Test ban for hypersonic missiles?

By Mark Gubrud, Rajaram Nagappa, Tong Zhao, August 6, 2015

The technology surrounding missiles that fly at five or more times the speed of sound is not mature. But several nations have either tested hypersonic missiles or intend to do so. The envisioned military value of hypersonic delivery systems lies in their ability to strike quickly over long distances while evading early-warning radars and ballistic missile defenses—but some proponents of the technology also argue that hypersonics could replace nuclear weapons in some roles. Critics, meanwhile, see hypersonic missiles as destabilizing: They could be mistaken for ballistic missiles, could be used in attacks against nuclear and other strategic military assets, and could even be outfitted with nuclear warheads. Amid these concerns, calls have emerged to halt a developing hypersonic arms race by enacting a moratorium on hypersonic testing and eventually establishing a test ban treaty. Below, experts from the United States, India, and China debate this question: How serious a threat to global security do hypersonic missiles represent, and is a test ban the best way to moderate such a threat?

Round 1

Banning hypersonics: Too much to hope for

If relationships between weaker and stronger nuclear weapon states are to remain stable, mutual assured destruction must be maintained in a robust, credible way. But nations' faith in the survivability of their nuclear deterrents could be seriously undermined by hypersonic missiles—either boost-glide systems or hypersonic cruise missiles—armed with conventional warheads. Some analysts in China suspect that the United States is seeking the ability to eliminate Beijing's nuclear deterrent in a first strike—and if Washington successfully develops hypersonic missiles, Beijing’s confidence in the credibility of its nuclear deterrent would only erode. (In a similar vein, Delhi might someday grow concerned about a Chinese hypersonic strike against India’s small nuclear arsenal.)

Already, some in China are discussing whether Beijing should, in the face of new conventional threats to its nuclear arsenal, alter its unconditional no-first-use policy. And a lack of understanding regarding future hypersonic missile policy has already begun to complicate strategic security dialogue between China and the United States—and between the United States and Russia. These countries' deeply-rooted mutual mistrust makes it inevitable that, if one nation deploys hypersonic missiles, another nation will perceive the threat in an exaggerated manner. Nations concerned about the survivability of their deterrents might build additional nuclear facilities deep underground—or begin to demonstrate less transparency about their nuclear policies. Such developments would hobble efforts to build confidence between national military establishments. Dialogue may help allay concerns—but only to a limited extent.

The greatest advantage of hypersonic missiles is their promptness, but promptness is also the technology's greatest source of risk. Decision makers in a crisis, if they wish to take advantage of hypersonic missiles' speed, will have to decide whether to launch preemptive strikes before fleeting windows of opportunity close. Risky decision making would be encouraged. And because hypersonic missiles would likely be intended for use against strategic targets—command and control centers, long-range surveillance systems, and even missile launch vehicles—conflicts could easily escalate if hypersonic missiles were used.

Tough obstacles. But can nations avoid a costly, technology-driven, hypersonic arms race by embracing preventive arms control? The prospects don't look very encouraging.

First, imposing technical limits on programs for hypersonic missile development would be difficult. No clear technical distinction can be made between hypersonic missiles and other conventional capabilities that are less prompt, have shorter ranges, and also have the potential to undermine nuclear deterrence. Nations would find it quite difficult to draw lines controlling the different technologies. Moreover, one possible US objective in developing hypersonic missiles is to gain the ability to preemptively strike small nuclear arsenals such as North Korea's—as opposed to, say, China's. But North Korea's nuclear and missile capabilities have been advancing quickly. By the time hypersonic technology is deployed, it may not be possible to structure US hypersonic capabilities in such a way that North Korea's nuclear weapons could be threatened but China's could not. And even if it were possible—through diplomatic arrangements or unilateral restraint—to keep US hypersonic capabilities limited to a small scale, Russia and China would remain concerned about the chance of future expansion.

Second, hypersonic systems are not necessarily intended only for delivering conventional weapons. Some nuclear weapon states, concerned about future advances in missile defense, are retaining the option of mounting nuclear warheads on boost-glide vehicles or hypersonic cruise missiles. Highly maneuverable systems such as these could significantly increase nuclear warheads' ability to penetrate midcourse missile defense. The stakes in developing hypersonic missiles are therefore high—higher than would surround the development of a new, purely conventional capability. So nations may be very reluctant to renounce hypersonic missiles.

Third, even though Washington may not be developing hypersonic missiles in order to target the nuclear arsenals of other major nuclear powers, some US analysts express interest in targeting such countries' non-nuclear strategic targets. Hypersonic missiles could become part of so-called "defense suppression" operations that would seek to counter the "anti-access/area denial" capabilities of China and others. Antisatellite assets could also become targets.

At a time such as this, when tensions between some of the major investors in hypersonic technologies appear to be rising, severe challenges face efforts to control such technologies. Increasing friction in the South China Sea is just one example of US-Chinese military tension in the Asia-Pacific region. In Eastern Europe, NATO and Russia appear headed toward a more hostile conventional military relationship. In such circumstances, national leaders are usually more interested in investing in new military technologies than in controlling them—especially technologies that may hold the key to prevailing on future battlefields.

Achievable steps. Given all this, banning research and development programs for hypersonic missiles will be difficult. Limited transparency measures, such as data exchanges and notifications, might be within reach—but even these mechanisms will require persistent effort and engagement from the major players.

In the short term, the best that can realistically be achieved might be unilateral risk reduction measures (backed up by diplomatic efforts that build confidence in these measures). For example, nuclear weapon states should for their own benefit refrain from developing strategies that involve using hypersonic missiles against nuclear targets. The 2013 US National Defense Authorization Act required the Defense Department to conduct a study on Washington's capability to "neutralize" Chinese underground networks, where some nuclear weapons are deployed, with "conventional and nuclear forces." Such a study suggests an actual interest in targeting nuclear weapons through conventional means—but anything of this nature should be scrupulously avoided.

Likewise, strategies that might exacerbate the "fog of war" should be carefully scrutinized. For instance, though preemptive strikes with hypersonic missiles against command, control, and communication centers might be a useful way to counter "anti-access/area denial" capabilities, they also risk "blinding" and confusing an adversary's leadership—to the extent that decision makers mistakenly believe a nuclear strike is under way. This would represent a serious risk of inadvertent escalation. Any strategy that blurs the line between conventional and nuclear warfare should be rejected. Nations deploying hypersonic weapons should vigorously pursue unilateral steps that will forestall destabilization—if in fact these technologies are going to be deployed at all.


New technology, familiar risks

Hypersonic missiles, if successfully developed, will cover long distances in a short time. Some observers argue that these missiles, in the hands of a nation that intended to overwhelm an adversary's early warning and missile defense systems, would pose a serious threat to global security and therefore should be banned. This is a contestable idea. The technology surrounding hypersonic missiles is still very much under development—but even if it is perfected, it will not add much to the security threats already posed by deployed weapons systems such as ballistic missiles.

Indeed, ballistic missile re-entry vehicles already operate at hypersonic velocities for a considerable part of their flight trajectory. For example, the re-entry vehicle of an intermediate-range ballistic missile whose range is, say, 3,000 kilometers travels at hypersonic speeds until it descends to an altitude of 30 kilometers (about 30 seconds from impact). But the threat that these weapons pose is generally accepted and accounted for. Sensors are capable of tracking ballistic missiles' flight. Missile defense systems are growing more robust.

The differentiation problem. Missiles travelling at hypersonic speeds—that is, at or above five times the speed of sound—offer the advantages of long range, high speed, and short flight times. No country has yet deployed a hypersonic system, but several are carrying out research and development. The main avenues of research are hypersonic cruise missiles and hypersonic glide vehicles. In nations pursuing hypersonic technology, glide vehicles appear to be the primary focus of development.

They can be used in combination with existing ballistic missiles (whether intercontinental, intermediate-range, or submarine-launched). The ballistic missiles would boost the glide vehicles to their release altitude, and the glide vehicles would then be allowed to glide downward at hypersonic speeds. Hypersonic cruise missiles, on the other hand, are boosted to operating altitude and velocity with an appropriate (non-ballistic) missile stage and are then powered by supersonic combustion ramjet (or scramjet) propulsion. The range of these missiles depends on the amount of fuel they can carry.

One potential problem that hypersonic missiles present is how to differentiate the launch of a conventionally-armed hypersonic glide vehicle or cruise missile from a strategic weapon launch. How are other nations to be certain what type of warhead a missile carries? Hypersonic missiles are also designed to be maneuverable—so it is possible to misunderstand a missile's intended destination. A nation might conclude, for example, that its nuclear forces were under attack when in fact its conventional forces were the intended target.

Impractical approach. The United States is the leader and trendsetter in hypersonic technology. Other countries are playing catch-up. China is now making investments in hypersonic missile technology, and more countries are bound to follow suit.

Whenever nations conduct tests that demonstrate the speed, range, precision, and accuracy of a weapons system, questions arise regarding that nation's intentions (as well as regarding the implications of the weapons system itself). Where hypersonic weapons are concerned, ambiguity surrounding national intentions is real. The result of this could be destabilization and perhaps even an escalatory conflict scenario. The solution to these problems, however, does not lie in banning hypersonic missile tests. Rather, it lies in understanding threats, managing them, and enacting confidence-building measures.

Even in the current scheme of things, with no hypersonic missiles deployed, ambiguity exists—when, for example, a nation's conventional and strategic missiles fall under a common command and control structure. And the missile launches of nations that carry out "anti-access/area denial" strategies can be ambiguous both in terms of warhead type and target.

Putting a moratorium on hypersonic testing is not the practical approach to solving such problems. The fact is that nations will make decisions about the deployment and testing of hypersonic weapons on the basis of relative power and competition. If the United States successfully develops hypersonic technology, one can be sure that Russia and China will do the same. Other countries, such as India, may follow. Nations at the early stages of hypersonic technology development won't wish to place themselves at a disadvantage to countries whose technology is more advanced. In fact, some nations would consider a moratorium on testing discriminatory.

And importantly, hypersonic technology has applications in the civilian space domain—in the areas of space transportation systems, re-entry capsules, and landing and reuse. Technological advancement in the civilian space realm requires testing, and nations with a stake in these civilian applications would oppose any mechanism that denied them the freedom to carry out tests.

Building confidence. Yes, hypersonic technology carries the risk that missile launches could be misidentified—but re-entry vehicles that are launched by ballistic missiles and re-enter at hypersonic speeds are not new. Understanding the re-entry trajectory of hypersonic missiles is complicated by maneuverable re-entry vehicles, but that is also true of existing ballistic missiles. The international community has responded to the ambiguity and escalatory risks of ballistic missiles with risk mitigation measures, detection and defense systems, and an effort to maintain a balance between deterrence and retaliation capabilities. This approach will need to be replicated for hypersonic missiles.

The United States has said it will use hypersonic missiles to supplement its conventional capabilities—not to deliver nuclear warheads. This is a welcome approach. Such a policy, from the very beginning of a conflict, could help keep the nuclear option at a remove. It is important for other nations developing hypersonic missile technology to adopt similar policies.

Another important step is to put in place confidence-building measures. These measures cannot involve only the United States and Russia, as often happened in the past; other countries that test hypersonic technologies, for either civilian or military applications, must be included as well. One important confidence-building measure would be to specify that hypersonic missiles will be used only with non-nuclear warheads. Other useful measures would include providing advance notice of tests; choosing separate, distinctive launch locations for tests of hypersonic missiles; and placing restraints on sea-based tests.

Technology for hypersonic missiles is still in the development stage. Production and deployment are not imminent. It is premature at this point to consider banning weapons tests—especially when hypersonic technology also has applications in the civilian realm. The best path forward is to use the time before deployment to debate the risks of hypersonic missiles and develop deterrents to their use—and to work out necessary confidence-building measures.


Just say no

Hypersonic flight may sound like screaming good fun—but it’s not meant for you. It’s meant for weapons that would probably be used only in the opening salvos of a nuclear war.

No nation has yet succeeded in developing non-ballistic missiles that fly long distances at or above Mach 5 (five times the speed of sound), but the United States and China are conducting tests. Russia and India say they are jointly developing a hypersonic missile. Pakistan, of course, must do whatever India does. France will find that it cannot be France without hypersonic missiles, while Britain must never falter… and on and on it will go, in a new round of an old arms race that still leads only to stalemate or oblivion. Fortunately, there is a simple, risk-free, and highly verifiable way to avoid this dismal prospect: ban tests of hypersonic missiles.

Why does anyone want hypersonic missiles anyway? For more than half a century, ballistic missiles have provided the capability to hurl warheads above the atmosphere and hit any spot on the globe within minutes. The concept of hypersonic missiles, which would plow through the atmosphere at a fraction of the speed, has been around almost as long—but the extreme stresses, high temperatures, and corrosive effects of hypersonic flight have frustrated efforts to develop practical weapons. Ballistic missiles are simpler, cheaper, faster, and can reliably defeat missile defenses with lightweight decoys and other simple countermeasures.

With their high costs and small payloads, hypersonic missiles would be ill-suited to a sustained military campaign, but could be useful as tip-of-the-spear weapons. Armed with conventional warheads and their own kinetic energy, they could attack ships, radar and communications antennas, command and weapons bunkers, airfields, missile launchers, and other strategic assets. They could also carry nuclear warheads, and could fly in under the radars that watch for ballistic missiles. US strategists propose that hypersonic weapons could be used for “conventional prompt global strike” without the risk of being mistaken for a nuclear attack—yet Washington alleges that China intends its hypersonics for nuclear delivery.

Testing so far. Hypersonic missiles come in two main flavors: boost-glide vehicles and powered-flight cruise missiles.

For boost-glide vehicles, a rocket is used to launch a glider on a high trajectory into space. When it re-enters the atmosphere, the glider pulls up to fly horizontally, unpowered, for up to thousands of miles at initial speeds in the high hypersonic range, Mach 10 to 20 (about 7,000 to 14,000 miles per hour).

The United States tested a boost glide vehicle at the high end of this speed range in 2010 and 2011, but the tests ended in failure. Another program, the Advanced Hypersonic Weapon, aimed at lower speeds (around Mach 12) and reportedly experienced success in November 2011. But in a second test in August 2014, the same weapon blew up over the launch pad. China, meanwhile, conducted three tests of its own hypersonic glide vehicle, known as the WU-14, in 2014. China’s second test, in August, was a spectacular failure; the January and December tests are widely assumed to have been at least partial successes. A fourth test, also apparently successful, was reported just weeks ago.

Hypersonic cruise missiles, on the other hand, would be boosted initially by a small rocket and then powered by a supersonic combustion ramjet (or scramjet) for flight in the low hypersonic range—Mach 5 to 10, or around 3,000 to 7,000 miles per hour. They would cover distances up to about 600 miles. Such weapons would be ideally suited for naval strikes, land strikes from air or naval platforms, or cross-border surprise attacks between neighboring countries.

In May 2013, the United States became the only nation known to have successfully tested such a missile, the X-51A, a prototype for the planned High Speed Strike Weapon, which would cruise at about Mach 5. But China is reportedly working on similar technology and studying concepts for its use. Russia and India, meanwhile, jointly market a ramjet-powered supersonic cruise missile known as BrahMos, based on a Soviet-era design. They have announced a project to produce a hypersonic follow-on, the BrahMos 2, which they say will fly at Mach 7.

Testing no more. In the tests conducted so far, successes have demonstrated that it's possible to build functional hypersonic weapons—indeed, if work continues, hypersonics are likely to become reality over the next decade. Failures, meanwhile, show that developing reliable and militarily useful hypersonic weapons is impossible without testing.

A hypersonic test ban would be strong arms control. No nation would base preemptive strategic attack plans on weapons that have not been thoroughly tested, debugged, and proven reliable.

A ban would also be verifiable. While development of hypersonic missiles can be conducted in laboratories and wind tunnels to some extent, the kind of full-up tests needed to confirm performance and debug problems can only be carried out in the open air—in full view of sensors based in space, at sea, on land, and even in the hands of ordinary people.

It could begin with an informal moratorium. The United States, China, Russia, or India could initiate a moratorium by announcing that it was putting on hold plans for future hypersonic testing—while inviting other nations to postpone their own tests and to seek a permanent ban. In time, a convention could be organized where the precise parameters of a global ban could be negotiated and a formal treaty could be drafted.

Initiating or joining a test moratorium and adhering to a ban would involve little risk. Hypersonic missiles represent an escalation of strategic threat but are hardly sufficient to ensure a successful disarming first strike. And no nation would be able to secretly perfect and then mass-produce the weapons so quickly that rivals would have no chance to catch on and catch up.

Babies and bathwater. Some will argue that banning hypersonic missiles would prevent the development of hypersonic “space planes” that could cross oceans in an hour, or fly to orbit. In reality, the economics of such concepts are highly dubious. But a hypersonic missile test ban need not stand in their way. Missiles are easy to distinguish from the much larger vehicles that might make sense as space planes. A treaty could specify the technical criteria needed to make that distinction, as well as express the intent not to block peaceful activities.

Hypersonic missiles are just one aspect of a renewed strategic arms race among the world’s major nuclear-armed powers. Sources of this resurgent danger include smoldering geopolitical rivalries, shifts in economic power, and new weapons made possible by emerging technology. The world has failed so far to put the nuclear genie back in the bottle, and new genies are now getting loose: space weapons, cyber warfare, drones, and autonomous weapons. Weapons based on synthetic biology and nanotechnology loom on the horizon.

Seen in this context, a test ban for hypersonic weapons stands out as an easy and highly significant opportunity to resist an onslaught of destabilizing weapons technology. Let's just say no to hypersonic weapons.


Round 2

Political obstacles, technical tangles

This roundtable asks its participants to assess the threat to global security posed by hypersonic missiles—but so far, the authors have expressed no serious disagreement about the idea that hypersonic missiles are destabilizing. So the question becomes whether nations will nonetheless embark on a full-scale hypersonic arms competition.

Most people, including me, would prefer to answer "no." As my colleague Mark Gubrud wrote forcefully in Round One, “The world has failed so far to put the nuclear genie back in the bottle, and new genies are now getting loose.” Hypersonic missiles are a genie that I, like Gubrud, believe should stay in the bottle. But banning tests of hypersonic missiles will not be as easy as Gubrud suggests.

First, in the United States, the conviction that technological innovation is the best way to address security challenges is close to an unshakable religion. Many US officials and analysts are convinced that hypersonic technology represents the next revolution in military affairs. And just as Russia and China have failed to persuade the United States to limit missile defense, it is hard to imagine anyone persuading Washington to agree to limits on hypersonic research and development.

Second, Russia and China—also major investors in hypersonic technology—do not perceive hypersonic missiles as the only threat to their nuclear deterrents. They also harbor serious concerns about precision conventional weapons that travel below hypersonic speeds. Banning hypersonic tests would not by itself address Russia and China's concerns about the survivability of their deterrents—so what are these nations' incentives for banning hypersonic tests?

Third, Russia and China appear to seek hypersonic missiles precisely because they are concerned about the survivability of their nuclear forces. Russia's investment in the technology, for example, seems motivated by the desire for a delivery system that can penetrate any future US missile defense system. The same may be true of China. If Moscow and Beijing's concerns about US missile defense cannot be resolved, it will be very difficult to persuade Russia or China to agree to a hypersonic test ban or moratorium. And, in fact, disputes about missile defense are only getting more intense amid the Ukraine crisis, with some US analysts openly proposing that US missile defenses should target Russian missiles.

Getting technical. Beyond these strategic considerations, a set of technical problems will make a hypersonic testing ban more difficult to achieve than Gubrud hopes. First, hypersonic cruise missiles rely on scramjet technology, which also has potential civilian uses. Gubrud, aware of this issue, proposed in Round One that testing of “vehicles that might make sense as space planes” should be allowed under a test ban. But this would create such a big loophole that the utility of a test ban would be destroyed. Indeed, the "space planes" whose testing would be allowed according to Gubrud's proposal would be very attractive vehicles for delivering munitions or conducting other military missions. Moreover, the development of large civilian space planes might well start with the construction and testing of smaller vehicles—which could be very difficult to distinguish from hypersonic cruise missiles. And it might even be possible to build missiles that in fact were scaled-down versions of large space planes.

Second, verifiably distinguishing boost-glide hypersonic vehicles from existing terminally guided ballistic missiles might not be possible. Both technologies rely on boosters to deliver maneuverable re-entry vehicles to their release altitudes, with the re-entry vehicles then traveling at hypersonic speeds. The only differences are where the ballistic trajectory ends and how maneuverable the re-entry vehicles are. Terminally guided ballistic missiles are already being tested and deployed—as demonstrated by China’s DF-21D antiship ballistic missile. Drawing clear distinctions between these weapons and hypersonic missiles may be technically impossible.

I would love to be proven wrong—but I don’t think a hypersonic test ban is going to be instituted soon. Political motivation is lacking. The technical challenges are real. Nonetheless, a thorough discussion about the pros and cons of developing and deploying hypersonic missiles is urgently needed. Hypersonic development programs cannot remain technology-driven. Rather, they must be guided by holistic, strategic deliberations.


Hypersonics are here to stay

My roundtable colleague Mark Gubrud argues for a ban on hypersonic missile testing—an unlikely proposition when the pace of hypersonic missile development is only accelerating.

On June 7, China carried out a fourth test of its hypersonic glide vehicle, the WU-14. The vehicle is said to have traveled at Mach 10; the test reportedly involved "extreme maneuvers." China has now carried out four hypersonic tests in a span of 18 months—indicating that Beijing accords great urgency and priority to the development of hypersonic technology.

Russia is developing its own hypersonic glide vehicle, the Yu-71. The three tests conducted since September 2013 (including a test in February of this year) appear to have been unsuccessful, but the Russians possess the technological wherewithal to field a successful hypersonic glide vehicle eventually.

The US military suffered a setback last August in a test of its Advanced Hypersonic Weapon. But the United States has a long history in hypersonic technology development, and last summer's setback will not dampen Washington's plans.

Weapon systems provide true deterrence only when their capabilities are demonstrated through testing. One cannot conceive of circumstances under which nations whose security plans include hypersonic missiles would champion or support a hypersonic missile test ban. To the contrary, they appear certain to conduct testing in order to perfect their technology. After they have perfected it, perhaps a test ban can be discussed.

A look back at the Partial Test Ban Treaty of 1963, which prohibited tests of nuclear weapons in the atmosphere and certain other environments, may be instructive. By the time the treaty was instituted, four nations had already carried out atmospheric tests (the United States, the Soviet Union, Britain, and France). The United States and the Soviet Union had also carried out nuclear tests in space—and gained first-hand knowledge of the disastrous consequences of space testing. Since 1980 no atmospheric tests have been conducted—but the test ban was successfully negotiated only after key nations had demonstrated the reliability of their weapon designs through an adequate number of tests.

Meanwhile, though some nations have conducted tests of kinetic kill antisatellite weapons—and the dangers surrounding such tests are well known—the international community is not working toward a ban on antisatellite weapons. Rather, it is debating codes of conduct, rules of the road, and so forth. Simply put, nations do not generally rush to ban tests of new weapons.

Gubrud's suggestion that the United States, China, Russia, or India might initiate an informal moratorium on testing is a non-starter. Hypersonic technology hasn't yet reached design maturity—unlike nuclear weapon technology in the early 1960s. Therefore it is far-fetched to expect Washington, Beijing, or Moscow to propose a testing moratorium. India's priority will be to reach the testing stage.

Even some nations not currently developing hypersonics will likely, in response to real or perceived threat scenarios, join the fray of hypersonic missile development. Still other nations, though technically incapable of developing hypersonic missiles, would oppose a test ban because they might someday wish to purchase hypersonic missiles, or because they believe they could benefit from the proliferation of hypersonic technology.

With so much destructive power already in existence, the need for hypersonic missiles is questionable. But in the real world, unfortunately, the agenda is driven by powerful and technologically advanced countries. Their agenda tends to be far removed from idealistic notions. Hypersonic missile technology is here to stay—though, as Tong Zhao wrote in Round One, nations planning to develop and deploy hypersonic weapons must "vigorously pursue unilateral steps that will forestall destabilization."


Hypersonics: Why and why not

To many people, hope for the future is epitomized by the words of George Bernard Shaw: “You see things; and you say, ‘Why?’ But I dream things that never were; and I say, ‘Why not?’” But when a resurgent arms race, propelled in part by the dreams of weapons designers, threatens the world, hope must begin with asking “Why?”

In Round One, neither Rajaram Nagappa nor Tong Zhao provided compelling reasons why hypersonic missiles should be developed. Rather, both authors illuminated some of the reasons that developing these weapons is dangerous and undesirable. But both seem to assume that, in the absence of a special, very compelling reason to do otherwise, hypersonic missiles will be developed.

I’ve never argued that hypersonic missiles represent more than a minor escalation of threat but, as Nagappa and Zhao seem to agree, these weapons do seem most suited to strategic attack. A test ban would be a simple, verifiable, and highly effective arms control measure to block one dangerous lane of an extremely dangerous arms race. So that’s my “Why not?”

Nagappa dismisses this idea as “not the practical approach.” Zhao writes that it cannot "realistically be achieved." But neither argues that a test ban would be counterproductive or unverifiable, or that it would fail to block development of hypersonic missiles. My roundtable colleagues are simply pessimistic.

Not especially hard. Both authors claim that a test ban would be technically difficult to negotiate. I believe that, compared with other arms control problems, this one is not especially hard. Nagappa blurs the boundary between ballistic and hypersonic missiles when he writes that ballistic missile re-entry vehicles travel "at hypersonic speeds." But most of this travel is above the atmosphere, where the concept of hypersonic flight does not apply; hypersonic missiles are defined by their ability to endure plowing through the atmosphere over long distances at hypersonic speeds. Zhao asserts that “No clear technical distinction can be made” to delimit the weapons whose testing would be banned. But size, speed, propulsion type, and distance of hypersonic flight are some of the criteria that can be used.

What might lead to difficulties in negotiations is a lack of political will, particularly if testing continues and the parties try to manipulate the technical parameters of a ban to include or exclude particular systems in development. This is one good reason for beginning the test ban effort with unilateral moratoria that could establish good faith and common purpose.

Nagappa argues that some nations would regard a test ban as discriminatory, since the United States, China, and Russia have already tested experimental prototypes. But under a test ban, all nations would forgo the development of actual, usable weapons. Meanwhile, the knowledge gap between nations would close over time due to the development and diffusion of related space, materials, and propulsion technologies (whose peaceful uses need not be impeded by a missile test ban).

Little use, real danger. Zhao gives considerable credence to the military usefulness of hypersonic weapons. I question how useful they can be. Hypersonic missiles are expensive. Their small payloads limit lethality unless they carry nuclear weapons. Ballistic missiles get to targets faster. Subsonic cruise missiles can be stealthy and can home on small targets, whereas the extreme temperatures and shocks produced by missiles in hypersonic flight would announce their presence and keep them blind. In Zhao’s scenario of a US attack on North Korean nuclear weapons, ballistic or subsonic cruise missiles launched from air, sea, or land nearby could achieve shorter flight times and greater lethality than hypersonics launched from far away. Nor are hypersonic missiles needed to ensure nuclear deterrence. They may be immune to ballistic missile defenses that are not designed to intercept them, but they would be vulnerable to appropriate defenses. They would also be unable to saturate defenses with lightweight decoys as ballistic missiles can.

Hypersonic missiles, if they are deployed, would not be the first weapons of dubious usefulness to poison international relations, escalate an arms race, and increase the risk of war. But why do that again? Shouldn’t a test ban be the preferred alternative?


Round 3

What’s possible: Hypersonic harm reduction

A central paradox of the hypersonic arms competition now under way is that the United States—the competition's initiator and frontrunner—has so far secured no military advantage from hypersonic technology but already perceives an emerging threat from it. Indeed, a US House of Representatives committee report on the 2015 defense authorization bill expresses concern that "China and other competitor nations pose an increasing challenge to the United States' technology edge in … hypersonic weapons." The report requires the Pentagon to "explain how the Department of Defense intends to develop and deploy a defensive capability to counter this emerging threat." So hypersonic competition, like other competitions in military technology, is quickly becoming a self-reinforcing spiral. Nations interested in hypersonic missiles, convinced that faster weapons are the weapons of the future, embrace hypersonics without thinking through the advantages and disadvantages—and especially without thinking through other nations' reactions.

My roundtable colleague Mark Gubrud, with his proposal for a hypersonic missile testing ban, is seeking solutions to hypersonic competition. I applaud him for it. And I share his general skepticism about the military value of hypersonic missiles. Where we disagree is on a test ban's feasibility.

Gubrud proposes that the movement toward a test ban begin with unilateral testing moratoria. But this idea will not go far unless the United States agrees to engage—and the United States has shown little interest in arms control commitments that cannot be effectively verified. A prominent example is the Treaty on Prevention of the Placement of Weapons in Outer Space, an arms control measure proposed by Russia and China in 2008 but repeatedly rejected by Washington, in large measure because of verification concerns. A hypersonic test ban, despite what Gubrud believes, would not be easy at all to verify—for the technical reasons that I covered in Round Two.

So what is a feasible response to the problems posed by hypersonics? One way forward, though it is far from an ideal path, is for nations to refrain on a unilateral basis from adopting destabilizing policies regarding the deployment and use of hypersonic technology. In Round One I offered some specific ideas in this vein. First, nations could pledge not to use hypersonic missiles against nuclear targets. Second, they could renounce strategies—such as preemptive hypersonic strikes against command, control, and communication centers—that could intensify the "fog of war" and lead to inadvertent escalations.

Meanwhile, my roundtable colleague Rajaram Nagappa has called for all countries to refrain from arming hypersonic missiles with nuclear warheads. Nagappa's proposal, by maintaining a clear distinction between nuclear and conventional delivery systems, would contribute to stability. But whether his proposal can be implemented will depend to a great extent on Russian and Chinese threat perceptions regarding future US missile defense capabilities. That is, Moscow and Beijing are pursuing hypersonic weapons primarily as a hedge against future US missile defenses, which might undermine Russia and China's ability to deliver their nuclear deterrents with ballistic missiles. Gubrud suggests that hypersonic missiles themselves would be relatively easy to defend against—but I am not so sure. In particular, it would be extremely challenging from a technical perspective to build an "area defense" (as opposed to a more manageable "point defense") against hypersonic missiles. At this point in the development of hypersonics, technical uncertainty makes it impossible to draw definite conclusions about the missiles' effectiveness and their vulnerability to defensive measures.

Building consensus in favor of a test ban will be very difficult. A more practical approach is for states to ensure that hypersonic missiles, if they are to be built and deployed, are included in nuclear arms control discussions and are accounted for in arrangements limiting or reducing strategic arms.


Hypersonic missiles: Where the technology leads

Participants in this roundtable display consensus on one point: that the world already possesses enough destructive capacity and there's no need to add more. But whereas Mark Gubrud advocates a ban on hypersonic missile testing, Tong Zhao and I feel that—for better or worse—hypersonic technology is here to stay.

Technology development generally takes the form of an S-curve. Improvements come slowly in the early stages of development. Later, breakthroughs allow rapid improvement. Finally, the technology's physical limits are reached, only modest improvements are possible, and the curve levels off. Ballistic missiles have reached the last stage. Limits on their performance can be overcome only through the development of new technology—such as hypersonic missiles.

Hypersonics provide, with their speed and promptness of delivery, a means to gain and preserve the military high ground. It is inconceivable that nations already invested in gaining that high ground would agree to a ban on hypersonic testing.

But even if they were willing, a test ban would be—despite what Gubrud argues—very difficult to verify. Both hypersonic glide vehicles and hypersonic cruise missiles must be boosted to their release altitudes by ballistic missiles. Consequently, they present an infrared signature (monitored from space) and a radar cross section resembling those of a ballistic missile. As Tong Zhao wrote in Round Two, "Drawing clear distinctions between [terminally guided ballistic missiles] and hypersonic missiles may be technically impossible."

A test ban would also—again, despite what Gubrud argues—discriminate against nations that have not begun testing programs of their own. Gubrud writes that a test ban would not discriminate in the military realm because "all nations would forgo the development of actual, usable weapons" and wouldn't discriminate in the civilian realm because "the knowledge gap between nations would close over time." But in my opinion, the gap wouldn't close. Hypersonic technology is inherently dual-use, so nations wishing to maintain military advantages would jealously guard against the diffusion of civilian hypersonic technology. And after all, what could guarantee that civilian hypersonic technology wouldn't be harnessed for missile applications?

Inevitable solutions. Gubrud wonders in Round Three "just what the advantage [of hypersonic missiles] would be" and writes that "without nuclear warheads they would be incapable of destroying many hard, fixed targets." Without knowing the design specifications of hypersonic missiles, it's difficult to speculate about their payload size, lethality, cost, and the like. But it's true that hypersonics would clearly be limited in certain ways—for example, it appears that only fixed, soft targets would be vulnerable to hypersonic attack. Targets in hardened, deeply buried shelters would be much harder to reach. Hypersonic missiles could achieve deep penetration by virtue of traveling at very high speeds, but in that case their explosive payloads would be smaller—and the damage they could inflict would be lower.

This is just one of many issues that nations developing hypersonic technology must overcome before they deploy these weapons—but as hypersonic technology proceeds inevitably through its S-curve, solutions will be found. The only question is how soon. This in turn depends on political will and funding priorities in nations pursuing hypersonics. What's certain is that countries already developing hypersonic missiles—powerful nations such as the United States, China, and Russia—will not agree to a test ban until they have overcome all the technological hurdles. A test ban simply isn't on the horizon.


Hypersonic missiles: Junk nobody needs

Last September in the Bulletin, I proposed a moratorium and eventual ban on hypersonic missile testing. The following month, US Air Force Lt. Col. Jeff Schreiner proposed a similar idea in Stars and Stripes. The principal obstacle to enacting this proposal is just skepticism—the same skepticism that every successful arms control initiative initially encounters.

My roundtable colleagues Rajaram Nagappa and Tong Zhao are skeptical about a test ban, but they make no argument for hypersonics. Zhao believes a test ban is unlikely to be instituted but “would love to be proven wrong.” Nagappa portrays hypersonics as offering little beyond “destabilization and perhaps even an escalatory conflict scenario.” But he believes that a test ban must wait until after the weapons have been perfected.

Nagappa suggests in Round Two that the 1963 ban on atmospheric nuclear tests came about because nuclear weapons had been perfected by that point. But I believe that, following the 1962 Cuban Missile Crisis, governments were compelled to act by worldwide outrage over the threat of nuclear war and the radioactive poisoning of air and water. “What have they done to the rain?” asked a song of the day. Today, as nations senselessly reheat the arms race, I want people to ask “What are they doing to tomorrow?”

As Nagappa observes, the development of not only hypersonic missiles but also antisatellite weapons is accelerating—and I would add autonomous weapons and other categories to this list. Analysts and nongovernmental organizations, rather than keeping a finger in the wind, must call for a change in direction.

Misguided faith. As an American, I urge my own government to take the lead in preventive arms control—not lead a race toward new danger. I don’t feel entitled to tell other nations’ governments they should set a better example than Washington does. But I am confident of this: Hypersonic missiles will not strengthen anyone’s national security.

Proponents of hypersonic missiles incant that “the race is on” to gain “a huge strategic advantage.” Yet nobody seems able to clarify just what the advantage would be. As Zhao writes, “the conviction that technological innovation is the best way to address security challenges is close to an unshakable religion” in the United States—but this religion is not restricted to one country. Russia and China display the same misguided faith by pursuing hypersonics as a counter to ineffective US missile defenses.

There is little reason to believe that hypersonic missiles would be harder to intercept than ballistic missiles. Hypersonics' ability to perform evasive maneuvers is often cited, but their ability to see interceptors coming would be severely limited by the heat involved in hypersonic flight and by corrosive effects on sensors. Ballistic missiles also could be equipped with maneuver capabilities, and could see interceptors. Ballistic missiles can also be hidden among lightweight decoys, whereas hypersonics would always be highly observable by radar and infrared sensors.

US officials tout hypersonic missiles as alternatives to nuclear weapons for strategic strikes, but without nuclear warheads they would be incapable of destroying many hard, fixed targets. They could not be made stealthy, and would have difficulty using sensors for precise navigation—or to locate and home on mobile targets that might scoot before the missiles arrive.

As Nagappa points out, a nation possibly under attack can’t tell where a hypersonic missile is going or whether it carries a nuclear warhead. And as Zhao writes, "Any strategy that blurs the line between conventional and nuclear warfare should be rejected.” But it’s just as risky to bet that the peril of nuclear war can ever be removed from any war between nuclear powers.

I don’t worry so much about definitions, distinctions, or other technical problems of arms control for hypersonic missiles, nor about some nation circumventing a ban through the putatively peaceful development of space plane technology. A sudden “breakout” from a hypersonic missile test ban couldn't be kept secret in any case. It would confer no decisive or immediately usable military advantage, and other nations would simply follow suit. The defector would only have blown the opportunity to avoid another round of a stalemated yet very dangerous arms race.

Let’s grasp that opportunity while it still exists. Hypersonic missiles are junk.


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