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date: 05 December 2020

Space Law and Weapons in Spacefree

  • Sa'id MostesharSa'id MostesharUniversity of London, Institute of Advanced Legal Studies


Although legal principles to govern space were discussed as early as the mid-1950s, they were not formalized until the Outer Space Treaty (OST) 1967 was adopted and came into force. The OST establishes a number of principles affecting the placement of weapons in outer space. In particular it provides that “the Moon and other celestial bodies shall be used exclusively for peaceful purposes” and prohibits the testing of any types of weapons on such bodies. More generally the OST forbids the placement of nuclear weapons or other weapons of mass destruction in outer space. In addition there are a number of disarmament treaties and agreements emanating from the United Nations Office for Disarmament Affairs and the Conference on Disarmament that are relevant to weapons in space.

Although the disarmament provisions and international humanitarian laws place some restrictions on the use or manner of use of space weapons, none prohibit space weaponization. The absence of such prohibition is not due to many attempts over the years to prevent an arms race in space. Notable among these are Prevention of an Arms Race in Space Draft Treaty and the Prevention of the Placement of Weapons in Space Draft Treaty.

In considering the laws affecting space weapons a fundamental question that arises is what constitutes a weapon and does its placement in space breach the requirement that outer space be used exclusively for peaceful purposes? As an example, does a satellite used to control and direct an armed drone breach the peaceful use provision of the OST? There may be risks that without international norms governments and substate groups may acquire and use armed drones in ways that threaten regional stability, laws of war, and the role of domestic rule of law in decisions to use force.

Given their orbital velocity, any object in space could be a weapon with capability to destroy a satellite or other space object. There is also a growing population of dual-use satellites with military as well as civilian applications. These present great difficulty in arriving at a workable definition of a space weapon in the formulation of a generally acceptable treaty. In addition, there are divergent views of the meaning of peaceful use. Some, in particular the United States, consider the meaning to be “nonaggressive” rather than “nonmilitary.”


In the excitement and optimism at the dawn of the human venture into outer space, there was a widespread expectation that space would be an area free of conflict and dedicated to peace. Proposals that space “would be used only for genuinely peaceful purposes and the common benefit of mankind . . . were made respectively by the United States in 1957 and the Soviet Union in 1958” (Cheng, 1997, p. 514).

This article shows that, despite such aspirations, military use of space has been contemplated and marks many of the early technological developments by the United States and the USSR,1 the two space powers. It explores the international law governing the placement and use of weapons in space and examines the laws affecting the use of outer space for military purposes (see Mosteshar, 2005, p. 473; 2008, p. 199). It also points to areas where a lack of agreed definition has an impact, as well as complications arising from dual military and nonmilitary use.

Law Governing Space

Prior to the adoption of the Treaty on the Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (1967; Outer Space Treaty [OST]), the use of outer space2 was subject to general international law. Members of the United Nations (UN) were bound by the terms of its charter (Cheng, 1997, p. 513; Waldrop, 2004b, p. 329 at 339) These laws continue to apply among members of the UN but are modified for those states that are parties to the OST. General international law and the Charter of the United Nations are a central part of the corpus juris spatialis along with the OST, which provides

States Parties to the Treaty shall carry on activities in the exploration and use of outer space, including the Moon and other celestial bodies, 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 (OST, Article III).

It is clear that the OST recognizes that human activity in space does not take place in a legal void “for which every rule has to be newly fashioned.” It has always been subject to general international law (Cheng, 1997, p. 526; see also Cheng, 1994).

In considering what laws apply to weapons in space, we must first review relevant general international law before considering any specific legal restrictions or relaxations resulting from treaties or other international laws. States are sovereign; they have their own lawmakers and law-enforcement officers. Therefore, at the international level they cannot be bound by “some fiat from on high.” Their actions can only be

made unlawful by the consent of the States concerned in the form of treaties or by the concurrence of the generality of States, including the dominant section of international society, in the form of general international law or what is traditionally called customary international law. This applies to the banning or limitation of weapons in outer space no less than to any other matter.

(Cheng, 1997, p. 523)

General International Law

Save for the limitations introduced by space-related laws, international law contains no rule relating to the military use of space or the placement of any weapon in space. It follows that such uses are permitted, subject to observation of the rules of international law including, for members of the UN, the Charter of the United Nations (Blount, 2012). This inter alia provides

All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any State, or in any other manner inconsistent with the Purposes of the United Nations (Cheng, 1997, p. 513; UN Charter, Article 2[4]).

But it allows for self-defense:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security

(Lakeshanan, 1985, p. 68 at 75; “Military Activities in Outer Space,” 1988, p. 259 at 267; UN Charter, Article 51).

Given the existing rules of general international law, which did not single out space from other areas of res extra commercium or res nullius,3 it was unrealistic, although understandable, to expect that space would be entirely free of weapons or military use. However, international humanitarian and the jus in bello and jus ad bellum applicable to warfare apply equally in space (see Boothby, 2017, p. 179).

Lex Specialis—Law Specific to Outer Space

In the absence of any prohibition or limitation on the military use of outer space, or placement of weapons in outer space under general international law, it is necessary to consider whether any such restrictions exist under the specific laws governing outer space. International law relating to weapons and warfare do impose limitations on the nature of weapons and military actions under humanitarian, environmental, and other laws (see Boothby, 2017, p. 179).

A consistent theme that ran through international pronouncements on the use of outer space from the earliest days was that it should be peaceful. Apart from UN General Assembly Resolutions, all referring to peaceful uses of outer space, the committee formed by the UN in 1958 to deal with space matters is named the Committee on Peaceful Uses of Outer Space (COPUOS). However, there has been long-standing debate about the meaning of peaceful in this context. Furthermore, the main instrument of space law, the OST, does not extend its application to all activities in outer space to require that they be peaceful.

Three treaties are relevant to the issues of weapons in space. The OST is a set of principles and is very widely ratified. The Agreement Concerning the Activities of States on the Moon and Other Celestial Bodies (1979; Moon Agreement). Moon Agreement makes certain specific provisions expanding on the OST dealing with celestial bodies. The Liability Convention addresses liability arising from activities in space. Each is only binding on states parties, that is, the states that have ratified them.

Outer Space Treaty

The OST, also known as the Principles Treaty, sets out the fundamental principles governing activities in outer space. These closely follow the earlier General Assembly resolution of December 1963 on the subject (Declaration of Legal Principles Governing the Activities of States in the Exploration and Use of Outer Space, 1963).

In relation to weapons, the treaty provides that

States Parties to the Treaty 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. (OST, Article IV, emphasis added)

The Moon and other celestial bodies are to be used by all states parties to the treaty exclusively for peaceful purposes. The establishment of military bases, installations, and fortifications; the testing of any type of weapons; and the conduct of military maneuvers on celestial bodies are forbidden. The use of military personnel for scientific research or for any other peaceful purposes is not prohibited. Finally, the use of any equipment or facility necessary for peaceful exploration of the Moon and other celestial bodies is not prohibited.

It should be noted that the rules applicable to “void” space and to celestial bodies, including the Moon, materially differ.

Void Space

Unlike celestial bodies, void space4 as a whole is not restricted to peaceful use. Only certain weapons in void space are prohibited, and then only in a limited sense. The prohibition applies only to weapons of mass destruction, including nuclear weapons (Aoki, 2017, p. 197 at p. 204; Blount, 2009; Lyall & Larsen, 2009, pp. 515–516; Fessler, 1979, p. 56). The term weapons of mass destruction generally encompasses nuclear, chemical, and biological weapons and probably also radiological weapons—yet apparently not, for instance laser and other directed-energy weapons. Note also that the Nuclear Test Ban Treaty prohibits nuclear explosions in space (Treaty Banning Nuclear Weapon Tests in the Atmosphere in Outer Space and Under Water, 1963). At the time the OST was drafted the UN definition of weapons of mass destruction was that of the UN Commission for Conventional Armaments.5 Others have since been discussed by the Conference on Disarmament and the UN Disarmament Commission.6

These may not be placed in Earth’s orbit or otherwise stationed in space. However, there is no restriction on conventional weapons (Mosteshar, 2008, p. 199).

The OST does not prohibit the testing, development, or deployment on Earth or perhaps even the deployment of ground-based nuclear systems designed for use in outer space or against space objects (Fessler, 1979). For this reason, no objection was raised by any state to the anti-satellite system (ASAT) tests conducted by China in 2007 (Kan, 2007) or those by the United States in 2008 (RIM-161 Standard Missile 3).

On January 11, 2007, the People’s Republic of China conducted its first successful direct-ascent ASAT weapons test in destroying one of its own satellites in space. On February 21, 2008, at 03:26 UTC, the Ticonderoga-class guided-missile cruiser USS Lake Erie fired a single SM-3 missile, hit and successfully destroyed the satellite, with a closing velocity of about 22,783 mph (36,667 km/h) while the satellite was 247 kilometers (133 nautical miles) above the Pacific Ocean. USS Decatur, USS Russell, as well as other land, air, sea, and space-based sensors were involved in the operation.

In relation to void space, the OST does not require that it be used exclusively for peaceful purposes. It is permissible to use space for military or aggressive purposes. The treaty does not require complete demilitarization of outer space (Rosas, 1983, p. 357 at 358).

The Moon and Other Celestial Bodies

In contrast to void space, the use of celestial bodies7 is reserved exclusively for peaceful purposes. Installing or stationing any weapon of mass destruction on celestial bodies is prohibited, and no weapon of any kind may be tested there. The OST is explicit in prohibiting military use of celestial bodies, disallowing the establishment of any military bases or structures and the conduct of military activities (OST, Article IV, para. 2).

However, the military may engage in scientific research or other peaceful activity. Military equipment and facilities can also be used when necessary for peaceful exploration of celestial bodies.

Moon Agreement

The Moon Agreement8 reiterates the provisions of the OST in relation to weapons and military uses (OST, Article IV, para. 2). The Agreement (Article 3) provides:


The Moon shall be used by all states parties exclusively for peaceful purposes.


Any threat or use of force or any other hostile act or threat of hostile act on the Moon is prohibited. It is likewise prohibited to use the Moon in order to commit any such act or to engage in any such threat in relation to the earth, the Moon, spacecraft, the personnel of spacecraft or manmade space objects.


States parties shall not place in orbit around or other trajectory to or around the moon objects carrying nuclear weapons or any other kinds of weapons of mass destruction or place or use such weapons on or in the Moon.


The establishment of military bases, installations, and fortifications and the testing of any type of weapons and the conduct of military maneuvers on the Moon shall be forbidden. The use of military personnel for scientific research or for any other peaceful purposes shall not be prohibited. The use of any equipment or facility necessary for peaceful exploration and use of the Moon shall also not be prohibited.

It is important to note that references to the Moon and the provisions of the Moon Agreement (Article 1, para. 1) include and apply to all celestial bodies within the solar system, except the earth,9 and include “orbits around or other trajectories to or around it” (Article 1, para. 2).

It has been suggested that the Moon Agreement could apply also to outer void space, by defining the Moon to include “orbits around or other trajectories to or around it” (Article 1, para. 2). Such interpretation would effectively prohibit militarization of at least part of void space (see Aoki, 2017, p. 197 at 205).

However, in its consideration of the draft Moon Agreement and the definition of the “Moon,” the Legal Subcommittee of COPUOS agreed “that the trajectories and orbits mentioned in Article 1, paragraph 2, do not include trajectories and orbits of space objects in Earth orbits only and trajectories of space objects between the Earth and such orbits.”10

There have, however, been differing interpretations of the Legal Subcommittee’s position. Canada, in its working paper before the Conference on Disarmament in 1985,11 expressed the view that establishing military bases, installations, and fortifications; the testing of any type of weapons; or any conduct of military maneuvers would be prohibited in the residual orbits and trajectories within the solar system (Aoki, 2017, p. 197 at 205).

At the Conference on Disarmament in 2006, China and Russia interpreted these provisions as not restricting weaponization of void outer space in a joint working paper.12 Their view, which may be taken to be the prevailing and better view, is that the provisions of Articles 3(2) and 3(4)

prohibit only tests and use of weapons of any kind on the Moon, and the use of such weapons from the Moon against the Earth, spacecraft and the personnel. However, activities of such kind in the Moon orbit and in outer space other than the Moon are not covered.13

They further express the view that Article 3(3) “bans only the deployment of weapons of mass destruction on the Moon and in its orbit, but does not deal with weapons of other kinds.”14

Liability Convention

The Liability Convention is mentioned here briefly because if military action in space causes damage by a space object, the relevant state could potentially be liable for that damage.

It has been argued that the absolute liability provision of the Liability Convention15 could require compensation for space-based attacks against ground or air-based targets (Ramey, 2000; Schmitt, 2006). However, belligerents incur no liability for lawful attacks on military objectives. Further, self-defense, duress, necessity, and other lawful acts could also apply to negate liability. However, it has been suggested that absolute liability would only be suspended vis-à-vis military space activities and might remain applicable to civil space activities (Bourbonnière, 2005). Absolute liability would apply to belligerents for damage caused in violation of international humanitarian law.16

Interpretation of the Terms “Peaceful Use” and “Weapon”

An examination of the international legal rules applicable to the placement or use of weapons in space requires understanding of the terms used and their context. The terms weapons and peaceful are clearly of primary importance (Cheng, 1997, p. 513).

Although there are numerous references to peaceful use of outer space in treaties and resolutions affecting outer space, in none is the term defined, and, in the present context, nor is weapon.

Peaceful Use

At the outset of space activities it was clear that they provided great military advantages. With time these advantages have become increasingly apparent and gained importance.

In their rhetoric and laws governing space activities, states continue to aver that space activities are to be conducted for peaceful purposes and for the benefit of humankind. However, in their actions and policies, states, particularly the major space-faring states, pursue military objectives in outer space (Cheng, 1997, p. 520; Rosas, 1983, p. 357 at 362). Many states use Earth observation and other types of satellites, space vehicles, or space stations for military purposes (Rosas, 1983, p. 357 at 358). In void space, states are perfectly entitled to do so, and such use does not breach international law or obligations under the OST.

Nevertheless, the United States has gone to great lengths to promote the interpretation of “peaceful” as “nonaggressive” rather than nonmilitary or civilian. This interpretation, even though it has been used by the United States for many years without objection by others, does not amount to acceptance by other states or form part of general international law. It has been cogently argued that this interpretation by the United States is unnecessary, wrong, and potentially noxious. (For a full and clear discussion of this usage and relevant international law, see Cheng, 1997, p. 520.)

If, contrary to the U.S. interpretation, “peaceful” means “nonmilitary” (and not “nonaggressive”). States are

perfectly entitled to conduct any military activity, including exercises and manœuvres in outer void space, and to test, deploy and station there any number of military reconnaissance satellites, early warning satellites, meteorological satellites, communications satellites, geodetic satellites, navigation satellites, anti-satellite weapons (ASAT), ballistic missile defence (BMD) systems, permanently manned space stations, and any other kind of weaponry or device, all either partly or exclusively for military purposes

(Cheng, 1997, p. 530).


There is no general agreement on the definition of “space weapon” (Waldrop, 2004b, p. 329; for a detailed discussion of space weapons and technologies, means and methods of warfare, see Boothby, 2017, p. 179). The dynamics of space and the laws of physics render virtually any object in space a potential weapon. Also, space systems are increasingly designed or deployed with dual-use capability, and many are used for both civilian and military purposes.

The Canadian Permanent Ambassador to the Conference on Disarmament articulated some of the factors that can be relevant in defining whether an object is a space weapon include (Meyer, 2004):


Description of the device;


The intended effect of the device; and


The method by which the effect is achieved.

In turn this would involve consideration of:


Severity of the action and its effect (level of destruction or permanence);


Method of achieving the intended effects (kinetic or directed energy);


Design versus intent, distinguishing between objects designed for an offensive purpose and those used with the intention of causing harm.

A major point of contention is whether weapons on Earth aimed at space objects are “space weapons.” An increasingly accepted definition of space weapon includes:


Terrestrial- and space-based weapons that can attack or negate on-orbit space systems (ASAT); and


Space-based weapons that can attack or negate targets on the surface of the earth (Waldrop, 2004b, p. 329 at 334, citing Hyten & Uy, 2004).

However, it is not clear that all states accept that ground-based weapons directed at objects in space (ASATs) are space weapons.17 In monitoring of space weapons, and in determining whether an action is legal, a clear definition of what amounts to a weapon needs to be established (For a detailed classification of space weapons, see Ekblad, 1992).

Another definition includes that suggested by the UN Institute for Disarmament Research:

A space weapon is a device stationed in outer space (including the Moon and other celestial bodies) or in the earth environment designed to destroy, damage, or otherwise interfere with the normal functioning of an object or being in outer space, or a device stationed in outer space designed to destroy, damage, or otherwise interfere with the normal functioning of an object or being in the earth environment. Any other device with the inherent capacity to be used as defined earlier will be considered a space weapon.

(Cronin, 2009, p. 179)

This definition has been criticized as too broad. The last sentence could arguably cover any space object (Khan, 2017, p. 314 at 331).18

Ballistic missiles that arc through space are not classed as space weapons. Rockets that orbit and that can attack satellites or missiles are so classified (Garwin, 2001).

A space weapon could also be one that does not cause physical damage but destroys the target’s command, control, and space surveillance equipment, which are vital to the efficient operation of spacecraft and missiles (Jasani, 2002, p. 347 at 360). This includes any device with the “inherent capability” to “destroy, damage, or otherwise interfere with the normal functioning of an object or being in outer space” or in the earth environment from outer space (Stares, 1991, p. 147 at 148).

Arriving at a workable and internationally acceptable definition of space weapon has become more challenging with the development of active debris removal and of satellite servicing systems. Both such systems have the capability to alter the functioning and orbit of the target space object.

Military Uses of Space

Militarization, or the use of outer space for military purposes has occurred since the inception of human activity in space. Soon after the end of the Second World War the United States and the Soviet Union embarked on development of military satellites. Both launched reconnaissance satellites early in the 1960s. The U.S. Corona satellites and the Soviet Union’s Zenit satellites date to the 1950s and were early examples of military recognizance satellites. The U.S. satellite program’s initial system, GAMBIT 1, first launched in 1963 carrying a KH-7 camera system that included a 77-inch focal length camera (see Guillemette, 2011).

Space systems used for military purposes include reconnaissance, meteorological, communication, and navigation satellites and ballistic missile defense and ASAT weapons; Boothby, 2017, p. 179; Jasani, 2002, p. 347 at 360.

The primary focus of the two space-active states was military, with military satellite launches accounting for three-quarters of the total during the Cold War (Aoki, 2017, p. 197). Due mainly to increasing commercial satellites, the percentage of exclusively military satellites has decreased, although military use of space has not. Many dual-use satellites are used by the military and carry military payloads (see Khan, 2017).

Militarization vs Weaponization

In considering the legal status of outer space, it is important also to distinguish weaponization from militarization. Space weaponization, is always a form of militarization, but space militarization—that is, the use of space by military spacecraft—does not necessarily involve space weaponization (Khan, 2017, p. 314 at 329).

Space weaponization has been defined as referring “to the placing in outer space for any length of time any device designed to attack man-made targets in outer space or in the terrestrial environment” (Viasic, 1995).

Military use of outer space began when the United States launched its first military observation satellite in 1960. This was followed by the Soviet Union launching a similar spacecraft in 1962. The first indication of the potential for aggressive action in outer space came from the Soviet Union when it tested an ASAT weapon in October 1968, exactly one year after it had signed the 1967 OST (Jasani, 2002, p. 347).19


Drones, or unmanned aerial vehicles, are generally not space objects, although the United States has used drones in space for some time, ostensibly to test propulsion systems and materials (Howell, 2015).

Space-controlled drones are now almost routinely used in warfare. But there is no space law prohibition on such use. The more difficult aspect of their use is compliance with international humanitarian law (Quine, 2012, reporting comments by Professor Steven Freeland).

Dual-Use Satellites

Dual Military and Civilian Use

Virtually all space objects are dual-use and may be used for military or civilian purposes. Commercial space systems provide extensive services to the military (Waldrop, 2004a, p. 157). For example, the majority of commercial Earth observation data is acquired by governments. (This was estimated to be between 60% and 80% in 2003; see United States Air Force, 2003, p. 60; see also Schmitt, 2006.) Such data has reconnaissance and military applications.

The continued use of commercial space systems was confirmed at a conference by Maj. Gen. Robert Dickman, U.S. Air Force deputy secretary for space, who stated that “the Pentagon would continue to build its own satellites for national security and economic reasons, but 80 percent of its capacity during the Iraq war was provided by commercial satellite operators, and that trend would continue” (Reuters Science, 2003). During the 2004 Iraq war, 68% of munitions were satellite guided (up from 10% in the 1991 Iraq War; Postnote, 2006).

Multistate Use

Complications arise where multiple states use a single dual-use space system. A question arises: If one of the states uses the system as a weapon, can the system as a whole to be treated as a weapon?

The placement of weapons, including dual-use satellites, in void space does not breach international law per se. A difficulty arises in assessing whether such satellites can be legitimate military targets. The answer to this question lies in the international law of warfare, which applies in space as it does on Earth (OST, Article III).

Traditional war theory would apply the proportionality rule to dual-use satellites (Khan, 2017). This involves balancing civilian harm against military benefit and necessity. Given the growing dependence on satellite communication and information in modern civilian life, these factors need to be included in proportionality analysis. Consequently attacks against satellites invoke the requirements of international humanitarian law.20 It may therefore be that the balance of proportionality will generally be against attacks on satellites.

A further consideration relevant to any kinetic attack of a satellite is the creation of debris. Any such action, therefore, will affect not only the target satellite but also potentially all satellites. It is arguable that direct attacks on satellites in Earth’s orbit are contrary to the requirement that states “shall conduct their activities in outer space, including the Moon and other celestial bodies, with due regards to the corresponding interest of all other States” and thus would be in breach of international law (OST, Article IX).

De-Weaponization of Space

Efforts in the UN to maintain outer space for peaceful purposes began in 1957, months prior to the launch of the first artificial satellite into Earth’s orbit. Early proposals for prohibiting the use of space for military purposes and the placement of weapons of mass destruction in outer space were considered in the late 1950s and early 1960s by the UN (UN Office for Disarmament, n.d.)

Over the years there have been several attempts to prevent the development or use of space weapons. Two notable proposals have been made with Russian and Chinese participation and backing, namely the Prevention of an Arms Race in Space Draft Treaty (PAROS) and the Prevention of the Placement of Weapons in Space Draft Treaty (PPWT). From early in the 2000s there has been growing discussion of the means by which space can be made safer and sustainable through transparency and confidence building measures (TCBMs).

It is clear that new agreements or treaties are needed if outer space is to be free of weapons. A consensus may arise that military use of space per se is not objectionable and may contribute to avoidance of civilian casualties.

Prevention of an Arms Race in Space

Following a series of UN General Assembly resolutions21 requesting the Conference on Disarmament (CD) to do so, the CD formed the ad hoc Committee on Prevention of an Arms Race in Outer Space in 1985. It aimed to negotiate and conclude one or more agreements to prevent an arms race in all its aspects in outer space (Nuclear Threat Initiative, 2017). The program of work of this ad hoc committee was formally accepted at the second session in 1986 and maintained until 1994, the last year the ad hoc committee convened. Subsequently, discussions have been conducted in the plenary and informal plenary meetings under the agenda item “Prevention of an Arms Race in Outer Space” (Waldrop, 2004b, p. 329).

One commentator has observed that

a prime reason why so little headway is being made in the prevention of such a pre-arms race is that, as of now, what has to be prevented is predominantly a race in certain advanced technologies and not in “arms” properly so called. The negotiations have almost entirely ignored this inconvenient fact.

(Dahlitz, 1988).

Prevention of Placement of Weapons in Outer Space

In 2002 Russia and China jointly submitted to the CD a Proposal for a Treaty to Prevent the Deployment of Weapons in Outer Space, the Threat or Use of Force Against Outer Space Objects (PPWT; Working Paper Presented by the Delegations of China, Russia, Vietnam, Indonesia, Belarus, Zimbabwe and Syria, 2002). It was aimed at banning certain behavior rather than weapons in space. An updated and more detailed Draft Treaty on PPWT was submitted by Russia and China in 2008 (Second PPWT; Draft Treaty Presented by the Delegations of China and Russia, 2008).

The third and most recent Draft PPWT was submitted by Russia and China in 2014 (Third PPWT; Draft Treaty presented by the Delegations of China and Russia, 2014). The United States opposed the Draft PPWT on a number of grounds, including the absence of any means of compliance verification, its scope, and the omission to address ASATs, regarded as the most pressing issue by the United States.22 In their response23 Russia and China indicated the proposed PPWT was not intended to address specific weapons and pointed to the OST in relation to lack of verification mechanism.

The third Draft PPWT forbids states parties from:


Placing any weapons in outer space;


Resorting to the threat or use of force against “outer space objects” of states parties to the PPWT;


Engaging in outer space activities inconsistent with the objects and purposes of the PPWT; and


Assisting or inducing other states and international governmental organizations as well as nongovernmental organizations and entities to participate in activities inconsistent with the objects and purposes of the PPWT (Article II).

By a resolution of the UN General Assembly (2017b), a new Group of Government Experts (GGE) was to be established to review the third PPWT Draft and to issue recommendations on the creation of a legally binding treaty for the prevention of an arms race in space and of the placement of weapons in outer space (Ministry of Foreign Affairs of the Russian Federation, 2017). The Resolution was opposed by, among others, the United States and the United Kingdom, for similar reasons as the U.S. opposition to the Third Draft PPWT (United States Mission to the United Nations, 2017).

It remains to be seen whether the matter can be resolved once the new GGE has reported. The focus appears to be on creating a series of measures to achieve transparency and confidence (TCBM) among nations.

Transparency and Confidence Building Measures

In 1993 the UN established a GGE to examine and report on steps necessary to ensure continued security and sustainability of outer space. The GGE reported in 2013 (Report of the Group of Governmental Experts on Transparency and Confidence-Building Measures in Outer Space Activities, 2013), recommending measures to be taken by states to achieve a secure and sustainable space environment that underpins a growing number of terrestrial infrastructures and human activity. In relation to space weapons the report states:

The Group acknowledged that the existing treaties on outer space contain several transparency and confidence-building measures of a mandatory nature. Non-legally binding measures for outer space activities should complement the existing international legal framework pertaining to space activities and should not undermine existing legal obligations or hamper the lawful use of outer space, particularly by emerging space actors.

The Group further agreed that such measures for outer space activities could contribute to, but not act as a substitute for, measures to monitor the implementation of arms limitation and disarmament agreements.

The GGE recommended states and international organizations voluntarily adopt the measures in addition to the observation of their international obligations. As intended by the GGE, the report has been circulated to UN entities concerned with disarmament (see Martinez, Crowther, Marchisio, & Brachet, 2014; see also Johnson, 2014).

Draft Guidelines for Long-Term Sustainability of Outer Space

The Working Group of the STSC of COPUOS has produced a set of guidelines for the long-term sustainability of outer space (Guidelines for the Sustainability of Outer Space Activities, 2017). The guidelines are divided into two parts. Part A comprises guidelines adopted by the committee, and Part B includes those still under discussion. Among the guidelines under discussion is Guideline 7, which aims to make outer space open solely to peaceful activity, calling on states and international intergovernmental organizations to “provide, in national legal and/or policy frameworks, for a commitment to conducting space activities solely for peaceful purposes” (Guidelines for the Sustainability of Outer Space Activities, 2017). In effect this would extend the regime under the Moon Agreement to outer void space. However, it would not necessarily prohibit the placement of weapons, other than weapons of mass destruction, in outer void space.

International Code of Conduct against Ballistic Missile Proliferation

The International Code of Conduct against Ballistic Missile Proliferation (Hague Code of Conduct [HCoC]; see Text of the HCoC, 2003) is a non-legally binding voluntary code that applies not only to ballistic missiles but also to space launch vehicles (SLVs; HCoC, Articles 4 (a)(i) and 4 (a)(ii), respectively). It is an early embodiment of TCBM in relation to SLVs. The code calls for prelaunch notifications of launches and test flights of ballistic missiles and SLVs and also for states to provide annual declaration of their SLV policies as well as information on the SLV launches and test flights of the preceding year (HCoC, Articles 4 (a)(iii). It also recommends that subscribing states24 invite international observers to their launch sites. The UN has welcomed the HCoC, confirming its importance in a number of resolutions.25

International Code of Conduct for Outer Space Activities

In 2008 the European Union (EU) proposed a draft code of conduct for space activities26 that was subsequently modified, following international discussions (Draft International Code of Conduct for Outer Space Activities [ICoC], 2014).

The ICoC is being negotiated outside the UN, as is the case with HCoC. It addresses both civilian and military activities. Its stated purpose is “to enhance the safety, security, and sustainability of all outer space activities pertaining to space objects, as well as the space environment” (ICoC, Article 1.1).

The ICoC includes some TCBM:

This Code establishes transparency and confidence-building measures, with the aim of enhancing mutual understanding and trust, helping both to prevent confrontation and foster national, regional and global security and stability, and is complementary to the international legal framework regulating outer space activities. (ICoC, Article 1.3)

Subscribing states are to “refrain from any action which brings about, directly or indirectly, damage, or destruction, of space objects unless such action is justified” by imperative safety considerations, to reduce debris creation, or as part of the right to self-defense (ICoC, Article 4.2). The ICoC does not seek to prohibit the placement of weapons in space but addresses what has become known as Principles of Responsible Behaviour in Outer Space (PORBOS; ICoC, Preamble 9; see EU Statement, 2017).

Missile Technology Control Regime and the Wassenaar Arrangement on Export Controls for Conventional Arms and Dual-Use Goods and Technologies

Arms control regimes like the Missile Technology Control Regime (MTCR) and the Wassenaar Arrangement (WA), essentially aim to prevent the proliferation of weapons and military technology to states lacking their own or the capacity to develop them.

Member states of MTCR adopt export policies in accordance with MTCR guidelines (Guidelines for Sensitive Missile Relevant Transfers, MTCR Guideline 8),27 providing the overall structure and rules, as well as the list of controlled items, called the “MTCR Equipment, Software and Technology Annex.” Member states adopt and implement their national export controls of missiles and SLVs28 to conform to the MTCR rules.

The Wassenaar Arrangement on Export Controls for Conventional Arms and Dual-Use Goods and Technologies29 was established in 1996 “to contribute to regional and international security and stability, by promoting transparency and greater responsibility in transfers of conventional arms and dual-use goods and technologies, thus preventing destabilising accumulations” (Wassenaar Arrangement Secretariat, 2017).

As with the MTCR, WA participating states adopt and apply their own national export controls to all items in the List of Dual Use Goods and Munitions List (Wassenaar Arrangement Secretariat, 2018). To assist in developing common understandings of transfer risks, participating states regularly exchange information of both a general and a specific nature. Participating states are required to report their arms transfers and transfers/denials of certain dual-use goods and technologies to destinations outside the WA on a six-month basis. In some cases, shorter reporting time frames apply (WA, 2018).

Although both the MTCR and the WA apply to certain space-related technologies, they do not address their placement or use in outer space. There are, however, limitations on the use of other weapons that apply both on Earth and in space, such as blinding lasers. These limitations would apply to use in space by virtue of the OST (Article III; see also Mosteshar, 2008).

UN General Assembly Resolutions

At its most recent meeting the First Committee (Disarmament and International Security) of the UN General Assembly (2017a) approved six draft resolutions, including one on a legally binding instrument on the prevention of an arms race in outer space.

The committee approved the draft resolution “Further Practical Measures for the Prevention of an Arms Race in Outer Space” (UN General Assembly, 2017b) by a recorded vote of 121 in favor to 5 against (France, Israel, Ukraine, United Kingdom, and United States), with 45 abstentions. By the terms of that text, the General Assembly would urge the Conference on Disarmament to agree on a balanced program of work that included the immediate commencement of negotiations on an international legally binding instrument on the prevention of an arms race in outer space.

The committee also approved three other draft resolutions related to disarmament aspects of outer space, including one on TCBM in outer space activities.30 By a recorded vote of 175 in favor to none against, with 2 abstentions (Israel and United States), it approved the draft resolution “Prevention of an Arms Race in Outer Space.”31 By its terms, the assembly would call upon all states, in particular those with major space capabilities, to refrain from actions contrary to that goal and to contribute actively to the objective of the peaceful use of outer space (UN General Assembly, 2017a).

Although encouraging to those advocating weapon-free space, the UN General Assembly has passed resolutions of this kind many times over the years. It remains to be seen whether these will be formalized in binding documents.


With the rapidly growing value of space to states and their citizens, the risk of conflict in outer space will become greater, and with it the possible deployment of space weapons.

As space systems and services become increasingly integrated into the security and daily life of the world population, there is a drive to balance these risks and to formalize, even if in nonbinding instruments, measures for responsible behavior in outer space. The various proposals for de-weaponization of space are evidence of this drive. Although they differ in details, the proposals all aim to foster TCBM and responsible behavior in outer space.


The author appreciates the invaluable research assistance of Jemma Queenborough.

Further Reading

  • Bourbonnière, M., & Lee, R. J. (2007). Legality of the deployment of conventional weapons in Earth orbit: Balancing space law and the law of armed conflict. European Journal of International Law, 18(5), 873–901.
  • Freeland, S. (2016). Peaceful purposes? Governing the military uses of outer space. Western Sydney University School of Law Research Paper No. 03/2017. European Journal of Law Reform, 18(1).
  • Maogoto, J., & Freeland, S. (2007). The final frontier: The laws of armed conflict and space warfare. Connecticut Journal of International Law, 23, 165–194.
  • Moltz, J. C. (2011). The politics of space security: Strategic restraint and the pursuit of national interests (2nd ed.). Stanford, CA: Stanford University Press.
  • Stephens, D., & Steer, C. (2015). Conflicts in space: International humanitarian law and its application to space warfare. Annals of Air & Space Law, 40(1).



Corpus juris
A body or compendium of laws that can include statutes and decisions; collections of laws that may be in several volumes
Jus ad bellum
Right to war; criteria establishing whether a war is just and therefore permissible; relates to legitimate reasons to engage in war
Law of war
Public international law concerning acceptable justifications to engage in war (jus ad bellum) and wartime conduct, encompassing international humanitarian law (jus ad bello)
Res extra commercium
Something outside commercial intercourse; not subject to ownership, acquisition, commerce, or trade, such as the high seas or air
Res nullius
Something that is not owned, or is without an owner, such as something that is abandoned
Lex specialis
Law governing a specific subject matter, such as juris spatialis, governing outer space; it overrides laws that govern general matters
In relation to international treaties, ratification defines the act whereby a state indicates its consent to be bound to a treaty. The process of ratification differs among states and is determined by their national laws
Inter alia
Among other things; denotes one example out of many possibilities


  • 1. Union of Soviet Socialist Republics, with Russia its largest republic, formed in 1922 and dissolved in 1991.

  • 2. Unless the context otherwise requires, in this article references to space are to be understood to be outer space and include celestial bodies.

  • 3. Subject to a common freedom of exploitation or not yet the object of rights of any specific subject.

  • 4. Void space, or outer void space, refers to the void between celestial bodies (see Cheng, 1997, p. 527).

  • 5. UN Doc. S/C.3/32/Rev.1 (August 18, 1948).

  • 6. See CD/2004 (September 10, 2014).

  • 7. In this article references to “celestial bodies” include the Moon.

  • 8. Only 17 states have ratified the Moon Agreement as of December 2017.

  • 9. An exception to this provision is where specific legal norms apply.

  • 10. UN Doc. A/34/20 (1979), paragraph 63.

  • 11. CD/618, CD/OS/WP.6 (July 23, 1985), 11.

  • 12. CD/1780 (May 22, 2006).

  • 13. CD/1780, paragraph 11.

  • 14. CD/1780, paragraph 13.

  • 15. Convention on International Liability for Damage Caused by Space Objects (Liability Convention); adopted by General Assembly Resolution 2777 (XXVI), November 29, 1971. Absolute liability for damage on the surface of the earth or to aircraft in flight provided in Article II.

  • 16. Hague Convention (IV) of 1907 respecting the Laws and Customs of War on Land, October 18, 1907, 36 Stat. 2295, Article 3. The Convention is now regarded as part of general international law, applicable to nonparties.

  • 17. The CD has had considerable difficulty in arriving an acceptable definition of “anti-satellite weapons” (see Aoki, 2017).

  • 18. As indicated, the velocity of objects in space, about 27,000 kilometers per hour (17,000 miles per hour), can cause significant damage to a satellite or other space object were there to be a conjunction between them.

  • 19. Jasani also provides a list of the types of satellites used by the military, beginning on page 349.

  • 20. International Humanitarian Law is largely contained in a series of conventions comprising the several Geneva Conventions and two Hague Conventions (see Schindler & Toman, 2004; Von der Dunk & Tronchetti, 2015, pp. 350–359).

  • 21. UN Doc. A/RES/37/83 (December 9, 1982). Two more UN General Assembly resolutions were needed to set up an ad hoc PAROS Committee. UN Doc. A/RES/38/70 (December 5, 1983); UN Doc. A/RES/39/59 (December 12, 1984). For a detailed account see Aoki (2017, 197 at 207).

  • 22. Analysis of the 2014 Russian-Chinese draft “treaty on the prevention of the placement of weapons in outer space, the threat or use of force against outer space objects” (PPWT) (CD/1985), CD/1998 (September 3, 2014).

  • 23. Follow-up comments by the Russian Federation and China on the analysis submitted by the United States of America of the updated Russian-Chinese draft PPWT, CD/2042 (September 14, 2014).

  • 24. As of June 2016 HCoC had 139 subscribing states, including the United States and Russia but not China.

  • 25. UN Doc. A/RES/59/91 (December 3, 2004); UN Doc. A/RES/67/42 (January 4, 2013); and UN Doc. A/RES/69/44 (December 11, 2014).

  • 26. Council of the EU, 17175/08, PESC 1697, CODUN 61 (December 17, 2008).

  • 27. The relevant equipment, technology, and software are defined in the MTCR Annex.

  • 28. Missile Technology Control Regime. As of October 2017 MTCR had 35 member countries.

  • 29. As of December 2017 the Wassenaar Arrangement had 42 participating states.

  • 30. A/C.1/72/L.46 (October 12, 2017).

  • 31. A/C.1/72/L.3 (October 12, 2017).