Hypersonics: Why and why not

By Mark Gubrud, July 6, 2015

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?


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