New fuel modelling system for KSP?

[AeroGav]

Can't help thinking this is an area the game could use an overhaul.   Switchable tank contents would greatly reduce the number of parts in game,  as would being able to have engines run off different fuels.   

However, which fuels should be in game, what's the best compromise between realism and needless complexity?

Stock

As it is we have just 3 liquid resources - monopropellant, liquid fuel, and oxidizer.   Due to it's lower ISP, there is no reason to ever use mono.

Real Fuels

This is a fun mod.  With Boiloff and density to consider, cryogens are not always the best choice.  It also means new fuels could be unlocked in career mode, giving a reason to spend tech points in this area of the tree.   On the other hand, the sheer number of fuel choices would make the game hard to maintain and balance between patches.  Also unless the number of engines was vastly increased you'd frequently find yourself in situations without an engine to match to your tank of choice, or vice versa.

Semi Realism (compromise)

Increase to four liquids.   Two oxidizers, one storable, one cryo, and two fuels, one storable, one cryo.    If one half of the propellant mix is cryogenic (eg. storable fuel with cryo ox or vice versa) you get a 15% boost to ISP.  If both are cryo,  30% more ISP.  However cryo tanks suffer boiloff.   This would at least force some choice on the player, depending on mission type.    Unlocking cryogenics could be something to put points in the tech tree.

[Hay]

Or, you could just use mods. I don't think the majority of the playerbase would want something like this.

[tater]

Cryo fuels would be a good middle of the road option for stock. There are already 4, adding 2 more is no big deal (LFO, LF, mono, xenon). The ability to make pros and cons of a new set of propellants provides for interesting design decisions... which is good.

[Wjolcz]

Eh. It's pretty easy to get anywhere in the solar system. 30% Isp boost isn't really going to do much difference me thinks.

But then I haven't played with any part/fuel upgrades mods. Maybe fine-tuning the rockets with fuel types and upgrades would actually be fun, but I spend too much time in the VAB anyway.

[AeroGav]

1 hour ago, tater said:

Cryo fuels would be a good middle of the road option for stock. There are already 4, adding 2 more is no big deal (LFO, LF, mono, xenon). The ability to make pros and cons of a new set of propellants provides for interesting design decisions... which is good.

It would only be one more, because i proposed getting rid of monopropellant. Anything it can be used for (in KSP anyway) could equally  be done with storable LF and O.

I don't know what Real Fuels mods are like these days, when i tried it a few months ago there was a vast number of choices but you were always struggling to find a suitable engine or tank for what you had in mind. Especially if you're building spaceplanes and hoping to mix and match different fuels to different engines.  Staged rockets I suppose its easier when you're just dealing with a one engine one tank relationship - and there's always tweakscale.

If you wanted to go above 4 liquid fuels (not counting solids or noble gases) I suppose you could introduce different tech tiers in each of those 4 categories.

Eg.

Storable fuel

Tier 1 Alcohol

Tier 2 Kerosene

Oxidizer Storable

Tier 1 Hydrogen Peroxide

Tier 2 Nitrogen Tetroxide

Rather than having to worry about the real ISPs of every possible combo, just give a 15% buff for each tier 2 propellant in use, which stacks with the cryo buff also.