Sunday 12 May 2019

Actively Cooled Armor: from Helium to Liquid Tin.

We have seen designs for long ranged particle beams and powerful lasers. Could they be the end-all, be-all of space warfare? Not if we fend off their destructive power with actively cooled armor.
Let's have a look at the different cooling solutions, from high pressure gas to liquid metal, and evaluate their relative effectiveness.

The armor curves away to hide the radiators from attack from the front.
The traditional solution for defeating directed energy weapons such as particle beams and lasers is to use solid plates of armor. The armor material would ideally have a high heat capacity so that it doesn't heat up too quickly, and an excellent melting or boiling energy.
Graphite excels in both. It is clearly superior when compared to steel or aluminium. 

We have written about the effectiveness of graphite when facing laser beams, and how we can use different techniques such as sloping, rotation and reflective surfaces to further increase the energy required to remove armor. 

However, certain techniques described in Lasers, Mirrors and Star Pyramids have limitations. Reflectivity in particular cannot be counted upon in all situations. While we might have broadband dielectric mirrors that effectively reflect a vast range of wavelengths, an enemy will eventually field lasers specifically meant to defeat them. 
They might select polarizations against which the mirror is less effective, they might use beams of wavelengths too short to reflect (usually below 200nm), or even replace lasers with particle beam weapons that ignore surface features entirely.

What can we do against such mirror-defeating techniques? Can we increase the effectiveness of armor even further than what was calculated in Lasers, Mirrors and Star pyramids?

Maximizing that energy value means you can get by with less armor and have more mass dedicated to winning tools such as propulsion or ammunition.

Passive armor

We can start with a reference to compare everything else to.

Passive armor is simple in design and construction. It is made to handle as much heat as possible and prevent it from leaking into the spaceship.
Graphite electrodes in an electric arc furnace.
A good example, as mentioned above, is graphite. It first needs to be heated to about 3500K before it starts being degraded. At 4000K, it turns into a gas. Between its heat capacity and vaporization energy, it takes roughly 60 MJ/kg to vaporize. A stronger carbon-based material would take an equivalent amount of energy while also being physically strong.

We can therefore expect graphite to handle a laser intensity of 8.5 MegaWatts per square meter for extended periods of time. This is a value calculated from the Stefan Boltzmann blackbody radiation equation, as it is the intensity required for a black surface to sit at an equilibrium temperature of 3500K.

For the laser beam to start digging into the carbon at an appreciable rate, it must first overcome a 14.5 MW/m^2 threshold so that the temperature rises to 4000K, then it must add 60 MJ for each kilogram of carbon to be vaporized.

We mentioned active cooling. Being able to remove 11 MW/m^2 using a coolant looping through the armor material significantly raises the damage threshold. In this case, it is increased to 19.5 and 25.5 MW/m^2 respectively.

Two other techniques covered in Lasers, Mirrors and Star Pyramids are valid in all situations: sloping and rotating.
We can add a good compound slope to the carbon surface: 80 degrees vertical and 67.5 degrees horizontal. This spreads the laser beam over a surface area about 15 times greater. Consequently, the laser now needs to reach an intensity of at least 292.5 MW/m^2.

Rotation spreads the beam further. We could have a situation where the beam diameter is 12.56 times smaller than the armor’s circumference, and the average beam intensity is reduced by the same factor.

All in all, carbon materials can survive 3.67 GW/m^2 for long periods of time or 4.8 GW/m^2 while ablating.

If we have a 100 MW laser with a wavelength of 450nm, being focused by a 4 meter wide mirror, we would be able to damage a simple layer of carbon at a distance of 27,025 km. Using all the techniques just mentioned, the range is shortened to 1,300 km.

Why shorten ranges?

At very long ranges, space battles are boring with little room for tactical decisions.
From here.
We cover this issue in The Laser Problem: any moderately powerful laser can render maneuvers pointless. Warships cannot escape beam weapons. Even at distances where light lag becomes significant, the beam can be divided to cover a wider area while maintaining its destructive intensity.

Shorter ranges allow for acceleration to matter more. Other weapon systems that do not have the supreme range of lasers and particle beams can come into play, such as missiles and kinetics. Angular separation starts to matter, allowing for flanking attacks against warships forced to be more well-rounded to fend off multiple weapons from different directions.

It is also important from a narrative and visual perspective. Actions taken have a more immediate effect. Events happen quicker and the danger or relief is greater. It is easier to depict battles and the faster pace will be more agreeable to viewers.

Actively cooled armor

The 1,300 km figure given in the previous example is situational.

It relies on the beam coming in from an ideal angle, which is straight down the edges of the star pyramid shape. If instead it came from a flanking angle, perhaps 80 degrees from the front, then the vertical slope of 80 degrees is completely negated. The benefit from sloping falls from a factor 15 to just 2.6, which makes the laser effective from a distance (15/2.6)^0.5: 2.4 times greater.

In other words, a warship that sustain laser fire from the front at 1,300 km is vulnerable to flanking attacks out to 3,122 km.

The benefit from rotation also varies with distance, as it changes the size of the beam’s spot relative to the target’s circumference.
  • Intensity reduction by rotation = Beam spot radius / (3.142 * Armor radius)
The reduction is a dimensionless number.
Beam spot radius and armor radius are in meters.
The beam spot radius decreases linearly as the distance decreases. 

If the warship is being shot at a distance two times closer, then the benefit from rotation is twice as great. This inverse relationship means significant gains from rotation at close distances and small gains at long distances.

Distances, mirror sizes, beam wavelength, warship radii and even spot shapes are all variable, so we are unlikely to ever have one single number to describe the effect of rotation.

What technique instead can we rely upon in all situations? Can we increase armor effectiveness without the enemy having to sit in certain positions and relative angles?

Active cooling is the solution.
We looked at figures of 11 MW/m^2 being removed by flowing water over hot surfaces. Further research shows fusion diverters and rocket engine chambers surviving 100 MW/m^2.

We can go further, to absorb much more power.

For the sake of comparison, we will be using a standardized model where a flat plate of armor sits under the glare of a laser beam. It conducts heat through a heat exchanging surface to a coolant flow underneath. The armor is 1cm thick and the coolant flow channel 1cm wide. We will calculate the power required to pump coolant to a certain velocity, and won’t allow velocities that cause turbulence in liquid or supersonic compression in gases. The heat is radiated away using simple 1mm thick carbon fiber radiators.

There are four factors to consider for a proper comparison. The first is the heat that can be removed per square meter. The second is the pumping power requirement. The third is battle damage resistance, which is not as straightforward. The last is the radiator surface area required to handle the heat.

We won’t be working out the effect of thermal conductivity as in most cases it is not the limiting factor.

Gas cooled armor
Gas cooled rocket nozzle
Gases are an interesting coolant as they have no upper temperature limit. If the armor material is carbon and it can withstand a 3500K temperature, then we can select any gas and heat it up to that temperature in the heat exchanger.
We are looking for the gas with the highest heat capacity. High heat capacity means less gas needs to flow through the heat exchanger to pick up the heat and carry it away. Less gas means reduced pumping power. We also want a gas that doesn’t condense at lower temperatures.

Hydrogen is the best. However, it is reactive. It will chemically reduce the carbon and degrade it. Helium is a second-best alternative that is chemically inert. We want it entering the armor at 500K, heating up to 3500K and exiting to be cooled in a radiator back down to 500K. If it does not reach the desired temperature in one pass through the heat exchanger, it can be recirculated through at the cost of doubling the pumping power.

The speed of sound in helium at 500K is 1315m/s. At 3500K, it is 3480m/s. We are limited to pumping below the smaller figure, so let’s give it Mach 0.9 (1183m/). This means we can push 1.13 kg/s under each square meter of armor at 1 bar of pressure, and 28.25 kg/s at 25 bar.

Helium absorbs 5.19 kJ/kg/K. Over a temperature rise of 500 to 3500K, 28.25 kg/s will absorb 439.7 MW/m^2.

Pumping power requirement depends on the pressure drop across the heat exchanger. It will be the highest of all designs considered in this post.

The radiators happily handle the heat using 4994 m^2 and 5 tons of mass.
Pumps will most likely resemble those of rocket engines.
Gaseous cooling has the advantage that it can increase its performance with increased pumping pressure, and can maintain some degree of functionality while sustaining battle damage. A sudden increase in temperature is not so dangerous as pressure build-up can be vented into space.

However, they have the highest pumping power requirements. While we are ignoring thermal conductivity in our calculations, gaseous cooling using helium has the lowest thermal conductivity of all the fluids we will be considering. This imposes certain design restrictions on the heat exchanger interface with the gas, which is trouble when we want the gas to be flowing through it at near Mach speeds.  

Metal vapor cooled armor

Helium has high heat capacity but low density. We need a lot of pumping power to push enough volume through the heat exchanger to draw a decent amount of heat away.
Metal vapour prepared for use as a lasing medium.
The gases with the highest densities are metal vapours. The same volume brings a lot more mass throughput and therefore cooling capacity.

We want a metal that is dense but boils easily. Mercury is ideal. It boils at 630K, so we’ll set the minimum temperature to 750K to prevent it condensing back into a liquid. As before, we heat it up to 3500K.
Boiling mercury.
The average density of a mercury vapor at 25 bar, between 750 and 3500K, is 48.7 kg/m^3. It would have a heat capacity of 104 J/kg/K and a speed of sound of 227 m/s at 750K. Putting all this together, we expect to push 99.5 kg/s through the 1cm wide heat exchanger and extract 28.5 MW/m^2. This is a much lower performance than with helium.

Pumping requirements are a significantly lower. It is estimated that mercury vapours remove 5 kW of heat from the armor for every watt of pumping power, which is about 20% better than for helium. Only 1563 m^2 of radiators weighing 1.6 tons are needed to handle the heat.

The reduced pumping requirements means that you can use many smaller pumps to push the mercury gas through heat exchangers, which helps with redundancy. However, a sudden pressure drop from holes created in the armor are likely to cause the mercury to suddenly expand, cool and revert to its liquid form. The droplets would quickly block gas flow through narrow channels in the heat exchanger.

Another difficulty is that mercury can solidify completely behind unheated or damaged armor. Re-establishing a coolant flow is impossible unless the mercury is boiled again to clear the heat exchanger’s channels. Armor would have to ‘go hot’ before battles and prevented from cooling down too much when not under beam attack.

Water cooled armor

The traditional cooling liquid is water. It is much denser than a gas, has good thermal conductivity and very high heat capacity.

Water’s temperature range is its main limit. If we use it as a liquid, we impose that we use very low temperatures to reject heat from the radiators. Consequently, huge radiating areas would be needed. If we use it as a gas at the same temperatures as helium or metal vapours, it will corrode the heat exchanger and chemically attack everything it touches.

Instead, we use a phase change design. High pressures allow water to stay liquid beyond the standard 373K boiling point. It is then heated into steam, up to the maximum temperature the heat exchanger can handle without corrosion. After passing through the radiators, it condenses back into water.
The complicated phase diagram of water
At 25 bar, we can retain liquid water at 480K. That will be our minimum temperature. It has a density of 1197 kg/m^3. We find steam turbine coatings such as chromium steel able to resist 873K steam for thousands of hours, or chromium-niobium alloys at 923K. That will be our maximum temperature. Steam has an average heat capacity of 2.56 kJ/kg/K between 480 and 920K.

The phase change from liquid to gas also absorbs energy. For water, this is a whopping 1840 kJ/kg when starting from 480K.

Adding the heat absorbed by the phase change and then rise in temperature, we obtain a total of 2966 kJ/kg.

We cannot allow turbulent flow through the heat exchanger, as this drastically decreases the heat transfer rate. Based on a fluid’s Reynolds number and viscosity, we can estimate the maximum velocity before the start of turbulent flow. In this case, it can only be 24 m/s when passing through a 1cm gap.

With that flow rate, we get as much as 286.8 kg/s passing through the heat exchanger removing 850 MW/m^2.

This is impressive performance. The pumping power requirements are drastically lower than any gas (on the order of 2 kW of heat removed per watt of pumping power). Water has the advantage of gaining most of its heat removing capacity through its phase change when cooling armor from as low as 373K. Increasing the temperature of the armor and therefore of the heat exchanger only improves performance.
Another advantage is that it is likely to serve a second role as propellant on spacecraft. Electric, nuclear and solar rockets can all use water. The consequences are that the coolant needed for the armor’s active cooling does not have to be dead weight, and that after being heated into steam, it can be pushed through a nozzle instead of passed into radiators. During battle, if radiators are hidden or destroyed, the armor can still be kept cool by using water as an open-cycle coolant.   

There are downsides though. Water increases in volume over a thousand-fold between liquid and gaseous states. Designing a phase change heat exchanger where liquid enters one side and gas exits the other is tricky to do, and is unlikely to work after receiving battle damage. In fact, creating a hole in the heat exchanger would release pressure and allow the water entering as a liquid to suddenly boil and practically explode in the pipes.
Just like mercury, water can freeze into ice when not heated. Damaged pipes can see themselves blocked by this ice, cutting further cooling. Thankfully, the phase change from liquid into solid also takes a lot of energy, so there is usually plenty of time to re-heat the water and get it flowing again. 

The biggest disadvantage is the maximum temperature restriction on the armor and heat exchanger. Above 920K, the thin layer of water or steam in contact with the heat exchanger starts corroding the protective layer quickly. 
If the armor is at 3000K, it will be superheating a small quantity of steam to a vigorous oxygen-hydrogen plasma, even if the average temperatures within the heat exchanger as within bounds. Therefore, if the laser intensity overwhelms the cooling capacity and the armor starts heating up to higher temperatures, we will start to see degraded heat exchangers and a decrease in cooling capacity. This is a self-reinforcing cycle that destroys the armor.  

Eutectic cooled armor
Sodium-Potassium coolants for use in TOPAZ-II space reactor.
Liquid coolants have much reduced pumping power requirements. Instead of water with its restrictive temperature limitations, we might select a coolant that can handle much temperatures. 
NaK properties.
Eutetics are mixtures of two or more elements that have a lower melting point than either pure element. A prime example is sodium and potassium used as ‘molten salt’ coolant in nuclear reactors or solar energy storage facilities. Sodium and potassium melt at 371K and 337K respectively, but their eutectic mixture melts at just 260K.
Looks a lot like mercury, but not toxic. From here.
We will be using Galinstan. It is a mixture of gallium, indium and tin. It melts at 254K and boils at 1573K. With a density of 6440 kg/m^3, a heat capacity of 296 J/kg/K and a laminar flow velocity of 85m/s, we find that we can remove 1738MW/m^2 while radiating away heat at 500K.  

This incredibly better performance is possible due to the fluid’s high density and high viscosity. Pumping requirements will be significant, and you’d need 490,606 m^2 or 491 tons of radiators for every square meter of armor receiving this intensity, but it is worthwhile when it can reduce ranges by so much.
Galinstan would work perfectly inside a liquid droplet radiator.
A note on the radiator requirements: this number is not to be used simply as it is presented. 490,606m^2 are only needed if the enemy beam covers an entire square meter with 1738 MW of power. It is much more likely that a much less powerful beam, for example 100 MW, is focusing its power onto a small spot, perhaps 27cm wide. This gives the same intensity (1738 MW/m^2) but the total heat that must be handled is only 100 MW. The radiator area needed to handle the heat is just 28,218 m^2.

One advantage of Galinstan is that it remains liquid at very low temperatures, so there is a much reduced risk of it solidifying and blocking cooling channels. Another is that as an electrically conductive mix of metals, we can use electromagnetic pumping that can end up being more efficient and more damage resistant than conventional pumps.

The main disadvantage is that lasers or particle beams can strike multiple spots along an armor surface without warning, so the coolant flow much be able to compensate for any heating across its entire surface. In other words, the pumps must consume large amounts of power to keep Galinstan flowing across the entire armor surface!

Another challenge is when beam intensity overwhelms cooling capacity. 1573K is a decently high boiling point, but it is still lower than the 3500K that carbon materials can handle. A hot spot can create vapor bubbles in the Galinstan flow that could cause destructive cavitation or blocked flow in small channels of a hat exchanger.

Liquid metal cooled armor
There are liquids that can handle much higher temperatures without boiling. Liquid metals have the highest boiling points.

To be a good coolant, we could use a metal with a fairly low melting point, a very high boiling point and the best heat capacity possible. There are many good choices, including plutonium, but we will look at these four in particular: tin, indium, aluminium and cerium.

Indium has a melting point of 430K and a boiling point of 2345K. It has a density of 7020 kg/m^3 and a heat capacity of 233 J/kg/K. We work out that 2944 MW/m^2 can be removed between 500K and 2300K.

Tin has a melting point of 505K and a boiling point of 2875K. It has a density of 6990 kg/m^3 and a heat capacity of 228 J/kg/K. We work out that 3666MW/m^2 can be removed between 550 and 2850K.

Aluminium has a melting point of 934K and a boiling point of 2792K. It has a density of 2375 kg/m^3 and a heat capacity of 896 J/kg/K. We work out that 3767 MW/m^2 can be removed between 980 and 2750K.

Cerium has a melting point of 1071K and a boiling point of 3697K. It has a density of 6550 kg/m^3 and a heat capacity of 192.4 J/kg/K. We work out that 2999 MW/m^2 can be removed between 1120 and 3500K.

For all of the calculations, we limited the flow velocity to 100m/s, despite maximum laminar flow velocities reaching double and more. This gives a more plausible 1m^3 per second volumetric flow rate.
We have ceramic pumps that can handle liquid metals, and we go further.
The performance of liquid metal cooled armor far exceeds that of other cooling solutions.

Indium is at the lowest risk of solidifying in the pipes, but has the highest pumping requirement and imposes the lowest temperature limit on the armor.
Aluminium provides the best performance and the lowest pumping power requirement, but it is the most reactive of the metals and so needs a protective layer in between it and the carbon armor.

Cerium, with its very high boiling point, is unlikely to ever create vapour bubbles in the heat exchanger and has the smallest radiators, but it is also at the greatest risk of solidifying inadvertently.

Tin is the overall best choice.

The danger of course is that a battle starts with the tin in its solid state. Directed energy weapons could add heat to an armor plate too quickly for the tin to melt and start flowing to draw it away. Ideally, the tin is constantly flowing at the minimum temperature, which is 550K in this case. For efficiency’s sake, it could be kept molten using waste heat from a nuclear reactor. However, pumping the metal would consume electrical power that has to be taken away from other systems.
Liquid tin as a thermal transport coolant to a solar energy storage system.
Spaceship designers could make use of the armor layer as another radiator. It would be durable and usable even in battle. Other than the sections under laser attack, it could be rejecting up to 3.5 kW of waste heat for each square meter sitting on liquid tin. This feature could compensate for the extra heat from a nuclear reactor that needs to operate at a higher power level to feed the pumps with electricity.

Reduced beam ranges

Let’s work out the effective range of a beam weapon facing a carbon armor layer using all the tricks available to us: rotation, compound sloping and active cooling.
As before, we set the weapon to be a 100 MW laser of 450nm wavelength, being focused by a 4m wide mirror.

The target will be an eight-pointed star (octagram) pyramid 6m wide at the base and 17.3 meters long. This gives it a vertical slope of 80 degrees and a horizontal slope of 67.5 degrees. Each face of the octagram is 1.76m long, which means a total circumference of 28.1m.

Before combat, the armor maintains a flow of liquid tin through it. It serves as a radiator which handles about 1.26 MW of heat on its own.

During combat, 3.6 GW/m^2 can be absorbed when the liquid tin gets really hot. The maximum temperature we’ll allow is 2800K to prevent any hotspots from boiling the tin. The heated carbon also radiates another 3.5MW/m^2, but this is a tiny contribution.

An enemy attacking the pointy end of the star pyramid would face a compound slope that spreads their beam over a surface area 15 times greater. This is a 15-fold reduction in intensity. Working it out, the armor can handle 54.2 GW/m^2 with ideal sloping. If the enemy attacked from the side, they would face only the horizontal slope that reduces intensity by 2.6-fold. The armor can only handle 9.4 GW/m^2 in that case.

We can see already that the intensities the armor can handle are much greater than in previous examples.

The laser we are considering can only produce an intensity of 9.4 GW/m^2 at distance of 812.6 km. If our warship is outnumbered, it would want to stay at least this distance away from its closest opponent.

54.2 GW/m^2 is only possible at a distance of 338.4 km. Our warship can get this close if it is confident that it can always face its pointy end to the enemy.
What about rotation?

In these scenarios, the benefits could be massive. At 338.4km, the spot radius of the laser is 2.4cm, and at 812.6km, it is 5.8cm. These are 1170.8x and 484.5x smaller than the circumference of our armor. In ideal conditions, it is a reduction in intensity of 1170.8x and 484.5x. A supremely confident commander could bring our warship to single-digit kilometres in front of the beam and expect to spread its power enough to never overwhelm its cooling capacity!

There are important consequences for this sort of cooling capacity and reduction beam ranges. Many depend on the specifics of the setting where space warfare takes place.
Laser attack, captured and edited from this Children of a Dead Earth video.
In general though, we can reasonably expect that battles will revolve around achieving a flanking position, suppressing the cooling capability of the armor or preventing electrical generation that powers the pumps. The latter two objectives can be achieved by pulsed lasers, penetrating particle beams, kinetic strikes and other weaponry that are not continuous beams.

At the very least, the threat of giant laser-equipped warships and their dampening effect on any sort of eventful space combat can be reduced or eliminated in science fiction.


  1. Thank you Macodiseas ( for spotting a few mistakes!

  2. At such close ranges, the sheer amount of kinetics flying at the enemy ship will probably necessitate the laser being taken off offensive duty and switched to active defence...

    1. Well of course any sane space warship commander won't actually put their ship in front of lasers at ranges where their active cooling system is teetering on the edge of collapse, but you make a good point.

      Active cooling only really deals with CW lasers and heavy particle beams. In a world with multiple weapon systems, the ideal ranges will shift to another point.

  3. Nice job as always.

    But I can't believe you even considered mercury as a coolant. A heavy metal when every gram counts?

    How about lithium and ammonia?

    And there was a book that claimed 1.25 GW/m2 heat pipes were developed for the NASP project in the early 90s. Almost certainly lithium in molybdenum pipe.

    1. Thanks.
      The coolant is in a closed loop and is reused endlessly, so it isn't so bad. It sure beats needing many tens of cm of ablative armor!

      Lithium and ammonia are good choices, but they come with restrictions. Lithium melts at 450K and boils at about 1700K, which is an impractical range of temperatures. Ammonia starts thermally breaking down above 1000K, which isn't a good thing to happen. But... you can specifically design around these restrictions. Unlike existing heat exchangers, the heat source is uncooperative and trying to break you stuff!

      I'll look into that. 1.25G/m^2 is really good performance!

  4. Wow, just wow. You may have just solved the laser problem in a way that not only makes sense but also makes ships look fantastic.

    However, I'm left wondering where would the weapons be mounted on the ship. Seeing as as any moderatly powerful beam weapom like a Laser, LCBP and PGoD would need to be keel mounted. Im just is with the outer hull spinning, how would you project the beam and where? Off centered shutter or hole? Turrets on hard points? How would you keep the turrets from being picked of one by one due to the fact they are going to peak over the horizen of the armour which would provide a very enticing target.

    On a related note, how would you rotate the armour while still having all you cooling equipment inside the armour, or even rotate it in the first place? Wheels? Magnets? Genetically modified super hamsters?! (I mean, the hook on the club of a colosul squid can rotate 360 degrees in any way so with advanced bioengineering...) And what about the inner armour, that has to be spinning to keep the ship stable. Yesh, all this cooling and spinnning is making me both dizzy and beleive that making the armour a secondary radiator nessacary.

    Also, how well would other shapes prefrom with active cooling and spinning?


    1. Thanks! There's still the issue with pulsed lasers to deal with, and I'm looking into that in a future post.

      Your weapons will have to shoot out of small shuttered ports in the armor. This is great when you only need a few millimeters' opening for a PGoD or a few cm for an LCPB, but is problematic when you want several dozen cm or even meters for a laser. You might be forced to have huge deployable mirrors for lasers that can only be used at extreme ranged, and have to switch to tiny beam ports at close range.

      For rotating armor, you would have a fully rotating 'shell' that contains all the pipes, armor and port holes, sitting on top of an internal drum that feeds coolant across sealed joints. The coolant is then taken to radiators sitting behind the shell. Or, if you also need weapons fixed to the firing ports, you could just have the entire ship rotate and the parts which need to stay non-rotating (crew, radiators, engines) would be attached to the rotating section. The design specifics matter here.

      All shapes that try to perform equally well from all directions (cones, star pyramids and other radially symmetrical examples) would have no trouble being rotated.

  5. Yesh, poor lasers. Is there any way to perhaps have a armoured window cover the shutter and, when damaged, can swabbed out or something of similar nature? Or you beam the laser behind the ship and have several mirror drones play peak-a-poo behind the rotating shell with the enemy counter attack.

    Also, seeing as the weapons would be firing while the armour is spinning, where they would compensate by minuet angle changes in the weapon and multiple pot holes, the effect I would be a lot similar to the laser mini guns that populate soft sci fi. Of course, LCPBs can be seen, not so sure about PGoDs though (unless they have tracers somehow).

    Finally, what about the peak-a-poo concept but with other weapons like a MAC that launches a big 'ol slug at 'close range'. Would that work?

    Well, either way, defence drones have there work cut out for them.

    1. Armored windows work well when they only have to deal with enemies using lasers. They can be made of diamond or sapphire and be quite tough. However, they are not great against particle beams and kinetic impactors, even as small as sand. Facing these means the armored windows quickly develop cracks, dark spots, rough surfaces and other sorts of damage that leave it mostly intact but unfit to pass your beams through.

      A large gun would simply have to rely on a physical shutter to open and close it just enough to let a projectile through. This shutter could be a slab of armor as thick as your main armor and with its own active cooling.

  6. Is there anyway that lasers can be put on the shell? Although the thought of mirror drones behind the ship is starting to grow on me (the crew, if they carry the drones with them along with the defensive drones, the crew could start giving them nick names, like wally).

    But then what would the "Mirror stars" purpose be? LCBPs and PGoDs can "out range" a laser in this setting, star forts would be big battle stations with a x-ray laser, and thus strike at long ranges, Laser webs span star systems, missiles can swamp any defence eventually and all together the only thing I see the Mirror stars being good at is point defence.

    Pulse lasers sound real useful now.

  7. New to the blog, love it, is very cool.

    I have to ask though if the cooling system would be worth the logistical strain.

    This honestly seems like an absolute nightmare to maintain far from home, and might be more trouble than its worth. Ofc, this is entirely dependent on the situation, but thats my two cents.

    In your opinion, do you think a passive system of helium baloons made of kevlar strapped to the hull of a ship would be a decent if cheap countermeasure against lasers? Maybe Im understanding the physics wrong, but I was wondering what you thought.

    What I think is happening here is the energy of the laser strike is being ablated by the round baloons, then the heat from the baloons is sunk into the helium inside, until the pressure builds to the point the helium escapes harmlessly into vacuum.

    1. Hi! Thanks.

      The plumbing and hassle of actively cooling your armor should be no more or less difficult than covering your car in engine radiators. It is not as simple as solid blocks of armor, but this alternative means you need much less of it, which is very important to spacecraft as every gram counts.

      Your idea of using strong helium balloons will work. It is a type of ablative armor: you absorb the laser energy in something and then throw it away. This means you must compare it to other types of ablative armor.

      Carbon armor like graphite must first be heated up to its evaporation temperature and then evaporated. This means each of kg of graphite can absorb 60MJ. Helium is much easier to heat up and is already a gas. If the balloon hold together up to a temperature of 720K, which is the thermal decomposition temperature of Kevlar, then it will absorb 3.7MJ.

      It is still a lot, but carbon armor is evidently more effective than helium balloons. It is also much more vulnerable to damage from anything besides lasers. Micro-impacts which would dig a little pit in carbon would instead hole the balloon and let the helium leak out!

  8. I do not think using external radiators to cool the armour would be too good an idea, since they themselves are highly vulnerable to flanking fire. However, the entire armour surface can also serve as a radiator! With your example, the tin-cooled armour radiates 1.26 MW at 550 K, which means it will radiate the full 100 MW of the laser strike at 1641 K - this does reduce the delta-T from 2250 K to 1159 K, reducing the maximum on-axis intensity to 27.91 GW/m^2 and the maximum flanking intensity to 4.84 GW/m^2, before armour rotation is taken into account. Even absorbing four laser strikes at once would still be possible, raising armour temperature to 2322 K and reducing delta-T (assuming still a 2800 K max temperature, so still conservative for graphite) to 478 K - but this armour can still survive 11.51 GW/m^2 frontally and 2 GW/m^2 flanking, still about 40 times better than the uncooled graphite armour.

    And having the armour cool itself means that you don't need any complex rotating-to-nonrotating transition that has to handle red-hot molten metal without leaking - hell, with the 1.25 GW/m^2 heatpumps an anonymous user mentioned above, you might be able to pull this off without needing any active pumping at all, a heatpump lattice in the armour effectively just giving an insanely high thermal conductivity in the plane of the armour plate.

    1. Not to mention it is possible to combine both actively cooled and passive armor to give it more resiliance to enemy kinetic or guided weapon hits from railguns and missiles etc

  9. Thank you so much for putting out articles like this one and your others! I read them for fun when I'm alone and tired, and they make me grin. I would love it if you continued to share your writing when and if you feel like it! (I'm a university student who gets a kick out of space combat. It would be so cool to work on these things, though the whole 'weapons kill people' thing is a compelling reason not to)

  10. Here's the thing, I think it's possible to do this for the engines to some degree, I know it be much harder with the engines that have gimbles on them for thrust vectoring and such (tho you cannot protect the exchaust). But heres my question, I'm sure you could mount these on turrets and such to protect them from enemy laser fire but if you have the turrets mounted on the hull of the ship and if they are able to destroy the turret, what happens when the barrbetts that the now destroyed turrets are mounted on become explosed and how the enemy laser fire can use that weakness of the now exposed insides of the turrents can be turned against itself, or if you have antennas and such how can you prevent the wires that need to run along inside of the ship can they be protected to make sure their are no gapes the lasers can get or punch through when you have active cooled armor? How can we prevent as many gaps the lasers could explote as possible while still those closed off gaps being covered in active cooling?

    Can you prevent this stuff within these structure weaknesses? Not to mention how are you gonna be able to protect the doors of the VLS launchers for the missiles or the torpedo launchers from enemy laser fire? when they have to open and close would be utterly hard to mount an active cooling armor on their or will their be like large doors that have active cooling to protect the launchers and such and open when they need to fire? These are things I need to ask, I'm sure some of these problems would be a little hard or challenging to solve at first but heres the question can it be done? And if so, what do you think the limitations will be and what exactly can be done to protect most if not, almost (like maybe 90 something or more percent) all of the entire ship from laser fire?

    Also another question if the actively cooled armor is punctured from kinetic or guided weapons how will that affect it's performance after it's hit? I'm sure with the many multiple conducting pipes and such that run along inside of it will be redundant to prevent the loss of that molten metal or gas coolant but if it was penatrated how can you prevent the layer below that now is bear and it's not the active cooling but is the main armor to stop or slow down incoming kinetic weapons or missiles etc is now exposed to be able to be taken out with laser fire (which I know depends sense if they can hit that point that's now exposed depends on the angle range, the hole size etc)n can that passive armor like with it being made up of composites, metal foam, and etc such can also be cooled while also acting as the main armor from kinetic weaponry? I know you could put water or hydrogen etc in metal foam to lower the effectiveness of laser weapons even more for passive armor but hydrogen can easily be boiled or burned off within the metal foam and while metal foam can withstand and last from much more heat than a regular plate of metal it still won't last long after a couple or so seconds depending and if we use water it's more effective but much more heavy.

    1. Hi there! I'll try to answer all your questions as soon as I can.

    2. I understand but I gave three massive comments that I couldn't give you all of it in one so keep that in mind please that's why you see three massive comments and all those are my me

    3. still awaiting your reply from my three massive comments matter beam!

  11. There are no results for Honestly combining passive armor with active cooling could give it as another way if the active cooled armor that protects you from laser fire would give you the advantage to have a second layer of protection from lasers if the first layer is breached but doesn't mean the first layer could also be passive armor as well but doing this with multiple layers adds complexity to the whole thing but if it is lighter and more effective and better at stopping lasers and such to the ships protection than the complexity costs willl likely make up for that. However, it doesn't mean we can't keep having as many layers as we want because that adds way more costs and complexity to the whole thing not to mention you can only protect the ship with so much reduancy and such before it fails but I think doing it like this is certainly possible, but it's very hard to pull off or it's just costly and complex to add another layer and only have two layers If it were me I would have two layers of actively cooled with both combined with passive armor like metal foam and diamond and such and the last layer just be a normal passive protection layer. Either way I'm very aware this can have pros and cons, but I wanna know the questions I'm asking will be possible and if they can be worth it even if it allows the ship to fight longer. Taking a punch matters but adding too much protection will make it out weigh the pros.

  12. Hopefully you dont' just reply to each and everyone of the three large comments I gave you but to answer them all in one or seperate ones sense posting this was kinda hard lol sorry matter beam.

  13. One of the other ways you could get rid of the need for pumps which you forgot to mention which is something that has needing little to no maintenance is using MHD or Magnetic hydro dinamics to move the Molten around at much higher speeds than what the best pumps could possibly do while they would probably need more power to run the beniefits are massive is you don't need complex pumps or such moving parts and redirecting the molten tin around is just only needing a simple valve or such to redirect or change where the molten tin without the pumps significantly could make the system much more reliable and could make it lighter if the tech gets good enough could make the need for pumps out of the question

    1. I'm sure some of the cons like higher power requirements and such as the electrodes on the MHD will be needed to be made to withstand the large amounts of heat if it gets high enough or that problem could be over come simply by speeding up the pumping and such but I think those could be solved over time