Are railguns in space intended to be something that causes massive kinetic damage upon collision? Why wouldn't a railgun shot go right through?

Question

Using the search engine here and on Google is not leading me to any answers.

Assume no shields here or any unobtanium technologies.

What happens upon impact of a projectile fired out of a railgun against a ship in space?

I am not sure of the physics behind it. If a projectile smashes into a surface at a very high velocity, wouldn't it pierce through? Shows make it seem like getting hit with a railgun shot will screw you up a lot harder than flooding you with a sea of bullets.

However this seems to imply if you get pelted with a railgun, the force of impact will somehow disperse throughout the ship. I could see it being a major problem if it strikes critical onboard equipment (ex: a reactor), but if it hits a part of the ship where there is not much material, wouldn't it make a hole and only that (ignoring the now-gaping-hole into the vacuum of space)? Or is there kinetic energy transferred into the surrounding material in a much more violent way than I am imagining?

This also raises the question as to whether ships in space would opt for a thin hull if railguns were a method of attack in space or not.

I tried looking into some videos like this and it looks like it pierces through its target and keeps going. Of course this is not at very high kinetic speeds to which one might get in the future, and it does seem to char the surface area around the impact site, but if you want various sci-fi shows it seems like it completely destroys or incapacitates the ship.

Answer 1

The smartest thing to do is be.. well.. smart.

At very high velocities metal acts like water. Your projectile (if it’s a solid slug or designed to fragment on impact) will pass through the target unless it’s armoured to the point of obscenity (remember that mass in space is expensive). Sure, it will punch a hole, but if it’s a combat vessel at a range where rail guns are going to be even vaguely useful I’d expect the atmosphere would already be vented and the crew on more isolated life support (suits). A railgun round won’t be a killer unless it hits something critical because it simply won't transfer enough energy, and it won’t be ‘inside’ the enemy ship long enough for an explosive to work effectively.

On the other hand: at very high velocities metal acts like water. If your projectile fragments into a series of smaller projectiles (say, like a flak shell) then either the enemy vessel will be sufficiently armoured to stop the cloud of hypervelocity shrapnel (and all the energy is transferred) or you’re maximising the number of potentially killer impacts across the entire profile of the enemy vessel.

So mount a small configurable fuse into your rounds. The targeting computer tells the round the optimal point at which to detonate, the round fires, then later bursts into a deadly hail of shrapnel instead of a single penetrator. If they are too heavily armoured for the burst approach the targeting computer can delay the trigger or turn it off altogether.

Heck, if you add a few targeting thrusters and a camera you could even have them be smart rounds that aim for points of critical weakness or previous damage!

Answer 2

A similar design problem has been faced by who tried to optimize bullets: a bullet that pierces clean through a target, in this case a human, has less chances of delivering lethal damage then a bullet that fragments or start to tumble on impact.

And that's why bullets are designed to fragment on impact or to be unstable to the point that once hit a target they start tumbling.

Identical considerations will hold in your case: if you want to maximize damage, your impactor will need to fragment on impact.

However mind that in order to fragment while in the target the velocity of the bullet has to slower or comparable to the speed of sound in the material of the bullet and the time of residence of the bullet in the target has to be longer than the time needed for sound to propagate across the bullet.

If that doesn't happen your bullet will "realize" it has hit something and has to break after it has gone through the target, greatly reducing the delivered damage (assuming we can neglect effects like atomic reactions induced by very high velocities of impact).

However don't forget that, being in space, a large enough hole pierced through a ship is a problem in itself, because it will let out the gas inside, presumably used to keep the crew alive. Unless you have a fully robotic operated ship.

Answer 3

It depends on the impact velocity. At high enough velocities the round is vaporized and the energy spreads out, doing a lot of damage rather than just punching through.

This is the principle behind the Whipple shield for protecting spacecraft from impacts. Several separated layers of very thin material can stop something that would easily have punched through the same material in a single layer.

Note that this does not happen at velocities used by ordinary guns.

Answer 4

Different shapes

In the video you can see being hit is never a good thing. The force is so big, fire and shrapnel do fly around. There's two things you don't want on a spaceship. Fire and holes. Fire eats up oxygen at alarming rates, while damaging a lot of components. Finally there is enough shrapnel. A truly high speed bullet simply has so much energy that even in "clean" penetration it can do incredible amounts of damage.

L.Dutch is referring already to it, but bullets can be designed for certain targets. Hitting with breaking up bullets sounds good, but at those speeds and powers they might not break apart fast enough to do significantly more damage. The slower method is not preferable, as space is BIG. To have good accuracy you want high speed bullets. However, what's missing is the shape of the bullet. In space there is no drag, so we don't need to use aerodynamic and thus easily penetrating bullets. We could use a bullet like a parachute, or even have it open some metal rods in all directions for a larger surface area after being fired. This will increase hit chance and more energy can be imparted on a larger area. The simply insane amounts of energy will do the rest.

Answer 5

"I am not sure of the physics behind it. If a projectile smashes into a surface at a very high velocity, wouldn't it pierce through?"

Sir Isaac Newton developed an approximation for the impact depth of a projectile hitting a surface, which is based on the idea that the momentum of the projectile will be completely transferred to an equal mass of the material being impacted. So if your projectile weighs 1 kg, then the hole made in the surface will be about 1 kg of material. It doesn't matter how fast the projectile is moving, the hole dug will be roughly the same size as the projectile, multiplied by the ratio of densities.

This is based on conservation of momentum, but is more familiar in the case of the Newton's Cradle toy, where a row of metal balls is suspended on threads touching one another. When one ball slams in to the end of the row, it stops dead, and one ball flies off from the other end of the row. If you drop two balls at one end, they both stop dead, and two balls fly off from the other end. Conservation of momentum means that the impactor stops dead when it has transferred all its momentum to an equal mass of the object impacted.

Obviously, the physics of impacts is a lot more complicated than that. The energy and momentum get transferred to the material being hit and spread out in shock waves and elastic waves, break up the solid material into fragments, generate lots of heat, and both the fragments and the solid body that remains carry away all the momentum and energy. The more energy the projectile carries, the more energy has to be carried away, but the means by which it does so depends on the properties of the material hit. A fragile material with weak bonds fragments and carries away the energy in a small mass of very fast moving fragments. A strong material transfers the energy as elastic waves into the bulk of the body, and results in either a larger mass of slower fragments, or even no fragments at all as the body absorbs the energy and turns it into heat (which may actually be more of a problem). With extremely fast projectiles, as with a railgun, no material is strong enough to resist the shear forces the shock liquifies or vaporises the material which is blasted out sideways, creating a broad, shallow hemispherical crater. For example, in one test a 1 cm aluminium sphere was fired into lead at 2 km/s and created a crater 1.8 cm deep and 4.2 cm in diameter. That's bigger than the projectile, but not by much.

So you are right that rail guns are probably not going to be as effective as scifi makes out. If the material is thin, it will punch a hole through. If thick enough, it will make a small crater little larger than the projectile. Space ships will be armoured anyway against hypervelocity micrometeorites. The main practical advantage I'd see would be that it gives the target less time to dodge the bullet, and given how fast real spaceships move relative to one another, you would probably need a hypervelocity gun for the bullet to be able to catch up to the target!

On space missions to capture micrometeorites intact, NASA has used aerogel, an incredibly light, low density material sometimes called 'frozen smoke'. The idea is that the penetration depth is still fairly small, by transfer of momentum to an equal mass of aerogel, but the impact is spread out so that the energy can be dissipated gradually without melting anything. This shows just how unintuitive hypervelocity impact physics can be!

Answer 6

What happens if the energy of the impact is great enough to vaporize the projectile plus whatever it hits? I believe this is what happens with depleted uranium penetrators on tanks. The impact has enough energy to vaporize the armor and turn the penetrator into plasma. When that gets out of the confinement of its track through the armor, it expands very rapidly inside the tank, essentially explodes. High temperature, high velocity, much expansion-everything inside the tank is heated to 1500 degrees C and combusts.

Those penetrators are travelling much slower than a railgun projectile.

Remember the vapor and plasma still has all the kinetic energy it had when it was traveling at 0.3 c, so that vapor/plasma cloud now spreads out and disperses that energy on the contents of the spaceship, eg crew. High energy explosions are not good for living beings.

As commenters noted about armor piercing shells, the question is whether they are able to dissipate their energy on the target.

I could imagine railgun projectiles made of steel powder that stays together while it's being accelerated, but impacts a target as dust at 0.3 c, discharging all the energy instantly on a 6 meter diameter section of hull. Boom. Smash.

The bottom line is, it's a little hard to predict, so there'd have to be some experimentation. But the general rule is that if you put a very very large amount of energy on a target, SOMETHING has to happen.

Answer 7

A spacecraft that is in any way designed to travel more than a short distance between two points in the same planetary body's SoI is dominated by the tyranny of Rocket design: It will be mostly fuel. In fact, it'll be possibly about 90-99% Fuel tanks!

Next, we should consult project rho for the question and what they say about kinetic penetrators, aka conventional weapons. Oh, and remember: the weapon is not recoilless, and so slugging another ship with a hypersonic slug also will throw your much bigger ship back, which could in the best case just rip the gun off your ship, or kill everybody on the ship from the impact onto the other side of the ship.

[A]nything hitting something at 3 km/s has kinetic energy equal to its own mass in TNT, or one Rick. Ricks scale with the square of velocity, so something at 6 km/s has 4 Ricks. Given that any scenario with enough human space presence for a war virtually requires transit velocities well above that, kinetics are both lethal and relatively cheap.

Now, what does the projectile do to the other ship? If they are smart, it is vented, so the pilot might survive a shot through the cockpit unless he is pinned by the projectile. On the bad side, any shot through the fuel tanks - which make the larger part of of the ship - will cripple the ship, leaving it to die without the need for anything else. Yes, any shot has a large chance to hit the most vital part of the ship: the fuel supply. Vented fuel doesn't blow up the ship. No. It just vents out and ruptures the tank. Even with several tanks and only hitting one redundant tank... suddenly the ship is left in the same position as Apollo 13: the one tank blowing apart will do damage to neighboring components, most likely other tanks, so they leak. The ship now is on borrowed time and bleeds out.

However, unless you have a really good idea where to shoot, you have a hard time hitting anything with what accounts to a pointmass compared to the ship target: engagement and travel times are just large enough that a tiny random change in the direction of the target ship will surely evade any shot unless one unloads a barrage of hundreds of thousands of shrapnel pieces to block all corridors and trajectories that are possible. Project Rho estimates it takes 129600 simultaneous shots to hit a target that can accelerate up to 1 m/s and has a diameter of 10 meters (11 yards).

The same target only would need some 1700-2000 lightly guided penetrators to be a guaranteed hit, if those could only home for the last 10 seconds while steering at 1 m/s. If you can guide the penetrator for the whole flight a single would suffice. It just needs to track and steer well enough for the entire flight - it's pretty much a missile then, just that it might not have a forward propulsion, and instead just needs to steer to keep the target in its target cone.

Not target cone, Guaranteed Kill Cone:

A hypervelocity impact can be divided into four phases. First, there is a transient shock, and the front of the projectile is brought to rest relative to the target. This produces very high temperatures and pressures, and a bright flash. During the next phase, the projectile continues to penetrate into the target, but is eroded as it does so. The length of this phase depends on the length of the projectile and the speed of sound in it. If the object penetrates the target, the shocked portion will disintegrate, spewing fragments. These fragments will come from both projectile and target, and will separate into two cones, one that is basically normal to the surface just penetrated while the other continues at about the same angle the projectile hit at. At the same time, if a portion of the projectile is unshocked, it will continue onward, penetrating deeper into the ship. This could allow a long-rod to go through multiple compartments, getting shorter each time, and leaving clouds of fragments in its wake. The fragments would spread, distributing the damage over a greater area. If an outer whipple shield was used to shock the projectile, the spreading fragment cloud might lack the energy required to penetrate the main armor behind it. Even if it fails to penetrate, however, spalling (shockwaves knocking fragments off the back of the armor) could result, with unpleasant consequences for anyone on the other side.

Or in a picture:

The impact of the tip of the projectile will rip everything in front of it into making shrapnel. Then the rest will break through the new hole and fill everything in its path with shrapnel by repeatedly losing its tip to create more holes and shrapnel. It'll destroy any and every piece of equipment that is there - and to armor against them would make you just carry more and more fuel just to get moving. And you are already required to be pretty much mostly a fuel tank anyway. The Whipple shield (a thin plate held at a distance from the ship) mentioned in the quote above? Useless, unless it is hit flat on orthogonally... and they only help against really small impactors. Not against several kilos of the penetrator.

So at the bottom line: projectiles are a cool idea, but uneconomic if unguided. Railgun shots will go straight through and either bleed out the fuel reserves, rip chunks from a hit ship, fill the target ship with shrapnel that creates secondary and tertiary destruction outside of the direct path, and in all results turn the ship into a (soon to be) wreck. Unguided you won't hit unless you are really close, which is unlikely because of the engagement range in free space: if you can see it, you can shoot at it. You usually fight at distances where light takes time measurable mechanically to get from the target to you. And it's hard to hit a moving target at those speeds. So it better be self-correcting in movement. Aka: it's a missile without a warhead. Oh, and remember: firing your railgun will kick your own ship quite a lot.

Answer 8

This question touches on several points:

If a projectile smashes into a surface at a very high velocity, wouldn't it pierce through?

Almost certainly. Any spacefaring vessel must either be constructed in zero-gravity or designed to be able to escape planetary gravity wells. Either way, it's far too resource intensive to haul enough materials into space to make your ship's hull thick enough to resist railgun fire.

However this seems to imply if you get pelted with a railgun, the force of impact will somehow disperse throughout the ship. I could see it being a major problem if it strikes critical onboard equipment (ex: a reactor), but if it hits a part of the ship where there is not much material, wouldn't it make a hole and only that (ignoring the now-gaping-hole into the vacuum of space)? Or is there kinetic energy transferred into the surrounding material in a much more violent way than I am imagining?

It would make a hole and only that. However, I think you will find sudden depressurization of the crew quarters to be quite violent, in fact. Unless your ship is crewed entirely by robots, one of the greatest risks to the crew is loss of atmosphere. Ships with bulwark doors can address this to some degree by sealing off the areas with holes until repairs can be made, but if you poke holes in all the places crew need to be to make the ship go, then it's dead in the water, as it were. But with accurate targeting, you don't even need to go that far. You said it yourself, just poke a hole in their reactor and let physics do the rest!

This also raises the question as to whether ships in space would opt for a thin hull if railguns were a method of attack in space or not.

Modern space shuttles already opt for as thin a hull as is possible while keeping the crew alive and safe. It is incredibly energetically and fiscally expensive to launch material into space from Earth, so weight is the number one variable to reduce if you want to reduce cost. The problem of inertia doesn't disappear in space either. The amount of force required to accelerate something is proportional to the mass of the object, even in space, so a giant hull thick enough to absorb a railgun shot would simply be economically unviable, even for spacecraft constructed in zero-gravity. You would burn way too much fuel just slowing down to dock with anything.

TL;DR

• Yes, spaceships will use hulls thin enough that a railgun will likely pass straight through.
• No, the railgun alone will likely not blow up the whole ship.
• Still, it's very bad to have a hole in your space ship!

Answer 9

Target Density

The idea that a hypervelocity round will penetrate a ship and pass through depends on one important assumption: there is nothing of significance to hit within the ship. And that implies that the ship has low density (i.e., lots of empty space). In fact, that is a pretty extravagant way to design a spacecraft, and our current technology demonstrates it's not true. Imagine if you shot a round through the ISS. How many different shots could penetrate the hull without also intersecting any other systems?

You don't need to hit something explosive to cause damage. You just need to hit something active, because odds are, the crew probably depends on that thing to operate (they depend on the hull as well, but that can be patched for pressurization, especially if you punch a clean hole through it). Also, the more things you hit inside the ship, the more chances you have to distribute your projectile velocity in very destructive directions.

A smooth hull will generally expose a more or less uniform surface which will not redirect a projectile in any preferred direction. But operational equipment will typically have an amorphous shape and density which will quite likely randomize the redistribution of kinetic energy

Spalling

The thing about metal is that when you break it, it doesn't just deform like putty. All metals have a certain amount of brittleness to them, and when you bang on them hard enough, fragments will break off. This process is called "spallation". So when the penetrator cracks the hull, some of the damage will manifest as spalled fragments turning the inside of the hull into a small grenade. The magnitude of spallation will depend on the size and density of the penetrator, as well as the thickness and composition of the armor. Bigger, thicker armor that might appear on a warship will produce bigger, thicker spallation fragments.

Of course, it is not only the hull which will produce this damage stream. Anything else impacted by the penetrator will also produce spallation damage. Equipment, internal struts, pipes, etc. can all be turned into miniature fragmentation grenades by a suitably energetic penetrator. The penetrator itself will not survive entirely intact, even if it has enough momentum to exit the target. In particular, the initial contact portion of the penetrator will almost certainly turn to shrapnel inside the target, as happens with APFDS rounds penetrating armor today.

Thermal Energy

The penetrator will convert its kinetic energy to thermal energy to compromise the hull. This thermal energy will mostly stay inside of the target ship until it is dissipated. If there's oxygen atmosphere inside, it will likely start fires (by providing well more than enough activation energy for deflagration). Any objects inside the ship which are struck by the penetrator will simply give it more opportunities to trade KE for thermal destruction.

The penetrator itself will also absorb much of this thermal energy, compromising its integrity. Some penetrators are designed to fragment once inside the target. Tuning this will require matching rounds to armor, which might be feasible for a well-armed navy, but likely not for opportunistic pirates. A perfect penetrator/shot will convert all its KE into shrapnel/thermal damage inside the target, without exiting. Making this happen consistently is probably not feasible, and would likely depend on a certain amount of luck. Even so, I would not count on railgun shots leaving clean holes in ships without much collateral damage. That's just too convenient and ignores reality.

Answer 10

Explosive projectiles: WWII era anti-aircraft guns fired shells that were supposed to explode in the air before making contact with the target. (Getting them to actually do that was a major engineering challenge of the day.) When it worked, instead of being hit by a single, compact projectile that had a good chance of passing right through the aircraft without hitting anything critical, the plane would be hit by a cloud of much smaller fragments, with that many more chances for one of them to take out some critical thing (possibly, including a crew member.)

With space-faring technology, and at space-battle distances, you could have a proximity fuze in the projectile that causes it to burst when it senses that it is at some optimum distance from the target.

Also, at rail-gun velocities, and in vacuum, even very tiny particles would be dangerous. So a shell that burst into tens of thousands or even hundreds of thousands of micro-meteroroid-like penetrators potentially could do quite a lot of damage.

Answer 11

Since a railgun fires hyper-speed rounds designed to blow clean through... and it's energy-expensive to fire .. and may require special, expensive amunition... it would be your sniper rifle on a space ship.

If you just wanted to blast a ship, you'd use a cheaper weapon, like rockets or a shotgun like scatter projectile gun.

But, a railgun could be used to target critical systems, and instantly blow a hole through them.

If the ship's computer had a schematic of the enemy ship (or could make certain assumptions about where critical systems are), it could plot the perfect firing trajectory to ....

• blast a hole clean through the engine / power plant / generator, or a key system that would bring that down, pretty much crippling the enemy ship

• blast a hole through the bridge, making everyone's life miserable on it as vaccum sucked out all the air

• blast a hole or slice through a key structural junction point, weakening the structural integrity of that part of the ship. If you blast a key structure point that connects a proplusion part of the ship to other parts, the part trying to create propulsion might create enough stress to rip itself off and cause massive damage. All because you targeted a weak structural point (like a key support beam or something).

While others have talked about oxygen loss, enemy ships may have self-healing hulls.. basically, the hulls would be like cream-filled donuts. When a hole showed up, the liquid sandwiched inside the hull skin would ooze out and react, hardening and sealing up the hole. Sort of like "fix a flat" for bicycle tires to help stop tiny holes immediately until crew can fix it.

So, a rail gun blasting through a hull that could do that... the vaccuum wouldn't be an issue.

But, a key system that the rail gun blew through would be the more severe problem.

The rail gun could also snipe people inside if you could track them.

Oh, there's the captain of the enemy vessel... BLAM ... the enemy ship is now captainless. Oh, look, another crewman is taking over... BLAM .. nope.

After you specificially snipe-murder command structure in an enemy ship, you just hail them and ask if they're ready to give up.

And, since the railgun took out key targets with minimal overall damage to the enemy ship, it's easier to salvage.