hypervelocity projectile question(s)

[Formless]

This is one of what might become a series of threads about hypervelocity weapons. No promises, though. For now, I wanted to ask a simple question: how does the shape and design of a hypervelocity projectile effect its terminal performance? In threads about Hard Science Fiction weapons or on sites like Atomic Rockets, whenever hypervelocity weapons come up (that is, weapons which sling projectiles at speeds of 8 km/second and faster) everyone seems to just assume either rod-shaped or spherical projectiles so as to simplify the math down to just kinetic energy. However, having done some initial research myself it appears that Nasa has done research suggesting that spheres penetrate less deeply overall than either rods or conical projectiles at any speed, and that at hypervelocity cones seem to penetrate more deeply than rod shaped projectiles. And, well, it just seems like common sense that penetration and other impact characteristics are going to be a product of more complicated variables than just kinetic energy and momentum, etc. Are there any other nuances that need to be taken into consideration? What shapes might be best for penetrating armor, for instance? What difference might it make if a projectile is monolithic in material composition (tungsten seems to be popular) vs a composite projectile (say one with a jacket of less dense material and a core of something harder)? Might more complicated designs such as hollowpoints, monad/THV style bullets, these screwdriver shaped things, and others have uses in space combat with hypervelocity slugs? Or are these velocities so high that the slug will vaporize before it will make much more of a difference than the basic difference NASA has already found?

Assume for a moment that the method of launching them is irrelevant; in other words, don't feel compelled to stick to only those metals that are ferromagnetic and can be launched by a coilgun. There are other kinds of launchers I might want to discuss sometime in the future, but I feel like that's a subject for another time.

[Sea Skimmer]

It depends on the actual velocity and actual materials, though in general above 3km/s all penetration becomes highly determined by hydrodynamic interactions, with the entire projectile becoming liquid like soon after impact, instead of progressive tip erosive mechanics which are what long rods fired from modern tanks are doing.

[Formless]

So if the metal is going to just melt on impact anyway, is it critical to use a hard and heat resistant metal like tungsten? Or could you get away with something just as dense but more common, like lead or good old iron? And would a composite of a hard shell surrounding a softer material be worth consideration?

[SpottedKitty]

So if the metal is going to just melt on impact anyway, is it critical to use a hard and heat resistant metal like tungsten?

I'm not sure if "melt" is the right description of what happens as the projectile impacts — it isn't exactly a temperature thing, it's more like a pressure thing. And tungsten is one out of a collection of good choices to use for this purpose, I think it's related to density rather than heat resistance (which is why depleted uranium is another frequent choice).

[LadyTevar]

http://www.schlockmercenary.com/2017-05-21

Funny about that timing.....

[Formless]

http://www.schlockmercenary.com/2017-05-21

Funny about that timing.....

Schlock mercenary is hot steaming garbage, and I resent the insinuation that I even read that crap, let alone that I would be inspired to create a thread because of something that idiot Howard Taylor would come up with.

[...]

Okay, so it is still in my RSS feed... but its a coincidence. I've been thinking about this idea since I posted that thread about space fighters a month or whatever ago. The problem with the Schlock Mercenary strip is that the weapon described is technobabble bullshit that I can't even make heads nor tails of (in fact, the problem with the comic as a whole is that Taylor thinks its Hard SF, when in fact its almost as bad as Star Trek). What I care about is real impact physics.

[Simon_Jester]

I feel like bellowing about how Schlock Mercenary is soft SF is... disastrously missing the point. Of Schlock, of literary criticism, of something.

On the other hand, since Skimmer's already here, further discussions of high speed impactors are kind of redundant except insofar as they involve him.

[Formless]

Well, I find it annoying because of how non-sequitor it is to bring it up just because it happened to be posted within a similar time frame. I don't understand how she even made that connection.

There was a time when I genuinely liked SM. Then it seemed to do some sort of weird soft-reboot with the characters getting amnesia and shit, and from then on I feel like the writer started taking himself too seriously. Well, even more-so than before.

I think what is bothering you is that it is definitely missing the point of the thread, even if there isn't a whole lot to say about the original question.

hmm....

Okay, how about this: what kind of impactor design would be best suited for defeating whipple shields specifically? I am particularly curious about whether something like this shotgun slug might be good for hole-punching the things with the front flyer plate before the rest of the projectile can break up, but I'm not sure of course. Would it be worth it to erode the armor away until you can reach the main hull?

[Sea Skimmer]

So if the metal is going to just melt on impact anyway, is it critical to use a hard and heat resistant metal like tungsten? Or could you get away with something just as dense but more common, like lead or good old iron? And would a composite of a hard shell surrounding a softer material be worth consideration?

Hydrodynamic impact is not melting. Due to extremely high compressive forces solids cease to behave as solids and flow as fluids. This is the essence of how HEAT type warheads work. Anything telling you they melt or burn through armor is 100% false, using simplications that go back to what was originally told to troops in WW2 to hide the precise nature of the various new anti tank weapons being introduced that were obviously not conventional guns. Also precisely to avoid the need to explain hydrodynamic theory to laymen. But you want reality, that's reality, and its pretty damn important to how anything moving above about 1000m/s will truly behave upon impact with another solid material. Above about 3km/s this principle becomes dominate and the whole penetration event starts to become very fluid. As far as I can tell not much of anything can retain useful solidity past 5km/s but in the 3-5km/s range high density ceramics may outperform metal as a penetrator cores.

This does not rule out the projectile being partly melted or vaporized during the impact event, but that behavior won't define how deeply it penetrates into armor or other robust targets. It's just incidental to a several million PSI compression induced event. Which also happens to be how we make implosion type nuclear weapons work.

[Sea Skimmer]

I'm not sure if "melt" is the right description of what happens as the projectile impacts — it isn't exactly a temperature thing, it's more like a pressure thing. And tungsten is one out of a collection of good choices to use for this purpose, I think it's related to density rather than heat resistance (which is why depleted uranium is another frequent choice).

100% right on this, its pressure induced. Tungsten is good because its dense, and physically strong with alloying. The heat resistance isn't too important, though its not irrelevant.

DU is physically weaker then tungsten and many steels, but penetrates better then either....up to a certain velocity. If your talking about 2km/s or higher impacts though tungsten outperforms it. However getting such a high MV out of a modern tank gun would be extremely hard and wasteful, so nobody is even bothering. It makes more sense to mount a bigger caliber gun on a modern tank then to try to greatly increase the MV past about 1,750m/s. It simply eats up too much gunpowder charge to do it. (Light gas guns could increase this, but only are only practical on large artillery pieces)

With a railgun meanwhile 2.5km/s firings are no trouble now, at which point tungsten is the way to go. That's why I say material and velocity matters, what the best option is will change. At extremely high velocities density is about all that matters. Eventually the compression wave will get so intense the entire projectile will vaporize as soon as it hits anything, subject to a delay of the actual shockwave propagation through the projectile at whatever speed it hit. That's the point where the military value might actually go down in some contexts, because in principle the round is now hyper vulnerable to defeat by even the most trival spaced armor plate.

[Q99]

Well, I find it annoying because of how non-sequitor it is to bring it up just because it happened to be posted within a similar time frame. I don't understand how she even made that connection.

There was a time when I genuinely liked SM. Then it seemed to do some sort of weird soft-reboot with the characters getting amnesia and shit, and from then on I feel like the writer started taking himself too seriously. Well, even more-so than before.

The fake-memory story?

Sooo much stuff has happened since then, a lot of it really good! (Obviously, they got most of their memories back, for starters, but it took awhile)


Agh, don't want to digress too much about Schlock, and I will say it's had rough patches, but I really dig how it works.

And, of course, on the hardness/softness thing, what the definition of hard/soft *is* is a shifting morass of quicksand ^^ They do have a consistent well-defined set of technology and it only breaks with known physics where that comes into place, and in defined ways, so I'd call that fairly hard, but of course anything with FTL can be called fairly soft and etc. etc. I'm sure we've all danced this dance, yes? It's harder than Star Trek or Wars by a good mile (no energy beings or psychic powers) but whether one wants to call it 'hard but not super hard' or 'in the middle' or 'soft just not as soft' is a matter of opinion and where one draws the lines.


The strip posted can be summed up as 'here's a fast thing using a gravity thing to go through a gravity shield without being destroyed, and then hitting a thing, fast. High speed debris results.' And, while it's fast, it's not hyper-velocity fast, as demonstrated by the debris puncturing people and not resulting in plasma and hard rads (which are things Schlock fully takes into account).

Actual hypervelocity in Schlock that comes to mind is the.... 0.9c cones the Partnership Collective dropped at the Toughs early on, and Petey's 'Fastball' missiles/'predictably destroyed' ships, used to rip out the powerplants of ships at hypervelocity before defenses can respond.

[SpottedKitty]

(Light gas guns could increase this, but only are only practical on large artillery pieces)

I wonder if anyone's actually planning to develop a light gas gun suitable to put into active service? I've only heard of them being used for scientific purposes, e.g. to simulate large meteor impacts. And, of course, in WW2 the Germans ended up building something similar with the V3 London Gun (never completed, it was discovered in time and blowed up real good by the Dambusters).

[Patroklos]

Okay, how about this: what kind of impactor design would be best suited for defeating whipple shields specifically? I am particularly curious about whether something like this shotgun slug might be good for hole-punching the things with the front flyer plate before the rest of the projectile can break up, but I'm not sure of course. Would it be worth it to erode the armor away until you can reach the main hull?

It would seem any duel action round would defeat a simple whipple shield. You could use something similar to a tandem charge with the second part being the solid penetrate vice another charge. The explosive warhead opens a whole for the inert penetrator to pass through to impact the actual hull. Or if the whipple shield is strong enough to make explosives ineffective you can have a double penetrator. Say a barbell looking round (similar to the video you posted) that separates from each other during transit so the pressure wave from the first impact doesn't travel to the second.

You would probably have something of an escalating race between ship adding layers of whipple shields versus rounds adding multiple precursor charges or penetrators to breach them in succession. Instead of a barbell looking round you end up with a string of pearls. The problem of alignment will eventual set a limit to though as unless your target is sitting still relative to the shooter or the gaps opened in whipple layers are particular large eventually the later rounds will not enter into the gaps created from the first and will instead start making repeat hits on earlier layers. It will depend on the target angle and relative movement.

[Formless]

I wonder if anyone's actually planning to develop a light gas gun suitable to put into active service?

I don't think so, but I have found a couple of patents on weaponizing Light Gas Guns. The trick is finding some way of eliminating the plastic piston that normally plugs up the first stage of the gun and grinds reloading to a halt. Not a problem if you are just using it as experimental equipment, but on the battlefield you want a firing rate faster than 19'th century cannons, not slower. Apparently, you can do that by either making it such that the piston can either leave the barrel of the weapon, or eliminate it entirely by using multiple gasses with different expansion rates. That seems to be how the second patent I linked to works, but they also have to combine the light gas gun technology with an even more obscure technology called an electrothermal gun. Basically, instead of using combustion exclusively to push and force the gasses to expand, they are also being heated by an electric spark plug. This allows you to not only dump more energy into the gasses, but also control the rate of their expansion as the bullet travels the length of the barrel.

At least, that's what I gather from these two patents. The interesting thing is that there apparently existed a scaled down proof of concept for the electrothermal light gas gun that could drive a (very light) pellet to 3km/s. The downside for anyone who wants to use these things in ground combat is that electrothermal guns require a bigass battery or generator to supply electricity to them. That's why it would have to be a dedicated artillery piece or maybe a tank gun. Then again, I'm interested in how they might be deployed in hypothetical space combat, so I don't have to worry about that!

[Sea Skimmer]

www.dtic.mil/dtic/tr/fulltext/u2/a462130.pdf
This is the furthest anyone ever got on a fieldable artillery type light gas gun, but it didn't use a complex piston system as its still based on combustion, and thus not scaleable to say, 4km/s, but did reach 2.5km/s which is thus comparable to any near term implementation of EM gun tech.

Electrically charged ETCs are a lot different, and vary radically in actual design and implementation, and implication. Anything from just using an electrical primer to full flashing an inert propellent to plasma falls under that heading.

[Sea Skimmer]

It would seem any duel action round would defeat a simple whipple shield. You could use something similar to a tandem charge with the second part being the solid penetrate vice another charge. The explosive warhead opens a whole for the inert penetrator to pass through to impact the actual hull. Or if the whipple shield is strong enough to make explosives ineffective you can have a double penetrator. Say a barbell looking round (similar to the video you posted) that separates from each other during transit so the pressure wave from the first impact doesn't travel to the second.

yes people have thought of this
http://patentimages.storage.googleapis. ... D00004.png

That image is huge but it shows a patent for a stacked ceramic cored round with a metal jacket to defeat spaced armor. Real whipple shields are just a niche application of the spaced armor principle, and in real life they typically have some kidn of fillter material between the hard layers, which will almost always number a lot more then two. But whipple shields are optimal against round or irregular shaped projectiles like space debris, the original purpose, while military projectiles will be long and narrow, like that example above. That makes them much harder to defeat. Relative to projectile size and mass stopping the military threat will be much harder. Its basically the same difference of comparing a grenade fragment to a armor piercing machine gun round.

You would probably have something of an escalating race between ship adding layers of whipple shields versus rounds adding multiple precursor charges or penetrators to breach them in succession. Instead of a barbell looking round you end up with a string of pearls.

Yup. Also a warship could mount huge amounts of reactive armor on top of whatever its passive armor is. Unlike a tank on land you aren't strictly width limited on this, and your won't knock your armor off hitting buildings and telephone poles in the tracked blitz to victory. Nor do you have to deal with crushing wave action the way a surface warship does.

The problem of alignment will eventual set a limit to though as unless your target is sitting still relative to the shooter or the gaps opened in whipple layers are particular large eventually the later rounds will not enter into the gaps created from the first and will instead start making repeat hits on earlier layers. It will depend on the target angle and relative movement.

Yeah, at some point a bending motion will ruin your shit. That's where composite penetrators like the above ceramic-metal idea come into play again, so you can make the jacket as rigid as possible, as opposed to the monolithic all alloy tungsten or all uranium shells favored for present day tank ammunition.

If you get your velocity high enough though details like this will just stop mattering, but that starts in the 12km/s range, at which point your launch energies are kind of crazy if you want real life, and a reasonable rate of fire, or missile that does not weigh 40 tons.

[Sky Captain]

What if you have torchships that can reach say 500 km/s in few days and you do something like drive by shooting doing high velocity flyby and deploying kinetic munitions to hit target. Or you have two fleets of such ships passing on opposite vectors. Then missiles or railgun slugs would need only minimal terminal guidance since 99,99 % of kinetic energy would be provided by main fusion drive. At impact energies that high would it really matter what is your projectile made of or what shape it has, or any random junk would be as effective as dedicated impactors?

[Formless]

What if you have torchships that can reach say 500 km/s in few days and you do something like drive by shooting doing high velocity flyby and deploying kinetic munitions to hit target. Or you have two fleets of such ships passing on opposite vectors. Then missiles or railgun slugs would need only minimal terminal guidance since 99,99 % of kinetic energy would be provided by main fusion drive. At impact energies that high would it really matter what is your projectile made of or what shape it has, or any random junk would be as effective as dedicated impactors?

The "lob beer cans out the window" jousting maneuver? Yes, as said at a certain velocity about the only thing that matters is projectile mass and projectile density (which would probably still favor a dense material like lead, steel or tungsten rather than literal trash bags), but the thing is its still preferable for the guns to be capable of achieving high velocity. If you are passing me from the side and lob trash my way, I as the defender can also put impactors in front of your ship(s), and probably while using a lot less fuel. The thing is, you still have to worry about relative velocity. The faster the projectile is going relative to your own ship, the more useful it becomes even in a "jousting" maneuver. Why? Because of geometry. When "jousting" like this, you are never going to head directly at your enemy, because that turns into ramming action instead of jousting. That's no good-- ramming action is a terrible idea at high velocity. Both vehicles would be annihilated in an impact at hundreds of km/s. So you want to pass your enemy at some distance from them, probably traveling either parallel to the enemy craft or at an angle so that you are not at risk of collision.

Now, if your missiles or bullets are launched at low velocity relative to your own vehicle, then you need to launch it long before you expect it to impact. This is because it will travel along a shallow angle relative to your vehicle (unless you make a burn to change the vehicle's vector), and again we want maximum distance between you and the enemy or else you are easily defeated by kinetic "mines". But the sooner you release the missiles, the greater chance your enemy has of detecting them and dodging (or burning them away with some sort of laser broom. Again, you wouldn't throw literal garbage at someone because of this). If, however, your ship has guns or the missile has its own engines that can put great distance between itself and your vehicle in a short period of time, you can shoot it at a steeper angle. A steeper angle means you can shoot the enemy from a time closer to the moment your vehicles pass each other, giving less time for the enemy to react. Moreover, it is conceivable that some passes might nullify the effect of the ship's absolute velocity entirely, such as in an orbit where both ships are going to pass from the side going in similar directions like racecars. Even torchships might do so, but while orbiting the sun rather than a planet. In these cases, it only makes sense for the ship's weapons to put significant energy into the projectile rather than relying on the ship's own kinetic energy to do damage. You have a brief window to shoot the enemy, but you damn well want to make it count. Release your weapons too soon and at a low velocity, and the enemy will probably just change course (not that this isn't sometimes tactically or strategically acceptable, but we want to blow him up). If you can shoot the enemy at the very moment he passes you, you have him dead to rights.

[Sky Captain]

Sometimes it may be good idea to briefly maneuver into collision course and dump a cloud of shrapnel against a space station, orbital fortress or other predictable target to cheaply saturate defense systems and damage exposed vulnerable systems to increase chances of your nuclear missiles to get through and achieve a kill.

[Formless]

For any vehicle that can be described as a "warship" and is intended to survive combat, that's insanely risky and wasteful of fuel. Again, you need to look at the actual geometry here. The important thing still isn't your absolute velocity, but the velocity of the projectiles relative to your own vehicle. The tactic you describe almost certainly will take you too close to the station for safety, and your own velocity will be even more dangerous to yourself than it will be against the presumably much larger, more heavily armored stationary target. Especially noteworthy is that in space, "stationary" is a relative term. Everything can move, although some things can accelerate quicker than other things. That means that even a fortress can dodge fire if it sees it incoming from far enough away. Plus, if they qualify as a "fortress" they presumably have more guns than a warship, and can use them to put up a cloud of debris which you will run right into because you are going too fast to dodge. Remember, your maneuvers are limited by momentum, and that makes your motion very predictable. Especially because big, powerful burns are easily seen in the dark void of space. A mass driver or cannon on the other hand will be almost impossible to see firing, making it practically impossible for you to know where the cloud of defensive fire will be-- assuming they can't just shoot in all directions and render the point moot. You would have to do a second burn of fuel to avoid getting shredded, at which point why aren't you just lobbing more missiles at the target? Against a stationary target, a kinetic impactor has no absolute range limit! It will follow Newton's first law of motion: an object in motion stays in motion. So just shoot the facility with everything you've got! Or don't bother with "warships" at all and just make gigantic anti-fortress missiles the size of warships. Then the only maneuvers you care about is steering the thing into the target.

I see no tactical purpose for this proposed maneuver. Its an idea that only makes sense to people who know more about physics than combat. Yes, the energies are high, but once you start factoring in enemy fire it ceases to make sense.