This week, U.S. officials representing the National Security Council and the Departments of State, Defense and Energy met with their Russian counterparts in a “Space Security Exchange.” Conducted under the framework of the Strategic Security Dialogue, this was the first engagement between the countries on space security matters in seven years.

The meeting could not have been more timely, for on July 15, Russia reportedly conducted a “non-destructive test of a space-based anti-satellite weapon” by releasing a “projectile” into orbit from its Cosmos 2543 satellite. U.S. Space Command asserted the test demonstrated “Russia’s hypocritical advocacy of outer space arms control,” while General “Jay” Raymond, its Commander and the U.S. Space Force Chief of Space Operations, warned, “[t]his is further evidence of Russia’s continuing efforts to develop and test space-based systems, and consistent with the Kremlin’s published military doctrine to employ weapons that hold U.S. and allied space assets at risk.” Similarly, Air Vice Marshal Harvey Smyth, who heads the UK Space Directorate, publicly accused Russia of threatening “the peaceful use of space” and cautioned that such operations “risk causing debris that could pose a threat to satellites and the space systems on which the world depends.”

The Russian Defense Ministry countered that the operation was not a weapons test, but merely involved “a small space vehicle” that “inspected one of the national satellites from a close distance using special equipment.” According to the Ministry, the inspection “provided valuable information about the object that was inspected, which was transmitted to the ground-based control facilities.”

Despite the Russian disclaimer, the Russian test of what has been described by U.S. officials as an on-orbit anti-satellite  (ASAT) weapon is part of the intensifying arms race in space. It is not unusual for a larger space object, such as a spacecraft, to release smaller ones into orbit, as with deployment of satellites comprising a navigational or communications constellation. However, the concerning aspect of the test is that the object released by Cosmos 2543 was fast-moving, thereby explaining its characterization as a “projectile.” Russia conducted a similar test in 2017 when its Cosmos satellite 2521 deployed a sub-satellite, also at high speed. And in April, Russia conducted a test of its ground-based, direct-ascent anti-satellite (DA-ASAT) missile system, which General Raymond had likewise condemned.

Moreover, earlier in the year Russian military satellites identified as Cosmos 2542 and Cosmos 2543 were observedmaneuvering near a U.S. KH-11 satellite, USA 245, that is part of the reconnaissance constellations operated by the National Reconnaissance Office and codenamed Keyhole/CRYSTAL. General Raymond described the Russian operations as “unusual and disturbing” and asserted they had “the potential to create a dangerous situation in space.” In particular, he noted that maneuvering one satellite to inspect another is an operation indistinguishable from preparing to attack the latter. The clear pattern here appears to amount to a Russian weapons-testing program of both space-based and ground-based weapons systems.

And Russia is not alone. For instance, China has been actively developing various anti-satellite capabilities, as notably demonstrated in January 2007 when it tested an ASAT to destroy its aging Fengyun-1C weather satellite, while India also has joined the ASAT arms race by conducting a successful test.

Weapons Testing in Space 

Paradoxically, Russia and China have been at the forefront of international efforts to ban precisely these kinds of space weapons through a treaty on the Prevention of Placement of Weapons in Outer Space. Proposed by those States to the UN Conference on Disarmament in 2002 (followed by a draft in 2008, updated in 2014), the treaty would prohibit the placement of weapons in outer space and the threat or use of force against space objects of Parties to the instrument. As explained in an analysis of the 2014 version by the U.S. delegation to the Conference, the United States opposes the draft treaty on the basis of its lack of an integral verification regime; the absence in the draft of a prohibition on the possession, testing, production, and stockpiling of the weapons, thereby enabling development of a readily deployable space-based weapons break-out capability; and its failure to address terrestrially-based anti-satellite weapon systems, which are considered the “most pressing, existing threat to outer space systems.” A treaty lacking these essential provisions is more likely to give cover to States racing to militarize space—who could readily use its loopholes and purposeful omissions to advance the weaponization of space—than to prevent those activities.

The recent activities in outer space by Russia and other States that the United States perceives as threatening, as well as the unlikely prospect of a comprehensive treaty banning the placement of weapons in space, beg the question of the extant legal regime governing weapons testing in space. In fact, a well-established framework of international law, centered on the Outer Space Treaty (OST), to which all major spacefaring nations are Party, constrains the manner in which space activities, including weapons testing, may be conducted.

Outer Space Treaty

Article III of the OST requires spacefaring nations to conduct their space activities “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.” The preamble also recognizes “the common interest of all mankind in the … use of outer space for peaceful purposes.” Yet, the OST’s only reference to peaceful purposes that is tied to the prohibition of particular activities is Article IV, which reserves the Moon and other celestial bodies “exclusively for peaceful purposes.” In particular, the article forbids “the establishment of military bases, installations and fortifications, the testing of any type of weapons and the conduct of military maneuvers on celestial bodies.” These specific prohibitions do not extend to any other part of outer space. Most important, State practice demonstrates that the concept of peaceful purposes does not bar military activities in space as such, for space has been a domain of military operations, especially with regard to communications, navigation, and intelligence, surveillance and reconnaissance (ISR), for many decades.

As to the specific issue of weapons testing in space, Article IV’s ban on testing weapons on celestial bodies textually suggests that the OST does not prohibit testing elsewhere. Similarly, Article IV also bars the placement of nuclear weapons and other weapons of mass destruction in orbit around the Earth, their installation on celestial bodies, and stationing them in outer space. Yet, there are no corresponding restrictions on conventional weapons. It appears clear that space-based weapons testing, as well as development and deployment of conventional weapons in orbit, is not in and of itself prohibited under the OST.

UN Charter: Weapons Testing as a Threat of Force

The fact that the OST does not prohibit weapons testing per se does not exhaust the inquiry. Article III of the OST provides that general principles and rules of international law also govern space activities. Of particular note for military activities is the prohibition on the threat or use of force found in Article 2(4) of the UN Charter and its customary law counterpart, as well as international humanitarian law.

Although self-evidently not a use of force itself because it is not directed at another State and occurs in a global common that is not subject to the sovereignty of any State, weapons testing could amount to a threat of force depending on how it is conducted. A prohibited threat of force occurs when a State expressly or impliedly communicates its intention to undertake an unlawful use of force and has the capability to execute it. There is no requirement that it be accompanied by any specific demand.

Since Cosmos 2543 reportedly operated “abnormally close” to a U.S. government satellite in low Earth orbit before maneuvering away and released a small object into orbit, this on-orbit ASAT test edges near characterization as an implicit communication of an intention to carry out such an attack. However, the operation would have to have been intended to communicate a threat that the system (or another) would be employed in the future against a U.S. satellite without justification, such as self-defense. Merely demonstrating a military capability does not rise to the level of a threat of force, both because doing so lacks the element of intent to use force and because the operation might be lawful in certain circumstances, most notably in situations of self-defense or pursuant to a mandate or authorization from the Security Council acting under Chapter VII of the UN Charter. Moreover, operating in an unsafe manner, even if endangering space objects of other nations, does not rise to the level of a threat because it lacks the requisite communicative element.


Air Vice Marshall Smyth’s statement regarding the risk of causing debris raises the issue of harmful interference with space activities, which is regulated under Article IX of the OST. Article IX provides, in relevant part:

If a State Party to the Treaty has reason to believe that an activity or experiment planned by it or its nationals in outer space, including the Moon and other celestial bodies, would cause potentially harmful interference with activities of other States Parties in the peaceful exploration and use of outer space, including the Moon and other celestial bodies, it shall undertake appropriate international consultations before proceeding with any such activity or experiment. A State Party to the Treaty which has reason to believe that an activity or experiment planned by another State Party in outer space, including the Moon and other celestial bodies, would cause potentially harmful interference with activities in the peaceful exploration and use of outer space, including the Moon and other celestial bodies, may request consultation concerning the activity or experiment.

This provision must be distinguished from that found in Article 45 of the Constitution of the International Telecommunication Union, which prohibits harmful interference with telecommunications, except for that involving military radio installations. In contrast, Article IV imposes only a consultations requirement. And with regard to the provision itself, Russia argues that it is difficult to measure “harmful interference” objectively. Even if interference is demonstrable, no specified remedy exists in cases where satellites are subjected to harmful interference except when there is a damaging effect that qualifies for compensation under Article VII of the OST and/or the 1972 Convention on International Liability for Damage Caused by Space Objects (Liability Convention).

Nonetheless, if they concluded that this particular on-orbit ASAT test risked causing harmful interference with their space activities, the United States and the UK could have relied on Article IX to criticize Russia for the lack of appropriate consultation. This legal mechanism has been under-utilized in State practice. Even with respect to the most obvious examples of potentially harmful interference—destructive events in space such as ASAT tests—consultation has been rare. Indeed, when the United States destroyed one of its descending satellites with an ASAT for safety reasons in 2008, its position was that it did not trigger Article IX’s consultation obligation. Further, the requirements as to when consultation is called for and what type of consultation is “appropriate” will remain abstruse until States start utilizing the mechanism, thereby setting clear standards and expectations through practice. Of course, the inherent secrecy surrounding weapons development will be a major impediment to engaging in such international consultation. The risk of not doing so, however, is that Article IX essentially becomes a dead letter that loses its intended function to minimize disruption with the peaceful exploration and use of outer space.

It also merits noting that international arms control regimes can prohibit interference with satellites used for national technical means (NTM) of verification. Article 10 of New START, for instance, provides that the United States and Russia agree “not to interfere with the national technical means of verification of the other Party operating in accordance with this Article.” One commentator has gone so far as arguing that the testing and use of destructive, debris-creating ASATs against any object in space would violate this obligation because of foreseeability that the resulting cloud of debris will, sooner or later, interfere with the operation of another State’s NTM satellites. Although, in this instance, no particular interference with NTM satellites is reported, it must be borne in mind that a space-based weapons test or other space operation that disrupts the operation of NTM satellites could violate an applicable arms control instrument.

Due Regard: A Maritime Analogy

A final consideration is the obligation to conduct space activities, including weapons testing, with “due regard” to the exploration and use of space by others, for, as the Air Vice Marshall pointed out, weapons testing can pose threats to other space objects. Like other global commons, States enjoy freedom to explore and use outer space but must conduct their space activities with due regard to the corresponding interests of all other States. For space, this obligation is set forth in Article IX of the OST.

Exactly what due regard requires of States conducting space activities is unclear. But it may be useful to analogize to maritime law, as an equivalent obligation is found in Article 87 of the Law of the Sea Convention. By that provision, States must exercise freedom of navigation “with due regard for the interests of other States in their exercise of the freedom of the high seas.”

The Arbitral Tribunal in the Chagos Island Arbitration between Mauritius and the UK observed that the requirement of due regard in the maritime context is contextual.

[T]he extent of the regard required by the Convention will depend upon the nature of the rights held by Mauritius, their importance, the extent of the anticipated impairment, the nature and importance of the activities contemplated by the United Kingdom, and the availability of alternative approaches. In the majority of cases, this assessment will necessarily involve at least some consultation with the rights-holding State (para. 519) (See also In the Matter of the Bay of Bengal, para. 508).

Illustrating this contextuality, and in light of the serious hazards posed by weapons-testing at sea, it is the general practice of States conducting weapons testing to take measures to ensure safety of other vessels, such as declaring a hazardous “warning area” that is announced in advance by means of a “notice to mariners” (NOTMAR) or “notice to airmen” (NOTAM).

Although no contact was recorded during the Russian on-orbit test, the United States and the UK could have argued that Russia was required to consider potential dangers that might be posed to other satellites, especially when a small object is launched at high speeds, and take feasible measures in the attendant circumstances to minimize the risk to those satellites. Subsequent State practice, including verbal practice such as the issuance of warnings, will hopefully contribute interpretive clarity as to the due regard expected of spacefaring nations when conducting weapons testing.

Toward a Rules-Based International Order in Space

More States are joining the space arms race by strengthening their military space capability. South Korea, for instance, launched its first military satellite, with the help of SpaceX, on July 20, while the UAE is expected to launch its reconnaissance satellite, Falcone Eye 2, later in the year. Other States will certainly follow suit. And, as space competition grows, so too does the risk of confrontation between the spacefaring nations.

Given the strategic and operational significance of defense space assets, States should be aware that although weapons testing is not unlawful per se, it can, depending on the manner in which it is conducted, violate international law. Even when it does not, testing can be destabilizing if interpreted as threatening, as illustrated by Russia’s on-orbit test. This makes it all the more important for States to seriously consider and implement their obligations to conduct space activities with due regard and to utilize Article IX consultation as a mechanism for avoiding inadvertent escalation of tension.