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Old 02-15-2020, 10:27 AM   #1
thrash
 
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Default Nerfing fuel purifiers

I am looking for a reasonable justification for restricting fuel purification plants to ground installations and making them impractical for PC-scale starships, in order to promote a return to an "old school" Traveller relationship with unrefined fuel.

In the original (1977) and revised (1981) three books of classic Traveller, the use of unrefined fuel was both a hindrance and a necessity. Refined fuel was available only at class A or B starports; unrefined fuel could be obtained at class C or D starports, by gas-giant skimming, or (1981) from oceans and lakes. (Note that the water was "used as unrefined fuel" (p. 6), rather than processed somehow.)

Using unrefined fuel, however, resulted in the chance of drive malfunctions or misjumps. This imposed a distinct "terrain" on the star map: voyages had to be planned around the availability of fuel sources, and visiting a better quality starport for refined fuel was a definite plus.

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. This removed virtually all restrictions due to lack of refined fuel and pushed most fuel-related considerations (even gas giant skimming) into the background.

If "refined fuel" is simply pure liquid hydrogen, and "unrefined fuel" is hydrogen-containing material with other contaminants (helium from gas giant atmospheres, oxygen from water, etc.), it's hard to see why this wouldn't be possible. All ships capable of gas-giant skimming must be able to compress and liquefy gaseous hydrogen (albeit perhaps inefficiently, with lots of wastage to carry away residual heat); this could remove most of the helium at the same time. The 1981 quote about using water directly as unrefined fuel implies that the process of "burning" jump fuel can separate oxygen from hydrogen in stream and dump the former. Separating hydrogen from oxygen by electrolysis of water (as, presumably, happens in a fuel purification plant) is energy intensive but simple.

So, what then? My thought was to instead define "refined fuel" as pure protium -- hydrogen without any deuterium present. Naturally occurring hydrogen is ~0.03% deuterium by mass. Removing this fraction (usually to capture the deuterium for nuclear power applications) is more complex than separating hydrogen from other elements, since the chemical and physical properties are very similar. My research suggests that these processes don't scale down as readily as electrolysis.

My questions to the hive mind are:
(1) Does this approach make sense, or is there a scalable method of refining light hydrogen I've missed because it would be uneconomic without (say) fusion power?
(2) Is there a different approach that would solve the original problem?
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Old 02-15-2020, 11:05 AM   #2
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Default Re: Nerfing fuel purifiers

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Originally Posted by thrash View Post
(1) Does this approach make sense, or is there a scalable method of refining light hydrogen I've missed because it would be uneconomic without (say) fusion power?
One dton is a lot of space; the normal methods seem like they would fit inside anyway. I suspect given Traveller power availability mass spectrometry might be viable.
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Old 02-15-2020, 12:38 PM   #3
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Default Re: Nerfing fuel purifiers

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Originally Posted by thrash View Post
My questions to the hive mind are:
(1) Does this approach make sense, or is there a scalable method of refining light hydrogen I've missed because it would be uneconomic without (say) fusion power?
(2) Is there a different approach that would solve the original problem?
It works fine for technobabble, and probably makes as much sense as anything will in reality. But while isotope separations are more difficult than simple chemistry, they aren't generally amazingly hard either. Protium/deuterium is the easiest of them, what with that 1:2 mass ratio, and boiling liquid hydrogen would be one of the easier ways to do it. If you can do industrial scale hydrogen liquefaction on shipboard you should be able to extract most of it just by doing it twice, with an intermediate boiling step. Given that you probably have to do intermediate boiling steps *anyway* - one of the things that makes hydrogen liquefaction much, much harder than it naively appears is the slowish para -> ortho spin isomer transition means your liquid self boils on sitting even with perfect insulators if you make it by fast cooling room temperature hydrogen - it's probably easier to justify you can't make liquid hydrogen at all with something that will fit shipboard than you can't separate the deuterium.

I suspect the only thing that is going to "really" restore the difference is to ditch the concept that jump fuel is liquid hydrogen and require something more complex (and probably undefined). I've said before that Traveller ships apparently burn "space oil" anyway, as it's the only way to make sense of how much of the stuff they guzzle, apparently derived from wet navy models.
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Old 02-15-2020, 06:24 PM   #4
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Default Re: Nerfing fuel purifiers

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Originally Posted by malloyd View Post
I
I suspect the only thing that is going to "really" restore the difference is to ditch the concept that jump fuel is liquid hydrogen and require something more complex (and probably undefined). I've said before that Traveller ships apparently burn "space oil" anyway, as it's the only way to make sense of how much of the stuff they guzzle, apparently derived from wet navy models.
It might be possible to define "fuel" adequately but you'd need to keep it superscience. There's too much real science that can be applied to problems with hydrogen.
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Old 02-16-2020, 07:34 AM   #5
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Default Re: Nerfing fuel purifiers

Well, dang. I suspected as much. Back to the drawing board.

Thanks, all.
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Old 02-16-2020, 08:22 AM   #6
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Originally Posted by Fred Brackin View Post
It might be possible to define "fuel" adequately but you'd need to keep it superscience. There's too much real science that can be applied to problems with hydrogen.
Probably, though I suppose there is always superscience applicable to hydrogen. Maybe the superscience refining process makes it into "metastable liquid hydrogen" that doesn't have to be kept at super-cryonic temperatures, or includes additives that do something ridiculous to the flow characteristics, either of which could reduce the stresses on the fuel delivery system enough to make it less likely to malfunction at a critical moment. The odds of unrefined fuel doing something bad are sort of high for that, and of course the alternate approach would be a more ruggedized fuel delivery system, but needs of drama and all.

Edit: come to think of it, useful additives that you *can't* make from water or gas giant atmosphere might be a reasonable approach to what's different about refined fuel even in a realistic case. Maybe the jump process works better for some reason when the hydrogen has 6842 (+/-1) parts per billion uranium hexafluoride mixed in. It rules out [unlimited] fuel refining on shipboard, but you could still carry enough of the additive inside the fuel processor to mix a few batches before you needed to visit a civilized port to refill it.
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Old 02-17-2020, 11:09 PM   #7
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Default Re: Nerfing fuel purifiers

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Originally Posted by thrash View Post
My questions to the hive mind are:
(1) Does this approach make sense, or is there a scalable method of refining light hydrogen I've missed because it would be uneconomic without (say) fusion power?
(2) Is there a different approach that would solve the original problem?
From a game standpoint, it makes perfect sense...

But from a reality standpoint, slightly weak, I think. Especially since Deuterium separation was doable in an office scale device in WW II... Heck, heavy water (D₂O) can be centrifugally separated and or fractionally distilled from light water (H₂O), and then cracked by hydrolysis in a basically washing machine sized device. The issue is primarily the low return rate of heavy water from water. (Ammonia, Methane, and Ethane also can be fractionally distilled for heavy in various states.).

Heavy water boils at standard pressure at 101.4C, vs light water's 100.0. Fractional distillation can get pretty close to pure with a typical high school lab's equipment.

The thing is, the big limit is the amount of D (H) & T (H) vs H.

But that there might be the key... It's not that a ship cannot do it, it's that it shouldn't be able to do it fast enough to be practical aboard ship.

Note that centrifugal separation should work for D₂O, the Methane spectrum CD₄, CHD₃ CH₂D₂, etc... Same for the spectrum of Ethane C₂H₆ vs C₂D₆ and the four variants between.. The trick is that you still have to crack the D & T out. Combine centrifugal and fractional distilling, like the Germans and the US did in WW II...

The more uniform the fuel in needs to be, the more time the refining takes. Likewise, the more esoteric the fuel (EG ⁴CT₄ aka ⁴CH₄)... perhaps the JDrive needs the resulting ⁵C and ⁶C for some interdimensional reaction.

It's likely faster with molecular sieves at TTL10+/GTL9+...

Aside:
It's an interesting phenomenonto me that the only specific named isotopes commonly known are those of Hydrogen... Are there others?
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Old 02-18-2020, 12:03 AM   #8
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Default Re: Nerfing fuel purifiers

Sometimes the best approach is not to give out justifications, since they tend to draw attention to the very things that everyone would be more comfortable studiously ignoring. To enjoy any Traveller campaign you have just not think about a lot of things you know: the number and whereabouts of nearby stars, the physical character of planets, the incompatibility of FTL travel with relativity and causality, the laws of thermodynamics, the third dimension of space. I think its best for RP not to seek nor offer justifications nor rationalisations.

Fuel is fuel. Worry about cargo.
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Old 02-19-2020, 05:10 PM   #9
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Default Re: Nerfing fuel purifiers

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I think its best for RP not to seek nor offer justifications nor rationalisations.
Which is why I once shut down a player going on about cube-square law by saying, "We're playing Firefly, not Traveller."

If it was a Traveller game I probably would have conceded the point, and God only knows where the adventure would've wound up.
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Old 02-25-2020, 12:00 AM   #10
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Default Re: Nerfing fuel purifiers

Whilst it is possible to extract unrefined fuel from oceans, is it written that water is unrefined fuel?

Consider the quantity of hydrogen in a given volume of water vs liquid hydrogen.

I always assumed that scoops had some form of hydrogen extraction mechanism. The unrefined aspect was that this still allowed minute quantities of impurities (and thus you only need a correspondingly small refinery shipboard). This would mean you couldn't just fill with water/mixed gas, but extract the hydrogen to the tank (or refiner) and dump the other material. For extraction of water you are talking only a small usable fraction.

Should the limiting factor therefore be the relative time required to conduct scooping vs loading refined fuel. Using refined fuel you just hook-up to the main tank. If you are scooping there is pumping into extraction chamber, extraction and dump then optional refining and finally compression into the main tank. The speed this can be performed is the speed of the slowest step since it is a production line.

Cracking water should use a lot of power, so some of the fuel you have just refined is used in the refining process itself further extending the refuel time.
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