cannons in space

[Red Fang]

Has anyone made a version which is not muzzle loaded?

[Dodgey]

Yea alright I can see what you mean now. There is a good website which is well worth a tad about all of this but I digress. The characteristics of the weapon systems can be broken down into smaller parts. Four example any weapon had to do two different things to be effective, hit the target and damage the target.

Firstly hitting the target. If we assume that the battle is taking place at a range of 20km and the muzzle velocity is that of the m1 Abrams tank (1.75 km/s) your target has approximately 11.4 seconds to react and move out of the way of your projectile. If we are at the point in the future where we are fighting in space then we can safely assume that this is enough time for your inboard computer to do that. You can increase your chances of a hit by multiple methods such as not letting your target see that you have fired (they won't see it until it's too late), fire so much that they can't avoid all of your shots, or an active targeting system like a missile.

If used explosives to launch your projectile you not only heat up your projectile, but also your cannon. Very obvious to anyone with a thermal camera. You could use pressurized had but again very obvious to thermal. Personally I think a mechanical launch system would be the best due to its lack of emissions. Though you would be hard pressed to achieve a high velocity. A missile has the advantage of being able to activity track and adjust its course but can be fooled by jammers and the like.

Which brings me to my second point, destroying the target. This really depends on what outcome you want. For example you might want to capture the ship but kill the crew so you would make your projectile long and thin to puncture and decompress the hull. If the armor is too thick a shaped charge could be used ect ect.

[Seret]

I also find highly questionable your stipulations that space combat would be between battleships at ranges of a few kilometers. There's a reason no one has built battleships in over 60 years; aircract and missiles can hit battleships long before battleship guns can hit back. That principle would hold true in space combat as well. Also, with modern guided weapons and innovations such as shaped charges, speed and maneuverability are better defenses than bulk and armor. If you do wish to limit the discussion to capital ship exchanges at fairly short range, then canons might indeed be the best choice, but that is a very arbitrary limitation and not likely to reflect future combat in space.

All of this.

Ravener, just because this forum is called "Sci Fi Theory" doesn't mean you have to confine yourself to the conventions of the softest of soft sci-fi. TV and movie scriptwriters aren't technical people, they often just transpose existing memes that the audience will understand (capital ships duelling with guns, fighters making sweeping turns, etc) into a space setting. That doesn't mean any of it makes any sense.

There's not much point in debating soft sci-fi tropes, because they don't really have any solid technical basis. You might as well have that debate about how Superman washes his costume, because of his indestructible Kryptonian pit stains.

[Nibb31]

once again, this is sci fi, so i was burdoned with selecting the setting the weapon is set in. also, the effective range of an L55 rheinmetall cannon is 4000m, hitting something at twice the range without the limitation of gravity seems reasonable. there are reasons to use bettleship sized ships, mostly the cargo capacity and more surface to mount countermeasures on.

Why would gravity be gone ? When you're in orbit, gravity is still there. As a KSP player, you should know that there is no such thing as a straight line in space. That's gravity working. Everything is in some kind of orbit and there is no range limit. If you fire a projectile in space it will continue on its own orbit until it hits something. That might happen anywhere between 10 seconds and never.

If you want it to hit a target, you need to insert your projectile into an orbit that intersects with your target. As such, it's much more practical to dispatch a smart weapon with its own propulsion, RCS and autonomous rendez-vous capability than to fire dumb slugs with a cannon.

Getting your capital ship up close and personal with a target is also a rendezvous. As a KSP player, you should know how hard it is to rendezvous with a target. In reality, it would take several burns to catch up with a target, to approach, and to cancel relative speed so that you could fire at a target. This is practically impossible if the target is actively evading the rendezvous.

The two opponents would basically chase themselves around a planet forever. The first ship that runs out of fuel loses.

once again, this is sci fi, so i was burdoned with selecting the setting the weapon is set in. also, the effective range of an L55 rheinmetall cannon is 4000m, hitting something at twice the range without the limitation of gravity seems reasonable. there are reasons to use bettleship sized ships, mostly the cargo capacity and more surface to mount countermeasures on.

If it is science fiction, then you can just use any technobabble to justify whatever magic you want your science fiction plot to support. No need for a debate.

Edited May 27, 2014 by Nibb31

[Dodgey]

Be that as it may Nibb31 it is still interesting to think about the the weapons used under those, unrealistic, circumstances.

[Red Iron Crown]

I just don't see the scenario where a cannon with dumb projectiles makes sense. If you're at 20km range where a cannon might have a chance of hitting, you're much better off just pointing your engines at the target and burning. An LV-N has an exhaust velocity of ~8km/s, meaning the exhaust gases can get to the target in less than 3 seconds, rather than the 11 seconds Dodgey calculated above. The engine can fire a continuous spray that can be adjusted to hit the target, rather than a single shot that's hit-or-miss. The gases spread out a bit, creating a cone of death that is more difficult to dodge. And the real kicker: you are already going to carry the engines for maneuvering, so there is no mass penalty like that associated with the cannon + ammunition.

Assuming the big capital ship has a propulsion system at least as efficient as the LV-N and a high enough thrust to move such a mass reasonably well, the engine itself is an extremely potent close range kinetic weapon, unlikely to be matched by a dedicated weapon system.

[Nuke]

Has anyone made a version which is not muzzle loaded?

the only example i could find was the german RMK30, a 30mm recoiless autocannon. more info here, but its in german.

Edited May 27, 2014 by Nuke

[Rakaydos]

I wonder if you could design a Sabot that doubles as a barrel extenion- that is, when the sabot reaches the end of the barrel it catches and creates a seal, and the shot continues to accelerate the length of the sabot. Sort of a "telescoping barrel" for a space cannon

[Seret]

I wonder if you could design a Sabot that doubles as a barrel extenion- that is, when the sabot reaches the end of the barrel it catches and creates a seal, and the shot continues to accelerate the length of the sabot. Sort of a "telescoping barrel" for a space cannon

Gas pressures in the barrel are pretty high, it'd be difficult to get a decent seal between the sabot and the muzzle. Also, the exact profile of the crown of the muzzle is critical for accuracy, so having a deformable object stuck there would result in spraying your projectiles all over the place. You want a nice predictable interaction between the projectile and the venting gases as the projectile transitions to free flight.

[meve12]

this is the setting/feel

http://www.giantfreakinrobot.com/wp-content/uploads/2012/08/Halo_unsc_infinitysm.jpg

we have the engines to move heavy armour, how are we going about penetrating that armour?

THAT armor?

Conventional cannon won't do it, not high enough muzzle velocity. Railgun/MAC, maybe. Missiles would either be KKVs or nukes. Or Casablanca-Howitzers.

[SpaceGremlin]

I just don't see the scenario where a cannon with dumb projectiles makes sense. If you're at 20km range where a cannon might have a chance of hitting, you're much better off just pointing your engines at the target and burning. An LV-N has an exhaust velocity of ~8km/s, meaning the exhaust gases can get to the target in less than 3 seconds, rather than the 11 seconds Dodgey calculated above. The engine can fire a continuous spray that can be adjusted to hit the target, rather than a single shot that's hit-or-miss. The gases spread out a bit, creating a cone of death that is more difficult to dodge. And the real kicker: you are already going to carry the engines for maneuvering, so there is no mass penalty like that associated with the cannon + ammunition.

Assuming the big capital ship has a propulsion system at least as efficient as the LV-N and a high enough thrust to move such a mass reasonably well, the engine itself is an extremely potent close range kinetic weapon, unlikely to be matched by a dedicated weapon system.

There is no way you're going to do damage with your propulsion system at that range unless the exhaust is as coherent as a laser. The gasses won't "spread out a bit", they're going to spread out a lot over 20km. Also, we already have heat shields that can protect against hot gasses impacting them at just about 8km/s.

Not to mention that eating a laser beam, cannon shell, or missile to your primary drive system that you were exposing to the enemy will probably disable your ship.

[KOCOUR]

Why cannons? why battleships?

Only reason to have battleship is to carry around amunition that you want to fire at enemy.

So the important bit is the projectile itself.

So what we have:

-Projectiles

-Fuel for the projectiles to reach a target.

-Projectile storage

-Launching tube or pylons or docking ports for the projectiles

-Projectile carrier (aka ship)

-Fuel for the projectile and projectile carrier to reach a initial firing possition.

-Projectile carrier navigation and controll

Thats lot of things to have just to deliver few projectiles to the enemy.

So why, instead of bunch of small projectiles, not to have just swarm of bigger projectiles?

Then we would have:

-Swarm of Projectiles

-Fuel for the projectiles to reach the target, in each projectile.

-Fuel for the projectiles to reach the initial firing/waiting possition, in each projectile. (lot less fuel for the swarm beacause we dont have to haul the ships mass along)

-Navigation and control system in each projectile.

So what we spared:

- Materials to build the ship (we spent little bit more materials for each projectile as they need to be bigger to carry the extra fuel, but still les than for entire ship with engines canons storage and stuff.)

- fuel to haul the ship along

+

-Its much harder to kill swarm of small missiles than to kill one big ship. Projectiles in dead ship are gift to the enemy, and we dont want to give the enemy presents, we want to kill the enemy.

-We now can make much more projectiles.

So we dont need any ships, so we dont need any cannons. So we can just sit back in safe remote Command ship or underground bunker, and send commands to our rocket swarms.

[Red Iron Crown]

There is no way you're going to do damage with your propulsion system at that range unless the exhaust is as coherent as a laser. The gasses won't "spread out a bit", they're going to spread out a lot over 20km. Also, we already have heat shields that can protect against hot gasses impacting them at just about 8km/s.

No, we don't. We have heatshields that can resist a 8-9km/s reentry into cold atmospheric gas, and only when oriented perfectly. Exhaust gases carry much more energy, because almost all reaction drives are designed to shed waste heat into their propellant. I'm not sure how wide the spread of the expended propellant would be. I know a rocket nozzle is sort of like a parabolic reflector for the exhaust so that it pushes against the ship in a useful direction, how much it spreads by interacting with itself outside the nozzle is something for which I don't have numbers.

Not to mention that eating a laser beam, cannon shell, or missile to your primary drive system that you were exposing to the enemy will probably disable your ship.

A rocket nozzle is likely the part of a ship most suited to resist laser fire, given that it must resist the tremendous heat of burns.

[SpaceGremlin]

No, we don't. We have heatshields that can resist a 8-9km/s reentry into cold atmospheric gas, and only when oriented perfectly. Exhaust gases carry much more energy, because almost all reaction drives are designed to shed waste heat into their propellant. I'm not sure how wide the spread of the expended propellant would be. I know a rocket nozzle is sort of like a parabolic reflector for the exhaust so that it pushes against the ship in a useful direction, how much it spreads by interacting with itself outside the nozzle is something for which I don't have numbers.

We have heat shields that can resist a more extreme reentry than that even (1). They endure incredible temperatures due to adiabatic heating, so I don't think the LV-N's waste heat is going to be a problem beyond point blank range.

A rocket nozzle is likely the part of a ship most suited to resist laser fire, given that it must resist the tremendous heat of burns.

A laser can impart far more energy per unit of area than the LV-N's exhaust can at the nozzle (or at any range). It wouldn't even take much, just weaken it enough and the LV-N's own exhaust heat and pressure will take care of the rest.

Engines make terrible weapons.

[Seret]

Engines make terrible weapons.

Any engine big enough to maneuver one of the OPs unfeasibly large ships at useful velocities would have insane quantities and velocities of exhaust. Tapping off even a tiny part of it to propel your projectiles would make for a LOT of smash.

Why bother with projectiles though? They're just a waste of mass. I'm with KOCOUR, just go for a swarm of engines. Warheads would probably be optional.

[jwenting]

Instead of launching the shell with a charge lit off inside the gun, why not have a rocket assisted projectile that's ejected from the gun hydraulically or using gas canisters and then light off that rocket?

Of course you'd then effectively have a rocket launcher instead of a gun, but gun launched rockets have been used and may still be in use even today, mostly in the anti-tank role but also to boost the range of traditional artillery.

[Nuke]

i actually rather like the rail-rocket approach, the missile is a fully guided warhead with enough delta-v to make minor course corrections en route to target. it is however launched from a big honking rail gun (or perhaps gauss, not sure which is better on power usage and dealing with waste heat) so that it may reduce the close in time (and thus the reduce deltav needed to stay on target), and increase the ke of the projectile. just because the idea is ripped from star trek, doesn't mean its not a good idea.