How Do Rocket Engines Work?

by Carson
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Rocket (shown as icon) surrounding Earth

We’ve all seen rockets launching. In fact, missions that involve sending things outside Earth’s atmosphere require rockets to succeed. But how do rocket engines work exactly? We’ll explain that in this article.

Newton’s Third Law of Motion

Rockets rely on Newton’s Third Law of Motion. That means if a force is exerted, another force with equal strength will be applied in the opposite direction. For example, if a ball is thrown to the ground, it will apply force to the ground. Also, the ground will exert a force on the ball in response due to the Third Law of Motion, and the ball will bounce upward.

This phenomenon also happens on a rocket but on a much larger scale. Specifically, the rocket exerts an enormous backward force, after which it’s accelerated forward. But how does the rocket apply such a tremendous force? We’ll explain that later in this article.

Quite counterintuitively, rockets work in the vacuum of space. This is because Newton’s Third Law of Motion works no matter what the surrounding environment is. Even when there is no air, there will still be thrust if the engine pushes the exhaust backward.

A demonstration of Newton’s Third Law of Motion using a rocket
Image created using Canva

How Can Such An Explosive Force Be Generated?

Well, you all know that rockets store lots of fuel. In fact, most of a rocket’s mass is the fuel tank, and that’s the ingredients of generating the backward force.

The propellant consists of fuel, such as liquid hydrogen, and oxidizers, such as liquid oxygen. Keep in mind that there are two types of rocket engines: Solid and liquid rocket engines. While solid rocket engines run on solid fuel and oxidizers, liquid rocket engines are fed from liquid propellants. Moreover, solid rocket engines cannot switch off once ignited until they run out of fuel, so they are suitable for making rocket boosters. On the contrary, liquid rocket engines can be turned off or decreased in throttle after it has been ignited, so they are suitable for the main stages of the launch vehicle.

Once the rocket’s ignition starts, the fuel and oxidizer will undergo intense chemical reactions in the combustion chamber, and the chemicals explode. In fact, a rocket launch is just a controlled explosion happening at the right place and time so that the payload can be accelerated very quickly. Then, the hot gases, known as the exhaust, go through the nozzle, which is the opening you see at the bottom end of the rocket, and the exhaust gets emitted outward.

How does the downward stream of gases make it out of the rocket?
Image created using Canva

How to Steer a Rocket?

Launch vehicles should be able to change their direction to reach the desired orbit. But how can they do it? Well, we should go back to Newton’s Third Law of Motion. Remember that when a force is applied in one direction, an opposite reaction exerts the same amount of force as the initial reaction but in the exact opposite direction? Steering the nozzle can redirect the exhaust exploding out of the rocket, changing the direction where the opposite reaction applies, thus steering the rocket.

Why Is Rocket Fuel Stored in Cryogenic Temperatures?

You may have noticed that rocket engines might use liquid hydrogen and oxygen for fuel. These elements are both gaseous at room temperature, so what’s the point in storing it at such a cold temperature? It’s all about the size of the fuel tank. You should already know that as the temperature of the substance decreases, its density increases, right? As a result, you can infer that more liquid fuel than gaseous fuel can be stored in the same fuel tank. And a smaller fuel tank means there is less mass and cost spent on the packaging, and the efficiency of the rocket substantially increases.

Conclusion

In this article, we’ve explained how rocket engines work using Newton’s Third Law of Motion, and mentioned how to apply the enormous backward force with propellant, how to change the direction of the rocket, and why the fuel is often stored in its cryogenic form. If you want to learn more about this, please read the articles in the references below.

References and Credits

  1. (n.d.). Rocket Propulsion – NASA. Retrieved November 25, 2021, from https://www.grc.nasa.gov/www/k-12/airplane/rocket.html
  2. Elizabeth Howell. (2013, April 9). How Do Space Rockets Work Without Air? Retrieved November 25, 2021, from https://www.livescience.com/34475-how-do-space-rockets-work-without-air.html
  3. (2011, July 13). What Is a Rocket? Retrieved November 25, 2021, from https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-rocket-k4.html
  4. (n.d.). Rocket Propellants. Retrieved November 25, 2021, from http://www.braeunig.us/space/propel.htm
  5. (n.d.). Gauging Systems Monitor Cryogenic Liquids. Retrieved November 25, 2021, from https://spinoff.nasa.gov/Spinoff2009/ip_7.html

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