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Old 10-27-2015, 12:41 PM   #11
Flyndaran
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Default Re: [Spaceships] Perpetual Motion?

Fuel cells have many wonderful features, but energy density ain't one of them. Hydrogen is also a mega-bear to store unless locked into molecules which messes up its energy density even further.
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Old 10-27-2015, 04:07 PM   #12
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Default Re: [Spaceships] Perpetual Motion?

Quote:
Originally Posted by VariousRen View Post
I don't see any problem at all, we do the same thing on earth. Oil refineries require some amount of energy (say 1 unit) to produce fuel. That fuel provides enough energy to power the refinery and have some extra left over (for example, the fuel provides 3 units of energy). This means infinite power, up until the point where you run out of raw materials.
But oil is already a fuel. Refineries just, well, refine it. They turn a messy fuel into a clean one.

This refinery processes water into rocket fuel. A fuel cell produces power by converting rocket fuel to water. Using the original numbers means this setup obviously violates the first law of thermodynamics with the addition of a pipe.
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Old 10-27-2015, 04:32 PM   #13
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Default Re: [Spaceships] Perpetual Motion?

As a side note, the math from the OP is incorrect (and underestimates the amount of perpetual motion going on). A 1 space SM+5 fuel cell will run for 12 hours on 1 space of fuel (i.e. 4x base endurance) and produces 1 EP. 1 space of fuel at SM +5 is, however, 1.5 tons, not 5 tons.
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Old 10-27-2015, 05:20 PM   #14
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Default Re: [Spaceships] Perpetual Motion?

Ah, my bad. I forgot that this was specifically about fuel cells and not fuel in general. Carry on!
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Old 10-28-2015, 08:53 AM   #15
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Default Re: [Spaceships] Perpetual Motion?

So- errata.

Any commentary on the other questions:

Quote:
Originally Posted by acrosome View Post
Also, since the chemical refinery makes rocket fuel, is there a rule to divide production by 9 if you're only keeping the hydrogen? This seems reasonable- an oxygen molecule is mass 32, and two hydrogen molecules are mass 4, so the mass fraction is 4/36 = 1/9.

Another question: For rockets that have the option of using water as reaction mass- can one switch between water and hydrogen at will, or must the rockets and tankage be fuel-specific? Clearly in the Real World it is the latter, but I don't see how making a multifuel rocket would be beyond the capabilities of a society that can make a ram-rocket. Perhaps double cost (since a ram-rocket is 5x cost)? There are also rules for other reactions masses, like ammonia; same question.

Related question: Clearly, one uses the Chemical refinery to crack water into LOX/H2 or to make hydrogen. I assume that one can specify a version that isolates ammonia or methane as well. But what about water? It only costs $20/ton, but I assume that's at the starport and is mostly infrastructure and handing costs. So if you have to do a true frontier refuel someplace that liquid water is available can I assume that one can just filter it and pump it into the tanks, and that any ship capable of using water will have such a filter/pump? If so, what is a fair pumping rate? One fuel tank per hour? Is it different if the water is ice?

Final question: Are there stats for what one power point is, somewhere?
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Old 10-28-2015, 10:03 AM   #16
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Default Re: [Spaceships] Perpetual Motion?

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Originally Posted by acrosome View Post
So- errata.
Not exactly - it's more just an issue of the simplification than an outright error in the document (like, say, when the projectile damage was written in Damage rather than dDamage, making them 10x as powerful as they should have been). Probably the ideal solution is to just have certain systems (like factories and refineries) have reduced output when powered by fuel cells.

Quote:
Originally Posted by acrosome View Post
Also, since the chemical refinery makes rocket fuel, is there a rule to divide production by 9 if you're only keeping the hydrogen? This seems reasonable- an oxygen molecule is mass 32, and two hydrogen molecules are mass 4, so the mass fraction is 4/36 = 1/9.
No rule, but making your own would be fine. Your numbers look fine here; I'm assuming you intend to use the hydrogen as reaction mass?
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Old 10-28-2015, 10:03 AM   #17
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Default Re: [Spaceships] Perpetual Motion?

Quote:
Originally Posted by acrosome View Post
Also, since the chemical refinery makes rocket fuel, is there a rule to divide production by 9 if you're only keeping the hydrogen? This seems reasonable- an oxygen molecule is mass 32, and two hydrogen molecules are mass 4, so the mass fraction is 4/36 = 1/9.
Seems correct, but I'm not aware of anything written to that effect.
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Originally Posted by acrosome View Post
Final question: Are there stats for what one power point is, somewhere?
Their official nonexistence is, I believe, quite intentional.

People have tried many times to puzzle them out, usually primarily from the beam weapon figures. I think there might be a revealing post from the author somewhere on the forum as well. (Possibly in connection with the beam weapon design Pyramid article instead of Spaceships, but you can work between the two...)
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Old 10-28-2015, 10:51 AM   #18
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Default Re: [Spaceships] Perpetual Motion?

Quote:
Originally Posted by Ulzgoroth View Post
Seems correct, but I'm not aware of anything written to that effect.
The example craft in staceships use the amount of HE3 in gas giant atmospheres as fraction of processed gas that is produced.

Quote:
Originally Posted by Spaceships 6 page 21
About 130,000 tons of
raw atmosphere yields one ton of helium-3. As the Tempestís
refineries process 20 tons an hour, this takes about 270 days
Quote:
Their official nonexistence is, I believe, quite intentional.

People have tried many times to puzzle them out, usually primarily from the beam weapon figures. I think there might be a revealing post from the author somewhere on the forum as well. (Possibly in connection with the beam weapon design Pyramid article instead of Spaceships, but you can work between the two...)
The problems with power points is that the resulting number is silly high for chemical/solar planel compared to the later options and the difference in TL 6 to 12 is only *5 and between TL 7 and 12 is only *2.5.

Compare that to the other source without numbers: ultratech where the difference between TL 9 and TL 10 is *10 and the addition of ^ to the fusion plant multiples by *5 again and the TL 9-12 is *100(the same for TL 9-11^) Also there you need *50 the mass to produce the same energy with solar panel than TL 12 antimatter.

But yes, the only "real" numbers we have on power are the beam weapon power numbers in spaceships.

The power situation is one of the great annoyances I have with gurps tech supplements.
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Old 10-28-2015, 11:16 AM   #19
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Default Re: [Spaceships] Perpetual Motion?

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Originally Posted by weby View Post
The example craft in staceships use the amount of HE3 in gas giant atmospheres as fraction of processed gas that is produced.
...Does this have anything to do with the subject of how much hydrogen you get from electrolysis of water?
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Old 10-28-2015, 11:33 AM   #20
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Default Re: [Spaceships] Perpetual Motion?

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Originally Posted by Ulzgoroth View Post
...Does this have anything to do with the subject of how much hydrogen you get from electrolysis of water?
It would indicate that the output is relative to the mass fraction and the capacity as given for chemical refinery is the input mass, as you were replying to just keeping the hydrogen question.
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