Is there a height limit to national airspace?
As it stands, that 'border' between FL600 and above is undefined, and unregulated.


  There is no international agreement on the vertical limit of
  state sovereignty. Today, the need to settle this gap in the law is
  growing in importance.
  
  More and more states are developing their own domestic
  space launch capability. Few of these new space powers will be
  able to freely access space, or utilize the most efficient launch
  azimuths, if neighboring states can claim sovereignty up to even
  62 miles (100 kilometers). They will have even more difficulty
  returning objects to Earth if the boundary is set at that altitude.
  Even the United States and Russia are facing limitations on their
  ability to freely access space. Setting a low vertical limit on state
  sovereignty will ensure all states have equal access to space.
  
  
  Dean N. Reinhardt, The Vertical Limit of State Sovereignty, (2007)
  


and


  Vertical Sovereign Territory.
  
  Interestingly, there is no international law (or agreement) defining the vertical boundary of a nation’s sovereign territory/airspace (the boundary between outer space which is not subject to national jurisdiction and national airspace). Obviously, there is a “white” unregulated area that should be defined, not at least from national security concerns. Presently the airspace between FL 600 and up to the border between the earth’s atmosphere and outer space (generally an altitude of approximately 100 km (62 mi) (the Kármán line)) is not regulated.
  
  
  H. Bertil Nordin, U-2 and the Vertical Boundary of Sovereign Territory, (2017)