On Characteristics of Upper Atmosphere Aerodynamics of Flying Vehicles

In order to gain the understanding on aerodynamics of flying vehicles in the upper atmosphere(100~300 km), aerodynamic characteristics of typical aerospace vehicles in this space have been analyzed, and a preliminary understanding on the key factors of the upper atmosphere aerodynamics has been obtained. The gas flow over objects in the upper atmosphere falls into the free-molecular flow regime due to its extremely rarefied air stream. The aerodynamic force of a typical vehicle with an upstream flow deploying area of 1 m² is at the order of 1 mN in the range of altitudes from 100 to 200 km, and it is much smaller than 1 mN at altitudes close to 300 km. Generally, the lift-to-drag ratio of space vehicles flying in the upper atmosphere is smaller than 1. However, it can be augmented by decreasing the accommodation coefficient in gas-surface-interaction. In exploration calculation, the lift-to-drag ratio can be larger than 1 when the accommodation coefficient is about 0.2, which indicates that the upper atmosphere zone between 100 and 200 km can be utilized for flying vehicles in terms of aerodynamic force. Therefore, it is meaningful to carry out the upper atmosphere aerodynamics research for the development of upper atmosphere vehicles.