Beyond spectrum coordination: A functional framework under international law for authorising high-altitude platform systems (HAPS) operations

High-Altitude Platform Systems (HAPS) are long-endurance stratospheric platforms proposed for broadband coverage, emergency connectivity, and network backhaul, although their large-scale commercial prospects remain uncertain. The framework of the International Telecommunication Union (ITU) already accommodates the radio layer of HAPS in the fixed service and high-altitude platform stations used as International Mobile Telecommunications base stations (HIBS) in the mobile service context. This means that HAPS communications should not be treated as an outer-space activity or brought within the freedom of use of outer space merely because the platform operates at stratospheric altitude. The use of HAPS remains tied to ITU service allocation and, where terrestrial users or national markets are involved, to national telecommunications authorisation. This article examines how international law should authorise HAPS communications in circumstances where spectrum and service allocation are already addressed, while the legal conditions for sustained platform access, aviation coordination, and security-sensitive review remain fragmented. It applies a functional approach that interprets the relevant rights and obligations under telecommunications, air, and space law by reference to the platform's service role and operational effects. It argues for a differentiated authorisation framework, including facilitated procedures for public-interest connectivity, coordinated arrangements for ordinary commercial services, and affected-State consent with strict case-by-case assessment where HAPS support artificial-intelligence computing, perform network-control functions, or raise security-sensitive concerns. By linking functional regulation with differentiated authorisation, the article treats HAPS communications as a concrete case of near-space governance and shows how a telecommunications-law framework built around ITU service allocation can provide a transitional starting point for coordinating physical platform access, aviation safety, and security-sensitive review in response to risks generated by emerging near-space technologies.