Effectiveness of Nuclear Weapons in Space.

[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.

[phongn]

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.

That won't do anything against the neutron flux and hard radiation, though. Might be able to product against some charged particle beams.

[Junghalli]

The best way of protecting a spacecraft against missiles is a good PD system. It's not unlike air combat really: the best protection is not to get hit.

[Crayz9000]

The best way of protecting a spacecraft against missiles is a good PD system. It's not unlike air combat really: the best protection is not to get hit.

Well, that goes without saying, I suppose my comment should have been called "the best last line of defense".

[Gil Hamilton]

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.

The long and short of it is that you've got a nucleus of some metal traipsing along, minding its own business and then BONK! A neutron manages to smack right into it. Most of the time, the neutron will bounce off, but occasionally, it will actually stick to the nucleus. This is a process called neutron capture. Because you are adding a neutral mass to an atom, you are increasing the mass without changing the number of protons in it becomes a different isotope. Problem is, while all atoms are subject to radioactive decay (though most common isotopes of atoms have such long half lifes that it is pointless to think of them as radioactive), chances are when you bash a metal nucleus with a neutron it isn't going to be very happy, and is going to become an isotope with a short half life and hookem up a bunch of radiation while moving to a more favorable atomic state (this is known as neutron activation, by the way, and what Sea Skimmer above was talking about).

Occasionally, however, the neutron will wang a nucleus in such a way that the neutron sticks, but spontaneously splits into a proton and an electron (or positron). This is a process called beta decay (beta particles being electrons or positrons). The electron shoots off an in effect, you've added a proton to the atomic nucleus, making it one element higher on the periodic table. This, incidentally, is how everything to the right of uranium on the periodic table is formed.

[JGregory32]

Thanks Gil that makes quite a lot of sense now. For the record while I did take physics in High School the class did not get indepth about nuclear physics. My next brush with nuclear physics was while taking a course in the History of Science that delt with post-18th Centruy discoveries and people.

I am not a science major, I'm a history major. Sometimes the discussion does go over my head and when I try to research I discover that my knowledge base isn't sufficent to make sense of the explinations offered by the world wide web.

[Nyrath]

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.

Maybe this will help:
http://en.wikipedia.org/wiki/Neutron_activation

[Nyrath]

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

The x-rays from the nuclear detonation are absorbed by the hull and turned into heat. The thermal stresses can cause mechanical damage.

http://www.projectrho.com/rocket/rocket3x.html#nuke

First, consider a uniform slab of material subject to uniform irradiation sufficient to cause an impulsive shock. A thin layer will be vaporized and a planar shock will propagate into the material. Assuming that the shock is not too intense (i.e., not enough heat is dumped into the slab to vaporize or melt it) there will be no material damage because of the planar symmetry. However, as the shock reaches the back side of the slab, it will be reflected. This will set up stresses on the rear surface, which tends to cause pieces of the rear surface to break off and fly away at velocities close to the shock wave velocity (somewhat reduced, of course, due to the binding energy of all those chemical bonds you need to break in order to spall off that piece). This spallation can cause significant problems to objects that don't have anything separating them from the hull. Modern combat vehicles take pains to protect against spallation for just this reason (using an inner layer of kevlar or some such).

Now, if the material or irradiance is non-uniform, there will be stresses set up inside the hull material. If these exceed the strength of the material, the hull will deform or crack. This can cause crumpling, rupturing, denting (really big dents), or shattering depending on the material and the shock intensity.

For a sufficiently intense shock, shock heating will melt or vaporize the hull material, with obvious catastrophic results. At higher intensities, the speed of radiation diffusion of the nuke x-rays can exceed the shock speed, and the x-rays will vaporize the hull before the shock can even start. Roughly speaking, any parts of the hull within the diameter of an atmospheric fireball will be subject to this effect.

In any event, visually you would see a bright flash from the surface material that is heated to incandescence. The flash would be sudden, only if the shock is so intense as to cause significant heating would you see any extra light for more than one frame of the animation (if the hull material is heated, you can show it glowing cherry red or yellow hot or what have you). The nuke itself would create a similar instant flash. There would probably be something of an afterglow from the vaporized remains of the nuke and delivery system, but it will be expanding in a spherical cloud so quickly I doubt you would be able to see it. Shocks in rigid materials tend to travel at something like 10 km/s, shock induced damage would likewise be immediate. Slower effects could occur as the air pressure inside blasts apart the weakened hull or blows out the shattered chunks, or as transient waves propagate through the ship's structure, or when structural elements are loaded so as to shatter normally rather than through the shock. Escaping air could cause faintly visible jets as moisture condenses/freezes out - these would form streamers shooting away from the spacecraft at close to the speed of sound in air - NO billowing clouds.

[Sarevok]

The conventional wisdom in space combat is not getting hit. But what if a flying fortress actually becomes the ultimate weapon ?

Most or rather anything built so far to fight wars will not survive a nuclear weapon hit. However asteroids are a different matter. A 8 km chunk of rock is a very tough target even for a megaton level nuclear weapon. So what if someone made a slow but invincible warship out of it ? It could be armed to the teeth and mount every form of point defense imaginable. The occasional nuke that might get through would just vaporize a few hundred meters of rock and dust.

Is this a viable idea or does it reek of Dr Evilness ?

[Sea Skimmer]

Is this a viable idea or does it reek of Dr Evilness ?

A giant warship like that would be either absurdly unmaneuverable because of its huge mass, massively expensive to have big engines, or more likely both combined, meaning that you only afford a fleet consisting of a single incredible large, slow target. This is not good, and all that rock still won’t let you shrug off direct hits from a burrowing nuke. Protection against proximity bursts would be very good protected that all external equipment is provided with the ability to retract behind armor (imagine the surface covered in missile silo like constructions for sensors, weapons and engine nozzles)

If you had some kind of FTL then it might be feasible to use an asteroid as a kind of mobile base for supporting planetary assaults. It would have almost no sublight mobility (maybe some kind of space tug could push it into a proper orbit around a planet), but that wont matter as long as FTL can bring it to a decently close position.

[JGregory32]

Asteroid Forts actually sound like a great idea for planetary defense.

You'd need at least six of them to give good coverage but wound't the mass screw up tidal forces on the planet?

If you handwave an FTL system that uses chokepoints then anybody worth their salt is going to station a few around the entrences and exits. Breeching those defenses is going to become a costly affair and might provide a measure of peace. If the cost of attacking a system is signiffigently higher than defending said system then an uneasy peace might reign. Of course the first person who figures out an alternative FTL drive is going to find themselves in deep, deep, trouble.

[Batman]

Asteroid Forts actually sound like a great idea for planetary defense.
You'd need at least six of them to give good coverage but wound't the mass screw up tidal forces on the planet?

See Destro's response.

If you handwave an FTL system that uses chokepoints then anybody worth their salt is going to station a few around the entrences and exits. Breeching those defenses is going to become a costly affair and might provide a measure of peace.

That entirely depends on the nature of those chokepoints. If they're two-way and anything can go through them, there's nothing keeping the invaders from missile-spamming through it.

[Almightyboredone]

If the cost of attacking a system is signiffigently higher than defending said system then an uneasy peace might reign. Of course the first person who figures out an alternative FTL drive is going to find themselves in deep, deep, trouble.

So, like, the Teraport wars from www.schlockmercenary.com ?

[Coalition]

If you handwave an FTL system that uses chokepoints then anybody worth their salt is going to station a few around the entrences and exits. Breeching those defenses is going to become a costly affair and might provide a measure of peace.

That entirely depends on the nature of those chokepoints. If they're two-way and anything can go through them, there's nothing keeping the invaders from missile-spamming through it.

The game Starfire was like that, where the only decent way to get from system to system was through warp points.

The attacker's advantage was that they could choose the time of the attack. A Defender can't stay at General Quarters 24/7, so in the first 'turn' of the battle, only a small percentage of the forces are at General Quarters and can return fire. As the battle goes on, more units activate, and can open fire.

The Defender's advantage though, is that only certain types of units can survive transit through a Warp Point. Individual missiles, fighters, towed items, and some small craft are too small to survive transit. Missile pods, pinnaces, and starships are tough enough to survive. However, when transiting a Warp Point, the electronics get knocked out for a bit. Advanced sensors and datalink are the main ones knocked out, forcing a ship to defend by itself, and with a targeting penalty as well. Even worse, if you try to send through too many ships, they will interpenetrate, and you will lose them anyway.

If it is an unsurveyed Warp Point, your exit vector is random also, meaning your squadron of Dreadnougts could have half its members heading one way, and half in another. They can turn in place if there are minefields surrounding the warp point (later redone to be weapon buoys that hold position relative to the warp point), but it is rather annoying.

So if you have a chokepoint system, try to figure out what keeps an attacker from steamrolling over the defender, and what keeps the defender from bottling up the attacker for a long period of time with no problems. Once you have a near-balance, you can have a story.

[starslayer]

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.

I seriously doubt hull plates will be ripped in half or shredded from a nuclear detonation in space. The radiation shock will be fairly evenly spread, so I don't think large surface cracks will appear.

OK, now I'll try explain how transmutation works starting from the ground up. I'm going to assume that you have no knowledge of what atoms even are, so if it seems a bit condescending at first, I don't mean it to be.

Atoms are the basic building blocks of every macroscopic material object. Each element (hyrdogen, oxygen, iron, etc.) is a different type of atom. In the atom there are three particles: electrons, protons, and neutrons. Electrons fly around in a cloud around the atomic nucleus, which is composed of protons and neutrons. Electrons carry a negative charge, and protons a positive one. Neutrons, as their name implies, have no charge. The vast majority of the atom's mass is carried in the nucleus; an electron has 1/2000th the mass of a proton or neutron. I will henceforth ignore the electrons, and concentrate solely on the nucleus, as the electrons have no impact on radioactive processes.

The elements are distinguished by the number of protons in their atomic nuclei; for example, carbon has 6 protons in its nucleus, while neon has 10. This is also what we call an element's "atomic number." The number of neutrons present in the nucleus has no bearing on what element the atom is; this is where different isotopes come in. Isotopes are merely two different forms of the same element that different numbers of neutrons in their nuclei; carbon-12 and carbon-14 are both carbon, for example, but C-12 has 6 neutrons in its nucleus, while C-14 has 8. Note that these are distinct from allotropes, which are very different things from isotopes. Graphite and diamond are two different allotropes of carbon, not isotopes.

You may also have heard of the four fundamental forces: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. There are two competing forces at work in the atom itself: the electrostatic repulsion of the protons, and the strong force interactions in between them, pulling them together. On the scale of an average nucleus, the strong force wins out, and holds the atom together. However, it drops off very rapidly with distance, much, much more rapidly than the electromagnetic force does. Thus, as the nucleus gets very large, it becomes less and less stable. This is why the heaviest elements, like uranium, are radioactive; they simply cannot hold their nuclei together against the electrostatic repulsion of their protons. Thus, we have radioactive decay. It should be noted that being an extremely heavy element is not necessary to be radioactive; the C-14 named above is also radioactive, as are many other isotopes of the lighter and middleweight elements. As well, the radioactive isotopes of an element are usually just called "radioisotopes" for brevity.

There are three main types of radioactive decay: alpha, beta, and gamma. Alpha particles are simply helium nuclei; two protons and two neutrons stuck together. Beta particles are electrons, spit out as a neutron decays into a proton, an electron, and an electron neutrino (not important for this discussion). Gamma rays are extremely high energy photons; they actually have enough energy to knock electrons out of their orbits around nuclei and thus are also called "ionizing radiation" along with some X-rays and beta particles. The weak nuclear force governs all radioactive decay; the details are governed by quantum mechanics, which we don't want to discuss here.

Now, what happens when something is irradiated? The material in question being subject to our nuclear blast is being subjected to high-energy gamma rays, free neutrons, beta particles, and pretty much everything else you care to name. Inevitably, some of these things will strike an atomic nucleus. The most important ones here are the neutrons. When they strike an atomic nucleus, one of two things could happen:

1. It is absorbed into the nucleus, and changes it into a different isotope. So, iron-56 would become iron-57, and so on.

2. It splits the nucleus in two. This is unlikely unless we made our plating out of uranium; since every kilo counts, this is unlikely for obvious reasons.

In our scenario, the neutron flux (that is, the amount of neutrons hitting our hull plating) is extremely high, so high in fact that it is extremely likely for many nuclei to be hit multiple times. So, if our plating were made out of carbon, and our atom got hit by two neutrons, instead of being C-12, say, it is now C-14. This means it is now radioactive, and will probably undergo a decay soon, spitting out radiation. This is Bad For The Crew for obvious reasons. Here's where we get to transmutation. When an atom undergoes radioactive decay, you may have noticed that it either gives up protons (alpha decay) or gains one (beta decay). The element has "transmuted" into another. Uranium goes through a very long decay chain before finally ending up as lead, for example.

This is what Atomic Rocket meant by the metal being "bumped up the periodic table." The atoms in the metal would gain lots and lots of neutrons due to the bombardment, and would then likely undergo either one or several beta decays, transmuting into elements farther up the periodic table. Thus, they are now different materials, and do indeed have different properties from the element they used to be.

[Darth Wong]

Very high-energy neutrons would probably have low reaction cross-sections for capture, so they would probably be scattered several times before capture could occur. This means that the neutron radiation would have a very strong heating effect, which would probably be a far greater threat to the crew than secondary radiation effects from spontaneously generated isotopes.

[Sea Skimmer]

Very high-energy neutrons would probably have low reaction cross-sections for capture, so they would probably be scattered several times before capture could occur. This means that the neutron radiation would have a very strong heating effect, which would probably be a far greater threat to the crew than secondary radiation effects from spontaneously generated isotopes.

I don’t know about that, the secondary radiation effects were a big factor in US lust for tactical neutron bombs in the Cold War. A tank could be rendered lethally radioactive (if you sat in it a while, as a crew would have to in combat) for about 24 hours at significantly greater distance then the incapacitation radius for the initial radiation pulse. This threat in turn led to the development of special anti radiation liners for the interiors of tanks in the 1970s and 80s, usually around 8-10mm thick. This thin shielding couldn’t really save you from the initial pulse at close range, but it would protect against those lingering secondary effects. I don’t think anyone really thought or cared about what happens when the crew had to get out to refuel.... everyones planning for fighting a mobile armored nuclear war was never super realistic.

[Darth Wong]

Keep in mind that the neutrons would experience no braking effects whatsoever in space, and would hit the spaceship at pretty much the exact same velocity they had when they were ejected from the nuclear blast.

Also, one must wonder just what kind of sci-fi civ we're talking about. Is this one of those sci-fi universes where ships have 20m thick armour belts?

[Sea Skimmer]

A remotely realistic ship wouldn’t have thick armor; but potentially even a highly realistic ship could still be using its own fuel mass to provide some substantial protection, especially if almost all of this protection is concentrated over a single arc. After all using your own fuel for armor is not a new idea; battleships and aircraft carriers used fuel filled compartments for anti torpedo defence. I have no idea how well compressed gas like hydrogen would work as radiation protection, but the combination of fuel and fuel tanks, plus a thin ‘final defence’ layer of actual shielding ought to accomplish something.