Space Law and Air Law: the thin red line
Hugo Ramos Alves
I. For those who have ventured into Air Law, in purely physical terms, Space appears as a contiguous area, which leads to the assertion that we are dealing with a mere extension of Air Law.
Cooper, for example, despite recognising that space law is not governed by the principle of sovereignty, asserted that there is a universal area above the Earth and beyond the atmosphere where it would be possible to carry out not only aeronautical flights, but also aerospace flights.[1], whereas Maatesco-Maate understood that, since there is no clear boundary between airspace and outer space, air law and space law should be understood as a single system. [2]. These are excessive assertions, failing to consider the particularities of each of these branches of knowledge.
II. Air law as stemmed from a fundamental treaty: the Chicago Convention, which reads in Article 1: “The contracting States recognize that every State has complete and exclusive sovereignty over the airspace above its territory.” Article 1 is supplemented by Article 2, which reads “For the purposes of this Convention the territory of a State shall be deemed to be the land areas and territorial waters adjacent thereto under the sovereignty, suzerainty, protection or mandate of such State”. This leads the interpreter to articulate the Chicago Convention with other international treaties to accurately define the areas of jurisdiction it covers.
In view of this provision, the absence of a definition of airspace, namely the vertical limit of Air Law, is clear[3]. This limit corresponds to the point in which we are already in the spatial domain[4]. Vertical jurisdiction corresponds to the airspace above the territory of a Member State covered by its sovereignty. Unlike the horizontal limit of Air Law, there is no specific legal regime. In fact, there is no binding rule[5]; hence, we face a gap in public international law, which, in practical terms, is filled by attempting to define an effective limit on air navigation.
This is not a trivial matter, as the Earth’s atmosphere does not end abruptly. On the contrary, it becomes increasingly thin as altitude increases, until its particles cease to fall regularly towards the Earth, gradually disappearing into space. There is a boundary layer, called the exosphere, which varies in width and height depending on the season and region of the world, estimated to be 500 to 1000 km. Given this situation, it is common to refer to Kármán Primary Jurisdictional Line, which usually marks the boundary between airspace and outer space, arguing that at altitudes above 100 km, the density of the air has decreased so much that flight based on resistance is not possible. There is, however, some uncertainty, as it is now argued that the theoretically absolute boundary line, up to which air traffic is physically possible, is 83 km above sea level[6], or, in the other hand, that, for the purposes of defining airspace and outer space, the vertical limit of 100 km above sea level should be taken into account[7].
III. The attempt to define outer space can be divided into two basic theoretical groups: the spatialist theory and the functionalist theory. Beyond these theories, there was also the attempt to call upon military reasons to justify a state’s sovereignty over outer space or, at the very least, to limit its use[8].
The spatialist approach is based on the notion of effective control over territory, arguing that sovereignty over airspace only applies to blocks where state sovereignty can be exercised in concrete terms[9]. This is an unsatisfactory approach. On the one hand, effective sovereignty could vary from country to country, depending on their military capacity to deal with intrusions into their airspace. [10]. On the other hand, even if the Kármán line was invoked, there would still be uncertainty, as it is set at approximately 100 km above the Earth’s surface for the purpose of establishing the boundary between airspace and outer space.[11]. Moreover, some authors argue that this line may be subject to change depending on technological developments [12], as well as the density of the air itself[13]. Bearing this is mind, some states opted to define this in internal legislation[14], which can lead to the erosion of uniformity in Space Law.
To answer this question, the functionalist theory emerged. Rather than seeking to establish rigid criteria for setting boundaries between airspace and outer space, this theory opts to consider the purpose of a specific spatial object, as well as its function.[15]. Thus, if a given object is constructed for the purpose of being launched into outer space, it will be governed by space law, whereas if it is intended to fly in outer space, it will be governed by air law. The main obstacle to this construction lies in the possible ambiguity of the activity carried out, but above all in the fact that it is based on the purpose, i.e. the intention underlying the use of a specific object, leaving in the shadows aspects that are not insignificant, such as the means involved in the launch or the location of said object itself.[16].
IV. Bearing the existence of gap and, also, that the core of the space treaties remains unaltered since 1979, the development of space activities – as the infant space tourism industry – would recommend a clear definition of the thin red line between Air Law and Space Law. Is this the time to revisit and develop the core of Space Law?
[1] Cooper, Aerospace law – subject and terminology, in Journal of air law and commerce 29 (1963), 89-94 (90).
[2] Mateesco-Matte, Traité de droit aérien-aéronautique – évolution – problèmes spatiaux, 2.ª ed., Paris, Pedone, 1964, 67-68.
[3] See Hugo Ramos Alves, Direito aéreo, 2.ª ed., Lisboa, AAFDL, 2024, 92-94.
[4] Morillas Jarillo/Petit Lavall/Guerrero Lebrón, Derecho aéreo y del espacio, Madrid, Marcial Pons, 2014, 864.
[5] Schaefer, Recht des Luftverkehrs, Munich, C.H. Beck, 2019, 31.
[6] See, for instance, Schaefer, Recht des Luftverkehrs, cit., 31.
[7] For further developments, Ruwantissa Abeyratne, Convention on international civil aviation – A commentary, cit., 34-36 or Reinhardt, The vertical limit of state sovereignty, in Air law & Commerce 65 (2007), 65-137.
[8] See Craig, National sovereignty at high altitudes, in Journal of fair law & commerce 1957, 384-397.
[9] See, for instance, Jacobini, Effective control as related to the extension of sovereignty in space, in Journal of public law 7 (1958), 97-119
[10] Lyall/Larsen, Space law: a treatise, 3.ª ed., London and New Iork, Routledge, 2025, 150.
[11] Hobe, Space law, 2.ª ed., cit.,13. For further developments, Gangale, The non-Karman line: am urban legend of the space age, in Journal of space law 41 (2017), 151-177.
[12] Diederiks Verschoor, An introduction to space law, 3.ª ed., Alphen an den Rijn, Kluwer Law International, 2008, 17.
[13] Lyall/Larsen, Space law: a treatise, 3. rd ed., cit., 152.
[14] Masson-Zwaan/Hofmann, Introduction to space law, 5th ed., Alphen an den Rijn, Kluwer Law International, 2025, 15.
[15] See McDougal/Lipson, Perspectives for a law of outer space, in American journal of international law 52 (1958), 407–431.
[16] Lyall/Larsen, Space law: a treatise, 3.rd ed., cit., p. 155.