The Raptor is a family of full-flow staged-combustion-cycle rocket engines developed and manufactured by SpaceX for use on the SpaceX Starship. The engine is powered by cryogenic liquid methane and liquid oxygen (“methalox”), as opposed to the RP-1 and liquid oxygen (“kerolox”) combination used in SpaceX’s earlier Merlin and Kestrel rocket engines.
The propulsive efficiency is a crucial parameter in evaluating the performance of a rocket engine, indicating how well it converts propellant energy into useful thrust. Practical rocket engines often have propulsive efficiencies less than 100% due to factors like incomplete combustion, heat losses, and other inefficiencies in the propulsion system.
The propulsive efficiency () is defined by the following formula:
where,
- is the propulsive efficiency,
- is the thrust produced by the rocket engine,
- is the effective exhaust velocity of the rocket,
- ṁp is the mass flow rate of the propellants,
- is the specific impulse of the rocket engine,
- g0 is the acceleration due to gravity (approximately 9.81 m/s²).