Hypersonic flight is usually defined as atmospheric flight at velocities of Mach 5 (five times the speed of sound) and above, although depending upon details, aspects of hypersonic flight may appear anywhere from Mach 3 to 12. Phenomena that occur at hypersonic speed include compression heating, dissociation and ionisation of atmospheric gases and chemical reactions among them, shock wave interaction with airframe materials and control surfaces, and air flow interactions requiring the entire vehicle and propulsion system to be designed as an integrated system, not independent components.