Misconceptions about Space Warfare

I see a lot of misconceptions about space in general, and space warfare in specific, so today I’ll go ahead and debunk some. In the process, we’ll go through the moment to moment of space warfare itself.

Zeroth misconception, no, there won’t be stealth in space, let alone in combat. It is possible through a series of hypothetical technologies or techniques, but it won’t be possible for any reasonable spacecraft under reasonable mass and cost restraints.

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Point defenses firing at a salvo of incoming missiles. The missiles are indicated by the red interface dots, because they are so far away that you’ll never see them until the brief instant when they’re right on top of you.

Now then, on to the first real misconception. Wouldn’t missiles dominate the battle space, being fired from hundreds of thousands of kilometers away? Wouldn’t actual exchange of projectile weapons never happen in reality?

The answer is no, actually. There is a prevailing hypothesis that missiles will soon be the only relevant weapon on the battle space, and it is likely borne out of current trends in modern warfare. ATGWs are already starting to upend tank warfare, and Anti-ship missiles are doing something similar to naval warfare. Indefinitely extrapolating this trend would lead one to conclude warfare will soon be nothing but people sitting in their spacecrafts launching missiles at one another.

But this is not true. CIWS point defense systems are already starting to shift the balance away from missile strikes. As suggested in an earlier blog post, military strategists are even beginning to suggest the development of CIWS systems may bring naval warfare full circle, all the way back to World War I battleship warfare. This isn’t to suggest that missiles are useless. Indeed, enormous salvos of missiles are effective at overwhelming CIWS systems, and they are in game as well.

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A gunship immediately after suffering a nuclear missile salvo. The Whipple shield is mostly vaporized, and the inner bulkhead is glowing orange-hot. Still alive, though!

Yet we begin to see the limitations of each system. Point defense systems, railguns, coilguns, conventional guns, or even lasers, are power limited in this exchange. There is a finite amount of power to use when firing, except for conventional guns. Conventional guns suffer from low muzzle velocities, and high muzzle velocities are crucial to intercepting missiles coming at you at greater than 1 km/s. This power limitation is what prevents these point defense systems from being impervious to missile salvos. Power consumption is limited by radiator mass actually, as simply slapping down more nuclear reactors is easy, but trying to deal with the added mass of all the radiators needed to cool those reactors is much more difficult.

Missiles, on the other hand, are also limited by mass. A hundred-missile salvo is sure to overwhelm any point defense system, but the amount of mass this requires the launching ship to take on is enormous, and will kill its mass ratio. In the end, it turns out the Rocket Equation governs just how effective missiles and point defense systems are. In game, the systems ended up surprisingly balanced, with neither being a dominant strategy, with either being more effective in certain situations, and weaker in others.

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After the armor cools off. The silvery armor up front is the remains of the Whipple shield. Note the multiple holes near the glowing radiators, indicating the bulkhead was penetrated there.

Next misconception, wouldn’t lasers dominate the battle space? Lasers do not suffer from many of the inaccuracy problems that projectile weapons do, and move at the speed of light, so they are literally impossible to dodge. So lasers are the king of the battle space, right?

Wrong. Lasers suffer from diffraction. Badly. The power of lasers in space drops painfully fast with distance, and frequency doubling only ameliorates the issue slightly. Lasers are notoriously low efficiency compared to projectile weapons. But that’s not the main issue. When comparing hypervelocity projectile impact research with laser ablation research, one discovers a stark contrast in their efficacy. Laser ablation is simply less effective at causing damage than projectile impacts. Whereas hypervelocity projectiles cause spallations and cave in armor effectively, laser ablation is poor, with energy wasted to vaporization, radiation, and heat conduction to surrounding armor. On the other hand, at very close ranges, where diffraction is not an issue, lasers outperform projectiles easily. Unfortunately, nothing aside from missiles will likely ever get that close, and even then, they will likely be within close focus ranges for milliseconds at most.

Lasers still useful at long ranges, though. Lasers fill a very specific niche in space warfare, and that is of precision destruction of weakly armored systems at long distances. Lasers are very good at melting down exposed enemy weapons, knocking out their rocket exhaust nozzles, and most importantly, killing drones. While missiles have very few weak points, and can shrug off laser damage with thick plating, drones have exposed weapons and radiators, which makes them very vulnerable to lasers.

In terms of actually destroying enemy capital ships, however, lasers can cut into the enemy bulkhead all day with basically zero effect (I measured the ablation of a monolithic armor plate at one point, and found that the ablation was happening at micrometers per second).

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Lasers can’t really hold a candle to a sustained railgun barrage.

Final, misconception, wouldn’t computers just control everything in combat?

Yes and no, but mostly no. CIWS systems are already computer controlled, and all weapon aiming is similarly already controlled by the computer in game. Anything that has easily computable maxima are solved by computers in game. But there are numerous choices in combat which have no obvious local maxima, and these require human decisions. In other words, you the player and commander need to make these choices. As it turns out, the right or wrong decision can mean the difference between victory and failure.

In game, you won’t be aiming any weapons and firing them, nor will you be flying drones around. The computer can do both better than you, and so the computer will be in control of these things (besides, do you really think you could effectively aim at a speck of light 50 km away moving at 1 km/s at you?).

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The enemy spacecraft is about 30 km away. You’re not gonna outperform the computer’s targeting software. That’s a planet’s city lights in the background.

What you will have control of are the higher level strategic decisions. The orders you give your missiles, drones, and capital ships are crucial decisions you must make in combat. Will you send your missiles in a beeline at your enemy, or perhaps order them to spend valuable delta-v dodging enemy point defense fire? Should you retract your radiators to reduce your heat signature to avoid enemy missiles, and risk the loss of your firepower for the precious few seconds? Should you hold your drones in reserve, close to your carrier, or send them guns blazing as the enemy capital ships approach?

Also as well, one of the critical choices you can make is what to target of the enemy. Each subsystem of every enemy spacecraft is simulated in real time. The reactors draw power, the radiators expel heat, the turrets and guns drain power, all in real time. If you want to disable the enemy’s ability to harm you, the obvious choice is to go for the weapons. But weapons are small, hard to hit unless you have a laser. Going for the enemy’s radiators might be an alternative strategy, with radiators being large, easy targets, although radiators, once armored, are surprisingly sturdy. Not remotely as strong as monolithic armor, but still able to take a reasonable beating of projectile and laser hits. Of course, maybe taking out of the enemy’s engines is more your style, the rocket nozzles being flimsy and poorly armored to allow them to gimbal easier. Plus, a ship that can’t move or dodge is a much easier target.

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This guy’s Whipple shield has seen better days.

But most importantly, orbital mechanics are king in Children of a Dead Earth. Indeed, orbital mechanics are the core mechanic of the game, even, counterintuitively, in combat. Once you reach weapon range, orbital mechanics lose most of their relevance, but everything up to that point hinges on orbital mechanics.

Your incoming speed and angle of attack entering combat, two critical attributes which govern how the combat unfolds, are determined entirely by your ability to use orbital mechanics to your advantage. How near or far you are from the nearest gravity well (planet, moon, or asteroid) has a huge effect on combat speeds. Additionally, evading the enemy before even entering combat is a big part of the game. If you can drain the enemy’s delta-v through effective orbital mechanics, they may fight at reduced effectiveness in combat. If you’re good enough, you might be able to run them out of delta-v entirely, and never even have to enter combat at all!

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Tightening one’s orbit around Venus in a delta-v gambit. Orbits deep in a gravity well force both you and your enemy to expend significant amounts of delta-v to both intercept or evade.

That’s all for now. Next time, we’ll dig into the science of the rockets themselves!

Why does it look like that? (Part 3)

Previously, we examined why lasers and exhaust look they way they do, in addition to spacecrafts’ shapes. Now we’ll look more closely at one specific part of spacecrafts: the heat radiators.

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Fleet Carrier cutaway, also showing all radiators glowing at peak temperature.

Heat radiators are necessary for spacecrafts in order to cool their internal systems. Nuclear reactors produce tremendous amounts of waste heat, and other subsystems produce smaller yet substantial amounts as well. Nuclear-enabled naval ships on Earth can cool their reactors via convection since they are sitting in an enormous bath of coolant already: the ocean. Aircraft and ground craft also have the air to use as coolant to constantly soak away heat.

No such solution exists in space. The lack of any sort of fluid medium in space prevents convective cooling, and there exists no solid material in space to support conductive cooling either. This leaves the one remaining method of cooling: radiation. All materials always radiate photons via Blackbody Radiation, and the amount and kind they do depends on the temperature: hotter materials emit much more energy.

This is where heat radiators come in. These are already in use on the ISS.

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Heat radiators on the ISS on the right and bottom. Solar panels on the left.

They are flat panels with tiny pipes running through their entirety, pumping in scalding hot coolant through one side, and cooled off coolant out the other side. In this way, the radiators form a closed coolant loop with the system that needs cooling. Each set of radiators cools a different system, which is also why some radiators glow orange hot, some glow yellow hot, and some don’t even glow at all (well, they’re actually glowing in infrared, too cold for the visible spectrum).

Unfortunately, you can’t simply dump all of your systems’ coolant loops into a single loop and pipe them through a single enormous radiator because of the second law of thermodynamics. Closed thermodynamic systems will maximize entropy over time. Put another way, heat always flows from hot to cold.

This means that if you have a nuclear reactor running at 1000 K (degrees Kelvin) with its radiators dumping out heat at 1000 K, and you hook it up to a crew module running at 293 K, you have a problem. The crew module and nuclear reactor coolant loop will combine to yield a temperature partway between the two. This will still cool off the nuclear reactor, but then it heats up the crew module until the people inside are cooked.

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Module design of a radiator. Silicon Carbide ceramic core with Stainless Steel finish.

Why are radiators shaped like that? Heat emitted is directly proportional to surface area, so flat plates are the most mass-efficient way to radiate heat: maximum surface area, minimum volume. The jagged shape is to allow them to be retracted inwards to temporarily reduce heat signature (if enemy missiles are homing on you) or to protect them from damage.

Certain other designs of radiators exist, but many of them have issues. Liquid droplet radiators use a liquid pumped between a sprayer and a collector. The liquid allows a much higher temperature since the boiling point of the material is the limiting temperature instead of the melting point for solid radiators. Problem with this is that temperature is by far not the limiting factor of radiators. Silicon Carbide and other similar refractory ceramics can be heated to excess of 3000 K without melting. Even more exotic materials, like Hafnium Carbide, can exceed 4000 K (For comparison, the Sun’s surface is 5778 K) without melting! Their material properties are weaker at that temperature, but they remain still usable as radiators, and as long as they are never dropped below a certain temperature, they will never crack from thermal expansion stress. For reasons I’ll outline below, the internal systems will never emit coolant hot enough to take advantage of these refractory materials’ high melting points.

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Another kind of liquid radiator, the Belt Radiator.

The radiators can never be hotter than the system they cool due to the laws of thermodynamics. However, the nuclear reactors in game can reach up to 3000 K, yet the radiators rarely ever exceed half that. In fact, for one of the reactors used for power production only in game, the reactor core never exceeds 1688 K and the radiators radiate at 1200 K. This reactor’s design is shown below.

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13 MW electric solid core nuclear reactor.

Why are the temperatures so low when the materials used can withstand temperatures twice as high? Two things: the machinery between the reactor core and the radiators all needs to be able to withstand this heat, and the system works best when the temperature drops.

The reactor uses a thermocouple to convert the heat gradient from the reactor into power (note that a turbine-powered system would have somewhat similar limitations). The thermocouple first must withstand the high temperatures. Thermocouples require materials with high Seebeck Coefficients, and these materials tend to have low melting points. On top of that, the high temperature difference involves very significant thermal expansion stress, which is also not something these materials are good at withstanding.

Secondly, thermocouples are most efficient when the temperature drops significantly across them. This yields an interesting optimization problem. If the temperature drop from reactor to thermocouple is high, then the temperature drop from the radiators to space must be low, and the reverse is true. Remember that radiators perform best when their temperature is high.

This means the more efficient the reactor is at producing power, the harder it is to cool the system. On the other hand, a low efficiency reactor is very good at cooling itself. This problem yields two different valuable qualities that are inversely proportional to each other, and no local maxima can be found for both simultaneously.

In the end, for the above system, the somewhat reasonable point for both properties was at 1688 K for the reactor and 1200 K for the radiators.

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Color temperature of Blackbody radiators.

That 1200 K temperature is why the largest radiators on spacecrafts glow orange. In fact, you estimate the temperature of radiators by their color, and from that you could estimate their purpose.

What about inter-reflection? Inter-reflection of radiators is a problem, since the heat from one radiator can be re-absorbed into another. This is exacerbated by Kirchhoff’s Law of Thermal Radiation, which states that the emissivity and absorptivity of a material is identical for any given wavelength of light.

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Tail end of a spacecraft, showing how radiators will re-absorb each other’s heat radiated to some degree.

Blackbody radiation emits not simply perpendicular to the emitting surface, but in a full hemisphere of directions. Note that the intensity does fall off with the cosine of the angle from the perpendicular, however, so emission is most intense perpendicular to the radiator, and it falls to zero directly parallel to the surface. This does mean that these radiators will suffer inter-reflection, which will reduce their total efficiency, but they still will do the job, and can still be placed next to each other at narrow angles to each other.

Finally, can these radiators be armored? The answer is yes, contrary to what other sources may claim. Radiators are simply panels with material with tubes hollowed out in them to pass coolant through. One can simply increase the panel thickness beyond the tubes to add monolithic armor, and the refractory nature of the radiator materials means they will remain very strong even at orange-hot temperatures.

But, thicker monolithic plating reduces the efficiency of the radiators, because it will negatively impact the Heat Transfer Coefficient of the convection-radiation system. Thus, this yields yet another optimization problem, with radiator protection being inversely proportional to radiator efficiency. One will generally find that the added mass and poorer efficiency is often a fair trade for radiators that can actually withstand a serious beating.

That’s all for radiators! Next time, we’ll look into moment-to-moment space combat itself.

The Essence of Space Warfare

Children of a Dead Earth started with the question “What would space warfare actually be like?” The game itself is the answer to the question, but in this post, we’ll also go over the answer, based on how the simulation turned out.

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Head to head combat between two fleets of capital ships.

Modern warfare doctrines have very little on space warfare. There are a few public documents from the cold war era concerning satellite warfare, but they all hinge on several conceits that are not terribly relevant to full space warfare. In particular, they always assume Earth’s gravity and atmosphere as the main celestial body, and they assume that everything will stay in very low orbit, hugging Earth’s atmosphere. As a result, these doctrines are much closer to high altitude aerial warfare or ICBM warfare than actual space warfare.

There is always a tendency to want to take a certain kind of present day modern warfare and extrapolate it to space, or to try to find parallels. Would space warfare be similar to modern naval warfare, carriers launching fighters and bombers at each other, without ever seeing one another? Or perhaps like World War 2 fighter plane dog fights? Or maybe it would be similar to submarine warfare? Most soft science fiction takes this approach, but as it turns out, space warfare ends up being very dissimilar to all of these.

But there are similarities here and there.

For instance, the spacecraft sizes tend to be similar to modern naval carriers and destroyers. Yet, despite being similar sizes and masses, the masses distribution is radically different. An Arleigh Burke class guided missile destroyer masses at 9.80 metric kilotons, while a spacefaring Laser Frigate in Children of a Dead Earth masses at 7.71 metric kilotons, despite them both being 155m long. Whereas the majority of the missile destroyer’s mass comes from the hull, in space, the majority of the mass is in the propellant. This is due to the rocket equation, and the resulting need for extraordinary amounts of propellant to get any delta-v. Inside spacecrafts, it’s mostly just propellant tanks.

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The basic stats of a Laser Frigate, a medium-large warship. Space Shuttle Orbiter for scale.

Similarly, the carrier and fighter model of modern naval warfare also translates over to space warfare well. However, fighters become drones, entirely remotely operated on the carrier (this evolution is already starting to happen in present day US Military doctrine with UAVs). And another important weapon shows up, the missile salvo, an evolution of the modern ATGW or ASM. A spacecraft carrying 100 nuclear missiles is just as common as a spacecraft carrying 100 drones, and it serves its own unique combat purpose as well.

A surprising parallel is found with World War 1 battleships. As point defense technology evolves, drones and missiles no longer rule the battle space. Indeed, very recent examinations of modern US Naval doctrine have suggested that as point defense technology advances, we may see a resurgence of battleship warfare as point defense technology outpaces missile and drone attack capabilities. In game, point defense in the form of lasers and projectile weapons both are very effective at anti-missile and anti-drone warfare, yet both can be overwhelmed given large enough salvos of missiles or drones. As a result, if you’re weak on drones or missiles, getting in close with the capital ships themselves is a viable tactic. The advent of better and better projectile weapons seals the viability of this tactic.

But while there are plenty of parallels, there are far more differences unique to space warfare.

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A highly periodic orbit around Luna.

For one, simple movement in space requires understanding of orbital mechanics. Everything is always moving, relative to nearly everything else in space. You can’t stop in space unless you land on a celestial body, and doing so usually costs so much delta-v that’s it’s not an option. Going in depth into the orbital mechanics will be covered in another blog post, but one should know that it does yield counterintuitive results. For instance, if in the same orbit as a target, you will never get catch up to them, and you have to slow down to catch them, or speed up to let them catch you. This is because decelerating increases your orbital speed, and accelerating reduces your orbital speed.

One byproduct of these orbital mechanics is the speeds in space are truly enormous, far greater than anything you’ll ever see on Earth. Approaching your enemy at 5 kilometers per second (about 10 times faster than machine gun fire) is quite common. High speed warfare makes missiles deadly, as the time to respond with point defense drops down to seconds or less. At the same time, high speed combat allows one to dodge incredibly easily. A small nudge in any direction when the enemy is 100,000 kilometers away means your enemy will miss by kilometers. Despite the high speeds, combat can take place at very low speeds, and indeed, this is often desired for capital ship broadside warfare. Approaching an enemy moving 5 km/s relative to you and entering their exact orbit to yield a relative velocity of 0 km/s is completely doable.

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A gunship fires three different projectile weapons at an incoming salvo of missiles in the distance. Neptune in the background.

The scale and environment of space is unique as well. With no stealth in space, you will see your enemy half the solar system away, and you’ll be able to track their movements six months out or more. This makes surprise and deception nigh impossible in space, and warfare often comes down to nearly evenly matched fleets engaging in combat. With these enormous scales, skirmishes between two fleets in orbit around the same body may happen days or even weeks apart. For instance, two fleets in the same orbit, but one running retrograde, may experience five seconds of combat where the enemy zooms by at ridiculous speeds, and then ten days of downtime while the crew prepare for another five seconds of combat.

Delta-v, a measure of the total amount of velocity change one has, based on propellant left, is critical in space warfare. Capital ships tend to have much more delta-v than drones and missiles, but much lower acceleration. This means capital ships can dodge drone or missile intercepts by running them out of delta-v, and it makes for a very effective defensive strategy. On the other hand, if plotting one’s orbital mechanics cleverly, drones and missiles can still intercept capital ships using raw acceleration. Running enemy fleets out of delta-v is a very effective way to choose how pending battles will take place: at high speeds or low speeds, and where along their orbit.

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A shrapnel payload impacts the side of a spacecraft and detonates. Ceres in the background.

A final surprising effect is caused by the lack of atmosphere in space: explosions are pitifully weak. Without an atmosphere, conventional explosives simply blast a thin layer of gas on their targets, nuclear weapons are reduced to nothing more than glorified flash bulbs. Of course, the amount of light released by nuclear weapons is still great enough that they can melt through thick armor at very close ranges, so nuclear missiles are still viable for combat. But their effects fall off so quickly in space that they are almost contact weapons rather than area of effect weapons. If a salvo of nuclear missiles can connect with their target, though, they can be quite devastating. Conventional explosives also only tend to be effective when used to detonate a payload of shrapnel at high velocity at the target.

That’s a high level overview of how space warfare actually unfolds. Later posts will examine it closer, the actual technologies used in combat, and how engagements play out second by second.

How Realistic Is It Actually?

Children of a Dead Earth was developed primarily to answer the question: What would space warfare actually be like? Various hard science fiction novels and other media have attempted to answer that question in the past, but these works have always come up short, at best relying on rampant speculation, and at worst, inventing fictitious technologies to support their conclusions.

Children of a Dead Earth solves these issues by first being a complete and utter simulation of space warfare, and second by relying only on technology that has been explicitly demonstrated to work. This is critically important: there is absolutely minimal guesswork in this game, instead everything is necessarily derived from equations, and the mathematical results of these equations.

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In case it is not obvious by now, Children of a Dead Earth was designed with no vision in mind, unlike just about every other videogame, novel, or movie attempting to do the same. This is because I never wanted to corrupt the ultimate goal of this project, which was to discover what space warfare would be like, rather than to say what space warfare would be like. To have an initial vision when building this game would have been starting with a conclusion, and then twisting reality to support that vision. By starting with no vision whatsoever, the conclusion would be generated by implementing the equations, and observing how they interact. In this way, the end result of Children of a Dead Earth was little like I had ever imagined actual space warfare would be like, and this will probably be true for you as well.

To reiterate: Children of a Dead Earth is a simulation first, and a game second. No amount of realism was compromised to make things more fun, or to make things prettier. It is science first, everything else second. Despite this, the game still remains fun, but you’ll find it plays very differently than any space warfare game you’ve ever played.

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Some assertions in making this game. All technologies implemented in Children of a Dead Earth have all been demonstrated to be feasible, and successful prototypes of all of them have been created in real life. For engines, this includes Nuclear Thermal Rockets, Combustion Rockets, Resistojets, and Magnetoplasmadynamic Thrusters. For weaponry, this includes Conventional Cannons, Railguns, Coilguns, Linear Induction Motor Launchers, and Arclamp Pumped Solid State Lasers. For powerplants, this includes Radioisotope Thermoelectric Generators and Thermoelectric Solid Core Fission Reactors. And of course, radiation shielding, monolithic armor plating, Whipple Shields, and heat radiators are all fully implemented in game as well.

Another assertion: stealth in space is not feasible. It’s a topic large enough for its own post, so I’ll summarize: if you actually want stealthy engines, you need to either to move so slowly that getting between planets will take centuries, or you need engines that are insanely efficient, more efficient than any technology ever imagined.engine.png

A final assertion. Spacecrafts will be crewed, but any concept of ‘fighters’ will not be a thing. The mass of having people is significant, and an issue. The spaceflight analogue to fighter jets do not need a pilot, and instead these drones can be remotely piloted by the nearest capital ship. Such a thing exists today already: UAVs. On the other hand, capital ships do need a crew, because of speed of light lag. Trying to command a spacecraft from across the solar system is not just highly prone to jamming and spoofing, but the seconds or even minutes of lag in command would prove fatal in combat. On the other hand, drones will be close enough to their carrier ship that speed of light lag is not a significant issue.

How granular is the simulation? Extremely granular. Let’s take railguns, for instance.science-railgun.pngTo determine the muzzle velocity of a railgun, an equation for the force applied on the armature was used. This equation was numerically integrated to determine the acceleration of the projectile over time steps sometimes as granular as nanoseconds across the entire rails. The equation itself requires knowledge of the inductance of the rails, as well as the resistance across the rails. Inductance is generated from another equation depending on the relations between the rail dimensions, and the resistance is calculated from the material properties and dimensions of the armature and rails. This also informs the size and mass of the railgun, which is critical for ship design later on.

But that’s just the beginning. A weapon is more than a projectile launched. It also generates heat, which can melt the rails or the armature itself. The ablation of the rails and of the armature are calculated separately from additional equations utilizing the material specific heat, conductivity, density, dimensions, and vacuum permeability. If the ablation is too significant, the railgun will not operate properly, and you will be unable to operate the railgun. Even if you do not ablate your rails, if the bulk temperature of the rails becomes too high, the materials will be unusable until they cool, and you must wait for the railgun to expel its excess heat via radiation.

All projectiles have minor imperfections. A tiny off centering of the armature can produce significant inaccuracies in firing, and this too is calculated. The recoil of the railgun can become imbalanced, and cause significant cantilever beam deflection with the railgun barrel. Based on the tensile strength of the rail material and the Elastic Modulus, this instability is another factor that one must work around when designing railguns in Children of a Dead Earth, lest they shatter when you fire them.

And finally, don’t forget about the turrets! The more massive you make your railgun, the greater the moment of inertia of the weapon, and the harder it is to rotate with the reaction wheels inside the mantlet housing. You will find that you have to make tradeoffs with your weapon, as a railgun which takes ten minutes to aim at a target is a railgun which is not usable for combat.

That’s a taste of the depth of simulation within Children of a Dead Earth. Next up, I’ll be tackling how space warfare actually ended up, based on what has sprung forth from these equations.

 

Why Does it Look Like That? (Part 2)

We’ve looked at lasers and engine exhaust, now let’s take a look at the spacecrafts themselves. They look something like cylinders with glowing prongs on the ends. Soft science fiction would have you believe spacecrafts would like anything from fighter jets to battle ships to strange, blocky constructs. Taking inspiration from NASA or SpaceX, one might assume future spacecrafts would simply look like rockets. So why do they look like they do in game?

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Something to note: All spacecrafts in game are spaceflight-enabled only, and are not designed for in-atmosphere operations, because the game takes place entirely in space. Atmosphere-enabled spacecrafts would look closer to modern fighter jets or to the space shuttle.

So, why is the shape a tapered cylinder? This spacecraft is a collection of internal modules (crew modules, propellant tanks, powerplants, radiation shields) wrapped in armor, with some external modules (heat radiators, rocket engines, and gun turrets). From the cutaway, you can clearly see the internal modules.

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Due to the rocket equation, mass is a premium on spacecrafts, as having heavy spacecrafts exponentially increases the amount of propellant needed to get your spacecraft around the solar system. Thus, everything needs to be as low density and light as possible.

So what exactly makes a spacecraft massive? Here’s a sample mass pie chart pulled from ship design of the above craft:

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Aside from propellant, armor is by far the heaviest part of the spacecraft. This immediately implies one thing: Armor must be a convex hull to save on mass. Concave shapes always have greater surface area than a comparable convex shape, and thus will always be heavier. The more concave the shape is, the more massive the armor will be.

If armor must be convex, then the shape of the spacecraft must likely be a geometric primitive: a cone, a cylinder, a tetrahedron, a sphere, a prism, a cube, and so on. (Maybe The Borg were on to something…)

The ideal shape, the one that has the greatest volume with the lowest surface area, is a sphere. But there are numerous problems with a sphere.

The other significant consideration governing spacecraft design is cross sectional area. In combat, the cross section of a spacecraft is the primary factor which determines the range of enemy projectile weaponry. A smaller cross section yields a harder target to hit, and requires the enemy to get closer to be able to hit it. Spheres are awful in that regard. Their cross section is a giant circle, easy to hit, easy to destroy, just aim for the center.

Additionally, the nuclear powerplants and nuclear thermal rockets emit tremendous amounts of radiations. The crew modules need to be both far away from these systems and/or heavily shielded against them. A sphere is a poor shape for both of these things.

Finally, it’s a lot harder to pack things into a sphere. Packing things into a cylinder is much easier, and packing them into a cube is easiest. With a sphere, you end up with a lot of unused space at the edges.

This leads us to the next shape, the cylinder. A cylinder is second to the sphere in terms of greatest volume to surface area ratio. Cylinders, if made long and thin, can have an extremely small cross section for their volume, making them very hard to hit. Additionally, they naturally provide distance between the powerplants and the crew modules, because of their length, lessening the need for radiation shielding. Modules, such as propellant tanks, pack very nicely into this shape, and waste little space in this way. An additional benefit of the cylinder is that it can be rolled very quickly to bring a broadside of weapons to bear.

Next, why the taper? Why not a simple cylinder? Sloped Armor is a way to drastically increase the effectiveness of a simple monolithic plate of armor. A plate of armor angled at 45 degrees reduces penetration by approximately cos(45 degrees), or about 29%, no small benefit!

A gradual taper from the start of the cylinder to the end takes advantage of sloped armor. Projectile weapons attacking from the front as well as from the side will similarly be reduced in effectiveness by this slope.

Thus, there you have the reasons behind the shape of combat enabled spacecraft. More on the heat radiators later.

Why does it look like that? (Part 1)

Children of a Dead Earth never compromises scientific accuracy for anything, especially not visuals. This leads to a lot of counter-intuitive visual effects, so this is a page explaining some of them.

The first thing you may wonder is why lasers appear to be visible and slow moving in the game, since they obviously are not in real life.carrier taking fire4.png

Those are not lasers, not the orange beams, not the red beams, not the purple ones! Those are all pyrotechnic tracers on projectile weapons. Tracer rounds are used to correct accuracy of bullets, and the differing colors are different pyrotechnic colorants (which all use real world emission spectra data to approximate their real life color). Different colors are used between different weapons to help targeting software distinguish between them.

This is an actual laser in game:laser hit.pngThe violet flash up high is a ship tens of kilometers away firing a violet laser, and the violet flash on the ship with ejected glowing matter is the laser impact. The actual beam is invisible, and all you can see is the firing location, and the impact location. The firing location is visible due to diffraction. When the laser is not in the visible range of light, all that you will see is the ejected matter, and the subsequent red or orange glow of melted armor.

Next up, why does engine exhaust look like that? I’ve seen SpaceX’s rockets launch, and their exhaust looks nothing like that.engines.png

First, the shape. One usually finds rocket exhaust to appear as curving away from the nozzle, possibly with bright shock diamonds. As a rocket gets higher in altitude, the curvature lessens, because the air pressure lessens. In space, with no atmosphere, the curvature vanishes entirely, and the exhaust plume expands outward linearly.

The angle of expansion is dependent upon two things: the exhaust velocity of the rocket itself, and the temperature of the plume at nozzle exit. The temperature is important because it directly governs the outward velocity of the plume: hotter temperatures means the gas expands faster. A plume which expands at the same speed as the rocket’s exhaust velocity will have a 45 degree angle of expansion. As you can see in the above image, the angle is less than that, so the exhaust velocity must be greater than the expansion velocity.

Second, why is it transparent rather than a bright orange or white plume? In atmosphere, the air pressure compresses the exhaust as it tries to expand, which causes it to curve back in on itself and form shock diamonds. As a result, the temperature of the gas remains hot, hot enough to keep emitting tremendous amounts of light. In space, the exhaust gas expands unrestricted, and the temperature drops immediately as soon as the exhaust leaves the nozzle. This is simple gas laws: in an unrestricted vacuum, a gas will expand in volume and reduce in temperature as the kinetic collisions between the molecules lower rapidly.

Finally, what about the shimmering effect? Is that supposed to happen in a vacuum? It does, whenever the gas’s index of refraction differs from that of the medium it is in (in this case, vacuum, which has an index of refraction of 1). In the above image, the exhaust is dissociated methane, and the carbon expelled does have a refractive index different enough from vacuum in the visible range. However, you will find that other engines, such as rockets which have only pure hydrogen in their exhaust plumes, will not have this shimmering effect, since hydrogen has an index of refraction very close to 1 at visible ranges.

That’s all for now, more to follow!

Children of a Dead Earth

Children of a Dead Earth is an upcoming hard sci-fi space warfare simulator. On this blog I will post developer musings, random tidbits, and the like. A quick primer on how scientifically accurate Children of a Dead Earth is:

Realistic Orbital Mechanics – With a full N-Body Simulator, all manner of orbital dynamics are supported, from Orbital Perturbation, Gravity Slingshots, Hyperbolic Trajectories, and Lagrange Point Orbits. By comparison, most other games use the Patched Conic Approximation, which is extremely inaccurate at certain scales, and can’t simulate most of the above features.

Realistic Scale – The solar system is modeled perfectly to scale. The sizes of planets and moons are just as enormous as they are in real life, and the distances between planets are equally vast. Other games fudge the sizes of planets, or the densities of things, and almost all fudge the distance between planets.

Realistic Technology – Every technology in game was implemented using actual equations from engineering textbooks and white papers, from the exhaust velocity of the nuclear thermal rockets, to the thermal expansion stress of the railguns when firing. You can even tweak the actual properties of these systems to see how they affect their performance, such as altering the length and thickness of your railguns to determine how that affects the inductance, or altering the nozzle length and expansion angle to see how that affects rocket exhaust velocity.

Realistic Space Warfare – All combat in game is a physically and scientifically accurate simulation. Every gun turret draws power not just for firing, but also for the reaction wheels that orient it. Every propellant tank, filled or empty, affects the delta-v and the mass distribution of ships, affecting how the ship will tumble when torqued. Every projectile impact damages each tile of armor based on actual hypervelocity impact studies. Nothing is handwaved, nothing is glossed over.

More on the nitty-gritty details of the game in later posts.