Dr. Mark Lewis: Hypersonics and the need for speed

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  • By Airman Magazine
  • Airman Magazine

Dr. Mark J. Lewis is the former Director of Defense, Research and Engineering overseeing the modernization of the portfolio in the Office of The Under Secretary of Defense for Research and Engineering. During an interview with Airman magazine, Lewis defined hypersonic technology, current research and development programs and why deploying hypersonic weapons is key to increasing force lethality and overall deterrence.


Airman Magazine: When I looked you up, Dr. Lewis, I typed your name in, and it just came up as “rocket scientist.”

Dr. Mark J. Lewis: Well, first of all, we like to say, “rocket engineer,” not a “rocket scientist.” I've spent most of my career as a research engineer teaching at the University of Maryland. I spent many years working at the Institute for Defense Analysis, and I view myself as having several research area focal points. One is advanced propulsion, that's rockets, that's high-speed jet engines. 

The other is air dynamics, the shaping of vehicles, especially things that go fast. And then the area that I'm most interested in is the area of essential integration, how you link an engine with the right shaped airframe for the best design for a high-speed vehicle.

Airman Magazine: Could you give us a simple explanation of hypersonics, and what are the varying degrees of its capability?

Dr. Mark J. Lewis: Sure. So hypersonics, first of all, does not have a fixed definition. There is no set definition for hypersonic speed, and I'll draw a contrast. So, we talk about flight regimes and the falling way; they're subsonic, that's slower than the speed of sound, there's transonic, across the speed of sound and then there's supersonic. 

When an airplane travels from the subsonic realm to the supersonic realm, the way air flows over that aircraft changes. The physics of the airflow changes in ways that we can describe mathematically. We can simulate computationally. That doesn't happen when we go from supersonic to hypersonic.

Hypersonic is fast supersonic. Several things start to happen, though, as you go up and up the speed scale. You get friction effects. Air is moving over the surface of an aircraft. That surface is getting hot; the air is getting hot; so, temperature starts to become significant. 

Any airplane that travels faster than the speed of sound produces what's called a “shockwave.” It's a sudden jump in pressure and temperature. As you move up the speed scale, those shockwaves can get stronger and get pressed close to the surface of the vehicle.

So we like to say that by the time I'm hypersonic, which we usually claim is around five times the speed of sound, my temperatures are hot enough that I have to care about it. My shockwaves are pressed very close to the surface of the vehicle, and that affects the way they perform.

Airman Magazine: Can you explain the importance of hypersonic systems as it relates to the DOD's modernization priorities? And in particular, what the Air Force should be focusing on as well?

Dr. Mark J. Lewis: Hypersonics does several things for the DOD. We tend to think of it as just speed, but it's more than that. It's the combination of speed and maneuverability and also the altitudes of which I operate. 

I should step back and say we've been building hypersonic systems for decades. The first hypersonic human-made system was flown in the late 1940s. Every spacecraft that has entered from orbit or the space shuttle, the Apollo spacecraft, Gemini and Mercury. Any spacecraft that enters another planetary atmosphere is generally traveling at hypersonic speeds, so we've been building these vehicles for a while. This is not a new discipline.

But today, when we talk about hypersonics, we're specifically referring to using it as shorthand, for hypersonic vehicles that can fly for sustained periods in the atmosphere. That means they're not only going fast, but we've got dynamic air forces, we've got lift forces that we can use to change the trajectory to control the vehicle, to bank, to dive, to do all sorts of things.

So, what does that combination of speed, maneuverability, and altitude do for me? One, it lets me get to a target quickly. I get inside an opponent's OODA loop, observe, orient, decide, and act. I'm going so quickly, that I don't give them enough time even to know what I am much less react. A rule of thumb, if I'm traveling at about five times the speed of sound, I'm going about a mile every second. Think about that. 

Count the seconds, that's how many miles you've covered and so a decision-maker, someone who's looking at one of the systems coming towards them, if they wait 10 seconds to decide, that's 10 miles I've traversed. All right, that's the first thing.

The second is maneuverability, that means I'm unpredictable. I'll compare it to an intercontinental ballistic missile, an ICBM. By its very nature, when an ICBM launches, and shortly after it lofts and then the warhead separates, you pretty much know where it's going to land. Physics governs the trajectory. It's governed by gravity, and it is the dominant force. 

A hypersonic vehicle in the atmosphere can add aerodynamic forces to other forces, to gravity, for example. So that means I can use control surfaces. I can bank right. I can go left. I can pitch. I can dive. I can do all these things, and so it's much harder to figure out where I'm going. Again, it makes it more difficult for an adversary to anticipate, intercept and act against: the other thing that hypersonics gives me.

A hypersonic vehicle, by its very nature, is going fast. It has energy. That energy can be part of what I deliver. So today you launch a missile, and in the end, you depend on a warhead, something that explodes to create an effect. A hypersonic vehicle traveling fast enough can create an effect all of its own just using its own kinetic energy, so that's a valuable contribution. When you put all those things together I think you can see why it's a very, very attractive capability.

Now, why would we want this? The way that we fight wars, the American way of fighting, we rely on technology. We also rely on our skilled warfighters. But it's that combination of technology and our skilled people that give us that edge. I would argue that's been true since the founding of this nation. That's one of the things that the American warfighter brought to the field of battle from the very beginning of this nation. Hypersonics continues that. Hypersonics is a result of how we've been operating for the last however many years. What are the next technologies that we need to focus on to modernize and change the way we do things?

One example that I'll give you, I'll roll back to the first Gulf War when we unleashed stealth technology. It was a fantastic revelation, and the entire world stood back and watched what we, and especially the United States Air Force and other parts of the military, were able to do with low observable aircraft that essentially were invisible to radar. Well, the world has had a generation to study that and so we need to be thinking about what comes next. I think hypersonics clearly comes next. With stealth, they can't see me. I'm invisible. 

With hypersonics, they might be able to see me, but they can't stop me. I think that's the next step that we need to be focused on.

Airman Magazine: There are some things that you mentioned in there. You used the anecdote of stealth. How else would you explain anecdotally the impact of a hypersonic weapon on the battlespace and how it affects the culture shift in technology going forward?

Dr. Mark J. Lewis: Hypersonics introduces several elements that truly make it game-changing. 

For example, a country that has tactical hypersonic systems can produce strategic effects with those systems. That's game-changing. If someone can sink an aircraft carrier or render an airfield unusable with a tactical system, a tactical hypersonic system, then they produced a weapon that in some ways is equivalent to using a strategic system.

That's one crucial element of what hypersonic brings, and I think it indicates why our adversaries should be so interested in developing their own hypersonic technology.

Put very simply, an adversary no longer needs to have a world-class Air Force to beat our world-class Air Force if they have these sorts of technologies. They no longer need to have a world-class Navy to beat our world-class Navy if they have these sorts of technologies.

Airman Magazine: When we're talking about that great power competition with China and Russia, where are we in that race in terms of hypersonic weapons?

Dr. Mark J. Lewis: The hypersonics race is a topic of considerable discussion in this building, and I think across the nation at large. And again, if I can, I'll provide a little bit of context. 

Hypersonics is a field that was invented basically in the United States. We flew the first hypersonic systems in the late 1940s. The concepts for hypersonic vehicles, it was pretty much developed here. The Russians did some development work, but, really, it's a field that we invented – that we developed. We did the experiments, and we did the principle tests. We had a few milestones in the field. I'll point to a couple of them.

In the early 2000s, NASA, the National Aeronautics and Space Administration, flew a vehicle called the X-43. X-43 was a hypersonic vehicle powered by a jet engine, and they called it supersonic combustion ramjet, which flew first at almost Mach 7 and then again at Mach 10. That was a milestone. I call that the “Wright Brothers moment,” and it was an American-made moment.

The next milestone for the United States Air Force is one I'm proud of. The Air Force Research Lab led a program called X-51. X-51 did a long duration hypersonic flight test starting in 2010. The last flight was in 2013 powered by, again, a jet engine, a supersonic combustion ramjet. What was terrific about X-51 is that it flew for almost 210 seconds, which is almost infinity in hypersonic speeds, powered by a very conventional fuel. 

We developed this technology and then, very honestly, we took our foot off the gas. We didn't follow through perhaps as we should have followed through. We didn't continue the programs as we should have continued those programs, and others read what we wrote and watched what we did and read our papers and decided, ''This is a pretty good idea.'' And they ran with it.

Today, we're faced with two other countries, and many countries around the world are developing the technology, but two that we specifically focused upon, and they have made no secret of their investments. 

One is Russia, and we know Vladimir Putin has bragged about their hypersonic capabilities. The other is China, and China, of course, has a broad range of activities that they have talked about. They love to brag about their hypersonic efforts. I think it's a source of national pride for them. They produce YouTube videos where you can look at the newest wind tunnels that the Chinese have built, and they show off what their capabilities are. But that's the situation that we're in.

I would say one of the goals that we had in our office, and the Office of the Under Secretary of Defense for Research and Engineering, is first to make sure that we're not left behind. Still, more importantly, we're going to leapfrog those capabilities. And we'll do it because again, this is an area we own. This is an area we invented, all right. There are smart people all around the world, but we've got the most innovative minds. We've got the most extended history in this field. We made the investments not just in the facilities, but in the people, and this is something that we're right now focused on ramping up the industrial-based workforce – making sure that the services are on track to not only meet but to exceed what peer competitors could deliver.

Airman Magazine: So which platforms is the Air Force going forward with in hypersonics?

Dr. Mark J. Lewis: So with hypersonic platforms, I tend to put them in several different categories. The first is what we call rocket boost systems. To get to a very high speed, you need some engine that gets you into the high-Mach realm. In a rocket boost system, I use a rocket motor. It gets me up to a very high speed, and then a payload or something separates, and it glides the rest of the way. And we sometimes call those “boost gliders,” because you're boosting and then you're gliding. That's one area of technology. The Air Force has made some significant investments there.

The other, and honestly, my personal favorite, is what we call air-breathing technologies. In an air-breather, I use oxygen from the atmosphere that comes in through the front on an engine to burn with fuel. Air-breathing technology is something that the Air Force should be especially proud of. The Air Force Research Lab has pioneered this area. It depends on the development of jet engines that can operate under the extremes of hypersonic speeds.

As one example, a molecule of air enters the front of one of these air-breathing engines, the scramjet engine, and it spends about 1,000th of a second inside the engine before it's out the back flowing out the nozzle. So that means that I've got to design an engine where I can squirt fuel, mix it with air, burn it to completion, release the energy, heat the flow out the back in a 1,000th of a second or in that time frame. That's quite short, and that's something that the U.S. Air Force has genuinely perfected. Air-breathers are complementary to rocket boost-glide systems, and that's an important point. Sometimes people say, ''Well, should I do one or the other? Rockets or jet engine air-breathers?'' And my answer is, ''we need both,'' because they both have their capabilities.

In a simple way to think about it, the rocket boost systems tend to go a little bit further. The air-breathers package better. I think of it as the old high-low mix, the F-16, F-15 mix, same thing with air-breathers and with rocket boost. Now there's another category of systems. There are rocket boost gliders that go the longer range. These are the things on a larger rocket. They might be land-based, and they might have other basing options. They wouldn't be something that comes off the wing of an airplane, for example. But it'd be something that would travel much longer distances for deep penetration.

Now, in addition to those, there are other things we can do with hypersonics. Hypersonic aircraft, for example. We often talk about an SR-72 a follow on to the legendary SR-71 Blackbird. The SR-71 flew at speeds higher than Mach 3. What if you could do that at Mach 5 or Mach 6? That would be a very, very powerful capability. It might not have a human being on board. It might be an autonomous platform.

Other things you could do with hypersonics; transportation. This is far off in the future, but we can imagine a time when it takes two hours to get anything anywhere around the planet using hypersonic technologies. I often point to what I call the brass ring of hypersonic flight, which would ultimately be using hypersonics to reach the space environment. Airplane-like operations into space. 

Today, if you want to go to space, you're doing it in a rocket. Rockets can be expensive. It takes much preparation to get a rocket ready for space flight. Compare that to how easy it is to get an airplane ready for a flight, well, relatively easy. Any Airman who's maintained a fighter jet knows there's much work involved.

But a commercial airliner lands at an airport, pulls up to the gate. They get the passengers off. They get the bags off. (They get) new bags on and new passengers on. 20 minutes later, it's ready to take off. If we can adopt that mindset for space flight, it opens up lots of possibilities, and especially for military operations. Again, that's far in the future, but that's part of the spectrum of hypersonic technologies we're thinking about.

Airman Magazine: Could you break down the concept of “S-cubed” and why that's important?

Dr. Mark J. Lewis: Hypersonics can do several things. It can do many things. It can blow things up. It can make holes in the ground, but it also gives you a fast way to penetrate forces. A hypersonic sensor platform will again be a desirable capability. That's not new, by the way. We used to have a program to fly drones off the back of the SR-71. D-21 drones. It wasn't hypersonic, it was supersonic. The same idea, D penetrator, it could fly fast. In that case, snap pictures, return those pictures to the source. So that is a desirable capability for hypersonics, and you could imagine linking a hypersonic sensor system with a much broader network of vehicles and sensors for a complete side picture.

Airman Magazine: Can you elaborate?

Dr. Mark J. Lewis: (I) don't want to tell you any secrets. One of the things that we spent much time worrying about is we understand now that our space assets are vulnerable. I think a previous secretary of the Air Force made the point that we built a glasshouse and forgot that people could throw rocks. I think I'm paraphrasing. We built a glass house then forgot that people could throw rocks at that house. So, our space systems are vulnerable. We're addressing that, and those are other technology priority areas that we're focused on.

But one of the things we talk about if we lost specific space capabilities – what could we do to backfill? And a hypersonic sensor capability could help us backfill. If we needed to get information quickly, if we needed to get over something quickly and if we didn't have a space asset to do it, a hypersonic platform could be an excellent way to do it. It gets back to that SR-72 concept that I mentioned earlier.

Airman Magazine: How does technological surprise play into our strategies?

Dr. Mark J. Lewis: In the DOD Science and Technology enterprise, we always say we want to avoid special surprises. I'll tell you, I have many historian friends, especially military historian friends, who will cite moments in history, moments in military history, when a country was faced with a special surprise. I like to think the United States has done that several times. I have my favorite examples of when we were able to pull off a technical surprise. 

Stealth aircraft over Baghdad is a perfect example. Rollback to the early 1800s. The U.S. Navy, when we first unveiled our original fleet of frigates like the USS Constitution. It was one of the first frigates that the U.S. Navy built. It was a generation beyond anything that any other Navy had on the oceans at the time, and those are great examples.

I think hypersonics could have fallen into that category, except we have so many other countries that are developing hypersonic capabilities. I have often asked the question, will we see hypersonic weapons used for the first time when the pointy ends are coming towards us? And we're working very hard to make sure that does not happen, and there are several pieces to it. One is developing our capabilities. Another part of it is developing our defense of capabilities that can address what someone else could throw at us.

Airman Magazine: How do you stop hypersonic weapons coming at you?

Dr. Mark J. Lewis: It's hard to stop a hypersonic system. That's why we want them. That's why other people want them. It's not impossible, and I think we generally think about it in that you would essentially take a layered approach. A lot of technical solutions, it might involve everything from direct energy to hitting a bullet with a bullet. I'll tell you one of the most important things we've got to solve is we got to be able to see it before we can stop it. 

Having the sensors in place, having the sensor capability and not just the sensors, but the processing capability to be able to decide quickly what it is and how to stop it is essential to that defensive capability.

Airman Magazine: So, it's a sensor race. It's an AI race. It's a hypersonic race. It all combines.

Dr. Mark J. Lewis: It is all the above, that's correct. It's got aspects of its fully networked command and control communication built into it. 
You mentioned AI. It's autonomy. There's got to be some degree of autonomy, and if we're depending on a human operator staring at pixels on a screen, it's going to be hard to figure out what it is in time to do something to stop it. Directed energy could play a role in this. There are other weapons that we might have to bear on this. It's even a human factors issue, right? Making sure that human operators can respond quickly can make decisions quickly when necessary. There's going to be an element of how we tackle this hypersonic threat.

Airman Magazine: What is the Air Forces' role in researching and creating these weapon systems and these vehicles?

Dr. Mark J. Lewis: I'll freely admit as a former Air Force chief scientist, I'm unabashedly a huge fan of Air Force science technology. The Air Force was created as a technology organization. It was created because of the unique technologies that the Air Force brings to the warfighter. And of course, the unique practitioners who understand that technology, understand how to develop it, understand how to use it. 

The Air Force Research Lab has been one of possibly the premiere developers of hypersonic technologies, and it extends across the board. Everything from the high-temperature materials that we need to build a hypersonic vehicle: the propulsion technology, the computational models that we need to build to study, to develop, to analyze these things, the testing technology that's required to validate and confirm the performance of our hypersonic systems.

I mentioned earlier the supersonic combustion ramjet: the scramjet engine. Well, this is an engine that was fleshed out in no small measure because of research work that was done at the Air Force Research Lab. Even the concepts that we talk about have been developed through the Air Force Research Lab. 

Now it's not just the AFRL, and it's other parts of the Air Force. The Arnold Engineering Development Center headquartered in Tullahoma, Tennessee. It's the nation's premier defense wind tunnel complex ground testing facility. They have several vital national capabilities that have allowed us to progress as we have and are playing an essential role in the work that we're doing today.

One of my favorites is a facility called Hypervelocity Wind Tunnel Number 9. It's an Air Force wind tunnel that's located just north of us in White Oak, Maryland. It's called Tunnel Number 9 because Tunnel Number 1 was Wernher von Braun's original wind tunnel that we captured at the end of World War II. Tunnel 9 is a Mach-18 facility. It can simulate flight conditions up to 18 times the speed of sound. Mind-boggling. It's become our premier testing capability. We could not develop the suite of weapons that we're talking about, the suite of vehicles that we're talking about, without that test facility.

Airman Magazine: You talked a little bit about facilities and hardware and everything else, but talk a little bit about the people that we need in the Air Force to be able to come up with these solutions.

Dr. Mark J. Lewis: So again, in the research and engineering enterprise, we worry a lot about the people because, at the end of the day, that's what it's all about. And the Air Force has been one of the places that the smartest minds in the field have tended to gravitate towards. Not just in the research lab, but also just our thinkers, our strategists: the people who are working through how you would use hypersonics. 

One of my favorite examples is the Air Force Warfighter Integration Center. AFWIC has done some phenomenal work recently thinking through how hypersonics plays in the warfighter. But at the same time, as a nation, we took our foot off the gas just as we did with some of our programs we did with the education of our hypersonic workforce.

Now here, I spent most of my career as a university professor, training students to do hypersonics, and I can tell you first hand, there is no field; there is no sub-discipline in aerospace engineering that is better at attracting the best and brightest minds. 

Hypersonics is flying higher. It's flying faster. Every year, a space engineer wants to fly higher and faster; it's captivating. It's a great way to get talent into our field. But we have to make those investments.

Now how do you make those investments? Well, in part, they're research investments. They're investments in universities. The Air Force Office of Scientific Research has been one of the most important organizations investing in our universities, and they've been pretty consistent over the years. 

The Office of Naval Research has also had a consistent program investing in our universities. But right now, we don't think it's enough. So great work that they're doing, but we want to supplement it. We want to augment it. Our office has developed plans to significantly ramp up the investments that we're making in universities.

What we can ask the universities to do is work hand in glove with the services, especially the Air Force, also the Navy, also the Army, and work with industry and work on real-world problems. We want them to do important things. We want to harness the best and the brightest, and we have many goals.


First, there are some incredibly smart, talented people at our universities, all right. Our university system is the crown jewel of our enterprise. We want to harness that brainpower.

Two, we want to produce the people who are going to come work for places like AFRL, go to air industry partners, and go to the universities to help train the next generation. 

Three, we want to expand the areas and the topics that we're thinking about. We want to bring in maybe the disciplines that we hadn't thought about before that could play in the hypersonic realm. Manufacturing, for example. New ways of doing modeling and simulation. New ways of doing computation. 

You mentioned artificial intelligence earlier. So up until now, we haven't thought about links between artificial intelligence and hypersonics. We want the academic community to help us think that through. What are the things that we do in artificial intelligence that can help us be a guide, detect and deter a hypersonic weapon, for example?

Airman Magazine: Talking just a little bit about people and personnel, you mentioned earlier about the OODA loop, and we're discussing and doing a story on mavericks for the Air Force. John Boyd is one of those thinkers, those outliers.

Dr. Mark J. Lewis: Right.

Airman Magazine: Are there any of those outside-the-box mavericks in this field? Are you that maverick?

Dr. Mark J. Lewis: I'd never put myself in the same category as John Boyd. I'm not worthy. 

I guess let me answer your question a bit obliquely. I do, indeed, embrace the maverick model. I think we've seen that historically. Thinking about John Boyd, thinking about Benny Schriever and the development of the ICBM. One of my favorite books is Neil Sheehan's description of how Schriever developed the ICBM fleet and the hurdles that he faced. And sometimes it takes someone like that. Hyman Rickover in the nuclear Navy. Sometimes it takes someone like that.

I would say we've got a small community of die-hards that have been advocating strongly for hypersonics. I don't know if I'd call myself a maverick so much. I think I've been a pretty consistent voice, but I've got many colleagues. 

Probably one of the most articulate voices in the value of hypersonics is former Air Force historian Richard Hallion, whom I think is the world's most celebrated military aviation historian. Dick Hallion has written extensively about hypersonics, and he's done so with his historical perspective, but he's helped us think through how hypersonics fits in the future warfighter. He's certainly one key example.

I think we've had some other heroes. My boss right now, Mike Griffin. I mean, he walked in, and on day one said, “hypersonics is my number one "priority”. 

Now I will tell you, I showed up in November and the first day of work I said, ''Okay. I'm ready to work on your number one priority” and we're making much progress on hypersonics. 

We got some other priorities now that are also rising. But I said, ''No, we're going with hypersonics as still towards the top of the list.'' 

Again, lots of other people who have contributed to the field and are making sure it has been advancing. I have to tell you when I look across the leadership in this department today, frankly, they all get it. The commands, our services, everyone understands the value of this, the importance of this, and that makes it a very exciting time to be working in the field.

Airman Magazine: Is there a Curtis LeMay type right now, fighting against the grain or the prevailing mindset about the need for hypersonic weapons?

Dr. Mark J. Lewis: I think Curtis LeMay gets a bit of a bum rap in Bennie Schriever's story.

It's true that Curtis LeMay, as a bomber pilot, came out of the war as the ultimate bomber pilot, and it's true that he was very skeptical of the ICBM. But when he saw what it could do, he embraced it. And that's what we look for. 

Skeptics are fine. As a researcher, I always say my number one job is to be skeptical. When I was chief scientist of the Air Force, it used to say my primary responsibility was to be the in-house skeptic for the chief and the secretary. Now when someone brought us their beautiful PowerPoint deck about all the great things they're going to do for the Air Force, I was the guy who was supposed to say, ''Yeah, but you violated the laws of physics in one or two areas.''

Skeptics are okay as long as it's reasoned, and it's sound because it helps us to improve. Right now, I don't meet very many skeptics. Everyone has gotten it.

Airman Magazine: We talk about the culture of the Air Force and its innovative ability, right? It's never static, its always transforming a little bit. We went from the fighter pilot to the bomber pilot to the ICBMs and now to stealth and now onto hypersonics and beyond. Can you just talk about the general nature of the Air Force and the culture of change?

Dr. Mark J. Lewis: The Air Force is indeed an incredibly innovative organization, and you see the way it has evolved over the years. Evolved to adopt new technologies, adapted to address new threats. 

One of the things that gets me most irritated, is when someone says, ''The Air Force was slow to adopt X, or the Air Force had to be dragged to adopt Y.'' You hear that sometimes with stealth. You hear that sometimes with unmanned aircraft. 

Absolute nonsense. The Air Force led in the adoption of stealth. No one else did it better, and it was the Air Force who defined the concepts. Unmanned aircraft, the Air Force led in that. The Air Force pushed unmanned aircraft. It's a myth, and I think this follows in that tradition. The Air Force is leading in the development of hypersonics. 

I don't want to take anything away from the other services. The Navy is entirely on board. They're doing some great stuff. The army is moving very aggressively in hypersonics. They've got some great programs. 

The other good news story is the services are working very well together. You see the exchange of technical information, exchange of ideas. Even exchange in some cases of geometries for systems. It should give the American taxpayer, if nothing else, a sense of pride in how their government is functioning.

Airman Magazine: How does all this evolve with the creation of the Space Force when it comes to hypersonics and some of the things that you guys are doing?

Dr. Mark J. Lewis: Space is going play directly into what happens in hypersonics. 

First, remember, I mentioned that one of the critical aspects of defending against hypersonic weapons is being able to detect them? We think space has a vital role to play there. Space sensing, hypersonic sensing, as we also mentioned earlier, they go hand in glove. I might fill in for something that I lose in space, or I don't have in space with a hypersonic sensor platform. It's all connected, and it's all related. 

Directed energy could also factor into what we do in hypersonics and the other disciplines that we discussed earlier.

Airman Magazine: When we're talking about what's next, is directed energy what's next?

Dr. Mark J. Lewis: I don't think the question is what’s next. I think we've got a suite of technologies that we've been developing over the years and that are just starting to come into their own. 

I tell a funny story of an Air Force friend of mine. He used to joke that hypersonics is the future, and it always will be. Well that was true until we actually flew some hypersonic systems, and again, I'll cite the Air Force's X-51. 

I call it the “Charles Lindbergh moment” when you saw that this was not only possible, but it was practical. And once we did X-51, we know hypersonics was the future. We could do it. It took the excuse off the table.

I think we're seeing the same thing now with directed energy. 

We see developments in directed energy that get us to the energy levels that we need it to be in order to make these useful systems. 

Part of it, as with hypersonics, was an understanding that directed energy changes the way we would prosecute warfare. It's a game-changer. 

Often in the past, there had been the mindset that I would replace a kinetic weapon with a directed energy weapon. Well, why would you do that? If you already have a kinetic weapon, you don't need to replace it with a directed energy weapon. You want to use your directed energy weapon for things that you can't do with your kinetic weapon, and I think we understand that now, and that means that directed energy weapons will very, very quickly become arrows in the quiver.

Airman Magazine: You're very passionate about this, and I can tell that you love it. It seems like there are pretty exciting times in just this community and what's going on.

Dr. Mark J. Lewis: I actually cannot imagine a more exciting time. 

I've spent four years in this building, and I had an incredibly fun job the last time I was in the building, and I've had a number of people ask me, ''So why are you back?'' This is the window. This is the window of opportunity. 

We've got senior leaders who get this. We're in a race to a certain extent. We have other countries that are developing these technologies, and this is a race that we need to first recognize we're in and then strategize to not only catch up to them, but we need to beat them in these areas. And being a part of that is absolutely invigorating. I couldn't imagine a better time to have been in the Pentagon.

Airman Magazine: I mean for the folks that are out there and they're reading this, and they're hearing about Russia putting out videos saying, “You'll never know. We can strike you. We strike anywhere.” Seeing this stuff, it's scary times too. But are you encouraged? I mean, does this stuff keep you up at night, or are you encouraged that we will meet the fight?

Dr. Mark J. Lewis: I have no doubt that we'll meet the fight. I have absolutely no doubt. 

It really comes back to American know-how and American innovation. I'll give you one indication of that.

I was talking to some colleagues just earlier today about the American university system, people are still beating down the doors to come to our universities from all around the world because they understand that we are the centerpiece of research and development science technology. 

Not to take anything away from other countries. Lots of smart people around the world. When people think about powerhouses in science and technology, they think about our research infrastructure. And I want it to stay that way.

Other countries are investing. China makes no bones about the fact that they're investing heavily in research, good on them. Let them invest. I'll meet that challenge, and I'll see them and raise them.

Airman Magazine: Well, those other countries are also investing in our college systems, sending their students here and then bringing them back to their countries. That's part of the competition, isn't it?

Dr. Mark J. Lewis: So indeed, yes. Competitions help drive us, but I think the other key, the other secret to American science and technology is that we do have the benefit of pulling the best and the brightest. 

Think about the scientists in the Manhattan Project. How many of them were foreign-born? Think about throughout the history of the development of our aerospace technologies. How much of that talent came from overseas? 

One of the fathers of the U.S. Air Force was Dr. Theodore von Karman. He was a Hungarian physicist and was the premiere aerospace engineer to the twentieth century. A close friend of Hap Arnold who helped found the Air Force. Think about that talent pool. And we see that continuing today.

There's a myth that America has closed the doors to foreign students. That's absolutely not true. If anything, we see key countries are increasing in the number of students that they're sending to us. So that's a truly important element. 

I'll give another reason why I have tremendous confidence, and it's the nature of our scientific ecosystem. We have so many mechanisms by which we can support good ideas. I can tell you first hand, as a university professor, if I had a really good research idea, I knew exactly where to go.

I can knock on the door of the right person at the Air Force of Scientific Research and say, ''I've got a good idea, and I think it'll help the U.S. Air Force,'' and we had the mechanisms in place so I could do that work, have students do that work and contribute to the mission of the Air Force. And the Navy does the same, and the Army does the same. NASA does it for that mission.

So it's that legacy research enterprise that is also one of the keys to our success.

Airman Magazine: We have treaties with Russia but hypersonics are outside of these treaties. Does that help or hurt?

Dr. Mark J. Lewis: The INF treaty basically had us operating with one hand behind our back and we had a treaty with Russia that was limiting what we could do. But meanwhile, China was not a part of that treaty. So, the Chinese could do what they wanted to do. It has opened up the aperture somewhat, and it enables us to think of developing some new capabilities that will be important to our future warfighters.

Airman Magazine: Is the Air Force still on target with air weapons systems?

Dr. Mark J. Lewis: The Air Force, I think all the DOD programs, are moving at a very, very aggressive clip, and that's deliberate. The services are pushing, and OSD is pushing. We're saying, ''We need to do this quickly. Time is critical here. We've got people breathing down our neck.”

Without getting into the program and its specifics, I think we're doing really quite well. And it's more than just, say, the Arrow program. We've got a couple of programs at DARPA that are moving along. Army programs. Navy programs.

I'll give you one exciting metric. One of the things that the Chinese have been able to do, they've been flying a lot of things. They've been flying a lot of hypersonic vehicles. They've been very open about that. Russians have also been doing some flights, they've been open about that as well.

We want to fly a lot of U.S. systems because that's how we learn. We want to build things, and we want to fly them, we want to test them in a fight. We want to be willing to fail, and we want to be willing to break stuff. 

If it breaks, we want to figure out what went wrong, and we want to fly again. In the next couple of years, we're talking about up to 40 new flight tests of various hypersonic systems at our ranges. That's exciting from the standpoint of accelerating our time scales. It's also important in building the skill set of our workforce to make sure they can deliver the capabilities that we need.

Airman Magazine: Can you speak on how important that is, and do you have an example in your career where you might have had that one failing forward moment?

Dr. Mark J. Lewis: My favorite example of being willing to fail is an old X-program from the 1960s. 

It was a program called the X-15 program. If you go to a museum of the Air Force, they have an X-15 on display. There's one at the National Air and Space Museum as well. X-15 was a rocket plane that flew throughout the 1960s. It ultimately reached almost seven times the speed of sound with a pilot in the atmosphere. 

They built three X-15s, and in the course of a decade, they flew them 199 times. But the key aspect of that and in addition to the great science that they did, the technology they developed, they weren't afraid to fail. They had several major failures in the program. 

At one point, a test pilot, Scott Crossfield, was doing a ground test, and he was testing a new engine on the X-15. The engine exploded, blowing the cockpit with Scott on board down the runway. And their response was, ''Okay. Get him out, he's fine. We build it; get it in the air again.''

At another point in the program, they landed hard, and they broke an X-15 in half. ''Great, we wanted to build one longer anyway. We'll just extend the fuselage.'' They're in the air very soon afterward. 

Even tragically, one of the X-15s was lost in the air. The tragic moment lost the vehicle and the pilot. It did not end the program. So obviously, we don't want those sorts of failures, and we're not talking about manned systems right now. But we want to get to the point where we're willing to break things. We're willing to fail, and then we'll learn from it, and we'll move on.

But I also want to step back. I put failures into two categories. There are noble failures, and there are dumb failures. 

We've had a list of dumb failures. When fins fall off that shouldn't fall off, and batteries have low voltage when they shouldn't have low voltage. We don't want to fail for those reasons. We want to fail for reasons that we didn't quite understand the physics, and now we do. We pushed that technology to its boundaries, and we found out what those boundaries are. Those are the sorts of failures that we want to embrace. I'll give you one of my favorite examples on that one.

I mentioned the X-51 program, the Air Force Research Lab program. X-51 had four flights in the course of its flight test lifespan. The first flight had a failure towards the end of the flight, and it was basically a high-temperature gas leak in the back of the vehicle. That was a noble failure. That was a failure. Basically, we had a seal on the vehicle that ruptured. We knew it was a critical element, but we weren't quite sure. We didn't understand. It didn't impact the flight very much, and we still got lots of good data.

On the second flight, we had a failure. That was due to the way the engine had been designed. That was also a noble failure, all right. We didn't get any hypersonic data, but we learned that something was wrong in the way the engine was designed, and we corrected it.

Third flight, I put it in the category of not a very noble failure. We had a fin fall off. Fins shouldn't fall off of vehicles. So that's in the category of dumb failure. 

But because of that legacy, when we got to the fourth flight, it was eye-wateringly perfect, all right. That fourth flight, the most exciting thing about that flight was it wasn't all that exciting because the flight data matched the ground test data which matched the computational data because we learned as we had gone. And that's the example that I would like to hold up as we go forward into this new hypersonic flight test program.

Airman Magazine: Is there anything else that you would like to add or something we should have covered?

Dr. Mark J. Lewis: I guess the main thing I would say is that I know of no area that is as important right now to the Department of Defense is the enterprise of hypersonics. It's just one of many capabilities. Hypersonics will not solve all of our problems. It's a bit of a cliché. It's just one arrow in the quiver, but I think it's a very important arrow in the quiver.

Hypersonics isn't just one thing. I will sometimes hear people in this building talk about, ''I want a hypersonic.'' And I say, ''Okay, a hypersonic what?''.

It could be an air-to-air missile or a big fan of air-to-air systems. It could be an air-to-ground missile. It could be a submarine launch system. It could be a Navy surface launch system. It could be a ground launch system—all of the above. And we have to be thinking about it as systems. We have to be thinking about it as integrating into the rest of our capabilities.

If I could, I'll end with a question that I get asked often. It's a basic question of so why do we really want these hypersonic systems? 

I answer a question in true academic mode, and I answer a question with a question. The question I respond with is, well, why wouldn't we want them? And then I provide my answer.

Here's why we wouldn't want a hypersonic system. We wouldn't want a hypersonic system if it were too expensive. That means we need to pay attention to costs. Not just the initial cost, but the cost of delivered capability. 

We wouldn't want a hypersonic system if it didn't give us the right performance. It didn't give us the right range, or didn't have the right other performance parameters, right? So, we need to pay attention to that. It needs to be a useful system.

But if I can get those right, if I can get the cost right, if I can get performance right, then why wouldn't I want something that travels at five times the speed of sound versus something that travels at 8/10ths of the speed of sound. Clearly, I would want it. And that's where I think our mindset needs to be. Why wouldn't we want this capability?

Airman Magazine: How much do you love what you do and how rewarding is it?

Dr. Mark J. Lewis: Oh gosh. I think I've got the best job in the building. And I tell my folks that we collectively have the most. There are lots of exciting jobs in this building, but we have the most exciting job because if we do our job right, then God forbid the United States is ever faced with a conflict in 2030, 2035 or 2040. We will have given those future fighters the tools they need to make sure that our nation is safe and secure.