On Sept. 14, Secretary of the Air Force Troy Meink, speaking at the Air and Space Forces Association’s annual Air, Space, and Cyber Conference, announced that “the United States has on-orbit space control weapons capable of defending the Joint Force against hostile adversary action.” His statement marked the first official acknowledgment that the United States had operational weapons in orbit.
Reaction from U.S. adversaries was swift. China’s Foreign Ministry spokesperson urged the United States to “stop expanding its military force and preparing for war in outer space,” while the Kremlin’s spokesperson claimed, “We believe that space must be free of any weapons.” Their protestations sit uneasily with the counterspace programs both States have pursued. Indeed, the Office of the Director of National Intelligence’s 2026 Annual Threat Assessment of the U.S. Intelligence Community found that the “space domain is becoming increasingly contested, with China and Russia developing counterspace capabilities to challenge our own space efforts and U.S. dominance more generally” (page 14). Of particular concern, the assessment found that “Russia is developing a new satellite meant to carry a nuclear weapon as an antisatellite capability” (page 16; see also 2025 Annual Threat Assessment, page 21), the deployment of which would, as discussed below, clearly violate international law.
The Secretary’s acknowledgment raises the question of what is permitted regarding placing weapons in space. It is an issue that is often misunderstood in light of the 1967 Outer Space Treaty’s preamble, which “recognizes” the “common interest of all mankind in the progress of the exploration and use of outer space for peaceful purposes” (emphasis added). The peaceful purposes reference is sometimes misinterpreted as reserving space for non-military purposes. But that is obviously not the case, given military activity in space since the dawn of the space age. In fact, as explained below, the United States is not a Party to any treaty that bars placing conventional weapons in Earth orbit. That said, placing weapons in space is far from unregulated. Treaty and customary law govern where weapons may be placed, what they may carry, how they may be positioned relative to other States’ spacecraft, and when and how they may be used, both in peacetime and during armed conflict.
This backgrounder outlines the law governing the placement and use of weapons in space. In doing so, it draws not only on the law itself but also on the conclusions and commentary in the Woomera Manual on the International Law of Military Space Activities and Operations, the most comprehensive restatement of this subject. Although non-binding, the manual is a restatement prepared by distinguished experts based on treaty law, customary law, State practice, and consultations with governmental and non-governmental experts. This backgrounder also draws on the McGill Manual on the International Law Applicable to Military Uses of Outer Space (vol. 1), prepared by a different group of experts and another key source for understanding international space law.
Space Weapons
The United States has refrained from describing the on-orbit weapons that Secretary Meink referenced. U.S. Space Force’s 2025 Space Warfighting: A Framework for Planners nevertheless makes clear that the United States contemplates offensive as well as defensive counterspace operations. It states (page 4),
Space superiority may shift from defense to offense and be conducted within the vicinity of enemy, friendly, and commercial spacecraft, or along shared lines of communication in both space and cyberspace. Space superiority may involve seeking out and destroying an enemy’s spacecraft, systems, and networks through measures designed to minimize the effectiveness of those systems, or countering enemy efforts in the other warfighting domains (land, maritime, air, and cyberspace).
Operationally, space weaponry falls into three categories: Earth-to-space, space-to-Earth, and space-to-space. The first includes direct-ascent anti-satellite missiles (DA-ASAT), ground-based lasers, electronic-warfare systems, and cyber capabilities directed at satellites, ground stations, or communications links. Space-to-Earth weapons, although not the focus of Secretary Meink’s announcement, would operate from orbit against terrestrial targets. (DIA, Challenges to Security in Space; Space Force, Space Threat Fact Sheet).
“Orbital or space-based weapons,” which were the subject of Meink’s comments, include “satellites that can attack other spacecraft, delivering temporary or permanent damage,” according to the Defense Intelligence Agency’s (DIA) Challenges report (page 47). The DIA offers examples such as “radio frequency jammers, kinetic kill vehicles, lasers, robotic mechanisms, chemical sprayers, and high-power microwaves” (page 47). Their employment varies widely. For example, a co-orbital kinetic kill vehicle destroys its target either by colliding with it or by maneuvering close enough to release a projectile that strikes the target. A spacecraft may also use a robotic arm to “grapple” a satellite and push it out of its operational orbit. Space-based lasers or microwave weapons can blind satellite sensors or permanently disable their electronics, while a chemical sprayer can coat a satellite’s optics or solar panels.
Orbital counterspace capabilities are not new. For instance, U.S. Space Command reported in 2020 that Russia had conducted “a non-destructive test of a space-based anti-satellite weapon.” The U.S. Space Force has similarly observed that Russia has, among other threatening operations, deployed “orbital ASAT prototypes” in low-Earth orbit. In 2024, it launched a counterspace satellite in 2024 into the same orbit as a U.S. satellite. For its part, China has launched “inspection and repair satellites” that can be used as weapons. In January 2022, China’s Shijian-21 satellite approached, grappled, and moved its own defunct navigation satellite into a graveyard orbit, thereby demonstrating a dual-use rendezvous-and-capture capability that could, in principle, be applied to an adversary’s satellite.
International Law and Weapons in Space
Weapons in Space Generally: Article I of the Outer Space Treaty, to which the United States, Russia, and China are Party, provides: “Outer space, including the Moon and other celestial bodies, shall be free for exploration and use by all States without discrimination of any kind, on a basis of equality and in accordance with international law, and there shall be free access to all areas of celestial bodies.” It makes no distinction between civilian and military uses. Accordingly, under the international law principle that “[r]estrictions upon the independence of States cannot … be presumed” (S.S. Lotus, page 18), leveraging space for military operations is lawful absent a specific rule prohibiting the operation.
As noted in the introduction, the treaty’s preambular reference to “peaceful purposes” has led some to wrongly conclude that military operations there are unlawful. Yet, as noted in the Woomera Manual, the treaty’s drafters intentionally placed the phrase in the preamble rather than in the operative articles to avoid suggesting that military operations in space would be barred (r. 3, commentary). Indeed, the only other place the term appears is in Article IV, which provides that the Moon and other celestial bodies are reserved “exclusively for peaceful purposes;” it does not address space as such. Indeed, it stands to reason that such express language only in Article IV means such a limitation is purposefully absent elsewhere. Longstanding State practice involving ISR, communications, navigation, missile-warning, and other military satellites confirms that military activity in space is not prohibited as such.
The United States has long accepted the premise that space is to be used only for peaceful purposes. That said, it has interpreted the term as meaning “‘non-aggressive and beneficial’ purposes consistent with the Charter of the United Nations and other international law” (DoD Law of War Manual, § 14.10.4). The Woomera Manual experts came to an identical conclusion, for Rule 3 provides, “[a] State that engages in exploration and use of outer space shall comply with international law, including the UN Charter’s obligation to not engage in the unlawful threat or use of force, and thus shall engage in only peaceful (i.e., non-aggressive) exploration and use of outer space.” By this interpretation, international law does not bar placing conventional weapons in Earth’s orbit unless they are used for unlawful purposes, such as the use of force in violation of the UN Charter or contrary to the law of armed conflict, topics addressed below.
It merits note that Article V(1) of the 1972 U.S.-Soviet Anti-Ballistic Missile Treaty barred the development, testing, and deployment of space-based ABM systems. The United States withdrew from the treaty in 2002. In 2025, Executive Order 14186 – initially titled “The Iron Dome for America,” although the program is now known as “Golden Dome” – directed the development and deployment of “proliferated space-based interceptors capable of boost-phase intercept” (§ 3(a)(iii)).
It is also worth noting that efforts to move toward a ban on conventional weapons in space have been unsuccessful. Russia and China first introduced, and later revised, a draft Treaty on the Prevention of Placement of Weapons in Outer Space and of the Threat or Use of Force Against Space Objects (the PPWT). Russia and China’s efforts in favor of that draft treaty provided yet further evidence that the Outer Space Treaty did not prohibit such weapons in space. The United States rejected the PPWT as fundamentally flawed. Russia’s “No First Placement” initiative at the UN General Assembly drew similar Western objections. And in 2024, the Security Council failed on two occasions to adopt a resolution on preventing an arms race in space. But diplomacy on the matter is not dead. An Open-Ended Working Group on the Prevention of an Arms Race in Outer Space (PAROS) has been tasked with producing recommendations by 2028. Whether Secretary Meink’s announcement changes the tenor of that process, or hardens positions within it, is a question worth watching (see July 2026 U.S. submission).
Weapons of Mass Destruction in Outer Space: Article IV of the Outer Space Treaty contains three related prohibitions concerning nuclear weapons and other weapons of mass destruction. States Parties undertake not to “place in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner” (see also DoD Law of War Manual, § 14.10.3.1; Woomera Manual, r. 5; McGill Manual, r. 145). Although the treaty does not define weapons of mass destruction, the Woomera Manual experts considered the definition set forth by the 1948 UN Commission on Conventional Armaments and adopted in many UN documents, as well as numerous statements by U.S. officials. They concluded that the “term ‘WMD’ in the OST thus includes at least chemical, biological, and radiological weapons, as well as nuclear weapons, and also includes future weapons that have comparable large-scale deadly or destructive effects” (r. 5 commentary). They cautioned that the definition does not include nuclear power sources, citing a 1993 UN General Assembly Resolution on that point (A/RES/47/68). Accordingly, a nuclear power source aboard a satellite that is carrying a conventional weapon would not be barred by Article IV.
Ordinary nuclear ballistic-missile flight through space does not qualify as placing or stationing a weapon there. The more difficult issue concerns fractional orbit and suborbital flight. A fractional orbit is one in which the weapon’s payload is launched into low Earth orbit but is brought down before completing a full revolution, while a suborbital flight path denotes one in which the missile or weapon enters space but lacks the speed to stay in orbit. The United States takes the position that Article IV “does not ban the use of nuclear or other weapons of mass destruction that go into a fractional orbit or engage in suborbital flight” (DoD Law of War Manual, § 14.10.3.1). However, the Woomera Manual notes that States have not agreed on how to apply Article IV to fractional orbits or suborbital flight (r. 5 commentary).
Finally, while Article IV’s first section addresses the placement and stationing of nuclear weapons and other WMD in space, its second separately prohibits the testing of any weapon on the Moon or another celestial body (see below). It does not, however, prohibit testing nuclear weapons elsewhere in space. That matter is addressed by the 1963 Partial Test Ban Treaty (the United States and Russia are Parties, China is not), Article 1(a) of which obligates Parties not to conduct “any nuclear weapon test explosion, or any other nuclear explosion” in space (on chemical and biological weapons in space, see Boothby, pages 195-97, Woomera Manual, r. 5 commentary; McGill Manual, r. 145(2)).
Weapons on the Moon or Other Celestial Bodies: The legal regime governing the Moon and other celestial bodies is more restrictive than that governing weapons in Earth’s orbit. As noted, Article IV of the Outer Space Treaty bans weapons of mass destruction on celestial bodies such as the Moon. It also specifies that “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” (although it allows military personnel and facilities engaged in scientific research or other peaceful purposes).
Article IV does not expressly prohibit an individual or spacecraft from carrying any form of conventional weapon onto a celestial body (e.g., personal protection weapons). But beyond such de minimis circumstances, a rule of reason applies. For instance, weapons installed at a site, stored as part of a military capability, or integrated into a facility would likely result in the site qualifying as a prohibited military base, installation, or fortification. Relevant factors would include the weapons’ purpose, permanence, and quantity.
The 1979 Moon Agreement repeats elements of Article IV and adds further restrictions, including a prohibition on placing objects carrying weapons of mass destruction in orbit around the Moon (art. 3(3)). Its practical significance is limited, for the United States, Russia, and China are not Party to the instrument, which has fewer than 20 Parties.
Threat or Use of Force and Self-Defense: Article III of the OST requires parties to conduct space activities “in accordance with international law, including the Charter of the United Nations, in the interest of maintaining international peace and security.” This makes it clear that the prohibition on the threat or use of force in Article 2(4) of the Charter, as well as the Article 51 right to engage in self-defense in the face of an “armed attack,” apply fully in space, a point acknowledged in the DoD Law of War Manual, Woomera Manual, and the McGill Manual (§ 14.10.2.2; rr. 21-23, 26; and rr. 151-152, respectively). The understanding is also consistent with the International Court of Justice’s (ICJ) conclusion in its Nuclear Weapons Advisory Opinion that the Charter’s provisions on the use of force “apply to any use of force, regardless of the weapons employed” (¶ 39).
Of course, using a weapon in space without either Security Council authorization or in the exercise of a right of self-defense would violate the prohibition on the use of force. But deploying conventional weapons into orbit and announcing that fact does not, standing alone, constitute an unlawful threat of force. To be unlawful, a threat must communicate an intention to carry out a specific unlawful use of force. As the ICJ noted in Nuclear Weapons, an unlawful threat to use weapons must be distinguished from “an inference of preparedness to use them” (¶ 48). Simply placing weapons in space to serve a deterrent function, or to be available if needed for operations consistent with law governing the use of force (jus ad bellum), does not cross the line.
The Woomera Manual offers the example of “the intentional placement of a weapon in space, including a satellite with co-orbital ASAT capabilities or with on-orbit servicing capabilities that could be used for hostile acts against other space objects.” The experts opined, correctly so, that the actions “would not – on their own – amount to prohibited threats of force because they demonstrate only capacity and do not communicate an intent to use unlawful force” (r. 22 commentary).
However, context matters. Weapons in Earth’s orbit could be used to convey a threat, as in the case of maneuvering one into proximity of another State’s early warning satellite in a manner that places the latter at risk during a period of heightened tension. The lawfulness of the maneuver would depend on whether an actual attack on the satellite would be lawful. It would, for instance, if conducted in self-defense, in this case, anticipatory self-defense.
An interesting question is whether self-defense would justify disregarding Outer Space Treaty rules. In this regard, Article 103 of the UN Charter accords Charter obligations priority over conflicting obligations under other international instruments. Its application is not completely straightforward, however, because Article 51 recognizes an inherent right of self-defense rather than imposing an obligation to exercise that right.
Nevertheless, the International Law Commission’s 2011 Draft Articles on the Effects of Armed Conflict on Treaties provides that a “State exercising its inherent right of individual or collective self-defence in accordance with the Charter of the United Nations is entitled to suspend in whole or in part the operation of a treaty to which it is a Party insofar as that operation is incompatible with the exercise of that right” (art. 14). The Woomera Manual experts likewise concluded that a State acting in self-defense would be entitled to engage in the actions prohibited by Article IV of the Outer Space Treaty, so long as necessary in the circumstances (r. 4 commentary). For instance, under this view, establishing military facilities on the Moon and other celestial bodies, and storing or positioning weapons necessary to effectively engage in self-defense, would be permissible despite Article IV’s prohibitions. Importantly, the experts hesitated to apply the same logic to the prohibition on WMD in space, choosing instead to set forth reasonable justifications on both sides of the issue (r. 5 commentary).
The Requirement of Due Regard: Although international law does not prohibit placing weapons in space, Article IX of the Outer Space Treaty requires that they be operated “with due regard to the corresponding interests of all other States Parties.” It also requires prior consultations with other affected States if an operation would “cause potentially harmful interference with [their] activities … in the peaceful exploration and use of outer space.” States that believe they might be affected may request consultation concerning the activity (see also DoD Law of War Manual, § 14.10.5; Woomera Manual, rr. 17-18; McGill Manual, rr. 120-121).
The due-regard obligation requires a State placing a weapons system into space to consider the reasonably foreseeable effects of its deployment and operation on other States’ lawful space activities and to adopt reasonable measures to mitigate those effects. Examples include information sharing, coordination, maintaining safe separation, and, where Article IX’s threshold is met, prior international consultation. The requirement bears in particular on the orbit into which the system is placed, since space is increasingly congested. Moreover, rendezvous and proximity operations must likewise be conducted carefully.
The due regard obligation would apply equally to weapons testing that might create space debris, since space debris poses a particular risk to space objects. Accordingly, in 2022, the United States pledged not to conduct destructive direct-ascent anti-satellite missile tests, which was followed by General Assembly Resolution 77/41 calling on States to do the same. The same logic would apply to space-to-space weapons testing likely to cause space debris or other potential hazards.
Transparency: Space law imposes a transparency regime for space objects that applies fully to weaponized space systems. Under Article II of the Registration Convention, a launching State must register its “space object.” Article IV(1) requires the State of registry to, “as soon as practicable,” furnish the Secretary-General information on the launching State or States, an appropriate designator or registration number, the date and territory or location of launch, basic orbital parameters, and the object’s general function. Article XI of the Outer Space Treaty similarly requires States Parties to inform the Secretary-General, “to the greatest extent feasible and practicable, of the nature, conduct, locations and results” of their space activities.
Although these obligations provide some transparency, they have limits. Neither instrument requires disclosure of detailed capabilities, in particular whether a space object carries a weapon. The dual-use nature of satellites capable of proximity operations also leaves significant room for uncertainty about the precise purpose and capabilities of the systems. Moreover, Article IV (2) of the Registration Convention makes subsequent updates on significant orbital maneuvers optional. Thus, systems capable of anti-satellite operations or grappling maneuvers can alter their orbital parameters after initial registration without triggering a mandatory space law reporting duty. And the “as soon as practicable” caveat will often be determinative during armed conflict, when operational security and secrecy are usually essential. The same would be true of the Outer Space Treaty’s “greatest extent feasible” caveat.
Placing Weapons into Space During an Armed Conflict: That a State placing a weapon into space is involved in an armed conflict, as the United States is with Iran, has no bearing on the lawfulness of that placement. Article II of the Outer Space Treaty precludes national appropriation of outer space, while Article I makes space available for exploration and use by all States “in accordance with international law.” Thus, space is a global commons that, like international waters and international airspace, is open to use by all States, including for deploying military space assets there and conducting operations into, through, or from it. However, as Article I’s “in accordance with international law” caveat makes clear, placing weapons into space to engage in unlawful operations, such as those in support of a violation of the UN Charter’s prohibition on the use of force, would be unlawful.
But armed conflict would not automatically suspend the space treaties. The International Law Commission’s starting point in its Draft Articles on the Effects of Armed Conflicts on Treaties is that armed conflict does not ipso facto terminate or suspend treaty relations (art. 3). Space law obligations concerning registration, jurisdiction and control, responsibility, and liability therefore presumptively continue to operate alongside the law of armed conflict. Of operational significance, the State that places and operates a weapon system in space must do so with due regard for the right of States not involved in the conflict to use space.
Moreover, the State would be bound by the law of armed conflict when operating the weaponized space system (DoD Law of War Manual, § 14.10.2.2; ICRC explanation). As with any new weapon, a space weapon system requires legal review before deployment (DoD Law of War Manual, § 6.2). The requirement to exercise constant care to spare the civilian population and civilian objects would also loom large given the significance of satellites serving civilian functions for civilian populations on Earth. So too would the rule of proportionality, given the risk posed by space debris in the event of hostilities there. When a satellite registered to or operated by a non-belligerent State is affected by the hostilities or is used to support a belligerent, the law of neutrality can also become relevant. (on LOAC in space, see Woomera Manual, Part III).
Bottom Lines and Concluding Thoughts
The international law bottom line is relatively straightforward. International law does not generally prohibit placing conventional weapons in Earth’s orbit. In particular, the placement of conventional weapons in space does not, without more, amount to an unlawful threat of the use of force. That said, the Outer Space Treaty prohibits the placement of nuclear weapons and other weapons of mass destruction in space and imposes constraints regarding military activities on the Moon and other celestial bodies. And the launch and operation of weapons in space is subject to a condition of due regard for the rights of other States.
The fact that international law permits conventional weapons in space does not answer whether it is operationally necessary or strategically wise to place them there; those are separate questions. Deploying or openly acknowledging such capabilities may fuel an arms race in space as actual and potential adversaries respond with their own weaponized systems. Public disclosure may also reinforce perceptions, already widespread in many parts of the international community, that the United States has become a destabilizing force in international relations. International law may permit space-based weapons capabilities; whether and when it is prudent to develop, deploy, or publicize them is an altogether different matter.
