Speeds above mach 6. Search for hypersonic books on Amazon.co.uk
High velocity flight, once passing around Mach 5, i.e. around 5500 km/h, the vehicle is termed hypersonic.
Operation at Mach numbers exceeding 4.
Flight faster than Mach 5.
operation at a Mach number exceeding 5.
Faster than Mach 4; faster than "high speed"
Referring usually to an object moving more than five times the speed of sound (Mach 5) in the gas or liquid surrounding it. Compare supersonic.
In aerodynamics, hypersonic speeds are speeds that are highly supersonic. In the 1970s, the term generally came to refer to speeds of Mach 5 (5 times the speed of sound) and above. The hypersonic regime is a subset of the supersonic regime.