OK, let's go through this step by step:
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Coolant provides cooling in Watts.
Electricity provides energy in Watts.
That's right
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Fuel provides thrust in Newtons.
The thrust isn't directly affected by the amount of fuel on board. It mainly depends on the engine. (Of course if the thrust-fuel-ratio of your engine is nonlinear and you have to travel a certain distance before refueling the fuel left affects the thrust you can give without running out of fuel. But this only works if you know the function of the engines and heavily depends on your planned traveltime/-distance) Much more interesting is the amount of chemical energy you have aboard. As you have to accelerate the ship (breaking without friction is just accelerating backwards and needs the same amount of energy) you have a difference in kinetic energy which you have to provide by using the fuel and therefore releasing the chemical energy you need. This also works with binding energy and nuclear reactions. Therefore my joice for measuring the fuel would be
Joule. As the chemical energy likely is distributed homogenous throughout the fuel,
litres would also be a fitting unit.
But: As soon as you add a fuelgrid which provides a room with a certain amount of fuel (aka energy) per time, we once again are with
Watts or
litres per second. Bear in mind, that the amount of Watts you then get from one fuel tank depends on the travel time (With 10 Ml fuel and 100 days travel time you of course only can provide 100 kl fuel per day whereas with 10 days traveltime you can provide 1 Ml per day).
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Air provides respiration in... breaths?
Basically. Much more intuitive is
litres as one breath "destroys" a (nearly) constant volume of oxygen. Thats without a grid floating the whole ship constantly with oxygen. I also don't think an air-grid makes any sense. In which units you would measure the effectivity of such a grid I can't tell right now. I'll think about it.
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Cooling is provided by coolant in... LN2?
LN
2 in what? atoms? litres? apples? Whatever: It doesn't matter. You have to hold the circuit under a certain pressure to provide the necessary flow. At the cooling hatches the absorbed heat is radiated into space and we get ready for another round. This requires a fixed omount of N
2 and has nothing to do with the amount of heat coming from the rooms. It doens't get vented into space or something...
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Energy is provided by electricity in Amperes.
What about the voltage? What about the really relevant thing, energy per time?
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Thrust is provided by fuel in Gallons/Litres.
Respiration is provided by air in Litres.
*see above*
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So, looking at those above, which seem more appropriate to use?
I guess this was a rhetorical question. Nevertheless, both contain humbug. My answers are highlighted.