Nukes, love them or leave them...

[Klempik]

Hello, I’ve been a ghost reader here for quite some time but felt no need to get a voice until now. But my SF-fan thoughts are wrestling with a problem I don’t know how to approach. So I appear, hoping that someone who has already answered this or know how to could enlighten me.

I’m wondering about the realism of nukes depicted in science fiction.
More specifically, let’s take the average heavy metal warship in a generic not too advanced sci-fi background (like B5’s Earth Alliance warships, or Galactica). It’s in the kilometer-long size range, looks quite sturdy and has an impressive armor plating.
Let’s assume it’s not made of unobtainium, superconductive or reinforced with some kind of structural field crap, but just several meters to a few tens of meters of state of the art modern armor (certainly multi layered, with thermal resistant and shock absorbing layers) supported by a huge internal structure and adequate compartmentalization and internal armor.

I don’t know how to get a rough estimation of what kind of yield is needed to cause significant damages to this ship with a nuke exploding on impact.
What effect would be the most damaging ? Maybe thermal deformations and melting of the hull, but that’s a pure guess.
Also, what if the nuke detonates in close proximity (one kilometer or so), can it still be deadly ?

Well as an afterthoughts, would it be possible for some kind of antennas on the ship to keep functioning after a small nuke goes boom against its hull ? And is it feasible to get some kind of specifically armor penetrating capacity (something like a shaped explosive charge) with a nuke (it’s not like we need this irl, but…) ?

Well I realizes this is quite question-heavy for a first post, but after seeing so many nuke explosions feeling horribly wrong (the worst one being probably the nuke exploding near a Minbari warship in “In The Beginning” which actually push a mile-long ship away), I’m afraid I won’t sleep well anymore until I can figure out what should realistically happen.

[Xess]

I suggest reading Atomic Rocket: Nukes in Space for the effects of nuclear initiations in a vacuum. In short they act like a really intense flash-bulb that drops off in intensity very quickly due to the inverse square law.

As for skin hits, I can't think of any realistic material that you could put on a spaceship in significant enough quantities to stop a direct initiation of a nuclear device. So for realistic intentions a skin hit with a nuke means the ship is destroyed. They simply contain too much energy for known materials to cope with.

[Winston Blake]

Well as an afterthoughts, would it be possible for some kind of antennas on the ship to keep functioning after a small nuke goes boom against its hull ?

Yeah, the ones on the opposite side of the ship should be OK. There's no blast wave, just radiation, so staying in the explosion's 'shadow' should help. If the ship survives, that is.

And is it feasible to get some kind of specifically armor penetrating capacity (something like a shaped explosive charge) with a nuke (it’s not like we need this irl, but…) ?

Project Orion had shaped nukes (also on Atomic Rocket), but as I understand it, that was more to convert heat into momentum; I don't know if they would help penetrate armour. Given that their purpose was propulsion, they may even be designed to have poorer 'penetration'.

As for skin hits, I can't think of any realistic material that you could put on a spaceship in significant enough quantities to stop a direct initiation of a nuclear device. So for realistic intentions a skin hit with a nuke means the ship is destroyed. They simply contain too much energy for known materials to cope with.

Considering Project Orion, I think small nukes could be warded off with several metres of solid steel and a layer of ablative graphite. That's a little impractical for all-around protection.

[Starglider]

Considering Project Orion, I think small nukes could be warded off with several metres of solid steel and a layer of ablative graphite. That's a little impractical for all-around protection.

Depends on the size of the ship and the strength of the available engines. B5 Earthforce vessels seem to have armour solid metal armour at least this thick.

[Feil]

If your ship isn't made of unobtanium, size is a weakness. It should be the minimum size needed to fulfill its design purpose, and it'll be made as lightly as possible with no more regard to armor plate than what's needed to protect against the occasional micrometeorite. If you are then unlucky or unwise enough to get hit by enemy fire... well, it sucks to be you. Every meter of hull makes it easier to see you on radar; every joule you need to squeeze out of your reactor to make your ship go makes it easier to spot your emissions; every kilogram of armor makes your ship slower, more predictable, and easier to escape, circumnavigate, or kill. The gunboat is the king of the extraatmospheric battlefield. The dreadnaught, barring unobtanium hull plating or magic shields of some kind, is nothing but an expensive target.

[Klempik]

Well thanks for the input and the link (very nice site).

So if I sum it up, it seems that as soon as you have something bigger than the smaller tactical nukes, a direct hit will cause havoc through any kind of realistic armor (except maybe hundreds of meter and rock and dirt, which makes me imagine a mobile space station deeply buried in an asteroid... Well that's off topic).

So if I want to "rationalize" an universe like B5 or Galactica, I must assume that they use all those battle lasers, particle beams, graviton thnikamagic... because they expect very low probabilities of a direct impact missile succeding ? Well that's a little lame but I suppose one can live with it .

[DPDarkPrimus]

Feil has the right idea.

The Colonial Marine Technical Handbook (Aliens universe) has the same approach to space warfare. He who fires first, wins.

[Ford Prefect]

every joule you need to squeeze out of your reactor to make your ship go makes it easier to spot your emissions;

I'd just like to point out that this isn't at all important. Fact of the matter is, if I were in earth orbit hotroding around in the Space Shuttle, and you were in orbit around Pluto, you could see me. Even with the engines turned off and with me just enjoying the life-support, I'd be more than two hundred kelvin warmer than the surrounding space.

There is no hiding in space. If you are in the same system, you will be seen. It may take hours accounting for lighspeed lag. It may take a couple of hours in order to scan the whole sky (it takes about four hours to do so today). In essence, trying to design a spaceship to be less noticeable is just pointless. Apart from that, I would have to agree with everything else you said.

[Zixinus]

I need to get to work, but when I get back, I should be able to show supporting maths for these assertations if you want to see it.

I know that this is not addressed to me, but I'd like to see it.

[Patrick Degan]

A well armoured, nuclear powered, laser armed space battleship will eat your gunboats and laugh about it.

And require several times its own mass in fuel simply to move it, nevermind being able to out-accelerate and outmanoeuver an opponent.

A better anti-laser defence would be to pump out a cloud of diffuse material around your ship to scatter the beam and prevent it from finding a dwell-spot on the hull. The hull itself should also be as light and heat reflective as you can make it, which would increase the dwell-time required to burn a hole. Combined with the refraction cloud, you can buy your ship added time and protection without imposing an impossible mass-penalty on your engines.

[Connor MacLeod]

Are we assuming "armouring" all around or is it more selective (IE critical parts of a ship or maybe just a given facing, etc.)

[FOG3]

And just how big of a realistic laser setup are we talking about to seriously threaten the hull integrity a vessel that can do re-entry? Last I checked beam weapons despite using humongous equipment were good for: wreaking havoc on/frying control/navigation/targeting circuitry and detonating explosives. The RADAR on a ship of the given size could probably cover those functions, so evidence for the practicality of AP LASERs vs say a ship using magnetic accelerator launched DU sabots?

[FOG3]

On second thought, why would a light ship have any advantage over a heavy in space? An AIM-9 style guidance system isn't going to particularly care, it'll pick up the heat and blocking of background radiation regardless, and should be easily designed to be unavoidable by the target ship. The heavy on the other hand has the advantage of being able to mount a larger AESA style array to fry normal missiles, mis-detonate inbound nukes, and mount either a bigger gun or make the existing gun have less potential accuracy issues due to the mass cutting down on drift.

Tracking and neutralizing the threat of a high velocity heavy metal sabot properly coated with an advanced RAM should be interesting.

[Sidewinder]

A better anti-laser defence would be to pump out a cloud of diffuse material around your ship to scatter the beam and prevent it from finding a dwell-spot on the hull. The hull itself should also be as light and heat reflective as you can make it, which would increase the dwell-time required to burn a hole. Combined with the refraction cloud, you can buy your ship added time and protection without imposing an impossible mass-penalty on your engines.

I think they use similar defenses in 'Gundam SEED' and 'Gundam SEED Destiny'.

[Patrick Degan]

A better anti-laser defence would be to pump out a cloud of diffuse material around your ship to scatter the beam and prevent it from finding a dwell-spot on the hull. The hull itself should also be as light and heat reflective as you can make it, which would increase the dwell-time required to burn a hole. Combined with the refraction cloud, you can buy your ship added time and protection without imposing an impossible mass-penalty on your engines.

I think they use similar defenses in 'Gundam SEED' and 'Gundam SEED Destiny'.

Interesting. I've never seen either.

[Xess]

Interesting. I've never seen either.

I suggest you keep it that way, save yourself the pain. Their system works by chucking out canisters full of some diffusing substance.

I don't see it working all that well since any acceleration on your ship's part would leave your defensive cloud behind requiring you to continually replenish it. Its usefulness would depend on whether you get more protection from it than an equivalent mass of armor.

[Nephtys]

A better anti-laser defence would be to pump out a cloud of diffuse material around your ship to scatter the beam and prevent it from finding a dwell-spot on the hull. The hull itself should also be as light and heat reflective as you can make it, which would increase the dwell-time required to burn a hole. Combined with the refraction cloud, you can buy your ship added time and protection without imposing an impossible mass-penalty on your engines.

I think they use similar defenses in 'Gundam SEED' and 'Gundam SEED Destiny'.

Interesting. I've never seen either.

Don't.

[Connor MacLeod]

the Minbari/Rangers (In Legend of the Rangers) and the Excalibur (In crusadE) supposedly had anti-beam countermeasures that worked like that. They sprayed out some field or cloud of crystals or some such nonsense that acted to refract/disperse the beam, weakening its effectiveness agianst a target.

[Patrick Degan]

And require several times its own mass in fuel simply to move it,

You can say the same thing about any rocket. Sure, the big ship will burn more fuel mass, but it also carries more - the ratio of fuel to its own mass may be the same as the small ship.

Your fuel tanks would be bigger, and presumably armoured, but you can make them of a size with minimal surface area to internal volume to help keep that arguably worth it.

The fuel tanks and the entire ship will end up being designed around its required fuel storage. There are no two ways around this problem: the more mass you add on, the more bulk which will have to be moved, hence the greater fuel requirement —which imposes it's own additional mass-penallty. This is why heavy armouring for any spaceship not powered by the Unobtanium Drive is never going to be practical.

A better anti-laser defence would be to pump out a cloud of diffuse material around your ship to scatter the beam and prevent it from finding a dwell-spot on the hull.

That's an interesting idea, but how does that material stay with the ship? As you pump it out, or if you thrust your ship, it would continue in its straight line path, away from the ship, unless stopped by something (magnetic fields?), meaning it would dissipate in effectiveness.

I had thought of a diffuse cloud of material polarised to make it manipulable by magnetic fields. As to the thrust issue, this would be problematic in terms of bringing on engagement (bear with me on this). It would be almost impossible for two ships to come to battle with one another in open space: either the one will be far ahead of the other and the pursuing ship would have to go full burn just to try to catch up (in which case the fleeing ship can defend itself by dumping out garbage behind it and let relativistic impact damage do its work), or two ships will be coming at one another but with such high relative closing velocities to one another that contact would be very brief. The most likely grounds for bringing on any meaningful engagement with an enemy would be in planetary orbit, in which your own ship would cross the other's orbit or come relatively close in its own orbital path multiple times and in which you would have the enemy in range with each orbit. In that case, the best and lowest-energy solution is to simply coast on orbital momentum and engage whenever the enemy comes up. In this scenario, you are not accelerating but maintaining a constant velocity and so would not end up thrusting out of the envelope of the refraction cloud. Of course, maintaining such a cover entails its own problems; such as potential interference with your own sensors.

What might be really cool is combining this idea with a iron/magnetic heat radiator (I forgot the name, but the one that sprays out hot iron with the ship's waste heat, and then it cools, becomes magnetic again, and is pulled back in by a magnet to repeat the cycle). Have your material both get rid of heat, and help stop enemy beams.

Hmm...

At the same time, this would reduce your own laser's effectiveness, wouldn't it? Unless your laser has an open path through the cloud, which would be right where the enemy would want to point his weapon too, to fry your laser's optics as quickly as possible.

As well as the aforementioned problem with sensor interference. This is where missile combat would take place in this phase of the battle, and then you're risking the degredation of your refraction cloud but the first priority is to prevent your ship from being immediately fried.

[Darth Holbytlan]

The acceleration needed to do this is width of the defending ship / (2 * the distance between the two ships, in light seconds).

That produces a velocity. I think you may want (2 * width of the defending ship) / (2 * the distance between the two ships, in light seconds)^2, instead.

[Jadeite]

In regards to the fact that more fuel is required to move an armored ship, which quickly becomes not practical, perhaps a nuclear pulse propulsion drive could be used?

[Patrick Degan]

In regards to the fact that more fuel is required to move an armored ship, which quickly becomes not practical, perhaps a nuclear pulse propulsion drive could be used?

Same problem, only the mechanics are slightly different.

[Darth Wong]

I don't see how any discussion of long-range detection is complete without mention of decoys. The biggest problem with missiles is that they're a finite resource. If you can get the enemy to waste missiles shooting at ghosts and decoys, you severely degrade his ability to damage your forces. So a long-range missile shootout doesn't just boil down to evasive maneuvers.

[Beowulf]

The problem with decoys in space is that they have to match the applicable characteristics of the ships they're mimicing fairly well. Same temperature (both the ship itself, and the drive), same radar signature, same optical image, same amount of mass in the drive exhaust. At that point, you've got something with the same size and mass as a real ship. You might as well just give it the guns and a crew and have a real ship instead of a decoy.

[Darth Wong]

The problem with decoys in space is that they have to match the applicable characteristics of the ships they're mimicing fairly well. Same temperature (both the ship itself, and the drive), same radar signature, same optical image, same amount of mass in the drive exhaust. At that point, you've got something with the same size and mass as a real ship. You might as well just give it the guns and a crew and have a real ship instead of a decoy.

That depends on how good the enemy sensors are, how much interference you've got, etc. At sufficient range, everything is just a blob as far as optical imaging goes, especially when you consider the fact that the enemy ship probably doesn't have a giant lens for a bow and will be maneuvering itself, with all of the resulting vibration and interference this will generate. You can't assume that every ship will get nice Hubble Telescope pictures of anything it wants.