Newtonian Aurora

[Arwyn]

And on kinetic kill defense...

I and some associates have actually been discussing this one at length.

Modern radar can track lots of objects that don't ever make it onto a screen.  It won't display all the returns from birds, etc, as they don't pass certain parameters.  The displays only show objects moving with velocities exceeding certain speeds/return signatures/etc.  I am not an expert on radar, but I expect the dopler shift on an incoming projectile moving at hundreds or thousands of km/s would give it a rather distinct signature.  How far out you can detect it is beyond me, but it should be obvious if you have an object closing at that velocity.

Problem is stopping something with the kinetic energy of a small nuke. So far the best solution we have come up with sounds more like a karate proverb about using your opponent's strength against them.  The laser hitting a slug would have an easy time striking, but a hard time deflecting enough in the short time needed to stop a hit.  But even a grain of sand far enough from the ship could cause the slug to turn into a ball of plasma - and could stop it.
Missiles would be poor for this as the time to accelerate would be inadequate to reach adequate standoff distance (I think, it depends on detection time).  But a mass driver projectile could be hundreds of meters from the ship firing it.  That would be adequate to disperse the 'energy/blast'.  If a mass driver was to fire - instead of a solid slug - a 'packet' of tiny projectiles of even perhaps a hundredth or less of a gram, it could disrupt the incoming weapon.  Your railgun could also act as its own defense.
The chance of intercepting an incoming slug could be based on the mass of the slug fired by the railgun.  Small slug (fewer projectiles) equals lower intercept chance.  Heavy slug gives a higher chance of successful intercept due to saturation of the target area.  Might not help against a thousand inbounds that will hit your ship, but if the shrapnel has that tight a spread it will be easier to avoid.  If they spread the shrapnel out to better cover a target area, it will be easier to intercept the few inbound projectiles.

It would also make larger payload railguns more useful (perhaps, or at least more versatile) than smaller slug, higher velocity railguns. 

Thoughts.....

So far this is just a concept in the initial stages, and could undoubtedly use some outside thoughts/improvements.  But it is the best we have come up with to stop the one shot kill railgun.

How about sandcasters? Originally a defensive weapons system from Traveller, the original concept was a low velocity weapon throwing out a canister of common sand. A bursting charge destroyed the canister and dispersed the sand. In that system, it was to defend against lasers, but when you consider the velocities that are being discussed here, it would work fairly well against any high velocity system.

At sufficient speeds, running into sand particles is just like running into a brick wall.

For that matter, if you had a good aggregate of powder sand up to small stones, it would work pretty well against any of the weapon systems discussed. You would still have stuff penetrating, but their would be an effect. Small stones in the path of a missile running 30,000 km/s is going to play hell with that missile.

Dispersion from the bursting charge is going to eventually spread the screen out, and the velocity of the firing ship is going to carry it past the screen rapidly. BUT if you dropped them along the bearing of the enemy firing at you, where you GOING to be, they could be fairly effective.

[bean]

How about sandcasters? Originally a defensive weapons system from Traveller, the original concept was a low velocity weapon throwing out a canister of common sand. A bursting charge destroyed the canister and dispersed the sand. In that system, it was to defend against lasers, but when you consider the velocities that are being discussed here, it would work fairly well against any high velocity system.

At sufficient speeds, running into sand particles is just like running into a brick wall.

For that matter, if you had a good aggregate of powder sand up to small stones, it would work pretty well against any of the weapon systems discussed. You would still have stuff penetrating, but their would be an effect. Small stones in the path of a missile running 30,000 km/s is going to play hell with that missile.

Dispersion from the bursting charge is going to eventually spread the screen out, and the velocity of the firing ship is going to carry it past the screen rapidly. BUT if you dropped them along the bearing of the enemy firing at you, where you GOING to be, they could be fairly effective.

I've thought about similar things, both for this application, and for destroying laser mirrors.  The laser mirror application turned out to be quite practical, but I'll have to do the math on the anti-kinetic use.


As to the viability of railguns, both sides are correct.  If the projectile could be accelerated entirely uniformly, then it would be possible for the projectile to undergo arbitrary accelerations.  However, something like the Roche Limit (which only applies to orbital bodies, due to tidal forces) will apply if "tidal forces" are present for whatever reason, either due to non-uniform force application, or due to non-uniform fields.  I'm not sure how assumptions like uniform charge distribution will hold up in these cases.  It could be that the electrons are physically ripped out of the material.  I also think that non-uniform fields will be a problem.  Normally, one can assume that, for example, the field inside a solenoid is uniform, but I'm not sure about it in this case.
The above comments can be taken about any for of kinetic launcher, be it railgun, coilgun, gravdriver, ram cannon, or what have you.
As for the specific case of railguns, I'm really skeptical.  They generally rely on physical contact with the rails, and good luck with that at 100 km/s.
And please, no force fields.  I do like the doppler radar idea, though.


Edit:
I've done some very rough math on the sandcaster thing.  I could be entirely out to lunch on how I went about it, but it should at least be a starting point.
Assume a grain of sand (Silica) impacts a tungsten projectile at 200 km/s.  The grain has a diameter of .5 mm, and a mass of 1.73e-7 kg.
It should produce a total impulse of about 24 N*s, and a force of about 57 MN.
Please take these numbers with a very large grain of salt.  However, I do believe that they should be indicative of the order of magnitude that we're dealing with. 
My conclusion is that it while a grain this size should be able to shatter or deflect the target projectile, I'm not sure if it is possible to achieve the required particle density.  To cover an area against a projectile that has a diameter of 2 cm will take 3183 particles/m^2 (assuming perfect distribution) and will take about .55 grams/m^2.  However, I'm not sure you could accurately disperse that many particles, and then, how do you get them to stop dispersing? 
Also, remember that the fragments of the projectile in question are still out there, and heading for your ship.  The main advantage to this is that the projectile is neither a long rod, nor guided anymore.

[Arwyn]

I've thought about similar things, both for this application, and for destroying laser mirrors.  The laser mirror application turned out to be quite practical, but I'll have to do the math on the anti-kinetic use.


As to the viability of railguns, both sides are correct.  If the projectile could be accelerated entirely uniformly, then it would be possible for the projectile to undergo arbitrary accelerations.  However, something like the Roche Limit (which only applies to orbital bodies, due to tidal forces) will apply if "tidal forces" are present for whatever reason, either due to non-uniform force application, or due to non-uniform fields.  I'm not sure how assumptions like uniform charge distribution will hold up in these cases.  It could be that the electrons are physically ripped out of the material.  I also think that non-uniform fields will be a problem.  Normally, one can assume that, for example, the field inside a solenoid is uniform, but I'm not sure about it in this case.
The above comments can be taken about any for of kinetic launcher, be it railgun, coilgun, gravdriver, ram cannon, or what have you.
As for the specific case of railguns, I'm really skeptical.  They generally rely on physical contact with the rails, and good luck with that at 100 km/s.
And please, no force fields.  I do like the doppler radar idea, though.


Edit:
I've done some very rough math on the sandcaster thing.  I could be entirely out to lunch on how I went about it, but it should at least be a starting point.
Assume a grain of sand (Silica) impacts a tungsten projectile at 200 km/s.  The grain has a diameter of .5 mm, and a mass of 1.73e-7 kg.
It should produce a total impulse of about 24 N*s, and a force of about 57 MN.
Please take these numbers with a very large grain of salt.  However, I do believe that they should be indicative of the order of magnitude that we're dealing with. 
My conclusion is that it while a grain this size should be able to shatter or deflect the target projectile, I'm not sure if it is possible to achieve the required particle density.  To cover an area against a projectile that has a diameter of 2 cm will take 3183 particles/m^2 (assuming perfect distribution) and will take about .55 grams/m^2.  However, I'm not sure you could accurately disperse that many particles, and then, how do you get them to stop dispersing? 
Also, remember that the fragments of the projectile in question are still out there, and heading for your ship.  The main advantage to this is that the projectile is neither a long rod, nor guided anymore.

Ok, I cheated a bit and Googled this since I am at lunch. The number I found were running around 8,000 grains per cm3. So, from a particle density perspective, you have the requisite number of particles and in a reasonably sized packaged (1xcm3). So, the issue is going to be dispersion. Any bursting charge is going to scatter the particles quickly, even a low powered charge. So the question is really, how fast the charge disperses the particles to fill a m^2 and how long the density is high enough in that m^2 to provide an effective defense. I would thing seconds at best, unless the size of the sand charge is larger.

Assuming a cubic centimeter weighs about 3 grams, you could pack a much large volume of sand per canister, plus the bursting charge. So, say 10 grams of sand + bursting charge per canister? That would be fairly compact from a delivery perspective. The question would be area of coverage and duration before dispersion renders it useless.

[Elouda]

If you wanted to go that route, an alternative to explosive bursting would be mechanical dispersion, along the lines of certain submunition weapons which disperse through centrifugal forces. This would probably rule out these being launched through railguns; they would probably require their own launcher system, but delivery would be much more uniform/even/predictable (although more limited in terms of range, due to the slower launch speed).

[Arwyn]

I think speed of delivery would be an issue, hence the bursting charge idea. But your right, it wouldn't have to be particularly fast or large. Ideally though, the farther out you can push the screen, the better the chance of causing a miss.

Even if the screen doesn't destroying an incoming, if it causes just a few degrees of deflection, than the longer the distance traveled from the interception, the better the chance the projectile will miss.

[jseah]

Made redundant by other replies I did not read. 

[bean]

Ok, I cheated a bit and Googled this since I am at lunch. The number I found were running around 8,000 grains per cm3. So, from a particle density perspective, you have the requisite number of particles and in a reasonably sized packaged (1xcm3). So, the issue is going to be dispersion. Any bursting charge is going to scatter the particles quickly, even a low powered charge. So the question is really, how fast the charge disperses the particles to fill a m^2 and how long the density is high enough in that m^2 to provide an effective defense. I would thing seconds at best, unless the size of the sand charge is larger.

Assuming a cubic centimeter weighs about 3 grams, you could pack a much large volume of sand per canister, plus the bursting charge. So, say 10 grams of sand + bursting charge per canister? That would be fairly compact from a delivery perspective. The question would be area of coverage and duration before dispersion renders it useless.

The density would be about half that, unless you're using something like iron for the payload.  And my impression of this was that you'd want enough particles to cover the entire ship, at minimum, so a few grams isn't going to be enough, unless you can launch a bunch of canisters.
Mechanical dispersion would work well.  Release the sand as the projectile spins up to get a nice velocity gradient.

I think speed of delivery would be an issue, hence the bursting charge idea. But your right, it wouldn't have to be particularly fast or large. Ideally though, the farther out you can push the screen, the better the chance of causing a miss.

Even if the screen doesn't destroying an incoming, if it causes just a few degrees of deflection, than the longer the distance traveled from the interception, the better the chance the projectile will miss.

Even if the projectile still hits, its effectiveness as a penetrator has been destroyed.

[procyon]

As to the viability of railguns, both sides are correct.  If the projectile could be accelerated entirely uniformly, then it would be possible for the projectile to undergo arbitrary accelerations.  However, something like the Roche Limit (which only applies to orbital bodies, due to tidal forces) will apply if "tidal forces" are present for whatever reason, either due to non-uniform force application, or due to non-uniform fields.  I'm not sure how assumptions like uniform charge distribution will hold up in these cases.  It could be that the electrons are physically ripped out of the material.  I also think that non-uniform fields will be a problem.  Normally, one can assume that, for example, the field inside a solenoid is uniform, but I'm not sure about it in this case.
The above comments can be taken about any for of kinetic launcher, be it railgun, coilgun, gravdriver, ram cannon, or what have you.
As for the specific case of railguns, I'm really skeptical.  They generally rely on physical contact with the rails, and good luck with that at 100 km/s.
And please, no force fields.  I do like the doppler radar idea, though.

Thanks, Byron.  You touch on one of the two points I would make
.
No 'force/information' can be transmitted faster than c.  This means that the impulse from a railgun will have a tidal effect as it begins acceleration.  As the rails begin the impulse to launch the slug the wave of force will travel in a wavefront as it imparts its momentum to the slug.  This force will create a sheer of around a quarter million Gs to the material.  Try and find one that will survive and you will be rich.

Number two, even if you could somehow cheat Einstien and create an 'instant' effect on the projectile, you would need a launcher will 0% error in distribution of force.  If the launcher has even a tiny fraction of a percent mal-distribution of its force you will see an immense load on the projectile.  In that no known material does not deform under a load, the launcher will have an associated yaw/pitch/occilation associated with the launch.  The finest weapons available today under lesser loads will occilate within a minute of arc under stress.  That will be more than enough with the Gs we are talking about to disintegrate any known material.  If your railgun is a few kms long this could be overcome as you lessen the Gs required.

EDIT
And as number three, it doesn't matter how you look at from the push/pull/whatever point of view, or how even this energy is distributed, you are moving this material in one direction.  Ie - you are applying a FORCE to it to accomplish work.  As in work/force/distance.  This force is beyond immense and will overcome this objects binding strength/tensile strength/etc/ad nauseum.  It will be destroyed.
EDIT

On the thought of sandcasters, I remember them from Traveller.  A mechanical distribution would be ideal, but it all depends on how you intend to launch the 'barrel of sand' and how far out it will be able to interdict an incoming projectile.  

Another issue is how accurate your 'interceptor' will be.  If a high level of accuracy is possible, then you wouldn't have to disperse the 'sand/particles' until you were relatively close to the target and a high saturation would be possible.  

How viable any method will be and how it will need to be delivered is probably going to be determined by how far out you can detect the incoming slug.  Long lead times will give you a wide variety of options.  Short reaction time will require that you use a fairly high velocity interceptor.

EDIT
Of course it occurs to me that if you have a long lead time and can see it coming a long ways out, you could just move out of the way... 

[procyon]

And as number three, it doesn't matter how you look at from the push/pull/whatever point of view, or how even this energy is distributed, you are moving this material in one direction.  Ie - you are applying a FORCE to it to accomplish work.  As in work/force/distance.  This force is beyond immense and will overcome this objects binding strength/tensile strength/etc/ad nauseum.  It will be destroyed.

Ok, I suppose a somewhat better illustration would be appropriate.  After a short chat with a colleauge he pointed out perhaps that some may not understand what I am seeing.

You can accelerate this slug evenly -that is not at issue.  It won't matter.

Assuming perfect distribution (not possible), you will be accelerating every particle in this slug.  EVERY PARTICLE.  Not just a solid object - but every last proton/neutron/electron.  Your acceleration is going to exceed the binding strength of the atoms in the material.  It won't behave as a solid, but as a mass of individual elementary particles being blasted along under incredible levels of energy.  You will rip electrons from atoms, quite possibly pressing nuclei into contact with one another.  Quantum Mech will not allow you to accelerate every particle in the exact same path.  It will behave more as a gas/plasma under this level of energy.   The only place you see this kind of energy is deep in stars or on collapsed remenants of them.  What comes out the end of the rail gun is anyones guess.

But it probably won't look like what you put in it to fire....

EDIT

Sorry for this rant.  As I said, I really like the idea of these guns and am willing to ignore physics on this one as it looks really cool.  But it is also why I like the idea of the force field projectiles.  If we include shields, they look to be the only 'projectile' that could survive being fired by one.

[Mel Vixen]

Can you provide some numbers Procyon (and slides since i am more a visual type) i see now from where you are coming but cant comprehend the implications.

Anyway from a engineering point of view wouldnt it be sufficient to keep the charge/accelerating force just under the Roche limit and still get our fast shells by lengthening the rails? (or have rails that consist of "segments") . Or maybe just increasing the acceleration lineary so that the stresses stay low enought?

[procyon]

End of shift (thank goodness, busy night.  Five deliveries with three needing intervention in the NICU) so maybe tomorrow night I can dredge up the numbers.  I am also trying to retype out my copy of part 27 for my fiction so I can get it posted between other things at work.

The biggest problem is the size of the ships.  If treated as spheres then you limit the length of the rails to the diameter.  This is much easier for Steve I am sure than trying to code for custom sized ships, etc. etc.

You have only so far of a distance to achieve a certain speed from a standing start, which requires a certain amount of energy.  In this case it is a bunch.

In that Steve does this for free, I don't want to make this something he doesn't want to do, as I doubt anyone else will.  If I have to deal with a spherical ship that should really be a fairly long skinny thing to house the rails, I am willing to deal with it.  A ship with a rail gun capable of the energy we are talking about should probably be a whole lot larger/longer with any materials we know.

But I am also accepting that we will make >c movement so this detail is not a 'war stopper' as far as I am concerned.  If it requires some intervention from the 'handwavium' in the weapon to 'suspend inertia' or some such that is fine with me.

[jseah]

Even if the projectile still hits, its effectiveness as a penetrator has been destroyed.

With gigajoule energy ranges, I don't think penetration is the idea...  In fact, I don't think I would even bother to make long rods for railgun shells.  More like sandcasters set to detonate near the target.  (what?  If sandcasters can be launched from railguns, they can be used offensively)
Or a flat disk with the flat side perpendicular to movement. 

We have the proposed problem of penetration and I certainly wouldn't want to risk wasting precious shot-energy.  The penalty of hitting more armour squares isn't really a penalty, since we can easily afford to burn through more armour. 

I mean, if the fragments hit and all the energy goes into the ship, it'll be more or less like a contact nuke. 

[bean]

EDIT

On the thought of sandcasters, I remember them from Traveller.  A mechanical distribution would be ideal, but it all depends on how you intend to launch the 'barrel of sand' and how far out it will be able to interdict an incoming projectile.  

Another issue is how accurate your 'interceptor' will be.  If a high level of accuracy is possible, then you wouldn't have to disperse the 'sand/particles' until you were relatively close to the target and a high saturation would be possible.  

How viable any method will be and how it will need to be delivered is probably going to be determined by how far out you can detect the incoming slug.  Long lead times will give you a wide variety of options.  Short reaction time will require that you use a fairly high velocity interceptor.

A lot of that depends on how sophisticated the interceptor is.  I see this as a minimum-tech method of shooting things down.  A small launcher (railgun/coilgun) that fires it out at a couple km/s, an electronic fuze, and a spinner rocket system.  Probably fire enough to lay a screen between you and the enemy.

EDIT
Of course it occurs to me that if you have a long lead time and can see it coming a long ways out, you could just move out of the way... 

Assuming the projectile in question isn't guided, of course.  The sand cloud would remove any chance of a projectile being guided, which is its own advantage.

With gigajoule energy ranges, I don't think penetration is the idea...  In fact, I don't think I would even bother to make long rods for railgun shells.  More like sandcasters set to detonate near the target.  (what?  If sandcasters can be launched from railguns, they can be used offensively)
Or a flat disk with the flat side perpendicular to movement. 

We have the proposed problem of penetration and I certainly wouldn't want to risk wasting precious shot-energy.  The penalty of hitting more armour squares isn't really a penalty, since we can easily afford to burn through more armour. 

I mean, if the fragments hit and all the energy goes into the ship, it'll be more or less like a contact nuke. 

The fact that a projectile is a long rod has a very significant effect on penetration.  A non-long-rod projectile will be disrupted by the whipple shield, and hit the main armor in a spray of fragments and plasma.  Dangerous, yes, but with the sort of armor we're looking at, not terribly effective.  A long rod will hopefully still have an intact section that can cleanly penetrate said armor. 
Offensive sandcasters make good anti-laser warheads, but they'll just splat on the armor.  At 200 km/s, the sand grain I used above dug about 5 mm into tungsten.  (If my math is good.  If not, it could vary quite a bit).  The same goes for disks, though to a lesser degree.
And remember that a contact nuke is less efficient then a focused blast.  You're intentionally making it more difficult to penetrate. 

[sublight]

The ships are only considered spherical for calculating active sensor cross sections and armor mass. Looking at the sample ships seems to indicate the descriptive length is 3.5x the spherical radius. For realistic railguns, it doesn't help.

When I pointed out that a theoretically optimal railgun shell is under uniform field acceleration, I first calculated how long the rails would have to be if the force was concentrated at one end. I guessed aluminum would be a good material since it is a good conductor with a high strength/weight ratio. Say, 400 MPa strength and 3000 kg/m3 density for a short, squat, 1kg cylindrical shell 50% longer than it is wide. If accelerated by a uniform pressure force on one end (one of the worst case situations) this round should withstand 138,000 Gs. However, even at that acceleration to reach 69 km/s the shell would need 50 ms and 1,760m long rails.

I spent maybe 10 seconds worrying at this length, before remembering that the sorium fuel has 10,000x the energy output of our nuclear missile warheads. Then I shrugged, tossed the math figuratively out the window, and declared that the Newtonian Aurora rail-guns appeared to be nearly theoretically optimal in design. Maybe the railguns are nearly optimal, maybe the shells use T-N materials themselves for better performance. It doesn't really matter either way. Newtonian aurora is operating a half step beyond what is theoretical possible. So what if a 100x acceleration increase is needed to make the rails fit inside a ship: compared to other game aspects a 100x improvement in material choice and/or field distribution over a suboptimal design with modern materials isn't much of a stretch.

No 'force/information' can be transmitted faster than c.  This means that the impulse from a railgun will have a tidal effect as it begins acceleration.  As the rails begin the impulse to launch the slug the wave of force will travel in a wavefront as it imparts its momentum to the slug.

It doesn't have to be an instantaneous change in acceleration. A ramp-up time to full acceleration is going to be essential to limit jerk and at least partial intrinsic to overcoming rail inductance. Ideally the ramp up time ought to be small compared to time spent accelerating, but a 1% ramp-up time (say 5e-6s) should be sufficiently small to avoid impacting final velocity. By comparison, the time required for light to cross the rail width is 2.2e-10s. I don't think light-speed tidal lag will be an issue.

Ok, I suppose a somewhat better illustration would be appropriate.  After a short chat with a colleauge he pointed out perhaps that some may not understand what I am seeing.

You can accelerate this slug evenly -that is not at issue.  It won't matter.

Assuming perfect distribution (not possible), you will be accelerating every particle in this slug.  EVERY PARTICLE.  Not just a solid object - but every last proton/neutron/electron.  Your acceleration is going to exceed the binding strength of the atoms in the material.  It won't behave as a solid, but as a mass of individual elementary particles being blasted along under incredible levels of energy.  You will rip electrons from atoms, quite possibly pressing nuclei into contact with one another.  Quantum Mech will not allow you to accelerate every particle in the exact same path.  It will behave more as a gas/plasma under this level of energy.   The only place you see this kind of energy is deep in stars or on collapsed remenants of them.  What comes out the end of the rail gun is anyones guess.

Ok... quantum mechanics and sub-atomic physics is beyond me, but this doesn't seem quite right. Railguns are applied electromagnetics, so it should only be the electrons, and maybe protons, that get accelerated. Binding forces then allow us to assume it the individual charged atoms getting accelerated. This seems similar to ion thrusters, which accelerate individual charged attoms to nearly the same speeds over much shorter distances. I guess particle stripping might be a concern at realy high accelerations, but I'm uncertain if even newtonian aurora railguns are accelerating that fast.

[jseah]

<...> The fact that a projectile is a long rod has a very significant effect on penetration.  A non-long-rod projectile will be disrupted by the whipple shield, and hit the main armor in a spray of fragments and plasma.  Dangerous, yes, but with the sort of armor we're looking at, not terribly effective. 

Are you forgetting that ship speeds are on the order of a thousand km per second or so?
Even plasma is not particularly healthy, with armour at 100s of MJ and shells starting at GJ all the way up to TJ ranges. 

A projectile vapourizing on your whipple shield is like a nuke going off right next to you.  And we all know what happens when one does that.