This graph shows how a rocket engine's thrust depends on the nozzle's exit area.
Click and drag the red "Extend" line to change where the nozzle exit should be along the pre-drawn contour. For example, dragging the red line to the right extends the nozzle and increases the exit area. The bars show the relative thrust values compared to the original SpaceX Merlin engine thrust (nozzle exit shown by gray line).
After interacting with the graph, what are some things you notice?
Things to Notice
- The maximum thrust is produced by the original SpaceX nozzle. Any exit area other than the original produces less thrust.
- The original rocket nozzle only produces momentum thrust. No pressure thrust.
This is because a rocket engine produces the most thrust when its exit gas pressure is equal to the ambient air pressure. A rocket converts the thermal energy from combustion into directed, kinetic energy. By doing this, the rocket lowers the exhaust gas temperature and pressure, but speeds up the particles' velocity along the axis parallel to the nozzle. The most efficient conversion occurs when the exhaust pressure is matched with the ambient air.
- Changes in the rocket nozzle near the throat have a much greater effect than changes made towards the nozzle end.