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 Calculate Specific Impulse, Mass Flow, Exit Velocity, Thrust of Rocket Engine at Standard Altitude

 Method to Calculate the Specific Impulse, Mass Flow, Exit Velocity, Mach Number at Exit, Thrust of the Rocket Engine at a Standard Altitude





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Thrust, Specific Impulse, Exit Velocity, Mass Flow of a Rocket Engine at a Standard Altitude

In this topic we would look into how to calculate the thrust of a Rocket Engine at a Standard Altitude above the surface of Earth.



The parameters we require are,

The Combustion Chamber Pressure of Rocket in atm.

The Combustion Chamber Temperature Rocket in Kelvin K.


Rocket Nozzle Throat and Rocket Nozzle Exit Areas.

Note: In the calculations we assume that the rocket is designed in such a way that the exit pressure = ambient pressure.


We would also require the Altitude where the rocket is flying in meters (m).

The value of gamma for the gas mixture

The value of the Molecular Weight M

The value of the Universal Gas Constant used in the calculation is R = 8314 J/(kg mol)K

Acceleration due to Gravity, g = 9.8 m/sec^2


Performing the calculation, gives us,

  • The specific gas constant value in J/kg.K

  • The Isp or the Specific Impulse of the Rocket in seconds.

  • The mass flow of the rocket engine in kg/sec.

  • To compute the Exit Velocity, the Nozzle flow inside of the Rocket engine is considered to be isentropic. Using Energy Equation, the value of Exit velocity is obtained.

  • Using the Thrust Equation, The thrust of the Rocket Engine is computed.

  • The equation of continuity and the equation of the state are used to obtain the exit area of the rocket nozzle.

  • And finally, the Mach number of flow at exit of Nozzle is computed.

Download Free Program to Calculate the Thrust of the Rocket Engine at Standard Altitude.