Planes in Spaaaace

We're gonna learn more or less how they work, why anyone was interested in building them, and some of the past and current projects that fall into that category. So to begin with, what the heck is a space plane? Well, like most stuff that has to do with space exploration, it's complicated. The general concept, if you're going super super high level, is that a space plane is a vehicle that can go into space, not necessarily into orbit, but at least into space and return to Earth, and it

can fly under its own power. That's in contrast with other space vehicles like the Apollo or the soy US. Those have the tried and true methodology of ballistic re entry, also known as plummeting towards Earth under the force of gravity and then deploying a parachute to slow you down, and in the case of the soy Us, also having a quick blast of a retro rocket before you touch down,

either in the ocean or on terra firma. A space plane would re enter Earth's atmosphere and then use the principles of powered flight or powered gliding to land at a designated landing strip, so they could actually not just control their descent, but steer and and go to a specific location for landing. This is actually way more complicated that I'm letting on at this stage, because you have to remember the principles of flight in space are very

different than the principles of light. Here in the atmosphere of Earth. You have a fluid dynamics that work when you're flying through an atmosphere, and then you have the near vacuum of space when you're out in space. So, despite what science fiction films like Star Wars would have us believe, you wouldn't bank in outer space because there'd

be no atmosphere for you to bank off of. In addition to these basic concepts I've just mentioned, we tend to tie to other things to the idea of space planes. One is that they should be reusable, meaning that you would refurbish a space plane after it's gone on a mission, and then you could use that exact same vehicle and a future mission, and that cuts down costs because you

don't have to build a whole new one. The second big thing is that they should be easy and by that I mean cheaper to launch into space compared to other spacecraft. That's ideal. If you can figure out a way to make it easier to launch these types of spacecraft into space, you again bring down the cost of getting stuff into space. Under these general guidelines, you could say the space Shuttle qualifies as a space plane that

totally is a type of space plane. It was reusable, it could return to Earth and powered glide so it can navigate to a specific landing strip. But the history of space planes dates way earlier than the Space Shuttle program. Perhaps the earliest design for a space plane would be the Silver Focal or silver Bird design. This was a proposal that dated in to the nineteen forties and it

was in Germany during World War Two. The design was essentially a liquid fueled rocket that had some wings attached to it that was meant for a German pilot to fly up high into the atmosphere, essentially entering into what we would consider to be space, but not orbit. It would be a suborbital flight then to cross the Atlantic Ocean and descend in a a powered glide to attack

a target in America like New York City. Now, while the Germans built some mock ups of this design, including one to use in wind tunnels, to make sure that the actual physical design of the body made sense, ultimately engineers concluded that it was too complicated to advanced to make practical. They just weren't quite there technologically to make

it a practicality. But we'll revisit this concept shortly. In the nineteen fifties, a British engineer named Terrence non Wiler proposed an interesting concept called wave riding that would find its way into various space plane proposals. That started with a wing design called the carrot wing, which is a wing that has a type of concave pyramids shape to it.

Non Wiler worked out a physical design that would allow an aircraft traveling at supersonic speeds to leverage the shock waves it was actually generating and use that as a lifting surface, which to me is incredible. That actually everything that has to do with supersonic and hypersonic flight physics to me is amazing. So what does that actually mean?

Was a shock wave? Why do those things happen? Well, shock wave is a phenomenon that happens with really any type of wave, but we're specifically talking about sound waves here. When in a flow moves higher than the speed of sound in a given medium, and by flow I typically mean an object like an aircraft, but it could be other things. In fact, it could even be um the

air itself moving faster than the speed of sound. So a cracking whip generates a small shock wave, a small little sonic boom type thing at the tip of the whip because it moves faster than the speed of sound when you crack it. So when you hear someone crack a whip, that means the very tip of that whip when it made that snap, was traveling faster than the speed of sound was. So let's get an understanding what's

going on from a physics point of view. First, when something makes a sound, it's a physical phenomenon, right, It's it's the changing of pressure of uh air. Essentially air molecules. It's pushing them together or creating gaps and thus creating kind of a vacuum between them, and this propagates outward from the source. So we can visualize the sound wave as a sphere that's moving outward from something that's making

the noise. So you've got a central object. Let's say it's a boom box or I guess if you guys don't know what a boom boxes, it's a it's a stereo, it's a radio, it's a it's a it's a smartphone playing Bruno Mars, it's playing music really loud, and the sound will travel out from a sphere from this central point. Technically, it travels out in all three dimensions, although obviously if you're playing something near the ground, it's gonna be bouncing

off the ground at some point. But the sphere size increases at the rate of the speed of sound, right, because sound is traveling outward at the speed of sound, and gradually the that sound wave gets weaker and weaker as it propagates further and further out from the objects. So the further out you are from the object making sound,

the quieter it's going to be to you. As the object continues to make sound, it's making more and more sound waves, so they're they're moving outward in this series of spheres that are growing out from the center of this sound storm. So we typically will illustrate this in a two dimensional format. It's much easier to understand that way.

So you would just put a central point that would represent whatever the object is it's making sound, a stationary sound source, and you would surround that with a series of concentric circles and uh that suggests a sound wave that's traveling outward from that source, and it's a series of sound waves, actually, each concentric circle being another sound wave in this progression. So the further out you are from the object, the closer you are to the largest

part of that of those circles. At this stage where you have an object making noise and it's stationary, all of the sounds are moving outward from the source and an equal rate of speed hitting things that are equidistant from the object at the same time. So if you were standing five ft to the right of the object, I'm standing five feet to the left of the object. The object is perfectly still. We're both gonna get hit by those sound waves at the same time we are equidistant.

Sound is traveling at a uh standard speed and which is dependent upon the pressure and temperature and some other stuff in the air, but it's going to be traveling at that same speed through that medium. We're gonna hear at the same time. If I'm standing ten ft away and you're standing five feet away, it's gonna take longer for those sound waves to hit me then hit you. Not a whole lot longer, because the speed of sound is pretty fast, but technically it'll take a little longer

to hit me than it does to hit you. If the object isn't stationary, then the picture changes a little. So imagine you've got a graph to show off sound in this way. Right, you're just looking at a graph. You've got a point that represents an object, and then you would draw circles around it to represent the sound

waves emanating outward from that object. Well, if you were to imagine that this object is moving, let's say it's moving in a straight line towards the right side of the graph, if you wanted to represent the sound waves of circles, Now those circles would be offset. They would no longer be centered around that point. The point would be closer to the right side of those circles. The circles would be bunched up a little bit on the

right and spread out a little bit on the left. Uh. You can think of it as like a stack of plates where you've shifted all the plates over, like each plate is slightly smaller than the one under it, and shifted them all over to the right a little bit. This means that if you were standing in the path of that object, as it got closer to you, as you would hear the sound, you would hear it at a higher pitch the sound waves. The wavelength between the

sound waves has been compressed. That means it comes in at a higher frequency or a higher pitch as we would perceive it. Then when the object would pass because the sound waves are further apart from each other, that would come in as a lower pitch. This is the Doppler effect. So that's that now sound you always hear when something's coming at you and then passes you very quickly. If the object is moving at the speed of sound, then all the sound waves get compressed at that point

of where the object is as it's moving. Uh. You know, again, if we say it's moving in a straight line to the right, all the edges of all the circles are overlapping right there at that point. This is the point of the shock wave. So let's say you can see this object. It's coming towards you. It's not at you yet, but you can see it. When you see it, you would not hear it make any sound because it's moving just as fast as the sound it is generating, so

you won't hear it until it gets to you. And when it gets to you, all of those compressed waves would hit you at the same time. This is a sonic boom. It's when all the sound that would have been spread out as the object got closer to you has hits you, hits you all at once, so all those waves hit you simultaneously, and you get the sonic boom. Now, if the object is actually moving faster than sound, then

it has behind it a cone of sound waves. The object is no longer even making contact with those circles. If we're if we're to draw it on a graph, you would have an object to the right and a series of circles that are semi overlapping and getting larger and larger as you go further to the left, and if you were to draw enough of them and then draw lines on either side, you would see this makes a cone shape. It's actually a three dimensional conical shape

spreading in all directions. The faster the object is going, the pointier the cone is going to be. When that cone makes contact with a listener, that's when the listener would hear the shock wave or experience the shockwave the sonic boom, So the object would actually pass the person

completely before the person would hear the sonic boom. In this case, because the objects moving faster than sound is uh that cone will trail behind the object as long as it's traveling at this speed, So if you're in the path of the cone, you'll hear the boom once the cones border crosses you. If you could then immediately teleport ahead of the traveling object so that the cone would pass over you again, you would hear it again

once it passed over you. The so the cone represents the crests of many waves of sound, and also within that cone, you have a rapid change of air pressure and temperature, meaning any air vehicle that's going to be traveling at the speed of sound or greater has to be able to handle these major changes in those factors.

NASA is currently working on developing a low boom supersonic aircraft, which will use special aircraft shapes meant to limit the intensity of the sonic booms they will generate, but that's a topic for a future episode. In the then Soviet Union, two engineers created a design later called the v K A Maya ziv Chev And I know I've totally butchered that, but you know, you've got to kind of roll with it.

It was also known as the M forty eight. Uh. It was designed to be a really tiny, one person space plane that would use an ICYB M as the launch vehicle. So how tiny am I talking about? Well, it was supposed to be eleven point four feet tall or three and a half meters and have a wingspan of twelve point four ft or three point eight meters, and it would weigh two thousand, two hundred pounds or

a thousand kilograms. That spacecraft was never built. Several other designs would follow, but they two remained almost just completely in concept mode. Well, only a few ever reaching the earliest stages of prototypes. None flew at that time, the so Union would instead focus on ballistic based re entry vehicles, not not flying ones. In the United States, NASA has a series of air and spacecraft that fall under the designation of the X series, and that stands for experimental.

These are vehicles that are meant to test designs and technologies that might be implemented in future aircraft or rockets or spacecraft. It's a testing bed for those technologies. The X one, fittingly was the first of those vehicles. And while the X one was not a space plane, it was an important aircraft. For one thing, the X one would become the first aircraft to break the sound barrier.

It was also a purely experimental craft. There were no commercial or military or requirements attached to it, so NASA was able to focus just on creating the machine that would do what they wanted it to do. They didn't have to worry about any other cerns and it would be up to later designers to incorporate that technology into practical aircraft. And I'll have to do a full episode

on the X one in the future. It is a fascinating story, but for our purposes, the important thing to keep in mind is that set the stage for later experimental aircraft, including some that were essentially prototypes of practical vehicles further down the road. I'll tell you about them in just a second, but first let's take a quick break to thank our sponsor. There have been many different

X vehicles. All of them were meant to work on different designs and strategies like wing shape, aircraft, material, power systems, propulsion systems, and experimental techniques like vertical takeoff and landing. And to be honest, most of those have contributed in some way or another toward the development of space planes, either directly or indirectly. But if I were to go down the whole list and explain each one, we would have at least another week's worth of episodes to get through.

So I'm just gonna hit some of the highlights that I feel are particularly relevant. But please keep in mind this is like the cliffs Notes version of space plane history. The X fifteen was a hypersonic research jet plane program NASA partnered with the U. S. Navy, the US Air Force, and a company called North American Aviation Incorporated. The aircraft traveled at a top speed of four thousand, five hundred

twenty miles per hour. That's seven thousand, two hundred seventy five kilometers per hour, also known as mock six point seven well also known as is being too glib and not entirely accurate, because mack is a way of expressing speed in relation to the speed of sound moving through air. Now, this gets a little complicated because, like I said earlier, sound will travel at different speeds depending upon different factors

like air temperature. So sound moves at a at one speed through cold air and a different speed through warm air. And that's because sound is a physical phenomenon and involves vibrating molecules. But the mock number actually takes that into account. The mock number is the ratio that describes the speed of a given thing. Typically we call it flow, but again it could be an object, uh and within an environment.

So in this case, we're talking about aircraft, and you compare that with respect the speed of sound within the same medium under the same conditions. So if I say an aircraft travels at MOCK one, I wouldn't be saying that it's going just as fast as the speed of sound within that medium, meaning the air that the aircraft is traveling through. Now, the one I just mentioned before,

the X fifteen was mock six point seven. That means that the X fifteen could travel up to six point seven times faster than the speed of sound through that same medium, which is wicked fast. There were three X fifteen rocket planes collectively, they flew one hundred ninety nine times. The X fifteen did not take off on the ground

on its own, nor was it launched via rocket. Instead, it would launch from a B fifty two aircraft at around an altitude of forty five thousand feet there's about thirteen thousand, seven sixteen, and the B fifty two would be traveling at a speed of around five hundred miles pur or eight hundred five kilometers per hour. The highest altitude the X fifteen ever reached, according to NASA, was three fifty four thousand, two hundred feet that's sixty seven

miles or one eight kilometers. The Carmen line, which most of the world acknowledges as being the border line for Earth's atmosphere and space, is generally in the one kilometer altitude range, So the X fifteen reached altitudes of suborbital space, so you could argue the X fifteen qualifies as a space plane, but one that was meant purely to conduct research for future vehicle designs. Following the X fifteen was a project called the Dina sore d Y in a Dash s O A R, also known as the X twenty.

NASA contracted Boeing to build the space plane. There was a related asset called Asset. This was sort of the nose cone section of the dinosaur. It was used separately to test various designs to find out what sort of shielding would best withstand re entry and the rigors that any material would undergo as it does re enter the

air's atmosphere. The Dinosaur was in parallel development in some ways to the X fifteen that it would take advantage of lessons learned from the X fifteen program, and it also had links back to the silver Vogel aircraft proposed in Germany. There was a man named Walter Dornburger or Valter Dornburger. He was one of the key figures in developing the Dinosaur project. He was in charge of Germany's

rocketry program in World War Two. He was also the direct superior to the famous rocket scientist Verna von Brown. He wasn't picked up by the United States during Project paper Clip. That was the secret project in which the United States out over a whole bunch of German scientists to work on the same stuff they had been doing over in Germany, but now for the United States. Dorn Burger instead go into British custody for a few years before being released and then immigrating to the United States,

where he found a job with Bell Aircraft. He advocated that the company tried to make real the vision of the Silver Vocal. Dorn Burger felt that rockets were the future of flight, even for commercial flight, though probably just for the really wealthy, and it would become the propulsion systems for a new type of aircraft that he would

call ultra planes. These were essentially very similar to what we would think of as space planes, and dorn Berger imagined a world in which a hypersonic glider would ride piggyback on a larger rocket propelled aircraft. At the appropriate altitude, the glider would launch off of rails that were mounted on this booster vehicle and ignite its own rocket propulsion system, which would push this smaller vehicle to great speed and

higher altitudes. At the peak of its journey, It would then switch off its engines and then glide quietly to its destination. The booster vehicle would return home for the next journey up, and this idea would coalesce into a program that was called Dinosaur. As one of several proposals that entered into debate during the Round three conference, which took place just eleven days after the Soviet Union had

successfully launched Spot Nick one into orbit. Dinosaur, which originally was pitched as a dual research and military platform that could potentially be weaponized, was able to move into the next stage of development. The program was actually revised multiple times, and this complicated the process of designing and prototyping because whenever you change the requirements, it changes lots of other

stuff down the line. One late edition was a feasibility study to make sure that the Dinosaur could also serve as an orbital vehicle, sort of like what the Space Shuttle would eventually become. Then in September, the United States SARA Force General Bernard A. Shriver changed things up big time by stating the program would be split into two parallel arms. One of the versions of Dinosaur would be

developed as a military application of the technology. The other would be intended for space faring projects, and a priority would be placed on No big surprise here the military one. Around this time, pilots were joining the program, including future astronaut Neil Armstrong. Armstrong was also given the task to figure out how to keep an astronaut safe in the event of a launch failure, such as a launch vehicle

about to explode. Ejection was not an option because the dinosaur cockpit was only about a hundred feet above the ground in the design they had created. Once it was attached to a launch vehicle, and the pilot would be essentially on his or her back UH in a seated position, but they're facing upward right the dinosaur would be the nose of the vehicle would be pointing towards the sky.

So there wouldn't be enough time if you ejected for the UH for your orientation to change and for the parachute to deploy, and so Armstrong had to come up with a different idea. His solution was to create a system that would actually engage the glider's engine and thus shoot it off of the booster rocket, launching the glider into the sky, and then the pilot would have to take control of this accelerating vehicle and stabilize it and

then fly the glider to safety. He was able to do this using a simulated test with an actual jet airplane, and he said he was later on said that he was glad he never had to test it on an actual dinosaur because it was hard to do. It was possible, but you had to be a really skilled pilot, and you were subjected to some massive uh stresses as you

did it. However, the course of nineteen sixty two, funding was pulled from the Dinosaur project, forcing it to scale back multiple times, and a night teen sixty three, the government formally canceled the project, largely because Project Mercury and then Jim and I were answering many of the questions that Dinosaur was meant to explore, and the ballistics model of returning astronauts safely to Earth was already proven to

be successful. So if you've already got a way to get people back to Earth, why bother working on a different way. Just focus on the way that works for now and worry about the other one later. That seemed to be the philosophy. I've got more to say about early space planes, but first let's take another quick break to thank our sponsor. One of the other designs that I feel we need to talk about is the concept

of the lifting body. A lifting body aircraft has, as the name suggests, a body that's meant to generate lift when the aircraft is flying through the air. The body itself does this. This is normally the job of an aircraft's wings, but with a lifting body aircraft, the body itself is behaving as if it's a wing. Uh. This idea dated back to the late nineteen fifties. There was an egghead named Dr Alfred JA Eggers Jr. Who was at the time the assistant director of the Research and Development,

Analysis and Planning Department at AIMES Aeronautical Laboratory. Leading up to Egger's proposal was a lot of work surrounding missile nose cones. The problem focused on ways to create a nose cone capable of surviving aeronautical heating due to re entry. There was an engineer named H. Julian Allen who concluded that if you made a blunt nose cone rather than a sharply tapered one, it would better hold up to the forces it would undergo, specifically the temperatures when undergoing reentry.

Eggers took this a step further. He found that if he modified this blunted nose cone shape slightly, the new shape would actually produce aerodynamic lift if the body was flying through the air fast enough. This design would mean a spacecraft would be able to fly back to Earth rather than to just plummet to Earth ballistic style. Egger's and his peers created a design called the M two.

So imagine that you have a cone shaped like an ice cream cone, and then imagine that it's on its side right, so you've got the wide end on one side, the point end on the other, round off the point end a little bit, so it's not two point, it's a little dull. And imagine that the top half of the cone is now flat. It is no no longer rounded at the top, it's flat, and the bottom half is still round. That's generally the shape they were working with.

They added in some stabilization fins towards the back of the vehicle that poked up on either side, and you have essentially the M two F one lifting body vehicle. This vehicle was an unpowered test vehicle. It would be towed behind other aircraft to test its aerodynamic capability, and it was unmanned. Obviously, later vehicles were built on that design and would incorporate an x l R eleven rocket engine, which was the same kind that is used in the

X one supersonic jet. Several lifting body aircraft designs followed. I think the X A is perhaps the weirdest one. You need to take a look at that aircraft. If you can go to Google image search type of X dash to four A, you're gonna see what looks like a jet that's missing its wings. That's a lifting body aircraft. Now. The reason I even mentioned lifting body designs is that's what the Martin X twenty three Prime aircraft used, and that was the next big space plane. This was an

air Force project in the mid nineteen sixties. Prime itself was an acronym. It stood for precision recovery including maneuvering entry, and this was to test a lifting body design in relation to re entering the Earth's atmosphere and being able to travel cross range up to eleven kilometers. That would mean the craft would be able to steer along a ballistics re entry path and land at a more precise location.

It was mostly made out of a titanium alloy, and it weighed in at nearly eight two pounds or four legrams. It was an unmanned vehicle and they held three successful missions with the various ones. They had built five of them, but after three flights, the Air Force canceled the rest of the project, which left two X twenty three a's completely unflown. Those were sent off to the United States

Air Force Museum at Wright Patterson Air Force Base. When Dinosaur got the AXE, the Air Force began to develop plans for space planes under the same umbrella project that the X twenty three A was under that was called Start. After the X twenty three project got the AX in nineteen sixty six, it would take nearly two decades before another space plane design would become a reality. That design would be the Space Shuttle, which debuted in nineteen eight one.

I've talked about the Space Shuttle recently, so this will just be a super quick overview version. First of all, the design of the Shuttle is similar to the earlier lifting body spacecraft I've mentioned, though the Shuttle also had a double delta wing configu duration. This particular shape is efficient for hypersonic flight and was good at giving the Shuttle a good lift to drag ratio, so it wasn't

a pure lifting body spacecraft. It also did have these wings in an earlier design before they actually had to commit to the final form of the Space Shuttle, it was supposed to launch off the back of a larger aircraft. The Shuttle would be kind of carried piggyback and would launch from that aircraft once it reached a certain speed and altitude, and then the Shuttle would make the rest of the journey up to low Earth orbit, But budget cuts at NASA forced engineers to switch to more conventional

rocket style launch vehicles. The Space Shuttle would ultimately launch in a vertical position using a pair of enormous solid rocket fuel boosters that would provide most of the thrust at lift off. The three main engines on the shuttle itself would provide the rest of the thrust at liftoff. In Between the two solid rocket boosters was a huge external fuel tank that held the liquid hydrogen and liquid oxygen that would serve as the fuel for the main engines.

The shuttle would first jettison the two booster engines about two minutes after a liftoff and then would later jettison the huge external tank. Once the shuttle would reach a velocity sufficient to insert into low Earth orbit, the booster engines could be recovered and reused. The external tank was not meant for reuse. At the conclusion of a Space Shuttle mission, the shuttle would fire its orbital Maneuvering System or o MS thrusters and leave orbit to re enter

Earth's atmosphere. The shuttle relied heavily on arrow braking, in other words, too maneuver in such a way where the air itself is slowing the descent of the shuttle through the atmosphere, and it would do so until it reached the lower atmosphere, where the shuttle could fly as a powered glider. Between two thousand and eleven, the shuttles in the Space Shuttle fleet collectively flew on on five missions. Eight hundred thirty three people flew on a Space Shuttle mission,

with some going multiple times. Fourteen people lost their lives and catastrophic accidents on the Space Shuttle program and the Challenger and Columbia disasters. The Space Shuttle program proved the utility of a space plane design a spacecraft that can maneuver both inside the Earth's atmosphere and an orbit is incredibly useful, particularly when you can fly the same spacecraft multiple times. The end of the space Shuttle program in two thousand eleven would not be the end of the

space plane era. In the next episode, I'm going to talk about some of the other space plane designs, including a super secret one that I covered in an older episode of tech Stuff, And we'll learn about those and other space planes, including a design from the United Kingdom. So stay tuned for that. And if any of you out there have suggestions for future episodes of tech Stuff. Maybe it's a technology, a company, person in tech, anything

like that, let me know. Send me an email the addresses tech stuff at how stuff works dot com, or drop me a line on Facebook or Twitter. The handle of both of those is tech Stuff H s W. Don't forget to check. Got our merchandise over at t public dot com slash text stuff. And finally, we've got this Instagram account. You may have heard of it. Go follow that, won't you, and I'll talk to you again really soon for more on this and thousands of other topics. Because it how stuff works dot Com