What is the Best Rocket Fuel?
Rocket engines are run on Hydrogen, Kerosene and lately Methane. Is there a best fuel?
Modern rocket building companies such as SpaceX, Rocket Lab, Blue Origin and Isar Aerospace are almost exclusively opting for rocket fuels such as methane, natural gas or propane. Does that mean methane is the superior rocket fuel? And if that is the case, why has methane been entirely ignored in the rocket industry for close to 70 years? Was it not technologically feasible before, or were rocket companies in the past plain stupid or ignorant?
No, there is no perfect rocket fuel. Instead, we have numerous pros and cons to weigh against each other. The reason why fuels such as methane and propane have become so popular lately is because the industry is transitioning to reusable rockets. To better understand why that makes methane popular, it makes sense to start with the two fuels which still dominate the industry: Kerosene (RP-1) and Hydrogen. But before jumping into that discussion, we need to clarify some important terminology.
Understanding Rocket Fuel Terminology
When discussing rocket fuel you will hear about terms such as propellant, oxidizer, LOX, hydrolox, kerolox, methalox, monopropellant and bipropellant. What does it all mean?
Difference Between Propellant and Fuel
Rocket guys prefer to talk about propellant rather than fuel because a rocket unlike an airplane or car needs to bring its own oxygen stored in tanks. Propellant is a more practical term for rockets because it generalizes better across different types of rocket engines. All rockets use propellant, but not all propellant contains a fuel. A combination of fuel and oxygen is referred to as a bipropellant. If the propellant is only made up of one compound, we call it a monopropellant. You could make a simple rocket engine using a compressed air tank. Space rockets have something called reaction control system (RCS) which is usually composed of tiny rocket engines using monopropellants. These engines are used when you need very delicate and fine-grained control, such as docking with another spacecraft or adjusting orientation of your spacecraft while in orbit.