Rail gun damage?

[Tex Jones]

Re: Rail gun damage?

 

ref: Robert Heinlin "The Moon is a Harsh Mistress"

 

Rail guns are a kentic weapon as such it gets mass x speed squared type of damage. Earth is a hard place for space launches and rail guns gravity and atmosphere work against you. The moon on the other hand 1/6 gravity 0 atmosphere and direct sun light makes the idea of shooting a slug of iron into space much easier.

 

dammage for low earth orbital (LEO) slugs str = weight of slug + speed / 5

 

5 hex / sec = 1 G

 

LEO 18,000 MPH = 14616000 HEXS PER HOUR

 

DIVIDE BY 3600 Seconds in a hour roughly 4000 hexs / sec (4060)

 

20Gee rail gun = flight 100" x 32 NC = 3200 at speed 12 32 seconds to launch

 

 

200 x 32 at speed 6

 

3200 / 5 = 640 d6 of dammage

 

ship scale 1/100 6d6 of ship dammage

[Nyrath]

Re: Rail gun damage?

 

So, if we posit that for mass driver weapons, then the maximum effective range is about 2-3 seconds travel time. An effective system would take into account all the possible vector shifts a target could make in that time, and bracket them with multiple mass drivers...so let's say an effective system has 20-40 "barrels" bracketing a fire zone in order to maximize chances to hit.

 

I remember reading somewhere that the practical speed limit for a mass driver is probably around 150km/sec. Applying that to the scenario gives an effective range of 300-500 km perhaps. At those velocities the projectiles could be fairly small, say in the 20-30mm range.

Well, as it just so happens, I was playing around with creating an equation to express the effects of weapon flight lag.

http://www.projectrho.com/rocket/rocket3y.html#dodging

 

H = Cm / (0.7854 * a^2 * ((Dm / 299,792,458) + (Dm / Wv))^4)

 

H = maximum percent chance to hit target given light-speed lag (0.0 - 1.0 with 1.0 = 100%)

Cm = target ship's mean cross section (m2, for a purely convex object this is approximately 1/4 of the surface area)

a = target's acceleration (m/s, where 9.81 = 1 g)

Dm = range to target (m)

Wv = weapon velocity (m/s)

 

To use it in this case, you have to know the mean cross section of the target ship, and its acceleration (to figure how much it can dodge), as well as the range to the target and the velocity of the shot.

 

If the individual shot was a 30 mm sphere composed of depleted uranium traveling at 150 km/s, it would have about, ummmm, {works with slide rule} 2.5 x 10^10 joules. This is about the same as 6 tons of TNT, a bit more than an average lightning bolt, and about three times the Oklahoma City bombing. Yes, that will do.

 

30 mm sphere = about 114 cubic centimeters

depleted uranium = about 10.1 grams per cubic centimeter

mass of sphere = about 2.2 kilograms

 

Kinetic energy = 0.5 * mass * velocity^2

Kinetic energy = 0.5 * 2.2kg * 150000m/s^2

Kinetic energy = 24,750,000,000 joules = 2.5 x 10^10 joules

Look it up on the boom chart

[Nyrath]

Re: Rail gun damage?

 

3200 / 5 = 640 d6 of dammage

I haven't checked the math, but did you take into account the fact that damage dice in the Hero system is on a logarithmic scale, not a linear one? I don't know, I'm asking.

[tkdguy]

Re: Rail gun damage?

 

Yes, every expert I've talked to say coilguns are superior. It's just that they are orders of magnitude harder to make.

 

The arc you strike with a railgun causes severe rail erosion. In current models you have to replace the rails after a few shots. On the other hand, we have close to weapons grade railguns now.

 

Coilguns have no such erosion. However, since each coil has to reverse its polarity as the projectile passes by, you need power switches capable of handling huge power loads. They are still trying to invent a switch suitable for a weapons grade coilgun, currently available switches are not good enough.

 

Coilguns will still have waste heat because of the second law of thermodynamics, but probably not anywhere near the waste from a railgun.

Coilguns also currently aren't as accurate as railguns IIRC. But that may change.

[Tex Jones]

Re: Rail gun damage?

 

since it's based on hexes per segment it should be logarithmic in function by the nature of movement. i played a traveler but rail guns get real power in the moon to earth shot! It makes nothing short of a nuke!

 

Thowing rocks down hill some 200,000 miles (i know moon 250K) Lagrange Point down to earth. you get all the adds for falling long falls. Using 12 ton ore cars big bang little force.

 

A weapon that I've thought about is dropping 1 inch dia super balls from a 747 in massive amounts it might be figured out to be something like 10 2d6 Normal attacks stun total one attack body of each pair separate.

Guess max speed for super balls somewhere close to tucked in skydiving

200 mph compared with 120 mph of stable spread. AOE very large!

 

Or same idea with steel darts around 4 to 5 oz a piece pointed aerodynamic for best max speed. Guess about 400 mph.

but the 500,000 pounds of therm is a staggering thought.

 

next ping pong balls filled with napalm type mixture that ignites as it melts the ping pong balls.

 

A CBU on steroids if you get two or three bounces before blowing you should have a good chance of putting a small fire bomb through every open window and door. Windows by Dow Chemical.

 

notes fron SAS during WW II most successful fire bomb of WW II was a book of Matches and a Cigarette. Lite the cigarette place it along the match heads fold cover over the cigarette to hold in place toss into pi;rd of rags and trash like;y to burn quickly and spread to other targets.

 

 

Tex Jones

designed after Kelly Johnson inventor of the Skunk Works, Tex Johnson a Boeing Test Pilor and Indiana Jones with fear of snakes total carries the o;d 45 Cal M1911A to kill snakes must make ego roll at 1/2 to avoid panic firing all the rounds in t he clip, second roll at ego -2 to avoid throwing gun at the snake. Gets a plus of 1 every 2 points per roll discovering snaked is dead.

Love low tech weapon in a high tech world. Run Coke through drip Coffee maker into air vents on back of computer. Bleach filled Super Soakers. pepper filled egg shells. paint ball guns filled with epoxy resin and catalyst must have two shots of auto fire to become a entangle

[Beast]

Re: Rail gun damage?

 

dodging out of the path may not be possible depending on how fast the projectile is compared to it's flight time

while you can fire various thrusters in random patterns to make it harder to predict where the target will be but there are ways to counter this

 

1)have multiple weapons to salvo fire at an area the target is predicted to be in(each weapon fires an a slightly different course in hopes at least 1 will hit)

2)self guiding weapons that can make mid course,course corrections

a)Torpedoes in water need power to overcome friction, in space that is not needed in space(these weapons may need segment to turns to hit their targets)

3)Shotgun munitions (at some point during the flight time the weapon deploys sub munitions so it covers a larger area

 

 

Those would have to be pretty huge thrusters. They have to basically put out the same amount of energy that the railgun round contains.

 

Newton's second law say that F = ma, i.e., momentum is mass times acceleration. If a railgun round of mass x is accelerated at rate a, it will contain xa momentum, which will shove the firing ship with that much force. The thruster will have to emit the same amount of force in the opposite direction to counteract this.

 

Which means you really don't want to in the thruster's exhaust plume.

 

 

 

This is a problem with all non-seeking weapons, be they cannons, railguns, laser batteries, or particle-beam weapons. And there is no real solution, short of time travel or telepathy.

 

Your target has a certain area that represents its possible future locations. The area is determined by the time-of-flight of your weapon from you to the target, the target's initial trajectory, and the target's engines (how much can it change its trajectory within the time-of-flight).

 

If this area is larger than the target silhouette, you probably will never hit the target.

 

Possible solutions include making your weapon home in on the target (despite the target's attempts to jam the homing mechanism), and area-effect warheads. Both of which work poorly with railguns.

[Beast]

Re: Rail gun damage?

 

Gerald Bull(a large gun expert who was building a gun that could hit Israel from Iraq

his gun had an erosion problem also due to the speed of the projectile

his solution was to use a spray on liner that was ment to ablate away to carry away waste heat and to eliminate wear on the barrel

this method could work on the rails of a railgun

 

 

Yes, every expert I've talked to say coilguns are superior. It's just that they are orders of magnitude harder to make.

 

The arc you strike with a railgun causes severe rail erosion. In current models you have to replace the rails after a few shots. On the other hand, we have close to weapons grade railguns now.

 

Coilguns have no such erosion. However, since each coil has to reverse its polarity as the projectile passes by, you need power switches capable of handling huge power loads. They are still trying to invent a switch suitable for a weapons grade coilgun, currently available switches are not good enough.

 

Coilguns will still have waste heat because of the second law of thermodynamics, but probably not anywhere near the waste from a railgun.

[megaplayboy]

Re: Rail gun damage?

 

I haven't checked the math' date=' but did you take into account the fact that damage dice in the Hero system is on a logarithmic scale, not a linear one? I don't know, I'm asking.[/quote']

 

If we want to get really goofy, we can use the velocity factor rules from FRED to calculate the DC of any projectile of a given mass at a given velocity, assuming the projectile is doing a "move-through" on the target (mass + (vf x 2)).

 

For small objects, you're actually subtracting DC before calculating the VF damage. I believe every doubling of velocity adds 2 to the VF(and therefore adds +4d6 to the damage).

 

I think VF = 1 is 3" per segment, IIRC.

 

VF 21 would be ...3000" per segment, I think.

 

So, a 1kg object (STR -25 or -5DC) traveling at 6000 m/sec strikes a target doing 37 DC of killing damage. You could probably convert that into AP damage to come out at about 8d6 +1 AP RKA, which doesn't sound all that unreasonable.

 

Escape velocity would be around VF 23.

 

20% of lightspeed (where there would be some modest relativistic effects) is 30 million hexes per segment. let's call it VF 48.

 

That same 1kg object traveling at 20 percent of lightspeed strikes a target doing 91 DC of killing damage. I guess we could call that 20d6 AP RKA, or perhaps 15d6 AP RKA X or somesuch.

 

The scale would top out around VF = 52 or so.

 

A Galaxy-class starship(3 million tons?) ramming a planet at 80% of lightspeed would do something like 131 DC of damage. Pretty sure that would be converted to a megascale explosion...

[Beast]

Re: Rail gun damage?

 

modern fighters gun weapons fire along the axis of the fighters thrust so there would be only a slight slowing of the fighter(I would be surprised if this was more than a mile per hr)

 

the big question is how fast is the railgun projectile compared to the flight speed of it's target

an M61 Vulcan cannon round moves at 3,450 ft/s (1,050 m/s) (with PGU-28/B round)2352.27 mph

Maximum speed of a SU 37: Mach 2.5(1,550 mph)

so you are looking at a x1.5 speed advantage(at max speed, more likely dogfight speeds will be under mach 1 700 mph)x3 speed advantage

 

Well, I suppose the analogy would be to jet fighters firing cannon at each other. The operative range of such weapons, relative to the speed of the jets is fairly small...if a jet is moving at 300m/sec (high subsonic speed) and the effective range of the shells is perhaps 1000 m, then transit speed is maybe 2-3 seconds.

 

So, if we posit that for mass driver weapons, then the maximum effective range is about 2-3 seconds travel time. An effective system would take into account all the possible vector shifts a target could make in that time, and bracket them with multiple mass drivers...so let's say an effective system has 20-40 "barrels" bracketing a fire zone in order to maximize chances to hit.

 

I remember reading somewhere that the practical speed limit for a mass driver is probably around 150km/sec. Applying that to the scenario gives an effective range of 300-500 km perhaps. At those velocities the projectiles could be fairly small, say in the 20-30mm range.

[Cancer]

Re: Rail gun damage?

 

the big question is how fast is the railgun projectile compared to the flight speed of it's target

an M61 Vulcan cannon round moves at 3,450 ft/s (1,050 m/s) (with PGU-28/B round)2352.27 mph

Maximum speed of a SU 37: Mach 2.5(1,550 mph)

so you are looking at a x1.5 speed advantage(at max speed, more likely dogfight speeds will be under mach 1 700 mph)x3 speed advantage

 

If it's a spaceship weapon (which I think is how the thread started), it's worth pointing out that the relative velocities of hostile spaceships are likely to be several km/s. That contribution to impact velocity is rather greater than the ~1 km/s that is contributed by the weapon itself.

[Markdoc]

Re: Rail gun damage?

 

modern fighters gun weapons fire along the axis of the fighters thrust so there would be only a slight slowing of the fighter(I would be surprised if this was more than a mile per hr)

 

It can be a lot more than that: the gatling gun on the A-10, which fires a 30 mm round has alot of oomph and the GAU-8/A product homepage states the recoil force as 10,000 pounds-force, or about 45 kN, which is more than half maximum combined output of the A-10 engines (82.6 kN). In other word, firing the gatling gun on an A-10 slows it significantly (the bit about stalling it seems to be an urban legend however). In early versions, since the weapon was not perfectly symmetrical, firing it drove the plane sideways.

 

cheers, Mark

[Nyrath]

Re: Rail gun damage?

 

since it's based on hexes per segment it should be logarithmic in function by the nature of movement.

Yes, I see. That will work.

[Beast]

Re: Rail gun damage?

 

that 10,000lb of force still has to over come the 42,000 lb take off wt of the A10(in the anti armor load out) along with the engine thrust and with being in a shallow dive

with only a 1 to 2 second burst

 

the A10 is also an extreme example and it is a air to ground not an air to air or space to space example

 

if not a coil gun(no arcing problem) for the wt what about conventional rounds that carry their own oxidizer so they can be fired in space

 

going with the rail guns they are in development now that need the rails replaced after 10 shots

 

what velocity are we talking about here?

(Ship speeds and weapon speeds)

what kind of engagement ranges are we looking at?

how well armored are the ships in question?

It can be a lot more than that: the gatling gun on the A-10' date=' which fires a 30 mm round has alot of oomph and the GAU-8/A product homepage states the recoil force as 10,000 pounds-force, or about 45 kN, which is more than half maximum combined output of the A-10 engines (82.6 kN). In other word, firing the gatling gun on an A-10 slows it significantly (the bit about stalling it seems to be an urban legend however). In early versions, since the weapon was not perfectly symmetrical, firing it drove the plane sideways.

 

cheers, Mark

[Markdoc]

Re: Rail gun damage?

 

that 10,000lb of force still has to over come the 42,000 lb take off wt of the A10(in the anti armor load out) along with the engine thrust and with being in a shallow dive

with only a 1 to 2 second burst

 

Right, but here we have an example of a weapon of a weapon with a kinetic energy output way below what's being discussed for rail guns and it has a substantial effect on the vehicle - even though the A-10's a pretty bulky aircraft. And you are right - the reason stalling is not a problem is because the plane already has a great deal of momentum: nonetheless, even at this level, firing the weapon has a noticeable slowing effect.

 

A 64 megajoule rail gun - the navy's goal - is going to generate 566,447,730 pound-force (if I've done the numbers correctly) or the equivalent of firing 56,000 gatling guns simultaneously. That's going to have an effect ....

 

cheers, Mark

[Tex Jones]

Re: Rail gun damage?

 

slug throwers even at the SR-71's speed become dusters. Put it up in front and let it run into it. The old phrase faster than a speeding bullet. Comes to mind. The sat crash the other week. Or the first car to car crash really bad luck and very small orbits. compared to interplanetary space.

[Beast]

Re: Rail gun damage?

 

which means the craft carrying that type of weapon will need to be much larger than the A10 in comparision to the GAU-8 gun(more like x10's the force pounds in wt

 

Tex

the reason you do not put a gun on the SR-71 is because

Once a round is fired it will start to decelerate after leaving the barrel

in space you do not have that problem

 

Right, but here we have an example of a weapon of a weapon with a kinetic energy output way below what's being discussed for rail guns and it has a substantial effect on the vehicle - even though the A-10's a pretty bulky aircraft. And you are right - the reason stalling is not a problem is because the plane already has a great deal of momentum: nonetheless, even at this level, firing the weapon has a noticeable slowing effect.

 

A 64 megajoule rail gun - the navy's goal - is going to generate 566,447,730 pound-force (if I've done the numbers correctly) or the equivalent of firing 56,000 gatling guns simultaneously. That's going to have an effect ....

 

cheers, Mark

[Nyrath]

Re: Rail gun damage?

 

If it's a spaceship weapon (which I think is how the thread started)' date=' it's worth pointing out that the relative velocities of hostile spaceships are likely to be several km/s. That contribution to impact velocity is rather greater than the ~1 km/s that is contributed by the weapon itself.[/quote']

Indeed it will.

 

And for those who didn't look closely, the important word is relative.

 

If the enemy cruiser Sky Trash is sitting "stationary", and you fire a railgun shell through it at 3 kilometers per second, it will do X amount of damage.

 

If the railgun shell is sitting "stationary", and the Sky Trash is flying at 3 kilometers per second and hit the shell, it will do an identical X amount of damage.

 

The key is that in both cases the relative velocity between the shell and the Sky Trash is 3 kilometers per second.

[Tex Jones]

Re: Rail gun damage?

 

Yes but I assume torch ships with acceleration to mid point flip and slow down. Which makes bullets in the samr bracket again they don't get the extra G's but on the other end they do speed up towards planets and other massive bodies. Star Trek's speeds are hard to think the few sat's I worked with the delta-Vee ability wasn't much. The life of a sat is limited mainly by how much fuel it can carry to correct it's "orbit" which it the geometry we use there is no such thing as a orbit. It's a straight following the folds of space. Most Gameing systems require artificial Gravity and gravity compensator. So you can ignore that problem or it's possible with the right charges the gun could be a part of the deflector system and firing it might even cause the ship to go faster behind a bigger bubble. But lets leave the two headed Lama's out of it. Push Me Pull You's but that's a longer story. the game system would all in all call it some form of a STR Min or Size Min.

[Nyrath]

Re: Rail gun damage?

 

Yes but I assume torch ships with acceleration to mid point flip and slow down. Which makes bullets in the samr bracket again they don't get the extra G's but on the other end they do speed up towards planets and other massive bodies.

Yes, this is true if you and the enemy are engaging around a stationary point. Say if force Alfa is trying to enter Mars orbit to drop bombs, while force Bravo is in orbit around Mars trying to defend it.

 

But if force Alfa is at the midpoint flip in between Earth and Mars, and is intercepted at that point by force Bravo also doing a midpoint flip, the relative velocities between the two will be very high indeed.

[tkdguy]

Re: Rail gun damage?

 

Another possibility is to make your railguns "recoilless" in the same way existing RCL weapons are recoilless. Include a reaction-mass projectile (doesn't have to be the same mass, probably better if it's more massive) simultaneously launched in the opposite direction. I.e., your railguns are "double barreled" with the second one pointing the opposite way of the first. It means you're cutting your launcher efficiency (KE of weapon projectile per unit of supplied power) by of order 50%, but it solves some other problems elegantly. (It's "of order" 50% because what you want is the reaction projectile to have equal but opposite momentum, not KE, as the warhead projectile.)

 

Just make sure no friendlies are standing behind when you fire....

 

If you are using real physics, another serious problem happens if your railgun is mounted in any way except fixed directly on the momentum axis. If you have the gun in a steerable turret, there's going to be a bunch of angular momentum deposited into the ship when you fire, that is, you're going to make your ship spin. Even a pair of coaxially-mounted guns will do this unless their firing is carefully synchronized; if they have the same rate of fire but are out of sync you'll wag the nose back and forth with a series of alternating jolts in yaw. How bad this effect is depends on the comparison of the mass of the ship and the momentum of the projectiles. I think the whole point of a simple kinetic-kill shot-type weapon is that the projectile's impact is substantial compared to the target, so assuming combatants of comparable mass, the firer's momentum is going to be altered if the railgun is at all effective.

 

Now, you could turn that into a feature rather than a bug, assuming an adequately high rate of fire; your fire control system could take into account the recoil-driven back-rotation of the firing platform and use that to deliver a preplanned pattern of projectiles, sweeping out an arc in the sphere centered on the ship's center of mass. I'd have to do some numerical experiments to see how that might work.

 

One of the reasons I thought of the thrusters was because of the recoil when the ship fired in a direction other than straight ahead or behind. I like your solution to this problem. Thanks.