Chamber pressure is the pressure of the gases in the combustion chamber. A higher chamber pressure will lead to a higher pressure ratio which in turn leads to higher exhaust velocities. Typical chamber pressure in a model liquid fueled rocket is ten atmospheres. The chamber pressure in the space shuttle main engines is about two hundred atmospheres.

Given the injector efficiency, pump boost and tank pressure the chamber pressure is calculated which in turn used to calculate combustion mass, pressure ratio and throat pressure. The combustion volume is assumed to be a sphere with a radius twice as large as the throat radius.

chamber pressure = injector efficiency * ( tank pressure + pump boost )
 

combustion volume = 8 * 4 / 3 * pi * throat radius * throat radius * throat radius
combustion mass = chamber pressure * combustion volume * 90 / effective tensile

pressure ratio = chamber pressure / exit pressure

k = 1.21
throat pressure = chamber pressure * pow( 0.5 + 0.5 * k, - k / ( k - 1.0 ) )
 
 

This is used in bipropellant rocket, tripropellant rocket, pumped rocket and rocket cost.
 
 

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