Why Single Stage to Orbit rockets SUCK. The wacky history and future maybes of SSTOs

Hello, it's me, Tim Dodd. Everyday astronaut

rockets

are HUGE, complicated and expensive. In fact, the rocket that took humans to the Moon, the Saturn 5, was 111 meters or 363 feet tall and had more breakup events than teen dating events. I actually didn't mean for that to happen. So why are

rockets

always divided into several parts? Isn't that complicated and risky? Why throw so much? I mean, there has to be a better way!!! Well, what if the rockets were just ONE

stage

? How wonderful would that be? Well, this idea isn't new... it's called

single

stage

to

orbit

, or SSTO, and is often considered the holy grail of rocketry.

Well, today I'm going to DISPLACE THAT HOLY GRAIL and explain why I think SSTO

suck

s. To delve deeper into this point, we'll teach you all about the tyranny of the rocket equation and help you understand why every

orbit

al rocket, well, is always multi-stage. Then we'll take a walk through SSTO

history

and look at some crazy designs that in some cases almost worked... And so as not to be a huge disappointment, we'll take a look at some SSTO designs that COULD work, including the Skylon Space Plane that uses that incredible SABER hybrid engine. Ok, Everyday Astronaut VS SSTO... oh man, the comments section will love this one... but hear me out, let's get started!

So if you've ever played Kerbal Space Program, you know that awesome computer game where you design, build and fly rockets with these little frog aliens and take them off their home planet, Kerbin, yeah, that game... so you know the SSTO. are trendy. Building an SSTO in Kerbal is a bragging right, something to brag about and post on reddit. But what if I told you that I can't think of any good reason to build an SSTO in real life? Well, there are some potential benefits, but do they outweigh all the negatives? Ok...ok...so before I sound like a grumpy old man: "Get off my lawn, you damn kids with your SSTOs," let's talk about why some consider SSTOs desirable and why people dream of a at which point launch vehicles are just one stage. …Imagine a world where a launch vehicle takes off, goes to space, comes back, refuels, and does it multiple times a day.

No problem. Sounds like a real-life Millennium Falcon. When most people use the term SSTO, the inference is that the vehicle would be reusable...it would go up into space and come back down all in one piece, discarding only fuel to get there and back. And again, when talking about reusable SSTOs, most people and concepts use a spaceplane design. A vehicle that takes off and lands like an airplane. Sounds great right? A vehicle to do it all! Nice and simple. Take off from any runway like a passenger plane at an airport, and then, instead of leveling off at a boring 10 km or 35,000 feet, keep accelerating and increase your altitude until you're in orbit.

Then, when your mission is over, simply return from space and land on any old runway, again, like any other airliner. Hmm, SSTOs don't sound bad... right? Uh oh, have I gone crazy??? Well, before we continue dreaming about our potential sci-fi

future

, let's take a quick look at the

history

of rocketry to see why SSTOs have not been possible until now. The first liquid-fuel rockets ever made had only one stage. Basically a rocket engine, some propellant inside the fuselage, and in most cases some type of warhead on top. At first, rockets were primarily used as an advanced weapons delivery system, but luckily for us, they can also be used for space flight!

The V2 rockets built by Germany were the first rockets to reach the edge of space. In June 1944, a V2 rocket on a test flight reached beyond the Karman line, the most commonly agreed upon limit of space at 100 kilometers or 62 miles altitude. Sure, a

single

-stage rocket can reach space, but what about staying in space? Well, to stay in space, an object needs to reach orbital speed. To orbit the Earth, a vehicle must travel at about 28,000 km/h or 17,500 miles per hour to stay in space. Ok… so now we have a new goal for humanity. Put something into orbit.

Well, on October 4, 1957, the Soviet Union managed to launch Sputnik 1 into orbit. The shiny metal ball with terrifying pointy antennas weighed only 83.6 kg or 184 pounds, hey, that's practically my weight! The vehicle that carried Sputnik into low Earth orbit was a two-stage launch vehicle more commonly known as R7. This rocket was revolutionary and allowed the vehicle to lose unnecessary weight during ascent by ejecting spent fuel tanks and rocket motors that were no longer needed. This is called staging. It was revolutionary and fundamental when it came to launching anything important into orbit. Staging is the number one cure for the tyranny of the rocket equation.

The tyranny of the rocket equation is basically the diminishing returns of fuel addition. If you doubled the amount of fuel in your rocket, you would not double the delta V or change the speed... Because you now have to push all the weight of the extra fuel and the fuel tank that contains it, the rocket is capable of burning for longer, sure, but you don't get anywhere near double the gear change. And it only gets worse as you go, until the rocket becomes too heavy for the motor and the next thing you know you're adding motors to lift the extra fuel, and so on.

So this is where staging comes into play. Once a rocket empties its fuel tank, why not throw it away? Even better, if the rocket is decelerating one engine to continue accelerating at a safe speed, why not scrap the heavy, unnecessary engines? This is what the R7 rocket did. It was basically a good sized rocket with 4 additional rockets attached. Once those side rockets were spent, they were discarded into this really cool formation known as the Korolev Cross, named after Sergei Korolev... who you can think of as the Werner Von Bruan of the Soviet space program. By the way, you can still see the Korolev Cross on any of today's Soyuz launches.

Separation events are often a breath-holding moment during flight. There are two main types of staged events. First of all, there is a parallel staging in which several stages are fired and activated at the same time, such as Soyuz, the space shuttle or the Falcon Heavy. Everyone holds their breath during staging because if a booster doesn't separate, the mission will fail. It was definitely a great moment when the Falcon Heavy's side thrusters separated safely. Or there is an even more complex and biting type of staging called tandem staging. This is what most multistage rockets do. First one stage fires, then the engine shuts down, the first and second stages separate, the second stage ignites and continues into orbit like a new rocket.

Not only is the second basically a new fully powered little baby rocket, but its engines are also optimized for the vacuum of space by having a much larger exhaust nozzle. But that's another big plus for staging. Have different engines optimized for different environments. The first rocket to perform any type of tandem staging was called RTV-G-4 Bumper. It was literally a V-2 rocket with a small sounding rocket on top. It was launched between 1948 and 1950 and was launched 8 times, generating a wealth of valuable data over multiple stages. But this stage separation event was really difficult to achieve and was almost considered impossible for a long time.

That's why many early rockets used parallel staging. In fact, separation events, or more specifically a failed separation event, almost led SpaceX to be another forgotten aerospace company that went bankrupt after only 3 flight attempts. Flight 3 of its Falcon 1 rocket had a separation event gone awry when the first stage had little residual thrust after stage separation, causing it to crash into the upper stage, leading to a failed mission. So if it was so coveted and necessary to manufacture multi-stage launchers, why are SSTOs so sought after? Well, there's something to be said about making a launch vehicle less complicated.

So maybe SSTOs are good for something... Well, I guess to see if SSTOs make sense... let's go to my computer where I'll start the Kerbal Space Program to help determine if the stages are friend or foe. ...Welcome to the Kerbal Space Program with Realism Review. Now Realism Overhaul involves about a million different mods for Kerbal Space Program to have a real solar system, it makes it much harder and much more realistic. Well, our goal today is to try to get a 1 metric ton satellite into an orbit at 250 km altitude. So I built a nice simple 2 stage rocket with an RL-10 vacuum engine, which is a great vacuum engine, and then it has a SpaceX Merlin 1D engine in its first stage, so together it's about 34, 9 meters high and has about 9,237 m/s according to Kerbal Engineer Redux.

Okay, now let's get ready to remove this and we'll start the engine in 3,2,1 HIP HIP! Yeah! Look at it! Alright, let's speed this up a little bit and see how it goes into orbit. All right, now notice that I have the map here too so you have an idea, you know, if this thing ran out of fuel right now, it would still be moving forward to its apoapsis, its highest point or apogee. So you can see we have the map open and it gives us a pretty good idea of ​​where things are going. Now, just like if you threw a ball it would go up and make an arc, if you threw it further it would make an arc further and further away.

Well, we're just continually accelerating making that arc extend even further and further and further. This is how rockets work. Ok, now we're running out of fuel on our first stage, so let's go ahead and separate the stages. And now we're going to light up that upper stage. And there goes the RL-10 upper stage and this is optimized to work in the vacuum of space. So it means it has a really high specific impulse. And specific impulse is something like the miles per gallon of a rocket engine. And this will continue to accelerate now. It will continue and go into orbit.

So there's still a long way to go umm, so this higher stage still has a lot of work to do. You know, look, it's still accelerating! And again, if it were cut off right now and ran out of fuel right now, even if it were a brand new rocket, barely halfway there, it wouldn't even make it to the coast of Africa! You know, look at it, you can see it on the map there, we won't get that far yet. Ok, we're going to keep accelerating and accelerating and accelerating until we reach about 7,500 meters per second, which is approximately 28,000 km/h or 17,500 mph.

We're just going to do an apogee kick that burns to the highest altitude just to fully circle us and get us into orbit. And wah la. A perfect orbit is fantastic, now that we've released the satellite and are good space stewards, so let's go ahead and deorbit the stage as well. And it will burn when it comes back in. Nice and easy. Here we go! Well, honestly, that was the perfect rocket for the job. It could barely carry that metric ton into space and would have a little fuel margin left to deorbit. It's perfect, it fit perfectly.

Ok, I know what we're thinking. So let's go ahead and turn this into a single stage to orbit the rocket! So the first thing is to go ahead and remove everything that was necessary for the second stage, so let's go ahead and remove that expensive RL-10 upper stage engine, we don't need it anymore! And we don't need any hardware between stages either. Uh, so let's go ahead and get all this stuff out of here. And good bye. Let's attach this again. We need to put those boosters back in there and now we need to make sure we replace all the fuel that was hydrogen for that upper stage with PR-1, which is the same fuel for the first stage engine.

And wa la now we have about 7,155 m/s, let's see what this thing can do! Alright, we have our first version of our SSTO without the upper stage ready for launch. Let's do this 3, 2, 1 hip hip! And here we go! Let's go ahead and advance this a little bit. Not bad, not bad. How far will this go? I am so curious. Get rid of the fairings. Up the coast, we're at 250,000 meters altitude, we're going to do an apogee kick here and we run out of fuel, and that's all we get any further! That? Yes, after all that we only had a small drop of fuel left.

And that's as far as our satellite will go until about 1/3 of the way into the Atlantic Ocean. Let's try to make it bigger, add enough fuel so it can go into orbit. Ok, so... I know what we're thinking, let's add some fuel. Good? We are at 7,155 m/s, we havespent debris that falls in populated areas. Ehhh. I'm not sure how I feel about that. I mean aerospikes, but I boo a rocket with such limited capacity. Ok... so all previous SSTOs have failed, all current SSTOs are either not going to be SSTOs or are somewhat useless in my opinion... and there really isn't much on the table for a usable SSTO in the near

future

without some advancement important. in materials science or propulsion.

BUT WAIT. There is one more thing. So far I'm here talking about how all the SSTOs failed... that's not true! In fact, one of the most famous spacecraft in all of history was an SSTO… the lunar excursion module! Of course, it could orbit in a single stage, but only on the Moon! The LEM was capable of reaching lunar orbit with a single stage. But… that's the moon. The Moon's gravity is much weaker than Earth's AND there is no atmosphere to fight against. And then we have SpaceX's BFS, which will not only be capable of performing SSTO from the surface of Mars, but will even have enough performance to return to Earth from the surface of Mars in a single stage.

Again, this is mainly because Mars has only 38% of Earth's gravity AND only 1% of Earth's atmosphere. Making reaching orbit much easier. So maybe SSTOs don't

suck

. Maybe the Earth sucks. It has enough gravity to make it barely possible to reach orbit with rocket engines, and it has that pesky atmosphere that also slows down ascending vehicles. I still stand by the fact that as cool as SSTOs are and as much as I love them, they simply don't work in practice with the technology currently available. Of course I'm not saying it will always be like this, but for now, give me stages!!!

After all. I think we can all agree that the most important aspect of an SSTO is reusability. So what if a multi-stage rocket IS completely reusable? Do you like BFR? Isn't that what matters most? The first stage does what it needs to do and then comes back, is refueled and reused. Same with the upper stage. So who cares if the vehicle is made in one piece or split into two more pieces? You can almost think of the booster stage as a giant catapult or something, which sends out a fresh new rocket, giving it extra speed and altitude, and then just comes back and lands.

I think that's amazing. I can't wait for the day when orbital flight is routine, reliable and fully reusable. And for the foreseeable future, I think it will continue to be done in stages… So, what do you think? Do you think SSTOs are still valid and practical or are you on a multi-stage team? #teammultistage Let me know your thoughts on SSTOs in the comments below. And PLEASE spare me your Kerbal SSTO designs... It works on the Kerbal Space Program, not a real plot... unfortunately. And before you tell me all about how SSTOs can take off and land on runways...remember, that's NOT unique to SSTOs.

That's an advantage for the aerial thrower or body lifter. This is not unique to SSTOs. Let me know if you have any other questions or anything you want me to cover in future videos! As always, I owe a huge thank you to my Patreon supporters for helping make this and other Everyday Astronaut content possible. I owe a very special thank you to the sponsors of our dedicated Discord channel and our dedicated subreddit for helping me with the script and research. We had a great debate about SSTOs. If you would like to help contribute, please visit patreon.com/everydayastronaut.

Don't forget to check out my webstore for t-shirts, hats, mugs, rocket launch prints and original artwork and lots of other fun stuff at dailyastronaut.com/shop. And as always, all the music in my videos is original. Feel free to check it out at soundcloud.com/everydayastronaut Tell a friend! Thanks to everyone who does it for me. I'm Tim Dodd, the everyday astronaut. Bringing space closer to Earth for everyday people.