Nozzles on Vacuum Optimazed Rockets vs. Nozzles on Sea Level Engines
Why are sizes of rocket nozzles in second or upper-stage engine bigger than those used by sea-level engines? A sea-level optimized Raptor nozzle (on the left) stands next to a vacuum-optimized Raptor nozzle (on the right) at the SpaceX development facility in McGregor, Texas. Credit: SpaceX Well, the answer is quite simple. A vacuum- optimized rocket engine nozzle is bigger then a sea-level engine nozzle since it needs to match the significantly lower air density in the upper atmosphere and in space. Let's have a look in more detail. For a rocket engine is important to operate at its most efficient level, which means to produce the maximum amount of thrust. It is a key for the hot gases exiting the engine nozzle to match the external air ambient pressure. The importance of this is clear when you realize that the air pressure at sea level is about 1000 millibars, or 100 kPa, and it decreases with increasing altitude. The value quickly decreases with altitude to 100 millibars,...