Arms control in outer space: Status, timeline, and analysis

March 14, 2022

Jessica West and Lauren Vyse

By Jessica West and Lauren Vyse

Lauren Vyse, from Wilfrid Laurier University, was a 2021 Ploughshares summer intern.

With funding from the Mobilizing Insights in Defence and Security (MINDS) program of the Canadian Department of National Defence

Thanks to Aaron Bateman, Paul Meyer, and Gilles Doucet for their advice and willingness to review sections of this report. Any errors or omissions remain the responsibility of the authors, who welcome additions and corrections. Send to

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Contrary to popular imagination, outer space is not a “Wild, Wild West” of lawlessness. Human activities in outer space are governed by international law, including the United Nations Charter, international humanitarian law (IHL), and, most critically, the 1967 Outer Space Treaty (OST), which sets out broad principles on how states are to conduct themselves in this domain, including commitments to registration, due regard, responsibility, liability, and non-contamination.

Efforts to prevent the escalation of conflict and the use or placement of weapons in space are longstanding but remain incomplete. While the OST is often referred to as a non-armament treaty, its arms control provisions – although essential – are minimal. Building on the 1963 Partial Test Ban Treaty, which restricts the testing of nuclear weapons in space, the OST bans the placement, installation, and stationing of nuclear weapons and other weapons of mass destruction in outer space or on celestial bodies. The OST also mandates that such bodies, including the Moon, shall be used “exclusively for peaceful purposes.” However, there are no comprehensive prohibitions on the development, testing, deployment, or use of conventional weapons either in or from space, or against objects in outer space.

Additional arms control provisions that touch on space include The Hague Code of Conduct, which requires participants to implement certain transparency measures. As well, the Environmental Modification Convention bars engagement in “military or any other hostile use of environmental modification techniques” that involve changing “the dynamics, composition, or structure of the earth … or of outer space” as a means of injuring another state party.

Numerous bilateral arms control agreements originally between the Soviet Union/USSR and the United States included provisions related to space-based capabilities, indicating the important role of space in strategic stability. Among the most important was the now defunct Anti-Ballistic Missile (ABM) treaty, which restricted ground-, sea-, air-, and space-based anti-ballistic missile systems.

All the above agreements, plus other efforts that address gaps in arms control and introduce bilateral and multilateral military restrictions in space are outlined in the timeline that follows. The list is lengthy, indicating both the continuing pertinence of the issue to a wide range of stakeholders, as well as the lack of consensus on long-term solutions.

Our timeline attempts to be comprehensive in its coverage of space-related arms control activities. For narratives related to specific elements of this work, see articles by Aaron Bateman on bilateral negotiations and coverage of PAROS at the Conference on Disarmament by UNIDIR (another short history here).

Because it is important to put these diplomatic efforts at arms control in context, the timeline includes developments in national weapons policies, as well as the development, testing, and deployment of new weapons systems. But because our focus is on arms control, we have restricted the number of contextual events. Additional information on weapons-related programs can be found in the annual counterspace reports by the Secure World Foundation and the Center for Strategic & International Studies, the SWF database on ASAT tests, and the History of ASATs  by the Union of Concerned Scientists.

Combined, this timeline reveals the dangers of the ongoing stalemate on arms control initiatives in outer space.


While the timeline indicates that the past half-century has seen a proliferation of arms control initiatives, gaps remain in the current arms control regime related to outer space. The need to fill these gaps is made more urgent by ongoing technological developments linked to weapons systems that are either in space or that target objects in space.

The key challenges that have hindered effective negotiation of additional arms control measures for outer space will now be examined.

The absence of a universal meaning of “peaceful purposes”

The principle of peaceful purposes is central to outer space governance and arms control. However, the idea has remained vague and its meaning has stretched over time. Initially, both the United States and Soviet Union stated that outer space should be preserved for exclusively peaceful purposes. In practice, both have long used space for non-aggressive military functions. Meanwhile the 1967 Outer Space Treaty preserves only the Moon and other celestial bodies exclusively for non-military, peaceful activities.

While there is broad agreement about peaceful purposes in principle, its substance is disputed. There are competing definitions of “peaceful purposes” and a variety of views on the objective of arms control, with some states wanting to ban military activity, while others focus on weaponization and preventing an arms race, and still others view space as a domain of warfighting. The result is that states are not all engaged in the same discussion, nor do they seek the same outcome.

The integration of space into terrestrial arms competition

Further complicating matters, arms control in space isn’t just about space. A recent UNIDIR report argues that the current arms race in outer space is an extension of terrestrial arms races. Indeed, military and nuclear rivalries on Earth have been manifested for decades in the development of space-based military capabilities for reconnaissance, early warning, and strategic command and control of weapons systems. Early bilateral strategic nuclear arms control treaties between the United States and Soviet Union included agreements not to interfere with the other state’s “national technical means of verification” – widely understood to mean reconnaissance satellites. This growing dependence of terrestrial systems on space capabilities has made agreements to restrict military uses of outer space complex.

For example, in the late 1970s and early 1980s, bilateral arms control discussions between the United States and Soviet Union, which included a possible ban on ASATs, were held in the context of other strategic arms control issues and were further complicated by the pursuit of ballistic missile defence (BMD) programs. This period saw various unilateral moratoria, but also the ongoing development and testing of new systems, as well as the eventual abrogation of the ABM treaty. The entanglement between ASATs and BMD has been one of the greatest obstacles to further arms control measures.

Different technological interests and priorities

The integration of space into terrestrial weapons capabilities also means that states have different strategic interests and priorities regarding arms control in space.

Arms control efforts in outer space focus on three different types of weapons systems: space-to-space, space-to-ground, and ground-to-space. Each system offers different technological advantages and vulnerabilities in outer space and control of each has been prioritized by different states.

ASATs or weapons in space?

Competing arms control priorities are evident in 1981 UN General Assembly Resolutions. Specifically, A/RES/36/97C “Prevention of an arms race in outer space” called for the CD to consider “the question of negotiating effective and verifiable agreements aimed at preventing an arms race in outer space” and “prohibit[ing] anti-satellite systems.” In contrast, A/RES/36/99 “Conclusion of a treaty on the prohibition of the stationing of weapons of any kind in outer space” prioritized an “international treaty, to prevent the spread of the arms race to outer space.”

Long the state actor most dependent on space, the United States, with the support of its allies, has consistently prioritized the threat posed by anti-satellite weapons and the use of force against space-based objects. In contrast, Russia and its allies, concerned about ballistic missile defence and the ability to maintain a nuclear deterrent, have been more concerned with the potential orbiting of weapons in outer space, including those that could strike objects on Earth.

This strategic divide has persisted despite the introduction by Russia and China of the draft Treaty on the Prevention of the Placement of Weapons in Outer Space, the Threat or Use of Force against Outer Space Objects (PPWT), which expressly responds to threats to objects in space. Some states are concerned about how the draft defines “weapons” and “use of force” (see more detail below).

Behaviour or hardware restrictions

There is also disagreement over what should be regulated/restricted: certain weapons systems (hardware) or the behaviours of actors in space and how they use specific hardware capabilities? Many states that advocate for a behavioural approach do so, in part, because they see technical challenges in a more traditional focus on hardware restrictions, as noted below.

However, hardware and behaviour are closely linked. For example, although there is no formal proposal currently at the United Nations, interest is growing in pursuing an international agreement that would restrict or ban any test or use of kinetic ASAT weapons in space that creates space debris. Here the focus is on limiting the effect of a behaviour or use of specific hardware in outer space. Noting a strong international commitment to the sustainability of the space environment, Canada has proposed such an agreement as one way forward on space security discussions at the Conference on Disarmament. Drawing on the model set by the Partial Test Ban Treaty in 1963, an international letter coordinated by the Outer Space Institute to present to the UN Secretary-General is currently collecting signatures from experts and concerned citizens from around the world.

The use of force or the escalation of below-threshold activities

In 2021, the United Kingdom introduced a process to develop “norms, rules, and principles of responsible behaviour in space.” In contrast to the focus on space weapons, this initiative is aimed at reducing opportunities for misunderstandings and miscalculations that can lead to unintended confrontation or conflict. This objective implies a focus on activities and behaviours in space that would fall below the threshold of the use of force, such as rules about jamming, lasing, non-cooperative rendezvous-and-proximity operations, and other non-destructive actions in outer space.

How to develop rules to prevent an arms race in outer space

States have also presented conflicting preferences for the types of rules that are needed to enhance the arms control regime in outer space.

A treaty or voluntary rules

The objective of PAROS is to achieve a new legally binding treaty to address perceived gaps in the existing legal framework governing outer space, specifically the use or orbiting of conventional weapons in outer space. The first such draft treaty was presented to the UN Secretary-General in 1981 and to the Conference on Disarmament in 1983 by the Soviet Union. A subsequent draft PPWT was presented to the CD in 2008 and again in 2014. A Group of Governmental Experts met in 2018-2019 to discuss the possible elements of such a treaty, but was unable to arrive at a final consensus report.

However, many states prefer voluntary – not legally binding – rules to govern activities and control threatening behaviours in outer space, with priority given to rules that prevent miscommunication and misperception, thus de-escalating unintended conflict in space. Many advocates of this approach contend that current international law – including the OST, UN Charter, and IHL – offers adequate regulation. Others have concerns about the technical feasibility of arms control proposals (see below). One significant example of this sort of effort is the draft code of conduct proposed by the EU in 2014, which failed to garner sufficient international support.

It should be recognized, however, that these two types of instruments are closely linked and many states see the value of both. By increasing and shaping transparency and confidence-building measures, voluntary rules can lead to a legally binding instrument. The current UK-led process on norms of responsible behaviour in outer space – structured as an open-ended process that could ultimately lead to a new legal agreement – reflects this spirit.


TCBMs are essential for the success of voluntary rules. They are also a critical component of treaties. UN General Assembly resolutions supporting TCBMs in outer space date back to the 1990s. A GGE report titled “Study on the application of confidence-building measures in outer space” was released in 1993. A second GGE study with recommendations on TCBMs was released in 2013. Efforts to identify practical measures to implement these recommendations are discussed at the UN Disarmament Commission. However, no practical initiatives or processes have yet been adopted.

Unilateral measures

Russia has co-sponsored an annual “no first placement of weapons in outer space” resolution that seeks political declarations by individual states not to be the first to place weapons in outer space. Some states object to it because it does not clearly define “weapons” or “placement” and is silent on the use of anti-satellite weapons based on Earth. Unilateral moratoria on the testing of anti-satellite weapons have had some success in the past. Such initiatives can also serve as TCBMs.

How to regulate specific weapons

Finally, there are obstacles that relate primarily with how legal restrictions are assigned to specific weapons or hardware in space. There is no universal, clear definition of a ‘space weapon’. It is not clear how to account for dual military and civilian uses of specific capabilities in outer space. And in the absence of such clarity, verification remains challenging.

While these challenges are not unique to outer space, attention must be paid to the particularities of the space capabilities and operations within the space environment.

Defining space weapons

The draft PPWT defines a space weapon as “any outer space object or its component produced or converted to eliminate, damage or disrupt normal functioning of objects in outer space, on the Earth’s surface or in the air, as well as to eliminate population, components of biosphere important to human existence, or to inflict damage to them by using any principles of physics.” Some states find this definition too broad and ill-suited to verification, especially when the dual-use nature of much space-based technology is considered. Other definitional challenges extend to behaviours in space and include such concepts as an armed attack in outer space and placement of weapons in space, which bring their own complexities.


Some states argue that almost any object in space could be used as a weapon and thus see insurmountable challenges in banning space weapons. While it seems obvious that most objects in space make poor weapons, it is certainly true that being able to distinguish among the uses of similar types of hardware is necessary for arms control.


Verification refers to the capability of states parties to determine if other states parties are complying with the agreement.

It is difficult to verify the nature or capability of any object once it is in outer space and too far from Earth to be closely observed or inspected by terrestrial-based instruments. However, some clues can be found by observing orbital parameters and orbit behaviours, which can be tracked with existing capabilities for space situational awareness.

Among the numerous studies and proposals that address this challenge are the following:

  • Canada’s proposal at the CD of PAXSAT, using satellites to monitor and verify the absence of weapons in space;
  • A proposal by the USSR for an international space inspectorate to conduct on-site inspections of launch sites before each launch;
  • France’s proposal to create a UN International Trajectography Centre (UNITRACE) that collects data to update registrations, monitor space objects, and conduct real-time calculations of space objects.

None have progressed.

A GGE on the role of the UN in arms control verification, including in space, was initiated in the 1990s, but concluded that there is insufficient support for a global verification organization. Instead, most arms control agreements include their own processes and mechanisms for verification.

The challenges with verification are both technical and political. On the technical side, the collection of orbital information through space situational awareness – which today includes robust commercial capabilities – has advanced significantly, especially in monitoring the behaviour of objects in orbit. But inadequate data sharing and global access to sufficiently detailed information, as well as the interpretation of such information, remain political obstacles.

Institutional challenges

The Conference on Disarmament was established as “a single multilateral disarmament negotiating forum of the international community” in 1979, and a PAROS resolution that asked the CD to establish an ad hoc working group to negotiate a PAROS agreement was first introduced in 1982. But the CD, which operates on the basis of both substantive and procedural consensus, has been largely deadlocked since August 1996 (except for 1998 and 2009).

Effort to discuss issues related to military activities in outer space at the UN Committee on the Peaceful Uses of Outer Space (COPUOS) have likewise been blocked by a strict interpretation of the Committee’s mandate and the operational requirement of consensus.

In an effort to navigate around these roadblocks, the EU sought to negotiate its international code of conduct for space activities outside these UN bodies, but it ultimately failed. The current Open-Ended Working Group on norms of responsible behaviours falls under the mandate of the UN General Assembly First Committee on Disarmament and International Security.


Arms control is urgently needed to ensure that outer space remains a peaceful domain that can be freely used for the benefit of all. The issue is complex and efforts to agree to specific arms control measures, either legally binding or voluntary, have been unsuccessful for decades. But the challenges themselves – including approach, scope, focus, and method – are not unique to space. Indeed, many of these challenges are inherent to arms control in general, and have been addressed through various means elsewhere. We can and should learn from these experiences.


ABMAnti-ballistic missileASATAnti-satellite weaponCDConference on Disarmament (UN)COPUOSCommittee on the Peaceful Uses of Outer Space (UN)EUEuropean UnionFOBSFractional Orbital Bombardment System (USSR)GGEGroup of Governmental Experts (UN)GPALSGlobal Protection Against Limited missile Strikes (US)IHLInternational humanitarian lawISIstrebitel Sputnikov (satellite destroyer; USSR)MIRACLMid-Infrared Advanced Chemical Laser (US)OSTOuter Space TreatyPAROSPrevention of an arms race in outer spaceSDIStrategic Defense Initiative (US)STARTStrategic Arms Reduction TreatySWFSecure World FoundationTCBMTransparency and confidence-building measureUKUnited KingdomUNUnited NationsUNDCUnited Nations Disarmament CommissionUNGAUnited Nations General AssemblyUNIDIRUnited Nations Institute for Disarmament ResearchUSUnited States of AmericaUSSRUnion of Soviet Socialist Republics (Soviet Union)