Aerodynamic map for soft and hard hypersonic level flight in near space

In this note, we design a velocity–altitude map for hypersonic level flight in near space of altitude 20–100 km. This map displays aerodynamic-related parameters associated with near space level flight, schematically or quantitatively. Various physical conditions for the near-space level flight are then characterized, including laminar or turbulent flow, rarefaction or continuous flow, aerodynamic heating, as well as conditions for sustaining level flight with and without orbital effect. This map allows one to identify conditions to have soft flight or hard flight, and this identification would be helpful for making correct planning on detailed studies of aerodynamics or making initial design of near space vehicles. The project supported by the National Natural Science Foundation of China (90716009).