The propulsion system used on the future space plane will have to accommodate a wide range of flight altitudes.

During takeoff, the propulsive jet exhausting from the engine nozzle will encounter atmospheric pressure at approximately 1 bar. In the upper atmosphere, the same jet will expand into air at pressures 100 to 1000 times lower. This transition results in gradual pluming of the jet.

This complex phenomenon is investigated in wind tunnels using schlieren photography is used to visualize the jet at the nozzle exit.

And This is Important Too :

Such aerodynamics experimental studies will contribute to the design of new propulsion system for future launchers and spacecrafts. These tests have been achieved in the framework of a Reseach Program for Advanced Hypersonic Propulsion (PREPHA), and sponsored by the "Direction des Recherches et Etudes Techniques (DRET), an agency of the French MoD.