We use the phrase “Rocket Science” to express something extremely complicated. This is for a good reason. Space is hard. Everything on a rocket has to go according to plan first try, or all is lost. You can’t rerun. You can’t update. You can’t fix a bug in real-time.
However in this article, I can give you a complete overview on how rockets work. First, a very general summary on the main parts of a rocket, but after we will dive deeper into each component.
There are so many different types of rockets. For our purpose we will be studying one of the most recently-built rockets. 🥁🥁🥁 Introducing to you one of the most functional of all time 🥁🥁🥁 Previously the bread and butter of SpaceX,🥁🥁🥁 the Falcon-9!!!
A rocket has five main components:
- Payload (Second Stage)
- Vacuum-Optimized Engine (Second Stage)
- Stage Separator
- Fuel & Oxidizer (First Stage)
- Sea-Level-Optimized Engines (First Stage)
A rocket is basically a big piece of metal zooming upwards since there is a controlled explosion underneath it. The Fuel & Oxidizer have pipes that lead down to the Sea-Level-Optimized Engines. The engines make the two substances react, and funnel all of the explosive energy downwards, so the rest of the rocket goes upwards. After some amount of time, the First Stage of the rocket runs out of fuel, so the Stage Separator pushes away the First Stage so that the Second Stage doesn’t have to use precious fuel to lug around dead weight. Now, the Vacuum-Optimized Engine activates to get the Payload to the desired destination.
This is rockets over-over-overly simplified for y’all. Who wants to go deeper into each one of these parts? I do.
Part 1: The Payload
Payload is really up to the purpose of the rocket. It is the thing that you want in space. This could be a capsule containing humans, a satellite, or even a rover. The aerodynamics of the payload is irrelevant, since it is transported inside of a shell around it, and when it reaches space, there isn’t any atmosphere around to actually give a reason to worry about heat shields, shape, aerodynamics etc.
Part 2: Fuel & Oxidizer
The fuel and oxidizer are basically 2 chemicals which react with each other to create an upwards force to push the rocket towards space, in the desired direction. So if you don’t have fuel or oxidizer, then you aren’t going to space today my friend. When thinking about which fuel and oxidizer you want to use, its best if you consider these 3 different qualities.
- It should not detonate when exposed to heat, sudden changes in pressure, or impact. It probably isn’t new to you that when a rocket is lifting off, everything in the area shakes like crazy. If the propellants are sensitive to shaking or impact, then it can blow up as soon as liftoff. You also definitely don’t want them to care about heat. Things can get pretty darn hot in the engines, and you don’t want detonation in any way, shape or form if the reactants are still in the pipes, since that can cause the engine to simply blow up. Sudden pressure changes can also be a problem that you want your oxidizer and fuel to withstand. Rockets pump out propellant at an enormous rate to keep going upwards, which obviously means less and less volume in propellant tanks occupied by liquid, decreasing pressure. You need your fuels and oxidizers to be able to tolerate this if you want to be able to actually use the propellants.
- High Density — It isn’t easy to get anything into space, so you want everything in a rocket to be as compact as possible. With a high density, you can fit much more propellant into the rocket, which means more upwards range.
- High burst output when reacting — do you think it would be effective to use vinegar and soda while lifting a metal construct the size of an apartment? No. You want a violent reaction when the two materials mix, since it can boost your rocket furthermore.
There are many examples of propellant pairs that all fit this quality, including hydrogen, oxygen, methane, fluorine, hydrogen peroxide etc. Using these chemicals you can get a reliable & strong boost upwards.
Part 3: Sea-Level Optimized Engines
The function of an engine is to react the oxidizer and the fuel safely, and also direct the blast energy to the opposite direction of the trajectory of the rocket so that we can make the most of the fuel which we have on board.
The best way to understand an engine is by building one. Let’s start off simple, and gradually get more and more sophisticated, so that you can understand every bit that I am talking about.
Here, we have two pipes, one of which is comes from the oxidizer and the other from the fuel. Due to gravity, the two reactants get pulled down the pipes and meet each other at the bottom where they can react.
Works: Half the time
By using this method, it is really easy to damage the engine itself since the chemical reaction can rupture the pipes of the engine, leading to engine failure. Another issue is the fact that you cannot fire these engines in zero-g. The only force that is pulling the reactants downwards is gravity, so how would you pull the fuels down if gravity isn’t present at all? You can see why this engine style sucks.
Another thing that doesn’t work about this engine is that it is incredibly inefficient. When you throw two reactants at each other, they explode. This is called a bomb. Bombs give out a pushing force at all directions. Thing is, if we use this engine, we are exploding bombs under the rocket. As I said, bombs use their chemical energy to give out a pushing explosion force in all directions. When a rocket is trying to go upwards, we want to direct all of the explosion force downwards, since that is the way we can make the most out of the fuel. Sideways pushing force never helps, which this “bomb” approach has a lot of. It does give an upwards force, however it also wastes a lot of chemical energy to give a bunch of sideways force.
To summarize, there are 2 main problems with this engine. First being that the force output is inefficient due to lack of direction, and the second being about the fact that we cannot use it in zero-g, since the engine itself relies on gravity to pull the fuels together to react.
There is a simple way of solving the direction/efficiency problem. You use a bell nozzle. A bell nozzle directs all forces opposite to the rocket’s trajectory, to optimize energy output. It is a mathematically designed shape, which directs any force downwards by reflecting it because of its shape. You can see how this gives a huge boost in efficiency.
But how do we solve the problem of gravity?
The idea is to use a bit of the fuel and a bit of the oxidizer to spin a turbine that pumps fuel and oxidizer at rapid speeds into the bell nozzle of the engine. We split the main pipes in 2, so that a little bit of fuel and oxidizer get funneled towards a “room” called the pre-burner. As these two react in the pre-burner, a turbine captures the kinetic energy of the burst inside of the chamber. This makes the turbine spin. As the turbine spins, it would be connected with a shaft to other turbines inside of the oxidizer and fuel pipes, so that it propels them forward into the bell nozzle. We are literally using fuel to push more fuel in a faster pace into the bell nozzle. As a result of this, the engine can work in zero-gravity, but also can accelerate at a much faster pace since we are pumping reactants into the bell nozzle for them to react.
The truth is that we pump more fuel than oxidizer into the pre-burner, since if the pre-burner had oxygen-rich, hot flaming gas inside of it, that would be a definite meltdown. This way, we have all of the oxygen react by pumping in more fuel than oxygen into the pre-burner so that this won’t be a problem.
Now, if you’re confused as to why there is no exit pipe for the pre-burner, that would be a correct inquiry. With the current design that we have, more and more fuel along with more and more oxygen being pumped into the pre-burner, simply wont work since the material has nowhere to escape. Pressures would rise, turbines could get clogged… All sorts of problems would arise.
To fix this, we get an exhaust pipe. It is also a huge boost in efficiency if we add a room called a “reaction chamber” to where the bell nozzle is, so that the fuel has more time to completely react with the oxidizer.
At this point, the engine would completely work. We actually use these sorts of engines all the time today. In fact, there hasn’t been a time in history where the engine that carried a spacecraft to orbit wasn’t open-cycle. For example, the Falcon-9 uses the Merlin engine, which is an open-cycle engine.
However, these machines also have their flaws. Think of what’s going through the exhaust pipe. A bunch of already-reacted material along with some unburnt fuel, since we put in so much more fuel than oxidizer. You are literally dumping some fuel overboard, with no contribution to the thrust power of the engine whatsoever. It might be trivial to say “just redirect the exhaust pipe into the reaction chamber, so that the unburnt fuel finally gets a chance to participate”. But the problem with that is we would be pumping already reacted material into the reaction chamber which can clog-up things pretty easily, leading to a concern of reliability and safety. This is what we are working with in the modern day.
However, there is a solution to this problem which uses closed-cycle engines.
With a closed-cycle engine like this one, we don’t waste any fuel at all. All of it is used inside of the combustion chamber, which is a great thing. This engine design has 2 different pre-burners, one of them running oxygen-rich, and the other running fuel rich. You can think of the two pipes leading to the combustion chambers as exhaust pipes from the previous open-cycle engine design. We pump in the oxygen-rich output, and the fuel-rich output from the two pre-burners into the reaction chamber. This causes no problem at all since at the end, you pump in the same amount of fuel as oxygen which causes everything to react, and there is no clogging or buildup in the end. Like I said, this type of engine has never been in orbit before. However, SpaceX’s Raptor engines do go by this design, and it has been proven that they can actually work. They just haven’t been to orbit yet.
Part 4: Vacuum-Optimized Engines
Vacuum optimized engines are the same thing as Sea-Level optimized engines, except they have a larger bell nozzle. This is because the engine tends to burst in a more ranged fashion in a vacuum since there is no pressure around, it is just empty space.
The atmospheric pressure angles all of the burst output downwards which increases the efficiency of the engine. However, when there is no atmosphere, there is no atmospheric pressure. This causes the propulsive burst to go somewhat sideways, making it useless. In order to angle everything downwards, we increase the length of the bell nozzle. This gives us more control over the angle of burst, making the engine more efficient.
This is the only difference between a sea-level optimized engine and a vacuum optimized engine. The vacuum optimized engine is always used for the second stage since it would be mostly a part of space travel (in a vacuum) while the sea-level optimized engines are usually stuck with the first stage since the first stage’s job is to get the second stage from sea-level to space.
Now that you have a pretty good overview of how each of the components of the rocket work, it is always good to go back to the big picture so that everything sticks.
- The rocket launches. This is where the sea-level optimized engines activate and start burning the propellants in the oxidizer and fuel tanks.
- When the rocket reaches close enough to the edge of the atmosphere, the first stage separates from the second stage. To not lose any momentum, the vacuum optimized engine in the second stage immediately activates.
- When there is enough speed and altitude, the first stage “hatches” to reveal the payload.
- The payload is now in orbit, going around the earth.
This article is a good overview, not a full explanation of how rockets work. If I were to try to explain rocketry in this article, the article could be weeks long. There are people who spend years trying to grasp this concept, so it is impossible to have a medium article to the fullest depth of rocket science. However, a good overview is possible.
Us humans, are a curious species. We constantly wonder about what is beyond our knowledge, and we strive to find out. We have been on earth for 300,000 years, so now it’s time to look upwards. It is time to think about the mysterious universe that lies ahead for this awesome species, think big on what we can achieve and, what we can become.
I see that you have made it to the very end of the article. If you enjoyed it, please consider following me on medium, or dropping some 👏’s! I have a youtube channel, and a personal newsletter which I send monthly updates to my subscribers. Feel free to subscribe if you don’t want to miss out on content that I put out regularly.