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Unit question - What do the numbers mean?


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They are entirely arbitrary units. There is good reason to believe they're not litres, most obviously by comparing the fuel quantities with the physical volume of the tanks. They're probably not even consistent between resources.

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Unless something has changed recently, I don't think there's an official definition of the volume units anywhere but if you assume a unit is five or six liters, it makes things work out reasonably. (Reasonably means that the rocket fuel tanks actually have most of their volume taken up by fuel and oxidizer, and the densities of fuel and oxidizer come out close to real-life equivalents.) The fact that there isn't an official definition means you can get a really good argument going about it though (e.g. the original thread you apparently posted this question in).

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According to my math, a "unit" is defined by mass, not volume.

It's convenient that 90 "units" of fuel plus 110 "units" of oxidizer weigh precisely 1 metric ton.

1 unit of fuel is 5kg.

1 unit of oxidizer is 5kg.

1 unit of monopropellant is 4kg.

1 unit of xenon is 100g.

1 unit of solid rocket propellant is 7.5kg.

Best,

-Slashy

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Thanks for the replies. Can someone help me write a ModuleManager config to standardize the heck out of the stock resource containers? Having OP and super-nerfed rockets in the same game bugs me... *shiver*

Can you explain what you mean by "standardize"? If you're talking about the physical size of the tanks as compared to their resource capacity, it's either very easy (if you just want to manually specify the capacity of each tank type, or apply a multiplier per resource type) or impossible (if you want to tie it programmatically to the physical size of the model; I don't think MM can see the model, you'd need to write code for that).

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I'd like to figure out what a "unit" is volumetrically, then figure out how many "units" each tank can carry based on their physical volume.[quote name='Snark']Can you explain what you mean by "standardize"? If you're talking about the physical size of the tanks as compared to their resource capacity, it's either very easy (if you just want to manually specify the capacity of each tank type, or apply a multiplier per resource type) or impossible (if you want to tie it programmatically to the physical size of the model; I don't think MM can see the model, you'd need to write code for that).[/QUOTE]
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[quote name='MAFman']I'd like to figure out what a "unit" is volumetrically, then figure out how many "units" each tank can carry based on their physical volume.[/QUOTE]

Mods like RealFuels start by throwing all stock numbers overboard completely and then define 1 unit as 1 liter. This is [I]required[/I], because as mentioned several times above, the meaning of 1 unit is not consistent in stock KSP. They then measure the volume of each tank (manually measuring the model, every single one of them), and then assign proper contents. This is [I]a lot[/I] of work. Which is why you are probably better off downloading RealFuels and stock RF engine configs as opposed to trying to do it yourself. Don't be like me and spend more time editing configs than playing the game :P
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Check out the community resource pack. It atempts to somewhat standardize at least the resources that various mods use. It's realy not useful to standardize everything. For example, you need very small quatities of certain resources (antimatter) while you need very large quatities of others (fuel). To think of that in volumetric units is just not useful.

Also, you'd not only have to change tanks, but engines aswell and every part that converts, harvests, consumes resources in any way.
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Nah, no need to change engines and resource converters. Just about everything already runs with mass ratios or mass-related metrics, IIRC. Engines for example completely ignore the resource definition. They care neither for the density nor for what a unit represents.

They only care for consuming a certain mass over time, as definied by their specific impulse. "How many seconds can this engine produce 1 kN worth of thrust when provided with 1 ton of fuel", that is (one of) the definition of Isp. Turn it around where you have a fixed timespan of 1 second and a certain amount of thrust, and you can calculate a mass flow rate in kg/s. Only after all that is said and done, the game looks at the resource definition in order to convert the mass flow rate into a "volume" flow rate (well more like a "unit" flow rate really) by multiplying in the density, in order to show the player a number in the game UI that's easily understood. But that last step is completely unrelated to the engine. Edited by Streetwind
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