China's vertical sovereignty argument has no basis in outer space treaty law and has been rejected before

Reliance on the absence of an explicit airspace-space demarcation ignores historical context by attempting to identify a minimum altitude at which space begins. In fact, there is no controversy that all current satellite orbits transit within the space domain.²¹¹ Irrespective of the demarcation argument, Articles I and II of the Outer Space Treaty (OST) expressly refute any conception of vertical sovereignty.²¹² Article I designates outer space, including the moon and other celestial bodies, as "the province of all mankind." This language has been universally understood to mean that "all nations have a nonexclusive right to use and explore space.²¹³ Article II further prohibits in space any "national appropriation by claim of sovereignty, by means of use or occupation, or by any other means." Thus, the OST clearly permits all uses of the space domain short of an appropriation by claim of sovereignty or the like.²¹⁴

It therefore seems clear that the plain language of the OST prohibits any claim of vertical sovereignty in space. Sovereignty denotes supreme authority within a territory,^2l5 "the right to command and correlatively the right to be obeyed," with the term "right" connoting legitimacy.²¹⁶ Thus, a claim of sovereignty over space, or any portion thereof, seeks, in some measure, to extend a state's territorial sovereignty into the space domain.²¹⁷ The holder of sovereignty derives its authority for sovereignty from some mutually acknowledged source of legitimacy.²¹⁸ In space, the OST's explicit prohibition on appropriation removes the essential support for legitimate sovereignty.²¹⁹

In this sense, the vertical sovereignty argument is akin to the 1976 Bogota Declaration that geostationary orbit was not part of outer space since its nature depends specifically on gravitational phenomena from earth.²²⁰ Thus, the Declaration further argued, those portions of geostationary orbit directly above equatorial states are sovereign territory of those states rather than part of outer space.²²¹ The international community rejected this argument²²² Likewise, it should reject the vertical sovereignty argument.