Although you’ve probably heard of some famous rockets of history, like the Saturn V or the Space Shuttle, have you ever stopped to think about how they work? Wonder no more. Here’s a brief explanation of what’s going on inside a liquid fuel engine.
To explain how rockets travel in one sentence, the fast-moving exhaust coming out of the back of the rocket pushes the rocket forward. This is because of Newton’s third law – for every action, there’s an equal and opposite reaction. In this case, the massive amount of force moving the exhaust backward is equally applied to the rocket moving forward and upward. Rockets travel past the main part of the atmosphere into space, which means that there’s little to no air where they’re going. This is why regular airplanes can’t travel to space – they need oxygen from the air. To combat this, rockets bring their own oxygen in a tank. In the rocket engine, where the fuel and oxidizer mix and combust, there are several important parts that one should know about:
The Combustion Chamber – This is where the fuel and oxidizer are mixed and ignited. Usually, there is already combustion occurring in the chamber, meaning that no outside ignition source is needed when additional fuel and oxidizer are pumped in. To start it in the first place, however, there are several ways to ignite the mixture, depending on the rocket. One is a high voltage spark, similar to what cars use. Another is to use a regular flame.
The Nozzle – This is where the exhaust leaves the rocket. There is a convergent-divergent design that increases the speed of the exhaust, which increases the force of the outgoing exhaust, which in turn increases the amount of force pushing the rocket upwards.
The Turbopump – To move all around the rocket engine, the fuel and oxidizer need a powerful pump, which in a rocket is called the turbopump. This is one of the most complicated parts of a rocket to design, as it has to be able to withstand the high pressures and speed of the fuel and oxidizer moving around. The turbopump also has to combat cavitation, which is when a liquid is moving so fast that small bubbles form inside the liquid. When those bubbles pop on a surface of the turbopump, they can cause severe damage.
The Gas Generator – the turbopump needs a source of power in order to work. This comes from the gas generator, which is a mini-rocket in and of itself. It takes in fuel and oxidizer, ignites them, and uses that energy to turn the turbopump (which usually connects to both the fuel and oxidizer, meaning rockets generally have only one turbopump).
The Gimbals and RCS – In space, it’s impossible to use the flaps that you see on an airplane to control a rocket, as there’s no air to push against. Instead, rockets generally use two control systems: gimbals and RCS. A gimbal moves the entire rocket engine and the way it points. This change in direction changes the direction of the force on the rocket, which leads to the rocket pointing a different way. A Reaction Control System, or RCS, uses bursts of gas to move the rocket and utilizes small thrusters placed around the rocket.
The Heat Exchanger – The nozzle, as you can imagine, gets extremely hot. One of the ways to cool the nozzle down is with a heat exchanger, where the cold liquid oxygen is pumped down and around it. This way, the cold of the LOX (Liquid Oxygen) is taken in by the nozzle, and the liquid oxygen takes in the heat.