Rail gun damage?

[Markdoc]

I submit this is the premise of most weapons -- putting large, irreparable holes in important things so the other people stop moving. Tanks, humans, Voltroids, don't matter. Put enough holes in it, and it seems to cease functioning at optimal levels. Very often with leaking some sort of fluid all over the place, or blowing up, depending.

Oh, I'd agree. It's just that this simple concept seems to have gotten lost somewhere along the way.

cheers, Mark

[megaplayboy]

I remember reading somewhere that the upper theoretical limit to railgun projectile speed was on the order of 150 km/sec(about 14 times escape velocity, or 1/2000 the speed of light), which one presumes would still make them pretty darn useful at ship velocities <100km/sec, and distances <10,000 km. I assume this would require 1)incredibly long rails(think star destroyer or Executor type length, in some kind of spinal mount); 2)massive energy generation(velocity squared, times mass, times one half, plus a little extra to offset inefficiencies) ; and 3) some kind of real material solution to the overheating problem(which would be even more dramatic at that level of velocity/energy)

Most likely such a weapon would be most useful as a planetary bombardment weapon--since the kinetic energy might be in the megatonnage range for a large enough projectile, but the energy requirements would be such that it might be impractical for ship to ship combat.

[Thia Halmades]

I remember reading somewhere that the upper theoretical limit to railgun projectile speed was on the order of 150 km/sec(about 14 times escape velocity, or 1/2000 the speed of light), which one presumes would still make them pretty darn useful at ship velocities <100km/sec, and distances <10,000 km. I assume this would require 1)incredibly long rails(think star destroyer or Executor type length, in some kind of spinal mount); 2)massive energy generation(velocity squared, times mass, times one half, plus a little extra to offset inefficiencies) ; and 3) some kind of real material solution to the overheating problem(which would be even more dramatic at that level of velocity/energy)

Most likely such a weapon would be most useful as a planetary bombardment weapon--since the kinetic energy might be in the megatonnage range for a large enough projectile, but the energy requirements would be such that it might be impractical for ship to ship combat.

Renegade Legion used Spinal Mounts, as does HERO: Combat Evolved. Both the In Amber Clad and Pillar of Autumn (a light Frigate and a medium cruiser, respectively) use a 16d6 Spinal Mount with limited ammunition and likely a ridiculous range. One wonders, if fired in space where there's no gravity, how long it would take the thing to slow down to the point where it won't annihilate something else in its path?

[Zeropoint]

Renegade Legion used Spinal Mounts, as does HERO: Combat Evolved. Both the In Amber Clad and Pillar of Autumn (a light Frigate and a medium cruiser, respectively) use a 16d6 Spinal Mount with limited ammunition and likely a ridiculous range. One wonders, if fired in space where there's no gravity, how long it would take the thing to slow down to the point where it won't annihilate something else in its path?

My initial estimate is "never". However, the interstellar medium is not quite--very, very nearly, but not quite--a total vacuum, so the projectile will encounter the occasional hydrogen atom or tiny dust particle. I'm not an astrophysicist, so I'm just pulling numbers out of the air here, but I'd be surprised if such a projectile slowed appreciably within thousands of years of being launched.

This raises the interesting possibility of having your ship blown up by a shot fired hundreds of years ago in a different star system.

[Thia Halmades]

My initial estimate is "never". However, the interstellar medium is not quite--very, very nearly, but not quite--a total vacuum, so the projectile will encounter the occasional hydrogen atom or tiny dust particle. I'm not an astrophysicist, so I'm just pulling numbers out of the air here, but I'd be surprised if such a projectile slowed appreciably within thousands of years of being launched.

This raises the interesting possibility of having your ship blown up by a shot fired hundreds of years ago in a different star system.

Well, space is curved, so the odds of that happening are lessened (because trajectories change, and there's always the odd asteroid or such) but yeah, that's why I was wondering. It'd make a great opening to a campaign.

We've been hit!
By what?!
Some kind of heavy shell!
... Does anyone use those anymore?!
Not for about a hundred and fitty years!

[ghost-angel]

I'm sure there are people better placed to answer that question than me on these boards (in fact, I know there are) but basically my answer is similar - no material we have to hand (and by that I mean "able to produce, even in minute quantities" fully meets the engineering specs.

But that's why it's sci-fi, right? Internally buttressed carbon nanotubes? Unobtanium cables? If you assume the material can be made, then you are basically food to go - as long as you build the concept that we now have relatively cheap, really, really strong fibres: it'd have implications for building body armour for a start

I thought they were able to build Bucky Tubes. . .

I know the structure concept is sound and in place though. It's more a matter of cost, politics and people being people than actual technology.

[Beast]

Tanks have almost no place in them that does not have something vital when going thru 1 side then out the other
now something like a 2000 ton WW2 destroyer having 8"+ sized AP rounds passing thru a DD and doing next to nothing for damage is more what I'm talking about and did happen because they had next to no armor on them
but when hit with an HE round major damge was caused
look at the space shuttle most of the vital compnets are either at the bow or stern of this space craft
there is lots of space in the middle that a shot went thru the shuttle it would not harm it except when it tried to land without repairs

while an A-10 straffing a DD might damage some systems on the ship and kill/wound some people
it would not destroy it unless it got a round into the magazine and detonated the ammo in there

Oddly enough, at the velocities being discussed for railgun / coilgun projectiles, the novel effects of impact make a dumb, solid slug more than sufficient to cause a lot of damage. Metal behaves like liquid at those energy levels, and "splashes" at the impact point, flowing out of the way of the projectile.

Even now, the GAU-8 cannon on the A-10 will often put the API rounds clean through some tanks, in one side and out the other. And yet somehow, that still manages to do a lot of damage to the tank. Huh.

[gewing]

Or rocket-propelled chainsaws

You're right, though. Overheating is the major problem right now with railgun design. You're pumping a huge current through something that isn't perfectly conductive - you're going to get induction heating (hence the earlier interest in superconductors). The current problem with the railguns being developed is that they are good for one or two shots: the rapid heating and reaction force of tossing a projectile heats and warps them so much that they need the "rails" replacing after every shot



There's also the limitations that most of the mass of the shell today for high velocity weapons is propellant, which introduces supply issues and the fact that there is an ultimate limit (speed of expansion of the gas) which sets an upper limit to energy transfer. In theory, the upper limit of railguns is much higher than that



Agreed. Against soft targets, there's no guarantee that railguns would actually do much - if any - more damage than conventional projectiles - if it makes a hole through you, it makes a hole through you. It's primarily the size of the hole that matters, not the speed at which it's made. Against hardened targets, more velocity means higher kinetic energy, so as long as you have a projectile that can efficiently transfer that energy, you should get better penetration. But there's no real reason it'd do more damage.

The real advantage of a railgun in space is the same as in real life - it gets your damage to the target faster, so they have less time to evade, and if you have the power to run it, you can carry more ammo for the same amount of weight.

cheers, Mark

well, there is afaik no absolute reason a rail gun cannot fire an explosive projectile, or flechette warheads, or what have you. Design might be a little more complex than for a traditional cannon, but the acceleration forces could actually be less, just more steady and over a longer period, and the sabot would be the part that bore the brunt of current etc.

I still like coil guns better. /pout/

IIRC a Navy study indicated that coil guns are better for heavier lower velocity projectiles. I wonder where the transition points would be?

It seems to me that while a 15k fps 10kg projectile is awesome, for some roles an 8k fps projectile weighing 50 kg would be even better!

[gewing]

I'm sure there are people better placed to answer that question than me on these boards (in fact, I know there are) but basically my answer is similar - no material we have to hand (and by that I mean "able to produce, even in minute quantities" fully meets the engineering specs.

But that's why it's sci-fi, right? Internally buttressed carbon nanotubes? Unobtanium cables? If you assume the material can be made, then you are basically food to go - as long as you build the concept that we now have relatively cheap, really, really strong fibres: it'd have implications for building body armour for a start

As to cost, I have no freakin' idea, but we can assume that if one gets built at all, the cost would have to be more than competitive with building rockets (or similarly climbing up out of the gravity well on some kind of fuel-powered ride) - so not outrageous. Once in place, most analyses have shown it'd be a very cost effective way of getting loads off planet.

As far as feasibility goes plenty of smart people have said "yes - if you can make a material strong enough" so I'm happy with that.

As for the other questions, you don't need to aim for the Lagrange point - all that's needed is a geostationary orbit - which is easiest at the equator. You either need a really long cable sticking out past the stable orbit as a counterweight or a large object (orbital platform?) to keep the cable upright and taut. Build both and you get an ideal launch point for interplanetary travel as anything launched off the cable gets effectively "free momentum" just from its distance from earth.

As to what it's anchored to groundside, you have two options. Like I said you need a geostationary orbit, so on the equator is easiest. Where? Well, one attractive option (cost wise) is not to send your elevator cars down the cable, but simply drop them. You don't want then landing in people's backyards, so why not drop them in the sea? Build your cable either seabed-anchored or on a massive floating platform and you not only avoid entanglement with the politics of equatorial nations - none of whom seem rich enough to build this themselves - but you get a simple landing place for your dropped elevators. You also get a major seaport/airport - which is easily protected by a strong navy - and by mass-drivers on the platform itself, providing increased security and also a small amount of protection from collateral damage, should (god forbid) something happen to the elevator itself. The offshore, equatorial location means that hurricanes and major storms are not a major concern (not impossible, just unlikely)

Sounds outrageous, but tiny little Dubai is building masses of artificial islands right now, which have an area of a couple of hundred square km - so it's not impossible.

Last of all, you could go the skyhook route where the end station is actually hanging in the air off the orbital - this sounds bizarre, but is apparently possible and has the advantage that it lessens the amount of cable you need (which is a big deal) - but it raises issues of power supplies and getting things onto your platform - most "plans" favour an earth anchor for that reason.

Since some enthusiasts say "we could start building by 2015!" (Yes, they say it and no, ain't gonna happen) the idea of a beanstalk in a near-future game is perfectly plausible - assuming improved materials.

cheers, Mark

I like using a modified oil drilling platform as the base, iirc some have very limited mobility. a cluster of similar platforms should be able to support the power generation, crew facilities, command and control, and defenses.

Or pull old carriers out of mothballs and use them.

[gewing]

Renegade Legion used Spinal Mounts, as does HERO: Combat Evolved. Both the In Amber Clad and Pillar of Autumn (a light Frigate and a medium cruiser, respectively) use a 16d6 Spinal Mount with limited ammunition and likely a ridiculous range. One wonders, if fired in space where there's no gravity, how long it would take the thing to slow down to the point where it won't annihilate something else in its path?

How good is your mapping of the space in front of it? I would guess that intersteller hydrogen would eventually stop it, but Cancer could give a much more accurate guess.

I would guess that unless they were being used as terror weapons, some kind of self destruct would be built in. Kind of like a lot of anti-aircraft rounds. It would really suck to get into a massive ship to ship battle, and win, only to have our resupply and reinforcements wiped out by stray rounds.

Imagine firing rounds a year before you actually intend to start the war. They would drift along, cooling to very close to the temperature of the cosmic background (is my 25 year old memory close?) and finally, 1 minute before they impact, you deliver your declaration of war.


Kinetic energy weapons that use no chemical or nuclear warheads might be rather tough to stop. 20 foot long osmium poles, for instance.

or old fashioned 10 lb cannonballs.




Some guidance could also be built in. Not manuevering like a sidewinder, but the ability to refine the trajectory. fire the manuevering thrusters at the beginning, you could shift trajectory a lot, but maybe not manuever at the end. Fire it at the end to refine your aim, and you might be able to kill the bridge instead of hit the right laser emitter.

or some such.

[gewing]

Tanks have almost no place in them that does not have something vital when going thru 1 side then out the other
now something like a 2000 ton WW2 destroyer having 8"+ sized AP rounds passing thru a DD and doing next to nothing for damage is more what I'm talking about and did happen because they had next to no armor on them
but when hit with an HE round major damge was caused
look at the space shuttle most of the vital compnets are either at the bow or stern of this space craft
there is lots of space in the middle that a shot went thru the shuttle it would not harm it except when it tried to land without repairs

while an A-10 straffing a DD might damage some systems on the ship and kill/wound some people
it would not destroy it unless it got a round into the magazine and detonated the ammo in there

IIRC FIRE is the big killer on ships, and depleted uranium is pyrophoric. COmbined with the dispersion of hits all over the ship... OUCH.

at the very least, everything near the exterior would be a mess.

[AmadanNaBriona]

How good is your mapping of the space in front of it? I would guess that intersteller hydrogen would eventually stop it, but Cancer could give a much more accurate guess.

I would guess that unless they were being used as terror weapons, some kind of self destruct would be built in. Kind of like a lot of anti-aircraft rounds. It would really suck to get into a massive ship to ship battle, and win, only to have our resupply and reinforcements wiped out by stray rounds.

Imagine firing rounds a year before you actually intend to start the war. They would drift along, cooling to very close to the temperature of the cosmic background (is my 25 year old memory close?) and finally, 1 minute before they impact, you deliver your declaration of war.


Kinetic energy weapons that use no chemical or nuclear warheads might be rather tough to stop. 20 foot long osmium poles, for instance.

or old fashioned 10 lb cannonballs.




Some guidance could also be built in. Not manuevering like a sidewinder, but the ability to refine the trajectory. fire the manuevering thrusters at the beginning, you could shift trajectory a lot, but maybe not manuever at the end. Fire it at the end to refine your aim, and you might be able to kill the bridge instead of hit the right laser emitter.

or some such.

neat post m'man.

All this keeps reminding me of a cute paraphrase of Robinson's 1st Law
"Anything moving 2 miles per second or faster is worth it's weight in blam"

[Nightlord256]

my ship's main gun is a 20d6 KA, 2xAP

of course this is modeled after a MAC gun, takes 2.5 minutes to charge, and is a game where the GM is notorious for not playing fair to the power level.

I don't know how much help this is

-Night

P.S. the slug travels at .35 C

[Basil]

One wonders, if fired in space where there's no gravity, how long it would take the thing to slow down to the point where it won't annihilate something else in its path?

Well, using megaplayboy's 1/2000th of c, and an average density of 7 x 10^-24 g/cc (which actually includes suns, planets, etc.---sorry, I didn't write down the source for that number), you will have a momentum of 1.573 x 10^-14 kg-m/s for every square centimeter of cross-sectional area of the projectile, every second. You'll have to determine the mass and cross-section of the projectile; the first to determine the projectile's forward momentum, the second to find the "pushing back" momentum.

Of course, the figure of "pushing back" momentum will drop with velocity, as you'll be going through less space, and running into less mass each second.

To pull an example out of thin air: A cylinder of lead one meter in diameter and three meters long masses about 26,743 kg. At 1/2000th c its momentum is ~4.009 x 10^9 kg-m/s. The cross-sectional area is about 7854 sq cm, so the "pushing back" momentum is 1.235 x 10^-10 kg-m/s. This is about 3.082 x 10^-20 of the projectile's momentum. IOW, if the resisting momentum and "forward" momentum stayed constant, it would take ~ 3.25 x 10^19 seconds (1.02 trillion years) to bring the projectile to a stop.

Or, in short, "It ain't never gonna stop."

[Thia Halmades]

I love you, man.