Shielding the Nation, Testing the Peaceful Purposes Principle: the Golden Dome as a Self-Defense Zone

[Louisa Handel-Mazzetti is an Assistant Professor at the Royal Netherlands Defense Academy (NLDA) and a PhD Candidate at the Institute of Air and Space Law at Leiden University]

In May 2025, President Trump unveiled the 175 billion dollar plan to build the Golden Dome missile shield, originally introduced in January 2025. Drawing inspiration from Reagan’s Strategic Defense Initiative (‘Star Wars’) and the Israeli Iron Dome, the Golden Dome envisions a multi-layered defense architecture involving hundreds of satellite in orbit, equipped with advanced sensors and interceptors, including space-based lasers. These would detect, track and neutralize incoming missiles and other threats at various stages of flight. 

As Lockheed Martin, the project’s lead contractor, points out: ‘This is a Manhattan Project-scale mission, one that is both urgent and crucial to America’s Security’. However, worries have been expressed that Trump’s Golden Dome would fuel (or continue) a new arms race in outer space. In their initial response, China, North Korea and Russia, American’s biggest adversaries, have all warned against the development of the Golden Dome arguing that the United States is ‘attempting to militarize outer space’; ‘turning outer space into an environment for placing weapons and an arena for armed confrontation’ and the envisioned Sino-Russian draft Treaty on the prevention of the placement of weapons in outer space would prohibit such a defense shield.

Indeed, the Golden Dome may well represent a Manhattan project-level undertaking, not only in terms of technology and defense, but also in terms of its implications for international space law. This blog will assess whether the Golden Dome aligns with existing legal frameworks governing outer space – particularly in the context of the ‘peaceful purposes’ principle enshrined in the Outer Space Treaty. 

The Peaceful Purposes Principle

The concept of peaceful purposes is prominently featured in the preamble of the Outer Space Treaty, which speaks of “the common interest of all mankind in the progress of the exploration and use of outer space for peaceful purposes.” While the preamble itself does not carry binding legal force, it plays an important interpretative role in clarifying the object and purpose of the Treaty. From this foundation, two competing interpretations have emerged: non-aggressionand non-weaponization.

The United States is perhaps the most vocal supporter of the non-aggression interpretation of the peaceful principles. According to this doctrine, military uses of outer space are permissible so long as they comply with Article 2(4) of the United Nations Charter, which prohibits the threat or use of force in international relations. In contrast, China and Russia advocate for a non-weaponization interpretation, which calls for a complete ban on the placement of weapons in outer space. They argue that such weaponizations contravenes the principle of peaceful use and violates key provisions of the Outer Space Treaty, such as Article I, which states that space activities must be carried out ‘for the benefit and in the interest of all countries’, and Article IX, which require States to conduct activities ‘with due regard to the corresponding interests of all other State Parties’. These provisions are invoked to argue that space weaponization, even if not explicitly prohibited, is inconsistent with the spirit and purpose of the Treaty, and therefore unlawful under a good-faith interpretation of its obligations. 

At present, there seems to be no consensus on the ‘correct’ interpretation of peaceful purposes. While the military use of outer space is both widespread and generally accepted, the issue of space weaponization remains contentious. Whereas rumors exist regarding Russian (nuclear-)weapon testing in outer space, there are currently no confirmed space-based kinetic weapons in operation. This situation has spurred numerous international initiatives regarding the prevention of aimed at the prevention of the weaponization of space. These include, conducted under the auspices of the United Nations such as the Group of Governmental experts and the Open-Ended Working Groups, both of which focus on advancing the agenda of Preventing an Arms Race in Outer Space (‘PAROS’). 

A ‘Peaceful’ Golden Dome? 

In the absence of a universally accepted definition of ‘peaceful purposes,’ it is useful to briefly examine how both interpretations apply to the Golden Dome. Whereas a preamble does not carry legal weight, it plays a significant role in the interpretation of a treaty, as it helps identify the object and purpose of a Treaty according to the Vienna Convention on the Law of Treaties.

State practice since the OST’s adoption has consistently supported a non-aggressive interpretation of ‘peaceful purposes’. Military uses of space, including reconnaissance, navigation, communications, and surveillance satellites, have been widespread and uncontested under the Treaty regime. These activities, while military in function, are not inherently aggressive and do not constitute an unlawful use of force. Consequently, the prevailing legal consensus interprets ‘peaceful purposes’ as prohibiting aggressive actions, rather than imposing a blanket ban on all military-related activities in space.

However, the emergence of space weaponization has reignited debates over the scope of this principle. Some argue that the mere deployment of weapon systems in outer space, regardless of their use, could contravene the object and purpose of the OST by escalating the risk of armed conflict and undermining the stability of space as a peaceful domain. This interpretation therefore argues that weaponization itself is incompatible with the OST’s principles. Yet, this interpretation remains contested. International space law itself does not contain a categorical prohibition on space weaponization, if this does not involve weapons of mass destruction. Nevertheless, concerns over the weaponization of outer space continue to feature prominently in multilateral forums, particularly within the United Nations. Initiatives aimed at preventing an arms race in outer space (PAROS) reflect the enduring unease over the strategic and legal implications of space-based weapons systems. While no binding legal instruments have yet emerged to expand on the OST’s existing provisions, these discussions underscore the ongoing relevance of the peaceful purposes principle in assessing new military technologies in outer space.

Nevertheless, the non-aggression doctrine is considered the leading interpretation pf peaceful purposes, still. Applying the non-aggression perspective to the Golden Dome is complex as it hinges on an assessment of legality under the UN Charter and is based on ‘aggressiveness’. Missile defense systems, such as the Golden Dome, take in a grey zone in this regard. On the one hand, if such a system is indeed limited to defensive functions, its deployment could be argued as non-aggressive and therefore compatible with the peaceful purposes principle. At the same time, the Golden Dome could be considered a self-defense zone, which is both problematic under international law and under space law. 

The Golden Dome as a Self-Defense Zone

The Golden Dome can be compared to the idea of a self-defense zone (‘SDZ’), a technique known to maritime- and air law. Protective zones, such as maritime security zones and air defense identification zones, regulate behavior within a designed perimeter, usually through identification requirements. These zones, however, do not authorize the use of force merely because of unauthorized entry. The idea of applying such zones to outer space gained traction during the Cold War, particularly in US defense policy debates of the 1980s. The US explored two models: ‘keep out zones’ and ‘self-defense zones’. Keep out zones were conceived as a protective bubbles around individual space objects, intended to deter unauthorized proximity by foreign spacecraft, though it remained vague on enforcement measures. In contrast, SDZ were meant to allocate orbital sectors to States and explicitly permitted force against intrusions. 

The idea of a SDZ is problematic under space law. The OST prohibits national appropriation of outer space, and scholars argue that SDZs amount to de facto territorial claims, nor does any practice show that force is authorized merely for entering a self-declared SDZ. If such enforcement rights were allowed nonetheless, this would give ‘effective control’ of a State over such an orbital zone, directly violating Article II of the OST. In effect, an SDZ transforms parts of space into areas of sovereign jurisdiction, contrary to international law. 

The distinction from air defense identification zones (ADIZ) is crucial. ADIZs enable States to demand flight information for security reasons, but intrusions are addressed through diplomacy rather than kinetic action. SDZs, however, make force the central enforcement tool, turning orbital areas into controlled territory. This is both incompatible with the OST and inconsistent with Article 51 of the UN Charter, which allows force only in response to an armed attack. Mere entry into a zone cannot amount to such a trigger.

Against this background, the key issue is whether the Golden Dome effectively constitutes an SDZ. As a space-based missile defense system, its operation raises important questions: will it respond automatically to any object entering its perimeter, even if not a missile? Will it engage indiscriminately with all detected intercontinental ballistic missiles, regardless of their targets? And will the system’s responses be automated and immediate, or subject to human authorization?

Affirmative answers would suggest the Golden Dome operates as a prohibited SDZ. If intrusion into its operational sphere triggers force by default, the system establishes a de facto zone of control in orbit. Such control is tantamount to appropriation, regardless of defensive intentions.

Conclusion 

For the Golden Dome to be consistent with the peaceful purposes principle, it must remain a narrowly defensive measure, carefully constrained by human oversight, proportionality, and credible threat verification. Without such safeguards, it risks sliding into the logic of a self-defense zone: an enforcement regime premised on automatic, indiscriminate responses that amount to de facto appropriation of outer space. This would not only breach the Outer Space Treaty’s non-appropriation principle but also strain the already fragile consensus that ‘peaceful purposes’ should be understood as non-aggression rather than non-weaponization.

Even if the Golden Dome were to avoid formal illegality, its very existence pushes the boundaries of what ‘peaceful purposes’ can plausibly mean. A system that normalizes space-based weapons platforms, establishes zones of effective control, and anticipates kinetic engagements in orbit cannot easily be reconciled with the Treaty’s spirit of keeping outer space free from confrontation. In this sense, the Golden Dome blurs the line between defensive preparedness and weaponization, eroding the normative restraint that has thus far prevented the deployment of weapons in space.

The true challenge, then, is not only whether the Golden Dome is lawful in the narrow sense but whether it undermines the broader project of preserving outer space as a domain of peaceful cooperation. By importing the logic of self-defense zones into orbit, the Golden Dome risks transforming ‘peaceful purposes’ from a guiding principle of restraint into a hollow formula, emptied of meaning.