Some thoughts on fusion power, very scientific, possibly boring to some.

[Antichrist]

I really can't help thinking in certain ways and of certain things, and recently I began thinking of the ramifications of fusion power and what it means, and will mean if/when humanity ever gets it going.

The thing is that fusion power is going to make amounts of energy available that are impossible to imagine at today;s combustion scale. Basically combustion is a molecular process that releases about 1/32 billionth of the energy contained in a given mass. Seriously, molecular level processes like burning or rapid breaking of molecular bonds like in some explosives releases one about 1 out of 32 billion parts of the enrgy contained in mass, that's a pretty small amount of power, really.

Now fusion is a nuclear process that releases 0.7% of the energy in a given mass (This is all based on what I've picked up over the years, BTW)

So a fusion power plant, fusing hydrogen at maximum efficiency, releases about 0.7% of the energy that the mass of the hydrogen contains under E=MC^2.

An ounce of mass contains roughly one megaton of energy, if it were possible to convert energy directly to mass (And it is with the help of antimatter, for example.)

This all means that when a starship in traveller "burns" a ton of liquid hydrogen fuel in it's fusion reactor, it's converting 32,000 ounces of mass into energy at an efficiency rate of 0.7%.

This would mean that it's creating 0.7% of 32,000 megatons of energy, or about 224 megatons of energy. Now we have to assume some of the power is lost thru various means, even so if we round it down to 200, it means that each ton of liquid hydrogen 'burned' in a good fusion reactor produces about 200 megatons of energy.

That amount may be comparable to the total combined power of all the explosives used in ww2, from just one ton of liquid hydrogen. Think of how much liquid hydrogen a beowulf uses every time it jumps, and we see that when the captain of a beowulf order a jump, he's essentially commanding an amount of energy that would make the total amount of force used in WW2 pale in comparision.

If all that energy were released as a single explosion... Well, think about it.

So in traveller fusion powerplants in private hands may be commonplace, byt by today's standards even a run down, sagging rustbucket of a free trader generates and uses power on levels no one alive today could command.

Asides from the power issue, there's the fact that while 0.7% of the liquid hydrogen tossed into the reactor gets turned into energy, 99.3% remains as helium. I was wonderign where it went. Does it just get vented into space? I guess it could be done but it seems wasteful, helium has some useful properties after all. Liquified it makes a great coolant, and if liquified then rapidly superheated it makes a great non polluting propellent for a reaction drive. Just heat it thru the fusion reactor, vent it out the rear and you've got a decent reaction thruster.

If you fuse helium again, tho it takes more energy and force to fuse elements the higher up the periodic table you go, you get useful elements like beryllium, a useful metal, or after a couple more fusionings you get oxygen, a very useful thing for people in space.

I was just thinking of the ramifications and inmplications of fusion power, and wondered if anyone has done rules or such for using fusion to create hiugher elemntns out of hydrogen and if regular fusion reactors were capagle of it. If so it would mean a lot of basic elements could be produced as 'waste products' of energy production, and, for example, beryllium would be very, very cheap and common which would be a good thing as beryllium is useful for making extremely strong and light metals, like, say, spacecraft hulls and armor.

 

[Stainless]

That's an interesting calculation and quite sobering. I suppose one could just argue that shipboard fusion reactors work quite inefficiently, say 0.007% instead of 0.7%.

I don't see any problem with venting the He produced as space is a pretty big place. It could also be used for attitude control.

 

[travlar]

I do think that ships use too much fuel. Making higher elements might not be doable by ship reactors, but planet based ones might do it.

 

[Rover]

It is whole lot of energy, but then again who really knows how much energy it take to rip a whole in space time and bend it?

I do not think the fuel usage was based on any real world calculations, but it is more of a limiting factor on how fast and how far a Traveller could go in a week. Changes in the 1 week 1 jump rule and fuel usage could seriously affect the flavor of the game.

 

[Anthony]

Okay, 1 ton of hydrogen, fused to helium, produces about 7 kilograms of energy, or a total of 6.3x10^17J. Over the course of 30 days, we get about 240 gigawatts.

The canonical power output of a 1EP high guard fusion plant (uses 1 dton/month) is 250 megawatts. This tells us that High Guard power plants use about a thousand times too much fuel. FF&S power plants have a somewhat lower power density and use less fuel, but still about a hundred times too much.

 

[robject]

Fusion power produces a staggeringly huge amount of energy. The number I once heard bandied about is "less than one cup of deuterium = one round trip to the moon".

What this means is that standard power plants in Traveller are not fusion power plants in the same way we think of them. They may contain a fusion reactor (hence the name 'fusion' powerplant), but

(1) it's probably tiny
(2) it's probably not what the fuel is for

In other words, the power plant is still a magic mcguffin used as a balancing element to the game.

It's quite possible that most of the power plant's volume is dedicated to some fancy high-tech fractal-ceramic heat sinks.


Side Note The "fusion plus" power plants in T4 had incorrect power output tables, giving them waaay too much power, though nowhere near the output of a true fusion plant.

 

[Plankowner]

Not to throw a wet blanket over this discussion, but several of the assumptions about the efficiency of the system are quite a bit over stated.

Your inefficiencies are not going to be "round 240MT to 200MT" they are going to be more like "round 240MT to 2.4MT". Not all of the hydrogen is going to fuse into helium, not by a LONG shot. Only about .1% of the hydrogen will fuse into Helium, THEN you get 7% of THAT for energy.

Now that you have the energy, you need to convert it to something useful, like electricity. Using a Carnot cycle, which is the theoretically most efficient possible, you will only get about 50% of the energy into useful work. BUT, since things are real world, and not theoretical, you will probably get less than 50% of that work.

The submarine that I was on was about 20% efficient through the entire work cycle. Even with advanced engineering, figure you won't get much more than 30%-40% and that is REALLY pushing the science, not just the engineering.

Take all that into account and you have a much lower efficiency. You also have another huge problem. For all that energy you converted to Electricity, you have all the REST of the energy which also must be dealt with. Typically, this will be HEAT. You HAVE to have an exhaust (unfused Hydrogen and fused Helium) just to get rid of the excess heat. If you want to use it for propulsion, go for it, but either way, the heat must be gotten rid of. Radiant Fins are all nice and good, but they probably won't be able to get rid of the necessary heat.

While I was still in the Navy and had all the numbers at my finger tips, some friends and I worked this same equation. We figured that an EP (1Dton/Month) was a maximum of 1 Gigawatt. That was a theoretical maximum using some pretty generous assumptions for material heat transfer rates etc. We used a Fission Reactor design as the basis of our work cycle, so we figured we were going to be close. HG's 250 MW for an EP, is a lot closer to a "real world" number.

 

[Anthony]

Why do you think only a small fraction of the fuel will fuse? If you can manage fusion at all, it's relatively simple to filter the exhaust so very little hydrogen ever escapes, which means probably 90% or so will fuse eventually. Generator efficiencies can vary quite a bit depending on how it's structured; MHD generators for fusion could quite possibly exceed 50%, since the maximum efficiency of a heat engine depends on the temperature ratio of hot to cold end, and the hot end is VERY VERY hot for fusion.

 

[Uncle Bob]

I like Plankowners numbers. Even if tyou could get a higher percentage to fuse, you still will waste a lot of "fuel" mass on heat transfer. Also running on "unrefined" fuel makes no difference to consumption rates and methane is only 25% H and water 10% (by weight),which implies the greater psrt of the fuel is not burned, but used in some other manner.

MHD much over 50% gets very problamatic, usually requiring extremely long, even multi-stage nozzles. But even 90% efficiency doesn't move the power much. At that, a single gigawatt of power (1 EP) will still need a superconductor to move it around the ship.

 

[TheEngineer]

Hi !

Well, I thought I already replied, but did not work well

IMTU I assume fusion plant to use the D-D reaction. Natural hydrogen only contains 0,01 to 0,02 % deuterium. The rest is needed to form a proper plasma matrix and as a heat carrier.
CT and MT use awfully clean plants and drives, so some aspects like exhaust behaviour and heat removal is covered by a magic layer

Well, in my assumption I need to get rid of the "rest", otherwise it could be recycled. So I just say theres a buffer which is released, when planetside is left ......

The key to Traveller power conversion is NOT to use a thermodynamic process, but a direct conversion of kinetic energy into electricity (like MHD). Those processes are not subject to efficiency limitations like a carnot process.

Because of the enormous mobility and engineering capabilities, I strongly believe, that high tech mining is much more efficient, than any try to create some materials via nucleosynthesis...

(TV show starts ...)

Regards,

TE

 

[Anthony]

Originally posted by Uncle Bob:
I like Plankowners numbers. Even if tyou could get a higher percentage to fuse, you still will waste a lot of "fuel" mass on heat transfer. Also running on "unrefined" fuel makes no difference to consumption rates and methane is only 25% H and water 10% (by weight),which implies the greater psrt of the fuel is not burned, but used in some other manner.-

It's unclear what unrefined fuel is, but liquid methane and water both contain more hydrogen per unit volume than liquid hydrogen.

As for Traveller ships using D-D fusion, there isn't enough D, and even if you ignore that problem, it implies the ability to reduce your fuel consumption by a factor of 1,000 or more by separating out the D.

 

[TheEngineer]

There isn't enough D ???
I see that problem of D separation and regular H recycling. Thats why I assume H to be exhausted ...

 

[robject]

I assumed unrefined fuel is plain old water or gas giant atmosphere, and refined fuel is liquid hydrogen... which doesn't seem to make sense to me, both being such different things yet able to sit in a tank and be used as fuel. But then I try not to think about it.

 

[TheEngineer]

Well, I would say refined = purified = no contents except D and H + perhaps a exactly defined proportion between D and H ??
At least the MT ruleset explicitly states that fuel is hydrogen.

 

[Anthony]

Originally posted by TheEngineer:
There isn't enough D ???

Not to support the indicated power levels, no.

I see that problem of D separation and regular H recycling. Thats why I assume H to be exhausted ...

But then you'll just wind up with someone creating a closed-cycle engine. A system that reprocesses spent fuel can't be any more massive than a standard fuel processor. Theoretically reprocessing might not make sense if the hydrogen is being used to carry off waste heat, but then the fuel consumption is too low; the hydrogen has to be so hot that it makes no sense not to cool it down to generate power.

 

[Plankowner]

MHD would be potentially more efficient than a Carnot Cycle. At the time I was making these calculations, I didn't have access to MHD numbers, but I did have access to efficiency numbers for RW Nuclear Submarine Fission Reactors. I goosed those a bit and went from there.

I agree that direct Heat to KE or Heat to Electricity (Piezoelectric circuits) COULD be what is really going on...

 

[Antichrist]

I diod not want this thread to start a lot of hostility, just to point out that while some people think traveller may be 'low tech' it actually has some pretty awesome technology to it, when you think about it.

I mean, the amount of energy even a common free trader can produce is staggering when you crunch some numbers.

 

[Valarian]

A layman's view ... potentially completely wrong

I assume that TL9 fusion plants are D-T reactors. The later fusion plants in Traveller using the D-D fusion reaction to create tritium and run combined D-D and D-T reactions. I assume the deuterium is created from the hydrogen in the fuel processing.

From a layman's point of view this is probably close enough. I'd be interested to know what any physicists think though. Is the processing of deuterium from water/gas giants possible?

 

[Anthony]

It's fairly straightforward (if possibly energy expensive) to separate D from H. However, liquid D2 is significantly denser than liquid hydrogen, so if fuel has a density of 0.07 kg/L, it's clearly not deuterium.

 

[TheEngineer]

Hi !

Anthony, agreed, natural D concentration is a bit low, but a concentration process about factor 4 or so (resulting in 0,5 %+ D/kg H), would be enough the provide potential for typical Traveller (MT) energy outputs.

Guess Valarians assumption is pretty good, as most real world research plants try to use the D-T reaction, too, because its much more easy to get a working D-T reaction than a D-D reaction.
The major drawback of the D-T reaction is, that T needs to be breeded, usually using Lithum (so Lithium would be a kind of fuel, too).
Down there is a link to my most favorite document regarding fusion research. Well, its in german language, but many figures are "international".
E.g. there a figure on page 9 showing temperature ranges and efficiences of different reactions.
The generation of deuterium during the purification is perhaps less likely as conditions for p-p reactions a pretty hard to reach, but anyway in our balckbox Traveller plant anything might be possible

I would suspect, that once we have starfaring capabilties processing of D from water or a gasgiant atmo would be no problem, too.

The link:
http://www.ipp.mpg.de/ippcms/de/pr/publikationen/pdf/berichte.pdf

Regards,

TE