Proposal for weapon balancing, for the combat system

[jsheikh]

So I was reading about the GAU-8, the 30mm gun on the A-10 (Warthog) and how the recoil from it is so strong that it counters the thrust of the engines! That got me thinking about momentum and how no space sim with railguns never takes it into account.

So it got me thinking: How about for railguns, we make it so the projectile momentum is the balancing factor i.e. You cannot have a massive or a fast-projectile gun without a massive ship to absorb the recoil!

Fast projectile - better effective range, more accuracy (smaller time-to-target)
Big projectile - more damage/explosive warhead; more momentum transferred

A really large ship would also be better at handling impact from larger projectiles - less recoil so it wouldn't bounce around so much.

It would give a real reason for building massive battleships.

The downside, ofcourse, would be a much bigger target size and poorer manouverability compared to smaller ships

Lasers/Energy weapons would have the advantage of not being mass dependent, so you can stick a really powerful one on a small craft (power permitting - but antimatter is pretty efficient). Ofcourse, their issue would be damage dropoff with range.

So you could have battleships as the only extremely long range heavy hitters and lasers as the go-to choice for pinpoint targeting and/or short range vaporizing.

Plus it lends itself to logistical issues too: lasers being less supply heavy than rails.

 

[EntropyAvatar]

Depending on the technology of the setting, it's plausible that the damage potential of a railgun depends a lot on the length of the barrel. So it makes sense that a very powerful railgun could only be mounted on a large ship. In general, the larger weapons of all types (even lasers) are going to be more powerful, so big guns tend to be the province of big ships.

However, I don't like momentum as a balancing factor. Sword of the Stars featured heavy momentum transfer from large ballistic weapons and it always looked cartoonish to me. The main problem is that for a mass driver to be effective at significant range, the projectile will have to be moving very quickly. The damage potential of a fast-moving projectile mostly comes from it's kinetic energy, which is proportional to the square of it's velocity while the momentum is only linear.

A gun like the GAU-8 is only designed to hit targets within a kilometer or so, and fires projectiles at about 1 km/s. A self-respecting space battleship will want much further range and would probably fire projectiles that are at least 10 km/s. That's 100x the kinetic energy per unit mass, but only 10x the momentum. So for each unit of damage, the rail gun is going to have less than 1/10th the momentum of a GAU-8. More advanced weapons would probably be even faster and further reduce the significance of momentum. Since the damage scales up so much faster than the momentum, I just don't see recoil being a huge factor.

 

[Fire of change]

A gun like the GAU-8 is only designed to hit targets within a kilometer or so, and fires projectiles at about 1 km/s. A self-respecting space battleship will want much further range and would probably fire projectiles that are at least 10 km/s. That's 100x the kinetic energy per unit mass, but only 10x the momentum. So for each unit of damage, the rail gun is going to have less than 1/10th the momentum of a GAU-8. More advanced weapons would probably be even faster and further reduce the significance of momentum. Since the damage scales up so much faster than the momentum, I just don't see recoil being a huge factor.

Third Newton Law: For every action there is an equal and opposite reaction.
With other word if you invest a 100 times the energy to accelerate something you have a 100 times the recoil. With other words it is not the momentum which the projectile reaches, it is the force with which the projectile is accelerated which determines the recoil.

 

[Kuschelflummi]

Recoil can be damped. Trough mechanical means. Just need a to let the gun swing and the recoil is damped. When shooting with a gun, you dampen the recoil with your body by getting a light shove.

 

[EntropyAvatar]

Third Newton Law: For every action there is an equal and opposite reaction.
With other word if you invest a 100 times the energy to accelerate something you have a 100 times the recoil. With other words it is not the momentum which the projectile reaches, it is the force with which the projectile is accelerated which determines the recoil.

I'm sorry to say that you are incorrect. You arrive at momentum by integrating the force over time. The gun is applying force to the projectile and (by the 3rd law), the projectile is applying an opposing force to the gun. So the final change in momentum of the projectile is equal and opposite the final change in momentum (recoil) of the gun (or attached gun platform).

You arrive at change in kinetic energy by integrating force over distance. In a gun, if I want a projectile to reach say double the speed, but using the same force, I have to apply the force over four times the distance. Let's consider a case with made-up numbers. Let's say a railgun wants to linearly accelerate a projectile to 1km/s in 0.1 seconds. The average speed of the projectile over that 0.1 seconds will be 500 m/s, so the barrel of the gun will be 50 meters long. Now we want to use the same acceleration to make the projectile go 2 km/s. During the first 0.1 seconds, the projectile travels 50m, but during the second 0.1 seconds, it has an average speed of 1.5km/s, so it travels 150 meters, for a total barrel length of 200 meters. If you compare the two cases, the gun was applying the force for twice as long (twice the momentum, twice the recoil), but it was applying the force for four times the distance (twice the speed, four times the energy).

I hope this clear it up.

 

[EntropyAvatar]

Recoil can be damped. Trough mechanical means. Just need a to let the gun swing and the recoil is damped. When shooting with a gun, you dampen the recoil with your body by getting a light shove.

Whether it is damped or not, you still ultimately need an opposing force to cancel the recoil. For ground-based artillery or someone shooting a gun, this is done through contact with the ground. A spaceship would normally have to cancel with some kind of thruster.

 

[Fire of change]

I'm sorry to say that you are incorrect. You arrive at momentum by integrating the force over time. The gun is applying force to the projectile and (by the 3rd law), the projectile is applying an opposing force to the gun. So the final change in momentum of the projectile is equal and opposite the final change in momentum (recoil) of the gun (or attached gun platform).

You arrive at change in kinetic energy by integrating force over distance. In a gun, if I want a projectile to reach say double the speed, but using the same force, I have to apply the force over four times the distance. Let's consider a case with made-up numbers. Let's say a railgun wants to linearly accelerate a projectile to 1km/s in 0.1 seconds. The average speed of the projectile over that 0.1 seconds will be 500 m/s, so the barrel of the gun will be 50 meters long. Now we want to use the same acceleration to make the projectile go 2 km/s. During the first 0.1 seconds, the projectile travels 50m, but during the second 0.1 seconds, it has an average speed of 1.5km/s, so it travels 150 meters, for a total barrel length of 200 meters. If you compare the two cases, the gun was applying the force for twice as long (twice the momentum, twice the recoil), but it was applying the force for four times the distance (twice the speed, four times the energy).

I hope this clear it up.

Arg I have mistaken momentum as another word for speed :/ .

But either way since you didn't wrote that the barrel on the battleship is longer, so your first post can still be interpreted false ^^:
Lets say this is the first gun:
v=1000m/s
m=1kg
a=1000m/s^2
t=1s
s=500m
F=1000N

If we say the length of the barrel stays the same, but the increase the speed by the factor 10:
v=10000m/s
m=1kg
s=500m

t=s*2/v=500m*2/10000m/s=0.1s
a=2*s/(t*t)=100000m/s^2
F=100000N

In this case which I thought you mean increases the speed by 10 and the needed energy by 100 and the applied force (->recoil) by 100.

You're argument was:

Since the damage scales up so much faster than the momentum, I just don't see recoil being a huge factor.

As you can see this argument applies only if the guns aka ships get bigger.

 

[jsheikh]

Depending on the technology of the setting, it's plausible that the damage potential of a railgun depends a lot on the length of the barrel. So it makes sense that a very powerful railgun could only be mounted on a large ship. In general, the larger weapons of all types (even lasers) are going to be more powerful, so big guns tend to be the province of big ships.

However, I don't like momentum as a balancing factor. Sword of the Stars featured heavy momentum transfer from large ballistic weapons and it always looked cartoonish to me. The main problem is that for a mass driver to be effective at significant range, the projectile will have to be moving very quickly. The damage potential of a fast-moving projectile mostly comes from it's kinetic energy, which is proportional to the square of it's velocity while the momentum is only linear.

A gun like the GAU-8 is only designed to hit targets within a kilometer or so, and fires projectiles at about 1 km/s. A self-respecting space battleship will want much further range and would probably fire projectiles that are at least 10 km/s. That's 100x the kinetic energy per unit mass, but only 10x the momentum. So for each unit of damage, the rail gun is going to have less than 1/10th the momentum of a GAU-8. More advanced weapons would probably be even faster and further reduce the significance of momentum. Since the damage scales up so much faster than the momentum, I just don't see recoil being a huge factor.

I was thinking more of the momentum of the recoil affecting the firing ship itself. Cause in space there's no friction and all. I too did not like SOTS' implementation of momentum transfer (equal sized ships making each other spin about),but I meant that a really large ship should significantly knockback a really small ship. I agree with your points on the Kinetic energy though, nice to see someone who knows his physics

 

[jsheikh]

Essentially I was thinking of how battleships IRL use the water to absorb the momentum they gain on firing (in addition to gun barrel recoil-reload system), and how this wouldn't be applicable in space

 

[EntropyAvatar]

In this case which I thought you mean increases the speed by 10 and the needed energy by 100 and the applied force (->recoil) by 100.

It's true that the applied force has 100x the magnitude in your example. However, that force is only applied for 0.1s instead of 1s. So the overall moment (the integral of force over time) is only 10x as great in the second part, while the energy (integral of force over distance) is 100x. Which is exactly what I said

 

[jsheikh]

Whether it is damped or not, you still ultimately need an opposing force to cancel the recoil. For ground-based artillery or someone shooting a gun, this is done through contact with the ground. A spaceship would normally have to cancel with some kind of thruster.

Exactly what I was thinking of. And the tactical ramifications thereof.

 

[EntropyAvatar]

Essentially I was thinking of how battleships IRL use the water to absorb the momentum they gain on firing (in addition to gun barrel recoil-reload system), and how this wouldn't be applicable in space

Definitely there will be recoil from any mass-driver system, and any space-battleship will need maneuvering thrusters or something to cancel that recoil. I'll grant the amount of recoil is fairly setting-dependent. If the setting calls for pretty cumbersome space battleships duking it out with chemical-propelled guns at less than a hundred kilometers, then I guess barrel velocities not much higher than WW2 battleships (something in that 1km/s range) would be viable, and recoil could be a significant factor.

However, I usually picture mass drivers in SF being some kind of high-tech weapon firing at 10 km/s, or even 100 km/s. In that setting, the shells they are firing is going to be much, much smaller, so recoil is relatively tiny.

 

[beckermt]

Third Newton Law: For every action there is an equal and opposite reaction.
With other word if you invest a 100 times the energy to accelerate something you have a 100 times the recoil. With other words it is not the momentum which the projectile reaches, it is the force with which the projectile is accelerated which determines the recoil.

W=F*d

Actually integrated, but HEY! Who cares. So, the distance over which you're applying this force is relevant! Longer rail guns can impart more energy, because they're longer! W is work, which has joules as its units (energy).

But really, you just need the total energy of a kinetic weapon and you're good.

"Energy" weapons would do damage by imparting energy into the impacting particles themselves, which would then be transferred to the target. Way more efficient than kinetics when it comes to recoil!

And lastly there's self-propelling munitions. What's stopping you from strapping a big rocket to that ex-railgun projectile? Heck, you could make it explode when it got there! We can call it a rocket.

 

[Fire of change]

However, I usually picture mass drivers in SF being some kind of high-tech weapon firing at 10 km/s, or even 100 km/s. In that setting, the shells they are firing is going to be much, much smaller, so recoil is relatively tiny.

Yes and no:
The problem is that in space is more space ^^. Means it is nearly always is your weaponary which sets the maximum battle distance.
Big battle distances and the fact that the target is more agile than a ship and argubly more than a aircraft (it don't need to turn to accelerate in another direction if the ship has sidethrusters), you can't target the ship, but you have to target the area where the ship is. If you're projectiles are fast and the enemey ship can't accelerate fast (can only accelerate in one direction etc.) the target area is small.

Long speech short sense:
To hit the enemy you have either to fire massive ammounts of small projectiles to increase the chance of hitting (and as we know the recoil of 20 shoots in a second are harder to handle than the recoil of 1 shoot per second)
Or you fire selfguided projectiles which needs to be bigger.

 

[EntropyAvatar]

To hit the enemy you have either to fire massive ammounts of small projectiles to increase the chance of hitting (and as we know the recoil of 20 shoots in a second are harder to handle than the recoil of 1 shoot per second)

Sure, 20 shots means 20x the recoil but it also 20x the energy expenditure. I think the systems need to provide the power (and waste heat) for 20 such high-speed shots would be more of a limiting factor in the design of a ship than dealing with the recoil. I think that in a situation where a kinetic weapon has to waste 95% of it's damage potential in order to have a decent chance of a hit, the kinetic is probably not competitive with a beam weapon. Though I guess it depends a lot on the details. A lot of surface gun fights had hit percentages in the single-digits.

Of course, it's a different situation if you aren't relying on the gun to provide most of the kinetic energy. Perhaps you are making a close-in, high-speed pass against an enemy fleet and just throw some BB's into their path, because hey, why not?

 

[Fire of change]

Sure, 20 shots means 20x the recoil but it also 20x the energy expenditure. I think the systems need to provide the power (and waste heat) for 20 such high-speed shots would be more of a limiting factor in the design of a ship than dealing with the recoil.

I agree with you that energy and waste heat are bigger problems than recoil, but you have to admit that recoil is a big factor too.

I think that in a situation where a kinetic weapon has to waste 95% of it's damage potential in order to have a decent chance of a hit, the kinetic is probably not competitive with a beam weapon.

Beams have their own problems:
1. "Energy lose" over distance
2. Can't be guided
3. Can be reflected
4. They have the same problem like kinetic weapons, only smaller (except recoil)

The best weapon system in space combat, is as far as I can see. A selfguided medium sized projectil from a railgun... Or a really big nuklear shrappnell torpedo

 

[Kuschelflummi]

Eh Guys.. in Space there is no gravitiy.. so if we accelerate the projektil trought some sort of magnets and it never even touches the barrel, - no Recoil

 

[Atlantians]

Eh Guys.. in Space there is no gravitiy.. so if we accelerate the projektil trought some sort of magnets and it never even touches the barrel, - no Recoil

With every action there is an equal and opposite reaction.

The force produced by the electromagnetic rails propels the projectile with vector +A, therefore an equal force pushes the rails with a force with vector -A.

So, the recoil in a rail or coil gun would be almost identical to a projectile using a combustion reaction, or any other propellant, because the force directed into the projectile would be directed into the mechanism as well.

Also, gravity has nothing at all to do with recoil.
And there is gravity in space. There is gravity anywhere there is matter.

 

[Kuschelflummi]

Never got recoil from using magnets Oo
Sure.. there is a reaction, but its normally on the other site of the magnet.

 

[Chilitoke]

Uneversity of texas paper on recoil in rail guns

turns out the recoil happens in the power supply, as the recoil is mostly magnetic aswell.
so you face a danger of burnout mostly.