Rail gun damage?

[Tex Jones]

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]

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]

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]

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]

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]

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]

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]

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.

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]

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]

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]

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]

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]

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, 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]

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]

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.