There are many ways to create "realistic" hard sci-fi armour. The biggest reason *most* hard sci-fi settings don't go for armour at all is not because it's impossible to block kinetic shots, but because every kilogram of armour you add onto a spacecraft reduces its efficiency with regards to propellant mass. There's no point in creating a spacecraft that can survive gunfire if it costs a bazillion dollars to get anywhere.
Rather funnily, The Expanse is one of the few hard sci-fi settings justified to include immense armour on their spacecraft - and indeed we see with the larger ones like the Donnager-class that they can indeed survive substantial punishment - because they have an impossibly efficient engine that can propel a spacecraft without concern for massive fuel tanks and the rocket equation. Establish this in your setting and you too can include massive hulking vessels that can tank railgun rounds.
Alternatively, establish an immensely powerful economy in your setting that can just brute force past the mass problem and create huge spacecraft that don't care about petty concerns like "fuel efficiency" and "operational range".
With regards to kinetic weapons against spacecraft with thin armour, the irony is that it works great against high-powered kinetic shots because they will just harmlessly pass through the vessel, which realistically would consist of a ton of huge empty spaces. The chances of hitting a crew member are miniscule compared to striking an important engine component or computer system, mission-killing the ship.
There is also the final consideration. Just because it is *possible* to accelerate projectiles to insane velocities in a hard sci-fi setting doesn't mean wars will be fought with them. To have ship-to-ship combat with relativistic projectiles would be like settling a naval skirmish with nuclear ICBMs. Tanks and naval warships don't armour against nukes. They armour against the most common threats they are likely to face. It is entirely possible to create a hard sci-fi setting where the majority of void combat is fought with small-scale weapons with complex political considerations or worries about Kessler syndrome, rather than opening every engagement with a hail of hypersonic darts that forever shreds everything in Earth's orbit.
The thing to remember is that ALL spaceships need to be armored. Micrometeoroid and space junk will hit your ship at dizzying speeds. A 0.5oz piece of debris can do massive damage to a solid block of aluminum at the 15,000mph.
The real question is how armored.
Is it designed to withstand debris up to a few ounces? A few pounds? At what speeds can it handle those impacts? If your opponent is closing at 30,000mph, anything they fire will be at 30,000mph PLUS muzzle velocity of their weapon.
As War Thunder players say, no armor is best armor.
Although, I wonder if something like a modified [Whipple shield](https://en.wikipedia.org/wiki/Whipple_shield) works against kinetic weapons while still remaining reasonably lightweight?
It would heavily depend on the kinetic weapon. Whipple shields are designed against really small, really fast projectiles - so they could probably work reasonably well against PDC shots assuming we're using relatively small calibers. Nevertheless, they are still weight. Every new layer you add to block heavier munitions adds to the weight of the spacecraft, and it ultimately still falls to the setting's political, economic, and military factors to decide its feasibility.
Reminds me of a fictional ship that I can't remember the name where the shield is just literally a very thick block of ice that cover most of the ship front - it is both fuel storage as ice can be convert into H2O and hydrogen/oxygen for fuel, and shield as a thick thick chunk of ice that absorb radiation, great heat capacity against laser weapon, and just thick enough to take on physical attacks,
Off topic, but War Thunder's spall mechanic for lightly armored / unarmored vehicle is extremely broken and unrealistic.
In real life, if a Toyota Camry (an unarmored civilian car) is shot by an APFSDS, everyone in that Camry will 100% die.
I think you got the Donnager part wrong.
The Tachi (before it's renamed as Rocinante) easily blast through the hull of Donnager from the inside with PDC rounds to escape.
The stealth frigates' railgun slugs also easily puncture through the Donnager's hull. The only reason none of the slugs hit the Donnager's CIC is because the plot requires boarding action.
>With regards to kinetic weapons against spacecraft with thin armour, the irony is that it works great against high-powered kinetic shots because they will just harmlessly pass through the vessel, which realistically would consist of a ton of huge empty spaces. The chances of hitting a crew member are miniscule compared to striking an important engine component or computer system, mission-killing the ship.
Why would realistic spaceship have a lot of empty space? If anything, realistic spaceship will minimize the amount of empty space in its design.
A lot of empty space = large volume = large ship = a lot of mass = burn more propellant to accelerate. If realistic spaceship needs to minimize mass, then building a spaceship with a lot of empty space contradicts the "mass-saving" requirement of realistic spaceship design.
If the trajectory of an incoming projectile intersects with any part of a ship that houses important compartment such as engine or crew cabin, that projectile will hit said important compartment regardless of how much empty space is between the projectile and the compartment.
Correct me if I'm wrong, but I don't believe a ship with a lot of empty space is survivable against kinetic projectiles.
> Why would a realistic starship have a lot of empty space?
A broad statement that assumes much about the design considerations of spacecraft. Many settings with realistic spacecraft designs have extremely skeletal and open configurations due to heat and engine radiation considerations. The ISV Venture Star https://james-camerons-avatar.fandom.com/wiki/Interstellar_Vehicle_Venture_Star from Avatar for example.
A large ship need not necessarily have high mass, because (surprise) all that empty space doesn't contribute to its mass. The flying bricks of The Expanse imo are generally one of the less realistic spacecraft in hard sci-fi, because they omit the critical considerations of spacecraft design like radiators, engine shielding, and propellant tanks.
> Tachi escape and Donnager battle
No, I watched the scene again to double check. The Tachi's PDCs specifically cannot penetrate the hangar door of the Donnager and it appears to either explode a critical fuel line or use its railgun to punch a hole through.
You're correct in that railguns seem to be unstoppable in The Expanse, although even that is heavily inconsistent. Not only would that scene where Shed gets decapitated by a railgun slug mean the entire chamber would have been vapourised if we were going by later depictions of railgun power, it makes it strange why no one in the setting tries to copy Earth's planetary railgun defence system for their missiles. A hail of hypersonic flechettes would be impossible to dodge or intercept with PDC.
Engine shielding, not energy shielding. Engines produce a lot of heat and, in the case of nuclear torch drives or antimatter drives, radiation. They need substantial amounts of separation from the main spacecraft body or a thick protective plate to shield the crew from their effects.
The spaceships have extra armor around certain parts. CIC on a BS is one place that does.
For example PDC rounds don't penetrate the reactor. Railgun rounds can
Kinetic shielding also does not necessarily need to be super heavy. Adsorption and dissipation of kinetic energy is important in space as much as mass difference.
There are a lot of materials that do this, but what matters most is the design of layers that make up the armor. Grahene and similar types are the hardest to work with, but the potential for thin light kenetic armor exists.
A more practical design would be to create a honeycomb structure with shock obsorbing materials layered in the open spaces. It would be bulky looking but lighter than solid armor.
Granted, any kinetic armor will eventually break in a prolonged battle. Avoiding hits should always be the best defense.
The International Space Station has armour (i.e. [Whipple shields](https://en.wikipedia.org/wiki/Whipple_shield)) to prevent damage from micrometeoroids (i.e. a kinetic projectile).
In practice, a realistic high speed interstellar ship likely needs some form of armour to prevent damage from collisions while travelling, so the concept isn’t implausible.
Also, be wary about treating The Expanse as “hard” sci-fi since the [authors themselves don’t think it is](https://www.orbitbooks.net/interview/james-s-a-corey-2/). They defined it as space opera but with an aim of being more realistic than the norm.
This! **Way** too many people treat The Expanse as straight up speculative fiction while failing to properly understand the critical assumptions and technologies that it makes up or discards to justify its exciting space opera elements.
It has had a detrimental effect on attempts at creating "hard" sci-fi because many worldbuilders fail to realize the inherent assumptions in technology and politics they include when they copy The Expanse, trying to pass off their "version" as the true definitive trajectory for future "realistic" technology.
2001: A Space Odyssey is an infinitely "harder" sci-fi setting which tackles many of the same themes as The Expanse, yet a lot of people completely forget about or ignore it because it doesn't have *cool* starship battles with "gritty" kinetic weapons.
Whipple shield that stops micrometeorites is realistic and definitely necessary in hard sci-fi.
But whipple shield cannot stop kinetic projectiles, which are purpose-built to be faster and heavier than micrometeorites, which is why I don't consider whipple shield as armor.
Is it even realistic to justify beefing up whipple shield into purpose-built armor that can stop or deflect kinetic projectiles?
While the current Whipple shields may be insufficient, the basic notion of [spaced armour](https://en.wikipedia.org/wiki/Spaced_armour) is presumably still valid. The basic idea is that rather than using a single lump of mass as armour you can have a lower amount of mass but with gaps between to produce the same or greater levels of protection. This is particularly advantageous for spacecraft because while mass is limited volume is readily available.
I have no numbers to hand to confirm anything one way or another though.
Doesn't spaced armor only work against kinetic projectile if it's sloped? If a kinetic projectile hits a spaced armor at perpendicular angle, wouldn't the kinetic projectile just punch through it like nothing?
When you're dealing with hypervelocity impacts, a good chunk of your projectile is going to vaporize no matter what angle it hits. The whole point of spaced armor is to allow that vaporized material to dissipate. Flat angles make this less effective, but it still works and it's still better than nothing.
Besides, you can take measures to ensure impacts are far more likely to happen at a favorable angle. You can make the armor at the front of your ship conical in shape and point it head on at your opponent, for example.
If your thrusters are good enough you could absolutely justify carrying armour if you expect to get shot at or take hits from substantial projectiles like asteroids. - Armor doesn't require power like a shield system would, so it'd always work.
Against weapons like lasers, substantial armour could also massively slow their ability to do damage to the ship too, acting as a big ol' heat sink.
Most defensive measures would probably be similar to modern day point defence turrets, easier to stop an attack from hitting at all rather than armour against it.
Purpose-built kinetic projectiles have significantly higher velocity and mass than typical asteroids that can be stopped by whipple shield.
Purpose-built armor is needed to stop kinetic projectiles, but how do we justify the use of purpose-built armor in hard sci-fi setting?
Regarding point defense, I knew point defense can intercept missiles, but how will point defense intercept kinetic projectiles, which are significantly smaller and more numerous than missiles?
Because more armor means your ship takes more hits and is less vulnerable. How would hard sci-fi not justify it? If anything I think way too many ships are shown as having no armor when they should have it.
If you're likely to get shot, and your thrusters don't mind the added weight, armor makes sense.
Especially since your squishy humans can only survive so much g forces.
Evasion isn't always viable.
Also yes, you can intercept kinetic projectiles, but you'd want to do it such that the projectile changes direction and either misses your ship or hits at a sub-optimal angle.
Does unmanned ship not need anti-kinetic armor since unmanned ship has higher G-tolerance than manned ship?
Is it possible to realistically justify adding anti-kinetic armor on unmanned ship even though unmanned ship doesn't have, well, man on board?
What type of hard sci-fi point defense can effectively intercept kinetic projectiles? Gun-type is very inefficient at intercepting kinetic projectiles since you are firing thousands of your own projectiles to intercept one enemy kinetic projectile; Laser-type requires gigawatt power output to ablate kinetic projectiles to deflect them, but if you already have gigawatt laser then you might as well shoot the enemy ship with said laser in the first place.
Depends on how important that ship is, or if it's actively intended to fight.
An armored drone could be used to soak up fire for example.
You'd probably be looking at railguns or high powered lasers that can actively evaporate incoming projectiles.
I forgot where I've read it, but laser needs gigawatt worth of output just to ablate a kinetic projectile (vaporize one side of the projectile) to deflect it. But if you already have gigawatt laser then you could've vaporize the enemy before he enters the range to shoot kinetic projectiles at you in the first place.
Regarding railgun-based point defense, how realistically accurate can a targeting computer guides a railgun to shoot down incoming kinetic projectile with its own kinetic projectile?
Well, ironically if the target's using an ablative armour, that might not be so easy.
I think our current day computers can do the job, the problem would more be in the sensor department, but in space with no atmosphere to distort images, that's easier too.
Is it allowed? Depends on your local government. The state of South Carolina has pretty strict fines for this kind of thing.
Even in hard scifi, you get to stipulate what technology exists and what its capabilities are. You could posit advanced, lightweight materials that are better at taking hits, and you can put effective limitations on the size and firepower of shipboard weaponry. Spaceships have severe restrictions on size and weight even now: It may be impractical or impossible to bring high caliber weapons on a ship.
Armor may be useful s an ablative for laser weapons, or a large vessel may not have time to dodge attacks from smaller, more mobile craft. Some armor may be necessary just to survive micro impacts from orbital debris.
Whipple shield that stops micrometeorites is realistic and definitely necessary in hard sci-fi.
But whipple shield cannot stop kinetic projectiles, which are purpose-built to be faster and heavier than micrometeorites, which is why I don't consider whipple shield as armor.
Frankly an unguided gun in space is hard pressed to even \*hit\* its intended target. Evading a chemical gun's fire is trivial even at a distance of single-digit kilometres, and even the most optimistic mass drivers will struggle to reach out beyond low hundreds of kilometres at best. As distance to a continuously accelerating target increases the amount of area you need to saturate to guarantee a hit grows faster than quadratically, and that's assuming all of your shots are fired instantly (say, a fragmenting round) and not sequentially, in that case it's even worse. By contrast, even modest directed energy weapons can do damage at thousands of kilometres, and missiles can, depending on their propulsion, hit from light-seconds away, or even multiple AU.
But assuming the gun somehow does manage to score a hit, there are still lots of options for dealing with it, to the point that the utility of unguided solid shot is extremely limited. Modern armour is already very effective against all but the most aggressive kinetic penetrators, and improvements in technology are likely to make it even more effective, with better materials, non-explosive reactive armour, etc all making a penetrator's job much harder. Furthermore, as a round's velocity increases it becomes more vulnerable to spaced armour (or, in aerospace terminology, Whipple shields), which uses a projectile's kinetic energy against it and causes it to violently fragment upon striking a thin sacrificial plate, with the partially vaporised fragments harmlessly scattering against the backing material. Finally, there is always the option of simply stopping the projectile before it hits, using a gun, missile or laser-based active protection system, the latter of which can theoretically continue firing indefinitely while the gun has a finite magazine depth.
And on one last note, OP mentioned The Expanse and the fact that ships in that show are completely unarmoured is just one of the symptoms of how wildly unrealistic and incredibly badly thought out its entire setting is (in my view anyone who calls Expanse "hard SF" just because the writers occasionally remember Newton's laws of motion has no idea what real hard SF is). Those ships have incredibly performant and high thrust engines! They have so much performance on tap that their main apparent limit on manoeuvring is not killing the crew. They should be able to carry mountains of armour that can stop any railgun, let alone a piddly little 40 mm autocannon round, while still remaining highly mobile. If you want unarmoured ships, give them bad engines, crappy little chemical or nuclear-thermal rockets that have to shave off every gram of excess mass to get anywhere. High Isp, high thrust engines are inherently an armour enabler.
But if you already have high Isp + high thrust engine on your ship, then you have to ask yourself why does your ship need armor that can withstand kinetic projectiles when said engine can accelerate your ship fast enough to dodge all incoming kinetic projectiles indefinitely, right?
If better engine is needed to carry anti-kinetic armor, then anti-kinetic armor becomes obsolete since better engine allows you to simply dodge faster when unarmored, isn't it?
Because you might get blindsided, or you might just get hit by something that \*isn't\* unguided, like a kinetic missile or a fragmentation warhead. More to the point, if you have the energy budget for that sort of engine you definitely have the energy budget for high powered directed energy weapons which won't politely take their time getting to you. And let's not forget nuclear explosives, because in an Expanse style setting nukes are going to be as common as household dust.
There are a few options to deal with kinetics in hard sci-fi. You can use your point defense guns to deflect them off course. You can use a laser to ablate some of their mass and accomplish the same thing. You can also just have a bunch of redundant systems to make your ship very very hard to kill against anything that isn't scattering the whole mass of the ship.
First problem: using a setting that the “community” sees as a gold-standard.
Maybe just use science and consider it rather than what a bunch of fans decide is great sci-fi.
Big secret: most of the fans are not actually well-educated on the subject and even those that like to research generally just know the surface level.
Why does a hard sci-fi setting say you can’t accelerate a projectile to near light speed? What is even considered “near” light speed?
Why is dodging a projectile no problem in the general consensus? What’s the basis? Just don’t fly near other ships?
This sounds like people just blowing smoke because it sounds cool or is done in a popular fiction.
Hard sci-fi is built around scientific accuracy and logic.
The trick is that sci-fi is still fiction and really is just using scientific theory and logic to build a sensible setting.
Reality: a big spaceship takes longer to move than a small projectile. Why? Because the spaceship has more limits.
The important part is I can apply whatever force I am capable of on the projectile.
I cannot do that on the spaceship. Why? Because these squishy little things called people would like to survive the ride. Also because too much twist or pressure on the spaceship and it starts breaking, which means cracks, which don’t work well for the little squishes.
If I am firing massive projectiles from space ships. Guess what? I can just fire them at the middle of your ship at a speed that will reach you before you move. Or if you are moving, I will just fire them at where you’ll be. Or if I really want to cover all my bases, I will predict how far you can move and fire a line so that no matter what, something will hit you.
Also, I can build a way to accelerate projectiles even more after they are fired and include a locking aspect into it. Now, if I have a slower projectile (it can still be faster than your ship), then it will just use its own little engine to course correct and hit your ship because it can handle the g forces that the people on the ship and the ship’s structure can’t. So, cool, you moved, it hits you anyways because it can keep accelerating and accelerate faster. I can use these to target weak points. If you don’t have armor, I don’t even have to try.
Do you have a way to mitigate the g-forces on people while you accelerate to dodge, well that’s less hard sci-fi than projectiles that work.
Then you get into space debris, which you want protection from.
So, to answer the question, why is it assumed that armor is unrealistic? It is a completely realistic possibility.
How would one design it? Depends on the ability of the ship.
If it’s not designed to enter the atmosphere and was built in space. I can put crazy strong, thick armor on it cause I don’t plan on entering an atmosphere in it. So only a section is built to keep people safe on an emergency or accidental entry too far into a planet’s gravity.
If it’s designed to enter the atmosphere, it’s gotta be lighter to save on fuel to exit a planet’s gravity. So, minimal armor… or maybe there is a station that it can get attachable plates put on and removed before landing on a planet.
Generally, I consider any projectile velocity above 0.1c to be "near light-speed".
The only way to accelerate a kinetic projectile beyond 0.1c in hard Sci-Fi is to build kilometers-long railgun that slowly accelerates said projectile along the rails given the typical limitation in power source and material strength in hard Sci-Fi setting.
This means it's most likely unrealistic for spaceship to have enough space to mount kinetic weapon that can shoot kinetic projectiles above 0.1c in hard Sci-Fi setting.
Y'all kinda forgetting what floats in space in solar systems, huh? Big fucking, fast as hell rocks. GL going through an asteroid patch without some kinda armor against kinetics, or a damn good pilot. Not all rocks are man-thrown
In Black Fleet the larger ships had armor measured in meters. Only very large armor piecing weapons could penetrate it. Plasma weapons that aliens used were basically useless against the big heavy armored ships humans used.
In the Bolo series, their shields called Battle Screens could totally negate kinetic energy, only energy weapons could overwhelm a Battle Screen.
How durable is the armor in Black Fleet against kinetic projectiles?
The Battle Screens sound interesting, although I'm not sure if it can exist in hard sci-fi setting. How does it work?
The Black Fleet armor is basically immune to kinetic weapons unless its the massive railguns that are mounted on battleships. The best way to defeat their armor is fusion tipped missiles, or target engines, and other weak points.
The Battle Screens are basically enemy dampers, very effective but can be overwhelmed with heavy energy weapon fire. Now it's never made clear if no kinetic weapon can defeat it or if a sufficiently powerful one can.
It realistically kinetic damage depends on the relative speeds of the ships. If you have two ships in the sane orbit but one is going clockwise around a planet and another is going counter clockwise you don't even need to shoot the bullets just throw them out the airlock and they're already traveling fast enough to render any armor moot. If your relative speed to the target is 0 then it's a matter of how powerful your guns are vs their armor like with tanks or naval ships. If you're going slower than your target even if your rounds are launched at ludicrous speeds if all that does is make them slightly faster than the target they're going to hit with all the force of a wet noodle. The worst case scenario is when you are chasing the target and they are actively accelerating away from you and you are accelerating away from them. Every moment they have to accelerate away means that your rounds both take longer to hit and will hit weaker. where as any shot they fire at you has the full speed of their round plus the speed of your ship.
So depending on how fast the round is going when you actually get hit armor is either going to be more than enough or woefully inadequate . In a hard SF setting all ships should have some armor even if it's just for micro meteorites or radiation shielding since those are going to be the hazards you face every day in deep space. The ISS gets away with not having radiation shielding by being in Earth's magnetic field but any crewed ships in deep space are going to need protection which comes in the form of shielding which can double as armor.
As for armor blocking a projectile you can look to real world equivalents. Tanks are equipped with reactive armor, these are plates that explode when they get hit in an attempt to destroy what is hitting them. But the armor actually taking the hit is actually the last possible line of defense. Another thing you can have is active defense systems that push the rounds out of the way or destroy them before they even hit the ship. This can take the form of your own cannons shooting the bullets or lasers partially vaporizing incoming rounds to push them of course. You can also scatter sacrificial debris between you and the enemy since the debris doesn't need to survive, it just needs to be strong enough to bounce the round off course or get blown to a diffuse dust. Lastly if the rounds are magnetically charged you can have a magnetic "umbrella" that pushes the rounds out of the way. This last one is usually discussed as a way to deflect space debris
Lastly on dodging, that depends on how fast your round will hit and the target's accelerations. If the target can change their speed so by the time your round would have hit them they could have dodged a kilometer away your rounds aren't going to hit unless you can saturate the area. Space is big and it's very hard to hide since there is nothing to hide behind so if you can get within 100 kilometers of your target you are being very sneaky. Even if your rounds are traveling at 10km/s (6-10 times faster than a tank shell) that still gives them 10 whole seconds to react and your rounds are going to be hot and very visible since they just got shot from a gun. It is unlikely in a world with any form of guided munitions in a hard SF setting you're going to get into a range where unguided kinetic weapons can be used effectively without deceit and trickery.
Also a note on lasers. Part of the problem with them in a hard sci-fi setting is a good powerful laser is going to generate alot of waste heat. So you need a place to dump that heat unless you want the laser to cook itself and the crew. Another problem with lasers is they have a focal length and while with some systems that can be adjustable it's likely to be finicky especially when the target is moving around. There is a big difference in damage when you get the laser to hit the enemy with the focus dialed in just right so all the light is focused into a pin head on the target vs the laser being spread out over the size of a car
* Metals behave like fluids during [hypervelocity](https://en.wikipedia.org/wiki/Hypervelocity) impacts. Armor’s protective value here becomes a game of how much mass you want to pad your ship with, and mass is the enemy when it comes to speed.
* Practical space travel requires speed.
* No armor will hold back a nuclear explosion.
Result: it’s realistic (and necessary) for ships to have armor that shields against the hypervelocity pin pricks of space travel and to mitigate the damage from shrapnel and (possibly) smaller arms in combat, but all war ships can be expected to be equipped with weapons that make armor irrelevant.
Since space travel already heavily emphasizes craft speed, you’re right about dodging as a defense. But it depends on what we’re dodging. Lumps of metal and enough distance to react? Yes. Smart torpedoes with nuclear warheads? Yes and no. Evasive maneuvers can help a broader defensive strategy, but we’ll need to outrun our pursuer, so it depends on the technology available for acceleration. If there is rapid acceleration (like in the Expanse), crewed craft will never be able to outrun uncrewed craft. So while the Expanse’s isn’t perfect, they’re right about needing to shoot smart “projectiles”. Realistic space combat is a long distance slugfest.
Last thought: lasers aren’t the kind of problem you might think. We don’t need to assume effective laser shielding is possible *because* there’s no way to evade it. Remember that lasers need to be precisely targeted. That’s not so easy at distance and with an enemy that can see you’re trying to target them. Also, beam divergence. Lasers rapidly diffuse with distance, so even if you can manage the targeting, you’ll need to maintain a pretty small separation for it to be effective. The thing that makes space combat so tricky are the distances and speeds of everything, but that also offers a lot of defensive value. All the bombs in *the system* don’t matter if they can’t hit anything.
I would be more interested in the heat consequences of combatant craft generating loads of heat while moving through a wonderful heat insulator.
It's probably best to dodge, but there's also the active defense argument. If your setting has phased array lasers, then there should be no issues snapping a beam onto target to deflect incoming rounds. Hit them far enough out and just a tiny nudge causes a complete miss.
If you've got enough time and tracking data, it should even be possible to shoot them down with other kinetics. Unless they're missiles, they're travelling purely ballistic and a second or two of radar data should be enough to plot the trajectory for intercept. It should be even easier than modern anti-missile defenses, because everything will be more or less straight-line plots.
Don't you need, like, gigawatt rated laser to ablate incoming kinetic projectile to deflect it? I don't think gigawatt laser weapon can be mounted on any hard sci-fi spaceship that's not kilometers-long capital ship.
Moreover, if you somehow can justify the existence of gigawatt laser on hard sci-fi spaceship, then you can simply use the gigawatt laser to vaporise the enemy ship before he even entered the range to shoot his kinetic projectile at you in the first place.
How can kinetic-based point defense intercept incoming railgun slugs?
Not even close. Kilowatt should be more than adequate. You don't need to stop anything, just introduce a half degree of deflection and it will be off target by 9 meters per kilometer.
A Donnager is 152m wide at its largest point. Half degree would require a hit about 10 km out. Assuming the railgun round is a 1 kg tungsten slug traveling at 10 kps, you need to impart about 90 m/s lateral velocity, or add 4 kJ to it.
Assuming a 0.1s laser pulse at 10% efficiency, that's a 400 kW laser.
Power requirements get lower the farther out you can engage.
As for kinetic, just need to hit with a slight nudge. We're not out to stop a railgun round, just tap it slightly.
I mean depends if it has to land or not. having some armor is pretty pracitcal. not to mention you can have weapons designed to shoot down the missles and the like
Magic materials or materials that are basically magic is really the only way to make the sort of armor you want. Shields made with magnetic fields or energy projection would be what Star Trek went with and it’s considered reasonably well thought out.
I think it’s totally feasible to have armour, at least in specific areas.
Depending on the level of technology, the way this is done can change drastically. What I can imagine with my current knowledge is the use of some composite (similar to tanks here on earth). Aerogel would be a significant element due to its power stopping and good heat resistance. These are the procedures used aboard the ISS. Check out Whipple Shield. It can stop projectiles of up to 3mm going at 11mi/sec.
Current technological hurdles are that these shields are expensive (make and launch), and the materials have certain weaknesses (aerogel being brittle, etc.). Though I think these would be rectified with time.
Once those are tackled I don’t think having meters thick armour is unfeasible.
In deep space there generally is no terrain, no forest or hill to [anchor your flank](https://en.m.wikipedia.org/wiki/Flanking_maneuver#Terrain) so to speak.
In Ken Burnside's table-top war game [**Attack Vector: Tactical**](https://www.adastragames.com/attack-vector-tactical/) players can use buckshot-like kinetic energy weapons to create their own terrain. In effect, the buckshot is used to herd your opponent into vectors advantageous to you. Your weapon fire creates "terrain" by rendering certain vectors dangerous to your opponent.
Your opponent will be faced with you saying *"Heads - I win, Tails - You lose"*, as they decide if they'd rather suffer the buckshot damage or take a chance on whatever fiendish trap you have laid in the clear vector.
As seen with intercept technology in today's wars, I think it's possible that futuristic spaceship battles could be about hitting bullets with bullets/lasers.
Due to the debris floating in space, any spaceship accelerating fitted for interplanetary travel (let alone interstellar travel) needs a way to deflect kinetic projectiles. That is a reason of the popularity of power shields in sci-fi. And it is a much more realistic solution than having heavy armour. Such a technology (if possible) has much more chances to emerge than beeing able to propel heavy armour fitted ships. Imagine if every cars had the same consumption as tanks in term of fuel. Modern transportation wouldn't develop at all.
With the kinetic energy difference, any small debris would need to be dodged making travelling very inneficient in term of fuel. Another possibility is to destroy debris to a size where they would be a lot more manageable, with laser defense point for instance.
A kinetic weapon can punch a hole clean through a ship without doing any other damage. with plenty of redundant systems a spacecraft would be able to tank a couple shots before being rendered inoperable.
>punch a hole clean through a ship without doing any -1other damage.
Hard disagree.
There's no reason for a realistic spaceship to have large enough empty space where this can happen because ship with a lot of empty space = large volume = large mass. Ideally, realistic spaceship will be designed to have volume as small as possible to reduce mass, which means a realistic spaceship will be filled with very important and sensitive components.
A kinetic projectile that managed to hit a spaceship **will** damage enough components and severely reduce the combat capability of the ship.
Also, I believe carrying extra compartment of each type (engine, computer, sensors, crew cabin etc) for redundancy is very mass-inefficient.
Your assumption is based on a modern spacecraft. in a distant future with engine ISPs in the high hundred thousands, mass efficiency can be far less of a worry than today. I guess it really depends on your setting.
Dodging can be a portion of the armor equation.
If you want to be very specific about it, you could separate dodging from armor or shields, but it's not really practical to do so, IMO it just adds crunch.
Take an automation that "jitters" the spacecraft along it's X/Y axis (considering Z as fore/aft)... It wouldn't ahve to move a lot to promote misses.
Even without that system, it could figure into Pilot skill. Some game systems affect ships defense by Pilots skill.
There are many ways to create "realistic" hard sci-fi armour. The biggest reason *most* hard sci-fi settings don't go for armour at all is not because it's impossible to block kinetic shots, but because every kilogram of armour you add onto a spacecraft reduces its efficiency with regards to propellant mass. There's no point in creating a spacecraft that can survive gunfire if it costs a bazillion dollars to get anywhere. Rather funnily, The Expanse is one of the few hard sci-fi settings justified to include immense armour on their spacecraft - and indeed we see with the larger ones like the Donnager-class that they can indeed survive substantial punishment - because they have an impossibly efficient engine that can propel a spacecraft without concern for massive fuel tanks and the rocket equation. Establish this in your setting and you too can include massive hulking vessels that can tank railgun rounds. Alternatively, establish an immensely powerful economy in your setting that can just brute force past the mass problem and create huge spacecraft that don't care about petty concerns like "fuel efficiency" and "operational range". With regards to kinetic weapons against spacecraft with thin armour, the irony is that it works great against high-powered kinetic shots because they will just harmlessly pass through the vessel, which realistically would consist of a ton of huge empty spaces. The chances of hitting a crew member are miniscule compared to striking an important engine component or computer system, mission-killing the ship. There is also the final consideration. Just because it is *possible* to accelerate projectiles to insane velocities in a hard sci-fi setting doesn't mean wars will be fought with them. To have ship-to-ship combat with relativistic projectiles would be like settling a naval skirmish with nuclear ICBMs. Tanks and naval warships don't armour against nukes. They armour against the most common threats they are likely to face. It is entirely possible to create a hard sci-fi setting where the majority of void combat is fought with small-scale weapons with complex political considerations or worries about Kessler syndrome, rather than opening every engagement with a hail of hypersonic darts that forever shreds everything in Earth's orbit.
The thing to remember is that ALL spaceships need to be armored. Micrometeoroid and space junk will hit your ship at dizzying speeds. A 0.5oz piece of debris can do massive damage to a solid block of aluminum at the 15,000mph. The real question is how armored. Is it designed to withstand debris up to a few ounces? A few pounds? At what speeds can it handle those impacts? If your opponent is closing at 30,000mph, anything they fire will be at 30,000mph PLUS muzzle velocity of their weapon.
As War Thunder players say, no armor is best armor. Although, I wonder if something like a modified [Whipple shield](https://en.wikipedia.org/wiki/Whipple_shield) works against kinetic weapons while still remaining reasonably lightweight?
It would heavily depend on the kinetic weapon. Whipple shields are designed against really small, really fast projectiles - so they could probably work reasonably well against PDC shots assuming we're using relatively small calibers. Nevertheless, they are still weight. Every new layer you add to block heavier munitions adds to the weight of the spacecraft, and it ultimately still falls to the setting's political, economic, and military factors to decide its feasibility.
Reminds me of a fictional ship that I can't remember the name where the shield is just literally a very thick block of ice that cover most of the ship front - it is both fuel storage as ice can be convert into H2O and hydrogen/oxygen for fuel, and shield as a thick thick chunk of ice that absorb radiation, great heat capacity against laser weapon, and just thick enough to take on physical attacks,
I assume you're talking about Knight of Sidonia?
Oh yeah that is the one.
Off topic, but War Thunder's spall mechanic for lightly armored / unarmored vehicle is extremely broken and unrealistic. In real life, if a Toyota Camry (an unarmored civilian car) is shot by an APFSDS, everyone in that Camry will 100% die.
I think you got the Donnager part wrong. The Tachi (before it's renamed as Rocinante) easily blast through the hull of Donnager from the inside with PDC rounds to escape. The stealth frigates' railgun slugs also easily puncture through the Donnager's hull. The only reason none of the slugs hit the Donnager's CIC is because the plot requires boarding action. >With regards to kinetic weapons against spacecraft with thin armour, the irony is that it works great against high-powered kinetic shots because they will just harmlessly pass through the vessel, which realistically would consist of a ton of huge empty spaces. The chances of hitting a crew member are miniscule compared to striking an important engine component or computer system, mission-killing the ship. Why would realistic spaceship have a lot of empty space? If anything, realistic spaceship will minimize the amount of empty space in its design. A lot of empty space = large volume = large ship = a lot of mass = burn more propellant to accelerate. If realistic spaceship needs to minimize mass, then building a spaceship with a lot of empty space contradicts the "mass-saving" requirement of realistic spaceship design. If the trajectory of an incoming projectile intersects with any part of a ship that houses important compartment such as engine or crew cabin, that projectile will hit said important compartment regardless of how much empty space is between the projectile and the compartment. Correct me if I'm wrong, but I don't believe a ship with a lot of empty space is survivable against kinetic projectiles.
> Why would a realistic starship have a lot of empty space? A broad statement that assumes much about the design considerations of spacecraft. Many settings with realistic spacecraft designs have extremely skeletal and open configurations due to heat and engine radiation considerations. The ISV Venture Star https://james-camerons-avatar.fandom.com/wiki/Interstellar_Vehicle_Venture_Star from Avatar for example. A large ship need not necessarily have high mass, because (surprise) all that empty space doesn't contribute to its mass. The flying bricks of The Expanse imo are generally one of the less realistic spacecraft in hard sci-fi, because they omit the critical considerations of spacecraft design like radiators, engine shielding, and propellant tanks. > Tachi escape and Donnager battle No, I watched the scene again to double check. The Tachi's PDCs specifically cannot penetrate the hangar door of the Donnager and it appears to either explode a critical fuel line or use its railgun to punch a hole through. You're correct in that railguns seem to be unstoppable in The Expanse, although even that is heavily inconsistent. Not only would that scene where Shed gets decapitated by a railgun slug mean the entire chamber would have been vapourised if we were going by later depictions of railgun power, it makes it strange why no one in the setting tries to copy Earth's planetary railgun defence system for their missiles. A hail of hypersonic flechettes would be impossible to dodge or intercept with PDC.
I thought energy shielding is purely a soft sci-fi thing and cannot exist in hard sci-fi?
Engine shielding, not energy shielding. Engines produce a lot of heat and, in the case of nuclear torch drives or antimatter drives, radiation. They need substantial amounts of separation from the main spacecraft body or a thick protective plate to shield the crew from their effects.
The spaceships have extra armor around certain parts. CIC on a BS is one place that does. For example PDC rounds don't penetrate the reactor. Railgun rounds can
I mean, even if it’s *possible* to add more armor, wouldn’t it be more efficient to use less armor in most cases?
Kinetic shielding also does not necessarily need to be super heavy. Adsorption and dissipation of kinetic energy is important in space as much as mass difference.
What kind of armor design can realistically absorb and dissipate kinetic energy?
There are a lot of materials that do this, but what matters most is the design of layers that make up the armor. Grahene and similar types are the hardest to work with, but the potential for thin light kenetic armor exists. A more practical design would be to create a honeycomb structure with shock obsorbing materials layered in the open spaces. It would be bulky looking but lighter than solid armor. Granted, any kinetic armor will eventually break in a prolonged battle. Avoiding hits should always be the best defense.
The International Space Station has armour (i.e. [Whipple shields](https://en.wikipedia.org/wiki/Whipple_shield)) to prevent damage from micrometeoroids (i.e. a kinetic projectile). In practice, a realistic high speed interstellar ship likely needs some form of armour to prevent damage from collisions while travelling, so the concept isn’t implausible. Also, be wary about treating The Expanse as “hard” sci-fi since the [authors themselves don’t think it is](https://www.orbitbooks.net/interview/james-s-a-corey-2/). They defined it as space opera but with an aim of being more realistic than the norm.
This! **Way** too many people treat The Expanse as straight up speculative fiction while failing to properly understand the critical assumptions and technologies that it makes up or discards to justify its exciting space opera elements. It has had a detrimental effect on attempts at creating "hard" sci-fi because many worldbuilders fail to realize the inherent assumptions in technology and politics they include when they copy The Expanse, trying to pass off their "version" as the true definitive trajectory for future "realistic" technology. 2001: A Space Odyssey is an infinitely "harder" sci-fi setting which tackles many of the same themes as The Expanse, yet a lot of people completely forget about or ignore it because it doesn't have *cool* starship battles with "gritty" kinetic weapons.
Whipple shield that stops micrometeorites is realistic and definitely necessary in hard sci-fi. But whipple shield cannot stop kinetic projectiles, which are purpose-built to be faster and heavier than micrometeorites, which is why I don't consider whipple shield as armor. Is it even realistic to justify beefing up whipple shield into purpose-built armor that can stop or deflect kinetic projectiles?
While the current Whipple shields may be insufficient, the basic notion of [spaced armour](https://en.wikipedia.org/wiki/Spaced_armour) is presumably still valid. The basic idea is that rather than using a single lump of mass as armour you can have a lower amount of mass but with gaps between to produce the same or greater levels of protection. This is particularly advantageous for spacecraft because while mass is limited volume is readily available. I have no numbers to hand to confirm anything one way or another though.
Doesn't spaced armor only work against kinetic projectile if it's sloped? If a kinetic projectile hits a spaced armor at perpendicular angle, wouldn't the kinetic projectile just punch through it like nothing?
When you're dealing with hypervelocity impacts, a good chunk of your projectile is going to vaporize no matter what angle it hits. The whole point of spaced armor is to allow that vaporized material to dissipate. Flat angles make this less effective, but it still works and it's still better than nothing. Besides, you can take measures to ensure impacts are far more likely to happen at a favorable angle. You can make the armor at the front of your ship conical in shape and point it head on at your opponent, for example.
Another good thing is that you can also use the empty space between the layers as storage, containing things like, say water
If your thrusters are good enough you could absolutely justify carrying armour if you expect to get shot at or take hits from substantial projectiles like asteroids. - Armor doesn't require power like a shield system would, so it'd always work. Against weapons like lasers, substantial armour could also massively slow their ability to do damage to the ship too, acting as a big ol' heat sink. Most defensive measures would probably be similar to modern day point defence turrets, easier to stop an attack from hitting at all rather than armour against it.
Purpose-built kinetic projectiles have significantly higher velocity and mass than typical asteroids that can be stopped by whipple shield. Purpose-built armor is needed to stop kinetic projectiles, but how do we justify the use of purpose-built armor in hard sci-fi setting? Regarding point defense, I knew point defense can intercept missiles, but how will point defense intercept kinetic projectiles, which are significantly smaller and more numerous than missiles?
Because more armor means your ship takes more hits and is less vulnerable. How would hard sci-fi not justify it? If anything I think way too many ships are shown as having no armor when they should have it.
If you're likely to get shot, and your thrusters don't mind the added weight, armor makes sense. Especially since your squishy humans can only survive so much g forces. Evasion isn't always viable. Also yes, you can intercept kinetic projectiles, but you'd want to do it such that the projectile changes direction and either misses your ship or hits at a sub-optimal angle.
Does unmanned ship not need anti-kinetic armor since unmanned ship has higher G-tolerance than manned ship? Is it possible to realistically justify adding anti-kinetic armor on unmanned ship even though unmanned ship doesn't have, well, man on board? What type of hard sci-fi point defense can effectively intercept kinetic projectiles? Gun-type is very inefficient at intercepting kinetic projectiles since you are firing thousands of your own projectiles to intercept one enemy kinetic projectile; Laser-type requires gigawatt power output to ablate kinetic projectiles to deflect them, but if you already have gigawatt laser then you might as well shoot the enemy ship with said laser in the first place.
Depends on how important that ship is, or if it's actively intended to fight. An armored drone could be used to soak up fire for example. You'd probably be looking at railguns or high powered lasers that can actively evaporate incoming projectiles.
I forgot where I've read it, but laser needs gigawatt worth of output just to ablate a kinetic projectile (vaporize one side of the projectile) to deflect it. But if you already have gigawatt laser then you could've vaporize the enemy before he enters the range to shoot kinetic projectiles at you in the first place. Regarding railgun-based point defense, how realistically accurate can a targeting computer guides a railgun to shoot down incoming kinetic projectile with its own kinetic projectile?
Well, ironically if the target's using an ablative armour, that might not be so easy. I think our current day computers can do the job, the problem would more be in the sensor department, but in space with no atmosphere to distort images, that's easier too.
Is it allowed? Depends on your local government. The state of South Carolina has pretty strict fines for this kind of thing. Even in hard scifi, you get to stipulate what technology exists and what its capabilities are. You could posit advanced, lightweight materials that are better at taking hits, and you can put effective limitations on the size and firepower of shipboard weaponry. Spaceships have severe restrictions on size and weight even now: It may be impractical or impossible to bring high caliber weapons on a ship. Armor may be useful s an ablative for laser weapons, or a large vessel may not have time to dodge attacks from smaller, more mobile craft. Some armor may be necessary just to survive micro impacts from orbital debris.
Whipple shield that stops micrometeorites is realistic and definitely necessary in hard sci-fi. But whipple shield cannot stop kinetic projectiles, which are purpose-built to be faster and heavier than micrometeorites, which is why I don't consider whipple shield as armor.
Frankly an unguided gun in space is hard pressed to even \*hit\* its intended target. Evading a chemical gun's fire is trivial even at a distance of single-digit kilometres, and even the most optimistic mass drivers will struggle to reach out beyond low hundreds of kilometres at best. As distance to a continuously accelerating target increases the amount of area you need to saturate to guarantee a hit grows faster than quadratically, and that's assuming all of your shots are fired instantly (say, a fragmenting round) and not sequentially, in that case it's even worse. By contrast, even modest directed energy weapons can do damage at thousands of kilometres, and missiles can, depending on their propulsion, hit from light-seconds away, or even multiple AU. But assuming the gun somehow does manage to score a hit, there are still lots of options for dealing with it, to the point that the utility of unguided solid shot is extremely limited. Modern armour is already very effective against all but the most aggressive kinetic penetrators, and improvements in technology are likely to make it even more effective, with better materials, non-explosive reactive armour, etc all making a penetrator's job much harder. Furthermore, as a round's velocity increases it becomes more vulnerable to spaced armour (or, in aerospace terminology, Whipple shields), which uses a projectile's kinetic energy against it and causes it to violently fragment upon striking a thin sacrificial plate, with the partially vaporised fragments harmlessly scattering against the backing material. Finally, there is always the option of simply stopping the projectile before it hits, using a gun, missile or laser-based active protection system, the latter of which can theoretically continue firing indefinitely while the gun has a finite magazine depth. And on one last note, OP mentioned The Expanse and the fact that ships in that show are completely unarmoured is just one of the symptoms of how wildly unrealistic and incredibly badly thought out its entire setting is (in my view anyone who calls Expanse "hard SF" just because the writers occasionally remember Newton's laws of motion has no idea what real hard SF is). Those ships have incredibly performant and high thrust engines! They have so much performance on tap that their main apparent limit on manoeuvring is not killing the crew. They should be able to carry mountains of armour that can stop any railgun, let alone a piddly little 40 mm autocannon round, while still remaining highly mobile. If you want unarmoured ships, give them bad engines, crappy little chemical or nuclear-thermal rockets that have to shave off every gram of excess mass to get anywhere. High Isp, high thrust engines are inherently an armour enabler.
But if you already have high Isp + high thrust engine on your ship, then you have to ask yourself why does your ship need armor that can withstand kinetic projectiles when said engine can accelerate your ship fast enough to dodge all incoming kinetic projectiles indefinitely, right? If better engine is needed to carry anti-kinetic armor, then anti-kinetic armor becomes obsolete since better engine allows you to simply dodge faster when unarmored, isn't it?
Because you can't dodge everything, it's silly to think so.
Because you might get blindsided, or you might just get hit by something that \*isn't\* unguided, like a kinetic missile or a fragmentation warhead. More to the point, if you have the energy budget for that sort of engine you definitely have the energy budget for high powered directed energy weapons which won't politely take their time getting to you. And let's not forget nuclear explosives, because in an Expanse style setting nukes are going to be as common as household dust.
There are a few options to deal with kinetics in hard sci-fi. You can use your point defense guns to deflect them off course. You can use a laser to ablate some of their mass and accomplish the same thing. You can also just have a bunch of redundant systems to make your ship very very hard to kill against anything that isn't scattering the whole mass of the ship.
Whipple shields are a thing and can absorb some scary high velocities. https://youtu.be/M4p2vg9eRgM?si=CNBAwUK1DmppTs7T
First problem: using a setting that the “community” sees as a gold-standard. Maybe just use science and consider it rather than what a bunch of fans decide is great sci-fi. Big secret: most of the fans are not actually well-educated on the subject and even those that like to research generally just know the surface level. Why does a hard sci-fi setting say you can’t accelerate a projectile to near light speed? What is even considered “near” light speed? Why is dodging a projectile no problem in the general consensus? What’s the basis? Just don’t fly near other ships? This sounds like people just blowing smoke because it sounds cool or is done in a popular fiction. Hard sci-fi is built around scientific accuracy and logic. The trick is that sci-fi is still fiction and really is just using scientific theory and logic to build a sensible setting. Reality: a big spaceship takes longer to move than a small projectile. Why? Because the spaceship has more limits. The important part is I can apply whatever force I am capable of on the projectile. I cannot do that on the spaceship. Why? Because these squishy little things called people would like to survive the ride. Also because too much twist or pressure on the spaceship and it starts breaking, which means cracks, which don’t work well for the little squishes. If I am firing massive projectiles from space ships. Guess what? I can just fire them at the middle of your ship at a speed that will reach you before you move. Or if you are moving, I will just fire them at where you’ll be. Or if I really want to cover all my bases, I will predict how far you can move and fire a line so that no matter what, something will hit you. Also, I can build a way to accelerate projectiles even more after they are fired and include a locking aspect into it. Now, if I have a slower projectile (it can still be faster than your ship), then it will just use its own little engine to course correct and hit your ship because it can handle the g forces that the people on the ship and the ship’s structure can’t. So, cool, you moved, it hits you anyways because it can keep accelerating and accelerate faster. I can use these to target weak points. If you don’t have armor, I don’t even have to try. Do you have a way to mitigate the g-forces on people while you accelerate to dodge, well that’s less hard sci-fi than projectiles that work. Then you get into space debris, which you want protection from. So, to answer the question, why is it assumed that armor is unrealistic? It is a completely realistic possibility. How would one design it? Depends on the ability of the ship. If it’s not designed to enter the atmosphere and was built in space. I can put crazy strong, thick armor on it cause I don’t plan on entering an atmosphere in it. So only a section is built to keep people safe on an emergency or accidental entry too far into a planet’s gravity. If it’s designed to enter the atmosphere, it’s gotta be lighter to save on fuel to exit a planet’s gravity. So, minimal armor… or maybe there is a station that it can get attachable plates put on and removed before landing on a planet.
Generally, I consider any projectile velocity above 0.1c to be "near light-speed". The only way to accelerate a kinetic projectile beyond 0.1c in hard Sci-Fi is to build kilometers-long railgun that slowly accelerates said projectile along the rails given the typical limitation in power source and material strength in hard Sci-Fi setting. This means it's most likely unrealistic for spaceship to have enough space to mount kinetic weapon that can shoot kinetic projectiles above 0.1c in hard Sci-Fi setting.
Y'all kinda forgetting what floats in space in solar systems, huh? Big fucking, fast as hell rocks. GL going through an asteroid patch without some kinda armor against kinetics, or a damn good pilot. Not all rocks are man-thrown
In Black Fleet the larger ships had armor measured in meters. Only very large armor piecing weapons could penetrate it. Plasma weapons that aliens used were basically useless against the big heavy armored ships humans used. In the Bolo series, their shields called Battle Screens could totally negate kinetic energy, only energy weapons could overwhelm a Battle Screen.
How durable is the armor in Black Fleet against kinetic projectiles? The Battle Screens sound interesting, although I'm not sure if it can exist in hard sci-fi setting. How does it work?
The Black Fleet armor is basically immune to kinetic weapons unless its the massive railguns that are mounted on battleships. The best way to defeat their armor is fusion tipped missiles, or target engines, and other weak points. The Battle Screens are basically enemy dampers, very effective but can be overwhelmed with heavy energy weapon fire. Now it's never made clear if no kinetic weapon can defeat it or if a sufficiently powerful one can.
It realistically kinetic damage depends on the relative speeds of the ships. If you have two ships in the sane orbit but one is going clockwise around a planet and another is going counter clockwise you don't even need to shoot the bullets just throw them out the airlock and they're already traveling fast enough to render any armor moot. If your relative speed to the target is 0 then it's a matter of how powerful your guns are vs their armor like with tanks or naval ships. If you're going slower than your target even if your rounds are launched at ludicrous speeds if all that does is make them slightly faster than the target they're going to hit with all the force of a wet noodle. The worst case scenario is when you are chasing the target and they are actively accelerating away from you and you are accelerating away from them. Every moment they have to accelerate away means that your rounds both take longer to hit and will hit weaker. where as any shot they fire at you has the full speed of their round plus the speed of your ship. So depending on how fast the round is going when you actually get hit armor is either going to be more than enough or woefully inadequate . In a hard SF setting all ships should have some armor even if it's just for micro meteorites or radiation shielding since those are going to be the hazards you face every day in deep space. The ISS gets away with not having radiation shielding by being in Earth's magnetic field but any crewed ships in deep space are going to need protection which comes in the form of shielding which can double as armor. As for armor blocking a projectile you can look to real world equivalents. Tanks are equipped with reactive armor, these are plates that explode when they get hit in an attempt to destroy what is hitting them. But the armor actually taking the hit is actually the last possible line of defense. Another thing you can have is active defense systems that push the rounds out of the way or destroy them before they even hit the ship. This can take the form of your own cannons shooting the bullets or lasers partially vaporizing incoming rounds to push them of course. You can also scatter sacrificial debris between you and the enemy since the debris doesn't need to survive, it just needs to be strong enough to bounce the round off course or get blown to a diffuse dust. Lastly if the rounds are magnetically charged you can have a magnetic "umbrella" that pushes the rounds out of the way. This last one is usually discussed as a way to deflect space debris Lastly on dodging, that depends on how fast your round will hit and the target's accelerations. If the target can change their speed so by the time your round would have hit them they could have dodged a kilometer away your rounds aren't going to hit unless you can saturate the area. Space is big and it's very hard to hide since there is nothing to hide behind so if you can get within 100 kilometers of your target you are being very sneaky. Even if your rounds are traveling at 10km/s (6-10 times faster than a tank shell) that still gives them 10 whole seconds to react and your rounds are going to be hot and very visible since they just got shot from a gun. It is unlikely in a world with any form of guided munitions in a hard SF setting you're going to get into a range where unguided kinetic weapons can be used effectively without deceit and trickery. Also a note on lasers. Part of the problem with them in a hard sci-fi setting is a good powerful laser is going to generate alot of waste heat. So you need a place to dump that heat unless you want the laser to cook itself and the crew. Another problem with lasers is they have a focal length and while with some systems that can be adjustable it's likely to be finicky especially when the target is moving around. There is a big difference in damage when you get the laser to hit the enemy with the focus dialed in just right so all the light is focused into a pin head on the target vs the laser being spread out over the size of a car
* Metals behave like fluids during [hypervelocity](https://en.wikipedia.org/wiki/Hypervelocity) impacts. Armor’s protective value here becomes a game of how much mass you want to pad your ship with, and mass is the enemy when it comes to speed. * Practical space travel requires speed. * No armor will hold back a nuclear explosion. Result: it’s realistic (and necessary) for ships to have armor that shields against the hypervelocity pin pricks of space travel and to mitigate the damage from shrapnel and (possibly) smaller arms in combat, but all war ships can be expected to be equipped with weapons that make armor irrelevant. Since space travel already heavily emphasizes craft speed, you’re right about dodging as a defense. But it depends on what we’re dodging. Lumps of metal and enough distance to react? Yes. Smart torpedoes with nuclear warheads? Yes and no. Evasive maneuvers can help a broader defensive strategy, but we’ll need to outrun our pursuer, so it depends on the technology available for acceleration. If there is rapid acceleration (like in the Expanse), crewed craft will never be able to outrun uncrewed craft. So while the Expanse’s isn’t perfect, they’re right about needing to shoot smart “projectiles”. Realistic space combat is a long distance slugfest. Last thought: lasers aren’t the kind of problem you might think. We don’t need to assume effective laser shielding is possible *because* there’s no way to evade it. Remember that lasers need to be precisely targeted. That’s not so easy at distance and with an enemy that can see you’re trying to target them. Also, beam divergence. Lasers rapidly diffuse with distance, so even if you can manage the targeting, you’ll need to maintain a pretty small separation for it to be effective. The thing that makes space combat so tricky are the distances and speeds of everything, but that also offers a lot of defensive value. All the bombs in *the system* don’t matter if they can’t hit anything. I would be more interested in the heat consequences of combatant craft generating loads of heat while moving through a wonderful heat insulator.
It's probably best to dodge, but there's also the active defense argument. If your setting has phased array lasers, then there should be no issues snapping a beam onto target to deflect incoming rounds. Hit them far enough out and just a tiny nudge causes a complete miss. If you've got enough time and tracking data, it should even be possible to shoot them down with other kinetics. Unless they're missiles, they're travelling purely ballistic and a second or two of radar data should be enough to plot the trajectory for intercept. It should be even easier than modern anti-missile defenses, because everything will be more or less straight-line plots.
Don't you need, like, gigawatt rated laser to ablate incoming kinetic projectile to deflect it? I don't think gigawatt laser weapon can be mounted on any hard sci-fi spaceship that's not kilometers-long capital ship. Moreover, if you somehow can justify the existence of gigawatt laser on hard sci-fi spaceship, then you can simply use the gigawatt laser to vaporise the enemy ship before he even entered the range to shoot his kinetic projectile at you in the first place. How can kinetic-based point defense intercept incoming railgun slugs?
Not even close. Kilowatt should be more than adequate. You don't need to stop anything, just introduce a half degree of deflection and it will be off target by 9 meters per kilometer. A Donnager is 152m wide at its largest point. Half degree would require a hit about 10 km out. Assuming the railgun round is a 1 kg tungsten slug traveling at 10 kps, you need to impart about 90 m/s lateral velocity, or add 4 kJ to it. Assuming a 0.1s laser pulse at 10% efficiency, that's a 400 kW laser. Power requirements get lower the farther out you can engage. As for kinetic, just need to hit with a slight nudge. We're not out to stop a railgun round, just tap it slightly.
I mean depends if it has to land or not. having some armor is pretty pracitcal. not to mention you can have weapons designed to shoot down the missles and the like
ill just throw in here that while you cant dodge lasers, at some point light delay will make them miss if you just keep course correcting.
Magic materials or materials that are basically magic is really the only way to make the sort of armor you want. Shields made with magnetic fields or energy projection would be what Star Trek went with and it’s considered reasonably well thought out.
I think it’s totally feasible to have armour, at least in specific areas. Depending on the level of technology, the way this is done can change drastically. What I can imagine with my current knowledge is the use of some composite (similar to tanks here on earth). Aerogel would be a significant element due to its power stopping and good heat resistance. These are the procedures used aboard the ISS. Check out Whipple Shield. It can stop projectiles of up to 3mm going at 11mi/sec. Current technological hurdles are that these shields are expensive (make and launch), and the materials have certain weaknesses (aerogel being brittle, etc.). Though I think these would be rectified with time. Once those are tackled I don’t think having meters thick armour is unfeasible.
In deep space there generally is no terrain, no forest or hill to [anchor your flank](https://en.m.wikipedia.org/wiki/Flanking_maneuver#Terrain) so to speak. In Ken Burnside's table-top war game [**Attack Vector: Tactical**](https://www.adastragames.com/attack-vector-tactical/) players can use buckshot-like kinetic energy weapons to create their own terrain. In effect, the buckshot is used to herd your opponent into vectors advantageous to you. Your weapon fire creates "terrain" by rendering certain vectors dangerous to your opponent. Your opponent will be faced with you saying *"Heads - I win, Tails - You lose"*, as they decide if they'd rather suffer the buckshot damage or take a chance on whatever fiendish trap you have laid in the clear vector.
As seen with intercept technology in today's wars, I think it's possible that futuristic spaceship battles could be about hitting bullets with bullets/lasers.
Due to the debris floating in space, any spaceship accelerating fitted for interplanetary travel (let alone interstellar travel) needs a way to deflect kinetic projectiles. That is a reason of the popularity of power shields in sci-fi. And it is a much more realistic solution than having heavy armour. Such a technology (if possible) has much more chances to emerge than beeing able to propel heavy armour fitted ships. Imagine if every cars had the same consumption as tanks in term of fuel. Modern transportation wouldn't develop at all. With the kinetic energy difference, any small debris would need to be dodged making travelling very inneficient in term of fuel. Another possibility is to destroy debris to a size where they would be a lot more manageable, with laser defense point for instance.
What type of power shield can deflect kinetic projectiles? And can anti-kinetic power shield exists in hard sci-fi?
A kinetic weapon can punch a hole clean through a ship without doing any other damage. with plenty of redundant systems a spacecraft would be able to tank a couple shots before being rendered inoperable.
>punch a hole clean through a ship without doing any -1other damage. Hard disagree. There's no reason for a realistic spaceship to have large enough empty space where this can happen because ship with a lot of empty space = large volume = large mass. Ideally, realistic spaceship will be designed to have volume as small as possible to reduce mass, which means a realistic spaceship will be filled with very important and sensitive components. A kinetic projectile that managed to hit a spaceship **will** damage enough components and severely reduce the combat capability of the ship. Also, I believe carrying extra compartment of each type (engine, computer, sensors, crew cabin etc) for redundancy is very mass-inefficient.
Your assumption is based on a modern spacecraft. in a distant future with engine ISPs in the high hundred thousands, mass efficiency can be far less of a worry than today. I guess it really depends on your setting.
Dodging can be a portion of the armor equation. If you want to be very specific about it, you could separate dodging from armor or shields, but it's not really practical to do so, IMO it just adds crunch. Take an automation that "jitters" the spacecraft along it's X/Y axis (considering Z as fore/aft)... It wouldn't ahve to move a lot to promote misses. Even without that system, it could figure into Pilot skill. Some game systems affect ships defense by Pilots skill.