A set of small, uninhabited Pacific islands, very close to China, may be the destination of some of America’s most sophisticated and controversial future weapons: hypersonic missiles that remain nimble even at five times the speed of sound. On Friday, U.S. Army Secretary Ryan McCarthy said the still-in-development weapons would likely change the future of war.

The Army — along with the Air Force, Navy, and Missile Defense Agency — has been advancing work on a variety of hypersonic capabilities. The Army expects to begin testing aspects of its Long-Range Hypersonic Weapon this year, with full flight testing expected in 2023.

Speaking at a Brookings Institution event, McCarthy said hypersonics would be key to a new kind of multi-domain task force that he was rolling out. These highly mobile units will be deployed to attack enemies at long ranges with electronic warfare, cyber attacks, and long-range munitions such as hypersonic missiles. He said the new units could be deployed to the Senkaku or Ryukyu island chains.

“You could put it down somewhere in the South China Sea” to help nullify Chinese anti-access/area denial capabilities: defenses to keep U.S. forces out of specific areas, he said.

“Hypersonics are the Pershing missile of the 21st century,” he said, referring to ground-based nuclear weapons deployed to Europe during the Cold War. “Because of the extraordinary speed and lethality of that capability, the dilemma is that if you don’t have essentially, a type of, almost artificial intelligence-like capabilities…you can’t find it, sense it, or shoot it. Because it will be there in a couple minutes.”

The Pershings came “to be seen as a hair trigger for nuclear war because of their short flight times — as little as 10 minutes,” the New York Times wrote last year. The missiles were a primary reason that Soviet leaders developed the “dead hand” system to automatically launch ICBMs at the United States.

The Army’s new concept drew skepticism from Tom Karako, senior fellow with the International Security Program and the director of the Missile Defense Project at the Center for Strategic and International Studies.

“The Army could put high-value, mobile hypersonic strike assets on a small place like the Senkakus, but why would you want to? If you just want to create a presence that the Chinese would be loathe to dislodge, less costly and scarce forces and fires might do just as well. If it is ‘provide a survivable base for these exquisite assets,’ some other place might be better. Maybe the joint force will one day have so many hypersonic rounds that they could be deployed everywhere, but in the near term I expect they’ll be deployed somewhere where they could be mobile and camouflaged,” Karako wrote in an email.

The Hypersonics Race

The Army is hardly alone in its rush to develop hypersonics. Delivering a conventional payload far more quickly is among the Pentagon’s top research priorities. China and Russia are ahead in some respects, though they have given themselves the easier initial task of developing missiles accurate enough to deliver nuclear weapons. A September 2019 Congressional Research Service report declared that both are “expected to field an operational hypersonic glide vehicle— potentially armed with nuclear warheads—as early as 2020.” Indeed, Russia claimed at the end of the year to have deployed some.

Meanwhile, American work is proceeding on a wider variety of hypersonic efforts. Last year, Lockheed Martin and the Air Force fired an AGM-183A Air-Launched Rapid Response Weapon, or ARRW, from a B-52 bomber. More tests are expected this year, moving toward the expected program completion date of 2022.

This year, the Air Force also expects to complete a critical design review of its Hypersonic Conventional Strike Weapon. The service and DARPA will continue testing the Tactical Boost Glide missile and and Hypersonic Air-breathing Weapon Concept, or HAWC. And DARPA and the Missile Defense Agency expect to test aspects of a weapon that could intercept incoming hypersonic missiles.

This multi-faceted approach sets the U.S. hypersonic effort apart from its competitors. “Hypersonics is more than a single weapon or a single system. It's a suite of capabilities, smaller scale, medium range, longer range,” said Mark Lewis, the Pentagon’s director of defense research and engineering for modernization. “Parts of the Department of Defense fund universities have very active programs on the fundamental science level all the way up to the applied programs.”

Hyperspeed, Hyper Hard

But hypersonics are, in a word, hard. Compared to an ICBM, which spends much of its flight in the relatively uncomplicated vacuum of space, air-breathing hypersonic missiles will remain among the drag and turbulence of the atmosphere.

“If I'm going to fly in the atmosphere as a hypersonic vehicle, which is one of the big characteristics of these vehicles, I have to have a relatively low drag shape, right?” Lewis said. “I can't have a lot of resistance to my motion to the atmosphere. At these speeds what that means is, I have to have sharp leading edges. I have to be able to slice through the atmosphere very effectively. The problem is that the sharp leading edge also gets very hot. So, a good rule of thumb is the heating to a leading edge of a vehicle at hypersonic speed scales inversely with the square root of the radius of curvature, right? So, what that means is when you get sharp, you get hot...So, I've got a trade-off right there. How sharp is the leading edge, or how blunt is it?”

Design choices lead to other tradeoffs, said Lewis. What materials can handle hypersonic heat loads without warping? There’s also the challenge of steering. A conventional jet has flaps to change the aerodynamic forces over the vehicle. But flaps on a missile create drag, limiting range, so one big challenge is coming up with ways to steer without damaging performance, said Lewis.

“Then, there are some big unknowns that we just don't understand in this realm, right? One of the key unknowns is the state of the flow over the vehicle,” he said. “When you look at the flow moving over the surface of any aircraft, you can characterize it in one of three categories. You can either say it's nice and smooth and laminar. You can say it's turbulent, it's got eddies and swirls. Or you can say it’s transitioning between those two states. The condition of that flow is very important in determining how much drag the vehicle has and how hot it gets, right? So, swirling turbulent flow tends to make the surface much hotter than the smooth laminar flow. We don't have a basic understanding, a basic characterization, of when the airflow goes from nice and smooth laminar to chaotic and turbulent at hypersonic speeds.”

Lewis says he is a fan of supersonic combustion ramcraft, or scramjet engines. But, he says, there's still a lot of technology to be developed. “We built them, we have flown them. We know they work, but improving their design, manufacturing them, making sure that we can produce them in the numbers that we would need for a credible weapons arsenal are among the research projects that we’re investing in.”

While the United States has some catching up to do, Lewis says that the Defense Department is finally in place where it's serious about developing new hypersonic capabilities. “It has clearly risen to the top of the attention of our leadership...Everyone in this building with a hand in setting our [science and technology] priorities understands the importance of hypersonics.”