Point defense? Why would you use a nuclear device as point defense? Knock down incoming missiles? A counter-missile can mission- or otherwise kill an incoming missile simply by smashing into it. In the vacuum of space, a nuclear device will produce a (very) bright flash of x-rays, a shower of alpha and beta particles, and a few kilograms of highly radioactive debris. This bright flash of x-rays and gamma rays will be about as hazardous to you as it will be to what you're defending against. Especially if the distances are short.

Orbital bombardment? Why would you need nuclear artillery? You could just dump the nuclear reentry vehicles out the back of the spacecraft. If you wanted to minimize excess irradiation, you could use your mass drivers to do pinpoint bombardment.

[Kuroji]

Nukes are nigh-useless as point defense. In space, you don't get a mushroom cloud or a shockwave to knock incoming projectiles off-target. Unless it's detonating very close to incoming projectiles they're not going to absorb enough radiation to affect them significantly.

[Purple]

Nukes are nigh-useless as point defense. In space, you don't get a mushroom cloud or a shockwave to knock incoming projectiles off-target. Unless it's detonating very close to incoming projectiles they're not going to absorb enough radiation to affect them significantly.

Just for the record, what exatcly does "very close" consitute?
Tens or hundreds of meters I presume? Or is it less, I really need an estimate.


Sounds viable as a form of last resort when all else fails and for hitting static targets that can't defend them self.

[Vendetta]

Nukes are nigh-useless as point defense. In space, you don't get a mushroom cloud or a shockwave to knock incoming projectiles off-target. Unless it's detonating very close to incoming projectiles they're not going to absorb enough radiation to affect them significantly.

Just for the record, what exatcly does "very close" consitute?
Tens or hundreds of meters I presume? Or is it less, I really need an estimate.


Sounds viable as a form of last resort when all else fails and for hitting static targets that can't defend them self.

Even then against an incoming kinetic projectile you're not going to do a whole heap of anything useful. Because the projectile is small, you have to be detonating really really close to do anything significant to it.

Even if you can get it to heat enough to fragment due to thermal expansion stress all the bits are still coming towards you.

[Kuroji]

Just for the record, what exatcly does "very close" consitute?
Tens or hundreds of meters I presume? Or is it less, I really need an estimate.


Sounds viable as a form of last resort when all else fails and for hitting static targets that can't defend them self.

For the record? Tens, maybe, but I haven't done the math to figure out which would be the best distance for that. It depends on the yield the nuke would normally have, and whether you're shooting it on a trajectory that gives it a near-miss or that has the nuke directly in front of it.

Just remember the inverse square law, despite the fact that nukes are less effective in space they're still spitting out lots of radiation, but the further away from it the projectile you're trying to intercept is, less of the radiation will affect it. If you're going for vaporization of the projectile you'd need an almost-direct hit, I imagine, but if you're intercepting it far enough out and it's not actively guided (or if the radiation fries the guidance system) the impact of the radiation may push it off course.

Of course, at that point it's not exactly point defense anymore...

[adam_grif]

To people saying nukes wouldn't be worth it for unguided munitions, why is that? Even if the shell does as much/more damage by striking, doesn't the ability to miss by a few dozen or hundred meters and still make a kill make it very useful? Especially since dodging is the most viable form of defense against high velocity slugs?

[Kuroji]

Well, that depends how big your supply of radioactive material is and how many warheads you plan to keep in stock on your ships. Keep them there too long and they won't be any good after a long enough span of time, depending on the material. Nukes are not cheap things, and even if they become cheap in the future by way of having your bomb be pure fusion forced by laser, eventually the cost for those will add up. You might be better off looking for a dedicated point defense solution and using nukes as a holy shit we're all going to die fire everything measure against something really nasty coming your way.

[adam_grif]

Nukes are cheaper than the delivery vehicles they ride on. A "~500,000 / physics package" figure got thrown around in a thread earlier in the year, which is chump change compared to the cost of missiles they get strapped too regularly. More costly than slugs, sure, but compared to the cost of several hundred meter long railguns to deliver them and the cost of building a spaceship it's going to be nothing.

U-235 has a half life of 703.8 million years, so I doubt we're going to run into problems from that, unless you were referring to other kinds of "going bad". We might also deal with pure fusion weapons, but that's less likely. We can get MT yield nuclear warheads in surprisingly compact packages, and KT yield ones in calibers far lower than the proposed Navy railguns.

Inverse square and all that makes destructive potential drop off rapidly, but iirc they still create impulsive shock at a few hundred meters.

[Sarevok]

Only 500k USD to make a nuclear device ? The world would be floating in more nukes than smart bombs and cruise missiles. Security be damned its hard to see how you contain spread of a city killer missiles when they cost no more than a equivalent explosive filled weapon.

[adam_grif]

Control of fissile materials obviously. I think that was a mass production price at the height of production. The difficulty has always getting fissile materials, everything else is standard engineering. If it was millions and millions of dollars per unit, I doubt they would have stockpiled as many as they did.

[Starglider]

Inverse square and all that makes destructive potential drop off rapidly, but iirc they still create impulsive shock at a few hundred meters.

You can either have a nuke pumping out X-Rays into that volume, or you can have a fragmenting warhead that fills that volume with heavy metal darts. The nuke is a unitary object that can be turned into an inert lump by point defences; the one thing 'point defence nukes' are actually good for is defending against other nukes, because the neutron surge can make other warheads in range fizzle. The darts are tiny (hard to track/hit) and inert (immune to neutron flux, unaffected by partial vaporisation). As I said, you might carry some nukes for special situations, but if you have high velocity launchers they will not be tactically optimal for attacking hostile warships.

[Sarevok]

Control of fissile materials obviously. I think that was a mass production price at the height of production. The difficulty has always getting fissile materials, everything else is standard engineering. If it was millions and millions of dollars per unit, I doubt they would have stockpiled as many as they did.

It was only around 50000 nuclear devices at the very height of the cold war. And achieved with the massive investment by superpowers. Other nations like India and Pakistan struggle to build more than a handful per year. Nukes are silver bullets for their nations if they could make 500 more nukes in 5 years they would literally eat dirt to do so.

[Purple]

For the record, where can I find the exact numbers on why nukes become less effective in space? Or are you just saying it like that?

[adam_grif]

For the record, where can I find the exact numbers on why nukes become less effective in space? Or are you just saying it like that?

You don't need exact numbers. The explosion that nukes create in atmosphere doesn't happen in vacuum because it's caused by the X-rays being output by the nuke super-heating the surrounding air. Without this, the only way to do damage is for the radiation to superheat the enemy hull, but because of the inverse-square law, the amount of radiation striking the enemy hull is going to be worthless at ranges out from 6-700 meters. At 1 KM, you basically have to be using stupendously powerful nukes to do anything approaching real damage. If you want to use reasonably sized devices, you'll want to strike closer than 500 meters, ideally no more than 250.

[GrandMasterTerwynn]

For the record, where can I find the exact numbers on why nukes become less effective in space? Or are you just saying it like that?

If you took the nuclear device by itself, it just produces a bunch of gamma rays and x-rays, a number of alpha and beta radiation particles, a spray of neutrons, and some tens of kilograms of vaporized, highly-irradiated nuclear device casing material. That's all. Nuclear weapons produce their destructive effects on the ground through a combination of thermal pulse and blast effects. These are both reliant on the interaction of the nuclear initiation with the Earth's atmosphere. The thermal pulse? You only get that after x-rays and gamma rays slam into the atmospheric gasses and shred them into plasmas. The photons keep bouncing around in there until they emerge as much lower-energy infrared and visible light photons. The blast? Well, the above produces a lot of hot, rapidly expanding gas.

None of which are possible in a vacuum. In a vacuum, all you get is a pulse of hard radiation and a rapidly dispersing cloud of plasma and incandescent gas that used to be the device's casing and delivery vehicle (which won't amount to much.) The pulse of hard radiation loses strength according to the inverse-square law (i.e. the intensity of radiation diminishes as a function of the square of the distance from the event.)

[Purple]

Thanks for the info. I flat out forgot about the ISL... :oops: