You searched for: “aeropause”
aeropause (s) (noun), aeropauses (pl)
The upper region of the atmosphere, between the stratosphere and outer space: In the aeropause gas particles are so sparse as to provide almost no support for man's physiologic requirements, or for vehicles that require air for burning fuel, or where air is so thin that aircraft can not operate properly.
It is not possible for aircraft to fly in the aeropause.
The aeropause is a region at the upper level of the Earth's atmosphere regarded as the boundary between the atmosphere and outer space.