125
© The Author(s) 2024
Scientific Article
DOI: 10.51940/2024.1.125-156
UDC: 347.85:341.229:347:355
Anže Mediževec*
The Right of Self-defence in the Earth’s Orbit
Abstract
The increasing presence of non-State actors in space raises a plethora of legal questions, 
including those related to the use of force, especially in the context of the right of self-de-
fence. The first aim of this article is to explain the legal basis for resorting to force in the 
exercise of self-defence in space, specifically in the Earth’s orbit. The second goal is to 
contribute to the legal framework concerning how States may exercise self-defence against 
attacks committed by non-State actors in space. In this regard, the author distinguishes 
between the rules of attribution of the use of force to a State and the “unwilling or unable” 
doctrine. It is suggested that the latter may be transposed into the space domain, mutatis 
mutandis, by a re-conceptualisation of the notion of a State’s “territory”, shifting from its 
sovereignty-based foundation towards State jurisdiction. Further on, in the realm of the 
rules of attribution of conduct to a State, the author compares the ARSIWA rules of State 
responsibility with the strict responsibility regime of the Outer Space Treaty (OST), to 
clarify which system applies when addressing State responsibility for the use of force by 
non-State actors in space. Three solutions are offered in this regard. The first rests on the 
premise that space law, specifically Article VI OST, may be seen as lex specialis in relation 
to ARSIWA. The second supports the view that the general rules of State responsibility in 
ARSIWA should apply, as they are secondary rules of international law, whereas Article VI 
OST encompasses primary rules. The third approach offers a combined reading of Article 
VI OST and ARSIWA, based on a systematic interpretation of the norms contained 
therein, to preserve the purpose of the secondary rules on State responsibility.
Key words
Outer Space Treaty, Article IV OST, Article VI OST, Peaceful Purposes, National 
Activities, Self-defence in Space, Strict Responsibility Regime.
* LL.B. & LL.M. (University of Ljubljana), LL.M. (College of Europe/Collège d’Europe), Faculty of Law, 
University of Ljubljana, Department or International Law, Teaching Assistant and Researcher, E-mail: 
anze.medizevec@pf.uni-lj.si.
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ISSN 1854-3839  •  eISSN: 2464-0077
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“We will engage terrestrial targets somedayships, airplanes, 
land targets—from space. We will engage targets in space, 
from space […] [The] missions are already assigned, and we’ve 
written the concepts of operations”.
Gen. Joseph W. Ashy, United States Air Force (USAF), 1996
1. A New Era in the Usage of Space
Since 12 April 1961, when Yuri Gagarin ventured into space on the Vostok 1 as the 
first human in history—opening new dimensions of human ingenuity and broadening 
the horizons of the imaginable—a plethora of questions on space remain unanswered. 
While scientists are searching for the elements of a complete theory of the universe, the 
so-called quantum theory of relativity1, to provide us with an explanation of our sur-
roundings, legal scholars and practitioners are trying to define the contours of the juris 
spatialis internationalis.
As explained by General Joseph W. Ashy of the USAF back in 1996, States globally 
seek to contribute and improve their space-related capabilities in the area of the use 
of force, with theoretical models of such usage being perfected as a matter of national 
strategic importance.2 It is noteworthy that, upon establishing the United States Space 
Force (USSF), former President of the United States of America (USA) Donald J. Trump 
stated that Space is the new warzone.3 With this, the USA’s plans for the militarisation 
of space became visible.4 The creation of the USSF naturally did not occur in a vacuum: 
it is said that this establishment is a direct response to the perceived threats arising from 
the Great Power Competition (GPC) in the space domain. Here, the aim is to shape the 
USSF in such a way as to ensure US military supremacy in space to deter, and if need be, 
prevail over competitors in the era of the GPC.5 Besides the USA, the Russian Federation 
(Russia) and the People’s Republic of China (China) are seen as major competitors build-
ing up their space related capabilities in the use of force, with Russia having established 
its own Space Forces on 10 August 1992, and China forming the People’s Liberation 
Army Aerospace Force rather recently, on 19 April 2024.6
The deployment of gear into space that could be used in the exercise of force is no 
longer a purely futuristic idea. At the outset, it is important to distinguish the terms mil-
itarisation and weaponisation of space when discussing a possible resort to force in space. 
1 Hawking, 2016, pp. 187–204.
2 Ramey, 2018, p. 193.
3 BBC, 2019.
4 Schladebach, 2020, pp. 60–61.
5 United States Space Force, 2024; Savoy & Staguhn, 2022, p. 1.
6 China Aerospace Studies Institute, 2024, p. 2.
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Although both terms are intertwined and a clear-cut distinction is difficult to ascertain, 
militarisation usually implies the presence of military assets in space, while weaponisa-
tion refers to the actual usage of those means for military activities.7 In contemporary 
debates on the weaponisation of space, the term “space weapons” most commonly refers 
to: a) any weapons (whether land-, sea-, or air-based) that can damage a satellite or inter-
fere with its functioning8; and b) any space-based weapons which are intended to attack 
objectives (i.e., targets) in space or on the ground.9 Throughout this article, whenever 
space weapons are mentioned, the term reflects these definitions.
Currently, the possibility of anti-satellite use of force is, worryingly, no longer a dis-
tant imagination but rather an ever-closer reality. Concerns have already been expressed, 
for example, regarding the Russian “nesting doll” satellite, possibly capable of perform-
ing kinetic attacks and serving as a model of a counterspace weapon to attack other satel-
lites in low Earth orbit.10 Interestingly, Russia deployed this presumed new counterspace 
weapon into exactly the same orbit in which a U.S. government satellite operates. Other 
weapons are also in development, such as lasers to dazzle satellites, as well as “grappling” 
satellites that can be used to grab and tow other satellites out of their orbit.11 Thus, the 
concept of space warfare as it is currently most widely understood gravitates around the 
destruction of unmanned military assets in space, most commonly satellites in the Earth’s 
orbit.12 With ongoing technological developments in the field, other military tactics will 
likely follow, continuously expanding the scope of the use of force.
Historically, space was considered State-ruled, but this is beginning to change rapidly. 
Nowadays, several actors are active in space, including manufacturers, launch providers 
and spacecraft operators. For example, in the USA, numerous corporations (e.g., Space 
Exploration Technologies Corporation (SpaceX), Virgin Galactic, and Lockheed Martin 
Commercial Launch Services) have been granted licences for space launches, with 
SpaceX alone having received 369 licences.13 The presence of private parties in space, 
together with the activities they undertake there, raises a plethora of questions.14 One of 
7 Tripathi, 2013, pp. 193–194; Krepon & Clary, 2003, pp. 29–30.
8 The latter are also known as anti-satellite (or ASAT) weapons.
9 In this group, space-based ballistic missile defence interceptors and ground-attack weapons are 
included. See: Boothby, 2017, pp. 206–213; Wright et al., 2006, p. 1.
10 Hadley & Gordon, 2024.
11 Ibid.
12 Ramey, 2018, p. 190.
13 Federal Aviation Administration, 2023.
14 One challenge is to define the scope of liability of private operators in case catastrophic accidents 
occur in space resulting in death. Precisely the lack of a sufficiently clear and coherent international 
legal framework on the civil liability of private operators is one of the main reasons why States have 
adopted their own national laws in this area, with international organisations following their lead, 
such as the European Union (EU) with its upcoming EU Space Law, see: Ziemblicki & Oralova, 
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those is the potential use of force by private actors in space—whether via an anti-satellite 
system they operate or through the use of kinetic energy projectiles against another space 
object—be it following the orders of a State or of their own accord. It is true that, until 
now, no clear case of the use of force in space has been established, whether by a State 
or a non-State actor. However, given the increasing global reliance on space systems, as 
well as the rising militarisation and weaponisation of space, especially in the Earth’s orbit, 
an evolution of space into a distinct theatre of military operations appears highly likely, 
rendering the study of the use of force in space a much-needed reality.15
In light of the above, this article aims to tackle a topic of growing importance in the 
space domain: the use of force, especially in the context of self-defence, and the challenge 
of attributing responsibility for the use of force by non-State actors to a given State in 
space. Since, for mostly technical and scientific reasons, military development is limited 
to the Earth’s orbit—at least for the moment and in the near future—the analysis un-
dertaken shall likewise be restricted to the Earth’s orbit, leaving the use of force in other 
areas of outer space only marginally addressed. The first aim of this article is to explain 
the legal basis for the resort to force in the exercise of self-defence in space, specifically 
in the Earth’s orbit. The second goal is to contribute to the framework concerning how 
States may exercise self-defence against attacks committed by non-State actors in space. 
In this regard, the article distinguishes between the ARSIWA model of responsibility of 
States for the use of force committed by non-State actors and the “unwilling or unable” 
doctrine. In the realm of the rules of attribution of conduct to a State, the article delves 
into the comparison between the ARSIWA16 model on State responsibility and the strict 
responsibility regime of the Outer Space Treaty (OST),17 to illuminate which system 
applies for addressing the use of force by non-State actors in space.
2. Resorting to the Use of Force in Space
At the outset, it is beneficial to first briefly sketch the international space law rules 
relevant to the topic of this article. The analysis that unfolds throughout the article will 
be based on this legal framework. Already in the 1960s, the United Nations General 
2021, pp. 1–2; Stefoudi, 2024; As regards the space-related activities of the EU, see: Cross, 2021, 
pp. 31–46.
15 Ramey, 2018, p. 205. See also: Buchan, 2023.
16 Articles on Responsibility of States for Internationally Wrongful Acts (ARSIWA), Annex to General 
Assembly resolution 56/83 of 12 December 2001, and corrected by document A/56/49(Vol. I)/
Corr.4.
17 Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, 
including the Moon and Other Celestial Bodies (the Outer Space Treaty, OST), Washington, 
Moscow & London, 27 January 1967, 610 UNTS 205.
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Assembly (UNGA) adopted several resolutions tackling what was to become the le-
gal regime for space activities undertaken by States or private entities.18 For example, 
in Resolution 1962 (XVIII), entitled Declaration of Legal Principles Governing the 
Activities of States in the Exploration and Use of Outer Space19, the UNGA Member 
States concluded that the activities of States in the use of outer space must be carried out 
in accordance with international law, most notably the UN Charter, in the interest of 
international peace and security.20 Such resolutions were considered as an expression of 
instant custom shortly after their adoption.21
The legal framework of international space law, composed of the most signifi-
cant treaties dates back to 1967 with the OST22 and the subsequent Convention on 
International Liability Caused by Space Objects23, the Convention on Registration of 
Objects Launched into Outer Space24, the Agreement on the Rescue of Astronauts, the 
Return of Astronauts and the Return of Objects Launched into Outer Space25, and the 
Agreement Governing the Activities of States on the Moon and Other Celestial Bodies 
(Moon Agreement).26 Adopted in the Annex of UNGA Resolution 2222 (XXI), the 
OST, which was largely based on UNGA Resolution 1962 (XVIII), is generally consid-
ered to provide the principal regulatory mechanism for human activities in space. The 
subsequent treaties mostly address specific issues of space law, thus clarifying the scope 
of the OST via a systematic interpretation of the norms contained therein.27 Since the 
OST represents the foundation of international space law, it naturally follows to begin 
assessing the possibilities for the use of force in space within the contours of the OST.28
It is argued by some legal scholars that, by virtue of Article I of the OST—which 
states that the exploration and use of outer space “shall be carried out for the benefit and 
in the interests of all countries”—virtually any form of military activity is prohibited, 
however exercised and for whichever purpose.29 Indeed, already in its Preamble, the OST 
recognises that UNGA Resolution 110 (II) of 3 November 1947, condemning any form 
18 Yun, 2018, pp. 1–3.
19 UNGA Resolution 1962 (XVIII), 13 December 1963.
20 Ibid., § 4.
21 Shaw, 2017, p. 405.
22 Washington, Moscow & London, 27 January 1967, 610 UNTS 205.
23 Washington, Moscow & London, 29 March 1972, 961 UNTS 187.
24 New York, 12 November 1974, 1023 UNTS 15.
25 Washington, Moscow & London, 22 April 1968, 672 UNTS 119.
26 New York, 5 December 1979, 1363 UNTS 3.
27 Borgen, 2020.
28 Martinez et al., 2019, pp. 28–29; Delegation of the European Union to the United Nations in New 
York, 2023.
29 Shaw, 2017, p. 406 and the references listed in fn. 343.
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of propaganda designed or likely to provoke or encourage any threat to the peace, breach 
of the peace or act of aggression, is applicable to outer space. Nevertheless, when it comes 
to regulating the use of force, Article IV of the OST is widely regarded as the backbone 
of the legal rules on the use of force in space.30 While it is true that, during the genesis 
of the OST, the idea of a peaceful usage of space was stressed on several occasions, one 
must distinguish between the text of both paragraphs of Article IV to understand how 
the OST regulates the reliance on force in the space domain.31
2.1. The Prohibition of Weaponisation of Space as per OST
According to Article IV(1), States Parties to the OST undertake not to place in orbit 
around the Earth any objects which could carry nuclear weapons or any other kinds of 
weapons of mass destruction (WMD). States Parties are also prohibited from installing 
such weapons on celestial bodies or from stationing such weapons in outer space in 
any other manner. The norm in paragraph 1 is a direct inclusion of UNGA Resolution 
1884 (XVIII), adopted unanimously on 17 October 1963, indicating such prohibitions. 
Hence, paragraph 1 unequivocally prohibits the placement of WMD in space. However, 
the norm does not prohibit States from placing weapons other than WMD into the 
Earth’s orbit. This appears to be the first material limitation of the OST on the question 
of militarisation and weaponisation of space, alongside the absence of a definition of 
what constitutes a WMD.32
Furthermore, nuclear weapons and other WMD which are not stationed in the 
Earth’s orbit but merely pass through it also evade a clear-cut prohibition. By virtue of 
this, weapons such as intercontinental ballistic missiles with a nuclear warhead (with an 
arc-like trajectory) and orbital bombs are missing from the prohibition of Article IV(1), 
as well.33 This legal loophole was historically addressed to a certain extent via treaties on 
the limitation of armament such as the SALT-II Treaty of 197934, Article VII of which 
states that “fractional orbital missiles” shall be removed and destroyed.35 Thus, worrying-
ly, as per the text of Article IV(1) OST, nuclear weapons and WMD may still venture 
into the Earth’s orbit, albeit only temporarily for the purposes of passage.36 On the other 
30 Lee, 2003, p. 93.
31 Dembling & Arons, 1967, pp. 425 and 432–435.
32 Ramuš Cvetkovič, 2024, p. 62.
33 Schladebach, 2020, p. 61.
34 Treaty Between the United States of America and The Union of Soviet Socialist Republics on 
the Limitation of Strategic Offensive Arms, Together With Agreed Statements and Common 
Understandings Regarding the Treaty, Signed at Vienna, 18 June 1979.
35 Schladebach, 2020, pp. 60–62.
36 Nevertheless, certain limitations on the usage of nuclear weapons stemming from general inter-
national law still exist, see for example: Legality of the Threat or Use of Nuclear Weapons, Advisory 
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hand, stationing conventional weapons in space appears prima facie not to contravene 
the OST. Since conventional space weapons can be divided into three main categories 
(Earth-to-space, space-to-space, and space-to-Earth), with a further subdivision into ki-
netic and non-kinetic weapons with either temporary or permanent effects,37 the choice 
of weaponry not expressly prohibited by the OST seems rather broad.
To mitigate these concerns at least to a certain extent, Article IV(2) OST provides 
that the Moon and other celestial bodies must be used by the States Parties “exclusively 
for peaceful purposes”. In this regard, the establishment of military bases, installations 
and fortifications, the testing of any type of weapons, as well as the conduct of military 
manoeuvres on celestial bodies, is directly prohibited, as it contravenes the idea of usage 
for a “peaceful purpose”. On the other hand, relying on military personnel for scientific 
research or for any other “peaceful purposes” is expressly allowed. Thus, for the Moon 
and other celestial bodies, there exists an unambiguous prohibition of militarisation 
within the OST. The norm of Article IV(2) OST is also applicable, among others, to 
the question of the use of force in the Earth’s orbit. This is the case since celestial bodies, 
mostly asteroids, may enter that orbit, while military activities technically could be exer-
cised on such bodies if the need arose.38 In light of the above, a crucial question arises as 
regards the general weaponisation of outer space: how is the term “utilisation for peaceful 
purposes” to be understood?39
2.2. Utilisation of Space for “Peaceful Purposes” as per OST
The interpretation of the term “peaceful purposes” in the OST indeed forms one of 
the centrepieces of the discussion on the use of force in space. As explained by Su, it used 
to be understood that it might only fit the purpose of Article IV to interpret “peaceful” 
as “non-military”.40 According to this notion, any military operation in space violates 
Article IV. This interpretation, however, does not sufficiently appreciate the distinction 
between militarisation and weaponisation of space. Schladebach reasons convincingly 
that Article IV must be interpreted41 in light of Article III OST.42 Article III provides that 
States Parties to the OST must exercise their activities in the exploration and use of outer 
space, including the Moon and other celestial bodies, in accordance with international 
law, including the UN Charter—all in the interest of maintaining international peace 
Opinion, I.C.J. Reports 1996 (Legality of the Threat or Use of Nuclear Weapons), p. 226, especially 
paras. 31, 79; Kütt & Steffek, 2015, pp. 402–407.
37 Gleason & Hays, 2020, p. 2; For more information on space weapons see: Harrison, 2020.
38 Harris & D’Abramo, 2015, p. 302; Santos, 2021.
39 Sandeepa & Kiran, 2009, pp. 210–211.
40 Su, 2010, p. 258.
41 Gardiner, 2010, pp. 177–188 and 278–287.
42 Schladebach, 2020, p. 63.
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and security. By virtue of this invocation of the UN Charter, the OST makes a direct 
reference to the norms contained therein, which is especially pertinent in the context 
of the law of treaties. Article 31(3)(c) of the Vienna Convention on the Law of Treaties 
(VCLT) provides that any relevant rules of international law applicable in the relations 
between the parties must be taken into account when interpreting a treaty.43 Thus, by 
virtue of the reference to the UN Charter in Article III OST, this provision of the OST 
should be interpreted, where relevant, in the context of the UN Charter.
Such an integrated understanding of the norms governing the use of force in space, 
linking the OST with the provisions of the Charter, was confirmed in the Declaration 
on International Cooperation in the Exploration and Use of Outer Space for the Benefit 
and in the Interest of All States, Taking into Particular Account the Needs of Developing 
Countries.44 In Article I, the Declaration stipulates that the use of outer space for peace-
ful purposes must be conducted in accordance with a joint interpretation of the provi-
sions of international law, the UN Charter, and the OST.45 A systematic interpretation 
of the “peaceful purposes” diction of Article IV of the OST is, therefore, a prerequisite 
since the OST must be interpreted and applied in the broader context of international 
law, including the UN Charter.46
Since Article III OST provides for the application of the UN Charter in relation to 
the notion of “peaceful purposes” in Article IV, the rules on the use of force of the UN 
Charter become especially relevant. As is widely known, States bear international respon-
sibility in line with the prohibition in Article 2(4) of the UN Charter, and customary 
international law on the unlawful use of force or the threat of its use.47 Nevertheless, in a 
few situations, the wrongfulness of such usage is precluded—one of them being self-de-
fence.48 Hence, Article III OST, via the UN Charter as a linking element, provides for the 
application of Article 51 on self-defence in the context of the OST, together with its cus-
tomary international law elements.49 The cross-reference of Article III OST to the norm 
of Article 51 UN Charter on self-defence shows that the use of force is indeed possible 
43 Vienna, 23 May 1969, 1155 UNTS 331; d’Aspremont, 2012, pp. 147–148.
44 Adopted in the Annex of UNGA Resolution 51/126, 13 December 1996.
45 Similarly, Section 3 titled “Peaceful purposes” of the recently adopted Artemis Accords stipulates 
that: “The Signatories affirm that cooperative activities under these Accords should be exclusively 
for peaceful purposes and in accordance with relevant international law”: the Artemis Accords, 
Principles for Cooperation in the Civil Exploration and Use of the Moon, Mars, Comets, and 
Asteroids for Peaceful Purposes, 13 October 2020. See: Bartóki-Gönczy & Nagy, 2023, p. 888; 
Smith, 2021, pp. 679–680.
46 Lee, 2003, p. 94.
47 Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda), 
Judgment, I.C.J. Reports 2005 (Armed Activities on the Territory of the Congo), p. 168, § 148.
48 Wilmshurst, 2005, p. 4.
49 Merkouris, 2017, p. 138.
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in space, encompassing both the Earth’s orbit and outer space in general, via the exercise 
of self-defence. Naturally, other conditions must be satisfied if a State wishes to invoke 
self-defence as a circumstance precluding wrongfulness, such as the customary interna-
tional law conditions of necessity and proportionality.50 Here, the particularities of space 
warfare in the Earth’s orbit ought to be considered. To indicate just one major challenge: 
as of 27 December 2024, there are 11,463 space objects orbiting Earth.51 Self-defence in 
the Earth’s orbit could thus affect the assets of other States, as well as cause harm to the 
space environment. Both factors must be addressed in any assessment of the criteria of 
necessity and proportionality of self-defence undertaken in the space domain.52
Exercising self-defence against an attack involves a response with military force to 
counter the attack. Thus, given that the right of self-defence is permitted in space, the 
term “peaceful purposes” in Article IV OST must not be understood as “non-military” 
or “without military force”, but rather as “without aggression” or “without aggressive 
force”.53 This is the case since, in light of Article 2(4) of the UN Charter, lawful self-de-
fence precludes the wrongfulness (i.e., the “aggressiveness”) of the use of force.54 An 
interpretation of the term “peaceful purposes” as “without military force” would thus 
deprive the reference in Article III OST to the UN Charter—especially Article 51 on 
self-defence—of its effect.55 Hence, if a State Party to the OST uses force in space within 
the bounds of lawful self-defence in accordance with the prerequisite conditions, such 
use of force is not prohibited in the Earth’s orbit, nor in any other area of outer space. 
By virtue of this, the militarisation and weaponisation of space are precluded except for 
lawful acts of use of force in line with the UN Charter (which also includes the Chapter 
VII powers of the UN Security Council). An analogous conclusion can be made for 
self-defence as a norm of customary international law, given that Article III expressly re-
fers to this source of international law, which continues to have its own separate existence 
despite being incorporated into Article 51 of the UN Charter.56
50 Oil Platforms (Islamic Republic of Iran v. United States of America), Judgment, I.C.J. Reports 2003 
(Oil Platforms), p. 161, §§ 43 and 76; Kretzmer, 2013, pp. 239–240 and 273.
51 Orbiting now, 2024.
52 Similar to the impact in terms of environmental damage caused on Earth by the use of force, see: 
Legality of the Threat or Use of Nuclear Weapons, p. 226, §§ 28–33.
53 Tepper, 2024, p. 481; see also: Cheng, 2000, p. 107. For a different perspective, see: Friman, 2005.
54 ARSIWA, Art. 21: Self-defence; cf. Kreß, 2016, p. 412.
55 Schladebach, 2008, p. 220.
56 Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of 
America). Merits, Judgment. I.C.J. Reports 1986 (Military and Paramilitary Activities in and against 
Nicaragua), p. 14, § 178.
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3. Self-Defence in the Earth’s Orbit: The Rules of Attribution for the 
Use of Force in International Space Law
Until this point, it was established that, pursuant to Article IV of the OST, the use 
of force in space, including the Earth’s orbit, is not prohibited if exercised in lawful 
self-defence. Naturally, as with all circumstances that may preclude the international 
wrongfulness of a State’s act, one must scrutinise which standards apply to such self-de-
fence for a State to successfully invoke it.57 This section will focus on the characteristics 
of the attack itself, against which self-defence can be exercised, specifically from the 
viewpoint of attribution of the use of force. Much ink has already been spilled on this 
question, yet the challenging part is whether it is suitable simply to transpose, by virtue 
of analogy, the existing rules on State responsibility in the realm of the use of force on 
Earth to the space domain.
According to the jurisprudence of the ICJ, self-defence is an inter-State question, 
with one State bearing responsibility for the attack and another State being subjected to 
the use of force. For the responsibility of a State to arise and for self-defence subsequently 
to be possible, the use of force must, therefore, be attributed to a given State—even if ex-
ercised by non-State actors. The latter derives from the Wall Advisory Opinion, in which 
the Court opined that self-defence, as an inherent right of States, only becomes relevant 
if armed attacks are imputable to a foreign State.58 By this reasoning, a State is barred 
from using force in self-defence against another State if the threshold for attributing 
the initial armed attack to that State is not met.59 This refers to the classic, State-centric 
concept of an armed attack, which was upheld by the Court in the later case between 
the Democratic Republic of Congo (DRC) and Uganda.60 In that case, the Court held 
on to the requirement that the notion of self-defence requires the involvement of anoth-
er State—thus following the “State armed attack” concept. In its reasoning, the Court 
stated that it had not found satisfactory proof of the involvement in the alleged attacks, 
direct or indirect, of the Government of the DRC. Further, as the attacks did not ema-
nate from armed bands or irregulars sent by the DRC or acting on behalf of the DRC, 
irrespective of the potency of the attack, they “remained non-attributable to the DRC”.61 
Consequently, Uganda was barred from successfully invoking self-defence to preclude 
the wrongfulness of its exercise of armed force against the DRC.
57 Farhang, 2013, p. 3.
58 Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory 
Opinion, I.C.J. Reports 2004 (Legal Consequences of the Construction of a Wall in the Occupied 
Palestinian Territory), p. 136, § 139; Oil Platforms, p. 161, § 51: “[…] the United States has to show 
that attacks had been made upon it for which Iran was responsible”.
59 Akande & Milanovic, 2015; O’Connell, 2013, pp. 380 and 383; Tladi, 2013, p. 572.
60 Starski, 2015, p. 462.
61 Ibid.; Armed Activities on the Territory of the Congo, p. 168, § 146.
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The premise of the ICJ is that successful reliance on Article 51 of the UN Charter 
thus requires the initial use of force in the form of an armed attack against the assets of a 
State to be attributable to another State. On the other hand, in the past 23 years, a new 
debate emerged on whether non-State actors per se (i.e., without their acts being attribut-
ed to a State) may also be regarded as capable of launching an armed attack in line with 
the dictum of Article 51 of the UN Charter.62 This newly emerged State practice appears 
to dispense with the requirement of attributing the use of force to a State.
Given the rapid development in space exploration and possible militarisation, a sit-
uation in which non-State actors per se exercise force against the assets of another State 
in space appears plausible. Thus, the concept of self-defence of States against attacks by 
non-State actors, whether attributable to a State or not, requires further examination 
in space law.
3.1. Self-Defence of States Against Non-State Actors: The Challenge of (Non)
Attribution
Globally, several States argue that the ordinary understanding of self-defence as rec-
ognised in the UN Charter is overly restrictive for the modern world.63 Within this tra-
ditional framework, the paramount criterion was attribution—the act of attributing an 
attack to a given State, whether force was utilised by State organs or non-State actors. The 
State to which force could be attributed would be seen as responsible for the use of force, 
rendering it a target of potential self-defence by the victim State.64 Nevertheless, since the 
attack of 11 September 2001 on the World Trade Center in New York, some States have 
expressed doubts over whether such an understanding of self-defence is still appropriate 
for the contemporary challenges of transnational terrorism. For example, it was widely 
claimed that the USA acted in self-defence against Al-Qaida in 2001, while Iraq, France, 
the United Kingdom, and the USA asserted the right of self-defence (individual or col-
lective) in their campaign against the Islamic State of Iraq and Syria (ISIS) in Syria.65
The situation in the immediate aftermath of 11 September 2001 seemed to suggest 
that the right of self-defence of Article 51 of the UN Charter is available against attacks 
62 For a discussion on the topic see: O’Connell, Tams & Tladi, 2019; Brunnée & Toope, 2016; Korošec 
& Tekavčič Veber, 2016.
63 Wood, 2013, p. 355; see also the 2002 National Security Strategy with the references to “preventive 
action” therein, in: The White House, 2002.
64 Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, p. 136, § 139, 
Military and Paramilitary Activities in and against Nicaragua, p. 14, § 195.
65 Paddeu, 2017, pp. 2–4; see also the summary record of the UNSC meeting of 20 November 2015, 
S/PV.7565, at p. 2 (France), 4 (USA), 9 (United Kingdom). See also the letters sent to the UNSC: 
UN Docs. S/2014/695 (USA); S/2014/851 (United Kingdom); S/2015/745 (France); Hakimi, 
2015. See also several blog posts, e.g.: Ohlin, 2014; van Steenberghe, 2015.
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committed by non-State actors without a need to attribute the actions of the non-State 
actor to a particular State. After the Twin Towers attacks, the Security Council adopted 
Resolutions 1368 (2001) and 1373 (2001), recognising “the inherent right of individual 
or collective self-defence in accordance with the Charter”.66 As indicated above, State 
practice, including that of the members of the North Atlantic Treaty Organization, the 
members of the Organization of American States and others, indeed supported such a 
right, in an apparent rift with the jurisprudence of the ICJ.67
In this context, the authors of the Chatham House study titled Principles of 
International Law on the Use of Force in Self-Defence concluded that necessary and 
proportionate action could be taken in a situation where the territorial State is itself 
“unable or unwilling” to take the required and necessary action.68 The drafters of the 
Leiden Policy Recommendations on Counter-Terrorism and International Law of 1 
April 2010, as well as Daniel Bethlehem in his set of principles on the scope of a State’s 
right of self-defence against attacks by non-State actors, reached a similar conclusion.69 
Several States have been strongly advocating since 2001 for this new understanding of 
self-defence to be acknowledged as a binding part of international law,70 with support-
ers of the “unable or unwilling” standard arguing that it now forms a part of customary 
international law.71
Considering the abovementioned State practice and academic opinion, the standard 
of “unable or unwilling” demands further attention as to its scope and meaning. In this 
regard, it is helpful to refer to the precise examples offered in 2016 by the White House 
in its “Legal and Policy Framework” on the use of force. The White House submitted 
that the standard of an unwilling or unable State might be invoked when a “State has lost 
or abandoned effective control over the portion of its territory’ from which a given non-
State actor operates”; or, alternatively, where “a State is colluding with or harbouring a 
terrorist organisation operating from within its territory and refuses to address the threat 
posed by the group”.72 In other words, on the basis of the “unwilling or unable” standard, 
self-defence could be exercised by States against non-State actors who have effectively 
displaced State control over the territory from which they operate. Alternatively, the 
standard covers situations where a State is providing a haven for terrorists and refuses to 
66 UNSC Resolution 1368 (2001), S/RES/1368 (2001), 12 September 2001; UNSC Resolution 
1373 (2001), S/RES/1373 (2001), 28 September 2001.
67 Wood, 2013, p. 356.
68 Wilmshurst, 2006, p. 963.
69 Leiden Policy Recommendations on Counter-Terrorism and International Law, 2010, p. 531; 
Bethlehem, 2012, pp. 770–777; Wilmshurst & Wood, 2013, pp. 390–395.
70 Brunnée & Toope, 2018, p. 282.
71 For a comprehensive analysis of this question, see: Williams, 2013, pp. 619–641; Corten, 2016; 
Jordan, 2024.
72 The White House, 2016, p. 10.
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act against them.73 Thus, instead of relying on the traditional link of attributing an attack 
by a non-State actor to a State, self-defence could be exercised as it is necessary “because 
the government of the State where the threat is located is unable or unwilling to prevent 
the use of its territory by the non-State actor for such attacks”.74
Nevertheless, it must be emphasised that the idea of pursuing self-defence against 
non-State actors within the territory of States deemed “unwilling or unable” is far from 
being universally accepted.75 In the opinion of dissenting States, the most lenient view 
vis-à-vis this standard is that the use of force by States in self-defence against attacks by 
non-State actors stemming from the territory of a third State is not “not unambiguously 
illegal”.76 One of the main challenges of this concept is the open vagueness regarding the 
parameters regulating when States can actually invoke it to exercise self-defence against 
non-State actors on the basis of Article 51 of the UN Charter. Namely, in the case of at-
tacks launched by non-State actors from the territory of another State, the latter could be 
arbitrarily labelled either as unwilling or unable to act. While it is unreasonable to expect 
States to remain passive in the wake of an attack by non-State actors, it is likewise unrea-
sonable to present a State that is willing but unable with a Catch-22 situation: either con-
sent to the use of force by another State to your territory or be subjected to it regardless.77
3.2. “Unable or Unwilling” States in Space and the Rules of Attribution of 
Conduct
When attempting to transpose the discussion on self-defence within “unwilling or un-
able” States into space, the challenges posed by this concept are amplified even further. 
This is because, unlike on Earth, in space there exist no sovereign borders or territories of 
States.78 The elementary rule in this regard is Article II of the OST, which stipulates that 
outer space, including the Moon and other celestial bodies, is not subject to national ap-
propriation via a claim of sovereignty, means of use or occupation, or by any other means. 
The dictum of Article II OST has been interpreted as precluding the possibility of property 
rights by any State, commercial entities, or private persons over any part of outer space.79 
73 Brunnée & Toope, 2018, p. 286.
74 The White House, 2016, p. 10.
75 Ruys & Verhoeven, 2005, p. 310; Paddeu, 2017, pp. 2–4; Wood, 2013, pp. 365–367.
76 Paddeu, 2017, pp. 2–4; for a similar position, see: Antonopoulos, 2008, pp. 159–180.
77 Ruys & Verhoeven, 2005, p. 310; Paddeu, 2017, p. 310; Brunnée & Toope, 2018, p. 285.
78 Sharma & Singh, 2012, p. 277; Lee, 2004, pp. 128–129; Pop, 2000, p. 275; Indo-Pacific Defense 
Forum, 2023.
79 Similar provisions can be found in Article 11, §§ 2 and 3 of the Moon Agreement: “2. The moon is 
not subject to national appropriation by any claim of sovereignty, by means of use or occupation, or 
by any other means & 3. Neither the surface nor the subsurface of the moon, nor any part thereof 
or natural resources in place, shall become property of any State, international intergovernmental or 
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Thus, with no possibility of a defined “territory” in space, the “unwilling or unable” stand-
ard, even if part of (customary) international law, faces a structural obstacle. If there can be 
no notion of “territory” in line with the conventional understanding of a State’s territory, 
how could States exercise self-defence against non-State actors acting from the “territory” of 
“unwilling or unable” States? Does this imply that the act of force by a non-State actor must 
commence on Earth, on the territory of an unwilling or unable State, and then culminate 
in space against the assets of another State—for instance, a satellite?
One potential way to overcome this predicament is to re-conceptualise, when in 
space, the concept of a State’s “territory” away from its sovereignty foundations and 
towards territorial jurisdiction. Both sovereignty and jurisdiction imply a State’s control 
over territory, but the notion of jurisdiction is broader. If outer space lies outside the 
traditional sovereignty rules of States, it is by no means entirely outside the rules on State 
jurisdiction. Sovereignty concerns a State’s control in a given territory, while jurisdiction 
refers to the ability of States to prescribe and enforce law and order within their territory. 
By virtue of this, jurisdiction is ascribed according to three dimensions: jurisdiction to 
prescribe, jurisdiction to adjudicate, and jurisdiction to enforce, each of which has al-
ready been observed in space.80 In this sense, even the OST stipulates in Article VIII that 
those States on whose registry an object launched into outer space is carried shall retain 
jurisdiction and control over such object, and over any personnel thereof, while in outer 
space or on a celestial body.81 Additionally, it is possible for a State to exercise extraterri-
torial jurisdiction in outer space. Thus, while activities can be extraterritorial—including 
in space—they are not necessarily extrajudicial.82
It is within this context that an argument could be made for re-interpreting the 
concept of a State’s “territory” as a part of the “unable or unwilling” standard, at least 
in space given its specific legal and factual circumstances, in accordance with the notion 
of territorial jurisdiction. Hence, if a State obliged to exercise its jurisdiction or control 
non- governmental organization, national organization or non-governmental entity or of any natural 
person. The placement of personnel, space vehicles, equipment, facilities, stations and installations on 
or below the surface of the moon, including structures connected with its surface or subsurface, shall 
not create a right of ownership over the surface or the subsurface of the moon or any areas thereof”; 
see also: Schladebach, 2020, pp. 53–54; Svec, 2022, p. 2; Angels, 2024; for a discussion on the prin-
ciple of non-appropriation as a rule of jus cogens, see: Cepelka & Gilmour, 1970, p. 46.
80 Sinclair & Patton, 2024, pp. 1–4; American Society of International Law, 2014, pp. 1–16.
81 See also Article VI OST, which provides similar duties of supervision in the area of State responsibil-
ity in space: “States Parties to the Treaty shall bear international responsibility for national activities 
in outer space, including the moon and other celestial bodies, whether such activities are carried on 
by governmental agencies or by non-governmental entities, and for assuring that national activities 
are carried out in conformity with the provisions set forth in the present Treaty. The activities of 
non-governmental entities in outer space, including the moon and other celestial bodies, shall re-
quire authorization and continuing supervision by the appropriate State Party to the Treaty”.
82 Sinclair & Patton, (2024), pp. 1–4.
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over its space object (used by a non-State actor) fails to exercise such control, and if the 
non-State actor proceeds to use force against the assets of another State, the State of juris-
diction could be deemed either “unwilling or unable”.83 The “unwillingness or inability” 
of a State to supervise or control the non-State actor using its space objects for the use of 
force is then equated to the “unwillingness or inability” of a territorial State to prevent its 
territory from being used as a launching ground for non-State actor attacks. This could 
then trigger the right of self-defence of the victim State against the State of jurisdiction.84 
Such an understanding transposes, mutatis mutandis, the concept of non-State actor use 
of force from within the territory of an “unwilling or unable” State to the space domain 
while adjusting it to the realities of space. Focusing on the lack of jurisdictional supervi-
sion and control when applying the “unwilling or unable” doctrine in space would also 
reflect the 2016 White House “Legal and Policy Framework” on the use of force as far as 
the specific circumstances of space law permit.85
While the “unwilling or unable” legal framework of self-defence against attacks by 
non-State actors in space is still evolving, as shown above, the rules for attributing re-
sponsibility for the use of force to a State are more developed. Attribution of the use 
of force in space to a given State could be scrutinised based on three different tests: an 
institutional, a functional, and an agency test.86 The institutional approach is reflected 
in Article 4 ARSIWA, which stipulates that the acts of de jure or de facto State organs are 
attributable to the State.87 The functional test attributes the use of force to the State if an 
act has been committed by entities empowered by that State to undertake governmental 
authority as per Article 5 ARSIWA. Another option is the use of force exercised by an 
organ of another State placed at the disposal of the first State, in accordance with Article 
6 ARSIWA. Lastly, the agency test, included in Article 8 ARSIWA, demonstrates that an 
ad hoc relationship between a State and a non-State actor performing an attack is some-
times required. In such a relationship, the State either instructs or directs the use of force 
by the non-State actor or exercises effective control over that non-State actor.88
83 See, mutatis mutandis, Principle F of UNGA Resolution 37/92, Principles Governing the Use by States 
of Artificial Earth Satellites for International Direct Television Broadcasting, 10 December 1982, UN 
Doc. A/AC.105/572/Rev.1, p. 39; see also Principle B providing for the general application of the 
OST, including its Article VI, to the subject matter of the Resolution; von der Dunk, 2011, p. 5.
84 Provided, again, that the standard of “willing or unable” actually applies as part of binding interna-
tional law.
85 The White House, 2016, p. 10.
86 Tsagourias, 2016, p. 805.
87 Müller & San Martin, 2024, § 9.
88 Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Bosnia 
and Herzegovina v. Serbia and Montenegro), Judgment, I.C.J. Reports 2007 (Application of the 
Convention on the Prevention and Punishment of the Crime of Genocide), p. 43, §§ 398, 400, 402–
406 and 413–414; United States Diplomatic and Consular Staff in Tehran, Judgment, I.C.J. Reports 
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For these tests enshrined in ARSIWA, the common thread is in linking the use of 
force to the responsibility of a State.89 However, given their specific characteristics, the 
attribution of acts by private, non-State parties in space to a given State appears to bear 
its own distinct predicaments—even outside the “unwilling or unable” doctrine. In the 
area of State responsibility in space, the challenge is to address the interplay between the 
ARSIWA rules of attribution of conduct to a State and the strict responsibility regime of 
States otherwise present in the space domain—most notably via Article VI OST.
3.3. The Attribution of Acts in Space: The Strict Responsibility Regime of the OST
Even though the space domain was once predominantly reserved for States and 
State-funded public procurement schemes involving private entities, this has dramati-
cally changed in recent years, with companies such as Blue Origin, SpaceX, and Virgin 
Galactic paving the way for the presence of private parties in space on their own accord.90 
Indeed, a surge may be observed in the development of satellite communications, space 
launches, and remote sensing capabilities by the private sector. It is expected that this 
trend will only increase in the future. In the USA, for example, the Department of 
Defense is increasingly reliant on commercial space systems, as they provide essential 
data for the armed forces.91 Thus, the commercial, private space sector plays a crucial 
role in Space Domain Awareness (SDA), the main goal of which is to provide knowledge 
of the space environment, including all operations in a given region of space, as well as 
the location of space objects and their missions.92 Nowadays, new technologies are being 
developed—among them weapons that could hit and destroy satellites in low-Earth and 
polar orbits—and private entities are at the forefront of such developments.93 Precisely 
this new involvement of private parties is central to the question of attributing the use 
of force in space, as it is becoming increasingly clear that non-State actors may become 
capable of exercising force in the space domain.
Unlike the traditional rules on State responsibility, as encompassed in ARSIWA, 
Massingham and Stephens write that States appear unequivocally responsible for the 
actions undertaken by private parties in space.94 This understanding may be derived from 
Article VI of the OST, which provides that the States Parties to the OST
1980, p. 3, § 58; Military and Paramilitary Activities in and against Nicaragua, p. 14, §§ 116–177 
and Separate Opinion of Judge Ago, § 16.
89 As regards the exercise of attributing the reliance on force by non-State actors to a State on the 
premises of the Earth, this notion has been extensively covered. See, for example, Lanovoy, 2017, 
pp. 563–585; Sancin et al., 2009, pp. 185–187.
90 Holmes, 2024; European Space Policy Institute, 2017, p. 3; NASA, 2014, pp. 11, 17 and 105.
91 Wehtje, 2023, fn. 31–32.
92 Ibid.; Baker-McEvilly et al., 2024, p. 1.
93 Thiruvanathapuram, 2010.
94 Massingham & Stephens, 2022, p. 18.
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“shall bear international responsibility for national activities in outer space, inclu-
ding the Moon and other celestial bodies, whether such activities are carried on 
by governmental agencies or by non-governmental entities, and for assuring that 
national activities are carried out in conformity with the provisions set forth”
in the OST. Additionally, to erase any possibility of doubt, Article VI subjects the 
activities of non-governmental entities in outer space, including the Moon and other 
celestial bodies, to authorisation and continued supervision by the appropriate State 
Party to the OST.95
With respect to Article VI and the question of attribution and responsibility, the 
reference to “non-governmental entities” in correlation with the imposition of responsi-
bility upon a State for these private parties is of particular significance. According to the 
genesis of the OST, Article VI, with its provision on “non-governmental entities” and 
State responsibility, reflects a compromise reached between the Union of Soviet Socialist 
Republics (USSR) and the USA at the time of intense negotiation over the OST. While 
the USSR argued that only States might venture into space and engage in space activities, 
the USA, with notable foresight, sensed the important future role that private parties 
would play in the space domain.96 The USA argued that States might wish to license a 
private firm to carry out certain activities in space.97
According to the drafting history of the OST, the main premise of Article VI was to 
establish a strict regime of responsibility for space-faring States for the activities of a non-
State entity, such as private companies, when it comes to “national activities” in outer 
space. This strict regime provides for the responsibility of a State regardless of whether 
the State was aware of the activity in question.98 The underlying reason for such a regime 
is the nature of space activities: since these activities are perceived as dangerous and capa-
ble of causing widespread damage, the desire was to avoid any a potential impunity for 
the damage caused, as well as to ensure that States act with due diligence.99
Unsurprisingly, the definition of what constitutes a “national activity” has been inter-
preted broadly. In 2013, the General Assembly proposed in its Resolution 68/74 titled 
95 Von der Dunk, 2011, pp. 5–8. Interestingly, according to Article VI OST, not only States but also 
international organisations bear the burden of responsibility for their activities carried out in outer 
space, including the moon and other celestial bodies. This provision may become particularly im-
portant for the EU in the development of its own space programme. See in this regard: European 
Union Agency for the Space Programme: 2024.
96 Committee on the Peaceful Uses of Outer Space Legal Sub-Committee, Summary Record of 
the Seventeenth Meeting, UN Doc A/AC.105/C.2/SR.17, 27 June 1963, p. 7; Massingham & 
Stephens, 2022, p. 18.
97 Committee on the Peaceful Uses of Outer Space Legal Sub-Committee, Record of the Twentieth 
Meeting, UN Doc A/AC.105/C.2/SR.20, 27 June 1963, p. 12.
98 Sancin, Grünfeld & Ramuš Cvetkovič, 2021, p. 50.
99 Ibid.; Massingham & Stephens, 2022, pp. 294–295.
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Recommendations on National Legislation Relevant to the Peaceful Exploration and 
Use of Outer Space, that the notion should include all activities conducted by a State’s 
nationals or from its national territory.100 It is true that, according to the making of the 
OST, the main premise of Article VI was to establish a very strict regime of responsibil-
ity for space-faring States for a non-State entity—such as private companies—when it 
comes to “national activities” these entities undertake in outer space. Hence, there exists 
a clear obligation for States, as part of their duty of due diligence, to supervise private 
parties and authorise their activities, usually by way of domestic legislation, licensing 
schemes, and other requirements.101 What remains to be addressed now is how the word-
ing of Article VI OST could be applied in the event of private entities (i.e., non-State 
actors) using force in space.
3.4. Attribution of the Use of Force to a State in Space: The OST Strict Regime 
Versus ARSIWA
States are deemed responsible for the use of force by private parties if it can be con-
cluded that the State exercised effective control over the non-State actor.102 The thresh-
old for what constitutes effective control is quite high. According to Article 8 ARSIWA, 
the standard is fulfilled and responsibility attributed to the State “if the person or group 
of persons is in fact acting on the instructions of, or under the direction or control 
of, that State in carrying out the conduct” concerned.103 This understanding reflects 
customary international law.104 In the Jan de Nul award, for example, rendered by the 
International Centre for Settlement of Investment Disputes (ICSID), the tribunal relied 
on the ICJ’s reasoning in Nicaragua v. USA. The tribunal held that international juris-
prudence prescribes a truly substantial benchmark for attributing the act of a person or 
entity to a State, as it requires two elements: (1) a general control of the State over the 
person or entity and (2) a specific control of that State over the given, concrete act for 
which attribution is sought.105
When comparing the strict responsibility regime of Article VI OST with ARSIWA, the 
main difference lies in the question of attribution.106 Erhart and Boutovitskai submit that 
100 UNGA Resolution 68/74, 11 December 2013, § 2; Massingham & Stephens, 2022, pp. 293–294.
101 Aoki, 2012, p. 397.
102 Crawford, 2013, p. 141.
103 ARSIWA, Article 8, Conduct directed or controlled by a State.
104 Ryngaert, 2021, p. 171.
105 Jan de Nul N.V. and Dredging International N.V. v. Arab Republic of Egypt, ICSID Case No. 
ARB/04/13, § 173; Boon, 2014, p. 19; Military and Paramilitary Activities in and against Nicaragua, 
p. 14, §§ 113–115.
106 ARSIWA, Article 2: “There is an internationally wrongful act of a State when conduct consisting of 
an action or omission: (a) is attributable to the State under international law”.
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Article VI OST is clear in its wording and thus suggests a much lower threshold for attrib-
uting the responsibility for any space activities by private parties to a given State.107 Thus, 
the main challenge is how to reconcile these two systems of norms. In other words, could 
Article VI OST perhaps be understood as lex specialis in relation to the general interna-
tional law rules enshrined in ARSIWA? On the other hand, since Article III OST expressly 
references the UN Charter as well as international law more broadly, would it not be ap-
propriate to extend the general international law rules in ARSIWA to the space domain?108
Three potential solutions may be discerned to answer these queries. The first rests 
on the premise that space law, especially Article VI OST, may be seen as a lex specialis 
norm in relation to ARSIWA. The second supports the view that the general rules of 
State responsibility in ARSIWA should apply, as they are secondary rules of international 
law, whereas Article VI OST encompasses primary rules.109 The third approach offers a 
combined reading of Article VI OST and ARSIWA, based on a systematic interpretation 
of the norms contained therein, to preserve the purpose of the secondary law rules on 
State responsibility.
3.4.1. The Strict Responsibility Regime of Article VI OST as Lex Specialis
This approach rests on the premise that the ARSIWA rules on State responsibility 
were not intended to constitute a comprehensive code of secondary rules of international 
law.110 According to Article 55 ARSIWA, the rules on attribution enshrined therein do 
not apply where, and to the extent that, the conditions for the existence of an interna-
tionally wrongful act or the content or implementation of the international responsi-
bility of a State are governed by special rules of international law. Thus, if another, lex 
specialis norm governs the rules of attribution, that more specific regime prevails over the 
Articles in ARSIWA. Here, Article VI OST comes into play as a lex specialis provision in 
the field of attributing the acts of non-State actors in space to a given State.111
The argument offered in this regard is that the OST regime better accounts for the 
particularities of space activities carried out by non-State actors.112 It is argued that 
Article VI OST was drafted to establish an over-arching responsibility for acts conducted 
by private parties in space, thus rendering any and all space activities the responsibility of 
at least one State.113 The motive behind this normative choice of the OST drafters—to 
attribute all acts of non-State actors in space to a given State—was the inherently dan-
107 See, e.g., Erhart & Boutovitskai, 2021, pp. 2–3.
108 Breccia, 2016, pp. 20–21.
109 Ramuš Cvetkovič, 2021, p. 19.
110 See especially ARSIWA, Article 56, as well as Crawford, 2002, p. 879.
111 Li, 2023, p. 4; Zorzetto, 2012, pp. 61–64.
112 Koskenniemi, 2003, p. 10.
113 Cheng, 1998, pp. 14–16; von der Dunk, 2011, p. 3.
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gerous nature of space activities.114 Consequently, a conflict of norms may be observed in 
the area of secondary rules of international law: between the rules in ARSIWA and the 
strict regime of Article VI OST.115
Given that Article VI OST provides for a specialised, strict regime of attribution 
compared to the general rules on attribution enshrined in ARSIWA, the former may 
prevail over the latter on the basis of its specificity: lex specialis derogat legi generali (Article 
55 ARSIWA). Hence, the initial conflict between both systems of norms is resolved, 
with the ARSIWA rules on attribution giving way to Article VI OST when assessing the 
responsibility of States for the acts of non-State actors in space.
3.4.2. Article VI OST as a Rule of Primary International Law
The second approach, which enjoys less support, departs from the application of 
Article VI OST as a lex specialis rule of attribution. This second interpretation is founded 
on a narrow reading of Article VI OST. According to this view, the strict responsibility 
regime applies to a State’s own actions or omissions. Consequently, a State is deemed 
responsible for the acts of private parties in space when it has itself failed to supervise 
such acts or to authorise them. Article VI OST is thus seen as a primary norm, not as a 
secondary norm of international law, merely demanding of States a heightened duty of 
supervision and due diligence vis-à-vis non-State actors.116
Since, in this scenario, the secondary law rules on attribution are not superseded by 
a lex specialis norm, the activities undertaken by private entities in space would continue 
to be attributed to a given State on the basis of the customary international law rules of 
ARSIWA.117
In this sense, Article VI OST enshrines a stricter primary law norm of due diligence 
for the State concerned in supervising the activities of non-State actors. Thus, a State 
would only be held responsible for the conduct of a non-State actor under its direction 
or control, or in a case of conduct adopted or acknowledged by the given State, if it failed 
to exercise diligent supervision.118 Following this approach, there is no conflict between 
ARSIWA and the OST regarding the attribution of responsibility to a State for the use 
of force by private parties in space. Article VI OST reflects a norm of primary law, while 
leaving the secondary law norms of attribution of conduct and responsibility for the 
activities of non-State actors to ARSIWA.
114 Marchisio, 2012, pp. 11 and 14–15.
115 Ramuš Cvetkovič, 2021, p. 20.
116 Ibid., p. 19; Grünfeld, 2022, p. 606; Arangio-Ruiz, 2017, pp. 126–127.
117 Dupuy, 2002, p. 464.
118 Grünfeld, 2022, p. 606.
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3.4.3. Interpretation of “National Activities” in Light of the Purpose of ARSIWA
Provided that the standard of effective control in Article 8 ARSIWA was substituted 
by virtue of Article VI OST with a lower standard of attribution, classifying the use of 
force as a “national activity” would suffice—without needing to fulfil the effective con-
trol test—to attribute the use of force by non-State actors to a State. In a scenario where 
the threshold for attribution of responsibility for the use of force in space is easily met, 
States could be drawn much quicker into an armed conflict by virtue of non-State actors 
using force in space. Alternatively, imposing a standard that might be unrealistic risks 
reducing Article VI OST to near-irrelevance in a situation involving the use of force by 
non-State actors.119
For these reasons, the last option (which enjoys the least support of all three) rests on 
a teleological and systematic interpretation of Article VI OST and ARSIWA, with the 
aim of safeguarding the purpose of the secondary law rules on attributing the conduct of 
non-State actors to a State. According to the purpose of these rules, only acts that can be 
attached to a State on the basis of an objective (i.e., real) link—whether legal, functional, 
or factual—may be attributed to that State.120 In this sense, it is important to recall the 
crucial role played by the principle of effectiveness in international law with regard to 
State responsibility. Based on the principle of effectiveness, when determining a State’s 
responsibility for acts of non-State actors, it is necessary to establish the existence of a 
real link between the non-State actors performing the act and the State in question.121
The question then remains how to interpret the term “national activities” in Article 
VI OST to safeguard the purpose of the rules on State responsibility. Article VI OST can 
be linked to Article 8 ARSIWA in the case of non-State actors by interpreting the notion 
of “national activities” in the light of the customary international law standard of effec-
tive control. This interpretive option may be viable given the explicit invocation of gen-
eral international law in Article III OST. Therefore, it is beyond doubt that a substantial 
part of international law and the UN Charter applies to human activities in space.122 To 
incorporate fully the purpose of the customary international law rules on State responsi-
bility into Article VI OST, and to ensure a systematic reading of the norms contained in 
ARSIWA and the OST via Article 31(3)(c) VCLT, the term “national activities” could be 
interpreted in line with the norm of Article 8 ARSIWA.
It is thus difficult to conceive that, e.g., the use of force stemming from a malfunction 
of a space object operated by non-State actors may be directly attributed to the respon-
119 Ramey, 2018, pp. 230–231.
120 De Frouville, 2013, p. 261.
121 Report of the International Law Commission on the work of its fifty-third session, Commentaries 
on the draft ARSIWA, appears in the Yearbook of the International Law Commission, 2001, Vol. 
II, Part Two, as corrected, p. 47.
122 Breccia, 2016, pp. 20–21.
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sibility of a State in the absence or a “real link”—just as it is equally inconceivable to do 
so on Earth on the basis of Article 8 ARSIWA and the rules on State responsibility.123 
It follows from this reasoning, and from the purpose of the norm in Article 8 ARSIWA 
(to which Article III OST makes reference), that the use of force by private entities in 
space may be attributed to the State via Article VI OST if the force in question was in-
structed or exercised under the effective control of that State. Such a use of force may be 
deemed a “national activity” in the terms of Article VI OST, and for such a use of force 
the responsibility of the State arises, thus leading to a possible invocation of Article 51 of 
the UN Charter. In other words, if a State instructs or effectively controls the exercise of 
force by a non-State actor in space, the latter exercise may be deemed a “national activity” 
in terms of Article VI OST for which the State could bear international responsibility.
4. Concluding Remarks
With contemporary developments in space technology, it may be observed—wor-
ryingly—that the notion of acts of force being committed in space no longer appears 
quite so remote. The possibility of the use of force in space raises questions regarding the 
weaponisation of space and the corresponding norms on the responsibility of States for 
internationally wrongful acts they commit, either in their capacity as States or via non-
State actors. While current prospects for space warfare mostly involve the destruction of 
unmanned military assets in space—usually satellites traversing the Earth’s orbit124—fur-
ther militarisation of space will, in all likelihood, follow. In the new space era, non-State 
actors will play a crucial role.
To address some aspects of the emerging challenges related to the weaponisation of 
space, this article focused on an issue of increasing importance in the space domain: the 
use of force—especially in the context of self-defence—and the question of attributing 
responsibility for the use of force by non-State actors in space to a given State.
With regard to the prospects for self-defence in the Earth’s orbit, it has been shown 
that, by virtue of Article III OST, which cross-references the UN Charter, Article IV 
OST must be interpreted in connection with the Charter. Hence, an integrated interpre-
tation of the “peaceful purposes” wording in Article IV OST with the norms on self-de-
123 In Military and Paramilitary Activities in and against Nicaragua, the ICJ pronounced that for a 
“conduct to give rise to legal responsibility of the United States, it would in principle have to be 
proved that that State had effective control of the military or paramilitary operations in the course 
of which the alleged violations were committed”: Application of the Convention on the Prevention 
and Punishment of the Crime of Genocide, p. 43, §§ 399–400; Breitwieser-Faria, 2021, pp. 84–85; 
de Frouville, 2013, p. 261; Corfu Channel case, Judgment of April 9th, 1949: I.C.J. Reports 1949, 
p. 18; see also Olleson, 2001, p. 40; Massingham & Stephens, 2022, p. 295.
124 Ramey, 2018, p. 190.
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fence in Article 51 of the UN Charter leads to the conclusion that the use of force in 
space is allowed when exercised in self-defence. The term “peaceful purposes” in Article 
IV OST is, therefore, to be understood in line with the prohibition of aggression (or 
“aggressive force”) in customary international law and Article 2(4) of the UN Charter, 
rather than as a blanket prohibition of any acts of force in space.125
After concluding that the use of force in self-defence in space is permitted, the article 
turns to the rules of attribution for the use of force exercised by non-State actors in space 
to a State. Here, a distinction is drawn between two models: the traditional, ARSIWA 
model on attribution of acts to a State, and the doctrine of “unwilling or unable”, which 
departs from the standard criterion of attribution. Regarding the latter doctrine, the “un-
willingness or inability” of a spacefaring State to supervise or control a non-State actor 
using its space objects to exercise force in space could be linked to the “unwillingness 
or inability” of a territorial State to prevent its territory from being used as a launching 
ground for non-State actor attacks. This could then trigger the victim State’s right of 
self-defence against the State of jurisdiction. Such an interpretation transposes, mutatis 
mutandis, the concept of non-State actor use of force from within the territory of an “un-
willing or unable” State to the space domain, while adjusting it to the realities of space.
Departing from the developing “unwilling or unable” doctrine and focusing on the 
much more developed and accepted model of attribution of responsibility for acts under-
taken by non-State actors to a State, the article examined the interplay between ARSIWA 
and the strict regime of Article VI OST. Three potential solutions were assessed to ad-
dress the apparent conflict between these two sets of attribution of conduct rules. The 
first option rests on the premise that space law, particularly Article VI OST, may be re-
garded as a lex specialis system in relation to ARSIWA. By virtue of Article 55 ARSIWA, 
the rules on attribution in Article VI OST could thus supersede the norms of ARSIWA, 
in their capacity as a more specific set of secondary law rules. The second solution sup-
ports the view that the general rules of State responsibility in ARSIWA should apply 
as secondary rules of international law, whereas Article VI OST encompasses primary 
rules. Here, Article VI OST is understood as reflecting a high due diligence obligation 
of spacefaring States—a primary norm—rather than constituting a lex specialis set of 
secondary rules. The third solution is founded on a combined reading of Article VI OST 
and ARSIWA via a systematic interpretation of the norms they contain, with a view to 
preserving the purpose of the secondary law rules on State responsibility. For this latter 
option, it is crucial to determine whether the use of force by non-State actors in space is 
always deemed a “national activity” within the meaning of Article VI OST. In light of the 
rules on State responsibility for internationally wrongful acts and relevant international 
jurisprudence, it was submitted that the use of force by private entities in space could be 
125 Buchan, 2023.
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attributed to a State via Article VI OST only if the force in question was either instructed 
by or exercised under the effective control of that spacefaring State.
Of the three options presented, the lex specialis argument appears the most convinc-
ing and enjoys the broadest support in literature. It follows from the inherently hazard-
ous nature of space activities that the OST purposefully sets out a specific system of strict 
responsibility in Article VI to ensure not only that States actively supervise non-State 
actors under their jurisdiction, but also to prevent impunity for damage caused in space. 
This creates a distinct set of secondary law norms intended to regulate the consequences 
of the acts and omissions of spacefaring States in space. Thus, the ARSIWA rules on State 
responsibility must give way to the strict regime of Article VI OST when assessing the 
responsibility of States for acts committed by non-State actors in space, including acts 
involving the use of force. By virtue of this, a more specific system of attribution rules 
supersedes a more general one.
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LjubLjana Law Review, voL. LXXXiv, 2024 – synopses
Znanstveni članek
DOI: 10.51940/2024.1.125-156
UDK: 347.85:341.229:347:355
Anže Mediževec
Pravica do samoobrambe v Zemljini orbiti
Z razvojem vesoljske tehnologije so v vesolju poleg držav čedalje bolj prisotni tudi nedr-
žavni akterji. Njihova vse večja prisotnost odpira številna pravna vprašanja, tudi v zvezi 
z uporabo sile, zlasti v okviru pravice do samoobrambe. Prvi cilj tega članka je pojasniti 
pravno podlago za uporabo sile pri izvajanju samoobrambe v vesolju, zlasti v Zemljini or-
biti. Drugi cilj je prispevati k pravnemu okviru, kako lahko države izvajajo samoobrambo 
pred napadi nedržavnih akterjev v vesolju. Avtor razlikuje med pravili o pripisovanju 
uporabe sile državi in doktrino nepripravljenosti ali nezmožnosti države »gostiteljice«. 
Predlaga, da se slednja lahko smiselno prenese na področje vesolja s pomočjo rekoncep-
tualizacije pojma »ozemlja« države od paradigme državne suverenosti v smeri državne 
jurisdikcije. Nadalje avtor na področju pravil o pripisovanju ravnanja državi primerja 
določbe v Členih o odgovornosti držav za mednarodno protipravna dejanja (ARSIWA) 
o odgovornosti države in režim objektivne odgovornosti iz Pogodbe o vesolju (OST). 
Njegov namen je pojasniti, kateri sistem pravil naj se uporablja pri obravnavi vpraša-
nja odgovornosti države za uporabo sile s strani nedržavnih akterjev v vesolju. Glede 
tega ponudi tri rešitve. Prva temelji na predpostavki, da se pravo vesolja, konkretno VI. 
člen OST, lahko obravnava kot lex specialis v razmerju do sistema pravil po ARSIWA. 
Druga podpira stališče, da bi se morala uporabljati splošna pravila o odgovornosti držav 
iz ARSIWA, saj gre za sekundarna pravila mednarodnega prava, VI. člen OST pa zajema 
primarna pravila. Tretji pristop ponuja kombinirano razlago VI. člena OST in ARSIWA, 
ki temelji na sistematični razlagi tam vsebovanih norm, da se ohrani namen sekundarnih 
pravil mednarodnega prava o odgovornosti držav.
Ključne besede
Pogodba o vesolju (OST), IV. člen OST, VI. člen OST, miroljubni nameni, nacionalne 
dejavnosti, samoobramba v vesolju, režim objektivne odgovornosti.
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Zbornik znanstvenih razprav – letnik LXXXIV, 2024 – povzetki
LjubLjana Law Review, voL. LXXXiv, 2024 – synopses
Scientific Article
DOI: 10.51940/2024.1.125-156
UDC: 347.85:341.229:347:355
Anže Mediževec
The Right of Self-defence in the Earth’s Orbit
Abstract
The increasing presence of non-State actors in space raises a plethora of legal questions, 
including those related to the use of force, especially in the context of the right of self-de-
fence. The first aim of this article is to explain the legal basis for resorting to force in the 
exercise of self-defence in space, specifically in the Earth’s orbit. The second goal is to 
contribute to the legal framework concerning how States may exercise self-defence against 
attacks committed by non-State actors in space. In this regard, the author distinguishes 
between the rules of attribution of the use of force to a State and the “unwilling or unable” 
doctrine. It is suggested that the latter may be transposed into the space domain, mutatis 
mutandis, by a re-conceptualisation of the notion of a State’s “territory”, shifting from its 
sovereignty-based foundation towards State jurisdiction. Further on, in the realm of the 
rules of attribution of conduct to a State, the author compares the ARSIWA rules of State 
responsibility with the strict responsibility regime of the Outer Space Treaty (OST), to 
clarify which system applies when addressing State responsibility for the use of force by 
non-State actors in space. Three solutions are offered in this regard. The first rests on the 
premise that space law, specifically Article VI OST, may be seen as lex specialis in relation 
to ARSIWA. The second supports the view that the general rules of State responsibility in 
ARSIWA should apply, as they are secondary rules of international law, whereas Article VI 
OST encompasses primary rules. The third approach offers a combined reading of Article 
VI OST and ARSIWA, based on a systematic interpretation of the norms contained 
therein, to preserve the purpose of the secondary rules on State responsibility.
Key words
Outer Space Treaty, Article IV OST, Article VI OST, Peaceful Purposes, National 
Activities, Self-defence in Space, Strict Responsibility Regime.