Introduction to the Notions of Military Activities and Peaceful Purposes in Outer Space

SPARC/ April 29, 2022/ Militarisation & Peaceful Uses of Outer Space, Research Lines

João F. Serra[1]


The Outer Space Treaty (OST), signed in 1967, established space law as a new branch of international law.[2] One of the main objectives was to maintain space as a peaceful environment. To that end, the OST elaborates extensive limitations to the use of space as a stage to wage nuclear war, and, to a lesser extent, certain constraints to conventional warfare.

The Outer Space Treaty: defining peaceful purposes and militarisation?

The definition of peaceful purposes and militarization of outer space will be explored in tandem with the relevant provisions of the OST, as they are intrinsically related. Article III of OST serves well as an introduction to this relationship because it states that space activities must be carried out “in accordance with international law, including the UN Charter, in the interest of maintaining international peace and security and promoting international cooperation and understanding”.

Consequently, general principles of international law such as pacta sunt servanda and good faith apply. Secondly, it also includes the principles dictated by the UN Charter, such as sovereign equality of States, non-intervention, non-aggression, the general prohibition of the use of force, the right to self-defence, and the peaceful settlement of international disputes.[3]

Article IV is divided into two paragraphs. The first one concerns a prohibitive regime to the weapons of mass destruction (WMDs), whilst the second has to do with the use of the Moon and other celestial bodies, purposefully leaving the space between the celestial bodies out of its scope.[4]

The second paragraph bans the testing of “any type of weapons” (not just WMDs), as well as military manoeuvres. Moreover, it allows the use of military personnel for scientific research or “any other peaceful purposes”. Therefore, the specific activities that military personnel can carry out depend on the interpretation of peaceful purposes. However, the OST says nothing to clarify its meaning.

This caused great debate and boiled down to two major positions. The non-military (headed by China and Russia), which aims to prohibit any type of activity for military purposes in outer space, and the non-aggressive (headed by the Western World), which argues that military activities in outer space are legal if carried out according to Article 2 (4) of the UN Charter (prohibition of the threat and use of force). This latter approach has gained more support, as States accept passive military operations such as reconnaissance and surveillance in outer space.[5]

Indeed, since the beginning of the space age, this environment has been used to support military planning and operations on Earth, such as to gather intelligence, for communications, navigation, and other functions that enhance military capabilities on the ground.[6]

However, it is important to emphasise that Article IV (2) states that “The Moon and other celestial bodies shall be used by all States Parties to the treaty exclusively for peaceful purposes”. The word ‘exclusively’ is important because it leaves no doubt about the scope of this specific provision concerning celestial bodies, that is, the prohibition of any military use, even if non-aggressive. In addition, the subsequent provisions creating exceptions to the rule, authorising certain military activities, emphasize the existence of this prohibition.[7]

Even though Article IX’s original purpose is related to avoiding potential harmful changes to the natural environment caused by space activities, it complements Article IV by establishing indirect limitations on military activities in outer space. It starts by stating that the exploration and use of outer space should be guided by the “principle of cooperation and mutual assistance” and with “due regard for the corresponding interests of all other States Parties”.

The principle of due regard, sought out in this provision, presents itself as the limitation of a State’s freedom by taking into account the interests and rights of other States. This is further emphasised by the notion of “corresponding interests”. This means assuring, beyond a reasonable doubt, that everything possible was done not to hamper or threaten the peaceful activities of others.[8] Therefore, if a State believes its space activities will produce harmful interference, then it is required to enter consultations before the authorisation of those activities.

Two important points noted by Sergio Marchisio are that i) Article IX deals with activities that are not prohibited by international law and ii) it is not a mere formality with no intention of reaching a solution acceptable to both sides.

Accordingly, its scope regarding peaceful activities in outer space is quite broad, as it goes beyond the prohibitions laid out in Article IV. It means for instance that it could be theoretically applied to the testing of conventional weapons (i.e., those outside the scope of Article IV) in outer space, in case a State Party has a reason to believe such harmful interference can be a result of that activity.

Although it does not provide any sort of veto power for that matter, it tries to strike a balance by relying on the procedure itself, that is, invoking corrective measures in consultations before the commencement of such activities. Furthermore, just the fact that the acting State informs the potentially affected State, gives the latter time to take preventive measures for mitigation of the harmful effects, even if no agreement is reached[9].

Final remarks

The OST helped to define these two concepts, not so much by its letter but by introducing these concepts in a widely accepted legal instrument, which fostered the debate. I think there are two major lessons here. Firstly, WMDs are prohibited, therefore they fall outside of the concept of peaceful purposes. Secondly, one can conduct military activities in outer space and still be within the meaning of peaceful purposes.

Militarisation as a “non-aggressive” activity in outer space is permitted by international law, as long as within the meaning of Article 2 (4) of the UN Charter, which prohibits the threat and use of force. The exception being in celestial bodies, where a stricter regime applies.

A potential problem here is understanding the full extent of the meaning within this article, for instance, what constitutes a threat of force and how can a State react to it? Nevertheless, it seems that the usage of capabilities to augment a State’s capabilities on the ground is within international law, and this entails, for instance, national technical means of verification for international treaties, such as spy satellites.

Another problem – which falls outside the scope of this article – is all the vacuum left by this definition of military activity. How can the testing of conventional weapons in outer space be seen as a peaceful purpose, especially considering the debris that it can produce, affecting Humanity’s freedom of exploration? While one could say that it cannot, the matter of fact is that the OST does not provide a comprehensive framework for conventional military activities.

This may not be surprising considering that the treaty was never supposed to lay down strict and encompassing rules, it is a treaty on principles to be complemented by other legal instruments. However, after more than 50 years, there is still no widely accepted legal instrument adopted specifically related to the regulation of military activities in outer space.

As we enter a new space age, with new actors and agendas, this issue is ever more pressing. Indeed, there have been different initiatives to expand the current lack of norms, but so far all of them have failed. This is attributable not only to the negotiation mechanisms that seem to be outdated (for instance, the kind of multilateralism and consensus in the COPUOS) but mainly to the lack of political will from the States.

[1] João Falcão Serra has a Bachelor’s degree in Political Science and International Relations and a Master’s degree in European and International Law, with a specialisation in space law, both from the NOVA University Lisbon. Currently, João is working as a Research Intern at the European Space Policy Institute and as a Research Assistant for Professor Walter Dorn, from the Royal Military College of Canada. João is also a member of  SPARC’s research line on Militarisation and Peaceful Uses of Outer Space.

[2] JANKOWITSCH, Peter, in Frans von der Dunk and Fabio Tronchetti (eds.), “The Background and History of Space Law”, Handbook of Space Law, Edward Elgar Publishing, 2015, pp. 1-29, 5.

[3] RIBBELINK, Olivier, “Article III”, in T. Hobe, B. Schmidt-Tedd and K. Schrogl (eds.), Cologne Commentary on Space Law, Volume 1, Berliner Wissenschafts-Verlag, 2017, pp. 271-285, 277.

[4] TRONCHETII, Fabio, in Frans von der Dunk and Fabio Tronchetti (eds.), “Legal aspects of the military uses of outer space”, Handbook of Space Law. Edward Elgar Publishing, 2015, pp. 331-382, 338.

[5] Ibid, pp. 339-340.

[6] HARRISON, Todd, “International Perspectives on Space Weapons”, report, Center for Strategic and International Studies, 2020, p. 3.

[7] SCHROGL, Kai-Uwe and NEUMANN, Julia, in T. Hobe, B. Schmidt-Tedd and K. Schrogl (eds.), “Article IV”, Cologne Commentary on Space Law, Volume 1, Berliner Wissenschafts-Verlag, 2017, pp. 285-351, 318.

[8] MARCHISIO, Sergio, in T. Hobe, B. Schmidt-Tedd and K. Schrogl (eds.), “Article IX”, Cologne Commentary on Space Law, Volume 1, Berliner Wissenschafts-Verlag, 2017, pp. 551-591, 568 and 570.

[9] Ibid, pp. 581-582.

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