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Conical flight body launched from a two-stage light gas gun flowing against a black background

Episode 15: Hypersonic Progress

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In this Episode

The future will be fast! That’s why our guests Dr. Nicholas Mueschke and Dr. James Walker launch projectiles faster than Mach 5, five times the speed of sound. They’re studying hypersonic speeds in an SwRI lab, reaching thousands of miles per hour and temperatures hotter than the sun. In this episode, we discuss their discoveries and where their work could one day take us. Think commercial hypersonic flights, coast to coast, in an hour!

In today’s Breakthroughs, earthquakes shake up a geologist’s view of nature, highlighting the vast connections that exist all around us. And how does sunlight reach Earth? A space physicist has the answer in Ask Us Anything.

Listen and learn from the people shaping our world through science, engineering, research and technology.


Below is a transcript of the episode, modified for clarity.

Lisa Peña (LP): Research in The Fast Lane. Our guests today launch projectiles faster than Mach 5 as they study hypersonic speeds. That's thousands of miles per hour. Their work could one day revolutionize air travel.

Plus, a geophysicist unexpectedly finds inspiration in earthquakes. Why he says they are just one step in the long walk shaping Earth. That's ahead in Breakthroughs.

And Ask Us Anything – a listener question takes us on a sunbeam's journey. That's all coming up on this episode of Technology Today.


We live with technology, science, engineering, and the results of innovative research every day. Now, let's understand it better. You're listening to the Technology Today Podcast, presented by Southwest Research Institute.

Hello, and welcome to Technology Today. I'm Lisa Peña. A new Breakthrough story that just might shake up your view of nature. And in today's Ask Us Anything, our expert discusses how sunlight reaches Earth. But first, we're flying into this new year and new decade at hypersonic speeds.

Our guests today are Dr. Nicholas Mueschke, an SwRI engineer, and Dr. James Walker, director of SwRI's Engineering Dynamics Department. They test-fire objects at hypersonic speeds, exposing materials to extreme heat, and in the process, making discoveries that could one day change how we travel and how quickly we reach our destination. Thanks for being here, James and Nick.

Dr. Nicholas Mueschke (NM): Thank you for having us.

LP: Well, so let's start with a definition of hypersonic. We are talking about unreal speeds here. So how fast are we talking?

NM: Well, hypersonics is typically or roughly defined as anything moving faster than five times the speed of sound. So the speed of sound is defined as Mach 1, so you'll hear us say Mach a lot. But Mach 1 is how fast a sound wave moves. And anything moving at hypersonic velocities is moving at least five times faster than that. But we're really interested in speeds of from Mach 5 all the way up to, let's say, Mach 30. Now, to put that in context, how fast is that? Mach 1 is about 770 miles per hour. That depends upon what you're flying through and the temperature of what you're flying through. But it's about 770 miles per hour.

But if you're talking about Mach 5, now we're talking about moving at around 4,000 miles per hour. And we're looking at stuff that, or we're interested in stuff that's moving up to 40,000 miles per hour.
James Walker, Lisa Peña, and Nicholas Mueschke against a solid blue background

Left to right: Dr. James Walker, Lisa Peña, and Dr. Nicholas Mueschke

LP: OK. And can you give us some examples so that we can kind of understand? What are we talking about when we talk about Mach 1, Mach 5?

NM: Sure, sure. So if you to put everything in context of, let's say, a commercial airliner, a commercial airliner flies at subsonic velocity, so less than Mach 1. It'll cruise at about Mach 0.8 or 0.85. And if you want to look at some military fighter jets, those things will fly at supersonic velocity, so Mach 1.5 or Mach 2. The stuff that we're interested in starts at about Mach 5 or higher. Now, it's interesting to put that in context. Some high powered rifles, you can launch bullets at Mach 5 or Mach 6 out of a high powered rifle. So that's about 2 kilometers per second or about 4,000 miles an hour.

But when we start talking about hypersonics, what do some of those vehicles look like? If you're returning from lunar orbit, let's say the Apollo missions, those all came back and reentered the Earth at about 11 kilometers per second. That's roughly a little bit over Mach 30. And then when the space shuttle reenters, that was reentering around Mach 20, Mach 20 to Mach 25. But it's trying to slow down during its descent back into the atmosphere. Some other interesting applications are the commercial flight industry. SpaceX is launching its rockets to deliver stuff to the space station or put stuff in orbit. Those rockets, whenever they cut off their main engine, they're moving at about Mach 8 or Mach 10, right near the upper edges of the atmosphere.

LP: OK. So James, you are recreating these crazy unimaginable speeds in a lab right here at SwRI. How are you doing this?

Dr. James Walker (JW): So we are launching relatively large projectiles with what's called a two-stage light gas gun. Guns typically have one stage, the ones you think about, say, like a rifle. And a regular rifle, say a 30 caliber rifle, will shoot a projectile around 950 meters per second, which is around, almost approaching Mach 3 is what a typical rifle will shoot. So with our guns, we can launch up to about 7 kilometers per second, about seven times that fast. And we can then launch various shaped projectiles, which we've done, looking at their behavior as they fly through a controlled atmosphere.

So the two-stage light gas gun, in particular, we have a regular gunpowder, a propellant that compresses hydrogen, pushes a piston that compresses hydrogen to really high pressures, high temperatures. And then the hydrogen, which is the light gas, is what accelerates the projectiles to these really high speeds. So it's done in two stages. It's just a laboratory device. It's really large. It has its own building here on the SwRI campus. And then it flies through various flight tubes and instrumentation chambers so that we can collect data on the projectile flight.

LP: OK. And we'll go back to Nick for this next question. How is photography used in your research? It's my understanding you're taking pictures of these projectiles.

NM: We are. It's actually really, really fascinating. We use a lot of high speed video in just about all of the experimentation that we do in our department. But for these experiments, we're actually launching a projectile that might be flying anywhere from Mach 10 to Mach 15. And as it's flying, we set up high speed video cameras that will record its motion in free flight. And typically what we'll do is we'll record images at 100,000 or 200,000 frames per second. And as this projectile flies by, we might get four or five pictures of it, and then it's gone.

LP: What do those pictures tell you?
Cylinder flight body launched from a two-stage light gas gun

High speed video image of cylinder flight body launched from a two-stage light gas gun traveling at 5.45 km/s (Mach 15.8, 12,200 mph). The shock wave in front of the flight body compresses and heats the air to an approximate temperature of 6,700 K (11,600 °F).

NM: Well, it sort of depends upon what we're looking at. We set these cameras up in different ways. Sometimes we're taking just raw color images of it. And what that means is it's just like sitting there with your own personal Handycam and recording a picture of it as it goes by. But what that tells us is we actually see what it looks like in flight. Because what's truly fascinating about these experiments is we start to chemically break down everything around us while we fly. The vehicle that's flying through the air is chemically decomposing. The air around this vehicle is so superheated that it is chemically decomposing. And then the chemically decomposing vehicle starts to interact with the chemically decomposed air, and everything is reacting with itself. And so it makes this beautiful picture of, you can see material that's been stripped off and have ablated off the front edges of this vehicle, just glowing white hot.

And so when we take a video of it, we can actually see where this material is and get a sense for where is material coming off, how hot is it, what is it composed of. The other ways that we take video, we actually set up a series of lights and mirrors and we create shadow graphs or schlieren images. And what we do is we actually bend the light rays through areas where their density changes in the gas around the vehicle. So you have something moving really fast and it has a shockwave around it. And that's the shockwave you hear on the ground whenever something flies by at supersonic velocities.

Well, that shockwave actually bends the light. And so we set up mirrors to actually capture where that light is bent, and then we can see where the shockwaves are, we can see perturbations in the fluid right around the vehicle to determine whether or not it's turbulent or laminar flow. And all of this is super important to understanding how these vehicles fly, where that flow transition occurs, and how do you design vehicles to account for where these transition occurs.

LP: So when you say vehicles, you are talking about projectiles made of different materials and in different shapes. Is that correct? You're testing different materials and different geometries?

JW: We make the projectiles out of different shapes, and we've even flown additively manufactured projectiles so we can have more complicated shapes. But the focus really is primarily on the shape and then also on, as Nick indicated, some of the material behaviors. There's interesting things that happen here. One is that that, Nick described the decomposition of the atmosphere. Oxygen has two atoms in a molecule, as does nitrogen. The fact that they dissociate is a benefit to helping keep temperatures down because energy goes into breaking those bonds. But then you can have reactions catalytic, they're called, where the material of the flight body actually encourages recombination right at the surface, which can add to more heat all of a sudden.

And as Nick indicated, we're also looking at this question of the shape primarily and how it affects boundary layer transition. Boundary layers are very important as to the heating of the vehicle in flight. We worked on the accident investigation for the space shuttle Columbia and we did work related to that. So we were involved in subsequent flights. And they showed gap fillers were coming out, which were between some of the tiles. And in the end they decided to leave them in. And it's interesting, you can look at scorch marks from having left those gap fillers in on the tiles because that led to a local breaking of the boundary layer and local turbulence, which added more heat going into the space shuttle during reentry.

So this question of boundary layer transition, which is something we're looking to examine in our flight tubes with this launch facility, is an important question as to heating during flight, and thus how practical or what kind of thermal protection is required.

LP: So what are the fastest speeds you've reached in the lab?
SwRI's 72-feet-long two-stage light gas gun in a test lab

SwRI’s 72-feet-long, two-stage light gas gun is capable of recreating hypersonic flight conditions, including speeds ranging from Mach 10 to Mach 15.

JW: So the fastest that we've shot this particular gun is 5.77 kilometers per second, which is on the order of a, trying to do a rough translation, about Mach 17 or, maybe, 13,000 miles per hour. This isn't our fastest gun, but it's our biggest gun that can launch at these kind of speeds.

LP: But what temperatures do these objects reach? I know we're talking about fireballs and seeing explosions inside the gas gun itself.

NM: Yeah. Well, it's actually interesting. So it is probably worth pointing out, and I don't think we mentioned this earlier, that the biggest part of studying hypersonics or what really defines hypersonic velocities as opposed to just flying at a supersonic velocity is the temperatures that you have to deal with and the heat load to whatever is flying through that atmosphere, it becomes the most important thing that you have to concern yourself with. When you fly at supersonic velocities, you have to worry about the aerodynamics, you have to worry about the heating, you worry about several things. But once you go beyond Mach 5, the total amount of heat just dumped into whatever is flying through the atmosphere dwarfs any other concerns. It becomes the primary thing that you have to concern yourself with.

So when you're flying through the atmosphere, you create a shockwave out in front of whatever object is flying. And behind that shockwave, you can reach extreme, extreme temperatures. So some of the stuff that we've launched in the last year or so, particularly these images right here, which we can...

LP: Sure. What are we looking at?

NM: So we launched some, basically, right circular cylinders. So it's about an inch and a half diameter cylinder. And the bow wave out in front of that projectile, right behind that bow wave, the gas is heated to about, I want to say it's about 6,700, 6,800 Kelvin, if I remember correctly. And that's hotter than the surface temperature of the sun, which is about 5,000 Kelvin.

LP: So this is happening in your lab?

NM: This is happening in the lab. So that's the gas temperature behind that shockwave. But now all that gas is now flushing over the object in flight. And so that's melting parts of it, that's ablating parts of it it. All of that energy, or a lot of that energy, gets dumped into the object that's flying. Now, our experiment is over after about one millisecond of flight. Imagine if you have to sustain these types of speeds for a minute or 10 minutes or an hour. If you have to get across the country or across the ocean, you have to sustain this flight velocity and deal with these temperatures for a longer period of time than just our experiment.

LP: So what materials perform best under these outrageous circumstances?

NM: Well, that's a great question because that's sort of where the cutting edge of the research is. There's a ton of work being done to develop material systems that can deal with these heat loads and deal with these temperatures and survive. There's a lot of work being put into composite materials that can withstand these temperatures, a lot of carbon-based materials that don't have a melting temperature. They'll heat to the point where they turn just to gas. Beyond carbon, there are a lot of refractory metals and tungstens being looked at. And then there are a lot of engineering questions about even if the material has a melting temperature that you have to be concerned with, can you engineer a means of controlling the temperature by putting systems underneath the surface of the skin of the vehicle to help draw that heat away or mitigate those extreme temperatures?

JW: Yeah, I think this is an interesting point in that historically when we look at flight vehicles that were going fast, they use titanium. So we have the SR-71, which could do about Mach 3. In fact, when we dream about where we could go in the commercial world with this, the SR-71 did London to Los Angeles in less than four hours. And that's Mach 3 and we're talking Mach 5. So it could be really great for those of us who are tired of sitting on planes at these subsonic, 80% the speed of sound kind of flights. The X-15, which was a rocket-boosted, briefly hypersonic vehicle, was also titanium. So its highest speed was about 4,000 miles per hour.

But now for these kind of sustained speeds, we have to go into some more modern materials. The nose and the leading edge wing of the space shuttle were made of a carbon-carbon composite. So that's one of the areas that we expect to be going into. And some of the materials that we're currently testing are these carbon-carbon materials, which, as Nick indicated, have really high melting temperatures or sublimation temperatures, and so they're able to deal with these high heat loads for an extended period of time.

LP: So all this is fascinating, and there is a purpose behind all this. You're not just launching projectiles for fun.

NM: We might maybe.

LP: Might be.


LP: I'm sure this is fun. I'm sure there's some element of fun there. But really, what are the possibilities with this research? Where do you see it going?

NM: Well, there's three application areas. There are certainly military and defense application areas. And that's the primary driver between the rapid funding increase in this area of research. There are also commercial air travel applications. Those, I believe, are a little bit further out, before some of this technology matures to the point where we'll be able to buy a ticket on an airliner flying at these velocities. But then there's also, the commercial spaceflight industry has a lot of hypersonic applications, as well as, I guess, government space flight. So Mars reentry, if we're sending somebody to Mars, we land, we enter the Mars atmosphere at extreme hypersonic velocities. We're talking Mach 30, Mach 40.

When we come back from Mars, we're re-entering the Earth's atmosphere at these extreme Mach numbers, Mach 30 or Mach 40. Just in terms of launching satellites, there's a burgeoning commercial spaceflight industry. All of the rockets that go up and launch something into orbit or that might bring even paid space flight, where if you want to take a ride and go into space, some of those flights are starting at Mach 3. But then even the SpaceX rockets that are launching stuff into orbit are breaching Mach 8, Mach 10 before they ever leave the atmosphere. And so understanding the physics and designing those rockets properly to handle the heat loads, the pressure loads, and fly properly and achieve their mission in launching satellites into orbit, they've got to grapple with all the problems that anybody else grapples with in the hypersonics realm.

JW: We're looking into two different regimes here. We have the historical one, which is the boost glide, the space shuttle was boost glide, so it re-entered hypersonicly. But now as we're moving towards, as Nick was mentioning, in the commercial sector, this focus on trying to reuse launch vehicles, this question becomes very important. Because we have boosters going up, we want to reuse them. They're just entering their hypersonic regime. And that's what they have to do to return to Earth for reuse. So that's a big hope we all have for cutting the cost per pound to orbit into space, is by reusing launch vehicles. To do that, you have to understand the hypersonic flight and the hypersonic regime because that's part of the reentry package that they have to go through in order for us to recover those vehicles and then reuse them.

So that's the first kind of exciting area, new area that's opening up for a hypersonics. Another new area which is a little further out, as Nick mentioned, but I think is super exciting is this notion of actual hypersonic airliners. Of course, we don't have supersonic airliners right now, but we're still hoping for the hypersonic airliners. And that leads to some new technology as far as engines go, which we really haven't touched on. But the US had a program called the National Aerospace Plane, which was in the late '80s, early '90s. A lot of research on can we actually do a single staged orbit that was out of reach. But a number of technologies were developed, but just need further development to try to have these kind of flight bodies. It's typically called a scramjet, supersonic burning aircraft engine, jet engine. And we need to have more breakthroughs in this area in order to have that hypersonic commercial airliner.

But right now we also need the supersonic ones. And NASA has a number of programs with a number of the airlines for maybe some small, private supersonic business-type jets. But there's also this hope of getting the hypersonic ones, where you really can do overseas travel in just a couple hours.

LP: That would be amazing. Who wouldn't want to do that, right? But how far off are we talking? When you say it's well off into the future, do you have a projection as to when?

NM: Well, it really depends. Right now, as was mentioned, we're kind of in a fifth or sixth wave of hypersonics. It started back when we talked about X-15 and Gemini and Apollo. We're now at another wave where Department of Defense is investing in it. And right now, their short term is the boost glide that we talked about, where you do hypersonic glides. But they're also investing in missiles that will have air breathing engines, which are the scramjet technologies, what we assume is the technology that will win out. So those we could see towards the end of the decade. You talked about we're new 2020s. That's this decade will probably happen missiles that have that technology.

Once that's in use and tested out and lots more research happening on it, it's very possible that the end of the 2030s could see something human-manned.

LP: All right. So any surprise findings so far? How long have you been researching hypersonics here at SwRI? And so far, any big surprises through your research?

JW: So we've been doing about two years now of the flight research that we've mentioned here with our two-stage light gas gun. And I think what's been the most interesting to me, and Nick can comment, is some of the pictures, where without any lighting, we actually see the glow of these high temperature air molecules during the passage and after the passage of the flight body, where we can see some of the color that's being given off. And we also see, of course, the mixing of the air, the turbulent mixing in the wakes. So that's actually pretty interesting and exciting to be able to see that directly.

LP: So I wanted to ask both of you, what do you enjoy about hypersonics research?

NM: I think that's a really easy question to answer. I am thoroughly fascinated by just how interconnected everything is. You have the chemistry of what's going on combined with the aerodynamics combined with the flight physics combined with the material science. All of those are so integrally connected that it's hard to isolate one from the other. And it makes it such a rich and complex problem to try to wrap your head around that I just find it fascinating.

LP: Yeah, it is. James?

JW: And I think there is also another aspect we really haven't touched on so far today because we've been focusing on the experimental end and the fact that we can launch these bodies at really high speeds, which is really amazing. But part of the way we understand, part of the way we analyze what we've actually done is through large scale numerical simulations. So we have software models of how these molecules break up in the air and how the flow goes past the flight vehicle. And comparing the experiments to these models is what leads to our understanding of what's actually going on, and also develops a predictive capability.

LP: Well, I'm looking forward to buying my first commercial hypersonic flight ticket. And when I do, I'll think of both of you.

JW: Well, as are we.


LP: OK. Well, it's truly fascinating work. Thank you both for sharing your insight with us today, Nick and James. It's been great having you.

NM: Thank you for having us.

JW: Thank you.



And now Breakthroughs, personal stories of discovery told by the people who live them. Today, a guest featured in Episode 11 returns to share why earthquakes are awe-inspiring and how they give us a glimpse into the power of nature.

John Stamatakos: So my name's John Stamatakos. I'm an Institute scientist now. I've been at the Institute for 25 years. Trained classically in geology and geophysics, although I've been working as a seismologist most of my career here at the Institute. So when I first arrived here, I was working with a great team of geologists, volcanologists. We were working on a big program then that was to support Nuclear Regulatory Commission on the Yucca Mountain project. We had a seismologist on staff and the Department of Energy had just started their own big brand new study to evaluate earthquake hazards for the Yucca Mountain facility, and he retired.

And so everybody just looked at me and said, well, your degree says geophysics, you should understand earthquakes, too. Why don't you take on that role? And I said, sure, can't be hard. How hard could earthquakes be? And so I just stepped into that role and started to go to these meetings and realized pretty quickly how interesting and different earthquake science was from standard geology and geophysics, that although we're all looking at the same phenomena, we're looking at them in very different ways over very different time frames. And just became enamored with earthquakes seismology and with all aspects of earthquakes and what people did to study earthquakes and what people actually did to use earthquakes to predict future hazards.

Well, earthquakes are like the individual steps of a long walk. That's the view from a geologist. So if you're standing in Yellowstone Park or you're standing looking at the Tetons, there's a really good example. The Tetons are a very young mountain range. They stand up 13,000 feet is the highest elevation. And you're standing in the parking lot there at 5,000 or 6,000 or 7,000 feet. So you've got this huge edifice in front of you. And what you realize when you start to study earthquakes is that edifice is really the product of hundreds of repeated earthquakes over several million years. So from a geologist, a million years doesn't sound like anything. From a seismologist, a million years is forever.

So you put the two together and you recognize that the cumulative effect of each individual earthquake is the result of this beautiful mountain range. But it took 600 to 1,000 individual big earthquakes to produce that mountain range. That was an interesting philosophy to adopt. Nature just reveals itself to you in ways that you don't predict as a scientist. And that, at least from my point of view, really captured my imagination. Like, wow, it is so much more complicated and beautiful than anybody can even imagine. So there's another aspect of seismology that I always love to talk about, and it was a discovery that was made by Gutenberg and Richter back in the 1950s. And that is that earthquake magnitudes follow a very simple power law relationship.

So every magnitude 6 earthquake is preceded or followed by 10 magnitude 5 earthquakes. And every magnitude 5 earthquake is proceeded or followed by 10 magnitude 4 earthquakes. So you get this very simple relationship. So if you know how frequently a magnitude 6 earthquake occurs, you know you're going to get 10 times more frequent magnitude 5 earthquakes. It's a very powerful and very universal relationship. That was really inspiring me to learn about that. And then to learn that that actually what we call scale independent or scale invariant relationships occur all over the place in nature. The Earth, this dynamic planet that we're lucky enough to live on, earthquakes are just part of a natural cycle of how everything occurs. And so I like to look at the whole range, small earthquakes to large earthquakes, the frequency that they occur and where they occur, why they occur. They're a complex beast, and yet, I think there's kind of a beauty in them.


A new and enlightening perspective on earthquakes and the connections in nature. Thanks for sharing your breakthrough story, John.

Ask Us Anything

And finally today, Ask Us Anything. You ask, our experts answer. Aarya M. submitted questions on

She asked, "Does light need air to travel? And if so, then how does the sunlight travel in space to reach Earth?" And her second question, "Does sound travel in a vacuum?" Great science questions, Aarya. We turn to our expert SwRI Space Physicist Dr. Heather Elliott for the answers. Thanks for joining us, Heather.

Heather Elliot (HE): Hi. It's nice to be here. Does light need air to travel? No, it doesn't. Sound waves and ocean waves are waves where a piece of material moves up and down or there is a vibration. I know that everyone has felt really loud sounds vibrate their chest. And then an ocean wave, you literally see the water move up and down. But light is a wave in electric and magnetic fields. And electric and magnetic fields can exist in a vacuum. So a vacuum is a region where there is no material, no mass.

Since space is almost a vacuum, and we know that electric and magnetic fields can exist without there being any material. So that means that the light can go straight through space and go from the sun all the way to Earth. So it's not like the sound waves and the ocean waves where you have to have material moving. It's like an energy source that can just travel.

Lisa Peña (LP): And her second question, "Does sound travel in a vacuum?"

HE: Yeah, so a vacuum doesn't have any material. And a sound wave, you need that material to move. And so since there is no material, it can't travel in a vacuum.

Thank you for submitting again, Aarya. To submit a question to Ask Us Anything, visit and scroll to the bottom, or post your question on social media with #askSwRI. You can also share your question by commenting on one of our Ask Us Anything posts. Your question may be featured on an upcoming podcast episode.

And that wraps up this episode of Technology Today.

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Ian McKinney and Bryan Ortiz are the podcast audio engineers and editors. I am producer and host, Lisa Peña.

Thanks for listening.


The development of hypersonic vehicles requires unique facilities that simulate realistic atmospheric, velocity and high enthalpy flight conditions. Southwest Research Institute (SwRI) provides the aerospace and defense sectors with world-class facilities to perform hypersonic research, modeling and testing solutions.