Science: Plug for Tail Cone

Newest wrinkle in rocketry is the "plug nozzle" engine.

In the conventional rocket engine, fuel is burned in a roughly spherical combustion chamber, and turns into hot, high-pressure gas. To keep the gas from expanding wastefully in all directions as it leaves the nozzle, it is channeled into a tail cone where its pressure is efficiently converted into thrust as it expands (see diagram). The cone should be long enough to reduce the pressure of the gas to that of the surrounding atmosphere. Thus rockets intended to work at very high altitudes must have extra-long tail cones.

In the plug nozzle engine, the...