How are Rocket Engines So Powerful?

This is the Rocketine F1 engine, it's the most powerful engine in the history of mankind. If we took the thrust of this engine and blasted it down onto a magical seesaw, it would take the weight of three statues of liberty stacked on top of each other just to balance it out. That's a lot of power coming from something so small. And if you had to guess, how do you think these engines are able to turn boring liquids into millions of pounds of thrust? Well, that's what I'm going to show you in this video. And not to spoil it too much, but it involves some pretty incredible engineering. Okay, before we get into the fancy rocket science stuff, let's go over the precredentials. A rocket moves in space using Newton's third law. Every action has an equal and opposite reaction. It's the same reason you have to push down to do a push up and pull down to do a pull up. NESI workout. This also means the bigger the action, the bigger the reaction. So for rockets, the more force we throw one way, the more force we'll have pushing ourselves the other way. This force we throw down is called thrust. We know that force equals mass times acceleration. So using the same idea, thrust also boils down to two things. The mass of the stuff and how fast it's going. When we design rocket engines, this means we want high exhaust speeds and high pressure, since pressure is just more mass for the same space. That's some basic rocket science right there. What we now know is that rocket engines want a lot of thrust, which means a lot of mass going at very high speeds. So let's just go over some simple rocket engines. Remember the engine I mentioned with the tank and the nozzle? Yeah, that's called a cold gas thruster. It works by storing as much pressure as possible in tightly sealed tanks and just poking a hole in them to let the air out. These engines are super simple. I mean, technically, if you blow a balloon and leave the knot open, that could be considered a cold gas thruster. It's a high pressure gas let out of a tiny nozzle pushing our rocket forward. These engines are actually used here in SpaceX's Falcon 9 when the booster needs to turn before landing. But they have one problem. To make the engine more powerful, you need more air pressure. That means stronger tanks. Otherwise, the tanks just burst. But then to lift heavier tanks, you also need more air pressure. But to hold more air pressure need stronger tanks. And so eventually the weight of the tanks overtakes the advantages of more pressure. And so the engine stays at a limit of how powerful it can be. Most of the time engines use chemical reactions to create more thrust. If you can get two gases that react together and generate heat, you can increase the thrust by a lot. So let's try that. We can just connect two tanks of rocket propellant one or RP-1, which is a highly refined form of kerosene, and mix it with an oxidizer, liquid oxygen. If we connect them together to a combustion chamber, they can mix and burn and push the rocket forward. But wait, these engines are still really bad at maintaining pressure. Remember, we need both speed and mass to create maximum thrust. And when propellants flow from tanks to pipes, the pressure decreases drastically because of that annoying little Bernoulli's principle. So we need something between the tanks and combustion chamber that increases the pressure of the gases to make our engines stronger. And this is where open cycle rocket engines come into play. Open cycle rocket engines increase pressure by using a pump. These pumps are just blades and screws that spin to increase the pressure of the gases. The only problem is these pumps need to be powered by something. How these pumps are powered is mainly what defines different types of rocket engines. So now we come to open cycle engines. And just as a review, we have two reactive gases going crisscross through two pumps. We just need to power them. This type of engine uses a turbine connected to the same shaft as both pumps. It spins the turbine by taking little portions of the oxidizer and fuel to create another mini rocket engine inside of the rocket engine called a gas generator. And then the thrust of this mini rocket engine flows through the turbine and converts the chemical energy into mechanical energy that spins the turbine very, very fast. This turbine powers our pumps. And now we have gases moving at insanely high pressures. But now you might be asking, why not just use electrical motors instead of pumps? And you would be right. That's actually a different type of rocket engine. However, the problem with electric motors is they're nowhere near as strong and they require tons of batteries, which is just unnecessary weight for the rocket. OK, so after the gases from the gas generator are done with their job, they're then just thrown out. And this is why this engine is called an open cycle engine. It's because the cycle is left open for the gases to go. Other cycle types, like full cycle and full flow, try to use this extra exhaust for thrust by connecting it to the combustion chamber. But that's an open cycle, mostly explained. There are a lot of finer details as well, but now I want to actualize these diagrams in your mind and show you what they actually look like on a functioning rocket engine. One of the most well-documented open cycle rocket engines is the Rocketine F1, the one that got us to the moon in 1969. This engine holds the record for the most thrust output at an incredible 1.5 million pounds per engine. So let's see exactly how this beast works. At the top of the engine are the inlets for the RP-1 and liquid oxygen. These propellants flow right into the pumps. Within this complex pile of tubing is the shaft for the pumps and turbine. This entire mechanism here is called the turbopump. It's the shaft where the turbine and pumps produce a total of 55,000 brake horsepower. The gas generator is located right behind the turbine. It receives its little bit of oxygen from this pipe and majority of its fuel consumption from this pipe. The two gases mix and ignite, Once the gases are done turning the turbine, they flow through this large pipe around the engine that dumps the gases out of the nozzle where they can't mess with any of the instruments. This is why the exhaust of the F1 has this black gas coming out of the nozzle. It's the product of the gas generator after it's done turning the turbine. The turbine connects to the pumps above and pressurizes the gases and pushes them into the lockstone. The lockstone is where the two propellants mix before they are injected into the combustion chamber. But wait, these engines are moving on a rocket and rockets don't just stay straight and smooth. While this all is happening, the engine is being shook at incredible pressures and this could let some air bubbles that would be catastrophic for the engine. To prevent this, the engineers filled the chambers with helium and oxygen, two non-reactive gases. These gases are heated here right below the turbine and then are sent up through these pipes to pressurize the lockstone. The lockstone is kind of like a hub for all the gases to go to. It filters the two gases into the injectors. The injectors spray the fuel into the combustion chamber and from there the hot pressurized gases flow out of the conversion-diversion nozzle that increases its speed to the speed of sound or Mach 1. But there's another problem. Our engines are too powerful. The combustion of the gases creates so much heat that the nozzle actually starts to melt down. That's obviously not good. A melting engine is not going to get us very far in space. So we need a way to cool back down these engines and I'm going to talk about two ways engineers do this. The first is fairly simple. It's called ablative cooling. In ablative cooling the engineers put a layer of material inside the nozzle to make the nozzle thicker. Then as the engine heats up this layer of metal it evaporates taking down the heat with it acting as kind of a sacrifice. The most common material used for ablative cooling is carbon but as you can imagine this method has its limitations. Obviously it's just a matter of time before all the material gets evaporated and it needs to be replaced. But you can't really replace it in space so that means it has a limited range. Although this engine has its pros and cons it does a good job of laying out the fundamentals of how to cool an engine. Basically what we need is something to take away the heat from the nozzle to avoid it from melting. But instead of using carbon what if we use something we already have? Fuel. This is called regenerative cooling. In regenerative cooling the nozzle is actually made of pipes. It takes in fuel before it enters the log stone and flows it through these little pipes around the nozzle. By making these pipes of material with high thermal conductivity meaning easier to transfer heat the heat from the engine can actually just be given over to the fuel. And yes this does actually evaporate the fuel in the pipes. But this fuel is going to be flown back into the combustion chamber to react with oxygen anyway so it doesn't actually hurt it in any way. And of course the F1 engine also uses regenerative cooling. The fuel is taken here right before the log stone. From there it flows through these pipes that make up the nozzle and cools the engine before reuniting with other fuel in the injector. The regenerative cooling only goes up till this point. That's because the lower in the engine exhaust we go the pressure and heat also tend to fade out. So to cool the lower part of this engine the engineers just rely on the gases from the gas generator that I mentioned before. This method of cooling is called film cooling. These gases are just dumped against the nozzle extension and prevent it from melting. This black gas here that I mentioned before. And with that the engines are saved from being melted by the exhaust. Above the log stone is the gimbal block that attaches to the main rocket. This also comes with the gimbal arms on the sides that work to shift the engine towards a certain direction. This is called thrust vectoring and it's what changes the rocket's trajectory in space. With that the five F1 engines are able to push the first stage of the Saturn V rocket at a top speed of 15,700 miles per hour. Okay that's the F1 engine mostly explained. There's a lot of other details I missed but as a whole I hope this engine has started to look a lot more like something a human could ever build. If you didn't get a grasp over everything the first time well this is literally rocket science. I have another video on the engineering behind hypersonic engines that might give you a lot more detail on how exactly these engines work. Otherwise consider subscribing. It really helps me improve making videos. And thanks for watching.