Use of Nuclear Artillery in space combat

[spartasman]

Ignore this first post.

[spartasman]

Watching shows like (new) Battlestar Galactica, I cannot help but wonder why it is that the main armament of many sci-fi series tends to be nuclear missiles instead of some form of nuclear artillery. Though they would have a much lower yield, they would be relatively invulnerable to anything other than impossibly accurate point defense weapons. With a higher fire rate than missiles, and without any real way to intercept nuclear-tipped shells, why is it not that these are the main weapons of space warfare (excluding series with shields and giant lasers).

[Nephtys]

Why exactly can't you intercept a nuclear shell? There's no difference between what could be called a 'shell' and a 'missile', except guidance and on-board delta-V. You've made a lot of assumptions. And in any space combat scenario with projectile weapons, a single guided projectile with a worthwhile warhead is going to be worth more than an unguided one.

[spartasman]

A shell would be far smaller than a missile without said guidance systems and rocket boosters, and unless I am mistaken that makes it harder to hit. Shells could have the capability of being fired very quickly, whereas missiles usually need firing tubes and near-constant maintenance. As in nBsG, the main armament of the Battlestar was its main anti-ship cannon, with 12 nuclear missiles as well. Would it not make sense to save the space on a warships by simply using nuclear shells?

[Kuroji]

Screw that. It would make more sense to adopt spinal gauss cannons and fire solid metal chunks at c-fractional. Then you don't need nukes anymore, you've functionally GOT them.

The problem with nukes in space is that their impact is quite limited, honestly. There's no atmosphere, so most of a nuke's power goes into vaporizing itself. If BSG was half as hard sci-fi as it intended to be, Galactica's crew would've been dead in a month thanks to radiation poisoning from the nuke that impacted. There's no atmosphere to produce shock or thermal effects, the only thing affected by that is the ship itself, and that's assuming it's basically right up against the hull. (Okay, okay, I'll admit they actually did handle it quite well aside from the effects of radiation...)

[Drone]

Screw that. It would make more sense to adopt spinal gauss cannons and fire solid metal chunks at c-fractional. Then you don't need nukes anymore, you've functionally GOT them.

The problem with nukes in space is that their impact is quite limited, honestly. There's no atmosphere, so most of a nuke's power goes into vaporizing itself. If BSG was half as hard sci-fi as it intended to be, Galactica's crew would've been dead in a month thanks to radiation poisoning from the nuke that impacted. There's no atmosphere to produce shock or thermal effects, the only thing affected by that is the ship itself, and that's assuming it's basically right up against the hull. (Okay, okay, I'll admit they actually did handle it quite well aside from the effects of radiation...)

Wouldn't the ship have to be shielded against radiation for the crew to survive long term in space?

[Stark]

Unguided projectiles are going to be less accurate than missiles. And if you look at the horrific accuracy in nBSG, they'd look pretty stupid throwing thousands of nuclear warheads downrange and praying on hits. Since they have little or no delta-v you can focus your point defence efforts. The call between missiles and guns is one based on range and visibility factors and not 'lol one is better'. Anyone can invent a situation where one or the other would be preferrable; at 50,000kms a gun will likely be totally worthless against a point target, but soft-launched, terminal-power missiles could sneak close and get a hit regardless.

'Hard' scifi with spinal mounts = rofflecoptors. Spinal mounts at nBSG ranges = rofflecoptors.

[Connor MacLeod]

Frankly I think the OP is making a number of assumptions that wouldn't neccesarily hold true for various reasons (For example, what sort of launch mechanism for missiles are we looking at? What launch mechanism for projectiles?) Propulsion/firing methods also make a difference, as do engagement ranges, and other factors.

Edit: I'm not even going to comment on spinal weapons, not even to question how you frigging aim the things.

[Starglider]

Edit: I'm not even going to comment on spinal weapons, not even to question how you frigging aim the things.

Spinal mounts are a perfectly good solution for shooting at things that are sufficiently far away that orienting the whole ship to track them isn't a problem. Fine aiming would probably be implemented by a magnetic deflection collar on the end of the barrel (likely a significant fraction of the weapon's length/mass). The projectiles themselves would have at minimum cold gas thrusters and IR terminal guidance (ridiculously cheap compared to all the other costs of combat spacecraft). The primary benefit vs a missile is crossing the point defence envelope so fast that there isn't time to vaporise or deflect it; if spacecraft are defending themselves with ABL type lasers (that pulse over several seconds) that's an important benefit. If extremely high power sub-microsecond pulse lasers are available then maybe not, but the other potential advantage of mass drivers is that more rounds can be carried (possibly a lot more). Exactly how useful this is depends on technological and strategic factors, but it's easy to construct scenarios where it's a decisive advantage.

[Stark]

Using large throwers like spinal mounts to throw missiles is a better use than praying the divergence on the shell doesn't make them horribly miss; but it still comes down to range and sensors. Spitting out an array of stealthy missiles that ignite close enough and from vulnerable vectors to avoid some point defence is at least interesting.

The idea of throwing anything significant at high fractions of c is pretty dumb for 'hard' scifi.

[Kuroji]

Wouldn't the ship have to be shielded against radiation for the crew to survive long term in space?

Yeah, probably easiest to assume this is the case. Depends on how their engines worked, not to mention their FTL.

Unguided projectiles are going to be less accurate than missiles. And if you look at the horrific accuracy in nBSG, they'd look pretty stupid throwing thousands of nuclear warheads downrange and praying on hits. Since they have little or no delta-v you can focus your point defence efforts. The call between missiles and guns is one based on range and visibility factors and not 'lol one is better'. Anyone can invent a situation where one or the other would be preferrable; at 50,000kms a gun will likely be totally worthless against a point target, but soft-launched, terminal-power missiles could sneak close and get a hit regardless.

'Hard' scifi with spinal mounts = rofflecoptors. Spinal mounts at nBSG ranges = rofflecoptors.

Flak cannons in space (and not expecting that flak to fly at high speed forever in all directions and bounce off your hull) = rofflecoptors. Just for the record. But no, seriously, I gave up trying to justify anything in nBSG when I saw the anvilicious final episode. Beside, the Colonials probably didn't have the right tech to do it -- I don't think their guns worked via magnetic principles or there wouldn't be anyone freaking out about assembly line sabotage of the powder charges because you'd just cast the slug and it's ready to go, unless it's using both powder and gauss to propel it for some reason.

[Starglider]

Using large throwers like spinal mounts to throw missiles is a better use than praying the divergence on the shell doesn't make them horribly miss

As I said, any realistic projectile is going to have some delta-v capability. Large projectiles will also most likely have a warhead consisting of a bundle of penetrator darts split by a small dispersal charge shortly before impact (improves PK and point defence workload).

The thing is, you only need enough delta V to account for (a) the inherent inaccuracy of the gun, which will be very small for a magnetically targetted device (certainly much smaller than for a physically trained barrel) and (b) any maneuvers the target might make in the time the projectile takes to get there. (b) doesn't depend on the engine power of the target, it depends on the rate of change in that engine power, which is quite limited. Having a big solid rocket motor in the projectile instead of cold gas thrusters reduces the hitting power, because the increase in KE you get from accelerating the projectile is lower than the KE lost by throwing the mass of the fuel away, and because you'll have less room for penetrator darts (or a nuke, if so inclined). I am inclined to believe that compromising gun/missile in this way will not work out very well; just like gun-launched missiles from tanks in fact. Better to carry a mass driver optimised for the most likely engagement envelope (maximal velocity and energy in the dart cloud, against a peer warship with point defence) and then a few racks of general purpose low-acceleration high-delta-v missiles (with restartable engines) for odd situations (long range strikes on poorly defended targets, reconaissance by fire, minimal-burn stealth attacks, lobbing pot shots to tie up defences etc).

Spitting out an array of stealthy missiles that ignite close enough and from vulnerable vectors to avoid some point defence is at least interesting.

To get any significant change in vector, the missile will have to have a lot of delta v (to change its direction in order to dogleg). A mass-driver launched projectile using cold gas thrusters can stay stealthy in IR, a missile will be instantly visible as soon as it lights off the engine. Can it accelerate fast enough to home on the target before getting picked off? Can it be stealthy to active radar/lidar in the first place, considering that it has a higher cross section than a mass driver shell (particularly since you're firing it off-axis to the target)? It's not impossible that this combination would make sense, but again I suspect having two different weapons systems optimised for different engagement modes will work better than compromising. Mass driver launched missiles are forced to be small, light and resistant to massive acceleration and EM field intensity, all for a very limited tactical improvement over either cold-gas guided shells or large conventional launch missiles (and numerous drawbacks).

The idea of throwing anything significant at high fractions of c is pretty dumb for 'hard' scifi.

Particle beams excepted of course (small mass I know but 'significant' in the 'tactically useful' sense).

[Stark]

Man, you can't make this stuff up. It's almost as if sensor and gun problems won't introduce variance in the fire at all! Good thing 'mass driver' only means one thing. Well, now we've settled that the future involves one boring type of gun, I wonder why nobody ever uses it in fiction?

[Traveller]

Flak cannons in space (and not expecting that flak to fly at high speed forever in all directions and bounce off your hull) = rofflecoptors. Just for the record. But no, seriously, I gave up trying to justify anything in nBSG when I saw the anvilicious final episode. Beside, the Colonials probably didn't have the right tech to do it -- I don't think their guns worked via magnetic principles or there wouldn't be anyone freaking out about assembly line sabotage of the powder charges because you'd just cast the slug and it's ready to go, unless it's using both powder and gauss to propel it for some reason.

That episode annoyed me as well. The colonials clearly have rail-gun technology, yet there vipers are armed with what looks suspicously like .50cal rounds. You would think they would at least arm those impratical and tactically worthless space-fighters with them, since your not wasteing all that space and mass on propellant and caseing, you can carry a lot more ammo. Given how small a viper is, how did they find room for life-support, engines,fuel, missles!, avionics AND any decent amount of all those volume-hogging chemically propelled slugs Rail-guns are an elegant soluton logistically, especially for a warship-on-the-run ,all you need is raw metal, no electronics, no chemcials, none of that. I can see why they would keep chemical slug throwers around for small-arms, but for a fighter?.

[Starglider]

The colonials clearly have rail-gun technology, yet there vipers are armed with what looks suspicously like .50cal rounds. You would think they would at least arm those impratical and tactically worthless space-fighters with them, since your not wasteing all that space and mass on propellant and caseing, you can carry a lot more ammo.

BSG has a lot of problems, but that isn't one of them. Firstly, I'm not clear if they even have rail gun technology, considering how much flash their main guns produce (no way that could be rail ablation plasma, wrong color and too much of it). Secondly even if you can make capship scale EM accelerator weapons, that doesn't imply you can mount them on fighters. Capships have giant fusion reactors capable of providing vast amounts of power. Vipers have engines that are probably based on direct thrust, with limited auxiluary power takeoff. EM guns without an adequate power supply would have low rate of fire and require big heavy capacitor banks in addition to the heavy electromagnets.

Given how small a viper is, how did they find room for life-support, engines,fuel, missles!, avionics AND any decent amount of all those volume-hogging chemically propelled slugs

Tylium is highly energetically efficient. The missiles are AFAIK external payloads, also the observed RoF on the guns is a lot lower than contemporary aircraft canon. A viper seems roughly equivalent to an F-16 with smaller fuel tanks and three gun mounts. As noted for fighter scale applications an EM weapon is not necessarily any more volume or mass efficient than a chemical one, after you allow for the necessary power supply and capacitor banks.

[Vendetta]

Why exactly can't you intercept a nuclear shell? There's no difference between what could be called a 'shell' and a 'missile', except guidance and on-board delta-V. You've made a lot of assumptions. And in any space combat scenario with projectile weapons, a single guided projectile with a worthwhile warhead is going to be worth more than an unguided one.

Shells are coming in "cold", no guidance and no delta-V means no or low emissions. Means they're harder to detect, so your CIWS is engaging them at shorter ranges.

Of course, if you're firing them fast enough to overcome the limits of an unguided weapon over long ranges of space combat, they're probably carrying as much or more kinetic energy as nuclear payload.

[adam_grif]

If it's unguided, jinking is going to be easier than intercepting.

[Starglider]

If it's unguided, jinking is going to be easier than intercepting.

Depends on the detection range. A cold shell is detectable by radar only, and since there are no aero concerns it can be shaped to have minimal RCS. Most likely the target ship will just be jinking continously, rather than to dodge specific shots, but remember that there is a limit to how fast engines (or even thrusters) can be throttled and vectored. As I was trying to explain to Stark before he regressed to baby speak, the projectile only requires enough delta V to overcome the launcher's pointing error and the amount the target can reasonably change their acceleration vector in the projectile's time of flight. Decent sensors and magnetic aiming reduces the former to a very low value, while high launch velocity reduces the former, making it practical to use cold thrusters for railgun projectile terminal guidance (presumably anyone who can build this kind of ship can build guidance electronics that resist the EM flux). Of course at very close ranges you can use unguided slugs, but if the ships closed to that distance their point defence systems (lasers or traversing EM guns) would probably become capable of killing the enemy.

[adam_grif]

Isn't LADAR as much / more of a concern than RADAR? And won't these "cold" shells still be readily detectable with optical sensors given that they aren't really low temperature, so long as the "muzzle flash" (whatever the term for the railgun equivelant is) is noticed?

[GrandMasterTerwynn]

Watching shows like (new) Battlestar Galactica, I cannot help but wonder why it is that the main armament of many sci-fi series tends to be nuclear missiles instead of some form of nuclear artillery. Though they would have a much lower yield, they would be relatively invulnerable to anything other than impossibly accurate point defense weapons.

Wrong. Utterly and completely wrong. Anything going less than some ridiculously high fraction of the speed of light will make for a trivial intercept, if fired on a ballistic trajectory. It will be a reasonably trivial one if fired on a powered trajectory.

Say we have a pair of ships at 20,000 km armed with railguns firing nuclear artillery. Say a Davy Crockett-sized nuclear warhead of 0.5 KT yield. Not a big warhead, true, but if it goes off inside a ship's water or fuel tanks, or inside a pressurized crew space, it will completely ruin your day. This artillery shell is launched from its railgun with a velocity of 20 km/sec. A paltry velocity, to be sure, but if the shell weighs 100 kilograms, it'll have 20 GJ of kinetic energy (this value here ought to tell you that our sci-fi might be softening up a bit.)

If the target ship has a peak acceleration of 0.1 gee, it'll only be able to effect a 1 m/s change in velocity in the 1000 second flight time of the shell. That will translate to about 490 meters worth of position change. Which leads us to our first problem, in many cases, the enemy ship can simply get out of the way.

We can fix that, though, by giving the artillery shell a small amount of delta-V for midcourse or terminal course correction. Or can we? There's a big problem here. For me to pump 20 GJ of energy into a nuclear artillery shell to kick it up to 20 km/sec, that means I'm (if we were trying to stay hard) generating at least that amount of waste heat which must be disposed of. All this means that the launch of that nuclear artillery shell is going to be a breathtakingly obvious event marked with considerable fireworks. The projectile itself will probably have its casing heated up to incandescence, which will make it obvious against the deep cold of space. Tracking it will be trivial.

If we have a reasonable idea of the shell's total delta-V and its motor performance, we can generate a plot that will look much like a skinny space-going onion. At one point will be the present location of the shell. At the other point will be the target craft. The shell's on-board fuel reserve and motor performance will constrain it to any point within that onion. Every move the target ship makes reduces the size of that onion. Conversely, the closer the shell gets, and every move it makes will further reduce the size of that onion. At some predetermined point where fire control has decided that a stand-off 0.5 kiloton nuclear initiation will be of little consequence, the target's point defense will only have to concern itself with that little window of space which the nuclear shell must come through if it hopes to impact. If the window is small, we'll use some sort of tactical high-energy laser to make the intercept. If the window is wider than that, then we do some sort of nBSG-esque dumping of kitty-litter (i.e. flak,) and then lase it.

"What if I shoot more of them?" You say. Well, they're all coming from the same point in space, have identical performance, and will come through similar sized windows in space. Some may get through the target's PD screen, but 100 kilogram nuclear artillery shells are a finite resource. Eventually you're going to shoot your magazines dry.

"What about decoys?" You ask. What about them? Sure, let's take a nuclear artillery shell and fill it with concrete and lead instead of a nuclear bomb. If it hits, it's still going to impart 20 GJ worth of fun-ruining KE transfer. Except then, we reduce the number of actual nuclear-tipped shells we can carry in our ship's magazine.

"But what if I shoot some sort of low-mass missile that looks like an artillery shell, but only weighs a third as much as a decoy?" Well . . . you're not going to get the same fireworks shooting one of these off, for it to have the same 20 km/sec velocity as an actual nuclear shell. If it was a soft-launched missile, I'm going to notice that it leaves your ship going slow and then accelerates up to speed atop a huge pillar of fire. It will be marked as an obvious decoy and moved to somewhere near the bottom of point defense's priority queue.

So, tl;dr: No, space artillery doesn't offer much advantage over a missile or beam weapon. It certainly isn't "un-interceptable."

[Uraniun235]

Maybe I saw it wrong, but I got the impression that nBSG missiles were like videogame missiles; they keep burning, but they only seem to stay at a constant velocity. Did anyone else perceive this?

[Starglider]

Isn't LADAR as much / more of a concern than RADAR?

Not really no. The surface coatings used in telescope construction scatter less than 0.1% of the incident light. Those coatings are impractical for anything exposed to atmospheric friction or weather, but they'll work fine in a space environment. Since the projectile will be arrow shaped and pointed straight at the target, the cross section will be way too low for LADAR to give a useful warning. There's also the fact that since we don't yet have optical phased arrays, LADAR has to be mechanically scanned, and that will add additional unpredictable lag to the detection.

And won't these "cold" shells still be readily detectable with optical sensors given that they aren't really low temperature

Cooling the projectiles is not only feasible, it may well be essential. High efficiency railguns will require superconductors, so you're probably looking at at least liquid nitrogen temperatures, possibly liquid helium temperatures, for the conductive sabot. Also remember that IR sensors aren't magic. Really hot things like rocket engine plumes will show up on simple staring arrays. Cold things will need telescopes to detect, and small cold things need long exposure times. Small cold fast moving things are almost undetectable even assuming the telescope is pointing in the right direction, because they don't put enough energy into any one pixel to show up over the noise. Alternatively if the firing ship and target don't have much relative movement the firing ship may mask the projectile.

so long as the "muzzle flash" (whatever the term for the railgun equivelant is) is noticed?

A coilgun produces no muzzle flash. A railgun may produce some ablation plasma from the gun, but detecting that at long range would be difficult. I suspect it would be possible to design a baffle in between the acceleration and deflection stages to absorb most of it.

For me to pump 20 GJ of energy into a nuclear artillery shell to kick it up to 20 km/sec, that means I'm (if we were trying to stay hard) generating at least that amount of waste heat which must be disposed of. All this means that the launch of that nuclear artillery shell is going to be a breathtakingly obvious event marked with considerable fireworks. The projectile itself will probably have its casing heated up to incandescence, which will make it obvious against the deep cold of space.

Incorrect. Accelerators of this nature are essentially linear motors and are already over 90% efficient. Superconducting versions would in principle be 100% efficient at the motor. Of course there would be considerable losses in the capacitors, switching, stray eddy currents in the ship structure, etc etc but that's a problem for the ship's heat rejection system, it doesn't make the shell hot. Even for conventional artillery, shell heating is limited simply because it isn't in contact with the hot propellant gasses for very long.

Every move the target ship makes reduces the size of that onion.

Remember that we are already compensating for the target's movement and acceleration. Where possible we may even be compensating for observed throttle inputs, e.g. engines ramping from cold to full burn. The uncertainty comes purely from the actual control inputs the enemy can make during the time of flight. Small thrusters have a short response time, but main engines have a much longer response time, and harsh jinking wastes precious reaction mass. If there are lots of incoming shells, either from multiple barrels or a rapid firing weapon, they will be spread to bracket the target and cover all possible trajectory divergences (as best as possible). So in short neither detection nor dodging are as easy as they sound.

[Simon_Jester]

The heart of the problem here is that shells can be intercepted just as well as missiles flying at the same speed; we already see the beginnings of this with THEL shooting down mortar bombs in mid-flight. A shell is considerably less visible than a missile, but not invisible, so it can still be targeted and countered. And unlike a missile it can't maneuver.

In space, all ballistic weapons (including relativistic particle beams and, to stretch the definition of "ballistic," lasers) are only effective at ranges short enough that the shot can reach the target before the target has time to dodge by a distance significantly more than its own width. Otherwise, the weapon can be defeated simply by making random evasive maneuvers. Depending on just how agile the ships are, that limits our time of flight to minutes (real spacecraft, which are slow to answer the helm), seconds (plausible hard-SF spacecraft that are capable of ~1g engine burns), or milliseconds (soft-SF ships with accelerations in the tens or hundreds of gravities).

Guided weapons are the way to go beyond that range limit.

[Shroom Man 777]

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

[Mr Bean]

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

Unless you were guarding something important he managed to blow up because you could not kill him.
No that's no where near as good as killing him. For defenders? Yes running them out of fuel is the next best thing to killing them. For attackers? If they still hit their target, fuel or no fuel, they succeeded and you lost.

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.

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.

This whole thread misses the entire point of deep space combat. Inside 250,000 km's laser rule because they are instant hit, you can't doge and the only issue they have (Dumping the waste heat) is something that has a dozen possible solutions. Meanwhile a deep space gun firing solid shells with nuclear warheads. Remember the instant your artillery shell can move after firing(slowing up or slowing down), it's pretty much a low grade missile which you imparted some extra momentum before launching.