A multistage rocket consists of multiple stages stacked on top of each other, with each stage having its engines and propellant. When a stage is depleted of propellant, it is jettisoned to reduce the mass the remaining stages need to accelerate. The total mixture ratio for all stages is considered to calculate the overall propulsive efficiency.
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).