How to cool ships, or, Why is my fuel tank so friggin huge?

[Commander Drax]

Aramis Posted:

Does this help? (I explained it this way to a 5th grader at one point... he got it. But he is an exceptional 5th grader...)

It certainly does, many thanks for clearing that up for me. I understood the principles and now accept that hull radiators can work in vacuum, best not to do an EVA anywhere near them though...

The Engineer Posted

But as it relates mass of the ship and thrust again, will You skip the 6g manuever drive limit, too ?

Oh yes!

I've never understood why most standard designs dont exceed 6G m-drive limits, some military types should be able to hit 10-15G accelleration with a sufficiently large drive. I suppose its because its easy to roll on 1d6 the incoming velocity of a ship. Later editions of traveller explain this away as a limitation of artificial grav/inertial compensation as designs typically only compensate for 1-6G of acceleration.

I don't see why robot fighters or automated transporters (carrying ore for example) couldnt make use of a gigantic M-drive to cross distances quickly.

For playability thought I think 1-6G is about right, as it allows STL transport within a star system in a decent enough time whilst still allowing the space in between to seem endlessly big and lonely.

I like a big, lonely, capricious game universe where one mistake could kill you.

 

[TheEngineer]

Sounds very well, Commander

 

[Fritz_Brown]

Good explanation, Aramis. As far as the concerns for stealth, remember the distances we are talking. Energy spreads out at a square of the distance. And heat is notoriously "low" energy. Witness how much farther away you can SEE a campfire than you can luxuriate in its warmth.

 

[aramis]

we're also talking about, in order to shed the heat mentioned, radiators radiating somewhere well into the visible spectrum, and beyond... 3000°C+, IIRC, at the surface... Sodium as a working fluid...

and if you put a 100 square meters glowing several megawatts per square meter, even with the inverse square law, that's still a considerable source.

More important, stealth-wise, is relative magnitude. If your rMag is less than that of the starfield average, you'll be hard to spot except as motion against said starfield.

 

[TheDS]

Cold fusion is still going to produce excess waste energy. Basically, the entire output of the power plant has to be shed as waste heat. First, the plant itself is unlikely to exceed 75% efficiency (we are lucky to get 50% in some applications nowadays). Reduced fuel consumption can be explained as improved efficiency, but a reactor sips so little fuel that we don't really care; we can just assume it can be made as needed from our water ballast. The ship's systems are probably going to be about as efficient as the reactor, maybe less.

Weapons and mass-throwing thrusters will be about the only way to shed energy without it having to be radiated as waste heat, but as you will recall from design sequences, only about 20% of the energy pumped into a laser is actually used to inflict damage (for grav-lasers and PAW-based weapons).

A little browsing on Freelance Traveller's Shipyard shows that the apparent average energy usage is about 2-4 Mw per Dton, depending on whether the ship is acting in a civilian (low power) or military (high power) mode, so my numbers weren't too far off. Judging by what i've already written, the reactor for out 1000 Dton ship should run at about 2000 Mw when not needing weapons or excess thrust, and 4000 Mw when it is, cutting our normal cruising range to 15 days, and our combat range to half that, but we can double it back up if we go with the suggestion to allow higher or lower water temperatures.

There is also no reason not to allow a ship to use radiators. First, we can suppose that most ships have them on various places on their hulls, like a second skin. We can also allow the use of a single large fin coming out the top or something, like a folding array. the reason for only a single fin is so that the ship can put the fin in its shadow, and thus use it even when close to the sun. Probably, the fin will not reverse heat gain, but should at least slow it down. This fin would be useful away from planetary atmospheres and battles, which is why pictures rarely depict it, because those are the most interesting pictures.

Military designs that make use of EMM forgoe using hull-covering radiators in favor of grouping the radiators into a smaller area and then directing it away from your potential enemy sensor platforms. Military ships will naturally have a harder time shedding their heat (or slowing their heat gain), and it will be even worse in combat. Still, 15 days to take a world isn't a bad value, and if you need more time than that, that's what tankers are for.

30 days for low-emissions, and probably 60 or more when in jump, since you won't need your thruster plates (but are using jump drive instead, so maybe still 30) is enough to allow 2 or 3 consecutive jumps; one for the misjump, 2 more to jump back to a world where you can get more coolant.

I am sure Imperial law would mandate that commercial ships had to replenish their cold water supply after every jump, to maintain the safety factor against misjumps; companies would be sorely tempted to risk the lives of their employees and passengers in the name of saving a buck and jumping twice on the same coolant.

The 30 day value also meshes nicely with MT's 30 day power plant endurance values. Does CT have something similar? I think it does, but don't know for sure.

If it can be made simple, I think heat management would make an interesting additional concern. 99% of the time, it would not be important, but that 1% of the time when something bad happens, when PCs try to stretch the performance characteristics of their ships... Anyway, heat management is an integral part of Battletech, and adds interesting limits on that game, and I think the same could be done here, and it would explain away a lot of the ambiguities that have developed over the different versions of Traveller, giving one concise reason for the huge volumes of fuel and lack of radiators.

 

[TheEngineer]

Hi !

Once I put together a spreadsheet for calculating waste heast amount, storage capacity of LHyd/Water and emission capabilties by hull radiators as "relaistic" as possible (tungsten is the material of choice, but a grav controlled fluid is a pretty idea Aramis)).

Even if I play MTU the "classic" way without those heat problems I fully agree with TheDS, that heat management add some spice to space engineering. Thats that sheet for

Hmmm would it be nice to have a simlation software for starship operation (not the travel and trade stuff but the "technical" things).
I am thinking of something like typical control center programs for industrial plants....colorful and quite dynamic...

Regards,

Mert

 

[gardclan]

I think what you are seeing here is a diference in what each edition's game designers thought was important. TNE attempted to become a "more hard sci-fi" setting, and imposed an emphasis on subcomponentry over major hull items. CT ships would have had to have radiators *somewhere* but the designers either didn't bother with the detail (more likely) or figured those items were just subsumed in each major item (power plant, j-drive, etc.)

The fact is, in reality you would have to provide some sort of cooling mechanism to dump waste heat off ship or the resulting thermal buildup would soon render your reactor inoperable due to component breakdown. Since you have no convective or contact medium to carry away your heat, RADiators are pretty much your only option. Vaccuum will transmit thermal radiation, its just not as efficient as convection. As a rule, your radiators should be capable of discharging an amount of heat on par to how much power your power plant is producing. The simple formula for this is:

q = (sig)(epsilon)A(Ts^4 - Tsur^4)

where q is heat (in watts)
sigma = stefan boltzman constant (5.67 x 10^-8 W/m^2K^4)
epsilon = emissivity of the surface (always less than 1.0, but around 0.7 for a fairly good radiating material)
A = surface area
Ts = radiator surface temp (must be in kelvins)
Tsur = environmental temperature (around 4 kelvins for deep space).

In practice, only some of your reactor's waste heat becomes usable energy, the rest becomes waste heat and has to be removed. This is a good reason for increasing reactor efficiencies at higher tech levels... less thermal waste. What the math will tell you fairly quickly is that in order to transfer heat effectively you need either a very large radiator, or a huge temperature differential. If your radiators are operating at less than 920K (1200°F, or a nice dull red heat), the panel is going to be HUGE. Efficiency increases dramaticaly with increasing temperature.

This ignores view factors, re-irradiation, and the like. We'll assume the radiators are flat for this discussion.

You can run hotter, with better grade materials, but you also become much more visible at distance and tend to degrade your materials faster. The military issue is the fact that you realy can't disguise your thermal dump without blocking it (and therefore not getting rid of it), or operating at a lower temperature... which means larger radiators.

So, opinion time. Civilian ships would want radiators that operated between 1033K and 1088k (1400°-1500°F) so as to conserve both mass and materials. After all, you are not so concerned about detection as you are efficiency.

Military designs could use one of two philosophies. The first would be a HUGE number of radiators operating at 800-900K, and would be fairly visible close up, but easily lost in the distance as background radiation... OR would have a number or redundant VERY HOT arrays. This would allow the crew to dump heat on the opposite side of the hull from any threat. Thus, the thermal load would be shifted back and forth as the ship maneuvers, rather like shining your "flashlight" away from your opponent instead of at him. Since your radiators take time to cool, violent maneuvers under this design would tend to make a ship "suddenly appear" as the thermal dump becomes visible over the hull's occlusion to the enemy sensors.

TNE could account for either of these as part of your EMM array. CT would just say its part of the existing component mass and handwave the rest.

YMMV

 

[TheEngineer]

Hi !

Few more thoughts..

Because of the mentioning of superdense or bonded superdense materials for a starships hull (at least in MT) I strongly assume that manipulative abilities regrading internal structure of materials advances with TL. As a result even properties like heat capacity and mealting points are subject to alteration (e.g. there is a Black Mesa outpost in Glisten belt..)
So radiators - if they a needed - might be contructed to be much more efficient as they could get along with much higher temperatures.

Sometimes we a strange people

We accept artificial g, jumpdrives and thrusters but seem to ignore possible advancements in basic things like heat to electricty conversion.
For myaelf I assume, that higher TL powerplants convert heat directly to electricity by using specially designed materials (like semiconductors in solar cells or super Peltier elements).

But its just a matter of tase to run "clean" or "dirty" Traveller

Regards,

Mert

 

[The Oz]

What about non-jump-capable ships? Assuming that the "jump fuel" is actually used as a heat sink wouldn't non-jump-capable ships run into heat disposal problems sooner? They certainly don't have as much "fuel" to use as a heat sink.

 

[TheEngineer]

Hmm, Oz. A strike.
And what about ships just leaving jump space and tanks are nearly empty ?

Perhaps this reduces jump fuel heat capacity to an optional thing, that could be done under special circumstances.
Regular operation might have to rely on those radiators or advanced heat conversion.....

 

[gardclan]

The whole issue with the jump fuel bunkerage I suppose depends on what its used for. If you assume your j-drive holds a pocket of real space to protect the ship during transit, then several posibilities exist (and depending on what edition of traveler or home universe you use, several variants as well).

One option is that the ship uses a fast burn reactor to "blow a hole" in space time, to form the jump tunnel, and all that fuel gets used up in one massive pulse. Borrowing a phrase from "TheDS", that is indeed a couple of cubic-butt-tons of energy.

Another option I have seen is that the fuel is used for powering and cooling the jump drives while in jump. No real explaination was given for this one and I can't recall where I saw it at the moment.

Yet a third option (and the one I use) is that the jump fuel is used to populate and pressurize the jump bubble to stabilize it during jump. Ships IMTU require more jump fuel at higher jump numbers because the resulting stress on the jump field is higher and more hydrogen is required to pressurize the field against the possibility of field collapse. It also gives the ship (which is in what ammounts to a pocket universe for the duration of the jump) a target to radiate its waste heat to. So, as the ship falls through the tunnel to the destination, the space inside the bubble goes from black at jump insertion, to a dull red mid flight, and finally screaming bright orange hot at jump exit.

Its perhaps not canon, but it does have a nice effect when ships exiting jump produce a huge thermal bloom of expanding hydrogen plasma. It also makes misjumps (especially ones with more time spent "in the hole") very dangerous for the ship's hull.

Now, if you are using your hydrogen for bunkerage, displacement mass, or cooling in jump, any of the above three are good. If you are using it for cooling in normal space you are pretty much wasting displacement. Consider, the space shuttle and the international space station both use radiators to cool themselves at present. A spray droplet stream radiator was considered at one point, but rejected as unfeasable. Granted, they don't produce all that much power relative to a traveller starship, but they are a real world example.

Should radiators be required for design? That depends on your philosophy. You can always say they're in the math somewhere like CT apparently does. In the end, I suppose its a matter of preference. The fuel requirements for drives, powerplants, and jump are all conjectural anyway and are pretty much just a way to balance game mechanics and economics to keep starships from being free ranging and cheap vehicles.

Or at least thats how it appears to me.

YMMV

 

[TheDS]

Lots of comments to make this time.

Engineer: You are missing one key thing: in the system I propose, the water is not dumped overboard during jump, it is retained on board to hold heat! Hot water isn't dumped until the ship gets someplace where it can replace it. Functionally, the ship loses fuel, but in reality, its mass is unchanged.

Which seems to me to be another interesting and useful side effect. The mass of the ship stays the same. Most renditions of Traveller simply assume this, or that the change of mass as fuel is used is inconsequential. FFS, with its realistic thrusters, makes the point that mass changes significantly for rockets, and also half-wise mentions that one must pay some attention to the thrust-to-mass ratio where you rate your design. Nothing blatant, as I recall, but it always made me want to compute thrust using average mass rather than an assumed 10*displacement.

So having your mass not change is another step toward compatibility with already established material. (We could get really bold and say we are MORE Traveller than everyone else for this, but who would believe us?)

Oz: You bring up a good point. A damning good point. The primary purpose of not having a jump drive is to not have all that jump fuel, which would limit our endurance.

But does it blow the whole thing out of the water? I'm not sure. I would imagine that if we went and figured out the energy requirement for a jump drive, we will find out that it takes a lot of energy to make and maintain the field (depending on your view of Jump, I suppose). It would not be too insane to say that the jump fuel is sufficient in itself to give 15 days of Jump drive operation, and that non-jump fuel is good for however long the designer wants it to be good for, but that it would probably be 15 days as a minimum (except for small craft like ship's boats and the like, which only need a few hours)

Judging by this, we must be sure that a J6 drive produces about 6 times the energy that a J1 drive does, and therefore needs 6 times the water mass to absorb the heat.

And we DO still have radiators as an option. Dunk into a gas giant or nudge an ice asteroid for a few minutes and you'll lose heat to conduction.

Rhys: Wow! Great post! I'll have to try out that formula, try and convert it to solve for surface area and give some example results. Crap, I'm just going to have to build a ship or something!

As to your real world examples of the space shuttle and ISS: Those objects do not generate much heat or power. I don't have figures, but it would surprise me if they generated 10 megawatts, so it is faarly easy for them to cool those things with simple radiators. The ISS in particular has a lot of surface area.

While hotter is more efficient, there is really only so much heat you can take. 400 Celcius is probably pushing it; you'll be radiating all that stored heat back into the cabin, and the crew will complain if some one gets the idea to baste them in all that heat. Of course, I don't know this for certain, that's just what I'm concerned about, is having all that hot water dumping its heat back into the cabin and making those poor air conditioners work even harder, generating even more heat, and the feedback cycle getting out of control at about that point.

The Starship Operator's Manual put forth the idea that jump fuel is actually coolant and "lubricant" used up during jump. It was much more believable to read that that huge mass of fuel was being dumped over the side rather than fused, or even combusted, for that matter. Unfortunately, we're SOL on using SOM to describe Jump, because it has unfortunately been decanonized, due to Marc Miller and Roger Sanger not being able to come to an agreement. So we must come up with something else, unless, I suppose, MWM wants to reinvent the idea or soemthing.

Anyway, I'll have to give some more thought to the non-starship question and how effective water tanks and radiators are likely to be, but I wouldn't mind one bit if some one beats me to the punch, especially with the holidays coming up.

 

[mike wightman]

FF&S2 for T4 gives a similar description of how the jump drive works to the one in SOM (which hasn't been decanonized by the way - it's just you can't quote from DGP stuff directly in new material).
There's a lanthanum hull grid, jump bubble, etc. and even mentions that hydrogen remaining in the jump fuel tanks is used to fill the protective bubble.

 

[Commander Drax]

Yet a third option (and the one I use) is that the jump fuel is used to populate and pressurize the jump bubble to stabilize it during jump. Ships IMTU require more jump fuel at higher jump numbers because the resulting stress on the jump field is higher and more hydrogen is required to pressurize the field against the possibility of field collapse. It also gives the ship (which is in what ammounts to a pocket universe for the duration of the jump) a target to radiate its waste heat to. So, as the ship falls through the tunnel to the destination, the space inside the bubble goes from black at jump insertion, to a dull red mid flight, and finally screaming bright orange hot at jump exit.

great idea, I love the imagery that goes with that.

 

[gardclan]

Originally posted by TheDS:
Lots of comments to make this time.

As to your real world examples of the space shuttle and ISS: Those objects do not generate much heat or power. I don't have figures, but it would surprise me if they generated 10 megawatts, so it is faarly easy for them to cool those things with simple radiators. The ISS in particular has a lot of surface area.

Actually, if the station generates more than 20kW I'd be shocked. Electrical systems are really very low powered relatively speaking. If you consider that a 250hp car engine is the equivalent of 186kW (which is in turn enough to power all the houses in a small TOWN), it pretty much puts things into prospective. Do consider however that the cooling systems are considered a CRITICAL component of the life support system. The station does absorb a great deal of SOLAR flux which must be removed from the habitat to protect the crew and components. If its that essential for such a small (compared to traveller) system, it would be far more so for a multi-megawatt drive system.

While hotter is more efficient, there is really only so much heat you can take. 400 Celcius is probably pushing it; you'll be radiating all that stored heat back into the cabin, and the crew will complain if some one gets the idea to baste them in all that heat.

Here I must respectfuly disagree. The idea is not to "store" heat, but to get rid of it. If you have access to any thermodynamics texts, the Rankine cycle is a very good example of how power plants work in theory. Heat rejection is critical to proper operation of a power generator facility.

I have made a living designing heat transfer systems. Proper use of shielding materials will easily allow much higher radiator temperatures without hazard to the interior of the vessel. The key item material wise to look for in a good radiator shield is a high reflective index in the spectrum you wish to reflext. In other words... "shiny" (to IR emissions at least). I have seen real world examples of 1300K radiator arrays. Not only do they work, they are quite durable.

Radiation is a very odd thing. Just because you "hit" a surface with several thousand kW/cm^2 doesn't mean it will ABSORB all of that energy. Better reflectors just bounce most of it away and heat up very little relatively speaking.

A good real world example of this is an electric stove heating element. See that bright red glow when it gets really hot? Thats pretty close to 1600°F (871°C) when you see that color, and the reflectors under the elements are actually a fairly poor design (driven by cheap, not efficient). Your stove top may get warm, but it certainly isn't damaged by the heat.

At the risk of muddying the waters, I will tell you that most radiator arrays operate at a much cooler temperature as they tend to be "tuned" to the wavelength (for that, read surface temperature) which will be most readily absorbed by the target material (whatever it is you are trying to heat). 1200°F (922K, or 648°C) is the most common radiator temperature in my experience.

The Starship Operator's Manual put forth the idea that jump fuel is actually coolant and "lubricant" used up during jump. It was much more believable to read that that huge mass of fuel was being dumped over the side rather than fused, or even combusted, for that matter. Unfortunately, we're SOL on using SOM to describe Jump, because it has unfortunately been decanonized, due to Marc Miller and Roger Sanger not being able to come to an agreement. So we must come up with something else, unless, I suppose, MWM wants to reinvent the idea or soemthing.

Well, I am unlucky enough to have never encountered that book. For my own part, I view canon as useless mutterings where my own campaigns are concerned. A referee should NEVER be held to what other folk want to impose on his campaign. It may be a published universe, but any ref is free to pick and choose what he or she wishes to use for his or her campaign. Canon be damned. If you have the source, you like it, and if it is that good, you would be foolish not to use it. Its your game. You owe it to yourself and your players to use what you feel is best.

Just my Cr0.02

 

[aramis]

The hydrogen "filling" the jump bubble is not SSOM.. it's FF&S.

 

[TheDS]

Originally posted by Aramis:
The hydrogen "filling" the jump bubble is not SSOM.. it's FF&S.

Well, filling was not so much the term as coating would be.

Now, from our good friend Rhys:

The idea is not to "store" heat, but to get rid of it. If you have access to any thermodynamics texts, the Rankine cycle is a very good example of how power plants work in theory. Heat rejection is critical to proper operation of a power generator facility.

I agree that radiating the heat is what we WANT, but we can't always get what we want. If you're in the pocket universe that is a jump bubble (to my understanding), then where is all your heat going to go? It can't go anywhere, so you MUST store it. Likewise, if you generate gigawatts to power your multi gigajoule spinal mount, you aren't going to have the radiator capacity to handle all the waste heat, so again, you MUST store it. Better to store it in a big tub of water than in the crew compartment.

So for those times when radiating away excess heat isn't possible, we have to store that heat.

You do bring up a good point about power plants needing a certain balance of heat wasted, but this is an area I'm sure you know a lot more about than I do. Nonetheless, I have difficulty in seeing how it would be so hard to provide a proper environment for the power plant (and crew) and cool the area by dumping the heat into a heat reserve somewhere else. I am fairly sure that I am oversimplifying, for the same reason that you can't draw energy from waste heat by using a bunch of thermocouples, but since I don't understand why THAT doesn't work, it won't be easy to explain to me why the other doesn't either. (Not impossible, I hope, so if it won't eat up your day, or bore everyone to tears, I wouldn't mind yet another attempt to pound it into my thick skull. Sometimes I understand it for whole minutes at a time!)

For my own part, I view canon as useless mutterings where my own campaigns are concerned. A referee should NEVER be held to what other folk want to impose on his campaign. It may be a published universe, but any ref is free to pick and choose what he or she wishes to use for his or her campaign. Canon be damned. If you have the source, you like it, and if it is that good, you would be foolish not to use it. Its your game. You owe it to yourself and your players to use what you feel is best.

Oh, of course, of course! I propound that argument quite often myself, though probably not so well. However, it is impossible to compare notes with people who do not use the same notes! I can talk all day about the way I do jump drives, but since it's not the official way, who's really gonna care? (If you really want to know, I'll tell you.) We discuss stuff here for two reasons: 1, we want to understand something that we aren't quite getting, and 2, we think we can do something better and want to convince others we are right (or find out why we are wrong) so that an "official" * change will be made. Only a few people will bounce some ideas off everyone else, with no desire at all to convince anyone else of their superiority.

* I say "official" because we all know that our suggested changes are doomed to not be incorporated into the existing games; those are already published and the companies dead or not listening (no slight intended, Hunter, but are you really going to recall all your product if some one comes up with a better idea?), but if the community accepts it as being the right-thing-to-do, then it will be incorporated into most people's games and that's the prize we want.

 

[aramis]

the jump bubble is a radiant source... but is it actually incapable of absorbing some heat?

IMTU, I've always assumed that energy sources can cross the jump bubble membrane without problem... the jump bubble, IMTU, simply keeps the atomic and molecular cohesion stable within Jspace... where they normally fail.

 

[Malenfant]

How do you get heat from the ship to the jump bubble?

 

[mike wightman]

Radiation and convection of the small amount of hydrogen???