# How, if at all, can space battleships mitigate gun recoil?

I am making a game universe involving spaceships. While chewing through the implementation issues, I also keep making story and environment plans.

Big battleships have big guns. However such guns have a recoil and there's nothing a battleship can brace against. Shooting a big conventional cannon or railgun has both the same effect as the engine thrust especially if the battle drags on.

My question therefore is what could spaceships use to mitigate their gun recoil? I aim to give this as a researchable upgrade to the players, but I would like to use something plausible, not just magical no-recoil gun.

• Big Recoilless cannon? Or just use missiles ;) – PTwr Apr 22 '16 at 8:58
• @TomášZato An alternative would be to have them on the exterior of the ship, like those pivoting ones you see on WWII Battleships. Then the cannon can vent the fumes directly behind itself without being channeled through the ship. – Devsman Apr 22 '16 at 20:05
• Alternatively, if your engines normally compensate, and your engines become damaged, you can fire the guns to move! Or even fire them to dodge! Recoil isn't inherently a bad thing if you can compensate after the fact unless it's so great it damages the ship or occupants! – aslum Apr 22 '16 at 20:11
• mandatory xkcd reference: what-if.xkcd.com/85 – njzk2 Apr 22 '16 at 21:20
• @njzk2 Actually, what-if.xkcd.com/21 is far more pertinent! Pay particular attention to the guns on the A-10 'warthog' "If you put two of them in one aircraft, and fired both guns forward while opening up the throttle, the guns would win" ;) – Michael B Apr 23 '16 at 0:51

Gear up boys and girls: Time to do some MATH.

I have no way of knowing what sort of tonnage your spacecraft will be displacing, but just for kicks let's assume you somehow got an Iowa-class Battleship into orbit and are worried her main cannons are going to cause a recoil problem when you fire on the enemy.

• The ship will weigh approx. 58,000 Tons, or from here forward a "Fuckton." This equates to about 52,000,000 kg of mass.
• The primary battery on an Iowa-class is its nine 16"/50 Mark 7 guns. These weapons can fire a wide variety of payloads, but their most potent non-nuclear is the Mark 8 Superheavy Shell, weighing 2700 lb with a muzzle velocity of 2500 ft/s.
• Now, momentum is computed based on mass x velocity, so a quick multiplication (after converting to metric; we're not barbarians afterall) yields a change in momentum of 925,830 Newton-seconds (a unit we don't really need to care about right now). This was from a single shot. A full broadside of all nine cannons would produce a change of 8,332,470 Newton-seconds. That sure sounds like a lot...
• ...But not when compared to the Fuckton of mass onboard the Battleship. A division of the change in momentum by the mass of the ship will give us a hypothetical change in velocity after the broadside, which comes out to be about 0.16 m/s, which is about four orders of magnitude beneath orbital velocities.

To keep a typical spacecraft in low orbit requires periodic stationkeeping to counteract atmospheric drag. This is usually on the order of a few mm/s. Our full broadside would require stationkeeping efforts of hundreds of mm/s, but based on the assumption we managed to get something as massive as a battleship into orbit, I would assume a few hundred mm/s is well within the delta-v budget of the ship.

Of course, your ships could be much smaller and fire much more energetic projectiles, and in that regard you may encounter a problem, but remember that orbital speeds are in the thousands of meters per second, and that a ship with the energy to fire highly energetic weapons will likely have equally energetic thrusters.

Plus you could always use lasers.

• Most sci-fi space battleships which fire kinetic projectiles do so at least at 1% of light speed. Still, recoil making up a huge percentage of the engine's power output is not unheard of in real life, and they can cope with it. The A10's main cannon has a larger recoil than the thrust of one of its two engines. This means than one engine out, and the other on full power, firing the cannon would propel the aircraft backwards: what-if.xkcd.com/21 – vsz Apr 22 '16 at 17:49
• @vsz I did some quick math just for giggles. Using the same projectile as above and a velocity of 0.01C, a single shot would produce a delta-v of about 70 m/s for the battleship. That is admittedly fairly significant, though definitely not insurmountable if the primary engines were used in reaction. Now the real question is: can a ship of an Iowa's tonnage withstand the internal stresses required to accelerate a projectile to that speed? I'm not confident I can calculate that, but I'll give it a shot. – MozerShmozer Apr 22 '16 at 18:13
• #vsz I ran the numbers (though I admit material science is not my area of expertise) and as best as I can tell, a ship the size of an Iowa Class would need something like 82 Billion kg of steel to withstand the accelerative forces required to launch the relativistic projectile I proposed in my above comment. This mass alone would reduce the delta-v of the recoil to 40 mm/s. That being said, carbon nanotubes or some other exotic material could reduce the structural mass requirements significantly, plus I did not take into account structural design at all. I think it could be done! – MozerShmozer Apr 22 '16 at 18:39
• Comments are not for extended discussion; this conversation has been moved to chat. @MozerShmozer perhaps merge some of the main point made in the comments in the original answer? – Serban Tanasa Apr 25 '16 at 18:08
• Though it does not apply for all situations, Shooting small projectiles Shotgun style as Super high speeds would also be a good solution when applicable. Shields are probably not going to be an issue in a more hard science situation, so hard projectiles traveling really fast could feasably create holes in a ship, which if they hit the right places cough bridge cough could be devestating, but due to low mass have negleable recoil even compared to the numbers here. Some important wires or Resource lines get cut, and the ship is disabled but completely salvageable. – Ryan Jun 22 '16 at 16:06

The simplest solution would be a control system that links the guns to the engines and fires the engines to counteract the effects of the guns, or just use the thrust from the guns to provide extra manouvering for skilled piloting.

Alternatively make each projectile actually a self-propelled missile that requires very little inertia from the firing ship, this would also give them the ability to home in on their targets to some degree.

• My ships will have missiles, but those are more expensive, take more storage and have a limit on rate of fire because of the slow inital speed of the projectile. Engine compensation is of course possible. – Tomáš Zato - Reinstate Monica Apr 22 '16 at 14:49
• I think this is the most efficient solution, assuming the recoil is enough to cause non-negligible changes in velocity and you don't have inertial dampening or anything of the sort. This sort of automated recoil compensation is very much like feedback-based stabilization systems, of which we have many, thus making it almost mundane. However it gives you a lot of opportunity: the quality of recoil compensation can affect targeting and targeting systems, large guns have penalties, small fighters can do clever stuff (as mentioned), ships have to be designed with recoil compensation in mind etc. – mechalynx Apr 23 '16 at 15:03

The same way we do it on Earth, use a recoilless rifle. An example in current use is the Carl Gustav anti-tank rifle.

The basic idea is the same propellant which fires your projectile also fires a stream of hot gases out the back with equal momentum. The two cancel out, and there is no recoil. This works because momentum is mass x velocity and the relatively low mass gas is moving at a relatively high velocity compared to the projectile.

The disadvantage is this limits the amount of pressure which can be built up in the gun, which limits the velocity of the projectile. For this reason, recoilless rifles don't use kinetic energy penetrators (like an arrow) but instead use explosives or an explosively formed penetrator (ie. a HEAT round).

To get around this disadvantage, a space battleship could have a much more complicated mechanism than what can be carried by a person or tank. They could instead use a traditional gun with another linked gun simultaneously firing hot gas in the opposite direction. At a certain point, this is just another engine.

• +1 For referencing His Majesty the King of Sweden. kungahuset.se/kungafamiljen/… – Bex Apr 23 '16 at 9:31
• Pretty random reason to upvote – Lightness Races with Monica Apr 24 '16 at 21:44
• @LightnessRacesinOrbit still better than half of the reasons to vote in most SE sites. Votes are evaluations, any and all human-made evaluation is subjective to a degree. – Mindwin Apr 25 '16 at 13:31

Waste not, want not.

War is not always about having the perfect weapons or the perfect armor. War is about using what you have as efficiently as possible.

If, for your ships, the guns impart a non-trivial delta-V, the captain that uses that delta-V in his strategy to propel him where he wants to go will be ever so more nimble than the captain who spends precious mass/energy to counteract it. I would expect space combat philosophy to evolve towards engagements that assume the gun recoil as part of their trajectory shaping. There might even be a subtle art of positioning yourself so that, if they fire they must fall into a weak position and get slaughtered,

• Although we only have seen so far (as of 2016) space battles in fiction, the most exciting are the ones where positioning and maneuvering were the key factors in the victory. IMNSHO – Mindwin Apr 25 '16 at 13:34

Assuming your guns do actually have recoil, and you're not just using a big recoilless cannon:

## Inertial Dampening

A number of space games use a technology they call "inertial dampeners". Essentially, these are sensors linked up to the engine controls. If the throttle isn't being held, they act to slow the ship down much as friction would on a road on Earth.

You can calculate how much force you need to do this, if you know the mass of the projectile you're firing and how fast it's going - the forward momentum of the projectile is equal to the backward momentum of the ship. With the backward momentum of the ship, you can calculate the force you need to stop it moving.

You say you're planning to offer this as an upgrade to your players. Great idea. How about taking that one step further with an upgrade path that looks something like:

1. Guns
2. Bigger guns
3. Bigger guns + inertial dampeners
4. Recoilless guns

Now you get to use both the dampening tech, and recoilless tech!

• Dampers, not dampeners, surely? – peterG Apr 25 '16 at 12:22
• @peterG no - they are dampening the inertia of the ship, hence they are dampeners. – ArtOfCode Apr 25 '16 at 13:54
• They are damping the inertia of the ship. 'Dampen' means to make slightly wet. Wikipedia seems to agree(en.wikipedia.org/wiki/Damper) although I see some minority support for your usage in some car and motorbike forums re. suspension etc. – peterG Apr 25 '16 at 17:24
• @peterG I suspect it's a UK/US thing, too. I'm UK, so I'm used to it being dampeners. – ArtOfCode Apr 25 '16 at 18:04
• I was going to suggest that, but the other way round! I'm in the UK too. But I've only ever heard suspension dampers, steering dampers . . . .have a look for MacPherson Strut on Wikipedia, for example. – peterG Apr 25 '16 at 20:39

A fusion drive is a weapon, powerful in direct ratio to its efficiency as a drive. - Larry Niven

Perhaps the engines and the guns are a single device. Both are designed to propel a small amount of material away from the ship as fast as possible. The only difference is that in one case you point it at the enemy, and in the other, you point it behind you.

This would have an interesting effect on tactics and formations. You would need to plan your approach route such that no other ships pass through your exhaust. A ship can easily retreat while firing, and has difficulty advancing while firing. In order to do so, ships could build up momentum, whip around, then fire at opponents while coasting forward.

• Given the opening quote, I think it's clear that this is a perfect weapon for a puppeteer. :-) – Bob Jarvis - Reinstate Monica Apr 24 '16 at 3:34
• Perhaps not, because it is less effective while retreating. The ship's velocity and the muzzle velocity are summed together, and so it is at its most effective when charging at the enemy. – Eldritch Cheese Apr 24 '16 at 17:33
• I'm really late here, but technically, at relativistic speeds, it is not the velocities of the ship and projectile that are summed, but rather their rapidities. – Gryphon - Reinstate Monica Jan 3 at 17:15

How are you planning on dealing with gravity in aboard ship?

I've previously written a short story where the gravitational systems aboard ship were vital in how the craft operated both by providing a source of gravity for the crew, and in providing a "sink" for the inertia of the craft and crew when under power, and also for the firing of weapons etc.

Long story short, damage to the generator meant lots of issues for the crew.

If you want to go a more "hard" SF route, have a compensation system - firing weapons from one side of the ship creates an equal and opposite "firing" of compensation thrusters from the other side, arresting the initial momentum and creating a lack of movement.

Alternatively, space is BIG. If the weapons are mounted so as not to cause rotation, simply thrust, a slight drift with each shot is something that even the most basic of spacefaring civilizations should be able to compensate for with computer assisted targeting.

• There is no artificial gravity in my universe. The ship has little gravity due to it's mass but that's irrelevant for small ships. – Tomáš Zato - Reinstate Monica Apr 22 '16 at 9:44
• @TomášZato If the ships are big enough to have any appreciable gravity at all, then they are positively huge -- think Death Star. Also, that gravity would be in largely random directions on board, based on the local vector to the center of mass; if a crew member goes closer to the center of mass, gravity decreases. This is one of the things that the movie Mission to Mars got right, showing a freefall environment in the central portion of the ship which used rotation for artificial gravity elsewhere. – a CVn Apr 22 '16 at 14:42
• @TomášZato if you're writing, know the difference between "it's" and "its" (in your Universe). – JDługosz Apr 23 '16 at 4:28

There are several ways out of the dilemma:

Mass vs. conventional guns. Yes, as long as the guns don't fire constantly in the same direction, the huge inertia of the ship will keep the ship on course to a good degree because of Newton: $\vec{F_{Ship}}=m_{ship} \times \vec{a_{Ship}}$, wherein $\vec{F_{Ship}}=-\vec{F_{Charge}}$, so the larger the bigger the charge the higher the force upon the ship (Newton's 3rd Law!), but the acceleration it gives is antiproportional to the mass involved, so in order to do some meaningful changes that affect the ship in the battle, the guns either have to be increadibly strong, or fired at increadible speed and repeatedly.

But there is more!

Missiles. Launching missiles is like dropping bombs: open the hatch, undock the weapon and it goes on it's way. The exhaust from the missiles will apply some force to the ship, but again, that is tiny in comparison to its inertia and will only result in very very tiny acceleration bits - which are neglectable. In fact, these could be used to counter the tiny ammounts of the guns to some degree.

Lasers. Just using (microwave or X-ray) Lasers is using one of the most easily overlooked, recoilless weapon. Aiming a microwave laser at the cooling system of a larger ship would most likely cause it to overheat and might even cause it to rupture!

Away Teams/Boarding/Fighters. If there is a way to send away/borading teams to other ships, that is for sure a recoil less way to fight other ships, even if the price in blood might be huge. Launching a boarding ship would not meaningfully impact a space hulk of battleship size. Likewise, launching fighter crafts would not impact either.

Set shavers to stun indeed!

The most physical weapon humans can have in space is an object like a satellite or a ship purposely crash into each other. The reaction would be like glass breaking very slowly as it splatters away into a million fragments.

This is why nations deter from shooting missiles into space the fear of alien invasions might catch up one day if the missile actually happens to reach its target a few billion years from now, though the estimate of that happening is one in a trillion. Suffice to say it is possible. Though if humanity survives to meet such an invasion or is already dead by that time remains a mystery.

To bomb a planet, you would basically only need to park yourself in a slightly decaying orbit and fire heavy high temperature tolerant projectiles backwards. This would accelerate your ship to prevent it from crashing, while the projectiles would end up in a definitely decaying orbit. By the time they hit the ground, they will be meteorites. Some timing and orbital mathematics will make them quite precise. In this case, the recoil is actually what propels your ship.

As for ship-to-ship combat, you probably want to use either guided missiles or drones - or use something very small accelerated to great speeds.

Unmanned but powered units can be built to withstand accelerations that would crush humans, giving them a tremendous advantage over any evasion manoeuvres a manned ship could do.

One of the most dangerous problems space flight has today is micro meteors - that is small things flying fast. Using for example a magnet accelerator you could fire a (stream of) very small and light particle(s) at a significant fraction of light speed without actually giving your ship all that much acceleration. The speed of the particles would make them very hard to outmanoeuvre. Of course, the most extreme example of this would be a laser.

The simplest way is to follow what all the modern (dreadnought) battleships use - a hydraulic recoil mechanism. This would enable the recoil action to go in the opposite direction that the gun goes in and also dissipate most if any force pushing the spaceship in the opposite direction.

Another way would be using something like an old-fashioned cannon which has to be run back everytime, but this would be basically stupid to do in space.

Maybe you could try making an item you could research called "Counter-Recoil Thrusters" (CRTs). These would be attached directly to the weapons (maybe enacting a weight/fuel penalty?) and would activate every time the weapon fires. The CRTs would counteract the recoil by turning on small engines pushing in the opposite direction. This could be an upgradeable item by making higher level CRTs negate more recoil than lower level ones, though they would be more expensive and use more fuel. Also, you could have weapons which have little to no recoil, but enact other penalties. For example, you could make laser weapons have no recoil (since they are just firing concentrated light, after all), but make their fire rate slow and the module itself heavy and costly. Or, maybe a machine gun with a high fire rate and low recoil, but dealing little damage. Another idea could be an upgrade to the ship itself that makes its thrusters automatically compensate for some of the recoil of its weapons.

Recoil in a game such as this (or any weapon-based game) will become a main focus in many ship and fleet builds. A ship with little recoil mitigation will likely have to waste a lot of time and resources constantly having to move back into position to fire again, but buying something like a CRT or a recoil-resistant weapon/module is costly in itself. Maybe you could take this to your advantage and make other ship modules which alter recoil (like a weapon which reduces recoil mitigation on ships it hits, or a weapon which has enormous recoil allowing a ship equipped with them to "dodge" attacks by firing them to one side, shoving itself out of the way of danger)

Spinning disks (*) at high speed, stooped at exact time of shot but that depends of amount of energy we talking about, mass of disks (size/diameter) and ability to stop them instantaneously. Also add some impulse engine on the other side of your dreadnought.

(*) (them disks probably should spin in different directions so in odd numbers per cannon)

• How does spinning disk solve the recoil problem? It rather seems to add even more recoil in hard-to-predict directions. – Tomáš Zato - Reinstate Monica Apr 25 '16 at 11:26
• There is no "instantaneous" stopping anything. Even in inelastic collisions, $\frac{\Delta v}{\Delta t} < \infty$ because $\Delta t > 0$ (time needed to stop is non-zero, regardless of velocities involved). Time needed to stop may be small, but it must be non-zero. – a CVn Apr 25 '16 at 12:03

A rail Gun provides some very attractive attributes in this environment.

In space we do not need to deal with atmospheric friction so the energy necessary to sling a projectile long distances without loss of velocity is relatively small. In a railgun where the projectile floats within the rail guides, there will be no friction between the projectile and the rail gun (barrel). Since the projectile is accelerated using alternating attractive and repulsive forces generated through magnetic fields along the guns barrel length, if these cyclical forces were precisely balanced, they would tend to cancel each other out, thereby negating the pushing force of just an attractive force or a repulsive force. This would result in virtually no perceived recoil. The projectile would need a form of guidance and stabilization control to correct for any contact with small space debris or other anomalies in its path.

• This makes no sense. As long as the ship accelerates the projectile, it will experience recoil, no matter the method used to accelerate it. – March Ho Apr 22 '16 at 23:57
• Interesting to compare this with the earlier answer by "Just Thinking", also a just-signed-up user. – JDługosz Apr 23 '16 at 4:23
• Upvoting because this could actually provide a good option. Frank said there is 'virtually no perceived recoil', not no recoil at all. With the only force acting on the projectile being magnetic, the only recoil you can expect is the repulsive effect acting on the gun as well as the projectile. The extreme difference in mass between the ship and one projectile however would make this recoil insignificant and easily counter able (exception being a rapid fire weapon). – アキオ Apr 25 '16 at 10:43
• The recoil momentum from firing a shell of weight X and speed Y using an explosion must be the same as the recoil from firing a railgun projectile of the same speed and size, by conservation of momentum. – pjc50 Apr 25 '16 at 12:34