Scramjet

A scramjet uses supersonic airflow to compress air into a narrowing passage before injecting it with fuel, igniting the mix. The resulting expansion produces thrust that allows a scramjet to operate at supersonic speeds and high altitudes, which jet-turbines cannot achieve, and reaction engines cannot sustain. The downside is that a scramjet lacks the turbines to propel air from a standstill, and therefore must be launched by an air carrier or some kind of assisted propulsion, whether with rockets or a mass driver. If a scramjet slows below supersonic speeds, its engine will flame out and force the pilot to eject.