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Old 02-25-2020, 09:04 PM   #21
Fred Brackin
 
Join Date: Aug 2007
Default Re: Nerfing fuel purifiers

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Originally Posted by Anthony View Post
Protium fusion is basically 4H (4.0313 AMU) -> 4He (4.0026 AMU) for a net loss of 0.0287 AMU, or about 7.2%, which is maximum energy yield of about 6.4e+12J/g; over a year (3.2e+7s) that is about 200 kW, so 140 grams is 28 megawatts, or less depending on efficiency (Traveller probably can't capture the neutrinos and likely doesn't have perfect efficiency, so I'd assume not more than 20 MW).

2 liters looks low, at least for a CT reactor outputting 250MW per EP; perhaps it was originally 2 kg.
I'm pretty sure the assumption was De+De.

One of the factoids in my head is that Gurps' fusion reactors that carry 200 years of fuel derive from some numbers from MA Lloyd where one half of the reactor's volume was liquid deuterium.

I can't tell you how I came up with the 2 liters number this long after.
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Old 02-26-2020, 12:45 AM   #22
swordtart
 
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Default Re: Nerfing fuel purifiers

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Originally Posted by Fred Brackin View Post
A fellow once wanted to know how much hydrogen his fusion power plant used per week. After some calculations I was able to tell him that his multi-MW power plant fused about 2 liters per year.

Cracking water does not use a lot of power on a scale that has multi-megawatt power plants as the norm.
I was working from the principle that a 100 ton Scout uses 20 tons of fuel for 1 month of life support and 2 G manoeuvre. Looking at it more closely, a 200 ton Free Trader only uses 10 tons for 1 month of life support and 1 G manoeuvre. This makes no sense to me. Even though we cannot use the tonnage as a mass (since it is a volume) we can probably assume that a Free Trader has proportionate mass. As f=ma, it needs the same force (thrust) to move a 100 ton ship at 2 G as a 200 ton ship at 1 G. Since both ships use the same A-type Manoeuvre drive, you would expect them to use the same amount of fuel. If anything I would expect the 200 ton Free Trader to use more fuel as it's power plant will be supplying more power as it has more staterooms to service and its surface area is larger (if heating is needed to offset thermal loss to space).

On that basis I am not sure CT fuel usage is anything more than "handwavium" anyway. If you accept that then delving into the science of it is rather pointless as clearly it isn't based on our current physics.

I note also that a domestic kettle is a multi-KW conversion device (turning cold water into slightly less cold water - from a fusion plasma standpoint - though water has one of the largets latent heats of vapourisation so we shouldn't be too sniffy), so a multi-MW device isn't that impressive other than for large values of "multi".

Let us assume plasma is generated by the drives/plants themselves (we'll assume there is a handwavium mechanism to get the power to generate the plasma (and any necessary plasma containment -maybe we use LIF?) - massive batteries perhaps and thereafter the plant taps off it's own power to maintain the plasma).

Now we could introduce water and thermally decompose it (and lets say it required little additional energy than thermally decomposing liquid hydrogen - "curse you Hydrogen Bond"). That still leaves the problem that you have lost 1/3 of your reactant compared to pure hydrogen. Now I suppose it depends where your fusion chain ends up, unlike fission where you are counting down, with fission you are counting up and in theory you could fission up to heavy elements. In reality there is a equilibrium to how much energy is produced by the reaction vs the amount of energy required to maintain the plasma. In our largest known fusion plant (the sun) it is about the iron (Fe) ion stage before gravity tends to collapse the core (if memory serves).

So on that basis we could easily get up to oxygen rich plasma as a by-product of fusion. If we are to believe that we can fuel with sea water then we are just starting with some of that oxygen in the mix already (but it might put extra strain on the handwavium which results in the extra risk of drive failure / misjump). This is analogous to a wood stove, you start with kindling and once it is burning well and the stove is hot, you add larger logs. If you put a big log in with the kindling at the start when the stove is cold, it will soak up much of the thermal energy, char and smoulder, produce acrid smoke full of un-burned wood gas and condensing steam which will condense as tar in the flue. Only once the stove gets up to a temperature to fully ignite wood gas will it start to burn clean. Burning incorrect fuel mix results in extra maintenance cleaning the flue and the risk of chimney fire, so the analogy isn't bad for fusion)

Normally for fusion we need at least deuterium as it has a neutron (and we need those to build the larger ions), but again we can invoke handwavium to maybe add a neutron source as part of the refined fuel mix. Unrefined water already has those of course in the oxygen and trace compounds. It might be easier to assume however that a neutron source (or generator) is part of the drive rather than an admix to the fuel.

Focussing only on the hydrogen end of the chain doesn't provide a complete picture, and we cannot stay there or we end up with the bigger problem of what do we do with all the other ions we produce. Part of your fusion cycle may be exhausting heavy ions out of the drive nozzles - since you need some reaction mass. This will be a balance of retaining plasma and generating thrust (a fusion rocket).

This is all a bit too "sciency" though for Traveller which is burdened with too much wet navy analogy.

Last edited by swordtart; 02-26-2020 at 03:47 AM.
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Old 02-26-2020, 09:17 AM   #23
Fred Brackin
 
Join Date: Aug 2007
Default Re: Nerfing fuel purifiers

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Originally Posted by swordtart View Post
I
On that basis I am not sure CT fuel usage is anything more than "handwavium" anyway.
Yes, stop there.
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Old 03-01-2020, 04:34 PM   #24
dcarson
 
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Default Re: Nerfing fuel purifiers

We always assumed that water was electrolyzed on the spot and the tanks filled with hydrogen. The unrefined part was the random other gasses from unpurified and non isotope separated hydrogen not storing water in the fuel tanks.
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Old 03-01-2020, 04:38 PM   #25
copeab
 
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Default Re: Nerfing fuel purifiers

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Originally Posted by thrash View Post
Using unrefined fuel, however, resulted in the chance of drive malfunctions or misjumps.
Military and scout ships weren't subject to unrefined fuel causing a misjump.

It is interesting that Book 2 says their drives are especially built for the use of unrefined fuel, but this affects neither chance of malfunctions or the cost of the drives.

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Book 5 (1979) introduced the fuel purification plant (p. 32), which processes unrefined into refined fuel on shipboard. These were cheap but bulky, with most of the cost in lost revenue space. (Paradoxically from a game design standpoint, this put the greatest burden on the small, PC-scale ships that needed it the most for the low-quality ports they serve.) The 1980 edition (p. 27) reduced the minimum installation to 3 dtons and Cr30,000 at TL15, well worth the cost for even the smallest starships.
Except that most commercial ships aren't TL15. TL12 is more likely, since that's sufficient for Jump-1 or Jump-2 drives, and TL 12 worlds are a lot more common than TL 15 worlds. It seems a major issue if only a handful of starports in a sector can repair or maintain your ship, rather than a couple dozen.
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