[3e] Statting a spaceship radiator
 

So, my crazy mind has decided to give me more things to do (damn plot bunnies being like their namesake), and one of them is cored around Transhuman Space and Sins of a Solar Empire, of all things, with elements from Tomrrow's War and Traveller. [looks at self in confusion, yes, my brain can scare me at times]

Now, I was prototyping a spaceship (the Alen T Shepard class Corvette), which had been designed in a time period like Transhuman Space instead of the usual 'ignores heat'/'super-efficient hull radiators' that sci-fi usually uses (in-setting, those come in later). This means it'll need radiators... and I haven't found much in converting it to Vehicles 2e, just a blurb in GRUPS THS (3e) and some references to a GURPS 4e Space radiator rule.

Is there a way to convert that, or am I forced to ignore radiators?

Re: [3e] Statting a spaceship radiator
 

What stats do you need? If we assume radiators operating at a reasonable-ish 500F, and 40% efficient reactors (pretty high, but this is SF), you need about 2 square feet of radiator area per kilowatt of power plant, which will rapidly turn into giant wings if you're powering high power components.

Note that the big energy consumers on a spaceship are drives and weapons, which may have their own methods of cooling. Low specific impulse drives can use their exhaust as coolant (this is why chemical rockets don't melt), nuclear pulse and Orion type rockets produce most of their heat outside of the ship where it directly escapes into space. For weapons, their use is often intermittent enough that expendable heat sinks are the way to go.

Re: [3e] Statting a spaceship radiator
 

A quick-and-dirty method is to just steal 4e Spaceships' handling of it - assume systems that require radiators include a retractable main radiator array as part of their mass. While extended, said radiator can be targeted as though it were the same SM as the vehicle if engaging from side-on (where its profile is largest) but at SM -5 from if engaging from the front or back. So long as the radiator is extended and functional, the vehicle can function normally; if retracted or disabled, the relevant systems will overheat and shut down in 30 minutes (coolant can extend this; coolant equal in mass to the system is consumed every 30 minutes to keep the system from overheating).

Or if you'd rather actually stat them out with Vehicles, Anthony's numbers should work. I'm not sure about how much they'd weigh, but you could probably do worse than assuming they have the same density as solar panels.

Re: [3e] Statting a spaceship radiator
 

Note that realistic radiators rapidly turn into "your spaceship is completely immobile on a tactical timescale".

Re: [3e] Statting a spaceship radiator
 

Oh boy, that would make things problematic, given that I'm already in the gigawatts for both propulsion and power requirements (thanks to the FTL drive alone, though I might have to rejigger that as it is).
Well, I am thinking of basing them on Transhuman Space radiators at the TLs I'm working at (TL10, for the most part).

Re: [3e] Statting a spaceship radiator
 

Well, if Children of a Dead Earth taught me anything, it is that the cooler the system, the less efficient the radiators are.

[most of the common fission reactor designs made by players tend to be in the 2000K range in terms of external coolant heat... usually via sodium]

EDIT:

Using GVB, and assuming that the old fission reactor is TL8 and using long-term access, a 1-space old fission reactor is a 1090kW reactor, a 4-space old fission reactor is a 7340kW reactor, and an 8-space old fission reactor is a 15,660kW reactor. According to the radiator appendix in THS's original book, you'll need 1,000sf per 8-spaces of old fission reactor and fission drives. Assuming new fission reactors are at least TL9 and using the long-term access option, a 1-space new fission reactor is 7,350kW, a 2-space new fission reactor is 15,700kW, and a 4-space new fission reactor is 32,300kW. With these and the old fusion reactors, you'll need 1,000sf per 4 spaces of reactor and engine.

Now, if CoaDE taught me anything, this suggests that we're dealing with radiators spec'ed to high temperatures (likely 2000 Kelvin) as a whole with very high-end materials (a radiator that I 'quick build' on CoaDE using 3D-Graphine can radiate GIGAwatts of heat for 53173.71745855sf using 60-degree tapering fore and aft) or consist of things like liquid droplet radiators.

Re: [3e] Statting a spaceship radiator
 

Yes and no. The problem with a high temperature radiator is that you need to get your heat to the radiator, which requires power (and additional heat production) if the radiator is hotter than the system it's intended to cool. If you want a 2,000K radiator... all your heat-producing components need to be able to run at 2,000K. There are a few components that really can operate at that kind of temperature, but most machinery really cannot (a 2,000K sodium cooled reactor will probably explode violently if you look at it funny).

Re: [3e] Statting a spaceship radiator
 

Couldn't we use different radiators for different systems though? Like, if our fusion engine produces a 1500k worth of heat to dispose of, we run it on some dedicated radiators, while our habs and their associated stuff use lower temperature radiators. Which probably gives us a really big set of radiators for our habs, and a much smaller one for our drive system.

Re: [3e] Statting a spaceship radiator
 

Yes, but you start running out of viable materials to make your reactors out of, and also you either need a heat differential or heat pump to get your heat to the radiator fast. You also need to be running the reactor core at a significantly higher temperature than the radiator -- how much higher depends on how much power output and efficiency you want (there's a hard limit on efficiency of (1 - ratio of temperatures), but there's some tradeoff in power density vs efficiency; a reasonable ratio is about 2:1), and you really start running out of reasonable materials somewhere in the 1,000-1,500K range, outside of some very specialized applications that generally don't produce electric power. If you're feeling really generous you might see 1,000K radiators that need only about half a square foot per kilowatt of power output.

Re: [3e] Statting a spaceship radiator
 

Yeah, so I generally figure around 1200 K as the operating temp for the engines. Hotter would help for a lot of things, but as you point out: material science starts to limit our options.

I don't know how many kilowatts the habitats of a manned vessel would have, but considering they need to maintain around 300K, then it's probably around 4 square foot per kilowatt?

Re: [3e] Statting a spaceship radiator
 

It depends on whether you're willing to use things like Graphine/Carbon Nanotubes/metamaterials in their construction.
This is what is done in Children of a Dead Earth. You need a radiator for any non-kinetic/VLS/engine component. They all have different heat pump outputs (for example, habitats consistently have the lowest heat dissipation requirements due to only needing kilowatts of heat to be dissipated while reactors -especially player-designed reactors- tend to require higher heat dissipation requirements. In contrast, lasers tend to be in the middle).

Re: [3e] Statting a spaceship radiator
 

It depends on whether you're willing to use materials that we know actually exist and work as required, or if you're speculating wildly on materials. Carbon compounds can absolutely do a lot of things, but they aren't universally useful for all purposes -- for example, they tend to be brittle with nasty failure modes (and 2,000K sodium has a vapor pressure of 80 atmospheres...), and they simply aren't a replacement for metals in electrical applications. Also, even if your reactor core runs at 2,000K -- that probably means 1,000K radiators.

Re: [3e] Statting a spaceship radiator
 

Oh boy, this is a lot harder than it looks... even with 'crash course into radiator design' that Children of a Dead Earth gives me.

However, with the RAW of THS's radiator construction rules, we're probably looking at a ratio of between 15.66kW:1sf and 32.3kW:1sf, depending on the tech level.

Re: [3e] Statting a spaceship radiator
 

In general the power emission is the black body constant (5.67e-8W/m^2/K^4) times area times temperature^4, so at 1,000K you get 56.7 kW/m^2 or 5.26 kW/ft^2. However, the total heat output of a reactor is generally somewhere around 2x the electrical power output, and the things you're using the power for also produce heat, so that's about 2 kW/sf, which is a reasonable TL 10 value, the TL 9 value is probably more like 1 kW/sf.

Re: [3e] Statting a spaceship radiator
 

Ouch, that makes THS radiators super-science levels from what you're saying if we use the assumptions I've made:

If we keep to RAW, then THS's radiators are pretty potent, depending on the designers' assumptions.

Quick question: What is a radiator's radiance when the temperature is 1200K, 1500K, or 2000K, respectively? Because that could explain a lot.

Re: [3e] Statting a spaceship radiator
 

I believe this may be a useful source, though it's very, very dense. Our own Anthony Jackson is quoted quite frequently too, for what it's worth. Atomic Rockets. Winston suggests you design your radiator for 3/4s of the temperature of your heat source or do the scary maths.

Now, one cool thing is that at tl10, I think it's reasonable to assume room temperature super conductors. With those, you could create pretty powerful magnetic fields. If you then heat up an iron based solution to a certain point, it will lose it's magnetic properties and be expelled in a cloud into space. While in space, the iron dust will radiate away the heat really effectively, cooling enough to become magnetic and be caught in the magnetic field and recollected. You now have a really efficient radiator with a lot of extra neat things. Due to consisting of a diffuse cloud of iron dust in magnetic fields, it's rather resilient and rugged, so long as the magnets have power.

A related idea is to use a magnetic field to contain some sort of plasma in a "bubble". In space, this could be used as a mag-sail, and would also make communication(and identification) with the ship quite difficult, if not nearly impossible, without shaping the magnetic field to provide some sort of window(which is likely possible) in the plasma bubble. In an atmosphere, this plasma bubble could be used as a sort of air foil and thermal barrier for the ship. In either case, the bubble will tend to swell to the limits of it's magnetic field, so it's inherently "adjustable", and it will tend to capture charged particles.

Visually, I think this works out to ships having rather small "active" parts, and then the vast bulk of the ship being a sort of ephemeral latticework supporting magnetic fields for fusion rocket nozzles, plasma sails and radiators.

Re: [3e] Statting a spaceship radiator
 

The scary maths have issues, which is why my numbers are considerably more conservative than his. If you assume a power plant operating at the Carnot limit, and all you care about is optimizing for minimum radiator area, you get the highest output with a 25% efficient power plant with a radiator temperature of 75% of the core temperature -- but typically neither of those statements is true (approaching the Carnot limit requires increasingly massive and complex reactor machinery, and fuel is generally not free).

THS is generally 'technically doesn't violate known physics but implausibly optimistic'.

Re: [3e] Statting a spaceship radiator
 

So, basically, stat a droplet radiator if I'm reading this right?

To be honest, some would say I'm ripping off Mass Effect radiator designs (though the idea of droplet radiators isn't Mass Effect; you know how the general populous perceives things).

Re: [3e] Statting a spaceship radiator
 

That's the funny thing about Children of a Dead Earth: all the numbers in the game are very conservative (the Dev made it clear that all the numbers were low-end, something that carried on with the Metamaterials Mod). However, given that it's made by a single person, it's understandable.

So, using the equation you gave me, P = A * ε * σ * T^4, I'm assuming 0.85 in this example because Atomic Rockets says anything less than 0.8 is a horrible radiator.

A= 32887.67616m^2 / 354000cf - based on THS's radiator area rules for a 708 Space septuplet (7) HePlaR rockets
ε = 0.00000005670373
σ = 0.85
T = 1500K

So, P = 32887.67616 * 0.00000005670373 * 0.85 * 1500^4, which goes to P = 32887.67616 * 0.00000005670373 * 0.85 * 5062500000000.

If I did the math correctly, then P = 0.0018648539093040768 * 4303125000000, ending with P = 4,303,125,000,000 (or 4.303125 PW).

... and I feel like I messed up somewhere here.

Re: [3e] Statting a spaceship radiator
 

I'm not sure where "A = 32887.67616m^2 / 354000cf " comes from -- I'm pretty sure A is just 32887m^2. Other than that, 4,303,125,000,000 is 4.3TW, not 4.3PW.

I will, however, observe that HEPlaR is not a THS term, and TNE HEPlaR is superscience.

Re: [3e] Statting a spaceship radiator
 

Well, HePlaR was on a THS list of alternate rockets a while back (the PDF's name is literally 'alternative engines'). Though, when designing this, it was an early 'star corvette' (aka FTL space corvette) designed for long-term patrol duties, requiring HePlaR to allow tankage for a long-term patrol (this is due to a quirk of the phase drive, as once a gravity well is of sufficient size, you have to drop out of phase space, meaning that sufficiently large asteroids or groups of asteroids can cause you to have to exit out of FTL, as the linked image demonstrates; please note that the gravity well scales with the object at the center of the gravity well) as early on the logistics network isn't entirely there yet due to most colonies being very underdeveloped as everyone is trying to set up colonies left and right.

In addition, I assumed that TL10 fusion rockets are 1000sf/2 Spaces, 708/2 = 354, and multiplying that by 1000 means 354000sf, which, when converted to square meters (via a unit converter), is 32887.67616m^2...

Also, thanks for checking my math. :)

Re: [3e] Statting a spaceship radiator
 

Note that a droplet reactor must operate at temperature where the vapor pressure of your droplets is very low, or the droplets will just boil in the vacuum and spread out all over the place, rather than being captured for recycling. That makes sodium a non-option at 1,500K (there are other options, but most of them are pretty awkward to actually use). Also, any form of droplet radiator makes maneuvering inordinarily difficult.

Re: [3e] Statting a spaceship radiator
 

So we'll have to work with traditional radiators then...

... oh boy.

Re: [3e] Statting a spaceship radiator
 

There are other nonconventional radiators that work at higher temperatures, but there isn't really any way to have thousands of square meters of radiating surfaces without some form of inconvenience, you just have some variance in what the inconvenience is.

Re: [3e] Statting a spaceship radiator
 

So, we're going to have to use things like plasma/dust radiators like ETHER and heat pumps like Mo/Li Heat Pipes, at least for combat ships.