Rocket Thrust

The extent to which thrust is produced by the rocket depends on the mass flow rate through the engine, the exit velocity of the exhaust, and the pressure at the nozzle exit
All of these variables depend on the design of the nozzle. The smallest cross-sectional area of the nozzle is called the throat of the nozzle. The hot exhaust flow is choked at the throat, which means that the Mach number is equal to 1.0 in the throat and the mass flow rate m dot is determined by the throat area. The area ratio from the throat to the exit Ae sets the exit velocity Ve and the exit pressure pe.

The Equation in the image can be used for both solid and liquid rockets
Liquid rockets
- stored fuel and stored oxidizer are pumped into a combustion chamber where they are mixed and burned. The combustion produces great amounts of exhaust gas at high temperature and pressure.
- are more complicated and costly, but are also more controllable, can reach greater velocities, and can be both shutdown and restarted.
Solid rocket-fuel and oxidizer combined as solid
- Normally used as boosters for launch, tend to be safer, more reliable, lighter, and lower in cost. However, once ignited, the engine cannot be shut down or restarted, and the amount of power cannot be controlled.
Vacuum
- Since the oxidizer is carried onboard the rocket, rockets can generate thrust in a vacuum where there is no other source of oxygen. That’s why a rocket will work in space, where there is no surrounding air, and a gas turbine or propeller will not work.

Watch the video below that gives a visual representation with animations of how certain rockets function.