Feasibility of active defense systems against kinetic weapons

Question

Spurred on from an earlier post over here. The general consensus was that if a depleted uranium round is coming your way, don't be in its way. And if you do get hit, disperse the damage as much as possible.

Essentially, with the introduction of long rod tank rounds (think like APFSDS- Armor Piercing Fin Stabilized Discarding Sabot), armor will have a tough time with those rounds slamming into it. Especially as the speed of those rounds increases. Someone in the other thread made an interesting point, essentially shells don't behave like normal projectiles at much higher speeds.

Modern armor designs are more of a system than a slab of metal these days i.e. ERA (explosive reactive armor) on top of solid composite armor etc. Something that was also brought up was that a long rod penetrator isn't going to do as much damage if the round is tumbling and hitting the armor on its side (ie long rod doesn't strike armor with its tip).

Using this principle, how feasible/effective would a system that intercepts long rod penetrators(LRP) to induce a tumbling or structural damage be. Target acquisition aside, imagine a system that shoots out either a projectile or an explosive to cause the incoming round to tip over and tumble. Currently the Israeli trophy system doesn't work against long rod types. Russia's Afganit supposedly intercepts kinetic rod weapons, however that fires a large heated mass to physically break apart the rod.

Two systems that I had floating in my head were:

A foam type weapon that detonates in a wide pattern and sticks to an LRP to cause aerodynamic instability or even detonates to cause structural damage.

A malleable explosive that's shaped larger in surface volume to an incoming round (think like size of a small pizza or a large pie dish). Upon hitting and wrapping around the tip of a penetrator, it detonates (imagine punching raw pizza dough, sure you go through it, but it gets stuck on your arm and stretches with your fist for a moment) to either cause a flight change or damage structural integrity. Or just immediately detonates when making contact with the tip of the LRP.

These are just ideas to help visualize what I mean, system can be anything really. So long as it goes out to meet the incoming projectile to destabilize the projectile. destroying it is a plus not a requirement.

Its main use case would be on a tank, whereby it would intercept or destabilize long rod penetrators so that if they do hit, then the rest of the tank's armor package can absorb it with relative ease. You'd be able to carry more of these small interceptors than the enemy can shells (enemy is single tank for question's purpose) due to the massive size difference the ammunition sizes of enemy round and interceptor round.

Ignoring target acquisition and assuming the speeds are anywhere from 1.8 ~ 4km/s would a system that works on destabilizing a long rod penetrator either by damaging its flight path or structural integrity be feasible. Or is this a developmental dead end. The system doesn't have to be perfect, just like existing active protection systems. Just good enough to increase survivability by a meaningful factor to warrant its inclusion as part of a tanks comprehensive defense package.

One major constraint is that laser systems to vaporize a shell isn't an option. Anything capable of eating through that much dense metal would be a weapon in its own regard, not an active defense system.

Answer 1

a long rod penetrator isn't going to do as much damage if the round is tumbling and hitting the armor on its side (ie long rod doesn't strike armor with its tip).

The penetration depth of a solid projectile is proportional to its length. If a penetrator is 80cm long and 2cm wide, then it only needs to rotate by less than 3 degrees about its centre to halve its effective length, even if the tip still bites into the target nicely. One of the things limiting making the modern day tank penetrators even longer is ensuring that they remain completely dead straight at the point of impact... small misalignments can waste an awful lot of energy.

A foam type weapon that detonates in a wide pattern and sticks to an LRP to cause aerodynamic instability or even detonates to cause structural damage.

A modern APFSDS projectile is travelling at nearly 2km/s, and your previous question posited things travelling twice that speed. Present day penetrators might be as long as 80cm. If a blob of your sticky foam is sort of floating in the air with zero velocity, the penetrator will pass it in 400μs. The blob needs to accelerate at over half a million gravities to end up travelling at the same speed as that penetrator. To put it bluntly, I don't think it is physically possible to make an adhesive that acts that fast, and bonds that hard. Even if it did, the penetrator is heavy and streamlined and has a lot of momentum and the foam is going to be subject to enormous drag forces... I suspect (though I'm not certain) that even if you did find some suitable miracle adhesive the foam would simply be blown clean off without making much of a impact on the projectile's path.

The problem only gets worse when you consider that the 2-4km/s projectile you're trying to intercept might actually only be travelling a few kilometres to get you. You have a very short window of time to detect the firing, acquire the projectile with your APS radar and then launch your countermeasure. You probably want that countermeasure moving as fast as possible, to disrupt the penetrator as far away as possible, so that it is as poorly aligned as possible by the time it hits you. The relative speeds of the countermeasure and the projectile could be enormous, making the difficulty of surviving the impact even more implausible.

imagine punching raw pizza dough, sure you go through it, but it gets stuck on your arm and stretches with your fist for a moment

This idea has the exact same problem as above plus new ones of its own... the bit of the "dough" that the pointy end of the penetrator strikes is going to be subject to colossal pressures by a device that was literally designed to penetrate things much that are much tougher. Even if the "dough" survived at the point of contact, the contact point is now subject to colossal accelerations, and it seems unlikely that the rest of the "dough" has enough tensile strength to withstand that without tearing.

If you had a material capable of wrapping around a 2km/s penetrator like this, then you might actually have a good material for making composite armor out of capable of stopping such a projectile!

Ignoring target acquisition

Honestly, target acquisition is basically at the heart of this problem. The actual shooty bits of Trophy and Afganit aren't that exciting... they're not radically different from the sorts of things that were available to the developers of the Drozd APS back in the late 70s. Afganit is interesting that that it uses explosively formed penetrators to give it enough striking power to disrupt a long-rod penetrator, but EFP technology is nearly 100 years old! The (alleged) effectiveness of Afganit, and the demonstrated effectiveness of Trophy, is down to small incremental improvements in projectiles and vast improvements to radar systems.

You'd be better off thinking about a next-gen version of Afganit than trying to stick things to projectiles moving at multiple kilometres per second.

One major constraint is that laser systems to vaporize a shell isn't an option. Anything capable of eating through that much dense metal would be a weapon in its own regard, not an active defense system.

A laser capable of blasting a penetrator out of the air, or vaporising it, would be a fearsome weapon in itself. But remember it doesn't have to destroy the penetrator, but if it can ablate a small portion of it with suffice energy to start it tumbling by a couple of degrees over its entire flight time then the projectile can have its effectiveness significantly reduced without needing the sort of laser that's capable of toasting a tank all by itself.

Laser countermeasures on tanks have their own issues though, which I won't go into here, and a laser this powerful is a pretty formidable weapon for other purposes (bye bye drones, and any other aircraft that aren't travelling at hypersonic speeds) and are somewhat more high tech than high velocity projectile weapons (to say the least).

Answer 2

This seems like a decent idea. But foam isn't going to do it. The point of the weapon is that is has enormous momentum; which is going to make it difficult to redirect; your defensive projectile needs an offset, i.e. it has to be unbalanced to create unbalance, and it needs a lot of energy.

By comparison, a bullet will fly straight through quite a bit of pizza dough before it get deflected in the slightest. What you need is one-sided drag, like an unbreakable carbon-fiber lasso around the offensive missile that attaches to a weight not struck by the offensive missile; and then makes it unbalanced.

So one idea is a net of heavy balls this is fired at the offensive weapon but spreads out, hopefully the strike is off-center. The offensive weapon gets snagged but now it is slightly slowed and dragging an unbalanced set of weights that will cause it to tumble. Even a few degrees might be enough to mitigate the damage.

For ideal targeting and maximum imbalance, the offensive missile should strike and get snagged on the edge of the defensive "net", and the wider the defensive net, the better. But the net material does have to be tough enough to reverse course instantly at 4km/s without breaking. So invent some damn tough cording for that. Heck, the defensive nets might even be reusable, collected after the battle.

Answer 3

The Royal Navy thinks structural damage might not be enough.

Everyone loves Phalanx. Defense by way of much shooting. But the problem with busting up something that will hurt you by hitting you is that the pieces will probably still hit you.

https://www.navylookout.com/last-ditch-defence-the-phalanx-close-in-weapon-system-in-focus/

Gun-based CWIS has its limitations when faced with the increasing speeds of modern missiles such as BrahMos, Sunburn or Zircon. Their speed makes them harder to detect and track but it is their vast kinetic energy that is particularly deadly. Assuming the CIWS manages to break up the missile somewhere under 1km before impact, then the ship may still be sprayed with high-velocity fragments. This is obviously preferable to the intact missile impacting and detonating deep inside the ship but deadly fragments are likely to disable delicate sensors and penetrate the light steel plate of modern warships. Phalanx may prevent the loss of the ship but may not be able to stop it from becoming eliminated as an effective fighting unit.

This is probably also true for tumbling. That is better for you than riding the spike but the thing is still going the same direction it was and it is still going to whack you hard.

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Ideally the thing to do is divert the entire rod to a different trajectory. Drones? Explosives?

Iron Man?

https://www.youtube.com/watch?v=JYoul9UtroU

Answer 4

Use QILD!

Quickly Inflating Liquid Deflection is the new ERA. A semi-active protection system for you! Unlike full active protection systems which use incredibly expensive camera's, projectiles and launch systems the QILD needs no projectiles or launch systems, just the equipment to calculate the impact point!

On top of the tank a series modified airbags are placed in a pattern, all slightly filled with water and covered with overlapping discs to protect against small-arms fire. The bags are designed to handle immense pressures after they reach a certain size. Once the impact point is determined a pressure valve is opened and a pre-pressured watertank releases water into the bag, inflating it further. The bag is shaped to offer a slanted surface compared to regular impact directions like the side or top-down attacks.

The projectile will hit the slanted angle of the bag and tear through, hitting the almost incompressible water underneath and starting a tumble. The pressure the projectile creates will cause it to pulverise itself before it hits the actual armor underneath. This helps spread the impact point and reduces the effectiveness of the projectile. After the impact a folded up bag with a shaped "lead" will be slightly inflated, the shaped "lead" causing the bag to unfold itself at the impact site to replace the previous bag. A limited amount of replacements would be available for each balloon but repeat hits are highly discouraged.

Buy your tanks a QILD today!