The cross-sectional area of the exhaust for a rocket engine is a critical parameter in determining the performance of the rocket. The exhaust nozzle is responsible for accelerating the high-speed gases produced during combustion and expelling them to generate thrust.
The cross-sectional area of the exhaust at the exit is a critical design parameter. It influences the speed at which the exhaust gases are expelled, and thus, it affects the thrust generated by the rocket. The actual determination of this parameter involves detailed engineering analysis and simulations.
The relationship between the cross-sectional areas and velocities at the throat and exit of a rocket nozzle can be described by the rocket equation:
where:
-  and are the cross-sectional areas at the nozzle Throat and exit, respectively,
-  and are the velocities at the nozzle Throat and exit, respectively.
which gives,
where,
- is the cross-sectional area of the nozzle at the throat,
- is the velocity of the exhaust gases at the throat,
- is the cross-sectional area of the nozzle at the exit,
- is the velocity of the exhaust gases at the nozzle exit.