# Are nuclear weapons useful in space?

On Earth, nuclear weapons can wreak enormous damage to a country and for that reason, large-scale wars between nuclear powers don’t happen. But what would happen if humanity progressed just enough to the point where countries expanded into space? Now powerful countries have fleets of spaceships (not fantastically advanced; no faster than light travel, no freak handwavium weapons; just what we might conceivably have within a century or so). Humans live scattered across the solar system, and have nations somewhat independent of Earth.

Would large-scale, territorial war again become common in this scenario? Would nuclear weapons fail to pose an effective MAD deterrent effect?

For the sake of a specific scenario to work with, consider two space powers, The Selenation, and Arianaland. They are both fierce rivals, and maintain hundreds of space stations scattered across the solar system. They have no strictly-defined borders, but each is concentrated in one broad area of the solar system, and have a region of space that they vaguely regard as their “territory”. They have ground colonies on large moons and asteroids, but there is a roughly comparable distribution between the “rock-bound” population and the space population. The “rockies” aren’t trapped on the surface per se; they regard moving into space as about as big a deal as moving house from the city to the suburbs. Neither country is tied to Earth, which is ruled by a third country Lovatoland and is regarded as something of a backwater. There are countless smaller powers across the solar system, most of which have a small territory carved out in one corner or another.

The technology level is not unrecognizable from what we have today. Their ships are about at the same level of what could be built in the movie Interstellar, only each country has more resources to build a greater quantity of them. Travel is still slow, and moving between stations within each country takes months—it’s common, especially among members of the military, but it’s considered a “big voyage” (like interstate travel in the US in the 19th century). There is substantial communication infrastructure, and the internet exists, but it’s somewhat balkanized due to the fact that it takes up to an hour for signals to make the jump between “clusters”.

Would Arianaland and the Selenation be quick to go to war with one another? Would we see something similar to the perpetual battles between Britain and France in the 18th and 19th centuries, only played out in space instead of at sea? Would nuclear deterrence only be a passing phenomenon, from back when humanity was jammed together on the same planet? Since this might be seen as too broad, let’s say that the question is simply would large-scale territorial war be conceivable in this scenario?

• Kelvin this is an interesting scenario but you are asking a lot of questions and those questions are quite large. I would suggest you try to narrow things down a bit. – James Jul 12 '16 at 17:18
• Okay, i clarified it. I'm just asking if in this situation, war could happen, yes or no – taylor swift Jul 12 '16 at 17:21
• given the distances involved, I don't think "quick" would be involved in any way, shape, or form in this war – Marshall Tigerus Jul 12 '16 at 19:39
• @MarshallTigerus quick in terms of whether leaders on both sides would not be as hesitant to declare war on each other as nuclear leaders today are – taylor swift Jul 12 '16 at 19:57
• As pointed out in The Expanse, if you live at the bottom of a gravity well (i.e. on a planet) "rocks" (asteroids, comets) can do far more damage than any sort of nuke. Mutually Assured Destruction between Mars and Earth (rivals of a sort) isn't about using nukes but said rocks. – Nick T Jul 13 '16 at 8:22

## Yes

Nuclear weapons would be highly effective in space.

But their effects are somewhat different than they are on the ground. I recommend reading this entire section of the Atomic Rockets website: Nukes in Space

On the ground, nuclear weapons damage things through 3 mechanisms:

Because the atmosphere is opaque to high frequency light (hard UV, XRay, & Gamma Ray), the primary worrisome radiation is neutrons when detonated in the atmosphere (also see thermal flash below).

In space, with no atmosphere, the high frequency light (primarily XRay and Gamma Ray) flies off without interference and this becomes one of the primary danger mechanisms of the nuclear detonation. In an atmosphere, almost all of the high frequency photon energy gets converted into the thermal flash and atmospheric blast mentioned below.

For a conventional nuclear weapon (i.e., NOT a neutron bomb), the x-ray and neutron flux is approximately:

$F_{XRay} = 2.6 \cdot 10^{27} \times \frac{Y}{R^2}$

$F_{neutron} = 1.8 \cdot 10^{23} \times \frac{Y}{R^2}$

where:

Fx = X-ray fluence (x-rays/m2)
Fn = Neutron fluence (neutrons/m2)
Y = weapon yield (kilotons TNT)
R = range from ground zero (meters)


This shows that for a standard (not neutron enhanced) bomb, XRay radiation is about 10,000x more damaging than neutrons at any given distance from the bomb. Which radiation flux is more dangerous to the crew depends upon factors like what sort of shielding is available and where the crew is located in the ship.

Neutron shielding is best (defined as the least amount of shield mass required to protect against it) composed of low mass atoms (e.g. Hydrogen in water).

What type of shielding to use for XRay and gamma ray radiation depends upon its frequency. At the lower energies, high Z metals (like lead and tungsten) work best, while at higher energies all mass tends to shield about the same.

Since water is terribly useful for spacecraft and ubiquitous across the Universe (from it you can make radiation shielding, water, oxygen, propellant, food, environmental coolant, and for some spacecraft fuel), I'd expect most ships to just use more water shielding in place of their high-Z metal, but otherwise dead weight, gamma ray shielding.

### Thermal Flash

Because the atmosphere is opaque to high frequency light (hard UV, XRay, & Gamma Ray), it converts those frequencies to lower frequency light (optical and thermal). This "thermal flash" is what caused memorable images (like the one below) and instantly vaporized some people in Hiroshima:

Nuclear Thermal Flash:

Since there is no atmosphere in space, the "thermal" flash is minimal and not really a concern.

### Blast

In an atmosphere part of the energy of the detonation is absorbed by the atmosphere and turned into an atmospheric pressure wave (the "blast" or over-pressure wave). Once again this phenomenon does not occur in space.

Therefore this issue can generally be ignored.

Nuclear Blast Effects:

### What it looks like

Assuming a near miss that doesn't actually vaporize the spacecraft...

Read this section of the Atomic Rockets: Nuke vs. Spacecraft section for the entire narrative. I'm going to quote a couple of key passages.

First off, the weapon itself. A nuclear explosion in space, will look pretty much like a Very Very Bright flashbulb going off. The effects are instantaneous or nearly so. There is no fireball. The gaseous remains of the weapon may be incandescent, but they are also expanding at about a thousand kilometers per second, so one frame after detonation they will have dissipated to the point of invisibility. Just a flash.

So a strobe flash. If you were looking at it, you'll be permanently blind if you're too close. If you had a camera/sensor looking at it, it would likely burn out too if it was too close.

Next is spallation - shocks will bounce back and forth through the skin of the target, probably tearing chunks off both sides. Some of these may come off at mere hundreds of meters per second. And they will be hot, red- or maybe even white-hot depending on the material.

To envision the appearance of this part, a thought experiment. Or, heck, go ahead and actually perform it. Start with a big piece of sheet metal, covered in a fine layer of flour and glitter. Shine a spotlight on it, in an otherwise-dark room. Then whack the thing with a sledgehammer, hard enough for the recoil to knock the flour and glitter into the air.

The haze of brightly-lit flour is your vaporized hull material, and the bits of glitter are the spallation. Scale up the velocities as needed, and ignore the bit where air resistance and gravity brings everything to a halt.

Followed by a halo of faint hazy "dust" flying away from the hull along with possibly some larger debris ripped off the ship. Some sections of the ship may be glowing red hot (or hotter) depending upon the proximity of the warhead.

It's possible that (depending upon many details) the ship may survive the detonation while the radiation kills the crew quickly or over the course of weeks. If the crew receives a deadly dose of radiation they'll likely know it even if they will likely live for a week or so in increasing agony due to the radiation damage.

## Would they go to war?

That's entirely up to you and your fictional Universe.

In space warfare, any target with a predictable trajectory (e.g. not accelerating) is a sitting duck that can be held hostage and/or killed at any time the belligerents decide to strike. The weapons would not need to be nuclear. Given sufficient time, a small asteroid would do the job easily and the belligerents might be able to maintain plausible deniability.

• @Kelvin Remember that we just hit Jupiter within a target on the order of tens of kilometers and a window of 1.2 seconds, and that's with today's technology. And it would be REALLY hard to spot something as tiny as a nuke. – corsiKa Jul 12 '16 at 21:20
• Regarding water as shielding: You can also pump it from one side of the ship to another as needed, unlike lead. This is much more mass-efficient than having static shielding on every side. It also gives an excuse to have a "reroute all power to forward shield" type mechanism. – Superbest Jul 13 '16 at 0:38
• @corsiKa: Yeah, but weren't they aiming for Saturn? xkcd.com/1703 – user21719 Jul 13 '16 at 1:29
• True, but EMP only works around bodies with a strong magnetic field AND a tenuous atmosphere. So above the Earth, Jupiter, Saturn, Uranus, & Neptune. Anywhere else and it won't have the dreaded effect. projectrho.com/public_html/rocket/… – Jim2B Jul 13 '16 at 3:19
• @Luaan The radiation would kill the crew before it heated the air, but for completeness it's worth noting. Also, any combat spacecraft is likely to have several separate sections, so the heating of one might cause pressure differentials in the narrow pipes and vents that connect them, or overtax the seals between them and areas of vacuum. The ship's own reactor (and its shielding) might also provide a "shadow" where parts of the ship would remain cool. Any windows or other transparent openings would also provide a way for more radiation to penetrate without causing as much damage to the hull. – anaximander Jul 13 '16 at 11:31

The thing that causes deterrence is the reliable ability for each side to cause huge levels of damage to their opponent if they're attacked.

On Earth, that is created by Intercontinental Ballistic Missiles, which are quite hard to intercept. If side A has 100 ICBMs, side B will need 250+ Anti-Ballistic Missiles to shoot most of them down, and those ABMs cost more than the ICBMs. So it's always possible to penetrate defence at lower cost than improving the defence, and both sides could do this. Further, neither side could attack the other by surprise without retaliation being possible. If A made a full-scale attack, B could launch its weapons before A's weapons arrived, and both sides would be destroyed. That realisation lead to nuclear arms limitation treaties, which were obeyed, because it was in everyone's mutual interest to do so.

But that kind of deterrence emerges from the technical, geographic and financial constraints of the place and time. It isn't necessarily going to apply in the completely different situation you describe.

How do you decide if deterrence is possible? You need to decide if your scenario allows one side to attack the other and cause vast amounts of damage irrespective of defences.

If it can, and the other side won't be able to respond to an attack by also inflicting vast amounts of unstoppable damage, then you have the reverse of deterrence, a hair-trigger situation where the first to shoot wins, and somebody will, soon.

But if the other side can respond to an attack by inflicting unstoppable destruction, then you have "mutually assured destruction" and deterrence.

• Agreed. MAD required both sides to value their own continued existence over the destruction of their enemy. MAD does not work when one or both sides values the destruction of their enemy over their own survival. Or as mentioned above, in cases in which survival almost certain goes to the side that strikes first. In these cases, the smartest move is to strike first. (read the book <a href="en.wikipedia.org/wiki/The_Killing_Star">The Killing Star</a>) – Jim2B Jul 12 '16 at 19:07

Nuclear devices are useful, but probably not in the way you are thinking.

Because of the vast distances between objects in space, and the high relative speeds they are moving at, the most damaging, low cost option is to simply fling inert mass at the target. The kinetic energy will be massive, because the "v" in the v^2 will be measured in kilometres per second. Even an object in orbit around the earth is travelling far faster than any rifle bullet, so a bucket of ball bearings transported into space on an intersecting orbit with a satellite or space station becomes a fearsome weapon (Atomic Rockets has a snarky little exposition of the idea where the astronaut ejects the litter box of the ship's cat out the airlock on an intersecting orbit with the target....)

Since the projectiles rely on their velocity to damage the targets, they can be made of wadded up kleenex, but as a practical matter, you probably want a dense core of stone or metal, and a simple homing device and a small thruster to make last minute orbital corrections. If you are firing at a moon or large space station, you can effectively launch across the solar system, but for targets capable of manoeuvre, one light second (just under the distance between the Earth and the Moon) provides a practical limit for targeting (too much farther and the target can move a substantial distance before the kinetic energy warhead arrives. It took New Horizons 9 hours to traverse the distance between the Earth and the Moon, for example). The kinetic energy weapons can be launched by virtually any sort of space propulsion system, so if your target is across the solar system, you could even use a light sail! More practically, mass drivers, rail guns or giant honking rocket boosters would provide the thrust to get to the target.

Laser and energy weapons are also limited to a light second against manoeuvring targets, but since you can ramp up the hardware as much as you desire, a Ravening Beam of Death [RBoD] could theoretically vaporize metal and ceramics in milliseconds at that range. See Rocketpunk Manifesto for the gory details.

At this point, you might want to reconsider how these spacefaring "nations" are going to conduct warfare. When a space station can be hit by a bunch of rocks collectively packing the energy of the Castle Bravo nuclear device, there isn't going to be much left of the target. These sorts of weapons are really only useful in a "war to the knife", where you offer no quarter and take no prisoners, but then you can expect to be on the receiving end of that sort of punishment as well.

As for nuclear devices, they don't really add much to the target effect unless you are using third and fourth generation warheads as accelerators to drive streams of pellets at 100 km/sec or plasma jets at 3% of the speed of light. This suggests that their primary purpose is not really as weapons in of themselves, but as a compact energy source to power defensive weapons that can attempt to shoot down incoming devices. The other, and probably more important use for nuclear devices is as the drive units for an ORION pulse drive.

This also the workaround for the spaceships in your setting, ORION is the only high thrust/high ISP drive system known to science, and you ORION drive ships will be bigger, faster and more capable than anything else out there. ORION drive ships can also bring teams of commandos, computer hackers, biological warfare experts or ninjas to your enemy space station, disguised as tourists, business people or traders, allowing you to actually capture the enemy station and "win" the war.

• what would happen if the target had modest laser defense systems, similar to what the Navy is developing right now? Could they be used to simply vaporise the missile or at least damage its guidance systems enough so the target could scootch out of the way? 9 Hours is a long time for a laser to burn away some critical components of a guided missile. And wouldn’t the defenders would see the enemy coming before they got within one light second, and send fighters to stop them before they reached any large target? – taylor swift Jul 12 '16 at 18:43
• Rocketpunk Manifesto did an analysis and it is possible to overwhelm even a RBoD with a sufficient number of kinetic energy devices. So all out space warfare involves filling the sky with weaponry. The "one light second rule" applies to manoeuvring targets. A RBoD is actually dangerous out to one light hour away, so it might be worthwhile to engage boosters and missile busses much farther away than one light second, accepting that they might have been able to manoeuvre to avoid the beam (but used valuable fuel to do so). – Thucydides Jul 12 '16 at 18:58
• A RBoD might be capable of destroying things out to 1 light hour, but it has to hit that thing first. For small maneuvering objects (like kinetic or explosive rounds), I don't think a RBoD would be effective out past 1 light second. For larger and slower accelerating things (like ships) something over 1 light minute might be impractical - that's still about 10,000,000 miles away though. – Jim2B Jul 12 '16 at 20:05
• – Bob Jul 13 '16 at 6:43
• @Luaan Making something miss or ricochet off a spaceship could be easier given that, unlike a tank, there's also the option of moving the spacecraft. The crew might feel an impact as a jolt as the projectile struck an armoured plate and shoved the spacecraft to the left. In fact, armour could be designed to use this - shaped such that an incoming round striking with insufficient energy to just vapourise or puncture the plate would cause the craft (or perhaps just a flexible part of the armour) to orient in a way that maximised the chance of a ricochet. – anaximander Jul 13 '16 at 11:38

# Are nuclear weapons useful in space?

Yes.

One of the other answers gives an extensive amount of information on how nukes behave in space, but there a couple of key points:

• It is hard to hit things precisely in space. Consider the immense amount of work that went into Juno's trajectory. Nukes ease this burden because they just have to 'get close'.
• Collateral damage is limited. Space is awful large. A successful nuclear strike is likely to take out a target and not as much else (since everything else is very far away).

I recommend reading Haldeman's Forever War for a visceral description of nuclear space combat, similar in tech level to that you describe.

# Would large-scale territorial war be conceivable in this scenario?

As you define 'territory', probably not. One thing to remember is that space is very dynamic compared to earth. The notion of 'territory' changes rapidly and constantly. Because bodies in space are moving at different speeds along different trajectories, the notion of 'territory' is constantly churning. Further, things that are close physically for a little while (such as Mars and Earth) are often quite far away. And when they are close physically, the time it takes to get from one to the other is not actually the shortest transit time (again, with conventional tech - or, I suppose, if you had a lot of energy to burn somehow).

Thus, to plan an invasion you have to calculate where your target is going to be when you get there. You have to figure out how much reaction mass it will take to get your troops in place. It's a lot of work, logistically, particularly because winning does not imply you have a secure supply line (important in war): because the target keeps moving it might well move past where you can support it. Further, supply ships might have to be sent without knowing if you won the fight on the far side.

For this reason, being high on a gravity well (as in Heinlein's The Moon is a Harsh Mistress) has an advantage, in that it's easy to go 'down' the well, and hard to come up. Fleets would have to be largely self-sufficient, would have to modify their plans as they get information, and the only 'territory' worth talking about would be areas around gravity wells. Capturing vast volumes of space with nothing in it doesn't really help.

The other thing to note is that space, being largely empty, makes it very easy to see things coming. Telescopes, sensors, optics and radar all become super important. If you can see a fleet launch, understand it's trajectory, you can pretty much tell what it's going to do and (if you're close enough) respond long before the fleet performs what it's doing. It's ability to turn around is limited.

This matters for nukes, specifically, as well: warheads are very observable, if only for the heat trail of the delivering rocket. If your nukes are hard to hide, it is all the harder to get them close enough. Arguably this makes them the only option, when a conventional warhead would stand no chance of getting close enough before being shot down. But it does suggest inert nuke 'mines' and other tactics would evolve in order to get around using nukes 'in the open'.

In short: with shifting territory, in the open vastness of space, nukes are probably a key weapon, but the strategy and tactics around their use would change drastically - such that comparison to historical combat is very hard to make.

• So it would be comparable to two countries consisting of a series of ships on the ocean and nothing else? – The Great Duck Jul 13 '16 at 2:34
• @TheGreatDuck Assuming those ships had no real control over where they went, yes. – Nathaniel Ford Jul 14 '16 at 1:53

Since the nukes have been comprehensively covered, I'll look at the chances of going to war.

Unlikely

The key to this is resources and the fact that the same resources are fairly evenly distributed around the asteroid belts. There may be vast unexploited resources on the asteroid your rival empire has just moved on to, but the same is true of every other large asteroid in your vicinity. There's no clash for space, no clash for resources, only a clash for pride. With travel times what they are, along with the risks of the weapons involved, pride is not a valid reason to risk a nuclear war.

Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. - Douglas Adams h2g2

When it becomes interesting is when something comes up that is actually worth fighting for, but in practice that's a large deposit of unobtainium, handwavium, or a planet with a breathable atmosphere. Everything else is plentiful on an unimaginable scale.

May you live in interesting times - Auriental Curse (Pterry)

• i don’t think this would be true. People always think a resource is unlimited until it’s not. When the US first started settling North America, it was thought that the land area was so vast, it would take 500 years for settlers to claim it all. Thanks for actually addressing the war-aspect of the question though. – taylor swift Jul 14 '16 at 13:40
• @Kelvin, one could say that North America is far from fully colonised even now. While the land has been 'claimed', compared to the UK it's pretty much empty of people away from the coasts and big cities. – Separatrix Jul 14 '16 at 13:47
• the key point is the land has been claimed and if someone else tries to claim it, the original owner will be very angry, especially if they have mining rights or a farm or some other land-intensive capital resource. Truly ‘unclaimed’ land in the US is rare, mostly in places like the parts of North Dakota that lack farmable soil or minerals. Whether or not something is being occupied is different from whether or not it is being used and very different from whether or not something is being owned. – taylor swift Jul 14 '16 at 13:52
• When the land ran out in the late 19th century, people started fighting over it; giving rise to the famous Turner thesis in American history. – taylor swift Jul 14 '16 at 13:55
• @Kelvin, you mean all those people who lived there before the Europeans showed up? Claims are easily displaced by power and money or just weight of numbers. Your powers in space will claim territories arbitrarily, they may fight over them, but the risks are much higher than they were during American colonisation. There'll be a lot more talk rather than conflict. It's a risk/benefit calculation and in nuclear war you stand to lose everything. – Separatrix Jul 14 '16 at 13:57