Is there any Real life variant of fuels used in KSP?

[LNorbert]

Hi Everyone!

So I been doing research all around and I couldn't find anything that even resembles the fuel...

It might be because I only looked at one aspect which is density.

There is no monopropellant that even aproches the 5kg/L density and no fuel that is 4kg/L dense either. Plus the oxidizer is the same density as the fuel.

LOX for example is 1.141kg/L.

Kerosene (Common first stage propelant) is from 0.78kg/L to 0.81kg/L.

Liquid hydrogen is 0.07kg/L.

Hydrazine (Most common monopropellant) is only 1.012kg/L.

I am really interested if anyone found somekind of similarities with real life fuels looking at any kind of aspects.

Have fun everyone! And thanks in advance for any replies on the topic.

[Dkmdlb]

And while we're at it, I can't find anything that even resembles Kerbin's density. Some help along those lines would be appreciated.

[Jouni]

The fuel units in KSP are definitely not litres. For example, an orange tank holds 6400 units of fuel and oxidizer, while its volume is over 36000 L.

The 11/9 mixture ratio of KSP liquid fuel is quite odd.

[cantab]

IMHO the fuel units are gallons, or at least about the same size. Imperial or US, it doesn't matter too much since KSP's not ultra-precise.

When the topic came up before I looked at candidates and came up with a combination that though unusual matches KSP's figures for fuel:ox ratio, best Isp, and fuel density quite well: Monomethylhydrazine+beryllium fuel and Dinitrogen tetroxide oxidizer. The addition of beryllium significantly shifts the fuel:ox ratio and boosts the Isp compared to regular MMH/DNTO.

Previous thread: http://forum.kerbalspaceprogram.com/threads/73997-What-kind-of-fuel-does-KSP-use-for-LiquidFuel?p=1049215&viewfull=1#post1049215

[Armchair Rocket Scientist]

IMHO the fuel units are gallons, or at least about the same size. Imperial or US, it doesn't matter too much since KSP's not ultra-precise.

When the topic came up before I looked at candidates and came up with a combination that though unusual matches KSP's figures for fuel:ox ratio, best Isp, and fuel density quite well: Monomethylhydrazine+beryllium fuel and Dinitrogen tetroxide oxidizer. The addition of beryllium significantly shifts the fuel:ox ratio and boosts the Isp compared to regular MMH/DNTO.

Previous thread: http://forum.kerbalspaceprogram.com/threads/73997-What-kind-of-fuel-does-KSP-use-for-LiquidFuel?p=1049215&viewfull=1#post1049215

At least for liquid fuel and oxidizer, Kerbal fuel units are actually mass, not volume. One unit of fuel has a mass of 5 kilograms.

Incidentally, an orange tank has a volume of just over 39 cubic meters and holds exactly 32 tons of propellant. If we assume 80% of the tank's volume is actual propellant, as opposed to structure, pressurization tanks, insulation, etc, it turns out that liquid fuel and oxidizer are on average very close to 1 ton per cubic meter.

Now, the S-IC stage held 770,000 l of RP-1 and 1,305,000 l of LOX, so the combined density of its fuels was 1.01 t/m^3.

So, KSP's LFO mixture is almost exactly the density of kerolox. However, its vacuum isp range of 330-390 s is closer to that of Metholox, and the mass ratio of fuel to oxidizer doesn't match with anything. There's also the nuclear engine, which gets hydrogen-like ISPs, but burns oxidizer.

However, that Beryllium-laced MMH looks darned interesting. Any idea why it isn't used in real life? Is whatever Beryllium compound ends up in the exhaust just too toxic?

[Streetwind]

Beryllium is quite toxic if inhaled as dust or vapor. But then again, so is everything else related to MMH and DNTO...

[Armchair Rocket Scientist]

Beryllium is quite toxic if inhaled as dust or vapor. But then again, so is everything else related to MMH and DNTO...

True, but the exhaust is nitrogen, CO2, and water, all of which are relatively benign. On the other hand, I'd guess adding beryllium would result in the exhaust spewing microscopic particles of beryllium oxide, which is still nasty stuff, in the upper atmosphere. Even the hydrochloric acid in solid propellant exhaust might be better than that.

[magnemoe]

At least for liquid fuel and oxidizer, Kerbal fuel units are actually mass, not volume. One unit of fuel has a mass of 5 kilograms.

Incidentally, an orange tank has a volume of just over 39 cubic meters and holds exactly 32 tons of propellant. If we assume 80% of the tank's volume is actual propellant, as opposed to structure, pressurization tanks, insulation, etc, it turns out that liquid fuel and oxidizer are on average very close to 1 ton per cubic meter.

Now, the S-IC stage held 770,000 l of RP-1 and 1,305,000 l of LOX, so the combined density of its fuels was 1.01 t/m^3.

So, KSP's LFO mixture is almost exactly the density of kerolox. However, its vacuum isp range of 330-390 s is closer to that of Metholox, and the mass ratio of fuel to oxidizer doesn't match with anything. There's also the nuclear engine, which gets hydrogen-like ISPs, but burns oxidizer.

However, that Beryllium-laced MMH looks darned interesting. Any idea why it isn't used in real life? Is whatever Beryllium compound ends up in the exhaust just too toxic?

Has been some thought of adding oxygen to the hot hydrogen exiting an nerva, kind of like an afterburner, it increases trust while reducing ISP.

In KSP its done to simplify things.

You should be able to run a nerva on lots of gasses, not oxygen but nitrogen would work well, perhaps also co2 unless it split, 2000 degree oxygen will react with anything.

Heavy gasses however gives far lower ISP.

[Red Iron Crown]

At least for liquid fuel and oxidizer, Kerbal fuel units are actually mass, not volume. One unit of fuel has a mass of 5

Monoporp and xenon are mass units, too. 4kg per unit of monoprop, 0.100kg per unit of Xenon.

[cantab]

Beryllium is quite toxic if inhaled as dust or vapor. But then again, so is everything else related to MMH and DNTO...

On the other hand there are similar proposals but using other metals, such as aluminium. It's probably just one of those things that's interesting on paper and small-scale but not worth it economically.

[EzinX]

Why didn't the game designers choose real fuel data? Surely looking up the density and ISP for RP-1/LOX, which is what I always assumed the fuel in the game was, wouldn't be all that difficult. Frankly, it doesn't sound any more difficult to spend 5 minutes getting real data (and using metric units for everything internally in the game engine) versus making up a fictitious unit of measurement and then "balancing" a fictitious substance for gameplay balance.

[Red Iron Crown]

Why didn't the game designers choose real fuel data? Surely looking up the density and ISP for RP-1/LOX, which is what I always assumed the fuel in the game was, wouldn't be all that difficult. Frankly, it doesn't sound any more difficult to spend 5 minutes getting real data (and using metric units for everything internally in the game engine) versus making up a fictitious unit of measurement and then "balancing" a fictitious substance for gameplay balance.

Once upon a time, there wasn't even separate fuel and oxidizer, just a unified "Fuel" resource. I don't think realism has ever been an overarching goal of KSP (see crazy aerodynamics, superdense planets, eternal life support, etc).

[Guest]

Why didn't the game designers choose real fuel data? Surely looking up the density and ISP for RP-1/LOX, which is what I always assumed the fuel in the game was, wouldn't be all that difficult. Frankly, it doesn't sound any more difficult to spend 5 minutes getting real data (and using metric units for everything internally in the game engine) versus making up a fictitious unit of measurement and then "balancing" a fictitious substance for gameplay balance.

Yes, well, this is ~KSP~. You're asking too much of it if you want realism or even common sense. This is why, for some of us, stock will always be a joke.

If you're interested in actual fuels check out the Real Fuels mod.

[Sean Mirrsen]

I personally consider fuel realism in KSP to be as silly as real mineral names in Dwarf Fortress. In a universe where a typical person's native name can be used as a Japanese tongue-twister and typical towns have names like "Bucketflowers", you have minerals like "tetrahedrite" and "pyrolusite". It just clashes with the rest of the setting.

It's pretty much the same here. Why have realism in fuels and real fuel names and parameters when the premise of the game forfeits realism in favor of accessibility from the get-go?

[Guest]

I personally consider fuel realism in KSP to be as silly as real mineral names in Dwarf Fortress. In a universe where a typical person's native name can be used as a Japanese tongue-twister and typical towns have names like "Bucketflowers", you have minerals like "tetrahedrite" and "pyrolusite". It just clashes with the rest of the setting.

It's pretty much the same here. Why have realism in fuels and real fuel names and parameters when the premise of the game forfeits realism in favor of accessibility from the get-go?

That's an excellent point. Why bother naming them "liquid fuel" or "oxidizer" or "monopropellant" or even "xenon". It breaks the immersion. Similarly, why bother with tonnage or some unified volume at all? It's silly.

[KerikBalm]

I often hear criticism of KSP's realism here, but I think that is unjustified.

Compared to any other space game out there (except Orbiter), KSP is leaps and bounds ahead in terms of realism.

Just because the astronauts are cartoonish, and there are jokes about snacks, doesnt make the game unrealistic.

To me, its realism is a large part of its attractiveness.

So what, if they scale some things down to roughly 1/10th... or that we don't have a dozen different types of fuel, and hundreds of different engines to choose from.

Its a simulation, and simplification is required in those.

So the atmosphere is like soup... its in development, and I remain confident that something like NEAR will be incorporated in the future.

Making it RL scale (as in the RSS mod) would result in too much load for people's computers, or the terrain being too borng and low res when one actually lands.

Its a computer game, and we don't have computers powerful enough to simulate the entire earth - to me KSP is nearly as realistic as is prealistically possible.

[Armchair Rocket Scientist]

Has been some thought of adding oxygen to the hot hydrogen exiting an nerva, kind of like an afterburner, it increases trust while reducing ISP.

In KSP its done to simplify things.

You should be able to run a nerva on lots of gasses, not oxygen but nitrogen would work well, perhaps also co2 unless it split, 2000 degree oxygen will react with anything.

Heavy gasses however gives far lower ISP.

According to this: http://www.projectrho.com/public_html/rocket/enginelist.php#ntrsolidcore

An NTR running on methane would have an ISP of around 640, which is about the same as for a LANTR (Lox-Augmented NTR) running on hydrogen.

Carbon dioxide is a bad propellant for an NTR designed for hydrogen or methane, since at high temperatures it decomposes and produces oxygen, which as you mentioned reacts with everything. Nitrogen is a monumentally awful propellant, with an ISP of 270 - worse than a decent solid-fuel motor!

Our LV-N has an ISP of 800, which is about right for a basic NTR design running on LH2.

[Streetwind]

Our LV-N has an ISP of 800, which is about right for a basic NTR design running on LH2.

The LV-N is more or less a direct clone of the NERVA XE, the only NTR ever assembled in full flight configuration. It has the same TWR and Isp values, fudged to the nearest nice round values. So yeah, that's a LH2 engine without question

[magnemoe]

According to this: http://www.projectrho.com/public_html/rocket/enginelist.php#ntrsolidcore

An NTR running on methane would have an ISP of around 640, which is about the same as for a LANTR (Lox-Augmented NTR) running on hydrogen.

Carbon dioxide is a bad propellant for an NTR designed for hydrogen or methane, since at high temperatures it decomposes and produces oxygen, which as you mentioned reacts with everything. Nitrogen is a monumentally awful propellant, with an ISP of 270 - worse than a decent solid-fuel motor!

Our LV-N has an ISP of 800, which is about right for a basic NTR design running on LH2.

Thanks, I suspected CO2 was bad but was not sure, was not aware that nitrogen had so bad. However methane looks good, more so as its easy to store and handle.

Would it be posible to have on nerva with two sets of tanks, one for H2 and doing the mars transfer burn then using methane for the later burns?

[Armchair Rocket Scientist]

Thanks, I suspected CO2 was bad but was not sure, was not aware that nitrogen had so bad. However methane looks good, more so as its easy to store and handle.

Well, basically the smaller the molecular mass of the exhaust gases, the faster it will move for a given temperature and therefore the more efficient your engine will be. With hydrogen, the exhaust is a mixture of H2 and atomic hydrogen, both of which move very fast. Likewise, methane and ammonia partially decompose, releasing some fast-moving hydrogen atoms that boost the ISP. Water doesn't work as well because oxygen forms stronger bonds with hydrogen than carbon or nitrogen do.

In nitrogen, the two atoms are linked by a very strong triple bond, so it barely dissociates at all. This leaves you with an exhaust stream of nothing but diatomic nitrogen, which has a rather high molecular mass.

Would it be posible to have on nerva with two sets of tanks, one for H2 and doing the mars transfer burn then using methane for the later burns?

That would actually be quite effective, particularly if the empty hydrogen tanks were either jettisoned or refilled with methane manufactured on Mars.