Right now we have Kerosene, Monopropellant, and Xenon. All of those are actually monopropellants in this context!
Let's embrace authenticity and go for a few different fuel types. The engines can be configured to run off of either.
- Kerosene and Liquid Oxygen: Roughly the same performance we have in the engines and fuel tanks now. Throttle response is slightly slow, as you need to get the turbopumps spun up.
- Liquid Hydrogen and Liquid Oxygen: Much less dense fuel compared to Kerosene, but far higher specific impulse--390s to 430s or so. Throttle response is slightly slow, as well. Low-density hydrogen behaves so different from higher density kerosene that it really does make sense to have separate fuels. Hydrogen will boil off over time.
- Monopropellant: Low TWR, low efficiency, reasonably dense fuel. Immediate throttle response.
- Liquid Hydrogen: Not burnable alone in chemical engines, but it can be used as a high Isp, low thrust propellant for Nuclear Thermal Rockets, which I will describe in another post.
- Kerosene: Not burnable alone in chemical engines, but it can be used as a mediocre Isp, high thrust propellant for NTRs.
- Liquid Oxygen: Not burnable alone in chemical engines, but it can be used as a mid-Isp, mid-thrust propellant for NTRs.
- Solid Rocket Fuel: Used for Solid Rocket Boosters, which I will describe in another post.