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

In this note,we design a velocity-altitude map forhypersonic level flight in near space of altitude 20-100 km.This map displays aerodynamic-related parameters associ-ated with near space level flight,schematically or quantita-tively.Various physical conditions for the near-space levelflight are then characterized,including laminar or turbulentflow,rarefaction or continuous flow,aerodynamic heating,aswell as conditions for sustaining level flight with and withoutorbital effect.This map allows one to identify conditions tohave soft flight or hard flight,and this identification wouldbe helpful for making correct planning on detailed studies ofaerodynamics or making initial design of near space vehicles.