Space Warfare: Deterrence, Dissuasion and the Law of Armed Conflict


We humans have a habit of allowing the latest technological marvels to overwhelm our more critical strategic sense.  

Colin S. Gray

Early in his administration, President Barack Obama emphasized that space is vital to U.S. national interests. Both the U.S. Department of Defense and the intelligence community underscored this same point, while also highlighting the increasingly congested, contested, and competitive nature of space. Despite all this official focus on space, U.S. military and intelligence leaders remain worried that American satellites are vulnerable to attack, because countries — like China — have been developing anti-satellite weapons capable of attacking vital U.S. space assets.

Secure access to space is a critical U.S. national interest because space provides a decision advantage and is vital to monitoring strategic and military developments. Yet, despite notable national security interests in space and potential emerging threats to those interests, U.S. space strategy remains unclear. A major reason for this is a misguided belief by some strategists and policymakers that war in space will somehow be “new,” where traditional principles of warfare have little applicability. Yet, as Colin Gray observes, war has a constant nature but an ever-changing character. Therefore, much of what is most important about war and warfare does not change, even as technology advances. Historical experience and thinking on strategy can therefore help policy makers consider the proper relationship between deterrence, dissuasion, and the Law of Armed Conflict (LOAC) in space. Without this fundamental understanding, the fear is that future space systems may be developed that fail to protect national interests in space.

Deterrence and the Law of Armed Conflict

Deterrence in space, like in other areas, is based on the view that credible and potentially overwhelming force or other retaliatory action against any would-be adversary is sufficient to deter most potential aggressors from conducting hostile actions in space. This is deterrence by punishment. Accordingly, deterrence is most effective if there is a credible threat of retaliatory action or force in response to a hostile act. Within the defense community, what is considered a credible action following an armed attack is typically governed by the LOAC, which is sometimes also referred to as the Law of War.

The LOAC is based on two main sources: The first is customary international law arising out of hostilities and binding on all states. The second is international treaty law, which binds only those states having ratified a particular agreement. The purpose of the LOAC is to reduce the damage and casualties of any conflict, protect combatants and noncombatants from unnecessary suffering, safeguard the fundamental rights of combatants and noncombatants, and make it easier to restore peace after the conflict’s conclusion.

Two principles contained in the LOAC are most germane following an armed attack in space (Note that armed attack is the phase used in the United Nations Charter, Article 51): these are the principles of lawful targeting and military necessity. Together, these principles form part of the basis to consider damage resulting from an attack on a legitimate military objective before the act occurs.

The principle of lawful targeting, which is inclusive of the principle of distinction, is based on three assumptions: a belligerent’s right to injure the enemy is not unlimited, targeting civilian populations for attack is prohibited, and combatants must be distinguished from noncombatants to spare non-combatants injury as much as possible. Military objectives — the only legitimate targets — are combatants and those objects which by their nature, location, purpose, or use effectively contribute to the enemy’s war-fighting or war-sustaining capability.

The second principle of military necessity calls for using only that degree and kind of force required for the partial or complete submission of the enemy, while considering the minimum expenditure of time, life, and physical resources. This principle is sometimes also referred to the principle of proportionality. Although the principle of military necessity recognizes that some collateral damage and incidental injury to civilians may occur when a legitimate military target is attacked, it does not excuse the destruction of lives and property disproportionate to the military advantage to be gained.

What this Means for Space Warfare

The connection between the LOAC and space warfare has four aspects. First, the inherent right of self-defense applies to satellites and other critical space systems. Some have questioned if this right applies to satellites, under the adage that “satellites don’t have mothers.” If no human life is directly threatened by an armed attack in space, then, in theory, there is no need to protect or defend satellites through military means. Under Article 2(4) of the United Nations Charter, the need to refrain from the threat or use of force against a state’s territorial integrity — which includes physical property — is described. More specifically, under the U.S. Chairman of the Joint Chiefs of Staff Standing Rules of Engagement, national self-defense and collective self-defense are defined as applying to both persons and property. Recent public comments by U.S. military leadership also support the view of the right of self-defense applying in space.

Second, taking into account the principles of targeting and necessity, it is not unlawful to cause collateral damage to the natural environment during an attack upon a legitimate military objective. Creating orbital debris to achieve military objectives is thus permissible. That said, during war, means should be employed to protect and preserve the natural environment in space, and the destruction of the orbital environment through debris generation not necessitated by mission accomplishment and carried out wantonly is prohibited. Any anticipated orbital debris resulting from an attack on a legitimate military objective should be considered during targeting analysis.

Third, during future conflicts, there may be the need to not only target a specific satellite but a specific subsystem on that satellite. Under the LOAC, targeting distinction between multiple hosted payloads or subsystems on a single satellite is likely needed. Because today’s commercial satellites may have multiple paying customers with different hosted payloads on each satellite, the principle of lawful targeting conveys the need to only target a specific subsystem on a satellite relating directly to the military objective. For example, the military may use commercial satellites for some communications, and so only that subsystem being the military object should be considered during the targeting process. This same idea of specific targeting also holds when considering jamming and interference of signal bandwidth used for military purposes.

Fourth, adherence to the principle of military necessity does not preclude responding to an armed attack in space in a different domain. Therefore, if a system or asset considered essential is attacked in space, a response can include actions on land, at sea, or in the air. Needing to protect national interests in space through military action means potentially risking human life to defend and protect critical space assets. Hence, those seeking to protect national interests in space may need to put service members in harm’s way, and a legitimate response to a hostile act under the LOAC may cause loss of life.

Counterarguments to Military Action

Two counterarguments against the views presented here are that military action in space is prohibited under the 1967 Outer Space Treaty, and there is no agreed upon definition of what constitutes armed attack in space. Some arms control advocates interpret the 1967 Outer Space Treaty’s phrase “peaceful purposes” as meaning non-aggressive and therefore equal to the prohibition on the use of force in space. Indeed, the treaty’s language delineates the need to limit the use of the moon and other celestial bodies exclusively for peaceful purposes and expressly prohibits their use for establishing military bases, installations, or fortifications, or testing weapons of any kind, or conducting military maneuvers. Therefore, the phrase “peaceful purposes” refers to the use of the moon and other celestial bodies. More importantly, the treaty specifically acknowledges the need to act in accordance with international law, including the Charter of the United Nations, to maintain international peace and security. Given that the charter legitimates military action in response to a hostile action or armed attack, such legitimacy would extend to space as well.

Another frequent counterargument against military action in space is that, because there is no agreed upon definition of what constitutes a hostile act or armed attack in space, a military response is not a viable consideration. Specifically, a future adversary could employ non-kinetic and reversible actions, such as jamming and electro-magnetic interference. Some strategists question whether non-kinetic and reversible actions are hostile acts or armed attacks that warrant a military response.  Without an agreed upon understanding of hostile act or armed attack, the concern is that it is difficult to determine whether a military response is warranted or legal under the LOAC.

Ultimately, what is a hostile act or armed attack in space will depend on the broader, geopolitical context. As Thomas Schelling underscores, intentions matter. More often than not, hostile acts in space will be undertaken to achieve some effect on Earth. So, following non-kinetic or reversible actions in space, the intentions of the action must be considered, including whether such action seeks an operational advantage or a political effect. If national security is threatened by an action in space, a military response remains a legitimate response option, per the U.N. charter.


The other aspect of a holistic space strategy seeking to influence the decision calculus of potential adversaries is dissuasion, which is meant to discourage the initiation of military competition. To be effective, dissuasion activities must occur before a threat manifests itself. Dissuasion includes “shaping activities,” which are typically nonmilitary in scope and conducted during peacetime. Within the U.S. military lexicon, dissuasion is said to work outside the potential threat of military action and has been called a kind of “pre-deterrence,” or deterrence by denial. A strategy incorporating dissuasion seeks to convey the futility of conducting a hostile act, thereby causing a potential adversary’s leadership to not pursue a military confrontation in the first place. Dissuasion in space should focus on two areas: resilience and space forensics.

A potential adversary may be dissuaded if it concludes that an attack in space will be ineffectual. In the parlance of today’s space professionals, this is the realm of resiliency. There are multiple and lengthy definitions of resiliency and they tend to lack clarity. In the end, measures that somehow dissuade a military confrontation should all be considered desirable and viable. These can include including distribution, redundancy, maneuverability, and protection. Any resiliency measures, however, must be widely publicized to be effective.

The second aspect of dissuasion is having a reliable and responsive space forensics capacity to assist in the attribution process following a hostile act. As defined here, space forensics includes catalog information, along with data and signal analysis from satellites or ground systems, to help identify details of a hostile act. Space forensics, along with information from law enforcement and intelligence community sources, support the attribution process in assigning responsibility following a hostile act. A robust and effectively communicated capability to rapidly identify and attribute the source of attack in space or on critical ground segments may help dissuade potential adversaries who would only attack if their identity would remain unknown. Following a hostile act in space, a forensics capability informing the attribution process may lead to prosecution through civilian courts or for more significant acts of aggression it may lead to targeting with kinetic or non-kinetic weapons against those attributed for the attack. A significant part of this forensics capability will be space situational awareness (SSA) capabilities, which are intended to provide knowledge of space objects and activities along with supporting timely attribution. These SSA capabilities may be either governmental or commercial in nature.

Moving Forward

Deterrence, dissuasion, and the LOAC have applicability when considering space strategy, just as in other media of warfare. Moreover, concepts like extended deterrence and the Third Offset may also hold promise in the space domain and deserve further study.

Despite the potential utility of deterrence and dissuasion in space strategy, the U.S. and international community have more work to do to achieve the greatest security benefits. To support credible deterrence efforts, norms of acceptable behavior in space should be developed and agreed upon and what constitutes hostile intent, hostile act, and armed attack in the space domain needs to be clearly articulated and understood. To support opportunities for dissuasion, improved SSA and space forensics capabilities are needed, to enable timely and credible attribution. Of note, improved resiliency measures do not necessarily require technological advancements but may instead rely on more distributed architectures, changing the way operators solve irregularities on orbit or cross-domain solutions using today’s technology.

History teaches deterrence will at times fail due to miscalculation, uncertainty, or chance. This may also be the case for deterring acts of aggression in space. If deterrence fails and hostile action occurs, having widespread resiliency measures in place will help mitigate the most severe consequences resulting from space attacks. Taking action now to develop sound space strategy grounded in the LOAC, including the roles of deterrence and dissuasion, will help promote peace and stability in space among the international community.


John J. Klein is a Senior Fellow at Falcon Research in northern Virginia. He holds a Ph.D. in politics, with a strategic studies focus, from the University of Reading. Dr. Klein is the author of Space Warfare: Strategy, Principles and Policy (2006), and he writes frequently on national policy, military strategy, and the implications of the Law of Armed Conflict. The views expressed in this article are solely those of the author and do not necessarily reflect those of Falcon Research or those of the U.S. government.

Image: NASA

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