Hypersonics sage

October 2024

Mark Lewis, CEO of the Purdue Applied Research Institute

Development of hypersonic weapons and defenses in the United States was limited to basic research a decade ago. Then, during the Trump administration, the Pentagon’s Michael Griffin warned in a 2018 Senate hearing about China’s hypersonics prowess. Russia had rattled its hypersonic saber a month before — and a year later, China did too. U.S. hypersonics research boomed into a multibillion-dollar annual enterprise, a level the Biden administration has maintained and even slightly increased. It was Mark Lewis, a former Air Force chief scientist with a Ph.D. from MIT, who guided much of the research from 2019 to 2021 as the Pentagon’s director of research and engineering for modernization. Lewis is now head of the Purdue Applied Research Institute, the Purdue University-affiliated organization that aims to be an incubator for transitioning research into real-world innovations in national security and other fields. I spoke to Lewis over the phone to learn just how worried the U.S. should be and what can be done to defend against these weapons.

Q: In May 2023, Russia reportedly launched a hypersonic Kinzhal missile into Ukraine. It’s a weapon Vladimir Putin’s been talking about for years. Why is this significant?

A: The most important thing we learned from that is the Russians build really crappy weapons. So the Russian weapons are really bad, and a lot of it is legacy technology from the Cold War era. They’re barely hypersonic. I won’t go into details, but they’ve made some really bad engineering decisions.

Q: Should we even think of the Kinzhal as a hypersonic weapon?

A: It’s clearly a hypersonic weapon, traveling hypersonic speeds in the upper Mach range. They modified an old missile that was a ground-launched missile and modified it for air launch. It wasn’t a particularly innovative idea. It wasn’t any sort of major breakthrough, and it’s got some features that I can’t go into that make it particularly easy to stop. So it doesn’t really concern me, and I don’t think it’s a particularly big threat. Except there’s one aspect of it that I think we need to take notice of: There was strategic messaging involved in the Russians’ use of that hypersonic weapon. If you stand back and say, “Why did they use a hypersonic weapon in Ukraine?” It frankly makes no sense from a tactical standpoint. I mean, they weren’t going against fleeting targets. They weren’t going against a particularly difficult integrated air defense system. They weren’t going after something time sensitive or anything like that. So what were they doing? It’s pretty clear what the Russians were signaling was, “We’ve got these weapons, and we are willing to use them.” And that is a bit of a sobering message, because it shows how hypersonic weapons can shape the future landscape of war. It’s not a hypothetical.

Q: So what’s the right takeaway?

A: Takeaway No. 1 is that the genie is out of a bottle; the toothpaste is out of the tube. They’re deployed, and they’re being used. No. 2, there is a wide range of hypersonic weapons, and not all hypersonics weapons are the same. They don’t fly the same missions. They’re not going to be used in the same way, and we have to be very, very careful about applying lessons learned from one particular type of hypersonic weapon to other types of hypersonic weapons. And we have to be careful applying lessons learned from one country’s investments to our own investments.

Q: What makes a hypersonic glider so much more difficult to defend versus a traditional ballistic missile?

A: The big difference is that hypersonic weapons spend a significant amount of time in the atmosphere, as opposed to ballistic weapons that are going up and coming down, where there will be less time in the atmosphere. And by virtue of being in the atmosphere, those hypersonic weapons can now use aerodynamic forces to maneuver, which is a key element of their performance. When we talk about hypersonics today, we’re really using that as a shorthand for hypersonic maneuvering. And let me explain that: So a ballistic warhead coming in is probably at hypersonic speeds, but it’s not maneuvering or not maneuvering much. When we talk about hypersonic weapons today, we’re talking about things that are moving very quickly but also maneuvering, and it’s that combination of speed and maneuverability that becomes critical to their effectiveness.

Q: We’ve heard for years that they’re harder to track from space. Why is that?

A: If I’m standing on the ground, I can see something up high more easily than if it’s lower down, and I have to deal with the horizon. So detecting these things from the ground is more difficult. You say, “OK, what about from space?” Detecting it from space is also more difficult. And the reason is, if I am imaging an object that goes to very high altitude, I may be imaging it generally against the black background of space. If it’s at a low altitude and if I’m seeing it from orbit, I’m generally looking at it down against the background of Earth — and Earth is warm, so certain sensors will have a harder time detecting the object against the warm background of Earth than they would against the black background of space. So either from the ground or from space, there’s a bigger challenge detecting a hypersonic maneuvering weapon than there is a standard ballistic weapon. Now, having said that, we know how to do this, and the HBTSS is the first major step.

Lewis is referring to the Hypersonic and Ballistic Tracking Space Sensor satellites, a joint project between the Space Development Agency and the Missile Defense Agency. The first two prototypes built under the program, one built by L3Harris and the other by Northrop Grumman, were launched in February. In June, officials said they recorded their first tracking of an experimental hypersonic vehicle, one built by Kratos and launched from Wallops Island in Virginia. — MG

It’s extremely well designed, extremely well engineered to do this critical mission, but it’s a mission that existing sensors have a challenge completing.

Q: From a missile warning and tracking perspective, how do you compensate for that speed and maneuverability? What’s the technical solution?

A: There are a couple pieces to it. One is, of course, the sensitivity of your detectors, the resolution of your detectors. But then there is absolutely a machine learning element to this. One of the reasons that hypersonics can make for such an effective weapon system is it gets inside the classic OODA loop.

That’s short for observe, orient, decide and act, an acronym that captures the decision-making behind firing a weapon or forcing an enemy to react. The term is attributed to U.S. Air Force Col. John Boyd, a Korean War-era fighter pilot and military theorist who died in 1997. — MG

A hypersonic weapon gives you very little time — first to figure out even what it is, and then figure out what its intentions are or even what the target is. It requires very, very quick processing, so the ability to couple machine learning and ultimately artificial intelligence techniques with exquisite sensors I think is going to be the key to help solve this problem.

Q: The missile warning and tracking of hypersonic weapons is largely done from space. Are you seeing progress there?

A: When I was in the Pentagon, we would often say, “If you can’t see it, you can’t stop it.” So step No. 1 is seeing it. The department has the HBTSS. You’re seeing some really good developments there. So that’s good progress being made.

Q: Has there been a moment in recent years where you realized, “Hey, we’re taking the steps we need”?

A: It was less a technical issue and more of a programmatic issue. Were we willing to put the resources against solving this problem? Especially when the stand-up of the Space Development Agency and everything that they brought to the table, that was when I thought, “Yeah, OK, we as a nation, certainly as a Department of Defense, are taking this problem seriously.”

Q: What do people get wrong about hypersonic weapons?

A: There’s the old adage, “the best defense is a strong offense,” but I think that’s absolutely true for hypersonics. We have to be investing in our own offensive capabilities — first to deter but also to respond quickly to hypersonic threats. If someone is lobbing hypersonic weapons at us, we need to be able to hit them on a timescale that’s comparable to the timescale at which they’re shooting at us. And that gets lost in this conversation. I’ll tell you a funny little anecdote. The National Academies has this process whereby there’s a thorough, thorough review, and they opened the review up to people who haven’t been involved in writing the report. We had this one reviewer in particular who took great, great offense at our report because he said we had mission creep; we were only supposed to focus on the defensive side, and instead, we had sections on the offensive side. But in fact, they go very closely together. The  offensive side informs how we do our defensive capabilities. Our defensive side informs how we shape our offensive capabilities, and that’s something that I would like to emphasize.

Q: What’s one thing that you’re watching for to see if there’s progress?

A: Obviously the most important thing is actually deploying systems. So we’ve got the Army system, the LRHW, that’s close to deployment.

LRHW is the Army’s Long-Range Hypersonic Weapon, sometimes known as Dark Eagle. The Army has described it as a truck-launched hypersonic glide body missile “that can travel well over 3,800 miles per hour. They can reach the top of the Earth’s atmosphere and remain just beyond the range of air and missile defense systems until they are ready to strike.” — MG

And you know, tip of the hat for the Army for pressing on that system. The other one I’m really looking forward to is the Air Force system, in particular the ARRW.

ARRW, pronounced arrow, is the AGM-183 Air-Launched Rapid Response Weapon. This glide vehicle would be released from a B-52 Stratofortress to travel as fast as Mach 8. The Air Force’s fiscal 2025 budget request did not include any research funding for ARRW, and Pentagon leaders in February declined to answer questions from a U.S. House committee about the program’s future. — MG

ARRW had an initial flight test that wasn’t successful, which is fine. We keep preaching the doctrine that we need to be allowed to fail, so we needed to allow them to fail. And they recovered, and then they had a very successful series of flight tests, so much so that the most recent flight test exceeded expectations. ARRW could go to deployment. We could turn it on tomorrow and start rolling ARRW weapons off the assembly line. And so I think we’re going to be looking to see where the Air Force goes with that. The Air Force could actually be the first service to deploy a hypersonic weapon. They’ve got this capability that works, and it would be great to see it delivered to the hands of the warfighter.

Q: Hypersonic weapons can feel abstract. How do you describe them in tangible ways?

A: If you have the ability to stop some of these, then wouldn’t you want to exercise it if you think about how devastating a hypersonic attack could be? Let’s take a China-invading-Taiwan scenario. So we know the Chinese have made a big point about the fact that they have built hypersonic weapons, that they display them. It’s not a secret. And some of those weapons are clearly designed to take out aircraft carriers. Well, think about what it would mean for us to lose an aircraft carrier to a hypersonic attack. The cost of an aircraft carrier rolling out of dry dock right now is coming in at about $14 billion. You add the planes onto that, you’re talking about maybe another $10 billion. And then you’ve got 5,000 souls on board. So imagine you lost an aircraft carrier: You lost a $25 billion asset with thousands and thousands of American lives on board. If I could stop that from happening, if I could defend against it, if I’ve got a reasonable chance of doing so, why wouldn’t I? It’s incumbent upon us to do so.