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The primary armament of the space warships of a race I am building use an armament that consists of explosive shells that have a rocket engine in them. The idea is that they are fired from the ship using chemical propellants (or rail guns in more advanced ships) and then the rocket engine takes over, driving the shell to its target. The idea is to reduce the recoil on the ship itself, and provide some "smart bomb" capability to the shell itself, allowing it to maneuver around obstacles or target a part of the enemy vessel besides a direct shot from the warship.

It was going to be fired from a turret, either as a railgun or a chemical charge, but the more I think about it, I realize that it doesn't make sense to have a turret, which is a complicated machine and has a lot of breakable parts (especially in combat) when these shells can operate more like rockets. Why would you need to rotate the ship and turret to line up a shot when the shell can maneuver itself around your vessel?

Is there a good reason to continue to have turrets with this kind of armament? Would the extra speed/force from the launching of the shell provide it a big enough benefit to outweigh the issues a turret brings?

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    $\begingroup$ For the vote-close for Primary Opinion Based: there is possibility of answers based on hard facts. We are talking physics here in a sense. - - - - - - - - - - - Marshall: add the physics tag if you feel like. $\endgroup$ – Mindwin Nov 1 '16 at 18:01
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    $\begingroup$ You're describing a torpedo or a rocket, therefore you don't need a turret. The only reason to have a turret is for aim, so the shell won't go towards your ship while looking for its objective. $\endgroup$ – Santiago Nov 2 '16 at 20:33
  • $\begingroup$ Did you mean to have a word like less in the phrase "the it makes sense" $\endgroup$ – Glen_b Nov 2 '16 at 21:20
  • $\begingroup$ This is like asking if it make sense that we have many types of guns. They are useful in different situations, its not a one size fits all deal. $\endgroup$ – Necessity Nov 3 '16 at 2:18
  • $\begingroup$ Also turrets have a lot less breakable parts than a rocket that is going to ecplode. The munition is a lot cheaper and easier to produce. $\endgroup$ – Necessity Nov 3 '16 at 2:25

18 Answers 18

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Why use guns or railguns?

They provide significant initial velocity to the projectile.

In this case, of course the gun must aim in the right direction. Two options here, turn the mount on the ship or turn the entire ship. If you turn the ship, you can only aim at one target. That might be acceptable for a small ship with a single gun, but not for a big ship that is supposed to engage multiple enemies.

They throw the projectile clear of the ship before the rocket ignites.

There could be many reasons why the engine of the projectile becomes a problem. It could scorch and damage the ship. It might be easily detectable, so that it betrays the position of the ship (cf the eternal Stealth in Space debate).

Decide what is best for your story.

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    $\begingroup$ This is misusing "delta-V". The guns provide no acceleration to the projectile, they apply acceleration to the projectile, which provides velocity. It's really pedantic, but the guns don't give the projectile more means with which to accelerate itself. $\endgroup$ – Delioth Nov 1 '16 at 17:06
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    $\begingroup$ @Delioth, edited. $\endgroup$ – o.m. Nov 1 '16 at 17:14
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    $\begingroup$ Turrets are also good for launching the projectile at the target before the rocket ignites, in addition to throwing it clear of the ship. For example, a turret firing towards the target has the projectile already on the direct path so the rocket's fuel is more for minor navigation, whereas a ship with the launching tube away from the target would require the projectile to navigate onto the direct path and require much more fuel to both get on the path as well as obtain collision speeds. It'd be faster by (likely, due to large distances in space) several-to-many seconds. $\endgroup$ – Daevin Nov 2 '16 at 15:04
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    $\begingroup$ @Daevin, that's what I meant by "initial velocity" in rthe first part of the answer. But a fixed mount would have the same effect. $\endgroup$ – o.m. Nov 2 '16 at 15:47
  • $\begingroup$ @Delioth The guns do however give the projectile much more "reactionary mass". This does in fact give the projectile much more means to achieve higher velocity. $\endgroup$ – Aron Nov 3 '16 at 5:14
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A railgun can achieve a muzzle velocity of around 3-4 km/s. This is a not-inconsiderable speed advantage, and the faster your munition is traveling, the harder it is for point defence to intercept it.

With respect to some other answers here, a VLS missile battery on a wet navy ship isn't really a good comparison. Compared to the missile it's launching, a wet ship is virtually stationary. That's not the case with a space ship, which is likely to be travelling at least 10 km/s, which is velocity the missile will need to counter to get where it's going.

If you just dump a missile into space, it has to 1) kill any velocity your ship has given it, then 2) accelerate from a standing start. This is going to burn propellant, reducing its range, its final speed, and its ability to manoeuvre around point defence.

If start off pointing your weapon at the enemy, you can use ship-board power to give it an initial velocity advantage. It no longer needs to kill its velocity with onboard propellant, it doesn't need to accelerate itself from a standing start - it can just blast away for the enemy. It now has greater range, can build up a greater velocity before it reaches the target, AND has more ability to manoeuvre to target the enemy.

Now, how you point your missile at the enemy is a good question. You can have just missile tubes at the bow and turn to point the whole ship towards the target, dogfighting-style; you can have turrets that can point in any direction you need; or you can have missile tubes on all faces of the ship, so you just have to point one face of the ship towards the baddies. That's your call. Remember that in space, you can easily orient your ship in any direction you want without affecting your course or velocity. If you have your engines a long way from the centre of mass, like on a Babylon 5 Starfury, you can flip your ship in any direction you want extremely quickly.

For inspiration, you might want to read some of the Honor Harrington books by David Weber. They have a situation not dissimilar to your own, though they use gravitic drives to propel their missiles at thousands of gravities of acceleration. They go into detail about the advantages of firing missiles from powered tubes rather than just dumping them into space.

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    $\begingroup$ Velocity relative to the target, which can be practically anything. If two ships on radically different vectors want to engage one another, a shot fired from one needs to create an intercept vector to the target, which will include cancelling any velocity the firing ship already has. A turreted mount allows you to use shipboard power to do that; just flushing a missile out of a tube requires the missile to burn its own power/propellant to do the same job. $\endgroup$ – Werrf Nov 1 '16 at 17:34
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    $\begingroup$ That's how it works in an atmosphere, not in space. Doing something like that works in space only if you're very close, or if your missiles have fuel and propellant for a brachistochrone trajectory. $\endgroup$ – Pedro Werneck Nov 1 '16 at 18:22
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    $\begingroup$ Um...no. I think we're talking past one another. How it works in atmosphere is manipulation of the atmosphere to induce changes in relative direction while preserving speed. Outside atmosphere you don't have that option. If you have two spacecraft that are, say, moving directly away from one another, first your missile has to kill the velocity from the launching ship before it can begin to move towards the enemy ship. $\endgroup$ – Werrf Nov 1 '16 at 18:25
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    $\begingroup$ No need “kill velocity”, whatever that means. Just need to compensate for the difference in velocity vectors between the two ships. Actually, if one ship is chasing the other, the velocity given by the ship is a huge help. In all cases, the point of the turret is to give additional velocity in the right direction. $\endgroup$ – spectras Nov 1 '16 at 18:58
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    $\begingroup$ @Werrf You don't need to kill velocity. If you want to hit another space ship, you must create an intercept. This means you need to change inclination, and then likely create a bi-elliptical transfer to the target that optimizes for time spent / speed within the delta-v constraints of the missile. So... to hit a target "in front" of you, you will likely drop the missiles orbit below the taget (decelerating from your point of view), while to hit a target behind you, you are screwed, because it takes much, much longer for you to hit them (need to go higher) then it takes for them to hit you. $\endgroup$ – Polygnome Nov 1 '16 at 21:40
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No need for turrets with steerable munitions

We are already moving away from turrets when we can, for exactly the reasons you mentioned: they are fragile and complex. Vertical launching systems are preferable when you have maneuverable munitions.

enter image description here

(Image source)

Your spaceship would most likely have similar "boxes" of closely packed munitions that pop out of the launch tube, direct themselves towards the enemy and then get going.

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    $\begingroup$ Disagree, but I like the idea of a closely packed box of munitions that are ejected from the ship, use onboard nav thrusters to orient and move away from the launch vehicle, THEN fire all rockets simultaneously or in series with multiple or singular targets. That just creates a cool mental image for me. $\endgroup$ – Jammin4CO Nov 1 '16 at 20:28
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    $\begingroup$ @Jammin4CO These "rocket bundle containers" are actually featured (minor spoiler incoming) in the Honor Harrington Series by Weber. Very interesting read :) $\endgroup$ – Andreas Heese Nov 1 '16 at 23:19
  • $\begingroup$ @Jammin4CO - they also were discussed as possible wet navy weapons. Go along, drop missiles behind you, have them fire when you're well away to avoid counter-battery fire. $\endgroup$ – Blackbeagle Nov 3 '16 at 3:30
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I see two benefits to turrets that may outweigh the complexity and fragility, YMMV.

  1. Posturing - Nothing says "I mean business" like opening a port, extending a projectile array or gun and pivoting it to point directly at a target. Perhaps bloodshed could be averted by simply deploying armament to encourage communication.

  2. Onboard Fuel - you are allowed a higher explosive payload if the projectile can get an initial velocity boost from a launch system, not to mention savings on full direction change. Fuel spent changing directions from the far side of the ship is fuel that can't be used for course corrections and long term acceleration. See also - Jason K & Werrf

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    $\begingroup$ Posturing is why you don't chamber a shell ahead of time in a pump shotgun. That racking noise is a sure way of explaining to someone how things are about to not go well for him. $\endgroup$ – Malvolio Nov 1 '16 at 22:55
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Unless your ship's weight is made up of like 10% ammo, The recoil isn't really an issue. If your ship can't correct for that very minor movement, you have bigger issues.

It should also be pointed out that War is a "Sword vs Shield" evolving system. People will keep building new 'Swords' (smart missiles in this case) to break peoples 'Shields' and others will build counter 'Shields' to deal with their enemies 'Swords' (Lasers that shoot down/redirect missiles in this case). If a faction becomes too married to one kind of weapon, they will be fighting an uphill battle once the enemy has effectively countered it (this is why no one really bothers with horses in war anymore. Or building Castle like defenses. They have become almost useless for the effort they require)

EDIT: (revising final point to make it clearer) Over time the weapons and defenses of spaceships will naturally keep changing. Once you find 'one really good offense', others will make it a high priority to make it a 'very meh offense'. A kinetic weapon launched at high speed, especially in larger numbers, can be just as effective as a guided missile. Since you likely won't be able to 'just swap out' weapons on your ship, having a variety of offensive abilities to counter your opponents defense will make a stronger ship. In other words, (in general) battle tactics (or versatility) > firepower (unless firepower is overwhelming, but such advantages tend to be relatively short lived as the enemy learns how to counter it.)

So the answer to "Why use weapon B over A?" is "How effectively are my opponents able to withstand weapon A vs weapon B". (In this case, if the enemy has really good anti-smart-missile systems, Than you may be better off with a dumb-fire or inert kinetic weapons)

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    $\begingroup$ There are also Sci-Fi stories that compare kinetic weapons to 'clean nukes' once you get them moving fast enough. $\endgroup$ – Tezra Nov 1 '16 at 16:14
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    $\begingroup$ Please use domain-useful speeds. "Mach 20" isn't a thing in space- sound can't travel in the vacuum, so "Mach 1" is a theoretical standstill, so even "Mach 200" would still be slower than my fingers typing. And also note that Earth's orbital velocity (on average) is about 67,000 miles per hour, while Mach 20 at sea level is only 15345.4 miles per hour. (alternatively, 30 km/s vs 6.86 km/s) $\endgroup$ – Delioth Nov 1 '16 at 17:12
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    $\begingroup$ @Delioth I meant Mach with respect to 'Earth normal air' so just make it 25,000 km/h. Speed is speed. My point is, regardless of the units, you can do plenty of damage if you get speed high enough. $\endgroup$ – Tezra Nov 1 '16 at 17:37
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    $\begingroup$ Since I can't edit my comment (or move this to a discussion) Please don't leave any more comments about 'mach'. The point was Speed=Damage. I recognize the error in my chosen unit (just replace 'mach' in my comment with '25,000 km/h' if you need it to be correct), So please keep comments relevant to the current wording of the answer. Thank you. $\endgroup$ – Tezra Nov 2 '16 at 13:35
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    $\begingroup$ Yes, a variety of weapons could be helpful as you say. In your case of going up against an enemy with an anti-smart missile system (e.g. a space laser), the attackers could send a cloud of hundreds of cheap "dumb" titanium slugs and hope a few hit. $\endgroup$ – Columbia says Reinstate Monica Nov 2 '16 at 21:13
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There's no atmosphere in space.

When you launch a missile in an atmosphere, it can use the ambient air to change its velocity (vector). You also have a maximum speed the projectile can have - a balance between the thrust and air resistance. Neither of these exists in space, which means that there's a significant cost to launching even a self-propelled projectile in the wrong direction.

Each self-propelled rocket has a certain maximum velocity change it can achieve - that's what delta-V is. Let's say that your missile has a dV of 20 km/s. If you shoot it away from the enemy at 5 km/s, the missile will have to pay for this out of its dV budget - instead of having 25 km/s of potential velocity (if launched at the enemy), you get just 15 km/s. And you want the projectile to be fast - not only does it make it more destructive (surface explosions aren't very useful), it also makes it much harder to intercept.

You also need to use dV for any maneuvering at all. The enemy ship changed your relative velocities? Your missiles must match that, or they're going to miss (and if you're fine with that, why are you using missiles instead of railguns?). The faster your missile is moving and the closer it is to the target, the harder it is to adjust the trajectory - you can't just make a turn in space, the only way to change your trajectory is to apply thrust, and that takes fuel. In an atmosphere, most of the fuel of a missile is used to overcome drag - which means that if the missile needs to make a "sharp" turn, it costs almost nothing. In space, you need to pay the whole cost of the velocity change - a 90° turn means that you lost all of your velocity; at best, you're a sitting duck with barely any relative velocity; more likely, you miss.

Now consider how the turn would appear from the point of view of the enemy ship. Let's say your missile launchers are at a right angle to their intended trajectory. At launch, everything is great - the missile has substantial tangential velocity (since it's travelling on the tangent :)); but now you need to steer it towards the enemy. As you steer, your missile follows a nicely predictable path that will tend to end in zero tangential velocity, which makes it much easier to shoot down with both guided and unguided munitions, not to mention lasers. If you don't get a zero tangential velocity, disabling the missile's engines will make it miss entirely - and you're wasting part of your impact force to the tangential velocity (quite possibly resulting in outright ricochets, given the typical speeds of such projectiles).

As you can see, dV is kind of the king in space. You can't really do anything without expending fuel, and thanks to the tyranny of the rocket equation, there's severely diminishing returns on adding more fuel to a rocket - if your turret can add 5 km/s to your projectile, that's essentially free delta-V, which means more maneuverability and more destructive power. You'd be crazy not to exploit this.

Are turrets weak points? Not really. They will likely be armoured. They will likely separate the magazines from the turret itself, containing most damage to the turret itself. The turret will likely be positioned in a way that impacts to the turret have little effect on the rest of the ship - think something like a Star Destroyer, where the whole hull of the ship (when attacking) is perfectly sloped to prevent penetration, and the turrets are offset so that even if a projectile penetrates all the way through, it will not penetrate the ship behind it.

Are turrets complex? Sure. But so are missiles - and a turret only pays the cost once, which makes the projectiles much cheaper. And unlike in an atmosphere, you don't get free changes in the direction - so smart munitions avoiding obstacles actually get all the more complicated. Even rotating the missile to allow it to fire its engine in the right direction is entirely non-trivial.

Why are missiles currently the state-of-the-art in fighting?

  • They allow you to specifically target the weakest part of the enemy armour, at exactly the right angle. This comes pretty close to nullifying any armouring strategy other than "armour everything, thickly" - and that's an expensive strategy that also makes you a sitting duck, despite all the improvements in engine power. This isn't quite as simple in space - you have nowhere near the maneuverability, and the enemy can use the full 3D space to avoid your munitions.
  • The anti-tank missile allows you to bypass most layered armours by forming a very long (and fast) kinetic projectile on impact. Since space is a premium in any tank, there's a limit to how thick your armour can be. In space, you can have very effective layered armour that has a low mass (in fact, we're already using it for protection against high velocity impactors on existing probes), while being able to defeat a typical shaped charge. And unlike ships, spaceships don't sink.
  • They allow small ships to engage arbitrarily large ships effectively. Guns must be big to pose a threat to a well-armoured ship - bigger guns mean more oomph, as well as bigger range. If you can't even get close enough to fire your guns, you're screwed. Also, it's a great response to the dominance of the aircraft carrier. It's telling that the US Navy is trying to develop a workable railgun for its warships - missiles are too damn expensive, and a railgun would keep most of the bonus small ships had thanks to missiles, especially if combined with a nuclear reactor for power. This will likely get even more important over time as anti-missile defenses get better. In space, even if you use missiles, you're probably going to want to launch them at as great a velocity as possible - there's no maximum speed limit, and any initial velocity imparted by the launcher means more dV for maneuvering.
  • When fighting a technologically sub-par opponent, you can keep your most valuable assets out of fighting range. Good intel combined with smart munitions means you can hit and destroy the enemy from far greater range than they are capable of retaliating. There's no maximum range in space - and there's nowhere to hide.

Obviously, it isn't one-sided at all. There's many weapon/defense systems that have their pro's and con's in space. There may be rocket boats that work similar to rocket artillery. There may be bombers that try to exploit their small size and maneuverability to squeeze as much as possible from their munitions (and can use spinal-mounted launchers effectively). But having one weapon makes you extremely vulnerable - find a good way to counteract that weapon/tactic, and you can crush a much stronger enemy. Look at battleships in WWII - naval bombers made them pretty much obsolete, despite being gigantic investments. Maneuvering in space is hard, so whoever steals the initiative has a huge bonus - and that's easier done if you have flexibility.

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More as a comment for Michael Karnerfors answer, turrets are needed to steer "non guided" munitions. As he said, your munitions are rockets, so don't need any mechanisms on the ship.

What will need steering is going to be any laser weapons. The beam moves at the speed of light and isn't affected by much that your spaceship is going to encounter, short of the event horizon of a black hole. Laser weapons will require the laser generator itself, an optical train to expand the beam, and a mirror to point the beam at the target and to adjust the beam to any manoeuvres the target might make to break the target lock.

Laser turrets will be pretty complicated devices. The illustration is of the turret fitted to the nose of a Boeing 747 used as the Airborne Laser Lab test vehicle, and any spaceship will have at least one comparable device (although, using the calculations provided in the Atomic Rockets site, you can determine the actual size including the size of the final mirror)

enter image description here

Oddly, you could have multiple laser turrets, but only one laser. If you picture the laser itself as a massive tube in the centre of the ship, and a set of mirrors at the end directing the beam through open spaces in the ship with the turrets at the end of these laser "conduits". Depending on how the optical train is arranged, the beam could be fed to one turret at a time, or divided between each of the turrets as then combat situation dictates. Obviously, if you have the beam is split between 4 different turrets, each turret will have 25% of the laser's energy (minus any losses in the optical train).

So it is possible to have turrets for the laser weapons (or even just laser communication devices or LIDAR scanners) along with the fixed launching boxes for the ships missile battery.

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    $\begingroup$ Your image was hanging off the bottom of my window, and I thought the "Pitch Mirror" started with a B instead. $\endgroup$ – Criggie Nov 2 '16 at 2:05
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    $\begingroup$ No, it is a BITCH MIBBOB!!! $\endgroup$ – vasin1987 Nov 2 '16 at 6:18
  • $\begingroup$ Stay clear of that mirror..... $\endgroup$ – Thucydides Nov 2 '16 at 16:32
  • $\begingroup$ A single laser in combat would be a bad idea. All it takes is one hit to remove your ability to fire back. You would want multiple lasers in multiple locations to increase resiliency. $\endgroup$ – boatcoder Nov 2 '16 at 17:19
  • $\begingroup$ You would have to do a fairly detailed analysis of costs and vulnerabilities, but the laser weapon would be more or less in the centre of the ship and surrounded by armour and ships structure and systems, so the laser itself would be difficult to get at. $\endgroup$ – Thucydides Nov 2 '16 at 17:25
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Probably not.

Unlike in an atmosphere, a missile in space doesn't have to constantly burn fuel just to avoid crashing into the ground. That means you can get it "pointed" in the general direction of its target and just let it coast, giving it a potential flight time not of a few minutes or hours like that of an atmospheric missile, but of months or years, if the target is across the solar system.

Now, you don't want to just burn up all the fuel for accelerating as fast as possible right from launch. That would just leave you with a dumb projectile, which is trivial for a mobile target to dodge with months of reaction time. You want to burn enough fuel to make sure you're closing on the target, and use the rest for course adjustments en route, to counter any movements the target makes.

The less fuel your missile has to burn to set its initial course, the more it has available for corrections, and the more likely it will be able to actually get near its target.

That suggests that you want to have the missile pointed in the right direction from launch (not necessarily directly at the target - orbital mechanics are weird to those used to typical human living conditions, but I digress...), which a turret would certainly help with.

But, I suspect it would be even cheaper to just make some really tiny adjustments with reaction wheels and turn your whole ship around to aim fixed missile tubes. Feel free to take your time turning slowly (and inexpensively). Remember, it'll be a few months before your missile gets close to the target anyway.

And, if you somehow manage to sneak up on someone in space, with your bright, heat radiating ship, and are close enough that your missiles can reach their target in a matter of minutes or less, then you can probably afford to have them burn fuel maneuvering around your ship when launched from fixed tubes. At that point, though, you're also approaching the point where dumb projectiles and lasers start to become feasible (and they would certainly need turrets).

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  • $\begingroup$ "it'll be a few months before your missile gets close to the target anyway" The target would just shoot those missiles with a weapon of choice. Missiles don't make sense at that range unless your target is defenseless. $\endgroup$ – user31389 Nov 2 '16 at 16:31
  • $\begingroup$ @user31389 They'd be limited to using a point defense missile initially, which indeed could be a problem. Dumb projectiles and lasers would work, but only near the very end of the flight, and you could design your missile such that it is a disposable, single-use drone, that fires a dumb projectile or a laser itself as soon as it reaches effective range, thus making short range point defense less than totally effective. $\endgroup$ – 8bittree Nov 2 '16 at 16:35
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Depends on the maneuverability

While it is true, that self-aiming ammunition wouldn't need to be fired into the direction of the target at all, the amount of fuel in the rocket motor is limited. To reduce the needed fuel to get from a launch bay to the final trajectory (where the engine could either cut out or just accelerate), the launch bay could be a turret in itself: it just angles and rotates until it is in a good launch angle. This can speed up the targeting process by shortening the path the missile has to travel considerably.

A roughly aimed launch becomes increasingly necessary if the munitions are not able to do a 90° to 180° turn or have a relatively large turning radius.

Giving the missiles an initial speed boost does further reduce the ammunition's fuel needs, allowing either a smaller & cheaper design, a larger payload or increased reach of the motor (which in turn increases the maximum effective reach before the missile electronic fails in space and the tactical reach, at which engagement with the enemy is considered useful.

Also: Point Defense

As the ships carry missiles to fight enemies, the species is well accustomed to methods to try to get rid of missiles fired at their ships. So they would very likely build PD systems onto the hull, and to reduce the total number of needed emplacements, these would very likely be placed in turrets, no matter if it is a Laser, counter-missiles or kinetic shells.

Caveat: Physics!

Now, for the things we have to take a look at when thinking about the rotating turrets, and mainly they are physics.

First of all, there is the conversion of rotational energy! Rotating our turret (no matter how light it is) around one axis applies a rotational force on the ship that is the other way than the rotation of the turret. This can be canceled out by just rotating a piece of the same weight in the counter direction on the same axis, so turrets might be aligned in quads and have linked movement patterns.

Second, Newton's Actio=Reactio. Accelerating the missiles a bit will apply equal force in the counter direction - but as the ship is much much heavier, the effect could be near neglectable (but matter for very long distance travel). If you want to counter this, either very specific fire patterns (that remove the effects by clever vector addition) or RCS will be needed - which is easier to calculate to do with fixed position launch bays.

Third, again, Newton's Actio=Reactio. Rocket engines are not really "ragdoll free", they just appear so for most Anti-Tank-Missiles, as they are just a tube without a floor from which the warhead is propelled. In space, exhaust gas particle continiue to travel with the same speed till they impact something or have dissipated enough to be indistinguishable from background particles. The first thing they'll impact is most likely the ship that fired the missiles, but again, the transmitted energy from them is neglectable because of the sheer difference in weight. Still it should be accounted for because this "vapor trail" (more like "gas trail"?) could be used to identify the trajectories.

Fourth is more the missile in question: Maneuvering in space. Remember, we are in an environment where gravity has much smaller effects than on a planet and there is little to no friction/drag. This means, the missile in question has only one way to steer at all: directing its exhaust. This again means, that the maneuverability of the weapon is directly related to two components: vectoring its main engine and the posession/lack of an RCS system to tilt it. With both in mind, there might be missile types that fire their engines for some time, then shut down for harder detection in travel, till they re-launch the engines for the last approach, others might fire the engines sporadically for maneuvering, and yet others just accelerate the whole time to impact as fast as they can, basically making them long-range-high-speed-kinetic-penetrators.

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Like you've said, turrets are complicated and completely unnecessary in the situation you describe where the projectiles themselves are 'smart' anyway.

For your ships, you can have lines of these rocket pods along the top, bottom, and sides. It makes sense to fire rockets in pairs from opposite sides of the ship, so that the kinetic force is cancelled out.

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  • $\begingroup$ In space, steering of munitions is not that uncomplicated, because they have to angle their engine to change direction, while in an atmosphere most missiles have a fixed engine and maneuvering fins. In both cases, any rocket engine/missile has a minimum turning radius based upon its vectoring engine/steering capabilities and its maximum acceleration. This is the reason, why fighter jets only fire missiles into the front 60-90° arc. Comparing to VLBs is not possible in space, as cruise missiles rely on gravity to achieve their target trajectory. This is most likely not possible in space combat. $\endgroup$ – Trish Nov 2 '16 at 14:08
  • $\begingroup$ @Trish Agreed in that the missiles can't work like conventional ballistics - they'd need to have vectored thrust for a start. But one vectored thrust nozzle is not much more complex than manoeuvring fins (at least, it won't be when we have fighting space ships) and the missiles' relatively small size means they will still be very agile. There's also a lot of 'space' in space, so turning circle won't really be a factor; ships will engage at extreme distance anyway. $\endgroup$ – Cooper Nov 2 '16 at 14:11
  • $\begingroup$ Turning circles do matter for constantly burning engines, because you have to burn fuel for the whole length of the arc you fly, so for a 180° turn (worst case), the maximum distance is cut by $\pi r(\vec v)", so you want a small r to keep maximum reach or maneuvering fuel. You likely acknowledge that r increases proportionally to the speed of the missile. If you can shut down the engine and have RCS to realign the missile, then fire it in the new target vector, the missile design gets much more complicated, but you gain the "free fire" ability you seem to think about. $\endgroup$ – Trish Nov 2 '16 at 14:32
  • $\begingroup$ @Trish Adding RCS systems is more needlessly complex than just increasing the fuel capacity of the missile. I'm thinking that a missile like this could turn 180° in about a second, so the extra fuel that uses up is negligible. $\endgroup$ – Cooper Nov 2 '16 at 14:54
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Turrets are very useful if munitions have to consume a lot of fuel in order to maneuver. A turret allows you to fire munitions ahead, adding the ships velocity to the munition, or to the flank or stern on an intercept course with the target while the ship moves away. If the munition can accelerate 1000x after being launched from a ship then the vector imparted on it by the ship is negligible and you could fire munitions in any direction you want and they could maneuver at will. But if the munition is heavily reliant on the host ship for an initial velocity push because maneuvering fuel is limited then you need to be very careful to fire it in a useful direction and a turret based launcher can help a lot with that (otherwise you have to maneuver the entire ship for each launch). Remember there is no atmosphere to help with maneuvering or downward gravity to counter, unlike conventional missile launches on Earth, so you can't arc missiles up and around without a significant cost in fuel.

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It depends on how much velocity your gun can provide vs. how much velocity your rocket projectile can provide.

If your gun's muzzle velocity is either higher or a significant portion of the velocity your rocket engine can provide, then there is a case to be made for having a gun. (and a turret) Otherwise it's superfluous.

Consider, for example, that you have a railgun that can provide a few km/s velocity, and your projectiles are propelled by a chemical rocket that can also provide a few km/s velocity. (this projectile would be about half propellant by mass) The upside of having a gun is that you can either have projectiles that go twice as fast, or you can have the projectiles carry less propellant, meaning they're smaller and cheaper and you can carry more of them. Note that in the latter case a gun becomes more attractive the more projectiles you expect to fire. You're saving mass on lighter projectiles at the cost of a heavy gun turret, which means you need to fire a certain amount of projectiles for it to make sense.

There are tradeoffs to both of these advantages. A common downside is that introducing a gun turret introduces more system complexity and mass. It also implies a lower effective fire rate - it doesn't take much to fire many missiles concurrently (just enough launch cells, which you have just to store them anyway), but your gun can only fire so often.

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Not enough rep to comment, but since people seemed to be confused by Werrf's answer I wish to clarify it a bit. Atmospheric guided projectiles can use wings to steer themselves, so they can convert vertical velocity into horizontal velocity with a bit of loss to friction and turbulence. This means that if you're travelling straight up at 200k/h, and want to start moving east at 1000k/h, you might need to only use enough energy for the acceleration from 150k/h to 1000 (the last 850 of delta-v). In space, it's a different story. There is no atmosphere to push against and turn without losing speed, so you must counter the entire 200k/h of starting velocity. Then you need to use propellant to get up to 1000k/h - for 1200 in delta-v.

So very roughly, atmospheric missiles benefit less from being aimed at their target than missiles in space. During a war in space, to reduce the size of the missiles and maximize the acceleration they get out of their onboard fuel you already want them flying at the target if possible, so turrets have a potential advantage.

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I think it's pointless to complain about the mechanical complexity of a turret mounted on a spaceship. Turrets are the go-to weapon mounting solution for armored vehicles and fighting craft for the past hundred years, so clearly they're not as fragile and accident-prone as you believe they are. What they are, however, is heavy, or more accurately, massive. You might immediately want to write off turrets because they're weighing down your spaceship, but don't be so quick to judge.

Turrets are heavy, but missiles are heavier. This is because a missile has to carry all of its fuel, maneuvering, guidance, ect for the whole trip, and its launching vehicle does nothing to help it. It's basically a miniature, self contained vehicle that has to fly all the way to its target. A gun/turret does all of this for its projectiles, so those projectiles can be much smaller, lighter, cheaper, and easier to store.

Imagine that I have two ships - One missile armed and one hybrid railgun-launched-mini-missile armed. Both weapon systems have identical yields, delta-V stats, and so on; the only difference is that the mini-missiles weigh 1 ton and the normal missiles weigh 2 tons. The size disparity is because the turret gives its projectiles 50% of their final speed, roughly halving the need for mass and fuel. We'll give the missile launching ship a benefit and say that its missile-tubes don't weigh anything over the normal structure of the ship. The hybrid railgun ship has a 20 ton turret, immediately taking quite a bit away from its mass-budget.

Let's assume for a moment that each ship has 100 tons to allocate to weapons and ammo.

Missile ship:

100 tons / 2 tons per missile = 50 missiles

Hybrid railgun ship:

100 tons - 20 ton turret = 80 tons of ammo storage

80 tons / 1 ton per hybrid missile = 80 missiles.

That's an extra 30 missiles. 30 more chances to slip past their point defense. If I can fire big volleys at long range, that's a 60% bigger volley to overwhelm their point defense. Even though I lose out on some payload, I more than make it back in being able use smaller ammunition. Even if I have two turrets, I still have an extra 10 shots that my enemy doesn't.

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Yes, if using chemical rockets.

This is about the "tyranny of the rocket equation", which essentially means that not only does every bit of delta-v you want require you to carry more propellant, it also means that more of your propellant is spent giving delta-v to propellant not the actual payload. So more delta-v your rocket has the less efficient it is.

Conversely having a turret that supplies some initial velocity means that your rockets are more efficient.The counter-mass for that delta-v is your ship not propellant that takes space and mass on the rocket.

And on a spaceship this is not an academical concern since less efficient rockets means you carry fewer of them in the same limited space. This is naturally balanced by the mass of the turrets.

So you might want to decide based on how many rockets you think the ships will carry. If the number is a single digit number, the turrets are probably overkill. If you want actual engagements and battles, the turrets will pay back themselves. In between you might have something like fixed mass drivers that double as storage pods for the rockets. Or modular storage pods with integrated single use mass drivers/cannons, really.

There is also real value at being able to launch the rockets in the correct direction without having to maneuver the entire ship. You can get this without turrets, if you use the pod option. You simply drop the pod and once detached it uses integrated thrusters to turn right way and then fires the rocket away using the pod as reaction mass.

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  • $\begingroup$ So more delta-v your rocket has the less efficient it is. - if under "actual payload" we mean destruction force in form of kinetic energy, then that sentence is incorrect. $\endgroup$ – MolbOrg Nov 3 '16 at 1:25
  • $\begingroup$ @MolbOrg Not really (the efficiency still goes down, effectiveness is separate), but you do have a good point.The way kinetic energy scales with velocity could very well lead to situations where you need some specific terminal velocity for sure kill. But that would probably be solved with a separate terminal stage making a very fast sprint. Or the classic nuclear pumped x-ray laser. $\endgroup$ – Ville Niemi Nov 3 '16 at 17:38
  • $\begingroup$ Efficiency for one stage rocket grows up 1/5 (payload/initial mass) and then it begins to drop. $\endgroup$ – MolbOrg Nov 4 '16 at 1:23
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Turrets would be very useful. Luann's answer covers most of what I originally was thinking, but after reading other answers, I have a few more.

With the turret you can fire at anything that you can point the turret at and isn't blocked by your ship. With a fixed launcher you have to maneuver the ship to point at the target or waste fuel maneuvering the missile to the target. The more fuel your missile has the longer it can track a ship performing evasive maneuvers.

Not pointing at the target may also become important as the ship takes damage. With fixed launchers if the area near the launcher is damaged, you will again have to waste fuel to maneuver or present the damage to the enemy. With Turrets you can rotate the damage away and still fire directly at the target.

Multiple targets will also be better handled by turrets. Each turret can independently be aimed directly at the target. Multiple fixed launchers will rarely be able to optimally target multiple targets.

Exposure time of the missile is decreased if it is fired directly at the target. If the missile has to turn, time to target will be increased, providing increased opportunity to shoot it down or to be destroyed by splash damage hitting the firing ship.

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Yes you want a turret of some sort on your ship. They are low tech solutions to a number of problems you might run into, especially with "Smart munitions". "Smart munitions" are great if you have no fear of ever running out of ammo and you know they'll work in the conditions you'll be in, and you don't have to worry about the communication lag, or hacking into their systems to blow you up rather than your enemy...

Ok but let's say none of that is a problem... which I don't even know why you would... you still want to have as little fuel tied up in your weapon as possible because you want to carry as many as possible, undetectable as possible, and light as possible, which means even if everything else is perfect you still want a launching mechanism to reduce all of those issues.

And as far as complexity.. A microchip and transmitter is a lot more complex and more error prone than turning on and off magnets and a few cogs... and to mention if the cogs or magnets break, you can fix them a lot easier than you can the chips in launched "smart munition". Also 1 attack could more easily disable your "smart munitions" with an penetrating round with an EMP... Or just Jam your signal so you can't control them. At least with a launcher system and minimal control you aren't completely disabled so easily.

I'm not saying they're completely useless, but they work much better as a single precision strike (which they're used for now) or a trick shot where you mix it in with regular munitions that an enemy that can predict tragectories would be thrown off by having most rounds miss them, but the smart round, not being taken into account gets a hit, where as a straight smart round can be accounted for and measures put in place to fight it faster when you're expecting it.

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The Soviets equipped one of their manned (and super secret) spy-stations with a 20-mm turret back in the 60's though it's generally presumed it was there for psychological comfort and to prevent the good guys from sending up a larger vessel to capture the station.

The first thing you have to do when designing realistic space warfare scenarios is to take everything you know about planet based combat and toss it out it the window. Nothing works in space the way it does on a planet. It's not going to be WWII in space.

The biggest difference is there is only one medium, vacuum and not three, water, air and land. You will never have a situation in analogous to a bullet, missile or shell, moving orders of magnitude faster than a ship on the water. In space, the biggest warship can move as fast, most likely faster, and for far longer than any small projectile. As pointed above, a size ratio of missile to ship that would work on earth would fail in space simply because the smaller missile would not have enough delta vee to catchup.

Likewise, and projectile fired from a ship, even a railgun, would likely not be able to reach the target.

The reason we use turrets on earth is so that slow or stationary weapon platforms can track targets as they move. A kinetic turret would have to move in a blur to even get a lock, and since the projectile would be traveling over vast distances at a speed close to that of the target, the target probably won't be anywhere close to where it was when the turret fired, and even if so, the projectile will be moving so slowly relative, it will be easy to dodge or intercept.

Directed energy weapons might need a turrent like structure for aiming. At least the point defense ones that would target small physical objects trying to hit the ship. The problem with these as main weapons is the incredible power it would take project and energy beam across the vast distances, then have enough "dwell time" focus on one spot, to do real damage.

I would give up on planet based analogies entirely and look at space craft as the special vehicles they are in their own special medium.

It's not an original observation, but the reaction engines powerful enough to move ships from planet to planet on routine basis, like nuclear or fusion drives, would themselves be more powerful energy projectors than any weapon you could mount on the ship. The Orion external nuclear pulse ship, was designed to defend itself with it's own drive, all they had to do was make a two sided shaped nuclear charge and they would project a jet of near relativistic plasma to a range that remains classified. (I'm not joking, I tried to dig up so of that old stuff, the e.g. Casaba Howitzer and all you get is a page of redactions.)

Even the exhaust of a less dramatic nuclear reactor drive could be made into a plasma weapon just by using a little more reactant mass or maybe tossing in some heavier elements as the exhaust stream exited the ship.

If you wanted to get super realistic, you'd also have to consider how the ships would get rid of all the heat their weapons would generate without having giant but fragile radiators sticking out all over. There was a realistic space combat board and dice game back the day in which ships fought till they over heated and then signaled surrender by retracting their radiators.

You really need to sit down and crunch some numbers about distances, ]velocities and energies to get a feel for just how bleeping-big space is, how intuition destroying fast everything moves and how much energy in is in even things like maneuvering thrusters. Even megaton nukes become firecrackers in space.

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