"[Arms Control Today is] Absolutely essential reading for the upcoming Congressional budget debate on the 2018 NPR and its specific recommendations ... well-informed, insightful, balanced, and filled with common sense."

– Frank Klotz
former Administrator of the National Nuclear Security Administration
March 7, 2018
Apes on a Treadmill in Space

April 2021
By David A. Koplow

In 1975, Paul Warnke published a celebrated article entitled “Apes on a Treadmill,” in which he criticized the wastefulness and the danger of the U.S.-U.S.S.R. nuclear arms race.1 Warnke likened the two superpowers to simian imitators who slavishly copy each other’s weapons deployments, endlessly pursuing and endlessly denying to the adversary any meaningful strategic superiority.

The Sodium Guidestar laser at the U.S. Air Force Research Laboratory at Kirtland Air Force Base in New Mexico is used for real-time, high-fidelity tracking and imaging of satellites too faint for conventional adaptive optical imaging systems. (Photo: U.S. Air Force)Shortly thereafter, Warnke became President Jimmy Carter’s chief negotiator for the Strategic Arms Limitation Talks (SALT) II treaty, director of the U.S. Arms Control and Disarmament Agency (and this author’s first professional boss). Warnke advanced the effort to cap and then reduce global nuclear arsenals, which he regarded as absurdly overdeveloped and as so mutually offsetting that they could offer neither protagonist a significant, sustainable advantage.

Today, the vision that Warnke abhorred is spooling out again, in a different but equally futile venue: outer space, where a third central character, China, has joined the original two apes in another hazardous, expensive arms race, all going nowhere, this time at rocket speed.

Jolted by the surging security dangers in space, the United States, its rivals, and its allies are devoting more attention at last to the sustainability of their vital spacecraft, on which so much of the world’s economy, military, and civil society have come to depend. U.S. Secretary of State Antony Blinken, speaking at the Conference on Disarmament in February, has called for “developing standards and norms of responsible behavior in outer space.”2 The UN General Assembly in December 2020 inched beyond its previous tepid resolutions by expressing the desire that member states “reach a common understanding of how best to act to reduce threats to space systems in order to maintain outer space as a peaceful, safe, stable and sustainable environment.”3 Even the U.S. Space Command has recognized the need for advancing arms control in space, with Major General DeAnna Burt calling for the articulation of additional, legally binding international restraints on threatening space behaviors.

These calls for action to reduce threats to space systems require prompt follow-through. The growing competition involving the United States, Russia, and China demands a more nuanced and comprehensive approach from leaders in Washington, Moscow, and Beijing that takes into account Warnke’s original insights, which are now more than 45 years old. The security environment in space today has become dangerously unstable, as all three leading states develop and test new iterations of space weaponry in their mirror-image pursuit of space control policies.

The United States in particular needs to promote more fully diplomatic options that put in place effective space arms control agreements and to provide a way out of the mutually reinforcing patterns of military competition. Negotiated measures of legal restraint for space could be especially effective in dealing with the contemporary challenges to satellites because deterrence-based concepts alone are less efficacious in the space environment.

Warnke’s Critique

Warnke in 1975 observed that the United States and Soviet Union were rushing headlong into research, development, testing, and deployment of new generations of nuclear weapons, inspired in large measure by their reciprocal fears. Each protagonist viewed with great alarm the military programs of the other, and each ascribed the worst motivations to its rival’s exercises. Triggered by the other, each raced toward accumulation of greater nuclear firepower, independent of any sound strategic rationale. That is the “apes” aspect of the title of his piece; whatever one actor perceived the other one doing, it would mindlessly copy or adapt for itself.

Warnke recognized the futility of the process. Each side could offset the programs of the other, so a rough parity was sustained, simply at higher levels overall of armaments and spending. Neither could gain a decisive advantage over its equally vigilant and dedicated opponent. That is the titular “treadmill” aspect; there was no meaningful superiority to be gained in the competition, and no end point at which a winner would emerge.

In addition, Warnke and others complained that the process was not merely frightfully expensive, with billions of dollars at the time being flushed toward nuclear programs, but the endless escalation resulted in sharply increased danger for all. As weapons inventories multiplied, the dangers of accidental, unauthorized, or mistaken use would rise accordingly. The world was unaccountably lucky during the Cold War, as brinkmanship never devolved into catastrophe. In the long run, however, luck is not a reliable national security strategy or a guideline for a budget.

The world learned something under Warnke’s tutelage. Nuclear arms control became a staple of superpower relations, with Republican and Democratic presidents bringing home a series of bilateral treaties on strategic arms limitation, intermediate-range nuclear force elimination, and strategic arms reduction, as well as multilateral nuclear test ban and nonproliferation agreements. There were vicissitudes in the process, of course, but the U.S.-Soviet dialogue continued even during the darkest and most crisis-marred days of the Cold War era. As a result, nuclear explosive testing has been halted, the number of nuclear-armed states has been limited to nine, and the operational nuclear arsenals of the two chief contestants have been reduced by 80 to 90 percent from Cold War highs to some 4,000 U.S. and 4,000 Russian nuclear warheads today.

Nuclear dangers persist in part because of the failures of the two major nuclear actors to continue to engage and to improve on earlier successes, the deterioration of U.S.-Russian relations, and decisions by leaders in Moscow and Washington to engage in a new, costly apes-on-a-treadmill cycle of nuclear competition. President Donald Trump exacerbated the situation by withdrawing from the Intermediate-Range Nuclear Forces and Open Skies treaties, stalling on a deal to extend the 2010 New Strategic Arms Reduction Treaty, and declaring that U.S. missile defenses are intended in part to counter Russian and Chinese offensive ballistic missiles—a series of shocks that some observers have labeled “the end of arms control.”

Yet, arms control has rebounded from egregious tough times before and can do so again. Indeed, perhaps it is during the most tension-strewn phases that cooler heads recognize the profound benefits in treaty-making, confidence-building, mutual accommodation and calm communications. The recent rejection of legacy treaties may prove to be simply a hiccup in the long-term articulation of sensible nuclear restraints.

The enduring arms control relationship between the United States and Russia, now triangulated with China, is maddeningly complicated. The three protagonists will shift among the roles of adversaries, competitors, and collaborators in the realm of nuclear weapons as in everything else. Yet, Warnke pointed toward the illogic of an exclusive focus on the esoteric military-related aspects of such relationships, cautioning against “[o]verestimation of the practical utility and the political potency of our armed forces.” Smart diplomacy, he argued, offers a more viable alternative or complementary path toward security.

Deteriorating Security in Space

Today’s competition has extended endlessly upward. The stakes in orbital space are enormous and growing, as space is a $400 billion segment of the annual global economy. The United States now exploits satellite services for the full array of civilian and military applications. On the civilian side, many communications (television, telephone, internet), commercial activities (ATMs, credit card purchases), transportation functions (GPS guidance), and remote sensing (weather forecasting) are satellite enabled, and the Internet of Things will only increase the traffic. On the military side, satellites have promoted expedited communications between headquarters and fielded forces, as well as greatly augmenting local and global situational awareness and the exquisite accuracy of smart munitions. It is no exaggeration to conclude that modern U.S. modes of intelligence gathering and warfare would simply not be possible without satellites; a return to analog-era warfare capabilities would be crippling.

Unfortunately, that phenomenally successful exploitation of space has become a reliance, which has bred a dependency, and degenerated into a vulnerability, and other states have not failed to notice. Russia and China have persistently bolstered their programs toward increased anti-satellite (ASAT) capacities, experimenting with a variety of technologies at a variety of altitudes that can hold U.S. satellites hostage. Russia and China may believe they are simply trying to catch up with the prior and ongoing U.S. programs and capabilities in space control, but it is clear that the earlier concept of space as something of a sanctuary from ordinary earthbound military rivalry is permanently imperiled.

Other countries have increasingly invested in satellite services too. Eleven countries or consortia have demonstrated an indigenous capability for launching objects into space, 60 or more own or operate their own spacecraft, and all benefit daily from satellite services. Even with this emergent “democratization of space,” the United States remains the predominant player, operating more satellites for more functions than any other actor and commanding by far the largest national space budget.

A U.S. Air Force F-15A a mile high over the Pacific Ocean launches a multi-stage ASM-135 missile as part of an anti-satellite intercept test on September 13, 1985. In 1958, the United States first began experimenting with ASAT weapons, beginning with air-launched ballistic missiles and later, ground-launched ballistic missiles. The Soviet Union pursued similar experiments, as well as co-orbital ASAT systems. In the late-1970s, the United States began to develop non-nuclear, kinetic ASAT capabilities, such as the air-launched ASM-135. (Photo: U.S. Air Force)The new era in space weaponization can be traced roughly to 2007, when China abruptly shot down one of its own satellites, rupturing an informal moratorium on destructive ASAT weapons tests. Since that wake-up call, China has persisted in pursuing its space control capabilities, often testing devices under the guise of missile defense interceptors, rather than ASAT systems. Russia has experimented with covert “rendezvous and proximity operations” to refine its maneuvering capability, which could be a precursor for inspecting and attacking other states’ spacecraft. For its part, the United States has pursued the development of a Counter Communications System for jamming satellite links and the maturation of the mysterious X-37B spacecraft, which is a small, unmanned knockoff of a space shuttle, as a long-endurance, reusable platform capable of a variety of offensive military applications.

In all three of the leading spacefaring countries, bellicose rhetoric has escalated alongside rising military space expenditures. Leadership statements now emphasize the pursuit of space dominance or control, and they categorically refer to space as just another domain for military operations, stressing that even as land, sea, and air have known arms races and armed conflict, space too inevitably will be fully weaponized. Just as U.S. authorities regularly refer to space as the “ultimate high ground” for future warfare, Chinese air force leaders have come to assert that “militarization of space is a ‘historic inevitability.’” The bureaucratic structures in each country reflect this newfound belligerence: Trump’s establishment of the new Space Force was sold partly as a necessary response to similar institutional reorganizations already implemented in Russia and China.

In sum, the portrait of space security today bears an eerie resemblance to Warnke’s description of the nuclear realm 45 years ago. There is a new cycle of zealous competition among the United States, Russia, and China, with each claiming to offset the provocative initiatives of the others, resulting in a nervous, diminishing security for all. Pursuit of absolute control or dominance in space is as futile as in nuclear realm, and it is likewise staggeringly expensive.

The Absence of Arms Control in Space

The early years of the space age were remarkably productive for international law. Within only a decade after the launch of Sputnik, leading states had concluded the 1967 Outer Space Treaty, the foundational instrument providing for the peaceful, lawful exploration and use of space, an instrument of constitutional significance, joined by almost all the leading space actors. The treaty contains prescient prohibitions against placing nuclear weapons into orbit and institutes restrictions on the testing of weapons or the creation of military installations on the moon or other celestial bodies. Three other treaties with wide adherence followed within another decade, quickly constructing much of the legal infrastructure for sustainable space operations.

Yet, the process ground virtually to a halt thereafter, and no major space-related treaties have been concluded since 1979. The Carter administration engaged the Soviet Union in three sputtering rounds of ASAT negotiations in 1977–1979, and a decade later, the Reagan administration injected space security into the agenda for the Strategic Arms Reduction Treaty negotiations. None of those proceedings amounted to anything lasting.

Indeed, the two most recent, somewhat feeble efforts at articulating additional rules for space have collapsed. The European Union hawked several sequential iterations of a proposed code of conduct, a non-legally-binding set of modest rules for safe space operations, but it withered due to failures in its substantive content and its negotiating process. Russia and China have likewise propounded their draft treaty on the prevention of the placement of weapons in space, but it too has run aground due to its impoverished content and resistance from the United States. The Moscow-Beijing drafts have addressed solely the phenomenon of space-based ASAT systems, which would exclude the ground-based systems of greatest current interest, and sequential U.S. administrations have also emphasized the proposal’s conspicuous silence about mechanisms for verification of compliance.

The Conference on Disarmament, a UN-affiliated entity previously successful at developing new international instruments for arms control, has been deadlocked for two decades, especially regarding concepts for preventing a new arms race in space. Despite Blinken’s recent exhortations, there is little prospect that fresh initiatives will spontaneously spring from that source.

Conspicuously absent in this cavalcade are any proposals, draft treaties, or concerted leadership from the United States. The Trump administration was thoroughly hostile to new arms control measures of any stripe, but the problem long predated January 20, 2017. The George W. Bush administration had been similarly frank in its opposition to new negotiations in the space field. The Obama administration was somewhat more forward leaning regarding the concept of non-legally-binding confidence-building measures in space, but it was content with offering only a passive willingness to “consider” more meaningful steps without ever sponsoring any positive concepts or texts of its own. The Trump administration, despite articulating a stream of novel space policy documents regarding topics such as exploitation of space resources, was thunderously silent about arms control in the space domain. The attitude and the concrete steps of the Biden administration are yet to be determined or unveiled.

As usual, it is difficult to beat something with nothing, and the leadership role for space diplomacy has inevitably flowed elsewhere or simply dissipated.

The Utility of Arms Control in Space

This pattern of persistent diplomatic inaction and resistance is surprising and costly. The practice of arms control could be especially valuable in the exoatmospheric environment, and the alternative tactic, relying exclusively on military buildups and the invocation of deterrence, is particularly inapt for the special circumstances of space.

Consider first the two traditional strands of deterrence theory: by threat of retaliation and by denial. Deterrence by threat of retaliation warns an opponent that “[i]f you strike us, we will strike you in return, and our counterblow will be so effective and painful that it will negate any gains you might have thought you could obtain via your initial aggression.” In two subvariants, the retaliatory blow could be symmetric, roughly corresponding to the enemy’s first strike in modality, location, and format, or asymmetric, with the initial victim selecting the time, place, and manner of its response to shift the battleground to its own advantage.

This rationale and these options are familiar staples in the nuclear realm; they underpinned the concept of mutual assured destruction, which earned at least a portion of the credit for preserving Cold War stability and avoiding a nuclear World War III. Their successful translation to the space environment, however, is much less certain.

First, the profound asymmetry in the current and foreseeable exploitation of and dependence on satellites confounds the notion of a fully symmetric retaliation in response to any attack on a U.S. space system. That is, if Russia or China were to strike a U.S. satellite and the United States were to retaliate in kind, the tit-for-tat ASAT weapons exchange would continuously harm U.S. interests more than those of the others. As noted, the United States relies on space systems for military and civilian applications far more than its competitors and has the most to lose when those assets are degraded. In short, the U.S. ASAT system will run out of targets long before the opponents do.

Alternatively, the United States might attempt to circumvent that futility by adopting a practice of asymmetric retaliation, striking, for example, at the aggressor’s ground-based installations from where their initial ASAT onslaught was launched or at the command-and-control facilities that directed the initiative rather than retaliating directly against the opponent’s spacecraft. That sort of asymmetric option provided considerable credibility during Cold War nuclear confrontations, where the United States might have transferred any conflict to a different geographic theater or domain of operation. In the space context, however, an asymmetric retaliation might be regarded as unhelpfully escalatory. That is, after suffering a first strike that may have damaged a U.S. space asset but did not directly inflict any human casualties or impact sovereign U.S. territory, it could be deemed unwise or illegal to up the ante by inflicting substantial numbers of deaths and injuries to people in the adversary’s homeland. Under the applicable international law of war, a second strike need not be identical to the provocation in location or manner, but it must nonetheless be proportional in scale and effects. Going beyond that level might impress participants and outside observers as moving in the wrong direction.

As the alternative form of deterrence, deterrence by denial is a strategy to persuade the enemies not to strike by convincing them that they will fail in the effort because the target possesses the means to intercept their attack or to frustrate their attempt to inflict significant damage. Within the nuclear realm, this strategy led to programs to disperse U.S. retaliatory forces among multiple platforms (the so-called triad of intercontinental ballistic missiles, submarine-launched ballistic missiles, and bombers), harden or hide those assets, and ensure against creating a single point of failure. It also inspired efforts to invent anti-missile systems, interrupt the enemy’s kill chain, and protect the civilian population by civil defense training and sheltering.

Some of those approaches retain a degree of validity for application to satellites, and U.S. planners have already begun to undertake steps to enhance the resiliency of the U.S. space architecture, such as the deployment of larger numbers of smaller, less expensive satellites dispersed at multiple altitudes and azimuths rather than relying on only a handful of exquisite, expensive multifunction behemoths. There are also nascent efforts to revivify some terrestrial alternatives to satellite systems as fallbacks in case GPS, broadband communications, and other now-familiar services degrade.

The limits on how well satellites can be immunized from attack are stark. Spacecraft will always be soft targets. They cannot be heavily armored or deft enough to dash away from an ASAT weapon, and they mostly follow known, predictable orbital pathways, constituting delicate, expensive sitting ducks. Just as it has proven futile and wasteful to pursue the chimera of a perfect anti-missile nuclear defensive shield, it also appears that the offense enjoys a perpetual advantage in military space operations—deterrence by denial may be unobtainable.

Conversely, a policy of arms control should be even more robust and successful in space than it has been in the nuclear realm for several reasons. First, the cat is not yet fully out of the bag: Although nine countries are widely attributed as having nuclear weapons, only four (the United States, China, Russia, and now India) have tested kinetic ASAT weapons. Moreover, the three chief actors have conducted 1,790 nuclear weapons tests, but they have been responsible for only 61 ASAT tests, most of which were completed decades ago by the United States and Soviet Union. Most vividly, unlike nuclear weapons, ASAT weapons have never been wielded in combat.

More importantly, each of the leading states has significant policy incentives for pursuing sensible arms control in space. For the United States, the primary inducement is to preserve the currently precarious security in space, protecting its burgeoning investment in satellite systems. Russia and China should feel an offsetting imperative to slow down the U.S. ASAT programs, restraining a potentially overwhelming U.S. technological leap for space control.

Moreover, new initiatives in arms control would not have to start from scratch. They could take root in the extant preliminary understandings about viable rules of the road, ensconced in organic space treaties and a raft of recent, non-legally-binding, internationally accepted guidelines about avoiding the proliferation of harmful debris in space and about the long-term sustainability of space activities.

The noted democratization of space also contributes to the viability of an arms control regime. As more countries and more private commercial enterprises become active in space, they will demand a stable, predictable regime, one in which their investments will be protected, not continuously jeopardized. The broad, multilateral support for avoiding an arms race in space has long been frustrated. It can now be marshalled to support meaningful progress.

Toward a More Effective U.S. Approach

There is no dearth of viable ideas for arms control innovations in space.4 Plausible structures could include test bans, restricting the altitudes for ASAT tests and banning debris-creating tests altogether; keep-out zones, establishing a safety sphere around critical national security spacecraft; and no-first-use pledges, modifying national declaratory policies and doctrine regarding attacks on satellites. The literature abounds with provocative proposals, some similar to tried-and-true measures that proved successful within the nuclear realm and some unique to space. Of course, arms control is no panacea, and it comes with no guaranties. Yet, the failure to try this technique for pursuing security in space is strange and counterproductive.

More fundamental than any particular proposal is the importance of the Biden administration deciding early and publicly to reverse the long-standing stasis in space arms control. The United States should recognize that a pattern of continued militarization of space is insufficient to provide the stability on which its economy and its armed forces depend, so the tools of diplomacy and international law should be marshalled too.


The most striking feature of the concept of deterrence is that it is fundamentally a psychological phenomenon, an effort to persuade an adversary not to exercise military power against the United States. Attempts are made to convince the potentially hostile foreign leaders that if they attempt to strike, they will fail or suffer unacceptable harm in return. In sharp contrast, arms control operates in the realm of physical reality—it attempts to reduce or eliminate an enemy’s armaments, interdicting their sheer ability to inflict pain. Arms control offers the only way—the only peaceful way—of directly diminishing the number and quality of destructive weapons that a potential enemy state possesses and points against its adversaries.

Both strategies have their place, and wise national security policy in the nuclear and space domains should draw intelligently on both approaches as the technology and the politics permit. What is so striking today is the monopoly power that deterrence and defense have come to exercise. They have virtually excluded arms control measures from the dialogue about security in space, a realm in which treaty negotiations could offer significant new promise.

Writing in 1975, Warnke addressed only the nuclear, bilateral U.S.-U.S.S.R. dimension of international security. Today, the problem has grown steadily more complicated, extending upward to space and embracing a third near-peer competitor in China. Yet, Warnke’s imagery and his central theme remain intact: the only victory the tired apes can enjoy will come from jumping off that overly worn treadmill.



1. Paul C. Warnke, “Apes on a Treadmill,” Foreign Policy, No. 18 (Spring 1975), pp. 12–29.

2. “Secretary Blinken’s Remarks to the Conference on Disarmament,” U.S. Department of State, February 22, 2021, https://www.state.gov/video-remarks-to-the-conference-on-disarmament/.

3. UN General Assembly, “Reducing Space Threats Through Norms, Rules and Principles of Responsible Behaviours,” A/RES/75/36, December 16, 2020.

4. For a recent survey of creative, intriguing concepts, see Victoria Samson and Brian Weeden, “Enhancing Space Security: Time for Legally Binding Measures,” Arms Control Today, December 2020, pp. 6–13.


David A. Koplow is a professor of law at the Georgetown University Law Center. This article is based on his essay, “Deterrence as the MacGuffin: The Case for Arms Control in Outer Space” (2020), in the Journal of National Security Law & Policy.