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I have an idea for with the ISRU unit actually does


MAFman
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I was looking around for how generic ore could be turned into generic liquid fuel an oxidizer, and I think I found a candidate. Perhaps the ore that you mine is actually methane clathrate (www.wikipedia.org/wiki/Methane_clathrate) trapped in the dirt, but I’m not sure how the methane is extracted.

Or (and I like this better), the ore is a carbonate mineral from which CO2 and hydrogen are liberated through heat, and then converted into methane by the Sabatier reaction, and the resulting water is electrolyzed to make liquid oxygen.

The issue is, how is this process reflected in the input to output ratio of ore to LF/O? Is it accurate or wildly off?

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Specifically, here's the reaction details.

 

Fuel and Oxygen Production

CaCO3 + 178 kJ -> CaO + CO2

4H2O + 948.96 kJ -> 4H2 + 2O2

CO2 + 4H2 + 165 kJ -> CH4 + 2H2O

2H2O + 474.48 kJ -> 2H2 + O2

 

Overall Reaction:

CaCO3 + 4H2O + 1766 kJ -> CaO + CH4 + 3O2 + 2H2

 

Methane Combustion

CH4 + 2O2 -> CO2 + 2H2O + 891 kJ

 

Products that could be used for electricity:

2H2 + O2 -> 2H2O + 474.48 kJ

 

This only took about an hour to figure out, LOL

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I turned the molar equations into mass equations, rounding to the nearest gram:

 

100g CaCO3 -> 56g CaO + 44g CO2

72g H2O -> 8g H2 + 64g O2

44g CO2 + 8g H2 -> 16g CH4 + 36g H2O

 

Useful products: 16g CH4, 64g O2

Waste: 56g CaO, 36g H2O

 

Can someone help me convert this into "units" of Ore, LiquidFuel, and Oxidizer?

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8 hours ago, MAFman said:

I turned the molar equations into mass equations, rounding to the nearest gram:

 

100g CaCO3 -> 56g CaO + 44g CO2

72g H2O -> 8g H2 + 64g O2

44g CO2 + 8g H2 -> 16g CH4 + 36g H2O

 

Useful products: 16g CH4, 64g O2

Waste: 56g CaO, 36g H2O

 

Can someone help me convert this into "units" of Ore, LiquidFuel, and Oxidizer?

One Unit is 5Kg of LF or Ox, and I think the Ore-LFO conversion is lossless, so Ore is 10Kg per unit.

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14 hours ago, Kerbals_of_Steel said:

One Unit is 5Kg of LF or Ox, and I think the Ore-LFO conversion is lossless, so Ore is 10Kg per unit.

So 16 kg of methane would be just over three units of liquidFuel, and 64 kg of O2 would be just under 13 units of oxidizer.

In order to make the 0.9 to 1.1 ratio of liquidFuel to oxidizer, I'd need 15 * 1.1 = 16.5 kg of oxidizer, wasting one kg of methane and 47.5 kg of oxygen.

So for 100 kg of ore, which is 10 units, and assuming the water just comes from magic (?) or something, I could make 3 units of usable LF and 3.3 units of usable oxidizer.

Is this correct-ish?

 

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Or, "ore" is just sub-surface ice:

H2O + energy > H2 + O

If you want, you can throw in some carbon (its often in asteroids), and do: C + 2H2 > CH4

Then you've got methane and liquid oxygen.

Of course, there is a bunch or ore often on equatorial places where ice shouldn't be just below the surface (like moho), so.... whatever

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On 9/16/2020 at 8:39 AM, king of nowhere said:

don't forget that you can also convert the ore to monopropellant, and those are generally hydrazine-based. so it would have to have nitrogen.

i don't think there is any chemical possible way to make it work

So if that's the case, it's just game magic?

On 9/16/2020 at 8:39 AM, king of nowhere said:

don't forget that you can also convert the ore to monopropellant, and those are generally hydrazine-based

Or, the game could be using hydrogen peroxide as monoprop, which can be produced from water, I think...

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I always understood LF to be kerosene-based, as it can be used in both jet engines (jet A1) and rockets (RP-1) and the ISP numbers tally pretty well with kerosene/O2 rockets on which they are largely based. Methane and hydrogen would produce higher ISPs and while there are gas turbines that can run on methane or even hydrogen, as far as I'm aware there aren't any jet engines that do so plus the jets in KSP are also modelled on real engines.

KSP uses generic terms like 'liquid fuel' and 'ore' to hide the complexity behind easy to understand terms, because they aren't really relevant to playing the game. You can go down the realism route using mods if you like, but turning 'ore' into 'fuel' and 'oxidiser' in the quantities that are used by rockets is far simpler and more straight forward than hunting for specific minerals that would only exist in certain places, performing complex chains of chemical reactions to produce chemicals that may be useful as fuels and then trying to juggle all the molar ratios to get fuel and oxidiser in the quantities that are needed. It's a space game, not an exomining simulator.

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3 hours ago, MAFman said:

Or, the game could be using hydrogen peroxide as monoprop, which can be produced from water, I think...

right now i'm reading a book on rocket propellants (ignition, you can find it on the internet, it is quite interesting if you like that kind of stuff and know some chemistry, as you clearly do); according to it, hydrogen peroxide was thoroughly researched, and it can be used as monopropellant, but hydrazine was favored because it is more efficient. a quick wikipedia search gave 160 s specific impulse for peroxide, and 220 s for hydrazine. this second value is much more in line with the game's monopropellant effectiveness.

 

On the other hand, from water you can get both LH/LOx fuel, and hyrogen peroxide. and if you make peroxide you wante a bit of mass, which is consistent with the loss of mass when making monopropellant (though you lose around 6% of the mass, not 20%). my headcanon is that ore is water, since it can be found as ice , or chemically bound to rocks, on most planets, and you can get rocket fuel from it with a 100% efficiency. but then, if that was the case, the mass ratio between fuel and oxidizer would be different. In fact, i can't think of any rocket fuel with that mass ratio. all rocket fuel has plenty of hydrogen, so the oxidizer always ends up much heavier.

so, i am afraid nothing real models the behavior of ore in the game

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21 hours ago, king of nowhere said:

so, i am afraid nothing real models the behavior of ore in the game

So it is just for fun, not intended to be anywhere realistic. Basically, if you want realism that's what mods are for?

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