Countering Space-Based Weapons of Mass Destruction

Russia’s alleged effort to develop a space-based nuclear weapon threatens to violate the Outer Space Treaty of 1967, undermine international peace and stability, and hold at risk the peaceful use of space for all nations. Other emerging threats, such as China’s orbital bombardment system, could do the same. While the Outer Space Treaty bans the stationing of nuclear weapons or other weapons of mass destruction (WMD) in outer space, it lacks enforcement mechanisms to prevent this from happening. However, other principles of international law and tools of statecraft provide a framework in which to deter and defeat such destabilizing threats.
This post will outline the key categories of legal options to counter the threat of space-based weapons of mass destruction: diplomacy; retorsion; countermeasures; and self-defense. While practical options must be developed to make full use of this framework, the law stands ready to support them.
The Law
Based on lessons learned from U.S. and Soviet nuclear tests that damaged satellites and terrestrial infrastructure, the 1963 Limited Test Ban Treaty forbids detonating nuclear devices in or beyond the Earth’s atmosphere. In Article IV of the Outer Space Treaty, States parties also pledge “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.”
Within a year of ratification, the Soviet Union probed the boundaries of the treaty’s text by testing a fractional orbital bombardment system (FOBS), in which the Soviets launched a nuclear-capable missile into an orbital trajectory, but diverted it back into the atmosphere before completing an orbit. The United States did not consider this to violate the treaty, and China replicated the Soviet feat in 2021 while upgrading it to include a hypersonic glide vehicle. There is no international consensus on how many orbits a nuclear space weapon would need to complete to violate the treaty, and it is unknown whether the Chinese capability could also be used as a multiple orbital bombardment system (MOBS). A WMD would likely need to complete at least one orbit to violate Article IV. What, then, are the remedies if it does?
Diplomacy
The space treaties were forged through international diplomacy at the height of the Cold War space race and diplomacy remains an essential instrument through which States communicate with each other. The Outer Space Treaty, Article IX, encourages States to engage in international consultations if they anticipate a space activity will cause potentially harmful interference. States also use diplomacy to refine the contours of international law and express their normative foreign policy goals. Law-abiding States should use all diplomatic venues at their disposal to say that they will not tolerate the stationing of WMD in outer space, especially by a State party to the Outer Space Treaty.
In April 2024, responding to the initial public revelation of Russia’s nuclear anti-satellite weapon program, the United States and Japan proposed a UN Security Council resolution calling on states parties to the Outer Space Treaty to abide by the treaty’s ban on stationing WMD in outer space. After Russia predictably vetoed the resolution, the UN General Assembly passed a non-binding resolution to the same effect. As these efforts illustrate, diplomacy is a necessary but not sufficient way to address wrongful behavior by other States, especially when those States wield a Security Council veto. However, diplomacy can become more effective when accompanied by credible warnings and actions in the remaining categories of retorsion, countermeasures, and self-defense.
Retorsion
Retorsion encompasses a variety of lawful means by which a State may respond to unfriendly or unlawful acts. These include the imposition of economic sanctions, expulsion of offending States’ diplomats, and prosecution of their criminal operatives. Retorsion is appealing because it sends a stronger message than diplomacy alone and imposes tangible consequences on bad actors. Russia’s aggression in Ukraine and related subversive activities have already provoked numerous responses that can be classified as retorsion, from trade penalties to ship seizures to NATO enlargement.
However, just as retorsion has been insufficient to dislodge Russia from its illegal invasion of Ukraine, it may not be adequate to counter the threats posed by space-based WMD. States hit with economic sanctions often find ways to avoid them, diverting trade and financial transactions through friendlier third countries and developing indigenous supply chains that can compensate for a fall-off in international trade. Still, any entities discovered to be contributing to a space-based WMD supply chain should be maximally sanctioned to cut off the flow of funding and technological components that enable the development of these illegal weapons.
Countermeasures
As the International Law Commission describes them in commentaries to its Articles on State Responsibility for Internationally Wrongful Acts (2001), countermeasures are measures, short of the use of force, “that would otherwise be contrary to the international obligations of an injured State vis-à-vis the responsible State, if they were not taken by the former in response to an internationally wrongful act by the latter in order to procure cessation and reparation.” In other words, they are analogous to self-defense, but limited to non-forcible means.
A countermeasure must be directed against another State’s breach of an international obligation and be necessary and proportionate to overcome the breach. A countermeasure should, if possible, be temporary and reversible, and the State undertaking the countermeasure should call on the offending State to cease its wrongful conduct. States disagree as to whether it is always necessary to announce the countermeasure itself.
Because the Outer Space Treaty’s ban on stationing WMD in outer space benefits all States—not just parties to the treaty—a breach of that obligation would also affect all States. Thus, any State would be entitled to undertake appropriate countermeasures to respond to such a breach. Countermeasures against space-based WMD, before or after launch, could include intentional interference with communications systems, offensive cyber operations, or other non-forcible measures to disrupt, deny, disable, or delay the use or deployment of the system.
However, these measures may be difficult to achieve or persist in as a practical matter. A countermeasure may cease to be effective as soon as a jammer stops radiating, the targeted satellite moves out of range, or the operator installs a software patch. For a persistent threat such as orbital WMD, a more permanent solution may therefore be required.
Self-Defense
The UN Charter requires States to settle their disputes by peaceful means “in such a manner that international peace and security, and justice, are not endangered” (art. 2(3)). It also forbids “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” (art. 2(4)). In addition, it recognizes that “Nothing in the present Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs …” (art. 51). Thus, States may use force against other States only in national or collective self-defense, or when authorized by the Security Council (art. 42). However, because any permanent Security Council member may veto action against itself or a client State, self-defense is the only reliable justification for the international use of force.
The right of self-defense has long been understood to include a right to use force to preempt an attack, but only in narrow circumstances. In 1625, Grotius argued,
apprehensions from a neighbouring power are not a sufficient ground for war. For to authorize hostilities as a defensive measure, they must arise from the necessity, which just apprehensions create; apprehensions not only of the power, but of the intentions of a formidable state, and such apprehensions as amount to a moral certainty.
Likewise, as U.S. Secretary of State Daniel Webster stated in his famous Caroline case correspondence, now recognized as an expression of customary international law, the necessity of self-defense must be “instantaneous, overwhelming, and leaving no choice of means and no moment for deliberation.” Put another way, an enemy must have both the capability and intent to launch an imminent attack or be so close to doing so that striking first is the only way to neutralize the threat.
Preemptive self-defense justified Israel’s strikes against its would-be attackers at the outset of the Six-Day War in 1967 and the under-construction Syrian nuclear reactor in 2007. Somewhat more controversially, it also underpinned Israel’s destruction of Iraq’s Osirak nuclear reactor in 1981 and the U.S.-led invasion of Iraq in 2003, which sought to eliminate threats that were arguably more remote, though no less dangerous.
I contend that a nuclear space weapon would be analogous to the former Iraqi and Syrian nuclear reactors as an unlawful and highly dangerous capability that deserves to be neutralized before it can become operational, and certainly before it is ever used. However, the threat would need to be recognized as imminent before any use of force in self-defense. The determination of imminence will depend on reliable and well-sourced intelligence, which may or may not be available before the danger manifests.
For example, now that Russia knows that we know of its desire to build a nuclear space weapon, it may redouble its efforts at concealment and obfuscation. Thus, substantial resources should be devoted to learning all we can about the status of any foreign space-based WMD program and the country’s intentions for it. Just as China’s 2021 FOBS test helped to spur U.S. development of the Proliferated Warfighter Space Architecture to track novel and maneuverable hypersonic weapon threats, both space domain awareness and all-source intelligence capabilities should focus on discovering and characterizing any attempts by other countries to station WMD in outer space.
In addition to being able to assess the imminence of a space-based WMD attack, questions about the feasibility of action and the risk of escalation loom large. Unlike Iraq and Syria, which lost their nascent nuclear capabilities before they were completed, Russia and China are mature nuclear powers with immense geographic depth and retaliatory capacity. Thus, not only must the assessment of a threat’s imminence be on solid footing, but any preemptive action must be calculated to be both achievable and more conducive to long-term peace and stability than the alternative. It should also be done, to the maximum extent possible, in a way consistent with U.S. policy and messaging about responsible behaviors in space.
To increase the odds of success—or better still, to amplify the prospects for diplomacy and deterrence to make preemption unnecessary—nations that want to be able to prevent a weapon of mass destruction from being stationed in outer space should develop a variety of means to negate such a weapon. These means could be overt or covert, reversible or irreversible, space-based or terrestrial. States should prefer means that are non-attributable and that result in low collateral damage, but destructive action should not be ruled out. A cloud of space debris from one dead illegal space weapon should be less worrisome than the risk of that weapon being used to wipe out a vast number of active satellites and render low-Earth orbit uninhabitable. However, an unsuccessful preemption attempt that precipitated a “use it or lose it” detonation would have consequences just as tragic as those it was trying to prevent.
Conclusion
A nuclear weapon in orbit threatens to undo decades of international achievement, undermine international peace, and wipe out a $384 billion space economy on which the world depends. That’s why it’s illegal under the Outer Space Treaty, and that’s why it can’t be allowed to happen. Diplomacy, retorsion, countermeasures, and self-defense are legal options that peace-loving States can employ to counter the development, deployment, and use of space-based WMD. May we use them wisely.
The opinions expressed in this post are the author’s own and do not necessarily reflect the views of the Department of Defense, the Department of the Air Force, or any of their components or members.
***
Major Brian D. Green serves as the Chief of Space and Operations Law for Space Training and Readiness Command (STARCOM) in Colorado Springs, Colorado.
Photo credit: NASA via Unsplash