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

[TheDS]

This is a multi-trav item, so don't zone out on the next sentence, this DOES apply to you.

Item 1: As I recall, in the initial FFS1 or FFS2 design sequence, they included radiators as part of the needs for a hull, whereas I believe they are not needed in any other version. I think they were later completely eliminated. As a side note, in the hard-science game Aurora, the designer also had radiators, but acknowledged that the radiators were insufficient to truly cool a ship of more than about 10,000 metric tons.

Item 2: Other, non TNE/T4 ships have large fuel requirements for powerplants, like the suckers are BURNING hydrogen instead of fusing it. TNE gives us the unique maneuver drive that sucks down the go-juice as a replacement for reactors that barely need to be fueled at all.

Item 3: Jump drives use a cubic butt-ton of fuel. Why? SoM (the beloved, yet banned book of perfection that it is) theorizes that most of the fuel is actually ballast, dumped over the side over the course of a jump, whereas I think every other game just assumes that it is used, again, burned instead of fused, considering the amount of energy that would be produced. Further, a ship in jump gets rid of its heat... how?

Thoughts: All these things add up. Firstly, a Traveller ship, no matter what rendition, devotes about half its space to fuel, give or take. Using a few formulas from the real world physics books, we can easily see that these ships carry WAY too much fuel for the amount of energy they use. Plus, where does all that waste heat go?

Answer: The large fuel reserves are actually a heat sink. We all know water can absorb a lot of heat energy. Now, I haven't whipped out my calculator, but I am reasonably sure that a ship devoting half its volume to water, starting at 1 degree celcius (or below if we add some really effective anti-freeze in small quantities) will be able to hold quite a lot of megajoules of energy until it hits 99 degrees celcius (or more, if we also have some very effective anti-steam), and that over the course of a typical 7-10 day journey, during which we have no other way to really rid ourselves of the waste heat (though maybe we'll carry retractible radiators for mergency purposes) we can probably have plenty of heat-storage capacity; enough to get us between destinations.

At the destination world, you can either have somebody power your water cooler for you (real ships run on shore power when they're in port), or you can trade your hot water for their cold water.

Frontier refueling means splashing into an ocean or grabbing an ice-asteroid. The starport can make money swapping out water. The hot water would raise local temperatures, but this can be balanced by building a solar shade around part of the planet, and it's not like all those reactors of industry aren't doing the same or worse as it is. Other things, such as liquified methane or perhaps liquid hydrogen can be used when skimming gas giants, assuming their thermal properties would allow them to store similar amounts of energy.

I would like to know if you guys think this is realistic, AND if you think it is canon-worthy, and I wouldn't mind a bit if the ideas expressed here were expounded or expanded upon a bit if it is a useful idea.

It seems to me that if this works, it means we can have reactors, Thruster plates, and jump drives, all with inconsequential fuel needs, but have our endurance limited by the amount of coolant we carry. Kind of like heat management from Battletech, in a sort of way, except the heat doesn't go away, and you have a lot more capacity for it. It also means we have a solid, realworld reason why we have cool-looking ships. My primary worry is that there won't be enough heat storage capacity to allow for deep space missions, but I guess that's what radiators are for.

Ok, your turn.

 

[Malenfant]

Is it the specific heat capacity that tells you how easy or hard it is to heat something up?

Because the specific heat capacity of liquid hydrogen (at 1 atm pressure) is 10 J/(g K) according to this

Whereas the specific heat capacity of liquid water at 1 atm pressure is about 4200 J/(g K), according to this (the value for hydrogen there is for the gas at r.t.p).

So water would be a vastly more effective storage medium for heat than liquid hydrogen. Unfortunately, starships don't run on water, and storing water takes up a lot more volume and weight than liquid hydrogen.

 

[far-trader]

Re: Item 1: Not sure it was specifically intended as heat radiators, there was a need to work with surface area as a factor*, but it was pretty insignificant. This was(is) always a hot topic (blatant pun intended) on the TML and iirc the energies purported to be used result in your ship melting even with 100% efficient radiators, including heat dumps I think.

* for jump and maneuver but not as I recall power, for FF&S1 anyway, never really looked at the second edition much

It is true (for a sphere at least) that as volume increases the ratio of surface area shrinks (I think). So simple radiators become less useful. Also radiators work much better in a convection medium and really suck in vacuum. Vacuum is a great insulator.


Re: Item 2: Well TNE uses it (I think) as a reaction mass (which could double as a heat dump, maybe). I always figured it this way for CT (pre-HG) too.


Re: Item 3: SoM is not so much banned as, erm, what's the term again, nope, can't recall. Oh well, anyway I still reference it

I also like that most of that fuel is a heat dump though that's not quite what I got from SoM. It suggests most of it is burned for energy with some fraction used for heat transfer, over the radiators. Others think you use most of the fuel as either a buffer in and from J-space or to ease the transition. It could do all three (heat dump, bubble, and shock absorber). A ship in J-space might be more worried about keeping warm, at least I've always thought it could be a super heat sink and that much of the waste heat from the jump drive is lost in making the hole, then the field keeps the cold away, insulating the ship.


Re: Thoughts: Yep, linking it all together is the way to go, with one more item (to my mind), the actual energy listed as needed for all these systems should be cut by at least 10x maybe 100x so we can deal with the heat issue. It seems nuts to me that thousands of years from now it'll take the energy requirements of a small city to run a small starship. Granted the jump drive and maneuver drive are very efficient no matter how you cut it but since they are totally science fiction there's nothing saying they need to use that much energy either.

So tie in the fuel is a heat dump and energy requirements are overstated and I'd be happier. No need to change the size of anything either. So the power plant stays the same size with the same fuel requirements only with an output of 10% or even 1% and all the systems the ship needs to power get the same scale back in power required.

Suddenly the reason for a set "fuel" over time makes more sense as it's mostly to keep the ship cool. And with cooled ships and lower energy signatures in general we can actually have ship's sneaking around again and make piracy and blockade running possible again.

Realistic? Maybe a little more so and that might be good. Canon worthy, who cares, it's not gonna happen. Did I say that? Am I actually advocating heresy?? Anyway, I've seen many good ideas suggested to fix problems in the game. I've never seen them adopted that I recall.

 

[TheDS]

While I would hope things would be a little more energy efficient in the future, there are a lot of things that really can't be reduced in power consumption. Weapons, as we learned in FFS1, consume prodigious amounts of power. A ship without weapons doesn't consume all that much power. Sensors also consume a lot of juice, though this is not at all well represented in the books. Real radars that see only a few hundred miles consume several megawatts of power (like about 5 of them).

In space, you would need a lot more power to see the couple light-seconds out that you would want to see. There is a fudge to this, and that is narrowing your search beam and using it much like you would a spotlight that eventually goes through the whole sphere, and use another omnidirectional radar for close in detections.

Most of the heating of the ship (to passenger-comfort levels) can be done by using the waste heat from the reactors, or simply basking in sunlight if you're in the hab-zone. At some point, you'll have to turn to cooling, though. At any rate, that will save you some energy, but running fans does take energy, as they have to move a LOT of air. I don't know if any of you have been aboard a ship, or perhaps in a large building, but the air ducts are large and have to have powerful fans to move the air through. Probably not a big energy drain, but enough of one that I mention it.

Let us not forget the computers and other electronics. These things use power, and when every stateroom has a computer or two for recreational use, well, that adds up.

I am sure there are some things that could be reduced in their power requirements, but I never really had a big problem with that. I did, however, have a problem with the gigantic reactors (as compared to a HCD engine of the same output), especially after learning that some experimental fusion reactors were capable of energy densities on the order of 100 or more Mw per kl. Then I realized this was just reaction space, and didn't take into account all the other things you need to extract energy from a reactor and keep the reaction away from the more sensative parts it is powering for, like the crew. Strangely, most people have some kind of allergic reaction to megaKelvins. Go figure.

Anyway, I have, with further study, found that reactor fuel consumption is negligible as a percentage of the ship, so we can just say we have it and leave it at that.

So anyway, I don't see a big power problem.

Mal: Yes, I believe that is the correct term we are searching for. I've never really liked LHyd that much. The stuff requires you to refrigerate and insulate it, costing you lots of energy and space and mass, it can't hold a lot of heat before it turns back into a gas (it's boiling point isn't much above 0 Kelvin), plus it has this irritating property of exploding at the wrong time. Water has so many great properties. It holds lots of heat, it doesn't explode all that often, and you can get free oxygen to breathe, plus you can also keep your reactor fueled from the hydrogen, just from cracking it.

I had hoped LHyd would hold more heat than that, but I guess not.

At 4200 Mj-Tn/K, the 100 degree difference that water is liquid means that it can store 420 Gj per metric ton of water. If our ship is half fuel tank, and 1000 Dtons, that's 7000 tons of water, and can hold almost 3 billion Mj. If our reactor is a 1000 Mw reactor (no book handy to tell me if that's reasonable), then the water can hold 3 million seconds of energy, or about a month. (!)

Of course, we're not going to be at full output for a whole month, so we can get by with 1/10th that easily, I'm sure, and still have plenty of capacity for normal operations. Combat operations will be limited to about 3 days, though.

Did I do that math right? And did I guess anywhere close to reasonable assumptions for power used for the ship's size?

If this is close to correct (or even a bit conservative), then I think we have stumbled onto a winner.

 

[Commander Drax]

Not that I am any kind of expert, but I think the problem begins with the original high guard, in which the traveller m-drive is described as being like a 'plasma gun' and the fuel requirements linked to the power plant (1 ton per EP per week etc)were assumed to be fuel for the reactor and also reaction mass enough to last a month. There's another sentence in there somewhere where it advises multiplying the duration in weeks by 4 or 5(? cant quite remember) if thrust is not being used.

Sadly the scientist in me tells me that using a plasma drive to cruise at 1-6G for 1 one whole month requires much more fuel than can be contained in the ship's entire volume.

MegaTraveller tried to fix this by explaining the m-drive away as a reactionless drive with the hydrogen being power plant fuel.

Amazingly TNE returns to form and explains the drive as Heplar with a small amount left over to power the fusion reactor, the bulk of the fuel being reaction mass making TNE closer in spirit to CT than anyone might have guessed. As for cooling TNE introduces hull radiators that I don't like because convected heat can't be carried away or dissipated in vacuum, which is why the sun stays hot.

I've got no problem with hull radiators for atmospheric craft though as they would work just fine.

T4 and indeed T20 have nothing further to say on this.

My own take is that ships for whatever reason generate lots of heat and have bigger problems staying cool than remaining hot, even in the deepest and blackest parts of space. Regardless of the M-drive used fuel consumed by the power plant is miniscule the rest is fed under pressure into the reactor housing as coolant that instantly vaporises and is then vented into vacuum carrying away the heat energy with it (hence no need for hull radiators)(and if in jump helping to maintain the jump bubble). I agree that water for a variety of reasons is better coolant but it's also heavier.

As a solution to these technical challenges what I would like to do (and please bear in mind this is only an idea)is explain away fuel as hydrogen consumed by a plasma drive (CT) that has built into it a means of switching of mass this technology I have described as MRT (Mass Reducing Technology) and has a real basis in science as mass is a property of particles at the quantom level and theoretically can be shut off at least partially reduced. In effect a 2000 tonne vessel fitted with this might from the drives point of view only have an apparent mass of 2 tonnes, enough that a moderately efficient plasma drive could push at for 30 days or beyond. Higher power delivered to the MRT would increase this effect thus allowing larger accelerations or the ability to overdrive the engine like in SOM and allow a 1G ship to safely escape a 1G gravity well. It would also explain a vessels ability to hover easily in a gravity well and take off and land with ease.

I originally thought this up to try and explain how Heplar could be so extraordinarily efficient and postulated that it contained MRT equipement in the drive which half justified the enormous amounts of power allocated to it.

I am currently in the middle of writing my own RPG rules (very much into hard science) and this is an explanation that I've included in the rule set.

What do you think?

It meets traveller tradition, makes the drives efficient and effortless to use whilst maintaining scientific integrity as the said drives are not reationless, and gets rid of the need for vast amounts of coolant

If you like it I'll include it in a new ship design system I am writing for T4 (and hope to have accepted for T5)

 

[Andrew Boulton]

I'm pretty sure the reaction drive idea was 1st ed HG only.

 

[Uncle Bob]

Book 2 and 2nd ed HG assume te maneuver drive is reactionless, although not "thruster plate". It could be gravitic, or Woodward/Machs Principle, or spin/momentum conversion, or something I haven't thought of.

That doesn't explain where the heat goes or why so many designs have glowing nozzles. But the hotter the radiators the smaller they can be. I assume what look like rocket nozzles are actually white hot radiators and flared shields to protect the ship from the hest.

 

[mike wightman]

IMTU the maneuver drive does several things:
it counteracts local gravity just like the null grav modules on an air/raft or the contragrav idea that TNE eventually introduced;
it reduces the inertial mass of the ship so that a small fusion exhaust is capable of achieving up to 6G of thrust, limited only by the amount of acceleration compensation and inertial mass reduction that the maneuver drive can generate;
it generates a plasma field around the ship that deflects harmful charged particles, and thus limits the radiation exposure of the ship crew.

 

[Commander Drax]

The reason why so many designs have glowing nozzles is because like all fiction Traveller is influenced by the portrayal of technology as seen in movies/tv etc in which case vessels such as ships in star-wars have glowing nozzles. I agree that in truth the thrust plates do not have to glow but probably would if used as a heat sink. As for where the heat goes, conducted heat can't go anywhere in a vacuum not unless the substance carrying the heat has the opportunity to expand or at the least interact with a cooler substance and transfer heat thermally, which is why I postulate that CT/MT drives vent plasma to stay cool (hence the fuel consumption) or that plasma is diverted through thrust nozzles and further heated by the power plant to provide thrust, whilst TNE/T4 vessels use radiator fins (not totally useful). This is one of the main reasons why I think starships of the future will most likely be nuclear powered as a nuclear powerplant can be efficiently cooled in a closed loop system with water (pressurised water reactor)as opposed to a fusion power plant that whilst more efficient at generating energy has some inherant problems.

 

[mike wightman]

Originally posted by Uncle Bob:
Book 2 and 2nd ed HG assume te maneuver drive is reactionless, although not "thruster plate". It could be gravitic, or Woodward/Machs Principle, or spin/momentum conversion, or something I haven't thought of.

1st edition book 2 implies that a small amount of the fuel needed for the power plant is used as reaction mass for the maneuver drive. 1st edition High Guard flat out states that the maneuver drive is some form of fusion rocket.
The module Beltstrike also implies that fuel is used by the maneuver drive as reaction mass.

I don't recall Book2 2nd edition or High Guard 2nd edition even implying how the maneuver drive functions.
It depends on interpretation I suppose, especially since a High Guard designed ship can have a maneuver rating of 6G and yet have an agility of 0 because all of the available EP's can be used for weapons and shields. Therefore the ship can maneuver at a full 6G for 0 EP - a powerless, reactionless thruster

The T20 system of requiring the maneuver drive to be powered removes any ambiguity though, and is a much better system because of this IMHO.

 

[aramis]

Originally posted by Malenfant:
So water would be a vastly more effective storage medium for heat than liquid hydrogen. Unfortunately, starships don't run on water, and storing water takes up a lot more volume and weight than liquid hydrogen.

Actually, water is very effective for storing Hydrogen... and oxygen.

Water: H20 2:16 mass ratio H to O, assuming Monohyd in the water. Density=1 Hyd Density per mass=0.111
LHyd: H2 4 mass per mol. Density=0.07 Hyd Density per mass=0.07

If one has the fuel-flow capability to crack the water in route, one can store about 1.5x the hydrogen as water than as LHyd. Additionally, the extra mass is useful for singking heat, and it means NO O2 needs be stored (in fact, such a situation will USUSALLY result in needing to DUMP O2 overboard anyway).

H20 is also non-cyrogenic, and not vaccsuit permiable. a MUCH safer way to store fuel. (in fact, this provides a means of cheapening the costs of CP's considerably: Refine on-site from water, rather than carrying it as LHyd.) OK, so it will require a small amount of power to crack...

Also, NO traveller ruleset requires you to have an FPP to use unrefined frontier refueling. You need either water, amonia, or methane to crack, in either liquid, compressed gas, or solid form... so, apparently, you can just slap water in to the Fusion plant... but you may get unexpected results from a jump if you run your JDrive on it.

This has always implied to me that traveller Fusion power is working up to the Oxygen+__ stages...and is producing a range of stuff up to Atomic number 16... Mostly He, Li, and C, in a variety of isotopes...

Under MT, I've built some scouts which could crack fuel fast enough to use it for the PP...

Hull radiators on starships work not by convection, but literally by radiation. (The US Space shuttle has to open the bay doors to expose the radiators within a couple hours, or she'll have to return. And she runs far less than a Mw...)

In theory, up to three fins could be used to increase radiative capacity... 2 on opposite sides of the ship is optimal performance per fin, as No radiation is recaptured on other radiators. At three, suddenly, the radiators are each losing 1/3rd of each fins radiation is landing on other fins, and hence is not lost; this assumes, of course, that the albedo is in fact 0... but many radiative materials will have albedos above 0.5, pushing the inter-radiative losses down to about 1/6th. At the point that albedo (if it is above the heat gain from the heat pump systems and such) will make 3 fin more efficient than two fin.

At four fins, you'll ABSOLUTLY NEED an albedo higher than 0.5, as half of the radiation lands on other fins.... if you can radiate in a zone where you are still at an albedo of 0.75+, 4 fins becomes workable.

Big ugly nasty discussions on this have been held on the TML...

Personally, I've always assumed that part of the cooling of the PP is pre-injection heating; much of the heat is vented as plasma while underway, and not all of it is post-fusion. (In any case, fusion plants with steady fuel inputs WILL need to vent product plasma...)

Likewise, I assume a large part of the Jump Fuel is used as a coolant, and vented into Jumpspace...

But, IIRC, the temperatures needed on the radiators, when someone worked them out, turned out to be on the order of 3000°C.... in order to support the TNE rates.

 

[Spinward Scout]

Re Item 1: Uh... I'm pretty sure Starship Operator's Manual had heat sinks on the hull. Wish I could find mine... [going to go pout before finishing]

Re Item 2: I've never quite understood this either. Fusion is supposed to produce enormous amounts of energy with very little fuel. Can't comment on TNE - me and Heplar don't get along. That one's just asking for a visit from the Interstellar Enviromental Protection Agency.

Re Item 3A: Energy is pulsed out into the "jump grid" (in the SOM only) in a certain pattern to create the jump opening, but then fuel is still needed over a week to maintain the jump bubble or misjump occurs.

Re Item 3B: Space is cold - real cold in shadows. Like colder than a Chicago winter. Heat radiators would work really well, I would think.

Thoughts: I've always thought that the fuel requirements should go down with each successive tech level. Waste heat? What ever happened to Cold Fusion? Considering us here on planet Earth (in real life) have never had a sustained fusion reaction that generates sufficient energy to make it more than just an experiment, fusion power is Science Fiction at this point. Make it work the way you want it.

Answer: Traveller isn't as "Hard Science" as everyone thinks it is.

Noooo, did I just say that?

Scout

 

[TheEngineer]

I regard the combination of heat sinks and radiators as a very interesting and "cinematic" aspect of spacecraft. (Yeah, I really like those spaceships fitted with square meters of 3000 K radiators

) Maybe this is more "pseudo-realistic", too. I made some contributions to this appearently frequently re-appearing topic in the TML, too... (Ok, I never will do such a thing again....)

Anyway, as "heat" never really was a point of interest in the rulesets or design sequences I use (CT/MT), I simply assume, that there is one component of the power plant, which is able to "convert" heat = kinetic energy directly into electricity, without using a typical conversion method like a turbine. This component is also useable to recyle waste heat of other areas back to electricity. Problem solved...

Regarding the vast amount of fuel/hydrogen needed to keep a power plant running I just assume, that its just a tech-level related design limitation to work at these efficiency levels.
A large amount of actual fuel might be needed to ensure a homogenous environmment in the fusion ring chamber and - as Aramis noted - to get rid of the waste products.

So, generally I just take it as given in the ruleset

Regards,

Mert

 

[mike wightman]

Jump drives, psionics, grav plates, acceleration compensators, neutrino detectors, "meson" guns, nuclear dampers, "meson" screens, black globes, no heat sinks, null grav modules, etc...

You may have a point there, Scout

 

[TheEngineer]

All these things already exist in reality !
Government just prevents us from using this stuff.

 

[Commander Drax]

Does anyone like my MRT idea?


Is it worth writing into the new ship design sequence I've been detailing?

Should I submit it for T5?

I still dont understand how these hull radiators would work by radiating heat in vacuum.

For heat loss to occur those plates whould have to be shedding particles making them brittle after a while (though probably changed as part of annual maintenance), not to mention incredibly bright to look at. As previously posted by Uncle Bob perhaps this could account for the characteristic engine glow of traveller ships.

 

[mike wightman]

Yes, I like the MRT idea

Especially since it is similar to how I have expained it IMTU for the last twenty something years

It's something that is definitely worth writing up for a MTU, but if you can get it accepted for T5 that would be even better.

Do a google on black body radiation to find out a bit more about the use of radiators as a method of cooling a ship. If Traveller ships were to include a realistic treatment of radiating away waste heat then you can forget about stealth

 

[Commander Drax]

Thanks for that Sigg,

I knew I could rely on you,

Many Thanks

 

[aramis]

Actually, ambient "temperature" in space depends on a lot of factors; the level of vaccuum is not absolute. (Measured in mols per kiloliter or less... sometimes even mols per liter in certain areas).

there are basically three kinds of cooling: Convective, Conductive, and Radiative; convective is actually a subset of conductive.

Conductive: The vibrational energy of the molecules (temperature) is transferred from one source to another. High-energy sheds to low energy; the larger the difference, the faster the rate of transfer.

Convective: when the conduction of heat goes to some forced flow or free-flowing working fluid, conductive cooling maintains a higher transfer rate by passing fresh, still cool, working fluid over the conduction point, resulting in optimal transfer of heat out.

Radiative: All objects transfer thermokinetic energy into radiation at a (fairly) steady rate; usually this is in the infared spectrum (but can be, based upon temperature and material, forced all the way into the far UV and theoretically beyond). if that radiation is not recaptured by neighboring molecules, it "radiates" in to space; anything it hits will either bounce or absorb said radiation (usually some combination, as nothing has a true albedo of 0 nor 1 across the whole of the spectrum).

Key example of radiative cooling: an incandescent lightbulb. That fillament is in a vaccum, so that it does not have significant conductive nor convective cooling. It is heated by electrical resistance until it's high enough energy that the radiation given off is into the visible range (it also gives off quite a bit of IR, which is why/how an EasyBake oven works). The bulb works because enough of the energy is shed as EM radiation (IR and Visible light) that the filament does not continue heating to the liquifaction point, but not so much as to cool below visibility.

Earth is heated mostly by radiation: all em radiation, when it strikes solid objects, has two effects: Current induction and thermokinetic heating. What proportion is dependant upon wavelength, material, and material temperature; I don't quite groc the details of how to figure which is what fraction. In any case, the IR-UV spectrum, where most of the solar energy falls, creates thermokinetic energy (heat) when it strikes the air, ground, and water. Which is why alaska is colder than hawaii; the same cross-sectional area of emmission lands on a larger area of surface, reducing the energy density. At night, a significant fraction of the gained heat radiates back into space (or bounces off clouds, back to the ground, on a cloudy night).

In vaccum, there is next to no conductive heating/cooling, and therefore convective cooling is either based upon shedding a working fluid, or transfer to a surface with good radiative properties.

Some theorize that conductive transfer of heat (thermokinetic energy) might actually be a specail case of radiative processes.

Additional complication: Once radiated, the heat remains radiation UNTIL ABSORBED... that radiation is subject to normal rules of reflection...

Since the specific heat of the working fluid is a factor, and the specific heat times the range between liquification and vaproization is the practical range for most working fluids (Actually, water can be used for over 100degrees, by keeping it under pressure and/or by using a closed loop steam system and hgih-temp steam; 400 decgree C steam is not unheard of for HP steam systems).

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...)

 

[TheEngineer]

Hi Drax !

MRT is truely another alternative.
At least it enables to keep most of the given design sequences.
But as it relates mass of the ship and thrust again, will You skip the 6g manuever drive limit, too ?

Regards,

Mert