The propulsive efficiency () of a cold gas propulsion rocket engine is a measure of how effectively the stored gas (typically compressed gas) is converted into kinetic energy of the exhaust gases, resulting in thrust. Unlike liquid or solid propellant rockets, cold gas propulsion systems don’t involve combustion; they simply release pressurized gas to generate thrust.
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,
- ṁ 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).