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Chinese ASAT debris illustration
A Chinese ASTA test in 2007, and the extensive cloud of debris it created, have raised concerns about how to deter any future use of space weapons. (credit: AGI)

Space and nuclear deterrence

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“Space deterrence” is defined here as deterring harmful actions by whatever means against national assets in space and assets that support space operations. Analogously, nuclear deterrence is defined as deterring harmful actions by means of nuclear weapons. Concepts of nuclear deterrence have been well developed. In contrast, attention to space deterrence has been sporadic during and after the Cold War, sparked mostly when anti-satellite (ASAT) capabilities have been tested. These concerns faded after the demise of the Soviet Union, and have now revived with the advent of China’s ambitious space program.

Demonstrable vs. inferred deterrence

Nuclear deterrence and space deterrence have common elements as well as distinct differences. No difference is more striking than with respect to the visibility of nuclear deterrence capabilities compared to the largely inferential nature of space deterrence. The advent of nuclear weapons was advertised with spectacular effect, with the mushroom cloud immediately becoming the symbol of the “atomic age.” Ever since, nuclear deterrence widely was presumed to be strengthened by visible displays. Tests of warhead designs were carried out in the atmosphere and were subsequently driven underground, easily confirmed by seismographs. Missile flight tests repeatedly affirmed vigilance and readiness. Some states possessing nuclear weapons still parade nuclear-capable missiles on national holidays.

In contrast, capabilities to harm space assets have been tested only occasionally in dramatic ways and mostly have been pursued quietly or by indirect methods. Consequently, space warfare capabilities rarely make headlines, unlike actions signaling nuclear deterrence, which are the subject of intense public and media attention. While nuclear deterrence rests on deployed or readily deployed capabilities, the weaponization of space —defined here as the placement of dedicated war-fighting capabilities in this domain—has yet to occur. The nuclear superpowers deployed large numbers of nuclear weapon delivery vehicles carrying thousands of warheads, many ready for launch on short notice. At the same time, military capabilities specifically designed to harm satellites were rarely deployed, had limited operational utility, and were subsequently mothballed during the Cold War.

Capabilities to harm space assets have been tested only occasionally in dramatic ways and mostly have been pursued quietly or by indirect methods. Consequently, space warfare capabilities rarely make headlines.

The Eisenhower administration considered contesting a Soviet “right” to have its Sputniks orbiting over US soil, but thought better of it: American satellites would soon follow—including ones revealing military secrets in a closed society. It took no great gift of prophecy to foresee benefits accruing from the norm of free passage. The Kennedy administration saw fit to position a crude ASAT capability in the Pacific after the Cuban Missile Crisis—a decision that extended into the Johnson and Nixon administrations. This capability was hardly worth the bother in military terms. Presidents John F. Kennedy and Lyndon Baines Johnson were far more interested in beginning to establish norms for the peaceful uses of outer space. The Soviet Union was soon eclipsed by the United States in the “space race,” and was amenable to downplaying the prospect of confrontation in this domain. In 1967, the nuclear superpowers agreed to the Outer Space Treaty, their second major codified constraint of their strategic competition, after an agreement four years earlier to stop testing nuclear weapons in the atmosphere.

There were, to be sure, periods of heightened military friction and competition in space, particularly following Soviet ASAT tests in the 1970s and after President Ronald Reagan’s announcement of the Strategic Defense Initiative in 1983. In retrospect, a striking aspect of these periods of heightened competition in space was how little residue they left on the strategic competition, and how careful both superpowers were not to cross each other’s red lines in space, as well as on the ground and at sea. Just as Washington and Moscow learned not to play with fire in particularly sensitive zones after crises over Berlin and Cuba, so, too, did they reach tacit and formal agreements not to create havoc with each other’s satellites—despite multiple capabilities that enabled them to do so.

One reason why demonstrable deterrence was deemed crucial for the nuclear competition, while inferential deterrence would suffice for space, was that military capabilities designed for one domain—including missiles deployed for the purpose of nuclear deterrence and for missile defense intercepts—could be used in the other. Another reason was that after crises in Berlin and Cuba, the United States and the Soviet Union acted for the most part as status quo powers. Will this Cold War record of uncommon restraint in space continue between a status quo power and a rising power?

Caution is warranted before reaching overly optimistic or pessimistic answers to these questions. Conditions have changed, and the competition between Washington and Beijing will be different in crucial respects than that between the United States and the Soviet Union. Besides, there has never been a consensus in the United States over the definition of, and requirements for, successful deterrence. Moreover, Beijing’s strategic objectives and the means that will be employed to achieve them remain opaque. What can be said with certainty is that the mix of US-Chinese cooperation and competition in space is not predetermined. Instead, this mix will reflect, and be influenced by, a much larger canvas of bilateral relations.

Extrapolating to China and to space deterrence

The United States maintains a great many nuclear weapons and diverse means for their delivery to deter a similarly armed and similarly vulnerable adversary. This force posture was sized in comparison with the Soviet Union during the Cold War and subsequently to the Russian Federation. Force sizing to deter the Kremlin appears sufficient for all lesser cases, including the objective of dissuading the People’s Republic of China from seeking to compete with the United States in this realm. US nuclear forces continue to be maintained in a high state of readiness—albeit not as high as during the Cold War—to deter surprise attack and to provide the National Command Authority with prompt and varied options in the event of a breakdown in nuclear deterrence.

In contrast, the requirements to deter attacks on US space assets, at present, do not appear to include kinetic-energy weapons dedicated to space deterrence that are deployed in space, on land or at sea. Dedicated ASAT weapon systems were considered deployed for portions of the Cold War, but they were rudimentary and poorly suited for operational requirements. They were not replaced, systematically upgraded and repeatedly tested to demonstrate vigilance, resolve and to reinforce deterrence, as was the case for nuclear weapons and their means of delivery.

The Soviet Union possessed far more formidable military space and nuclear capabilities than the People’s Republic of China does now. The United States engaged in minimal commerce with the Soviet Union, compared to significant trade and financial interactions currently with China. The Cold War contest between the United States and the Soviet Union was ideological, global and geopolitical. In contrast, the competition between the United States and China lacks an ideological dimension and is, at present, more regional than global. These contrasts suggest that the relatively relaxed US-Soviet military competition in space might carry forward in a competitive relationship between the United States and China. On the other hand, Beijing’s intentions and ambitions are unclear, and bilateral cooperation in space between the United States and China is minimal compared to the US-Soviet and US-Russian experience.

Will this Cold War record of uncommon restraint in space continue between a status quo power and a rising power?

There can be no doubt that space has become, as the Obama administration has noted repeatedly, more competitive, contested and congested than during the Cold War. Features of space operations have changed markedly, including the advent of commercial space operations and profit-taking related to satellites, the increase in the number of nations utilizing space for varied purposes, and the criticality of space systems for military operations. All major space-faring nations increasingly rely on satellites, but none more so than the United States. Multinational partnerships in space now figure prominently; the sharing of benefits and risks might alter deterrence calculations, as well. All of this, and more, is significantly different from the first three decades of the Space Age. Does this mean that Cold War-era calculations of the requirements for space deterrence have fundamentally changed?

To answer this crucial question, we must first try to reach an informed judgment as to why the requirements for space deterrence were presumed to be so different from nuclear deterrence during the Cold War, and then to assess whether these conditions remain in place. One possible reason is that major powers have long considered warfare in space to be linked to nuclear warfare. If so, the requirements of the former might have been subsumed in the latter. The linkages between nuclear warfare and activities in space are numerous and well understood. Satellites are connected in many ways to the execution of nuclear war-fighting plans by helping with weather forecasting; targeting, indications and warning of attacks; assessing damage and maintaining command, control and communications. During the Cold War, the contestants understood that to disable or attack these satellites by whatever means was unlikely to be viewed in a vacuum. Instead, attacks on critical assets and infrastructure in space commonly were viewed in the gravest terms, regardless of whether they were precursors to attacks on nuclear forces. These conditions continue to remain in place.

An appreciation of the linkages between space assets and nuclear assets does not, however, explain why nuclear tests were so prevalent and why ASAT tests were so limited during the Cold War. Despite the clear linkages between nuclear and space deterrence, requirements for the former were excessive and requirements for the latter were relatively relaxed. As noted earlier, this dichotomy can probably be explained, in some measure, by the abundance of other means to interfere with, damage or destroy critical assets in space, including non-kinetic kill mechanisms such as lasers and jammers. Counter-space capabilities reside in conventional- and nuclear-armed weapon systems, including missiles of various kinds, along with missile defense interceptors. The perceived requirements for dedicated systems to engage in space warfare might well have been reduced significantly because of these residual or latent capabilities. These conditions remain in effect. Indeed, latent capabilities to engage in space warfare have grown, and have become more prominent because missile defense interceptors have been tested dramatically in an ASAT mode by China in 2007 and by the United States in 2008.

A third possible explanation for Cold War restraint—albeit one that has become far more appreciated of late—might relate to the indiscriminate, abhorrent and self-defeating nature of some means to engage in warfare in space. This first became apparent with respect to atmospheric nuclear testing. These tests generated public revulsion and political activism. By the early 1960s, concerns over public health dangers arising from atmospheric tests overrode the arguments of those who desired their continuation to clarify military and operational requirements. Less well known were the potential hazards of atmospheric tests to the health of the first astronauts and cosmonauts, as well as to the first satellites placed in low Earth orbit. One particularly powerful US test on July 9, 1962, Starfish Prime, damaged at least six fledgling satellites.

Space debris poses a clear and present danger in space analogous to the danger atmospheric testing posed to satellites and human exploration at the dawn of the space age. The hazards of ASAT tests involving “hit-to-kill” technologies first became apparent during the Cold War, when a 1985 US ASAT test created over 250 pieces of trackable space debris, one of which came within one mile of the newly launched international space station 14 years later. The abhorrent, indiscriminate and self-defeating consequences of debris-causing ASAT tests were not widely appreciated during the Cold War because few of these tests were carried out.

A kinetic-energy ASAT test conducted in 2007 by the People’s Liberation Army (PLA) ended complacency over the hazards of space debris. This ASAT test produced more than 3,000 pieces of debris large enough to track, and tens of thousands of smaller pieces, endangering human spaceflight and hundreds of satellites, without regard for ownership and nationality. The Pentagon demonstrated an agile, sea-based ASAT capability in 2008 by shooting down a non-functioning intelligence satellite, in a manner that minimized debris consequences. As a result of these tests, as well as other significant debris-causing events, recognition of the potential environmental consequences of space warfare is unquestionably greater now than during the Cold War. Reaction to the PLA’s 2007 ASAT did not spark mass protests, unlike the case of atmospheric testing. This ASAT test did, however, alarm space operators to such an extent that an international norm against further tests of this kind might take hold.

While the fragility of the global commons might induce restraint with regard to kinetic-energy ASATs, there are other means to interfere with and damage satellites. As noted above, lasers and jammers could also be employed to disrupt space operations, and could do so without creating debris fields. In this event, one critical element of space deterrence, as with nuclear deterrence, is the ability to determine who has sought to damage space assets, or succeeded in doing so, by non-kinetic means.

Attacks on critical assets and infrastructure in space commonly were viewed in the gravest terms, regardless of whether they were precursors to attacks on nuclear forces.

Attribution is a critical prior step to the choice of retribution. The attribution problem is likely to be harder with regard to space warfare, if for no other reason than the list of potential suspects is longer, including perpetrators that may not be under the control of governments. The attribution problem is, however, not unique to space warfare; it also applies to acts of terrorism, including nuclear terrorism. One means of deterrence across domains is the distribution of varied means of observation: some perpetrators might not carry out hostile acts if they have reason to expect discovery. Thus, redundant means of space situational awareness can serve deterrent purposes. Similarly, the development of forensic capabilities to attribute responsibility backs up deterrence across domains, but is likely to be more difficult in space, where physical evidence cannot be examined properly. In all domains, the context within which hostile actions are taken is likely to be strongly suggestive of the perpetrator, but may not be definitive.

Another common aspect of nuclear and space deterrence is the requirement for resilience. The value of any attack on space assets diminishes in proportion to the victim’s ability to compensate, recoup losses and respond appropriately. Deterrence against limited attacks, including attacks by non-kinetic means, is thereby reinforced by the evident ability to adjust to disruptions and losses of capability. Limited attacks and disruptions might well be more likely in asymmetric warfare than in confrontations between major powers because the weaker party can expect to have less to lose in space warfare. At the same time, the weaker party might have insufficient means to disrupt the space operations of the dominant power—except by using nuclear detonations that would badly affect space assets of all major powers. Outlier states might have few friends, but they are unlikely to want to alienate them by disrupting their space operations.

Worst-case projections of a failure in space deterrence—as with the worst case projection of a failure of nuclear deterrence—involve catastrophic losses from a surprise attack. For some, the worst case of a “space Pearl Harbor” has displaced Cold War concerns over a disarming “bolt-out-of-the-blue” attack against US nuclear forces. Only major powers have the capacity for massive attacks against a wide range of space assets in low Earth and geosynchronous orbits, as well as in between. The most persuasive deterrent against the low probability, but high-consequence nature of worst cases is the evident ability to respond with devastating effect to grievous injury. In the worst case of a bolt-out-of-the-blue, massive nuclear attack, deterrence was reinforced by clarifying the degree of difficulty for the attacker’s success and the horrific consequences of failure.

The worst case of a bolt-out-of-the-blue nuclear attack postulates that a nuclear response would cause insufficient retribution, or might be withheld to avoid even more fearsome punishment. Those who focus on the worst case of a breakdown in space deterrence argue that the aggressor has a greater likelihood of success than with a surprise nuclear attack, and that the victim will be reluctant to respond by crossing the nuclear threshold. While worst cases lie on the improbable end of the spectrum of possibilities, they cannot be ignored. US and Soviet leaders spent excessive amounts of money and deployed improbable numbers of nuclear weapons to guard against worst cases. The resulting nuclear force postures built to deter bolt-out-of-the-blue attacks were not very reassuring. To the contrary, the buildup of nuclear war-fighting capabilities to deal with worst cases raised insecurity. In a far more constrained budgetary environment, US national leaders must decide now how much of a deterrence and insurance policy to buy against a low probability/high consequence scenario of a massive surprise attack in space.

A severe crisis between major powers that plays out in space will reflect the magnitude of the stakes involved—a space age Cuban missile crisis. National leaders contemplating the first move of space warfare will face the same unalterable dilemmas of choice that Kennedy and Khrushchev faced. A leader can choose limited warfare for extremely uncertain gains and the possibility of uncontrolled escalation, or seek victory with the potential of all-out warfare and devastating consequences.

In the first-ever severe crisis between major powers in space, both contestants will possess the capacity to deny each other’s pursuit of space dominance. In this way, the nature of the space domain, where offense easily trumps defense, is like the nuclear domain. Consequently, the contestants will be unable confidently to ensure decisive victory by means of surprise attack. Just as protection from fallout in nuclear exchanges cannot be secured, so, too, will the first use of kinetic-energy ASATs be self-denying: mutating debris fields will make large swaths of space inoperable to one’s own satellites, either quickly or over time. The use of non-kinetic-energy ASATs on a modest scale invites retaliation in kind or retaliation across domains. The use of non-kinetic-energy ASATs on a massive scale invites massive retaliation, if not in kind, then across domains. In the event of a severe crisis between Washington and Beijing, would a Chinese leader risk everything with this cosmic throw of the dice?

In the event of warfare in space between major powers, national leaders will face an abundance of risk, just as they would in the event of warfare on the ground or at sea. The presumption inherent in worst case projections of space warfare is that disabling violence in space will dissuade conventional military responses and will not spill over to nuclear warfare. This assumption of compartmentalization weakens deterrence in all domains. The “space Pearl Harbor” scenario also assumes that warfare in space, unlike warfare in other domains, can be executed without unwelcome surprises, miscalculations, accidents or breakdowns in command and control.

US and Soviet leaders did not presume this to be the case during the Cold War, and US and Chinese leaders need not presume this to be the case in the future. The conclusion reached by Kurt Gottfried and Richard Ned Lebow during a dark Cold War chapter of heightened military competition in space seems equally relevant in a US-China context: “ASATs possess a considerably greater capacity for transforming a crisis into a war, and for enlarging wars, than they do for assisting in military missions or enhancing deterrence.” This conclusion seems equally applicable to space warfare by kinetic or non-kinetic means. With the benefit of hindsight, concerns over the worst case of a bolt-out-of-the-blue nuclear attack now seem quite overdrawn. While military plans to execute this scenario existed, political leaders sought to avoid executing them. Worst case assessments of a space Pearl Harbor seem unlikely, as well.

If a breakdown in space deterrence occurs, it could be as a result of seeking tactical advantage in conjunction with limited military operations. Alternatively, a breakdown of space deterrence could be a defensive act for signaling purposes, as has often been postulated with a breakdown of nuclear deterrence. In either case, deterrence breakdowns are most likely to happen on a limited scale alongside attempts to maintain, as much as possible, the military use of space. While worst-case scenarios appear implausible, there may well be a greater potential ambit for limited warfare in space, since satellite interference and disruption can be reversible. The requirements to shore up deterrence or to compensate for a breakdown of deterrence in these scenarios are far more modest than the requirements to deal with worst cases.


The US dependency on space will grow as Chinese military space capabilities grow. As a consequence, the United States is obliged to reinforce space deterrence capabilities while engaging in diplomatic initiatives aimed at reassurance. This combination of initiatives proved successful during the Cold War, and can continue to be successful in the future.

The key elements of space deterrence, as with nuclear deterrence, are secure retaliatory capabilities sufficient to deny advantages to an attacker, effective command and control mechanisms, and redundant safety and security mechanisms to prevent accidental as well as unauthorized use of military capabilities. In addition, successful deterrence requires situational awareness, attribution capabilities, as well as resilient space assets so that the United States is able to identify the perpetrator of harmful actions and continue to utilize space for national and economic security despite these acts.

If Beijing decides to ramp up its space warfare capabilities, the Pentagon will not be found wanting in this competition. A far more preferable posture would be one of “contingent restraint”.

These requirements are not controversial, although they may not be affordable in sufficient measure—as was the case with the perceived requirements of nuclear deterrence. The crux of debate over space deterrence is whether to continue to rely very heavily on latent or residual capabilities to engage in warfare, if necessary, or to shift toward more evident, dedicated, kinetic and deployed means of dissuasion. There are several powerful arguments for the United States to continue to rely on inferred rather than heavily demonstrable deterrence in space. To begin with, a non-dedicated, non-deployed, non-kinetic space deterrence posture has been successful in the past. An inferred posture is also more conducive to stabilizing deterrence than the deployment and testing of dedicated, kinetic counter-space capabilities. These hallmarks of an intensified arms competition did not produce a great sense of security in the nuclear domain, and are unlikely to offer a greater sense of security in space. Instead, more demonstrable space deterrence efforts are likely to increase requirements and costs while decreasing assurance.

An accelerated competition in the development, testing and deployment of US and Chinese counter-space capabilities is likely to spill over into the nuclear domain. The practical effect of this linkage would be to increase nuclear requirements in China, while retarding reductions in deployed US nuclear capabilities that are in excess of the Pentagon’s needs. In a constrained budget environment, the United States could apply defense dollars more wisely and enjoy added security if this dynamic could be avoided. Another reason to avoid an intensified competition in dedicated and deployed counter-space capabilities is that residual and latent US counter-space capabilities are growing significantly, particularly with respect to new missile defense interceptors. The growth in inferred capability provides the basis to avoid a competition in dedicated, deployed counter-space capabilities—if China is amenable to inferential deterrence.

This is an essential qualifier. A continued US preference to avoid a heightened competition marked by repeated displays of dedicated capability to disrupt, damage or destroy space assets depends on Beijing’s acceptance of inferred deterrence. The United States and China have both demonstrated counter-space capabilities. If Beijing decides to ramp up its space warfare capabilities, the Pentagon will not be found wanting in this competition. A far more preferable posture would be one of “contingent restraint,” whereby the Pentagon does not exercise options well within its capabilities, as long as the PLA is similarly constrained. Parallel policies of contingent restraint worked during most, but not all, intervals of the Cold War. This dynamic can also succeed under far less demanding contemporary circumstances.

Deterrence is based on threats. Deterrence, by itself, is not reassuring. The Cold War did not become hot because deterrence was complemented by reassurance in the form of diplomatic accords to reduce nuclear dangers. Contingent restraint can be inferential, or it can be reinforced by diplomatic accords. Stable deterrence requires reassurance when competitors possess devastating military options.

Washington and Beijing have yet to demonstrate successful diplomatic engagement to moderate a military competition in space. Neither have they agreed on cooperative joint ventures in space, like those that helped diminish pressures to ramp up US and Soviet space warfare requirements during the Cold War. Reassurance during the Cold War took the form of treaties. Senate consent to, and the entry into force of treaties regarding military space capabilities seem unlikely. Executive agreements remain possible, however. One means of reassurance—an International Code of Conduct for responsible space-faring nations—is readily available. Another, in the form of collaborative ventures in space science and exploration, awaits the commitment of far-sighted leaders.