Check 6 Revisits: Hypersonic Hopes—The Legacy Of The X-30 Orient Express

Hypersonics expert and former chief scientist of the U.S. Air Force Dr. Mark Lewis joins the podcast to examine the X-30 NASP program, and how—decades later—its legacy still lives on.

Check 6 Revisits delves into Aviation Week's more than 100-year archive. Subscribers can explore our archive here and read key Aviation Week articles on NASP here: 

• Reagan Endorses Station, Advanced Transport (Feb. 10, 1986)
• X-30 Technology Advancing Despite Management Rift (March 7, 1988)
• The X-30: Leading The Way Into The Hypersonic Era (Nov.13, 1989)
• Senate Balks At Raising X-30 Funds, Placing NASP’s Future In Doubt (June 29, 1992)
• Editorial: Recommit To Hypersonics (Nov. 30, 2009)

Audio Clip

Feb. 4, 1986: President Reagan's State of the Union Address (C-SPAN)

Subscribe Now

Don't miss a single episode of the award-winning Check 6. Subscribe in Apple Podcasts, Spotify or wherever you listen to podcasts.

Transcript

Christine Boynton:

Welcome to Check 6 Revisits, where we comb through more than a century of Aviation Week & Space Technology archives. On this podcast, our editors explore pivotal industry moments and achievements of the past, while considering how they might relate to the events of today.

Ronald Reagan:

This nation remains fully committed to America's space program. We are going forward with our shuttle flights, we are going forward to build our space station, and we are going forward with research on a new Orient Express that could, by the end of the next decade, take off from Dulles Airport, accelerate up to 25 times the speed of sound, attaining low-Earth orbit, or flying to Tokyo within two hours.

Christine Boynton:

I'm your host, Christine Boynton, Aviation Week Senior Editor for Air Transport, and you've just heard President Ronald Reagan describe his vision for a Mach 25 airliner during his 1986 State of the Union address, the Rockwell X-30 National Aero-Space Plane, or NASP. It was an ambitious vision, and not without its critics. In his memoir, former director of Lockheed Skunk Works, Ben Rich, would have a fairly brutal assessment of the speech. He writes in part, "Reagan called the hypersonic plane the Orient Express, because it would fly from New York to Tokyo in only two hours. Reagan wanted to build it in 48 years. He'd be lucky to do it in 50. I was outraged by that speech, not at the president, but at his technical team, which apparently had sold him a hypersonic version of the Brooklyn Bridge."

So on that note, let's jump in. And here with me today to dissect this topic, our Aviation Week executive editor, Graham Warwick; senior editor, Guy Norris; and special guest, Dr. Mark Lewis, chief executive officer for the Purdue Applied Research Institute, and former chief scientist of the US Air Force. Thanks for being with us here today, Dr. Lewis.

Mark Lewis:

Thanks for having me.

Christine Boynton:

Before we get to reactions on what we've just heard, I wonder if we can start, Guy, can you give us some context on this program? As the dream of hypersonic flight became more and more prominent, this was really the focus for all the US efforts at the time as they were working to stay ahead of the competition. Is that right?

Guy Norris:

It was a very interesting time, because obviously as we know, the dream of high speed flight had never been far from the agenda. It was just a question of how to get there. You've got to sort of put yourself in the perspective of where things were in the late '70s and early '80s. The Strategic Defense Initiative had just sort of been launched in '83 by President Reagan. And at the same time, NASA, of course, was flying the space shuttle for the first time. And there was sort of two real competing ways of getting into space, and this idea of actually a rocket-powered propellant getting into space with rockets, or could you use an air-breathing system, a sort of a dream that had been around since the end of World War II, essentially, thanks to people like Antonio Ferri, who was this pioneer really and sort of one of the originators of breathing hypersonics.

So you get to the late '70s and the early '80s, and the Air Force begins to see that the shuttle is not really their baby after all. They don't have any control, really, over it, and that they would like to use it. And so out of nowhere, really, maybe ... well, we can talk to Dr. Lewis about this, but out of nowhere really seems to come this idea of this single stage to orbit dream that you can actually do it with air-breathing, hypersonic propulsion systems.

It's sort of like the stuff of dreams, really. And yet there was DARPA, the Defense Advanced Research Projects Agency, really talked them into this idea of this Copper Canyon project. This was a way of sort of delivering this hypersonic single stage to orbit type capability to the Air Force. They wouldn't have to worry about rockets and the shuttle. They could do it their own way. And so this Copper Canyon project really was the sort of the genesis of what became, dressed up as a civil project in some ways, the Orient Express. Maybe we can go from there.

Christine Boynton:

Yeah. Well, I think I'm going to pick up on something you said where you said, "out of nowhere." So Dr. Lewis, over your career, you've led efforts on hypersonic research and development as one of the world's leading experts. Can you bring our listeners back a bit further before that speech and pick us up on that point? What were the origins of this project and what had led up to it?

Mark Lewis:

Sure. So the National Aero-Space Plane, NASP, actually wasn't the first attempt at building or thinking about building an air-breathing, single stage to orbit vehicle, the magical airplane that takes off from any runway, flies up to space, does the mission, comes back and lands. As Guy pointed out, people were talking about this actually back in the 1950s. When I was Air Force Chief Scientist, I found a document from the organization that became the Air Force Research Laboratory, and they were evaluating approaches to get into space. And some researcher, I don't know who, had written in the margins next to some concepts for rocket systems, "Anything without wings and jet engines is a stunt."

So that was the idea. You think about how we were evolving our experimental planes, going Mach 1, then Mach 2. We had the X-15. It just seemed we were doing this steady progression of faster and faster airplanes that would ultimately lead into the space vehicles. There was even a movie in the 1960s about the X-15 rocket plane program. And at the end of the program they have an orbital flight, which of course the X-15 could never get close to the orbital speed, but that was the thinking. There, of course, was also work going back to the late 1950s, and the sort of propulsion systems, the jet engines that would allow us to fly at very high speeds. The idea that the engine we think is the engine of choice for this speed range, the supersonic combustion ramjet, that dates back to the 1950s. So it's not a new idea, but oh my God, talk about the overly optimistic exuberance associated with NASP.

Christine Boynton:

So a February 1986 issue of Aviation Week & Space Technology, at that point in time, we report that the technology development phase would start later that year, involving areas such as propulsion and aircraft design necessary to build an experimental flight research vehicle. Engine modules were set to be built and wind tunnel tested at speeds of about Mach 8. So sort of tossing it back to the group here for some reactions to what we heard at the very beginning, Reagan announcing this vision and Ben Rich's very frank assessment of his timeline, your thoughts here of Rich's words?

Graham Warwick:

Yeah, I suppose I'm a technology optimist, so I was covering X-30 from the UK in the early days. I'm also a bit of a canceled project geek, so I collect all this stuff about aircraft projects that never came into reality. And to be honest, the '70s, the '80s were just like technology madness when it came to aviation, particularly in the US. I mean, we went through some quite extraordinary projects that we convinced ourselves going to make sense.

We had a whole series of sort of Mach 3, we had the XB-70 bomber, we had the XF-108 fighter, we had the XF-103, the Republic, which was the most extraordinary looking airplane you've ever seen. And they all ... the XB-70 flew, but the others never even got off the drawing board. And it was just this sort of belief that anything and everything was possible. I mean, I would love to add up how much money the US spent on all those programs that never came to anything in that time. So X-30, it seemed incredibly ambitious. And we didn't really know where the technology was coming from to make it work. But it kind of fitted with the attitude of the industry at the time, and particularly in the hyped up by the Cold War technological ... whatever you want to call it. It seemed okay. Fair enough. Here we go again.

I just want to say that, a little personal though. I moved to the US in '91 and lived in Atlanta. And not long after I moved to Atlanta, I went to Chattanooga, Tennessee for an AIAA Aerospace Planes conference. And I thought it was so cool, I was at a conference called Aerospace Planes. Now, I think that was right about the time when X-30 was heading towards a brick wall at enormous speed. But I think the technological exuberance, ambition, overweening, whatever the word is, was not out of keeping with the way that we were thinking about... We just thought everything was possible back then.

Christine Boynton:

Well, and what were the ultimate goals of this program? Because it could have satisfied many different constituents, right, maybe starting initially with military applications and then onwards from there. Breakfast in New York and lunch in Tokyo I think was one phrase we wrote in one of the past articles. So what were the goals?

Graham Warwick:

I think Mark mentioned this, and I'll hand back over to Mark, but there's always been this absolute ... like the north star of the space industry is single stage to orbit. I mean, it was behind the DCX, which of course led ultimately to ... informed SpaceX and its reusable technology, but there were tons of them.

I remember when I was living back in the UK, I had a massive file of just single stage to orbit projects that were going on. But they were all incredibly brute force. I mean, some of them were like these giant conical ... dozens and dozens and dozens of engines to get these things into orbit. And then along came this really quite attractive, very elegant looking solution to the problem. And we all went, "Oh, that's cool," not really thinking that, yeah, it's cool, but it's completely impractical.

Guy Norris:

One of the sort documents that I've been looking at was a brochure from MacDonald Douglas in 1986, and it was really laying out where they were, where they thought they were going at that stage with this vehicle. As Graham says, it's extraordinary. It was huge all already by then. They'd sketched out a 305 passenger aircraft, take off gross weight of 530,000 pounds, of which 225,000 pounds was liquid methane, which was their preferred option over liquid hydrogen. It was 106 feet span, 250 feet long. So about the same sort of size as the 777 300. And by the way, it was meant to go between Mach 5 and Mach 5.5.

And what sort of strikes me about this thing is this was obviously a very sharp down ... it was an 80 degrees sweep angle. This thing looked amazing. It looked so cool, but I just can't imagine anybody in their right mind thinking that it could possibly work, especially when you think about the low speed environment, handling this thing on approach coming into LAX or over the traffic pattern, or takeoff. I mean, it's just extraordinary. Maybe get it into low earth orbit if you can, but this thing was ... I don't know, what were they thinking? It was great, but what were they thinking, Mark, tell us.

Mark Lewis:

And that was actually the conservative version, because as you say, it was a Mach 5 airplane. NASP was going to be Mach 25. So, oh my God, talk about optimistic exuberance. And you point out the size of the airplane. So you may recall the original design for the National Aero-Space Plane, and it was a project that was pitched by a gentleman named Tony DuPont, and his airplane was going to be 30,000 pounds. And by the time they canceled the NASP program, it was in the 500,000 pound category. And the deep, dark secret is there was no way it was ever going to close. The design would never close. By the way, Graham, I was at that 1991 conference in Chattanooga. I remember it like it was yesterday. And you're right, that was kind of as things were winding down, because I think everyone was realizing this thing is going to require a few miracles if it's ever going to work.

Graham Warwick:

The thing that struck me when I go back and think about it, A, was it in Chattanooga? Which kind of surprised me. Secondly, everybody I met there, I continued to meet in the decades that followed, because X-30 was what created the hypersonics experience expertise base that we continued to draw on. And I remember many, many years later, one of my most favorite visits was going down to the hypersonic wind tunnel at NASA Langley and going inside the tunnel, which is quite an extraordinary experience because it's like being inside a warhead after it's exploded, because it has this smell of sort of like gunpowdery type of stuff. That's because they flood it with this high temperature air to get that to simulate the flight conditions. But it makes the whole place smell weird. And of course you have this big copper engine that was sitting in the middle of it, but the people that were there, were taking me around, were people I'd met back in Chattanooga in 1991.

Mark Lewis:

Yeah. So I've often heard the discussion about, what did we get from the NASP program? And I think in the positive column ... I mean, we spent a lot of money and didn't get an airplane. But in the positive column, I think we can trace everything we're doing today in hypersonics to the NASP program. I mean, it created a whole generation of engineers, aerospace engineers focused in hypersonics. If you look at all the senior folks working in the field today, we were all junior engineers working on the National Aero-Space Plane. So I'll give the program credit for that.

Christine Boynton:

I think that's a great point, and I'm going to come back to that in a minute. But before we get there, we've mentioned weight. We've talked about that as being one of the major challenges, but this was also going to require an entirely new base of materials. Can you, Dr. Lewis, jump in here and walk us through some of the engineering challenges that were achieved, and what some of those initial main stumbling blocks were, maybe in addition to the weight?

Mark Lewis:

Sure. Wow. How much time do we have on this podcast? The engineering challenges were amazing, but let's actually start with the engine. All right? So it was going to be an air-breathing engine, an engine that uses oxygen from the atmosphere. So in order to get up to orbital speed, you'd have to be traveling at about 25 times the speed of sound. Great. The engine that was going to do that, the supersonic combustion ramjet, had never, ever been flown. And in fact, we didn't fly a supersonic combustion ramjet until arguably ... well, if you credit the Australians, it's 2002. If you credit NASA, it's 2004. But many years after the cancellation of the NASP program. And to this day, the maximum speed we've ever gotten out of a scramjet engine is about 10 times the speed of sound, so nowhere close to 25 times the speed of sound.

And I like to argue that the difficulty scales with the cube of the velocity because power scales with cube of velocity. So Mach 25 is an awful lot more difficult than Mach 10. So that's challenge number one. We didn't know how to build the engine. In fact, we didn't even know if you could build the engine. There were questions about, could you inject the fuel, could you mix it, could you get it to burn it? The joke was the fuel would be burning somewhere over New York while the airplane was over California. So that was problem number one.

Problem number two was the fuel. So you got the mass fraction of the vehicle. I mean, it basically was a flying fuel tank. And the fuel of choice was hydrogen, because that's the only thing we thought could power the vehicle all the way up the Mach scale. Well, hydrogen stores as a very, very low density liquid, which means you've got a tank of hydrogen, the tank is really big, which means the structure of the airplane is really big, and that's bad. So there was this major effort to try to densify the hydrogen, including using what was called slush hydrogen. So slush hydrogen, basically you have a semi-solid version of hydrogen. We had no idea how to do that. We had no idea how to store it.

So we didn't know how to do the engine, didn't know how to do the fuel. Then there were all the issues of how you integrate the engine on the airframe and what the thing would look like. We thought we knew how to build something that would fly at hypersonic speeds, but we weren't sure if it could ever get off the ground. There was some modeling that suggested that any of the shapes of the NASP vehicle could never take off. There was the running joke that you find a really high cliff, you build a runway on a cliff, you can just kind of shove it off and let it pick up velocity. Oh my gosh, so many things wrong.

I'll point out one other problem with the NASP program, and it was actually contained in ... you can hear this issue in President Reagan's own speech, because he talks about a vehicle that was going to go all the way up to space or fly from New York to Tokyo in two hours. But the problem is those are actually very different vehicles. One's an accelerator, one's a cruiser. So figuring out what the mission of this vehicle was going to be was kind of important, and we never quite got there.

Christine Boynton:

So by November 1989, another piece from our archives, things were still relatively optimistic. We reported at the time that the era of hypersonic flight was ready to begin. Six nations were working on aircraft designed to cruise at speeds over Mach 5, and the US was leading the way with the X-30. But there was a decision coming up, right, sort of a go, no go decision, due to be, I think, in about 1990, with flight testing in about '94, '95, and potentially to enter service in 2000. So can we walk through the final chapter of this program? What brought it to an end?

Mark Lewis:

Basically NASP went along until about almost '93, but even by the timeframe you're quoting, even by the late '80s, I mean, it was pretty obvious that this vehicle was just a bridge too far. There's a joke that any aerospace program that requires more than one miracle is not going to happen. With NASP, you needed a whole bunch of miracles. And I think the community was realizing that.

But maybe a little bit later we can talk about the legacy of NASP, but NASP didn't die completely. And in fact, you can trace most of what we're doing today in hypersonics to technology that was developed from NASP, including supersonic combustion ramjets. So all the hypersonic cruise missile work that you hear ongoing today, that all traces back to the NASP program. Much of the aerodynamics traces back to the NASP program. I talk about some of the challenges of fuel; so even our understanding of how you use fuels, how you inject fuel in the engine, but more importantly, the best fuels to use, that really traces back to knowledge we got in the NASP program.

Guy Norris:

I was sort of looking at some of the ... you mentioned Tony DuPont, Mark, as well, and the fact that the idea of this hypersonic research engine that he had pioneered in the '60s as well, which was very much one of the early kernels of NASP as well, one of the sort of seed projects, even though I guess the appetite for hypersonic research came and went, didn't it? It depended on budgets.

I mean, I think by the late '60s with the Vietnam War and Apollo taking out all of NASA's money, they didn't want to continue this HRE work that had been begun with Tony DuPont's engine. But he's the one that seems to come back and back through this story, always wanting to push it back. And he was the one, I think, who actually came up with the tiny little model of the original NASP, wasn't it, and shoved it across the table when the NASA team met with the ... Who was the defense secretary? Caspar Weinberger. And I think somebody said at the time, "This little needle shaped object was so sharp that when he shoved the model across the table, it almost pierced Caspar Weinberger's shirt."

So one of the thoughts I had was when they tested this model engine, hypersonic research engine, it was like a regular engine that we would see today, sort of in the cell around it. It was axisymmetric. And of course, it was only through all of this research that everybody began to realize that when you're talking about hypersonics, you have to integrate airframe and propulsion system as one. You can't have things hanging off the end. I mean, I remember when they eventually persuaded an NASA to fly a model of the HRE engine under the X-15, it burnt off because of aerodynamic heating burnt through the little pylon, and they lost it. It's probably still somewhere out over the Mojave Desert.

Mark Lewis:

No, no. They recovered it from the desert. That's how.

Guy Norris:

Did they find it?!

Mark Lewis:

Yeah, there was a gentleman by the name of Johnny Armstrong, a legend at the Edwards Air Force base. And as a young engineer, when it melted off the X-15, he figured out where it would've landed. And they went out in a Jeep, and sure enough, it was right where Johnny said it would be.

Graham Warwick:

So can I just draw a thread between what Mark said and what Guy said there? Because Mark talked about how X-30 never really entirely finished. And Guy talked about this on-off thing that the US has done with hypersonics, which is that if there's a single greatest thing ... There's two things that define US and hypersonics. One is over-ambition, and two is over-achievement. Because the US could never ... talk about attention span. This is worse than your teenage son in the basement with his Gameboy or whatever, or that. I mean, the US would go for about 5, 6, 7, 8 years and then just achieve something and then just go ... And usually, it was because the customer, the end customer, who was usually the military, either didn't know anything that was going on in this research community, because they didn't read Aviation Week, or they didn't see a need for it because there wasn't a threat they could address with hypersonics, right?

Well, as we well know, that all changed. But back then, there was this technology push, and no requirements. So what you see is this kind of sine wave of hypersonics, where X-30 peaks and declines. Then same technology, almost exactly the same flow path, we get the NASA X-43A, and then that peaks. There was supposed to be a 43B, there was supposed to be a 43C; never happened. We go down the slope again, and then we come back up the slope with the AFRL DARPA, or the AFRL X-51A, Boeing AFRL; in the end, a very successful scramjet engine demonstration with the same flow path, essentially a scale model of one of the engine modules from the X-30, basically, from the Pratt & Whitney or Rocketdyne.

And forgive me, Guy, if I get any of these details wrong, but they flew that X-51 however many times it was. They got to Mach 5 something or other with the X-51. Success. That was a demonstrator. We were supposed to then go into a missileized version of the X-51, which would've taken everything we'd learned with the demonstrator, package it into a missile. And what happened? We gaily put our skis on and skied down the slope into oblivion again, right?

Mark Lewis:

Yeah, you are absolutely 100% right. And talking about the NASP legacy, so X-43 was based on a concept for a vehicle out of NASA Langley. It was something called the dual fuel hypersonic vehicle, this idea for a hypersonic vehicle that would fly anywhere around the globe. Dual fuel because you flew out on hydrogen, you came back on jet fuel, which was dumber than DERP. Don't get me started. But it was actually derived from a NASP configuration. So if you trace the history of X-43, it was a NASP configuration. And by the way, we're just the 20th anniversary of X-43's Mach 10 flights, X-51. You're exactly spot on.

Now, here's the thing that really kills me about all this. So I was just talking to some friends over the weekend about being at the last flight of the X-43. And it was the most remarkable experience, because here you had a team of engineers who pulled off an incredible accomplishment. They flew an air-breathing jet-powered vehicle at almost 10 times the speed of sound. And they were the most depressed group of people you'd ever seen because the program was being canceled and they were being scattered to the four winds. It was a name.

And then as you point out, we had the exact same thing with X-51. So X-51, we had four flights. First one was mostly successful, second and third were not. Fourth flight was 100% successful. And then what did we do? Nothing. And the kicker on this is if you look at the total cost of X-51, it came in at about $300 million at the time. I think the numbers were roughly about 300 million. Each additional flight would've been about $11 million. So talk about penny wise, pound foolish. You make this big investment, you build this program, it all works, and what do you do? Instead of continuing to fly it and expand out the envelope, no, we stopped, and arguably even tried to move on to something else. Remember the DARPA Blackswift program? So that was going to follow on to X-51 instead of flushing out the flight test envelope. So yeah, we made some really bad decisions here.

Graham Warwick:

I think one of the things that's marked US hypersonics, I got to be very careful here about the US hypersonics, is because we're early in the days of hypersonics, there's still so much we don't know. We've not done any sustained flying at high speed. We've not done any maneuvering at high speed. We don't know 90% of the things we need to know to make it a successful vehicle. But hypersonics is a field where there's always something better just around the corner. And it's unfortunately a very US approach where we go, "Oh yeah, that worked, but yeah, but look, if we do this, if we go from that square of scramjet to a round scramjet and streamline whatever, we can get" ... Yeah, but we still don't know what happens at Mach 5 if we try to talk to the missile or something. There's all these ... How do we get a seeker onto something doing Mach 8 or something?

Well, these basic things we don't know, and we're always going, "Oh look, if we just do this, we can go" ... whereas, I mean, one of the things I've always thought, what's really intrigued me is that ... because the US took a lot of stick when it was finally realized that it had fallen behind the rest of the world in hypersonics, i.e., we didn't have a deployable weapon and China and Russia did China. China and Russia in essence took a brute force approach. So they just took a rocket and put a glider on it, and they pushed the glider to high speed. Perfectly good way of doing it. It's a very sort of aggressive, offensive, but relatively simple weapons system.

The US always wanted to do something else. And Mark, I remember talking to you about this when we started the early days of what became Hawken Aero and all those other programs. The US wanted a flexible, tactical, air-launchable weapon. The US, at any point in all of this ... In fact, they did. Sandhya demonstrated this. The US could have put a glider on a missile booster and had a weapon in service at any time in the last 20 years. We had all the pieces. We had the Sandhya glider, we had boosters up the wazoo, but we always had this idea of, "Oh no, we want to put this on a B-52 or a B-1 or an F-15. And we want it to be" ... because that's the way the US operated. The US doesn't really field simple, threatening, up-yours weapons. You know what I mean? It's always got a con-ops, a concept of operations, and a desire for tactical flexibility, which of course drives you to these weapons systems that get increasingly complex, except we were not doing the research to support the complexity.

Mark Lewis:

The one thing I might disagree with you, I think you actually have to draw a distinction between what the Russians do and what the Chinese do. So the Russians, indeed, brute force. And in fact, a lot of it is just Cold War legacy. They had programs that were sitting on the shelf for a while and they restarted. If you look at the hypersonic missiles they've been using in Ukraine, they're not particularly impressive. They're basically took something that was launched in the ground and made it an air launch system. But the Chinese, I think, are different. The Chinese have been fleshing out the technology. They read all the US papers. I mean, they saw all the US programs. And they have a pretty broad range of hypersonic systems.

So I agree with you in part. I am going to take part of the blame, actually, some of the personal blame for the emphasis on air launch systems, by the way, because I've been a huge ... I think that's one of the killer applications for hypersonics. But even there, as you pointed out, so starting with X-51, we had this beautiful path to an air launch hypersonic system. And there are a lot of reasons I think that you go to the air launch systems. There are a lot of reasons you want to fly sitting in the bomb bay of a B-52. They're less expensive. They package better. You can build more of them. You can launch more of them. I'm not generally a fan of the $50 million a round hypersonic systems. They have their applications. But if I can do a $1 million or even a $2 million a round hypersonic system, I think I've got a weapon that's frankly just more practical.

But even there, we just haven't been consistent. So after we flew X-51, DARPA picked up the Hawk program. And Hawk was the obvious technological successor to X-51. But instead of building on what we had done in X-51, we almost started over again. And I don't blame DARPA for that so much as that the nature of DARPA is DARPA doesn't redo someone else's technology. DARPA exists to do far-reaching technology, to do more advanced technology. So as soon as we gave responsibility for building an air-breathing hypersonic weapon over to DARPA, it's no surprise that they didn't build on what we had done in AFRL. They kind of started all over again. And the result is, it's more than a decade gap between the first flight of X-51 and the first flight of a Hawk missile.

Guy Norris:

I think that's part of the issue really, isn't it? It's this stop, start thing that we've discussed, is that the pull has never been strong enough to pull it over that kind of transitional ... the valley of death kind of idea that everybody talks about in the development world. And yet, every single time, there's a new hypersonic project sort of emerging on the other side of that gap. I mean, for example, DARPA is now looking at the Next-Generation Responsive Strike, NextRS program, which our colleague Steve Trimble has written recently about.

So the dream of X-30 still lives on in a way. There's always got to be somebody out there saying, "No, we've got to have this." Even if it's not single stage to orbit, it's going to be a cruise hypersonic vehicle. And again, DARPA, looking at the Hawk that you mentioned as well, Mark, they've now got the Mohawk, more opportunities for Hawk. So there's this sort of continual ... everybody still wants to have an air-breathing hypersonic system. Of course, China and Russia, as Graham mentioned, have sort of taken essentially either a combination of brute force, and China a bit more nuanced with more air-breathing aspects. But essentially, it almost seems as if they're still waiting for the US to come up with the next great idea.

Mark Lewis:

Well, except I'm going to tip my hat to the Chinese researchers, because for a while, yeah, they were pretty much mimicking what we were doing in the US, but they've come up with some pretty interesting stuff on their own. And they don't suffer from the phenomenon, Graham, that you point out. They don't have this start, stop. I guess it's one of the advantages of being an autocratic dictatorship.

Graham Warwick:

Yeah, I mean, I think that's right. And when it became clear ... Guy’s story that came in Aviation Week, when it became clear that the US was at least at risk of losing its hypersonic fleet, several things came out of that. One is that clearly all the work that we had done on X-30, X-43, X-51, a lot of it went into the public domain and gave the Chinese a leg up. I mean, they didn't start from scratch with this. They took everything that was out there in public domain. But because of the autocratic regime thing, they invested heavily in infrastructure. Because to be honest, if you really look at the history of US hypersonics, that's been one of the bottlenecks, is you have to get to flight to test hypersonics, because we don't really have the ability to test it on the ground. And if we do, we only can test it on the ground at some sort of smaller scale than the real thing we want to do.

China's put this huge investment into ground infrastructure, test infrastructure, and also, as you quite rightly point out, they have flown and flown and flown. I mean, they just don't have this, "Oh, we've achieved it," tick that box. Oh, the customer isn't interested because he wants to buy a tank or he wants buy a bigger ship or something like that. And nobody's waving the appropriate sword at him that he needs to respond to.

The Chinese just have this different approach to tackling these issues. And even now that the US has an understanding of what hypersonic ... the US military, from a threat basis, and therefore we need to respond. We're still not seeing the US really get apace to it. We're still seeing this incredible delay between you fly something, it either works or it doesn't, and then we go through endless analysis and whatever, and then maybe we go fly again. But it's like a year or two years or something like that. We're still not getting any sort of pace of consistency to push the technology forward.

Christine Boynton:

Guy, what do you think about this?

Guy Norris:

I was just going to say Graham raises a great point there. So much of what we've sort of seen is this sort of bottleneck of test infrastructure. And Mark, I was there 20 years ago at what was then Dryden, I guess, Edwards Air Force Base, witnessing the X-43 flight, which reached the record speed. And I remember that half the battle was just getting to the test condition with the B-52, and making sure the B-52 was working, and that they could get the range conditions. And everything had to line up like the pieces of cheese in an accident almost. It was like a one-off. And the same thing happened with X-51, as you remember. That was such a big part of the whole equation.

But I think one of the legacies of looking down the road of if you trace all that back to NASP, is also the fact that now you've got this new generation of Stratolaunch, for example out there, which is dedicating to the Talon as launching a hypersonic test vehicle for the industry and for the services. You've got Hermeus, for example, coming up with sort of their self TBCC-powered vehicles. So you've got this new wave of different approaches, I suppose, to the problem. And next year, we should see the HASTE mission, I think, the Hypersonic Accelerator Suborbital Test Electron mission, which will launch the Australian, the Hypersonix DART scramjet-powered vehicle. So if you really look down into the roots of it all, NASP still is producing ... decades later, we're still looking at some of the results, I think.

Mark Lewis:

Yeah, I think you're exactly right, and especially to Graham's point. So one of the things that happened, I mean, we allowed our infrastructure to wane, and wind tunnels, but also, as Graham points out, our ability to do flight tests. So I think there's kind of a good news story there. And the good news story is if you look in the past few years, you've had a number of organizations that have recognized the challenges we have with infrastructure and are trying to rebuild that. So in the Pentagon, you've got the Test Resource Management Center, led by George Rumford and his hypersonic deputy, Jeff Wilson. They're investing heavily into new ground test facilities, but also flight test capabilities, with MOPP TB.

You mentioned Stratolaunch. So full disclosure, I'm on the advisory board for Stratolaunch, but it's a much needed concept. The idea is to build a hypersonic vehicle that can enter the hypersonic flight regime not once a year, but in principle, hopefully on an almost weekly basis, kind of reliving the days of the X-15. The number of wind tunnels that are being built ... My day job at Purdue, we've got a wind tunnel that dates back to the 1960s from NASA that we just rededicated, refurbished, rebuilt. It's in a state-of-the-art facility. Other universities as well are stepping up. Notre Dame has just dedicated a new high-speed wind tunnel, Texas A&M, other organizations. In my mind, the question is, and the question I keep getting asked is, "Okay, now that we're investing in this, is it different this time? Are we going to see that slope?" And by God, I hope not. And I honestly don't think so, because we have countries like Russia and China that have already gone to deployment. So I think we've gotten the wake-up call.

Christine Boynton:

So with that wake-up call in this momentum, Dr. Lewis, what's going to be possible over the next couple of decades? Best case scenario, where do you see us heading?

Mark Lewis:

Look, I think, and I'm also going to credit it as a legacy of NASP, so I really do think calmer heads will prevail. No one's talking about Mach 25 scramjets, but Mach 5, yeah, we know how to do that, and Mach 6 and maybe Mach 7. I think there's also, and this is a recognition coming out of NASP, the first applications are military applications. As much as I would love to fly on a Mach 6 jetliner that's going to take me from Dulles Airport to Sydney, Australia in a couple of hours, oh my God, that would be the ultimate dream, the reality is the first missions are clearly military missions. And they start with the weapons applications.

So if you extrapolate from where we are now to where we will be, I'm pretty certain we're going to see the continued advancement of our weapons systems, hopefully at a faster pace. We're on pace to be deploying hypersonic weapons on the US side by the end of 2023. I don't think we made that deadline. I haven't checked lately, but I don't think we made that deadline. But I think you certainly are going to see the first deployment of US hypersonic weapons.

I think the question then becomes, do we continue to be dedicated to doing that? Do we continue to be committed to rolling out our hypersonic weapons? I don't know the answer to that. I think the answer should be yes, I think it has to be yes, but we'll see. We've got a new team coming into the Pentagon. We've got a new national leadership team. Honestly, we'll see what happens.

Guy Norris:

Well, certainly when you look at the past, I think one of the things, as Mark has mentioned, is the fact that there's, I think, more of a realism, you would hope. I mean, looking back at NASP, in 1986, they thought X-30 would cost 3.1 billion, and flight tests, as you mentioned, Christine, starting in the mid-'90s. But by the time they got to the mid-'90s, in fact, by '93, they estimated cost had risen to 15 billion, and first flight had slid to 2004. So by the time NASP was actually canceled, I think it was specifically in '93, maybe, Mark, it was 5.5 billion roughly had already been spent. But I think the lesson learned there is the fact that there does seem to be the lesson of history and that realism has crept perhaps back into the ... at least now, all of these projects are hemmed in by actual flight testing and results of what is capable; as you mentioned, Mach 5, Mach 7, we know that's good and doable.

Mark Lewis:

I laugh, because talking about price tags, so the much maligned Blackswift program, which in my opinion actually deserves to be maligned ... So I was still on the air staff at the time, and DARPA was pitching it as a $750 million airplane, and half was going to be Air Force, half was going to be DARPA. And by the way, I often point it out, that was in the middle of the X-51 program for that same 750 million, I could have flown about 70 X-51 vehicles. Thinking about expanding the flight envelope. But I digress.

And there was a very famous meeting with the then-Air Force Research Lab commander with the head of DARPA. And the Lab commander basically told the head of DARPA, "Well, the biggest problem with this program is DARPA is going to put in your half, and then the Air Force will put in our half, and another half and another half and another half and another half," because there was no way we were going to be able to build that airplane for 750 million.

And by the way, that was an airplane that was going to take off from runway, accelerate to Mach 6, do a barrel roll, fly for about 60 seconds, and then it wasn't clear you could continue flying the airplane, because the airframe might no longer be airworthy. There was some debate about that. So in Graham's point about the always pursuing the next shiny thing, oh my God, that program exemplifies it.

But bottom line, as you say, what's the cost of a hypersonic vehicle? Funny incident, when that Blackswift program was kicking in, I was in my Pentagon office and I got a phone call from one of the Air Force's four-star generals. And he basically called me up to yell at me. And the reason he was yelling at me was because Blackswift was a hypersonic vehicle. He assumed I was the one behind it. And he starts yelling at me. He says, "Where's your integrity? There's no way we can build this for 750, man."

I'm like, "Whoa, whoa. Wait, wait, wait. I'm on your side on this one. I agree with you." And at the time, we talked about what it would cost to build that airplane. And our best estimate at the time was probably about 4 billion. And that was for an airplane that flew to Mach 6, did a barrel roll, and then came back and landed. So you put that in perspective, a Mach 25 airplane flying into space? Yeah, you'd be lucky to do that for 15 billion.

Guy Norris:

Well, and of course talking about access to space, because here's another weird lesson learned or emerging result out of NASP, when NASP failed, of course, as we've said, the SSTO, single stage orbit dream, has never really gone away. But the Strategic Defense Initiative Office, SDIO, then thought, "Well, let's go back to the tried and trusted rocket approach." And of course, that gave birth to the McDonnell Douglas DC-X, which I think Graham mentioned earlier on as well. For those that don't know, it was a vertical takeoff and landing rocket demonstrator that actually proved that you could do that. And of course, hey, presto, two decades later, we've got SpaceX Falcon 9s landing pretty routinely, exactly using that concept. So that's another strange legacy of NASP, is one of SpaceX's great technologies.

Graham Warwick:

I'm hoping that hypersonics, to Christine's question about, "Where do we go from here," I'm kind of hoping that there is a, "Where do we go from here?" I want this to continue, because I want an excuse to go back to Chattanooga.

Mark Lewis:

So it's funny, I have had conversations with Elon about air-breathing propulsion, and he had absolutely no interest in it whatsoever. But for space, well, at least for the foreseeable future, he may very well be right.

Christine Boynton:

Well, we are approaching the end of our hour, so I guess I'll just open it up to any final thoughts, optimistic, pessimistic, somewhere in between of where we go from here for this dream of hypersonic flight.

Graham Warwick:

I think I'll just put my six-pence in here, that it's clear from this conversation that X-30 as a program was a failure, but a generator of technology that then kept us busy for decades afterwards, not just us, but the Chinese, kept the Chinese busy decades after, it was an extraordinary effort. And I think in the end, what came out of X-30 was a whole bunch of people with unique experience and unique understanding. And those same people continue to play a role in everything that followed. That experience that was built in X-30, and before it, in some ways, before it in X-15, is why we are where we are today. We've made the best use of it, but the use we've made, we've been able to make because of the people that worked on X-30.

Guy Norris:

Yeah, and just following up from that, I mean, obviously I think X-30 was the platform upon which really every single stepping stone, including, for example, as I mentioned earlier, the airframe propulsion system integration approach, which really, again, came out of the idea of using the airframe itself for compression and as part of the inlet and the nozzle ... And there are hallmarks of basically every single air-breathing hypersonic approach since. So the roots of NASP, I think, will continue to be a force forever, really, in the history of hypersonics.

Mark Lewis:

If I could put a very personal spin on it; so when the NASP program began, I was a graduate student at MIT, working in the gas turbine lab, working on gas turbine engines. And there were some fascinating, fascinating problems associated with gas turbine engines. It really challenges us in aerodynamics and thermodynamics. And I was bored silly. And the reason I was bored is, I mean, it was proven technology. You could walk into a gas turbine engine store and buy a gas turbine engine. And everything we're working on was trying to make them a little bit more efficient, a little bit more fuel efficient, but it really wasn't pushing the flight envelope.

And then this NASP program gets announced. And I started working ... my PhD thesis was associated with the NASP vehicle. It was such a heady, exciting time. The dream of this vehicle, it was just amazing. I've spent now almost about 40 years working in hypersonics, because I started when I was five years old. And it was all because of NASP. I mean, if not for NASP, I'd still be trying to figure out heat transfer to turbine blades. And not that there's anything wrong with that, and I'm not alone in that. I mean, as both Guy and Graham pointed out, there's this whole generation of engineers, we all got our start with this dream of building this hypersonic vehicle. So I put it in the category of a very, very noble failure, and one that really has gotten us to the point where we are today, where we are seeing practical hypersonic systems being built, utilized, deployed. So that's a pretty good legacy.

Christine Boynton:

Well, that is a wrap for this episode of Check 6 Revisits. A special thanks to Dr. Mark Lewis for joining us today. And thanks also to our podcast producer in London, Guy Ferneyhough, and to Graham Warwick and Guy Norris. For links to our archive, check the show notes on aviationweek.com, Apple Podcasts, Spotify, or wherever you get your podcasts. And to delve into our archive for yourself, Aviation Week subscribers can head to archive.aviationweek.com. If you enjoyed the episode and want to help support the work that we do, please head to Apple Podcasts and leave us a star rating or write a review. Thank you for listening, and have a great week.