Hypersonic flight is flight through the atmosphere below altitudes of about 90 km at speeds greater than Mach 5, a speed where dissociation of air begins to become significant and high heat loads exist. Speeds over Mach 25 have been achieved below the thermosphere as of 2020.
Reentry vehicle (RV) after an 8,000-kilometre (5,000 mi) flight, 1959. Note the blackened tip of the RV due to aerodynamic heating. Compare to the aerodynamic heating effect on the iron meteorite on the right.
Hypersonic weapon, demonstrating its non-parabolic trajectory (denoted in red), has a distinctive signature which is being tracked by one of the layers of the National Defense Space Architecture (§ NDSA) beginning in 2021. Tranche 0 is to begin deployment in 2022. The satellites of the NDSA, in gray, are to be deployed in constellations orbiting Earth, and constantly keep Earth in their view, depicted by the blue cones representing the fields of view of the satellite constellations. The satellites are to intercommunicate and serve the defensive systems arrayed against enemy hypersonic vehicles, and build a
In aerodynamics, a hypersonic speed is one that exceeds five times the speed of sound, often stated as starting at speeds of Mach 5 and above.
CFD image of the NASA X-43A at Mach 7