Is my space combat system realistic?

Question

The Basics

There is no FTL.

Most spacecraft use He3-De fusion Torchdrives, capable of performing sustained multi-gee burns. Most torchdrives can also use fuel that is delivered by accelerators elsewhere in the system, so fuel doesn't have to be used until the actual battle begins.

Stealth exists in the setting, but it is very limiting and requires specialised rockets. It relies on cooling, anti-radar coating, meta-materials and on specialised rocket designs. Stealth vessels are generally limited to Hohmann-Transfer orbits and their effectiveness depends on the state of the sensor networks. (Interplanetary space is usually save, but going inside a well settled planets orbit is very risky.)

Automation is high and if there is a crew of biological humans present, they are genetically and biologically enhanced. Pure AI, robots or uploaded minds are more common alternatives.

While defence has beaten offence in the realm of cyber-security, breaking into the systems on a hardware level is usually possible and most factions have a numberof backdoor into each others systems. Ultimately, cybersystems have taken on a rather biological structure, with defence systems acting much like our immune systems. Data is often filled with misinformation, propaganda, computer and memetic viruses and other nasty stuff. So everything must be done with caution.

Weapons

Missiles are used over long ranges (most commonly a lightminutes to a few lightseconds, though their range isn't actually limited, as they can just enter a cruise mode). Usually missiles have an acceleration stage (metallic hydrogen, fusion or antimatter rocket or a beamed energy based propulsion system). This acceleration (hot) stage is then scuttled and a stealth (cold) stage is employed alongside a cold gas thruster, which operates on evaporating liquid helium. Additionally, cooled balloons are deployed as decoys, if the missile believes, that it has been discovered. This stage is only used to avoid the attention of long range energy weapons, which could otherwise begin decemating the missile swarm from a few lightseconds away. As soon as the missiles have been discovered (either the enemy missile wave has closed in or they start taking effective energy weapon fire), they scatter their submunitions. The submunitions have been brought up to speed during the acceleration stage and focus on manovering. They fight enemy missiles and attempt to get a killing shot on the enemy vessel. Common submunitions are kinetic impactor (crude diamond blocks, but their impact energy creates a shock wave that can disable an entire spacecraft), shaped nuclear lances (small angles with huge ranges, wide ones against submunitions, additionally they work well against sensors), lasers (chemical or nuclear powered, short lived and more interesting for electronic warfare than actual damage), radio jammers, thermal particles, radio shaff and sometimes nukes for planetary bombardment.

Energy weapons fall into several categories and work best as soon as targets are about a lightsecond away. Inefficient Gamma and X-ray lasers, UV-Lasers (most commonly used and often capable of operating in the visible part of the spectrum as well, if more efficiency is required), ultra long range (several AU) laser guided particle beams and macron cannons, which fire nano-particles filled with fusion fuel at a few percent of light.

Point defense is done by batteries of masers and infrared lasers, kinetic or macron cannons are sometimes used to provide a final shield against incoming submunitions. Some navies use nuclear bombs instead. While those do indeed clear away incoming submunitions, they cause damage to the spacecraft as well.

Armor is made from carbon super materials, which are further strengthened via electromagnetic effects. Most sections of armor rotate rapidly to offer the largest possible depth against energy weapon fire. Many levels of redundant point defense and sensor systems are buried inside. Armor is usually several meters thick. Non-rotating sections are even more massive. Strong magnetic fields are often used to further reduce the effects of plasma weapons.

Radiators never truely converged on one design, however all designs today pay the energy tax of using heat pumps to achieve as high a temperature as possible to reduce surface area Either short, solid radiators are used all over the hull, operating at a few thousand kelvin and ready to be replaced several times over or particles and droplets are ejected and brought back in by powerful magnetic fields as soon as they've cooled down again. Additionally large, dumpable heatsinks are used to allow the vessels to operate even when their standard heat budget has been exceeded.

Drones are commonplace. The most common drone is arguably the missile. However, most other drones operate closer to the spacecraft itself and offer high acceleration with very limited abilities. Scouts are sent ahead and very versatile, telescopes deploy behind the battle and try to spot cold missiles (there is a trade of between keeping their spin-stabelised multikilometer mirrors save and keeping them close enough to deliver information in time.), deflectors have strong mantetic fields and try to deflect particle beams by a few parts of a degree, so it misses big static targets (they are commonly used by stations) and mirrors allow the vessel to fire its laser at the enemy from a better angle. Other designs like breaching pods exist, but they are niche systems.

Combat

Generally combat begins at about a light minute out. Missiles are fired. Pincering the enemy with missiles can be very effective. This is why a single stealth vessel can devestate a constallation of spacecraft if it can launch it missiles via gauss gun from an unexpected angle. The number of attack vectors, density of the swarms and number of waves depends on the situation. Additionally the missiles are highly modular and programmable, so their setup, complement of submunition warheads and behavior can be determined as the commander sees fit. Usually there is a lot of missile on missile combat. Either the passing swarms fight each other or an attacking swarm fights an defensive swarm. Point defense is good, but far from perfect. Once the submunitions have closed in to a distance of a few thousand kilometers, they can use particle lances and lasers to surpress sensors. Defensive nukes make trying to overwhelm the point defense ineffective, so the attacker tries to avoid offering on good target for such a sweeping defensive strike. Instead they try to grind down the defensive with an optimal number of submunitions to get at least one fatal hit (either a kinetic impactor or particle lance that will penetrate the armor). The chances of annihilation, critical damage, noncritacal damage and a perfect defence are roughly equal over all battles.

Energy weapon combat begins around one lightsecond. It is rare, as it can only happen if one combatent was ambushed or both want to engage. Normally one side retreats or surrenders after the missile phase is over. If the enemy isn't a combat craft, it will be annihilated in seconds. If both are combat craft and in a roughly equal state, the looser will take almost as much damage as the winner.

Shiptypes

Scout drones are usually employed as gunboats.

Stealth craft either operate as spies, missile carriers (using a gauss gun to lauch cold missiles before sneaking away), strikers (which dump their stealth superstructure and trun into regular torch craft in a fight) or carries for torch craft. Stealth crafts are usually much bigger that combat craft, as they need huge amounts of coolant to operate.

Torchdrive vessels all tend to fall into six groups. Destroyers, Armored Crusiers and Battleships, which are optimised for the combat constallation. In practice most navies use just two or even one type in the battle constellation. Size doesn't translate into endurence or performance. Nukes and kinetic impactors destroy a 100m vessel as throughly as a 1000m one. Performance depends on the thrust to weight ratio.

Frigates, Cruisers and Battlecruisers tend to be more diverse and trade versatility for combat performance. They can operate independently, sometimes for years.

Size and Design

Stealth craft tend to be tapering tubes about a kilometer long, as this allows them to carry enough coolant without occluding too many stars, even while using light bending meta-materials. They always try to keep their front towards the sun.

Combat craft tend to be between 50m and 150m. This usually allows them to preamptively dodge energy weapons with their heigh acceleration. Independent craft are generally bigger and tend to have centrifuges and auxiliary craft as well as slots for mission specific modules. Depending on the type they are between 75m and 500m. Their form is optimised for the use of rotating armor, so long, outwards curved cones are the norm. The main energy weapon tends to sit in a transperent frontal cone, that is optimised to let the weapons wavelengths through. Particle beams and macron cannons use shutters.

Is this system of space combat plausible? Did I miss anything obvious?

Thanks for reading this rather long question, I build this system over a long time and am interested if it holds up as a whole.

Answer 1

Fortifications.

1. The action is 99% concentrated in solar systems. Interstellar space is empty.

2. Action will be concentrated around some planets. The area is physically large but practically small because there is nothing else there.

3. It is hard to hide in space. There is no topography. There is little to hide behind. For an area of interest around a planet, multiple fixed sensors will be present. Spacecraft in the areas of interest will be known.

4. It is nice to not have to worry so much about defense. Fortified moons and asteroids in orbit around planets of interest do not have to worry as much about defense.

These fortifications armed with the weapons you describe with multiple distributed eyes over the system will control 99% of spaces of interest. Heavily armed fortifications will quickly obliterate unwanted ships entering the area and closely monitor the rest.

Fighting will be rare.

Answer 2

Why Battleships?

As you said, nukes can destroy even the biggest ship - there is no point in trying to out-armour your enemy's weapons. Also, combat is fought at missile range, making other weapons more or less useless.

I'd argue that the only needed warships are missile frigates / corvettes. Bigger ships will just be slower and less manoeuvrable without featuring more capability to absorb hits, and it isn't like you would need to fit bigger guns either.

So a large ship is just a large target - IMHO it would be way more effective to have a dozen frigates instead of a single battleship.

Answer 3

I think this is well thought out, however I didn't do the math on anything and maybe you overestimate the capabilities of some of your systems. A lot will depend on the relative capabilities of your various systems, the basic logic appears sound.

I doubted anything can hit a target at 1 lightsecond distance, when said target can sustain several g acceleration - however: To get from zero speed to 200m distance (one ship's length + safety factor) in one second ("flight time" of the laser) needs 400g, which is way beyond what your torch drives can do. So hitting a target at these distances is certainly possible. If we assume 1.1 s for target aquisition (0.1 s for calculation and lining up the shot), we are still at ~90g. So we can assume that lasers could hit within m or tens of meters where tah shot was aimed, even if the target random walks at high accleration as long the accleration is not ludicrous.

What struck me when reading your description is two questions:

• who's gonna pay for all that highly advanced and energy-hungry stuff?
• what are they actually fighting about?

To answer my second question, one goal military / political goal that can be achieved with the fleets you describe is total control of space around a planet.

What is less clear to me if a planet or planetoid sized target can be protected within your universe - but I would assume that many planetary defences couldbe overwhelmed with lots of rocks or something. So a large fleet can domiate space around a planet, it can't protect said planet from attacks and no space dominance can guarantee the the population on this planet will be obedient and productive.

From my first question, I think it follows that all sides in a conflict will look for high effect, low cost weapons and tactics - the idea from Kim STanley Robinsons 2312 comes to mind, acclerating or nudging microasteroids from many different places so that they converge at one point. Possibly supercooling them to 4K first to make detection harder.

This also means that evera space combat asset has to be a ship, must be able to evade low tech weapons at short notice.

The battle fleets need missile supplies, He3 supplies, energy supply from microwave stations or so, the telth ships need coolant tenders ... in the end, the fighting craft are not so much the tip of the spear as the end of a very long and complicated supply chain. Which could be disrupted by any of the weapons or tactics we discussed so far.

To sum up my ruminations:

• I don't think stationary defenses in space make much sense in your system
• you should look for more low cost, nuisance attack options, though I'm not sure there is much beyond small and large rocks

Answer 4

Concerning torchships

As I understand such ships are designed with one main thruster which propel them in one direction only. Meaning: They do not have maneuvering thrusters and are not able to change their course rapidly. Also, those ships seem to be very huge and weigh a lot - meaning their inertia is high and maneuvering thrusters would need to be very strong in order to move that ship out of the way.

I think this renders them to something like "fly-by attackers"? Like they are in one course tangential to the target, fire their ordnance and -because physics- they need to follow their tangential course, bringing them out of range. Maybe they are able to use gravitation of planets to "turn around" or even going into orbit of a planet in order to have multiple striking opportunities. Otherwise they need strong reverse thrusting capabilities to decelerate and come to stand still at the right spot.

Another possibility would be to utilize those ships as "drop ships". They approach like described, deploy all other vessels like battlecruisers and smaller and then may or may not participate in the following fight.

Concerning evasion of lasers

You mentioned ships to be able to doge lasers because of their high acceleration. I would doubt that, because high acceleration is not the only factor to consider.

For example, are there people on board? Because if so, the sustainable acceleration is limited by human factors.

First of all, laser beams are not detectable until it is too late, until they impact (you know, they do not emit "extra" light but are the light).

The only way of evading is by detecting the ships that fire them and also be able to detect the laser turrets direction to decide where they are aiming at.

But how would you possibly detect such things? If you send out light signals, like radar, the wave travels at c towards the target ship and has to return to the sending ship. Meanwhile the target ship detected that they were hit by a radar signal and immediately fire they laser into that direction (or be able to project the most likely position). The sending ship, receiving the signal back again, "sees" the past situation of the turrets and cannot decide where they are pointed at "now". And about some milliseconds later the laser from the targeted ship impacts. No chance to react. Or alternatively: Also because of the travel distance of c, the sending ship also has moved and the laser misses. This means, the whole laser cannon phase is useless.

Meaning: The first to emit/reflect any signal towards the enemy is the one who get shot/hit and the other one can (probably) evade and shoot back.

The whole combat situation would probably be more like submarine stealth combat style. Not like a shoot-out as two ships on sea would give each other.

Concerning stealth ships

I think I did not get how they are designed and operate. What is the effect of tapering tubes a kilometer long? And why are they pointing their front towards the sun? This is like standing in front of a lamp and your shadow is projected outwards, isn't it? I don't think you would be in a beneficial position anywhere between the enemy and the sun. You need to be at the backside of the enemy planet and sling around quickly to hit the enemy.

Also, it does not matter how many stars it does or does not occlude. As long as it does not emit or reflect any light towards the enemy, it is already undetectable. No need for extra hardware. Any ship can be "stealthy" this way. The problem is: The enemy will probably flood the whole system or at least as much area as possible with radar or (sweeping) lasers to detect incoming ships early.

Plausibility vs. Realistic vs. Fun

I think you can make your combat system plausible, just by stating that it is like you want it to be. That is always true :)

If you want to have a realistic combat system, considering the laws of physics, speed of light, possible moving trajectories, and impact of moving trajectories on strategy, etc. I think it does not cover it. But you have to decide what you want to have.

As long as it is fun to play, I'd say it is well done!

Answer 5

A ship should not have several meter thick armor

This is probably one of the better though out Hard-scifi combat systems I've seen, but there is one sticking point that I think is a real problem:

Armor is usually several meters thick.

Ships need to move, armor makes them heavy, you already have much lighter and more effective active defenses against most threats, and the square-cube law makes armor less useful the bigger a ship becomes. Every modern navy has stopped armoring thier ships with super thick armor like this for good reasons: The tradeoff for armor on a large ship simply is not worth the sacrifice in performance that a ship must take vs how easy really thick armor is to overcome. To put this in perspective, the thickest armor on a 333 meter long Nimitz Class aircraft carrier is only about 33cm thick, and the newer Ford Class carriers have even thinner armor maxing out at only 25cm.

Instead, what large ships do to protect themselves is focus on the quality of thier active defenses and damage control. A point defense gun can protect a 100m ship just as well as it can protect a 10m ship, but armoring a 100m ship takes 100 times as much material to achieve the exact same quality of armor. So, when it comes to going big, armor is the worst possible defense you can invest in. Less armor also means more maneuverability. If you are firing shots at ranges of several light seconds, then a ship that has a higher thrust to mass ratio will be better at evasion; so, when you get into range of laser weapons, the armored ship will be able to be predictably targeted at longer ranges; so, lighter smaller warships will simply be able to kite the heavier ones and wear them down from a safe range.

That said, armor is not completely useless, but useless when envisioned as a thick outer shell. An outer hull will fail when the energy of an attack is focused on it, but if you move that armor inside of the ship to compartmentalize it, a 3-5cm armored blast wall several meters inside of the ship can contain a collateral explosion better than a 3-5 meter thick outer hull can survive a primary impact from an armor penetrating missile. So on large warships, you should think of armor as a distributed system that contains damage, not like the outer shell of a tank where it is designed to stop it.

Answer 6

Welcome to Atomic Rockets.

You just found one of the fundamentel problems with writing Hard Science Fiction: It's fucking hard. And Atomic Rockets has some very good points:

Space is fucking Huge - and ships are tiny!

You talk about combat happening in a distance of lightseconds to lightminutes. That is equivalent to saying you see the other spacecraft that is between the moon and about 12% of the distance to the sun. The spacecraft is about the size of a building. It takes huge sensor arrays to see any item on that distance that is smaller than a planetary body.

Evading requires warning - Weapons in Space

Now, let's take for granted that we have Spacestation Alpha with such a huge array. They passively spy the sky for the emissions of a spacedrive, which is a heat signature moving. Easy to spot if you know what to look for and your sensor is large enough. They calculate the trajectory, aim the giant space gun on them, and fire.

If it's a laser and they are precise enough, the targeted ship is dead. The laser moves at C, they have a known trajectory, and thus know where the ship will be when their laser impacts. The signature of the firing also moves at C, and thus the ship shot at does not know they are shot at till the shot impacts. The only chance to not die for the target ship is if the station misses.

If the gun isn't a beam, but a mass driver of sorts, it will give a signature that arrives some seconds to minute before the projectile comes through - the projectile isn't moving at the speed of light after all. But are those seconds enough to get away from the point they aim at? Not if Spacestation Alpha is shooting something akin to FLAK shells - these bloody things blow up into submunitions somewhat close to the target. Another problem is, that the projectile, once fired, has only a very small signature and coasts, making it nigh undetectable after its launch. The real question is: can you turn your ship around and burn so hard that you avoid the death-zone created by the gun?

If it's a rocket, they get the much-prolonged launch signature, if the weapon is Hotlaunched. Again, the warhead is moving at speeds akin to slower than the last category. To avoid them the target faces the same problem normal surface warships faced with normal torpedos: It does not just matter that you spot the torpedo in time, it also matters if you can turn your ship in time to avoid it. Now, these are not dumbfire straight flying torpedos to the projected target direction, they are maneuvering and go on a fast blast after their coasting stage.

But, there's the equivalent of an electric torpedo: Coldlaunching them with some means (which might detect as a kinetic weapon), and only trigger the boosters close to the target to maneuver. Try avoiding a shot you thought you already avoided, but fired from proverbially right behind your head

In other words: The defender is screwed HARD, no matter what they do. Oh, and on an aside: If they blow up the missiles, then the debris will pepper them because Newton says that any object that is in motion stays in motion...

And that is just the tip of the iceberg. To say it frank, Atomic Rockets is pretty much a book on how fucking hard it is to properly envision space combat with our means at hands...

Answer 7

The fog of war

As with advanced combat on earth, battles will be fought at a distance. Because most hits are disastrous in a vacuum environment, the primary mode of defense will be misdirection.

Long range

At the longest ranges, lasers will be the primary form of attack as they travel the fastest. The initial laser strike cannot be dodged as it cannot be detected. This would be a huge problem depending on how powerful they are. Subsequent shots can be dodged by employing random evasive tactics. At the light-second range, a ship has seconds to move before struck by subsequent shots.

Chaff

The best defense agains laser weapons is not armor, but cover. Lasers attenuate quickly in particulate clouds. It's why laser weapons aren't very effective in earth's atmosphere. At the first laser strike a ship would deploy a large particulate cloud and perform a high g burn in any direction. Let's call this the cephalopod response.

By laying down reflective cover, lasers would become ineffective and targeting more difficult.

Medium range

Torpedoes are medium range weapons. They can only go so fast and their approach detected before impact. If used at long range, the target ship will have plenty of time to pop it before a strike.

Decoys

Torpedoes need a target lock. Any way to break a lock in the vast distances of space would be an effective countermeasure. The chaff cloud can be effective, but has a key vulnerability. The ship must remain in or behind the cloud. Because a nuke as a large detonation area, you could just carpet bomb the cloud and be done with it.

Target lock would be broken with decoy drones which would mimic the radar cross section of the flagship and eat the torpedoes.

Close range

Close range battles would be basically suicide. Laser tracking would be faster than any pilot. Nukes would be deployed in grid formations, and radiation would be deadly. Only low powered smaller ships with ballistic projectiles would make for believable close encounters.

Answer 8

How long does a battle take?

I don't understand the time scales involved here. Without FTL, we're presumably limited to our own solar system, and you mention a distinction between interplanetary space and planetary orbit.

A Hohmann transfer between Earth and Mars takes 9 months, and the optimal window to do so comes around every 26 months. Similar timescales apply for voyages between any of the four inner planets. Most of these ships will probably be robots but I imagine there's a few humans on the trip too.

That's not an unreasonable time to spend in a spaceship, particularly a large and luxurious one. Tall ships take months to cross the Atlantic and Pacific oceans, but it was still possible for the colonial powers to establish and hold onto empires at that distance. So maybe this is a story about the Space Spanish Treasure Fleet carrying silver back from the mines in the Space West Indies (it's in the asteroid belt) and being attacked by Space Pirates and/or Space Frenchmen.

But missiles have an engagement range of light-minutes? (1 light-minute = 18 million kilometers.) So you can fire a missile and it won't hit until... days? weeks? later. Let's give it 200km/s so it can make it in a day.

If you're passing the enemy at 200km/s, there's not really any time for maneuvering or fighting enemy missiles - you either hit or you don't. Point defences would have an easier time tracking and shooting down individual bullets (even high-velocity rounds barely do 1km/s). Not that it would help, shooting down a missile just means that you get hit by 200km/s shrapnel instead of a 200km/s missile. Adding a nuclear warhead is redundant at that point, the plutonium is probably more useful as extra fuel than as a weapon.

There's a disconnect between the speeds involved and the time to react. Other than light, nothing here moves fast enough to cross interplanetary distances in a reasonable length of time. You could fire a bullet and find that a diplomatic summit has been held and a peace treaty signed before the bullet hits.

How do they protect their people on the ground?

Strategic targets that can't wear armour and can't dodge bullets - cities, military bases, and so on. Even if they're protected by anti-missile interceptors, nothing can intercept a laser.

A single battleship can track and shoot down any target in the Earth-Moon system with energy weapons, including individual people (they're about the same size as missiles and they move a lot slower) and the factories where the enemy is making their battleships (which don't move at all). Why would you need a fleet of them? It's an entire military by itself!