Countering Space-Based Weapons of Mass Destruction

By Major Brian D. Green

Article published on: May 30, 2025 in the Army Lawyer issue 1 2025 Edition

Read Time: < 47 mins

A NASA spacecraft carrying a satellite payload launches atop a SpaceX Falcon 9 rocket from Space Launch Complex 40 at Cape Canaveral Space Force Station in Florida. (Credit: Denny Henry, NASA)

How should the United States respond if another country attempts to station a nuclear weapon in outer space? Although the Outer Space Treaty of 1967 (OST) forbids stationing nuclear weapons and other weapons of mass destruction (WMD) in outer space, prohibition does not guarantee prevention. ¹ Certain powerful states, possessing significant space and nuclear capabilities, habitually violate international law and have tested capabilities that probe the OST’s boundaries. For example, since February 2024, U.S. Government officials have warned the public that Russia may be preparing to violate this core OST mandate. ² This chilling prospect is far from inconceivable. This article will outline the reasons why a state might seek to station a nuclear weapon in outer space, why a state might refrain from doing so, and detail a range of legal response options for the United States and the rest of the world to consider. If another country does decide to flout international law by placing a nuclear weapon in orbit, installing it on a celestial body, or otherwise stationing it in outer space, other states must be prepared to act with all lawful means at their disposal to deter and defeat such actions. Only then may humanity be protected from the threat of space-based nuclear weapons.

Nuclear Space Threats

Russia

Russia’s full-scale invasion of Ukraine in 2022, accompanied by its nuclear saber-rattling against countries that might seek to intervene, has raised the specter of nuclear war to a level perhaps not seen since the Cuban Missile Crisis. ³ Like the Soviet Union during the Cold War, Russia developed an “escalate to de-escalate” doctrine ⁴ that could lead it to employ relatively low-yield “tactical” or “non-strategic” nuclear weapons ⁵ to gain an offensive advantage or to compensate for conventional battlefield losses ⁶ —of which it has suffered many in the Ukraine conflict. ⁷ Although some analysts believe Russia now has a higher threshold for nuclear use, ⁸ the continuing bellicose rhetoric of Russian officials, ⁹ combined with Russia’s illegal claims to have annexed Crimea and four other Ukrainian oblasts, ¹⁰ suggests that the threshold may still be too low for comfort. ¹¹ Russian leaders also claim to be developing new kinds of nuclear or nuclear-capable weapons, ¹² and Russia has violated numerous arms control treaties and commitments, ¹³ culminating in Vladimir Putin’s February 2023 announcement that Russia was suspending its participation in the strategic arms reduction treaty known as New START. ¹⁴ In general, Russia under Putin, as under Soviet leaders before him, has taken an instrumentalist approach to international law. ¹⁵

In addition, Russia, China, and other countries have been developing and testing a wide variety of space-based and counterspace weapons. ¹⁶ As then-Lieutenant General B. Chance Saltzman said in his confirmation hearing to become the U.S. Space Force’s second Chief of Space Operations, “I’m worried about the pace with which they are making those changes, China first amongst them but Russia also which is committed to investing heavily in the kinds of capabilities that are going to disrupt, degrade or even destroy our on-orbit capabilities.” ¹⁷

A key demonstration of such capabilities occurred in November 2021, when Russia conducted its first-ever direct-ascent anti-satellite (ASAT) missile test to successfully destroy a satellite in low Earth orbit (LEO), irresponsibly doubling the debris conjunction risk for the International Space Station and endangering the lives of the ISS crew, including Russian cosmonauts. ¹⁸ Indeed, although he did not explicitly claim that Russia had violated the OST, the immediate response of General James Dickinson, then-Commander, U.S. Space Command (USSPACECOM), was that “Russia has demonstrated a deliberate disregard for the security, safety, stability, and long-term sustainability of the space domain for all nations.” ¹⁹ Although many countries condemned the test, ²⁰ Russia displayed no remorse. The Russian Ministry of Defense claimed that the fragments “did not pose and will not pose a threat to orbital stations, spacecraft, or space activities” and that they were “immediately taken under surveillance until they were destroyed.” ²¹ Meanwhile, state television host Dmitry Kiselyov broadcasted that Russia now had the ability to destroy the entire U.S. Global Positioning System (GPS) satellite constellation. ²²

Russia’s co-orbital ASAT testing and “inspector satellite” stalking of U.S. intelligence satellites also suggest a willingness to flout the New START restrictions on interference with national technical means of treaty verification by conducting uncomfortably close approaches with a capability designed to fire a high-velocity projectile in orbit. ²³ Russia allegedly launched its newest version of this type of orbital weapon on 16 May 2024—mere weeks after insisting that the United Nations (U.N.) Security Council should ban all placement of weapons in space while vetoing a resolution to reaffirm the OST’s ban on stationing nuclear weapons in space. ²⁴

Russia’s Security Council veto was all the more troubling because of what it sought to conceal. On 14 February 2024, the House Permanent Select Committee on Intelligence Chairman, Congressman Mike Turner of Ohio, alleged that there was a serious national security threat that should be made known to the public. ²⁵ The next day, White House Deputy Press Secretary John Kirby acknowledged that this threat was “an anti-satellite capability that they’re developing,” while stating, “We are not talking about a weapon that can be used to attack human beings or cause physical destruction here on Earth” and parrying press questions about whether the capability was “nuclear-capable.” ²⁶

As details were sparse, some commentators initially speculated that this could be a nuclear-powered electronic warfare system rather than a satellite designed to produce a nuclear detonation in space. ²⁷ While a nuclear-powered space weapon would be troubling, it would not necessarily be illegal. However, Assistant Secretary of Defense for Space Policy Dr. John F. Plumb added more details when he testified to Congress in May. He stated,

Russia is also developing a concerning [ASAT] capability related to a new satellite carrying a nuclear device that Russia is developing. This capability could pose a threat to all satellites operated by countries and companies around the globe, as well as to the vital communications, scientific, meteorological, agricultural, commercial, and national security services we all depend upon. ²⁸

This characterization suggests that a satellite-mounted “nuclear device” will be the key mechanism by which the “ASAT capability” threatens “all satellites” in orbit. The remainder of this article will therefore focus on the very real risk that Russia will attempt to place a nuclear weapon in orbit, and argue that such threats demand a serious, deliberate, and full-spectrum response.

China

Russia is not alone in flouting international law and posing a nuclear threat to the United States. Like Russia, China tends to discount the idea of a rules-based international order to which China is accountable, preferring instead to engage in “legal warfare” in which the law is just one more weapon in the Chinese Communist Party’s arsenal. ²⁹ For example, China recently violated international law and U.S. sovereign airspace by flying a high-altitude spy balloon across Alaska, Canada, and the continental United States. ³⁰ It continues to assert, and at times violently enforce, illegal maritime claims in and around the South and East China Seas, ³¹ fires potentially blinding lasers at Philippine coastguardsmen and Australian military pilots, ³² attempts to expand its land territory through border skirmishes and redrawing maps, ³³ and has been engaged in an ongoing genocide and crimes against humanity against the Uyghur people in Xinjiang province, in violation of the Genocide Convention and jus cogens requirements of customary international law. ³⁴

China is also rapidly building its nuclear arsenal to achieve parity with the United States, with the U.S. Department of Defense (DoD) estimating that China “has surpassed 600 operational nuclear warheads in its stockpile as of mid-2024 and will have over 1,000 operational nuclear warheads by 2030, much of which will be deployed at higher readiness levels.” ³⁵ This is in spite of China’s recent reaffirmation that it would “pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date.” ³⁶ And, of course, the DoD assesses, “The PRC continues to develop counterspace capabilities—including direct-ascent [ASAT] missiles, co-orbital satellites, [electronic warfare], and directed-energy systems—to contest or deny another nation’s access to and operations in the space domain.” ³⁷

The risk of the International Space Station (pictured) colliding with space debris doubled as a result of Russia’s November 2021 ASAT missile test. (Credit: NASA)

Despite China’s longstanding claim of a “no first use” policy for nuclear weapons, its rapid expansion of nuclear capability could still enable it to commit malign conventional aggression. Chinese officials have threatened nuclear strikes against the United States during previous diplomatic confrontations. ³⁸ According to Dr. Jonathan D.T. Ward, a writer and strategist with extensive experience living and working in China, and whose writings about the coming “decisive decade” in Sino-U.S. relations informed the 2022 U.S. National Security Strategy:

China’s 2021 test of a hypersonic missile and fractional orbital bombardment system, as well as its expanding nuclear silos in its western regions . . . would allow them to rely much more aggressively on conventional capabilities and even lean much more heavily into an expanding conflict below the threshold of nuclear war. ³⁹

Thus, just as Russia forestalls direct foreign intervention in the war in Ukraine by brandishing its nuclear weapons, China could threaten to use its expanding nuclear and counterspace arsenals to prevent other countries from intervening in its conquest of Taiwan, or to radically turn the tide of a war it is losing. ⁴⁰ In these scenarios, China would challenge law-abiding states to defend Taiwan without risking devastating reprisals on their own vital interests. It would also contradict China’s pledge that nuclear weapons “should serve defensive purposes, deter aggression, and prevent war.” ⁴¹

As a result of these adversaries’ threatening and often illegal activities, the 2022 U.S. National Security Strategy describes China as the “pacing challenge” for the U.S. military to deter, and Russia as an “acute threat” to be managed. ⁴² Their demonstrated willingness to violate international law, combined with their rhetoric and development of novel nuclear, space-based, and counterspace weapons, should cause U.S. and allied political and military leaders to consider what to do if Russia, China, or another country such as North Korea chooses to violate another fundamental precept of international law by stationing a nuclear weapon in outer space.

International Law Forbids Stationing a Nuclear Weapon in Outer Space

Treaty Requirements

The OST, to which all major spacefaring countries (including Russia and China) are parties, forbids states parties to place nuclear weapons or other WMD in orbit around the Earth, install them on the Moon or other celestial bodies, or station them in outer space in any other manner. ⁴³ The Limited Test Ban Treaty of 1963 also prohibits states parties from detonating a nuclear device in or beyond the Earth’s atmosphere, including outer space, or underwater, or in any environment if it would cause radioactive debris to be present outside the state’s territory. ⁴⁴ In addition, the Environmental Modification Convention prohibits using environmental modification techniques as a weapon of war, including by deliberately manipulating natural processes in outer space—a prohibition that could reasonably be understood to encompass exoatmospheric nuclear detonations that create harmful artificial radiation belts. ⁴⁵ The Soviet Union was among the first signatories and depositaries to all three treaties, and Russia remains bound by them. ⁴⁶

Mr. Dean Rusk (2nd from right), Secretary of State of the United States, signs the Outer Space Treaty at a White House ceremony. At the table (right to left): President Lyndon B. Johnson of the United States; Ambassador Arthur J. Goldberg, Permanent Representative of the United States to the U.N.; Sir Patrick Dean, Minister of State for Foreign Affairs and Permanent Representative of the United Kingdom to the UN; and USSR Ambassador to the United States Anatoly F. Dobrynin. (Credit: U.N. Photo)

Despite these clear prohibitions, neither the OST nor the Limited Test Ban Treaty is self-enforcing. Although the OST and the subsequent Liability Convention assign responsibility and liability for damage caused by space objects to launching states, ⁴⁷ and the OST includes requirements to exercise due regard, avoid harmful contamination, and engage in international consultations if states parties foresee potential harmful interference resulting from space activities, ⁴⁸ the treaty texts contain no penalties or enforcement mechanisms for a breach of these duties—or of the OST’s Article IV ban on stationing WMD in outer space. As for the Limited Test Ban Treaty, the International Court of Justice (ICJ) has opined that it is presumptively limited in scope to testing scenarios and does not necessarily constrain its parties’ actions in wartime. ⁴⁹

A FOBS Loophole?

Article IV’s scope is also limited by its own text and subsequent state practice. The fact that it requires states parties “not to place in orbit around the Earth any objects carrying nuclear weapons . . . or station such weapons in outer space” ⁵⁰ suggests that there must be a degree of permanency to the weapons’ placement in outer space for a violation to occur. The ban has been narrowly construed since its inception. In 1968, the Soviet Union tested a “fractional orbital bombardment system” (FOBS), in which ballistic missiles would be launched into an orbital trajectory but descend to strike their targets before completing a full orbit. ⁵¹ This would, in theory, have made it easier to avoid the United States and allies’ northern-tier missile warning network by sending intercontinental ballistic missiles to strike them from the south. ⁵² However, U.S. leaders concluded at the time that the testing and even the wartime use of this system would not violate the OST. ⁵³

More recently, China has tested a similar capability, mated to a hypersonic glide vehicle whose speed and maneuverability could enable it to evade modern missile defenses. ⁵⁴ It is also unclear whether China’s capability is only a FOBS or if it can function as a multiple-orbital bombardment system (MOBS) if left in an orbital trajectory for a longer period. ⁵⁵ As with the earlier Russian FOBS tests, the non-nuclear Chinese test did not violate the OST, and it probably would not violate the OST even if it were to deploy a nuclear weapon on only a partial orbital or sub-orbital trajectory. However, it increases China’s potential to violate the OST by placing a nuclear weapon into orbit and keeping it there with very little warning. Journalists have also speculated that China’s Shenlon reusable spaceplane, which has deployed and recaptured other objects in orbit, could also be used for short-notice orbital bombardment. ⁵⁶

Recognizing the muted international response to their exploitation of the FOBS loophole and other provocations, countries such as Russia and China might be tempted to test the limits of other countries’ strategic patience, space domain awareness, and willingness to enforce international law by placing a nuclear weapon in orbit. As outer space becomes more clearly recognized as a warfighting domain, it is vitally important to deter the deployment of, and be prepared to defend against, a nuclear-armed satellite and other possible space-based WMD.

Why the Space WMD Bans Make Sense

One may ask, what makes the possibility of a space-based nuclear weapon uniquely dangerous? After all, the U.S. nuclear triad of land-based intercontinental ballistic missiles, submarine-launched ballistic missiles, and bomber aircraft is designed to be able to strike anywhere in the world at high speed and with minimal warning or detection. ⁵⁷ Why shouldn’t a state opt to add a fourth domain of outer space to deliver its nuclear weapons?

There are two crucial differences: illegality and the inherently indiscriminate and offensive nature of space-based nuclear weapons. First, even the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) and the ICJ recognize that terrestrial nuclear weapons programs may lawfully exist for deterrence and self-defense. ⁵⁸ But space-based nuclear weapons are unlawful under the OST, at least for all its parties, which include all states that are known or believed to possess nuclear weapons. ⁵⁹

In addition, while individual nuclear weapons may conceivably be used in a terrestrial conflict in a way that their effects are largely localized and proportionate under the circumstances, a nuclear weapon detonated in Earth’s orbit would inevitably cause severely deleterious effects for a large number of satellites, irrespective of their state of registry. In addition to ending or significantly reducing many satellites’ useful lifespan, the nuclear radiation could render them unable to conduct station-keeping, collision avoidance, or end-of-life disposal maneuvers, thus exacerbating the problem of long-lived orbital debris and the risk of a “Kessler cascade.” ⁶⁰ For all these reasons, the treaty prohibitions against stationing or detonating a nuclear weapon in outer space remain utterly sound and should be honored by all nations.

Potential Motivation to Deploy Nuclear Weapons in Space

Why might a state attempt to station a nuclear weapon in outer space? Why would a state be willing to risk the international opprobrium that would ensue? Perhaps more importantly, why would a state be willing to put its own space assets—and potentially even its own astronauts—at risk from the effects of a nuclear detonation in outer space? Didn’t the world learn enough about the harmful effects of exoatmospheric and high-altitude nuclear testing in the run-up to the Limited Test Ban Treaty that it should now be unthinkable to seek to detonate a nuclear device in space in the first place?

As to the first of these questions, a country might want to have a nuclear weapon in outer space for a variety of reasons. A space-based nuclear weapon could take different forms, depending on whether it is designed to be detonated in outer space or deliver a nuclear payload to a target on Earth. A space-based nuclear bombardment system could be used for coercive leverage as an orbital sword of Damocles, hanging over the heads of any country below.

What if the weapon were intended to be used against targets in outer space rather than on Earth? The nuclear device tests that preceded the Limited Test Ban Treaty had a variety of effects on space systems, mostly harmful. ⁶¹ In outer space, they created artificial radiation belts that shortened the lives of many other satellites in orbit. ⁶² For example, U.S. and Soviet exoatmospheric nuclear testing degraded the functional life of Telstar-1, the first commercial communications satellite, and Ariel-1, the United Kingdom’s first satellite. ⁶³ On Earth, they created electromagnetic pulse effects that disrupted communications and energy transmission, often inadvertently harming the countries that conducted them. ⁶⁴ The effects of a nuclear detonation in space are impossible to localize and may run afoul of the law-of-armed-conflict principles of distinction and proportionality depending on how they are used in war. ⁶⁵

Perhaps if a country believed it could conduct a nuclear attack in space that would inflict more harm on its enemies than on itself, it would consider the attack as in its interest to commit. As with the kamikaze attacks of World War II or the suicide bombings of modern terrorists, perhaps if a country had relatively little to lose in space, but could cause a disproportionate amount of damage to its foes through an indiscriminate nuclear attack, it would do it. North Korea and Iran, with their nascent space programs and burgeoning missile programs, might most closely fit this profile, although Iran has not yet announced a nuclear weapon capability. ⁶⁶ Russia, with its deteriorating space program, ⁶⁷ high tolerance for losses on its own side, ⁶⁸ and disregard for the interests of other states, might also resort to such measures in extremis, or even for offensive advantage. Any of these states might see a nuclear attack in space as an effective way to counter other countries’ attempts to assure resiliency in space through widely proliferated satellite constellations such as Starlink. ⁶⁹

One potential upside to China’s growth as a major spacefaring nation is that its own extensive use of space probably reduces the appeal of a nuclear strike in space. Indeed, in response to Vladimir Putin’s recent intimations about nuclear readiness, Chinese foreign ministry spokesman Wang Wenbin reiterated the five major nuclear powers’ agreement that a nuclear war “cannot be won and must never be fought.” ⁷⁰ However, China’s FOBS development requires recognition of the risk that China could someday seek to bombard another country with space-based nuclear weapons, even if they are not in orbit for long.

Launch of Shenzhou 13 a Chinese spaceflight to the Tiangong space station. (Source: Creative Commons)

Response Options in International Law

In international law, states have a variety of means available to respond to internationally wrongful acts. Options, ranging from least to most severe, may include diplomacy, retorsion, countermeasures, or even the use of force in self-defense. This article will discuss these options and then look at historical examples of state responses to other states’ development of WMD for insights into potentially appropriate responses to WMD in outer space. Vignettes will include the Israeli strikes on under-construction Iraqi and Syrian nuclear reactors, U.S. and coalition use of force to end Iraqi and Syrian chemical weapons programs, the Stuxnet cyberattack on Iran’s nuclear program, and the international response to North Korea’s nuclear weapons program.

Diplomacy

In international relations theory, a state’s “instruments of national power” are often summarized with the acronym DIME to represent the state’s means of exerting diplomatic, informational, military, and economic leverage over other states or institutions. ⁷¹ Diplomacy, the “D” in DIME, refers to the way a state conducts its foreign policy, and it encompasses statements and actions by the head of state, the foreign minister or secretary of state, ambassadors, and other political appointees and career diplomats in the country’s foreign service. ⁷² It also includes the negotiation and enforcement of treaties and other international agreements. ⁷³ It is often seen as a “soft” instrument of national power, insofar as it largely relies on state officials speaking with each other, with the public, or in international forums, to advance their respective foreign policy interests. ⁷⁴ However, if a state’s diplomacy takes the form of coercive threats, backed up by the economic and military instruments of power, it can become “harder.” ⁷⁵

When a state believes another state has wronged it, diplomacy is often one of the first means of recourse. The affected state may engage in private back-channel communications to complain of the wrong and request redress, including by a démarche—

a strongly worded diplomatic letter demanding the other state cease its bad behavior. ⁷⁶ If the state views these means as insufficient to produce the desired change, it may lodge its complaint in public. ⁷⁷ This may even take the form of a proposed U.N. General Assembly or Security Council resolution, or a request for action by another treaty-monitoring body.

What would the right diplomatic strategy for addressing space-based nuclear weapons look like? Initially, it should focus on deterring any state from developing or deploying them. This campaign would include continuing to promote accession to the OST among countries that have not ratified it yet, emphasizing the treaty’s benefits for ensuring peaceful coexistence in space, and advocating for continued adherence to treaties such as the Limited Test Ban Treaty and the NPT. If a country appeared to be developing space-based WMD, those who detected it could privately warn the bad actor to stop or could reveal what they know to other countries to build international pressure against the illegal weapons development.

Venues for discussions within the U.N. should include the Committee on the Peaceful Uses of Outer Space, the Conference on Disarmament, the First Committee, the Security Council, and the General Assembly. Although Russian and Chinese diplomats representing their countries’ permanent seats on the U.N. Security Council and other bodies are often intransigent on space security matters, ⁷⁸ they may be marginally more receptive to arguments directed against the likes of Iran or North Korea rather than themselves. ⁷⁹ Even if they refuse to cooperate, presenting a draft Security Council resolution to condemn and authorize action against space-based WMD would put them on the record as having accepted, abstained from voting on, or vetoed the resolution. ⁸⁰

In fact, that has already happened. On 24 April 2024, the United States and Japan presented a Security Council resolution, backed by sixty-five total co-sponsors, to reaffirm that all OST parties should comply with the treaty’s ban on stationing WMD in outer space and should not develop WMD intended for placement in space; Russia vetoed the resolution, and China abstained. ⁸¹ Subsequently, the General Assembly passed a non-binding resolution to the same effect. ⁸²

Could a country simply withdraw from the OST or decline to ratify it in the first place to evade the prohibition? Perhaps. By nature, treaties are only binding as a matter of affirmative consent between their parties. ⁸³ However, some treaty provisions have become so widely followed that even non-parties have affirmed them as customary international law. ⁸⁴ Even as he exercised Russia’s veto of the proposed U.N. Security Council resolution discussed above, Russian U.N. ambassador Vasily Nebenzia affirmed that the OST’s Article IV obligation remained binding and averred that the U.N. Security Council resolution was therefore unnecessary. ⁸⁵

In the wake of Russia’s veto, the United States and like-minded countries should begin seeking to promote the notion that OST Article IV’s ban on space-based nuclear weapons has crystallized into customary international law, and seek to garner official statements from as many states as possible affirming the same. Although the formation of customary international law may be hindered by persistent objections from leading states such as Russia, any existing state party to the OST would be on shaky ground to raise such an objection, given that they have already agreed to the rule in the treaty. ⁸⁶ If they decided to disregard the rule anyway, having it widely recognized as customary international law could help to enhance the international legitimacy of any response to the breach.

Of course, diplomacy without a credible promise of action to back it up is ineffective at best, and often counterproductive. Recall former President Barack Obama’s stern warnings that Syrian dictator Bashar al-Assad would cross a “red line” if he used chemical weapons against his own people again—and the lack of meaningful consequences when Syria crossed that “red line.” ⁸⁷ It wasn’t until years later, when the United States, France, and Britain launched strikes destroying Syria’s chemical weapons facilities that Syria finally stopped using chemical weapons against civilians—and even then, only for a time. ⁸⁸ Diplomatic messaging must be accompanied by follow-through. If leaders determine that additional legislative support is necessary or desirable to accomplish that follow-through, they should seek to build and gain assurance of that support before committing to act. This is especially important if leaders perceive a significant risk of escalation.

It remains to be seen what options the world might pursue now that Russia has vetoed the Security Council resolution calling for compliance with the OST’s WMD ban. If diplomacy fails to deter a country from developing space-based WMD, it would face similar challenges in dissuading the weapon’s deployment or use. Therefore, additional options must be considered to strengthen the diplomatic hand.

Retorsion

Retorsion refers to unfriendly but lawful ways a state may respond to another state’s unwelcome acts. ⁸⁹ These are means within a state’s inherent legal authority, such as the ability to unilaterally impose or advocate for other countries to support international economic sanctions and the ability to expel another country’s diplomats or prosecute their spies. ⁹⁰ The United States and its allies have made extensive use of retorsion to respond to Russian aggression in Ukraine. While not desiring for NATO members or any other countries to become a party to the conflict, the free world has imposed unprecedented economic sanctions against Russia and many of its key officials, expelled Russian diplomats suspected of spying, reduced participation with Russia in many international cooperative endeavors and forums, expanded the NATO alliance to include Finland and Sweden, and sold, lent, and donated hundreds of billions of dollars’ worth of military equipment, training, and humanitarian relief aid to Ukraine. ⁹¹ While Russia continues to criticize these actions, it has not conducted an overt armed attack on any NATO member in response.

Retorsion is appealing because it sends a stronger message than diplomacy alone and imposes tangible consequences on a bad actor. Its measures can be calibrated to the needs of the situation and easily stopped if the offending country ceases its bad behavior. Retorsion should certainly be considered as part of a response to space-based WMD development. For instance, individuals involved in any space WMD program could be targeted with travel bans, international arrest warrants for crimes they are suspected to have committed, asset seizures, or financial restrictions on foreign transactions.

However, just as retorsion has been insufficient to end the conflict in Ukraine, it may be inadequate 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 maintain resilience despite a fall-off in international trade. ⁹² If a country is committed to developing space-based nuclear weapons, diplomacy and sanctions may delay them, but they will not ultimately prevent them from doing so.

For example, even though most countries adhere to the NPT, ⁹³ Russia and China have stymied international efforts to protect Ukraine’s Russian-occupied Zaporizhzhia nuclear power plant and restrict the development of fissile material for nuclear weapons; ⁹⁴ several countries besides the original NPT-recognized nuclear powers have developed their own nuclear weapons; ⁹⁵ and Iran may be on the verge of a nuclear breakout. ⁹⁶ No amount of economic or diplomatic pressure has caused these countries to forswear the buildup of their own nuclear arsenals.

Countermeasures

When a state violates an international obligation without using force, a state injured by the violation may respond with countermeasures. In the international law context, 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.” ⁹⁷ In other words, they are analogous to self-defense, but limited to non-forcible means. Although these means would normally be considered wrongful in the absence of another state’s provocation, the wrongfulness of a countermeasure may be precluded if it is directed against another state’s breach of an international obligation, and if it is necessary and proportionate to overcome the breach. ⁹⁸ A countermeasure should, if possible, be temporary and reversible, so that the states involved may resume fulfilling the obligations they owed each other before the breach that provoked the countermeasure. ⁹⁹

The ICJ has opined that the state exercising a countermeasure must also warn the offending state to stop before it undertakes the countermeasure. ¹⁰⁰ As an example of this, the United States notified Russia of countermeasures the United States planned to take in response to Russia’s violations of the New START Treaty. ¹⁰¹ However, some states have denied that notification is always a requirement; they observe that, at least in the case of countermeasures in cyberspace, it may undermine the effectiveness of the countermeasure to provide notice to the offender because the originally offending state could take the notification as a cue to start circumventing the countermeasure. ¹⁰² This argument should apply in the space context as well. If a state conducting a countermeasure reasonably expects the state committing the original breach to evade a countermeasure if it becomes aware of it, yet that the countermeasure would likely be effective if unannounced, the state undertaking the countermeasure should not be required to give notice in a way that would defeat the purpose of the countermeasure.

What might countermeasures look like in space? The U.N. Charter recognizes that “complete or partial interruption of economic relations and of rail, sea, air, postal, telegraphic, radio, and other means of communication, and the severance of diplomatic relations” are all “measures not involving the use of armed force.” ¹⁰³ While this section is in the chapter that enumerates the powers of the Security Council, its language defining these measures as “not involving the use of armed force” is not expressly restricted to its context. Thus, space electromagnetic warfare techniques or defensive and offensive cyber operations that disrupt or deny satellite communications would not involve the use of force. Therefore, they could potentially qualify as valid countermeasures, provided they met the other criteria of necessity and proportionality and were directed at achieving the cessation of another country’s breach of international law.

It should be noted that, ordinarily, intentionally causing harmful interference with satellite communications violates international law. The International Telecommunication Union (ITU) Constitution prohibits causing harmful interference with radiofrequency communications. ¹⁰⁴ However, it also recognizes that military radio installations “retain their entire freedom,” while providing that they “must, so far as possible, observe statutory provisions relative to . . . the measures to be taken to prevent harmful interference.” ¹⁰⁵

Construing the “entire freedom” for military radio installations broadly, as the language itself suggests, it would appear that the ITU Constitution encourages military radio installations to avoid causing unintentional harmful interference in accordance with their country’s domestic laws. However, if a military radio installation’s purpose is to conduct communications jamming in the context of an armed conflict, it would not be “possible,” consistent with mission requirements, to avoid causing harmful interference. ¹⁰⁶ Therefore, intentional satellite communications jamming, when done by a military unit for a valid military purpose, would not necessarily violate the ITU Constitution. ¹⁰⁷

However, even if military satellite jamming were considered to violate the ITU Constitution under some circumstances, if a state sought to jam a satellite’s signals to induce the satellite’s launching state to cease its own violations of international law (in this case, stationing WMD in outer space), the jamming could be a lawful countermeasure. ¹⁰⁸ Under these circumstances, any perceived wrongfulness of the jamming would be precluded. Thus, military units could legitimately conduct electromagnetic spectrum operations against a satellite with a WMD payload or its supporting infrastructure if appropriate authorities determined it constituted a threat hostile to national interests. ¹⁰⁹

A Russian Soyuz-2.1a launch vehicle with a payload of three satellites is pictured at Vostochny Cosmodrome in Russia. (Source: RIA Novosti).

Similarly, while the OST requires consultations if a country believes its planned space activity or experiment “would cause potentially harmful interference with activities of other States Parties in the peaceful exploration and use of outer space,” ¹¹⁰ the OST would not appear to require consultations if a country expected to cause harmful interference with non-peaceful uses of outer space. Traditionally, most military uses of space, such as missile warning, reconnaissance, weather, communications, and navigation, have been regarded as peaceful insofar as they are not used for aggression in the space domain, even if they support terrestrial military operations. However, WMD stationed in orbit in violation of Article IV of the OST should not be entitled to claim protection under the consultation requirement as a “peaceful” use of space. Thus, a country seeking to negate the use of orbital WMD should not be required to notify the offender beforehand under either the OST itself or the modified countermeasures doctrine described above.

While countermeasures are an appealing avenue for action, their efficacy for dealing with space-based WMD threats may also be questioned because they tend to be temporary and reversible. While countermeasures are encouraged to be reversible, ¹¹¹ the nature of countermeasures such as radiofrequency jamming and certain actions in cyberspace means that they may cease to be effective as soon as the jammer stops radiating, the targeted satellite moves out of range, or the operator uploads a software patch. A more permanent solution may therefore be required for a persistent threat like orbital WMD.

Self-Defense

The U.N. Charter requires states to settle their disputes by peaceful means “in such a manner that international peace and security, and justice, are not endangered” ¹¹² and to “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 [U.N.]” ¹¹³ However, it also states, “Nothing in the present Charter shall impair the inherent right of individual or collective self-defense if an armed attack occurs against a Member of the [U.N.], until the Security Council has taken the measures necessary to maintain international peace and security.” ¹¹⁴ In doing so, it recognizes the pre-existing right of states to national and collective self-defense when force is threatened or used against them.

Despite the conditional language “if an armed attack occurs” in Article 51 of the U.N. Charter, most countries recognize that the right of self-defense also applies against imminently threatened attacks. In the famous “Caroline Case” formulation, the United States and the United Kingdom agreed that the anticipatory use of force could be justified as self-defense, but only when the threat is “instantaneous, overwhelming, and leaving no choice of means and no moment for deliberation.” ¹¹⁵ The standard is grounded in even older standards of the requirement for necessity in self-defense, such as Hugo Grotius’s argument in his 1625 treatise, De Jure Belli ac Pacis:

[A]pprehensions 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. ¹¹⁶

After World War II ended, the Nuremberg war crimes tribunal applied the Caroline standard as customary international law in ruling against Nazi claims that their invasion of Norway and Denmark was justified as preventive self-defense. ¹¹⁷

As discussed below, the logic of anticipatory self-defense justified Israel’s strikes against the Syrian nuclear reactor that was under construction in 2007, as well as strikes by various nations against Syria’s chemical weapons facilities in more recent years. More controversially, it has also been cited to support the Israeli strike against Iraq’s Osirak nuclear reactor in 1981 and the U.S.-led invasion of Iraq in 2003.

The preceding examples help to cast light on state practice as an element of customary international law. The Statute of the International Court of Justice requires the court to apply “international custom, as evidence of a general practice accepted as law.” ¹¹⁸ When no treaty provision is in place to govern states’ behavior, state practice and opinio juris can be examined to assess whether an unwritten rule of customary international law exists and, if so, whether a state’s behavior has violated that rule. ¹¹⁹ State practice can also provide evidence of how states interpret their obligations under treaties. ¹²⁰ Thus, it is useful to examine various instances of how states have conducted self-defensive actions to counter WMD in the past and draw out lessons that could support action against space-based WMD.

The Cuban Missile Crisis

In the early 1960s, the Soviet Union began covertly sending missiles into Cuba to target the United States with nuclear weapons from a much shorter distance and with a much-reduced warning time. ¹²¹ When the United States discovered the plot, with help from space-based surveillance capabilities, a period of brinksmanship between U.S. President John F. Kennedy and Soviet Premier Nikita Khrushchev ensued. ¹²² To break the stalemate, President Kennedy imposed a “quarantine” of Cuba to prevent further arms transfers, while offering in private to remove U.S. Jupiter missiles from Turkey. ¹²³ The Kennedy administration sought to distinguish the quarantine on arms shipments to Cuba from a naval blockade, which attempts to prevent all maritime trade with the targeted state and has traditionally been considered an act of war. ¹²⁴ This high-risk “carrot and stick” combination induced Khrushchev to back down and remove the missiles from Cuba. ¹²⁵

Similarly, serious and overt threats to use military force against space-based WMD might be useful in a crisis. However, the situations are markedly different. Whereas the Soviet Union was able to extract its missiles from Cuba relatively easily, it would likely not be nearly as feasible to safely remove a nuclear-armed satellite from orbit, to deactivate it in a verifiable manner, or to move it to a disposal orbit where it would no longer pose a threat to active satellites. Deorbiting such an object could cause a disaster similar to the crash of the Soviet nuclear-powered spy satellite Cosmos 954, whose debris irradiated hundreds of miles of northern Canadian territory in 1978 and resulted in millions of dollars in damages. ¹²⁶ Leaving it in outer space would make it difficult to assess any purported deactivation, and it may not be capable of exiting its initial orbit to pass into deep space where it would no longer endanger other spacecraft. The WMD satellite’s owner may also simply deny its nature and purpose and refuse to do anything about it, particularly if it doubts the credibility of any threats. ¹²⁷

Israeli Strike on Osirak Nuclear Reactor

In 1981, Iraqi dictator Saddam Hussein had begun to build a nuclear reactor at Osirak, Iraq, with help from French contractors. ¹²⁸ When Israel learned that it was being fueled, Israeli Prime Minister Menachem Begin became alarmed. ¹²⁹ Iraq had joined coalitions of Arab states against Israel numerous times before—in 1948, 1967, and 1973—and Hussein continued to express anti-Israeli rhetoric and support Palestinian terrorism. ¹³⁰ If Iraq developed a nuclear weapon, Israel was likely to be one of its first potential targets. Prime Minister Begin authorized a daring long-distance raid in which Israeli F-16A fighter jets struck and destroyed the reactor. ¹³¹ U.S. officials publicly condemned the attack at the time, as did the U.N. Security Council. ¹³²

However, after Saddam Hussein later invaded Kuwait and was expelled by the U.S.-led coalition in Operation Desert Storm, then-Secretary of Defense Dick Cheney sent a letter thanking the raid’s architect, former Israeli Air Force Chief David Ivry, for making the coalition’s job much easier. ¹³³ Saddam Hussein had restarted his efforts to develop a nuclear capability, which the United States itself had to terminate in 1991, 1993, and again in 2003. ¹³⁴ Thus, the passage of time, combined with continued Iraqi aggression and pursuit of WMD, softened the views of U.S. leadership as to the justification for Israel’s action. Likewise, a preemptive attack against illegal space-based WMD may be controversial when it occurs. However, opposition to such a strike can be mitigated with adequate intelligence sharing or public disclosure of the nature of the threat, as well as by conducting the strike in a responsible manner that leaves little or no collateral damage and does not result in escalation. ¹³⁵

Operation Iraqi Freedom

After suffering nearly 3,000 casualties in the terrorist attacks of September 11, 2001, the United States saw a need to more proactively counter terrorist threats, especially if those terrorists could potentially obtain access to WMD. ¹³⁶ Al-Qaeda’s operatives had turned civilian airliners into flying bombs when they crashed them into the World Trade Center towers, the Pentagon, and a field in Pennsylvania. ¹³⁷ U.S. authorities shuddered to think of what they might do with access to chemical, biological, radiological, or nuclear weapons. ¹³⁸ One potential source of such weapons was the aforementioned Saddam Hussein, who, despite the loss of his nuclear program, had a record of killing Iranians and his own civilians with chemical weapons; had attempted to conceal the extent of his chemical weapons program from international inspectors; was continuing to shelter notorious terrorists such as Abu Musab al-Zarqawi; had regularly attacked U.S. and allied forces enforcing the no-fly zones over northern and southern Iraq; and had plotted to assassinate former U.S. President George H.W. Bush. ¹³⁹ These and other activities violated a variety of U.N. Security Council Resolutions. ¹⁴⁰

U.S. Secretary of State Colin Powell addressed the U.N. Security Council to argue that Saddam Hussein was a threat to the world and should be removed from power. ¹⁴¹ When the Security Council took no action, the United States, in concert with a broad coalition of nations, launched Operation Iraqi Freedom, which commenced on 19 March 2003, and notified the Security Council on 20 March that the coalition was doing so in self-defense, among other reasons. ¹⁴² The coalition quickly defeated the Iraqi military, deposed Saddam Hussein, and began rebuilding the country. ¹⁴³

Unfortunately, the aftermath of Hussein’s downfall proved to be substantially more challenging than the initial invasion. Moreover, Hussein’s stockpile of illegal chemical weapons turned out to be much smaller and more decrepit than Western leaders and intelligence analysts had believed. ¹⁴⁴ While the invasion of Iraq made sense to most Americans at the time based on what we knew then, many later criticized the war as a mistake in light of how costly the counterinsurgency became and how small a threat, in hindsight, the chemical weapons posed. ¹⁴⁵

The Iraq war and its reappraisal remind us that it is critically important to develop reliable intelligence and sound judgment about the threats we perceive and how to deal with them. The more distant an adversary is, in terms of both capability and intent, from threatening or using force against us, the more challenging it is to justify military action in self-defense, particularly in the case of preemptive action. However, we should also be careful not to unduly minimize past threats just because they no longer seem so dangerous in hindsight.

U.S. and Canadian forces clean up Cosmos 954 radioactive debris. (Source: Royal Canadian Air Force)

Israeli Strike on Syrian Nuclear Reactor

In 2007, Israeli intelligence identified an undeclared nuclear reactor under construction in eastern Syria, with North Korean nuclear scientists present at the site. ¹⁴⁶ Israeli Prime Minister Ehud Olmert feared that the Assad regime intended to use it to create fissile material for a nuclear weapon, with Israel as the most likely target. ¹⁴⁷ The fact that Syria, unlike Iraq, shared a border with Israel, made it an even more pressing threat than the Osirak reactor had been. Having learned some lessons from the Osirak strike, this time, Israeli officials quickly approached U.S. authorities, shared their intelligence findings, and sought to gain U.S. support for an Israeli airstrike against the Syrian reactor. ¹⁴⁸ Unlike in 1981, the U.S. administration and key allies recognized the nuclear reactor as a mortal threat to Israel, shared intelligence that corroborated the Israeli assessment, and pledged not to condemn or interfere with Israel’s action. ¹⁴⁹ In a raid on 6 September 2007, Israeli Air Force fighters quickly turned the illegal nuclear site into rubble. ¹⁵⁰

Factors that helped the world to see this strike as justified included the illegality of Syria’s covert actions under the NPT; Syria’s history and ongoing stance of hostility toward Israel; Syria’s geographic proximity to Israel; the accurate intelligence data and assessments shared between Israel and the United States; and Israel’s well-founded judgment that lesser means, such as exposure of Syria’s malfeasance to the International Atomic Energy Agency (IAEA), would be ineffective. ¹⁵¹ Israel’s precision attack also resulted in little or no collateral damage, thus satisfying the law-of-armed-conflict principles of distinction and proportionality.

Just as Israel was threatened by the possibility of a hostile nuclear-armed power on its border, the whole world would be threatened by the existence of a nuclear weapon in space. Whether intended for detonation in orbit or for nuclear bombardment of terrestrial targets, such a weapon would be profoundly destabilizing, as well as patently illegal for any party to the OST. Therefore, countries that believe themselves threatened by the placement of a nuclear weapon in outer space should develop the means to destroy it before it becomes operational, just as Israel destroyed the Iraqi and Syrian nuclear reactors. As the U.S. Department of Justice Office of Legal Counsel opined in 2002, “[A]s the magnitude of the possible harm caused by an attack increases, the probability that the attack will occur may be reduced and still justify an exercise of the right to anticipatory self-defense.” ¹⁵²

Payload farings are fitted around a satellite to secure and protect it during its launch atop the Atlas V 541 rocket at Cape Canaveral Space Force Station. (Credit: Ben Smegelsky, NASA)

U.S., Coalition, and Israeli Strikes on Syrian Chemical Weapons Facilities

At various points in the Syrian Civil War that began in 2011 and continues in part to this day, Syrian dictator Bashar al-Assad used chemical weapons against both rebels opposing his regime and Syrian civilians not participating in the conflict. ¹⁵³ In 2012, U.S. President Barack Obama warned that such behavior was crossing a red line and needed to stop. ¹⁵⁴ However, when Assad attacked rebels in Damascus with sarin gas in August 2013, President Obama deferred to Congress to authorize the use of military force to punish Assad, and Congress did not grant such an authorization. ¹⁵⁵ Instead, special envoy John Kerry accepted Russia’s offer to mediate and monitor the situation and pressured Assad into signing the Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction, also known as the Chemical Weapons Convention (CWC). ¹⁵⁶

Despite Syria’s putative accession to the CWC, Assad continued attacking Syrian civilians with chemical weapons over each of the next five years, ¹⁵⁷ even after President Donald Trump authorized missile strikes against an airfield used in Assad’s 2017 chemical attack. ¹⁵⁸ Still undeterred, Assad’s forces dropped barrels full of toxic chemicals to poison rebels and civilians at Douma in April 2018. ¹⁵⁹ This time, French and British forces joined the U.S. Air Force and Navy in striking targets that included chemical weapons research laboratories in the heart of Damascus. ¹⁶⁰ These strikes, along with ongoing efforts at deterrence, set back Syria’s chemical weapons program for another year. However, after President Trump decided to disengage from Syria, ¹⁶¹ Assad used them once again. ¹⁶² Finally, as the Assad regime collapsed in December 2024, Israel launched airstrikes to finish off the Syrian chemical weapons facilities and keep them from falling into the hands of the militants who toppled Assad. ¹⁶³

Lessons from this episode include the risks associated with negotiating with Putin’s Russia and the demonstration that in some situations, the military instrument of national power—especially when wielded in concert with allies—is far preferable to diplomacy alone. Like the OST, the text of the CWC does not provide for the use of military force as an enforcement mechanism. ¹⁶⁴ However, illegal WMD create risks to civilian populations that many nations find especially intolerable. Therefore, Syria’s repeated use of chemical weapons in violation of the CWC demanded a harsher response than merely sending inspectors or filing reports with the U.N. The multinational military response degraded Syria’s chemical weapons capabilities and restored deterrence against their further use—but once it appeared that the United States was no longer interested in Syria, deterrence vanished. Thus, the international community must remain vigilant and poised to act repeatedly against WMD threats if these threats are to remain under control.

Stuxnet Cyberattack on Iranian Nuclear Program

Iran’s ongoing efforts to develop a nuclear capability have provoked a wide variety of reactions from other states, including economic sanctions, ¹⁶⁵ U.N. Security Council resolutions, ¹⁶⁶ IAEA inspections, ¹⁶⁷ the ill-fated Joint Comprehensive Plan of Action (JCPOA), ¹⁶⁸ and even assassinations of Iranian nuclear scientists and military officers. ¹⁶⁹ One of the most notable incidents involved the cyber worm known as Stuxnet, which is widely believed, though not acknowledged, to have been developed by U.S. and Israeli intelligence agencies. ¹⁷⁰ The Stuxnet code infected the control systems for Iranian nuclear centrifuges and caused them to spin out of control, reportedly physically damaging or destroying around 900 centrifuges in fourteen Iranian nuclear facilities. ¹⁷¹

The Stuxnet event illustrates both the promise and the peril of seeking to affect nuclear programs via cyberspace. It caused a significant setback in Iran’s nuclear enrichment program, destroying numerous centrifuges without causing any direct collateral damage. However, it did not permanently eliminate Iran’s path to a nuclear capability, and once Iran discovered it, Iran was able to protect itself from further damage. ¹⁷² Similarly, cyber methods may offer a subtle, sophisticated, and difficult to detect and attribute way of impairing an adversary’s space-based nuclear weapons capability. However, they may be challenging to implant, and, if discovered, could potentially be turned against their original developer or third parties.

North Korean Nuclear and Missile Developments

North Korea has been hostile to the United States, the Republic of Korea (ROK), and the free world, often including the U.N. itself, since its inception. Exchanging Japanese occupation for Soviet occupation at the end of World War II, the Communist-dominated portion of the Korean peninsula soon launched a war of aggression against the ROK, its neighbor to the south. ¹⁷³ U.S. and U.N. forces intervened to restore South Korean sovereignty over the ROK’s internationally recognized territory, and hostilities were suspended with the declaration of an armistice in 1953. ¹⁷⁴ However, the ruling Kim dynasty in Pyongyang has remained implacably opposed to the mere existence of ROK, the United States, and democratic values ever since. It continues to threaten South Korea and the United States, occasionally resorting to the unprovoked use of force. ¹⁷⁵

To back up its threats, North Korea has developed nuclear weapons, having conducted six known underground nuclear detonation tests to date. ¹⁷⁶ It has also rapidly advanced its long-range ballistic missile capabilities in tandem with its space launch program, having developed multiple intercontinental ballistic missile (ICBM) variants capable of hitting most of the continental United States. ¹⁷⁷ It frequently tests ballistic missiles by shooting them up into outer space such that they splash down in the seas on either side of Japan. ¹⁷⁸ It is unknown whether North Korea has successfully mated a nuclear weapon with an ICBM, but its demonstration of both technologies likely indicates that their integration is not far off if it has not already occurred.

U.S. and allied efforts to isolate, sanction, condemn, and deter North Korea over the past seven decades of armistice have met with mixed success at best. While the primary goal of deterring another massive attack on the ROK seems to have succeeded so far, North Korea’s continuing bellicose rhetoric and increasingly fearsome nuclear and missile arsenal suggest that we may not always be so lucky. ¹⁷⁹ If North Korean dictator Kim Jong-Un gives the order to finish what his grandfather Kim Il-Sung started in 1950, his forces could potentially launch an attack at any time, resuming the Korean War and causing inconceivable amounts of suffering. ¹⁸⁰

North Korea’s ability to develop extensive nuclear weapons and ICBM programs despite international sanctions illustrates how even an impoverished rogue state can protect its illegal nuclear weapons development through concealment, lies, and threats while deterring any possibility of a preemptive anti-nuclear strike, such as those Iraq and Syria experienced. Fears about how the Kim regime would retaliate against the ROK deterred preemptive actions even before the North Korean nuclear breakout. They became insurmountable once North Korea’s nuclear weapon capability was confirmed.

Closing Thoughts on Preemptive Self-Defense

Comparing the North Korean nuclear situation to a potential space-based nuclear weapons development situation, we see some similarities and some differences. In both situations, there are substantial risks to acting preemptively to neutralize a weapon possessed by a known nuclear power. Even if a space-based nuclear weapon itself were not fully activated, the possibility that its owner might retaliate in space or another domain would need to be accounted for. If a space-based nuclear weapon’s owner wanted to deny its nature and purpose and claim to be the innocent victim of aggression, it could accuse any state that attempted to negate the weapon of interfering with its peaceful use of outer space—and undertake reprisals accordingly. The state that acted to negate the weapon would also need to explain its action to counter this false narrative and be prepared to deal with any further retaliation that might ensue. Professor Louisa Handel-Mazzetti has helped to lay the legal groundwork for preemptive self-defense through her argument that stationing a nuclear weapon in outer space is inherently an unlawful threat of force in violation of Article 2(4) of the U.N. Charter. ¹⁸¹

Neutralizing an illegal space-based nuclear weapon might also be substantially less escalatory than attempting to neutralize a well-defended terrestrial nuclear program. Strikes against hardened nuclear facilities, perhaps underground and defended by antiaircraft missiles, within a nation’s sovereign territory, would require a massive investment in resources and would undoubtedly invite counterstrikes if the targeted country were not sufficiently chastened. In contrast, neutralizing an illegal space-based nuclear weapon would not have to involve penetration into enemy territory, ¹⁸² human casualties, or the types of damage that tend to provoke genuine grief and outrage among the populace and condemnation by other countries. Rather, most countries, even if normally aligned with the country that stationed a nuclear weapon in space, might privately breathe a sigh of relief that such a menace was neutralized.

One might also ask whether preemptively neutralizing a space-based nuclear weapon would risk harmful escalation by threatening the nuclear balance of power. U.S. policy takes pains to avoid interference with other countries’ nuclear command and control, ¹⁸³ and Western countries such as the United States do not go about attacking potentially hostile nuclear ballistic missile submarines, ICBM launchers, or nuclear bomber bases and depots just because of the possibility that they could launch a devastating nuclear strike some day. However, those capabilities are largely recognized as legitimate tools of deterrence and self-defense, which a nuclear state has the authority to possess. ¹⁸⁴ A nuclear weapon stationed in outer space, by contrast, would be manifestly unlawful and destabilizing. Because of its prohibition in the OST and its indiscriminate nature affecting all spacefaring nations, it would make no sense for responsible and law-abiding states to respond in kind by fielding a comparable capability that they could never justify using. Thus, targeted efforts to neutralize the illegal space weapon would be preferable to traditional forms of nuclear deterrence that rely on achieving some degree of parity in delivery methods for a first- or second-strike capability.

The degree of international acquiescence to any preemptive action against space-based WMD will likely depend in part on what means are chosen to carry it out, and their foreseeable long-term effects. For example, a kinetic strike that causes large amounts of long-lived, possibly radioactive, space debris would be less likely to garner international support or toleration than a non-kinetic strike, perhaps with some form of directed-energy weapon or cyber mechanism. The latter method could, in theory, render the weapon harmless without splintering it into thousands of shards of space shrapnel—and may also be more difficult to detect and attribute, mitigating the risk of retaliation. Non-

kinetic actions to disable the capability before launch, or kinetic or non-kinetic actions to neutralize it in the early launch phase before it achieves orbit, should also be considered. ¹⁸⁵ However, launch disruptions might carry a higher risk of discovery or terrestrial damage.

Certain prior U.S. policy proclamations, such as the ban on destructive direct-ascent ASAT testing (now echoed by dozens of other countries and endorsed in a U.N. General Assembly Resolution) ¹⁸⁶ and the tenet-derived responsible behaviors in space, ¹⁸⁷ suggest significant reluctance to cause permanent harm to any other country’s satellite—particularly if collateral damage is expected. However, if that other country’s satellite contains an illegal WMD payload, it could be more responsible to neutralize it than to leave it alone.

As General Stephen Whiting, Commander, USSPACECOM, recently argued at the 40th Space Symposium, “It’s time that we can clearly say that we need space fires, and we need weapon systems. We need orbital interceptors. . . . We call these weapons. And we need them to deter a space conflict and to be successful if we end up in such a fight.” ¹⁸⁸ A new U.S. Space Force doctrinal document also makes clear that the United States needs space superiority to ensure “the enemy is no longer able to act in a meaningful or dangerous way against friendly celestial lines of communication,” ¹⁸⁹ which may require “seeking out and destroying an enemy’s spacecraft, systems, and networks.” ¹⁹⁰ It is difficult to imagine a target more worthy of such destruction than a satellite with an illegal WMD payload.

When it comes to defending against a nuclear FOBS or MOBS, the announcement of a new “Golden Dome for America” ¹⁹¹ is also a heartening sign. Building on the legacy of President Reagan’s Strategic Defense Initiative, the Golden Dome initiative directs planning for a next-generation missile defense architecture with significant space-based components that will enable identification, tracking, and interception of “ballistic, hypersonic, advanced cruise missiles, and other next-generation aerial attacks from peer, near-peer, and rogue adversaries.” ¹⁹² If such a system is fielded and operates as intended, it could potentially interdict a FOBS-type threat in the pre-launch, boost, or terminal phases. ¹⁹³

Finally, effective deterrence must rely on more than legal arguments that self-defense is a valid option. It must be backed up by hard power, and the training, ability, and willingness to employ it in a disciplined and lethal way. Even if the first Russian satellite that provoked so much consternation is not already armed, it could be followed by one or more successors with a live nuclear payload. ¹⁹⁴ Before that happens, we must urgently build the capability to deny any attempt to deploy or use a space-based nuclear weapon before it lays waste to the world’s satellite constellations, imperils our cities and military forces with orbital bombardment, or enables terrestrial military adventurism by presenting a constant threat to render space unusable. This will require significant investment in counterspace systems, space domain awareness, and an operational test and training infrastructure to prepare U.S. Space Force Guardians acting in concert with other joint and combined forces to face and defeat the threat.

Conclusion

In this new and dangerous era of great-power competition, irresponsible states threaten to cast aside the hard-won legal prohibitions on space-based WMD that the international community collectively achieved during the Cold War. The United States and its allies must use all lawful means at our disposal to protect our space assets, our homelands, our allies, and our modern way of life from these threats—and to deter or prevent them from materializing in the first place. These means may include elements of diplomacy, retorsion, countermeasures, and, if necessary, anticipatory self-defense, as circumstances and capabilities warrant. This article has detailed some of the ways to do so, recognizing the risks and benefits of each type of action. What we cannot afford is inaction. We must not allow WMD to be stationed in outer space. Si vis pacis, para bellum. TAL