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  • Richa Maria & Shagnik Mukherjea

International Humanitarian Law and its Application to Armed Conflicts in Outer Space


“I do not say that we should or will go unprotected against the hostile misuse of space any more than we go unprotected against the hostile use of land or sea, but I do say that space can be explored and mastered without feeding the fires of war, without repeating the mistakes that man has made in extending his writ around this globe of ours.”

Technology enabled by space-based systems pervades almost every facet of human life; for example, satellite communications, space situational awareness, and position navigation demonstrate our dependence on space technology for performing tasks critical to sustaining life as we know it today. Since the dawn of the space era, space activities have been associated with military use for nations to fortify their military, security, and defense prowess. As General Lance W. Lord wrote, “Space superiority is the future of warfare. We cannot win a war without controlling the high ground, and the high ground is space.” However, it was soon realized that military operations and armed conflicts conducted in, or concerning, outer space could lead to a catastrophe with irrevocable ramifications giving rise to potential humanitarian crises.

Understanding the necessity of a consolidated international legal framework, five international treaties were developed under the auspices of the United Nations to regulate military and civilian activities in outer space. Each treaty, namely – The Outer Space Treaty, The Rescue Agreement, The Liability Convention, The Registration Convention and The Moon Agreement – deals with various matters ranging from the liability for damage caused by space objects to the exploitation of natural resources in outer space. From the beginning, the development of space law has been premised on the hope of avoiding armed conflict in outer space while maintaining outer space as a sanctuary for peace. As the prospects of this hope wane, uncertainties arise concerning the constraints governing the potential utilisation of force in the event of armed conflicts originating from or occurring in outer space. In light of this, this article aims to elucidate the prevailing legal framework and examine the extent to which international humanitarian law applies to armed conflicts in outer space.

Provisions of the Outer Space Treaty and its Need for Development

The aforementioned five international treaties, or the corpus juris spatialis, collectively form the foundation of space law. The Outer Space Treaty, also known as the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (hereinafter ‘OST’), is a keystone treaty of space law which highlights that the use of outer space shall be carried out for the benefit and in the interests of all countries and outer space should be used exclusively for ‘peaceful purposes.’ There has been a longstanding discourse vis-à-vis the term ‘peaceful purposes’ since it has not been clearly defined by the OST, leaving its meaning ambiguous and unclear. While some members of the international community interpret ‘peaceful purposes’ as ‘non-military,’ others interpret it as ‘non-aggressive or non-hostile.’ Interestingly, there is no internationally binding obligation that outer space has to be used exclusively for ‘peaceful purposes’ even though the peaceful use of outer space is often quoted at international forums as an underlying principle governing space activity. There are explicit prohibitions on certain weapons, such as ‘nuclear weapons and ‘weapons of mass destruction’ and military activities on ‘celestial bodies, such as the Moon, under Article IV of the OST. However, if one strictly follows the wording of the article itself, these restrictions do not apply to outer void space as a whole, highlighting a significant loophole in the OST.

The Preamble of the OST explicitly mentions that the use of outer space is for ‘peaceful purposes.’ Even though a preamble does not enforce legally binding responsibilities on states, it aids in the practical interpretation of the aims and purposes of a treaty and often imbibes the treaty’s spirit. Nevertheless, the term ‘peaceful purposes’ in the Preamble of the OST is only helpful in interpreting the treaty articles and does not per se define the terms themselves. Furthermore, in an attempt by the United Nations to strictly interpret the use of outer space for peaceful purposes, the Agreement Governing the Activities of States on the Moon and Other Celestial Bodies, popularly known as the Moon Agreement, was created as a supplement to the OST and reaffirmed the de-militarisation of celestial bodies. According to Article 3 of this Agreement, ‘the moon shall be used by all States Parties exclusively for peaceful purposes. Any threat or use of force on the moon is prohibited.’

Furthermore, Article III of the OST is significant because it applies the full breadth of general public international law to outer space and contains provisions directing State Parties to ‘carry on activities in the exploration and use of outer space, in accordance with international law, including the Charter of the United Nations, in the interest of maintaining international peace and security and promoting international cooperation and understanding.’ This means that the laws of armed conflict and the UN Charter’s Article 2(4), which relates to the prohibition of the threat or use of force against any state’s territorial integrity or political impendence, applies to state action in outer space. Thus, the use of weapons would be permitted if the purpose was justified under the exceptions to the use of force (jus ad bellum), one such exception being self-defence.

Following Article 103 of the UN Charter, when conflict arises between the obligations of the Members of the United Nations and their obligations under any other international agreement, their obligations under the Charter shall prevail. In light of this, the OST and the UN Charter must be interpreted and read together because Charter obligations supersede other treaties, as further reinforced under Article 30 of the 1980 Vienna Convention on the Law of Treaties. Furthermore, under Article 42 of the Charter, the Security Council ‘may take action in order to maintain or restore peace and security.’ Accordingly, any use of space, including the use of force, following the orders of the Security Council would be valid and legally justified because, as established under Article 25 of the UN Charter, members have to accept and carry out the decisions made by the Council.

Enshrined in Article IV of the OST are provisions relating to the question of the military uses of space and the prohibition of the placement of weapons of mass destruction in orbit around the earth, weapon testing and the installation of nuclear weapons on celestial bodies. According to the Article, ‘the moon and other celestial bodies shall be used by all State Parties exclusively for peaceful purposes, and the establishment of military bases, installations and fortifications, the testing of any type of weapons and the conduct of military manoeuvres on celestial bodies shall be forbidden.’ While ‘the testing of any types of weapons’ is not permitted on ‘celestial bodies,’ there is no mention of such testing being prohibited in ‘outer space,’ which raises pertinent questions regarding whether ‘outer space’ is excluded from the testing of weapons. However, this is likely to be a drafting error since Article III, Article IX and Article XIII of the Treaty include the Moon and celestial bodies within the definition of ‘outer space,’ which is a broader interpretation in comparison.

Nonetheless, a stringent interpretation of the language used in Article IV prohibits only the placement of ‘nuclear weapons’ and ‘weapons of mass destruction’ in orbit, failing to acknowledge the permissibility of other conventional weapons and dual-use military space objects. Regrettably, the narrow focus of the article and its inadequate definition of ‘weapons of mass destruction’ allow for considerable room for improvement. Presently, international space law permits the placement of weapons into orbit if they do not fall within the scope of ‘weapons of mass destruction.’ Consequently, due to these interpretational challenges, States have construed these provisions in a manner that allows for the utilisation of weapons such as Anti-Satellite (ASAT) missiles, as long as they are not employed aggressively against another State. This circumstance, therefore, necessitates an examination of the laws of armed conflict, which seek to regulate the behaviour of parties involved during periods of hostilities.

The Application of the Laws of Armed Conflict in Outer Space

Since the launch of Sputnik 1 in 1957, space has been a critical theatre of military operations as satellites and other space-based systems have emerged as indispensable tools for a state’s military force to gather intelligence, conduct surveillance, and enhance reconnaissance capabilities. In light of rising tensions and the threat of proxy wars, applying IHL to military activities in outer space has become a pressing concern for the international community. It is only further escalated with the rapid advancement of technology that blurs the boundary between civilian and military applications. In this regard, initiatives like the International Committee of the Red Cross Publications on Contemporary Armed Conflicts and the Woomera Manual pave the way for establishing a rule-based legal framework for regulating military operations in space.

As previously noted, it is worth highlighting that the OST does not explicitly forbid military operations in space but refers to the prohibition of aggression, akin to the jus contra bellum regime. This understanding would still not negate the application of IHL in space-based military operations, which derives its relevancy from Article III of the OST, referring to all obligations being carried out “in accordance with international law.” Whether IHL applies depends on whether the conflict is a Non-International Armed Conflict or an International Armed Conflict. In short, once a conflict is deemed an IAC or NIAC, IHL principles and obligations are in effect. This was further evidenced by the International Court of Justice in its 1986 Nuclear Weapons Advisory Opinion, observing that the principles of IHL apply to “all forms of warfare and to all kinds of weapons, those of the past, those of the present and those of the future.” Similarly, the ICRC affirms this stance in their Working Paper on Armed Conflicts in Outer Space, citing Article III of the OST as the basis for the relevant international law that governs such conflicts and explicitly refers to the UN Charter, specific treaties, the law of neutrality and the principles of jus in bello. While an exhaustive overview of all use cases concerning the analysis of IHL principles is beyond the scope of this article, it does delve into issues surrounding the principles of distinction and proportionality that are uniquely applicable in this setting.

Principle of Distinction

The principle of distinction, regarded as a cardinal principle of IHL, is crucial in determining the legitimacy of military attacks. It distinguishes between combatants and civilians, only authorising military attacks against the former when it results in a definite military advantage. Consequently, it not only safeguards but also upholds the status of non-combatants throughout such hostilities.

However, two pertinent issues regarding its applicability arise in the context of armed conflicts in outer space. Firstly, regarding the status of military astronauts in outer space when their respective countries are involved in an ongoing armed conflict. In this regard, while IHL would traditionally consider them combatants, international space law, on the other hand, unequivocally treats astronauts as “envoys” of humankind, guaranteeing protection and assistance at all times. The question, therefore, would boil down to the determination and application of lex specialis. While IHL has traditionally been regarded as lex specialis, governing the conduct of belligerents during armed conflicts, recent discussions have emerged regarding the precedence of international space law. These discussions emphasise the unique position of astronauts operating in a highly specialised and complex domain, contending that international space law should be treated as the lex specialis for such circumstances. It is reliant on the fact that space exploration, whether for military or civilian purposes, typically necessitates international collaboration and the cooperation of nations for successful operations. Additionally, the existence of Rescue and Return Agreements, even during the Cold War era, adds weight to the notion of providing protections to astronauts regardless of their nationalities.

Secondly, various conflicting interpretations arise concerning the identification and classification of intended targets. Reliance is primarily placed on the “nature,” “location,” and “purpose” of the object. However, given the unique circumstances of conflicts in outer space, neither of the standards provides a compelling threshold. The nature standard permits attacks on objects utilised by the military, but it raises the question of whether insignificant equipment, such as broadband TV signals for entertainment purposes, would also fall within this standard. Similarly, the location standard permits attacks on strategically positioned objects to provide military advantages meaning that a civilian satellite could become a legitimate military target if it is merely located near a military satellite. Lastly, the purpose standard focuses on the objective and function of the object. While determining the current use of a satellite is relatively straightforward, predicting its future uses becomes exceedingly challenging. Furthermore, “potential” functions do not serve as a legitimate standard, requiring conclusive evidence during the attack. This task is challenging in outer space, as such intended objectives are often not communicated or only partially communicated.

A central aspect of this issue concerns the intertwined nature of civilian and military space industries. Military satellites are often launched into orbit using civilian launch systems, and while these are commonly regarded as valid military objectives under Article 52(2) of API, the use of hosted payloads further complicate the object’s targeting legitimacy. In this regard, such “dual-use” objects include hosted payloads separate from the satellite’s primary payloads and serve distinct objectives that can be utilised by other users (for instance, the armed forces) to enhance their space-based capabilities. In such scenarios, the challenge is to differentiate between the military payload and civilian payload aboard the satellite, only the former being considered a valid military objective, thus raising issues related to the purpose standard.

Principle of Proportionality

Outlined in Article 51(5)(b) of the API, the principle of proportionality imposes the obligation that the harm caused to civilians or civilian objects should not be excessive in relation to the concrete and direct military advantage achieved through a military attack. It is important to emphasise that several jurists have acknowledged the inherent challenge of balancing military considerations with civilian objectives as they involve fundamentally distinct considerations. However, when applied to the context of outer space, this principle assumes an even more complex and elusive nature in terms of its applicability.

An assessment of proportionality remains when it comes to targeting civilian objects. For instance, the destruction of dams, water-generating facilities, and electrical grids, which possess both military and civilian utility, requires a thorough evaluation of proportionality. And it is worth noting that the same requirement applies to the unique circumstances of conflicts occurring in outer space. The Global Navigation Satellite Systems (GNSS) is particularly important in this regard. Various states possess their technological infrastructure in this domain, such as the United States Global Positioning System (GPS), Russia’s GLONASS, and China’s BeiDou System.

While the crucial role of GNSS in the modern world cannot be overstated, its legal status remains unclear. Originally designed to fulfil military objectives for armed forces, these complex infrastructures now serve increasingly vital civilian purposes. Civilian activities rely on GPS frequencies for navigation and timing synchronisation, which is integral to numerous modern technologies. Internet connectivity, aviation, maritime transportation systems, and specialised sectors like healthcare, energy production, mining, and agriculture depend on such infrastructure.

Apart from its civilian applications, GNSS also serves numerous military purposes, justifying military attacks under the principle of dual-use objects. The critical question, therefore, revolves around whether such attacks meet the test of proportionality. Although the standard is necessarily speculative, as there are no direct civilian casualties in such attacks, it requires considering foreseeable and proximate consequences in the assessment. In this regard, there appears to be a consensus among jurists that attacks targeting GNSS equipment would constitute an unlawful attack unless the attacking state is capable of satisfying and justifying the expected direct military advantage, thereby setting a high threshold for acceptance. Assessing this matter presents significant complexities within space-based warfare, primarily due to the escalating dependence on “soft” methodologies. These techniques involve interference with an object’s operations, such as signal jamming, rather than resorting to “hard” methodologies that directly obliterate the object itself. Adopting such “hard” methods also carries distinct implications, like generating space debris.

Furthermore, as stipulated in Article 58 of the API, the principle of precaution necessitates undertaking all necessary measures to minimise foreseeable harm to civilians and civilian objects. In this context, legal scholars conclude that a comprehensive application of both the principle of proportionality and precaution contributes to the preservation and protection of valuable objects, the destruction of which would have far-reaching consequences for civilians. However, critics maintain that such an approach leads to a blanket prohibition on military attacks, even if the infrastructure or satellites serve military purposes.

Conclusions and the Way Forward

Although there is widespread recognition that IHL, incorporating the progressive balancing of principles like military necessity and humanity, has the capacity to regulate future conflicts in outer space, this article highlights the numerous challenges involved in establishing a rule-based framework for implementing existing IHL principles within this unique theatre of warfare. In light of this, we assert that a comprehensive adherence to the principles of distinction, proportionality, and precautions does not necessarily render kinetic attacks illegal from the outset. Instead, it obligates states to explore alternative and less destructive means of achieving their intended objectives, thereby placing a heightened burden on the attacking state to justify its use of force. Similarly, the ICRC has advocated for formulating national and international policies encompassing general prohibitions on weapons and conduct during hostilities based on the same conceptual frameworks.

Undoubtedly, the OST establishes a robust foundation by incorporating provisions restricting utilising space for military purposes. However, its efficacy is limited due to the brevity and vagueness of its articles. Consequently, it fails to adequately address the imminent challenges associated with military activities in space, which are also unaddressed by the general principles of IHL. As a result, there is a pressing need to clarify and resolve issues concerning the threshold for the use of force, armed attacks, self-defence, the legality of space exclusion zones, and the international responsibility for the actions of non-state actors, particularly as states continue to increase their space-based military capabilities.


This article was authored by Richa Maria, Associate Editor and Shagnik Mukherjea, Junior Editor at RSRR. This blog is a part of the RSRR Editor’s Column Series.


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