(Editor’s Note: The absence of a comprehensive analysis of the legal framework for military operations in outer space represents a troubling deficiency in the understanding of the applicable law. Such uncertainty increases the chance of a strategic error in the conduct of military operations in space. This three-part Just Security forum introduces and analyzes key emerging legal issues raised by space-based military operations, which are the focus of the ongoing Woomera Manual Project, an international research project that is spearheaded by The University of Adelaide, The University of Exeter, the University of Nebraska and the University of New South Wales – Canberra. The mission of the project collaborators is to develop a Manual that objectively articulates and clarifies existing international law applicable to military space operations. More information on the project is available here. This Just Security forum concludes with the third and final installment below.  See installments 1 here and 2 here).

The prospect of armed conflict in outer space unfortunately appears to be growing. Beyond geopolitical tension between space powers, the extent to which countries rely on space for national security purposes and the related proliferation of counterspace capabilities are contributing to the risk of “space war.” U.S. Air Force Chief of Staff General David Goldfein has warned that, should such a war occur, “everybody loses.” In light of this risk, there is a clear need to clarify how international law would regulate an armed conflict that begins in, or extends to, outer space. This post examines some of the key international humanitarian law (IHL) issues that might arise in the event that hostilities reach into space.

Does IHL apply to warfare in space?

There has been much debate as to whether the preamble and Article IV of the Outer Space Treaty, which both emphasize the use of outer space for “peaceful purposes,” prohibit all military operations in space. They do not, nor is there any such analogous customary international law prohibition. Indeed, it is now generally accepted that peaceful does not mean “non-military” but simply equates to “non-aggressive.” This fact is demonstrated by the extensive State practice of using space for military purposes.

However, even if such a prohibition existed, it would have no bearing on the applicability of IHL to operations into, through, or from outer space. This is because IHL is never dependent on the lawfulness of the decision to employ force. Rather, its applicability is a question of fact — specifically, whether the situation at hand amounts to an international armed conflict (IAC) or non-international armed conflict (NIAC). If an IAC or NIAC has begun, all operations with a nexus to the conflict are subject to IHL’s obligations, prohibitions, and restrictions. This is clear from Article III of the Outer Space Treaty, generally deemed to reflect customary law, which provides that States Party to the instrument must use outer space “in accordance with international law.” There is no cogent reason to suggest that the reference to international law was meant to exclude IHL. Further, the International Court of Justice (ICJ), in its 1986 Nuclear Weapons Advisory Opinion, confirmed that IHL applies to “all forms of warfare and to all kinds of weapons, those of the past, those of the present and those of the future.” The ICJ did so without proffering any distinction based on the domain of warfare in which hostilities occur or, indeed, the means or methods utilized therein.

The position of the United States expressed in the Department of Defense Law of War Manual is in accord with the ICJ in this regard:

[L]aw of war treaties and the customary law of war are understood to regulate the conduct of hostilities, regardless of where they are conducted, which would include the conduct of hostilities in outer space. In this way, the application of the law of war to activities in outer space is the same as its application to activities in other environments, such as the land, sea, air, or cyber domains.

The International Committee of the Red Cross (ICRC) also takes this position. In its 2019 Challenges Report, the ICRC pointed to the 1949 Geneva Conventions’ reference to “any … armed conflict” in Common Article 2 to support its position that IHL would apply directly to armed conflicts in space. The ICRC further noted that while the 1977 Additional Protocol I (AP I) to the Geneva Conventions contains a geographic applicability limitation in Article 49(3), the rules therein specifically apply to any warfare affecting civilians on land. Accordingly, the ICRC rightly concludes that “IHL applies to any military operations conducted as part of an armed conflict, including those occurring in outer space.”

Although the applicability of IHL to space operations carried out during an armed conflict triggered by terrestrial military force is indisputable, whether space operations can alone initiate a state of armed conflict is a more challenging question. This challenge is most pronounced with respect to NIACs. Indeed, for hostilities in space to rise to the level of a NIAC, a threshold of “intensity” must be met.

By contrast, an IAC occurs whenever “hostilities” occur between the armed forces (or other organs) of States. As with cyber operations, this begs questions of both intensity and nature. The ICRC has long maintained that there is no intensity requirement for hostilities to qualify as an IAC, although that assertion is not universally accepted. Clearly, a space operation causing significant damage would qualify as hostilities, as in the case of a kinetic anti-satellite (ASAT) attack.

Yet, it is uncertain whether incidents involving slight or no physical damage would ever initiate an IAC. In this regard, consider, for instance, a satellite rendezvous and proximity operation (RPO) that blinds a satellite used for missile early warning by positioning itself so as to obstruct sensors. Other examples might include a cyber operation that permanently or temporarily disrupts a key military communication satellite’s functionality, or the use of a space object to nudge a non-maneuverable navigational satellite out of its intended orbit.

Whether and when States would treat such operations as hostilities in the IHL context remains to be seen. Of course, even if it did not cause damage directly, if the reasonably foreseeable consequence of a military space operation is physical harm, as in the case of interfering with a navigational satellite in a manner that results in maritime collisions or aircraft crashes, a putative IAC would be underway.

The Term “Attack” in the Space Context

In IHL, the concept of “attacks” is the fulcrum upon which many rules rest. For instance, civilian objects may not be “attacked,” all “attacks” must comply with the rule of proportionality, and an attacker must take precautions “in attack” to minimize harm to civilians and civilian objects. The applicability of these and many other IHL rules depends on the space operation in question qualifying as an “attack,” defined in Article 49(1) of AP I as an “act[] of violence against the adversary, whether in offense or in defence.”

Undoubtedly, any military space operation that causes physical damage, whether in space or on earth, amounts to an attack where that damage surpasses a de minimis threshold. Nevertheless, difficult questions remain regarding where to draw the line between space operations qualifying as an attack and those that do not.

It is instructive that the uncertainty pervading the issue in the cyber context applies mutandis mutatis to space operations. For instance, a general consensus exists that permanent interference with functionality qualifies as damage. This would be the case, for example, if a cyber operation permanently disabled a military satellite, even if no physical harm resulted to the satellite and it remained in orbit. Similarly, it is reasonable to conclude that taking full control of a satellite on a permanent basis, a technique that was demonstrated decades ago, would equate to a permanent loss of functionality and therefore be an attack.

But beyond such relatively clear-cut cases, many legally ambiguous scenarios loom. For example, it is unclear whether temporarily jamming a civilian satellite’s downlink or uplink such that it could not perform its intended function would be an attack in violation of the rule against attacking civilian objects.

Also unsettled is the issue of whether self-destruction of one’s own satellite (as China did in a 2007 ASAT test) would, during an armed conflict, amount to an attack. Though the position is far from settled, our view is that, standing alone, it would not. However, if such a self-destruction operation was designed to generate orbital debris that would likely result in catastrophic damage to enemy satellites, the operation would qualify as an attack to which IHL rules would apply. In such a scenario the damaged satellites would be the “object of attack” in IHL terms.

Or consider regional denial of the GPS signal by the United States over enemy territory. Would denying GPS service, which is provided by a U.S. Department of Defense satellite constellation, be an attack if damage or injury resulted, as might be the case if a civilian emergency response system relies on GPS data? If not an attack as a matter of law, because the United States provides the service, the rules regarding indiscriminate attack and proportionality presumably would be inapplicable. If so, what rules would apply? As with cyber, the definition of attack in the space context will prove a determinative factor vis-à-vis IHL’s effectiveness in governing space conflict.

The Principle of Distinction and Military Space Operations

At the core of IHL lies the principle of distinction, according to which parties to an armed conflict must distinguish between combatants (fighters) and civilians, and between military objectives and civilian objects, when engaged in hostilities. Labelled a “cardinal principle” of IHL by the ICJ and given expression in treaty form through Articles 48, 51 and 52 of AP I, the principle of distinction undoubtedly reflects customary international law.

Article 52(2) of AP I, which also echoes customary international law, further clarifies that objects may only be attacked if, “by their nature, location, purpose or use [they] make an effective contribution to military action and [their] total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage” to the attacker. The ICRC’s official Commentary on the Additional Protocols notes that the text of Article 52(2) constitutes a valuable guide but also readily admits that its text will not always be easy to interpret for those who, in practice, have to decide on whether to proceed with an attack (para. 2016). This is a perceptive statement generally, but is especially apposite with respect to space warfare.

The common practice of using civilian launch systems to place military satellites into orbit offers a fairly straightforward case study of qualification as a military objective under Article 52(2) and customary law. To illustrate, a United Launch Alliance Delta IV (i.e., civilian) rocket carried the Wideband Global SATCOM satellite into space for the U.S. Air Force in 2019. This satellite forms part of the U.S. military’s global satellite communications backbone, which provides high-capacity communications for U.S. military personnel. During an armed conflict, both the military satellite and the civilian launch system would clearly be targetable, the former because it is a military objective by nature, the latter due to its use by the armed forces.

Yet, other cases are less straightforward. Of significance in this regard are “hosted payloads.”  Technology carried aboard a satellite can be classified as either part of the “bus” or the “payload.” The bus refers to the metal or composite frame on which various subsystems are mounted. Typical subsystems include an attitude control system (to keep the satellite pointed in the right direction), power source (e.g., solar panels), and on-board computers. Satellites also carry mission-specific equipment to perform specialized tasks (payloads). For example, where a satellite’s mission is to take detailed images of the Earth’s surface, the satellite’s payload will likely be an optical camera or infrared sensor.

A hosted payload “allows users, such as military forces, to add transponders or other equipment to a commercial satellite already scheduled for launch.” Such hosted payloads have missions that are distinct from those of the primary payloads aboard the bus. By way of example, in 2011 the U.S. Air Force launched the Commercially Hosted InfraRed Payload (CHIRP) as a hosted payload on a communications satellite owned by a commercial satellite operator. CHIRP was designed to test a new infrared sensor to be used by future missile warning systems.

Despite some practical drawbacks, the use of hosted payloads is likely to continue and possibly proliferate. Indeed, in 2018, the U.S. Government Accountability Office recommended the use of commercial satellites to host government sensors or communications packages as one way the U.S. Department of Defense (DOD) can achieve on-orbit capability faster and more affordably.

The initial IHL challenge posed by hosted payloads is identifying the “object” that qualifies as a military objective. One approach is to treat the satellite and all payloads thereon as a single object. This approach would mean that if any one payload makes an effective contribution to enemy military action, the entire satellite would become a military objective. This has the attractiveness of simplicity but, in certain circumstances, could have negative consequences for civilians because the rules on proportionality and precautions in attack would not apply to damage to the non-military aspects of the satellite.

For some, however, the principle of distinction requires treating any civilian payload as a civilian object. This approach would require the attacking force to try and minimize harm to such a payload. Any damage to a civilian payload would also have to be considered as “collateral damage” when applying the rule of proportionality. In some circumstances, harm befalling civilian payloads might be “excessive,” thereby barring attack on the satellite altogether despite the presence of the hosted military payload. It bears mentioning that the satellite bus, however, would be a dual-use object relied on by the military payload (e.g., as a source of energy) and thus be targetable as a military objective; harm to the bus would not, therefore, influence the proportionality analysis.

The experts who authored Tallinn Manual 2.0 on cyber operations occupy a middle ground in this regard. They opined that an attacker is required to consider any expected harm to “clearly distinguishable civilian components of the military objective” (Rule 101, para. 3). If the civilian components are not clearly distinguishable, the entire object qualifies as a dual-use military objective. Yet, in the space context, even this approach poses practical problems. For example, given that payloads aboard a bus rely on the bus to operate, for instance by providing power, and the bus clearly qualifies as a dual-use military objective, can such civilian payloads be unambiguously said to be distinguishable? As is apparent, the textual simplicity of Article 52(2) of AP I masks particular complexity in the space context.

The law of neutrality exacerbates issues of space targeting. Consider the two satellites being built for Space Norway, each equipped with payloads for Inmarsat (a commercial entity), the Norwegian Ministry of Defense, and the U.S. Air Force. The U.S. Air Force payload will enable Extremely High Frequency (EHF) military communications. If the U.S. is party to a future IAC in which Norway is not a co-belligerent (i.e., fighting on the same side), could the satellites, which will be registered in Norway, be attacked by the forces fighting the United States? This scenario may further influence how States choose to deal with the hosted payload question. The practice of leasing or sharing bandwidth, exemplified by the Australian Defence Forces’ use of U.K. or U.S. military satellite communication systems, raises discrete but related issues.

Clearly, the growing commercialization of space activities, reliance on commercial space systems by military forces, and dual-use nature of many space technologies will provide myriad challenges in identifying military objectives in order to apply the principle of distinction during armed conflict in outer space.

Indiscriminate Attacks and Space Conflict

The proscription on indiscriminate attacks is theoretically distinct from the prohibition on directly attacking civilians or civilian objects just discussed. According to Yoram Dinstein, the difference between these two IHL concepts is the effect of intent: in an indiscriminate attack, a belligerent is not actively trying to harm civilians or civilian objects but instead demonstrates reckless disregard for such consequences.

As a matter of conventional law, the prohibition on indiscriminate attacks is formulated in Article 51(4) of AP I:

Indiscriminate attacks are prohibited. Indiscriminate attacks are: (a) those which are not directed at a specific military objective; (b) those which employ a method or means of combat which cannot be directed at a specific military objective; or (c) those which employ a method or means of combat the effects of which cannot be limited as required by this Protocol; and consequently, in each such case, are of a nature to strike military objectives and civilians or civilian objects without distinction.

The ICRC is of the view that State practice establishes this rule as a norm of customary international law applicable in both IACs and NIACs. India (p. 3) and Israel (para. 109), both non-State parties to AP I, appear to accept the customary status of Article 51(4). The U.S. view on the status of Article 51(4) is not directly addressed in the Department of Defense Law of War Manual (DOD Manual), but statements by the United States at the United Nations (see para. 1(g)) indicate it agrees the treaty text has attained customary status.

The most significant issue in applying the prohibition on indiscriminate attacks to military operations in outer space involves the potential effects of space debris. Technically, space debris is comprised of both human-made orbital debris and the natural meteoroid environment. However, the term is typically used to describe any human-made artifact discarded, accidentally produced, or deliberately generated in space.

Debris-generating events can vary from a tool bag lost by astronaut Heidemarie Stefanyshyn-Piper during a 2008 spacewalk, to the aforementioned 2007 Chinese ASAT test on one of its weather satellites (Fengyun-1C). The ensuing fragmentation and debris from the Chinese test created thousands of objects of 1 centimeter or larger (i.e., considered large enough to cause “catastrophic” damage to a satellite mission, or at least disable a spacecraft).

According to the Secure World Foundation, within minutes of the Chinese ASAT test, debris entered the satellite’s orbit. By day 10, the debris had spread throughout that orbit. Three years on, the debris “effectively covered much of low earth orbit” (LEO), which continues to pose unique problems. Over half the debris will remain in orbit until the beginning of the next century.

This example of what a kinetic strike in space might look like during armed conflict has led some commentators (e.g. here and here) to conclude that the effects of this method of attack “cannot be limited as required by international law” (i.e., any such attack would necessarily be indiscriminate under Article 51(4)(c) of AP I).

Such a conclusion has major implications for States committed to operating within the parameters of IHL. If correct, it equates the customary prohibition on indiscriminate attacks to a ban on the use of kinetic weapons in outer space. Our view is that any evaluation of the application of the rule in this context must factor in the quantity and decaying timeline of the ensuing debris.

For example, in Operation Burnt Frost in 2008, the United States destroyed a non-functioning National Reconnaissance Office satellite. A majority of the resulting debris is said to have re-entered the atmosphere within 48 hours and all remaining debris within 40 days. This reflects the expert view that in circular orbits below 500 km (i.e. where orbital decay is fairly rapid) major long-term increases in the debris population are unlikely. In comparison, at higher altitudes (e.g., geosynchronous orbits) and in some high-eccentricity (elliptical) orbits, debris may remain for tens, thousands, or even millions of years.

Certainly, conduct lawful in peacetime is rarely prohibited during armed conflict (a notable exception being the ban on “dum-dum” bullets). In this regard, it is worth highlighting that Germany took the position that India did not violate international law when conducting an ASAT missile test on its Microsat-R earth observation satellite in 2019, a test that NASA Administrator Jim Bridenstine said increased the risk of small debris hitting the International Space Station by 44 percent.

Our conclusion is that the prohibition on indiscriminate attacks does not automatically prohibit the use of kinetic weapons in outer space. Nevertheless, it is essential to recall the customary IHL rule that demands States take all feasible precautions to minimize incidental loss of civilian life, injury to civilians and damage to civilian objects. The application of this rule means that, where a military satellite could be effectively disabled in a manner less harmful to civilians or civilian objects than a kinetic attack, and it is reasonably practicable to choose such an alternative in the circumstances, IHL would prohibit the use of an ASAT missile.

Examples of such alternative means could include an RPO, jamming the specific part of the electromagnetic spectrum utilized by the satellite for the transmission of communications, or some form of cyber effect on the computer sub-system of the satellite. The rule of proportionality, again a customary norm of IHL, would additionally prohibit any attack expected to cause excessive harm to civilians or civilian objects irrespective of how discriminating the immediate attack itself is.

Concluding Thoughts

The current vice chairman of the U.S. Joint Chiefs of Staff, General John E. Hyten, has emphasized the necessity of addressing an inevitable conflict in space. As a general matter, IHL is up to the task. Yet, as illustrated by the non-exhaustive examples set forth above, military operations in outer space, and the unique physics of that domain, can render the interpretation and application of existing IHL principles and rules especially challenging. This being so, efforts such as the Woomera Manual on the International Law of Military Space Operations project have the potential to make a major contribution to ensuring the effectiveness of IHL in any future conflict involving outer space.

(Part 1 of this series introduced key legal issues raised by space-based military operations. Part 2 focused on some of the implications of NATO’s recognition of space as an operational domain.)

Image – Japan’s H-IIA rocket carrying the Kirameki-2 satellite is launched from Tanegashima Space Centre in southern Tanegashima island, Kagoshima prefecture, on January 24, 2017. Japan on January 24 launched a satellite to modernise its military communications and reportedly to better monitor North Korean missile launches. / AFP / JIJI PRESS / JIJI PRESS / Japan OUT (Photo credit should read JIJI PRESS/AFP via Getty Images)