How Do Rocket Engines Work?


Rocket engines are the workhorses of spaceflight. They provide the thrust needed to lift spacecraft off the ground and send them into orbit. But how do they work? In this article, we’ll explore the basic principles behind rocket engines and how they generate the incredible amounts of thrust needed to reach space.

The Basic Principle of Rocket Engines

At their core, rocket engines rely on the principle of action and reaction. This is commonly referred to as Newton’s Third Law of Motion, which states that for every action, there is an equal and opposite reaction. For a rocket engine, it expels high-velocity exhaust gases out the back of the engine as the action, and propels the rocket forward as the reaction through the forward thrust it generates.

Types of Rocket Engines

There are three main types of rocket engines: liquid-fueled, solid-fueled and hybrid. Liquid-fueled engines mix a liquid propellant and an oxidizer and burn them together to produce hot gases that generate thrust. On the other hand, solid-fueled engines burn a solid fuel to produce thrust. Hybrid engines use a mixture of solid and liquid fuels.

Liquid-Fueled Rocket Engines

Liquid-fueled rocket engines are more complex than solid-fueled engines, but they offer greater flexibility in terms of thrust control and efficiency. In a liquid-fueled engine, the fuel and oxidizer are stored in separate tanks and then pumped into a combustion chamber where they are mixed and burned to produce high-velocity exhaust gasses. The exhaust gasses then flow through a nozzle, which is designed to accelerate the gasses to supersonic speeds, creating thrust.

Schematic of a liquid fuel rocket engine. Credit: NASA

Solid-Fueled Rocket Engines

Solid-fueled rocket engines are simpler in design than liquid-fueled engines, but they offer less control over thrust and are less efficient. In a solid-fueled engine, the fuel and oxidizer are combined in a solid form. This is typically in the shape of a cylinder or tube. When the engine is ignited, the solid fuel burns and produces hot gasses that generate thrust.

Schematic of a solid fuel rocket engine. Credit: NASA

Hybrid Rocket Engines

Hybrid rocket engines are a type of rocket engine that use a combination of solid and liquid propellants. In a hybrid rocket engine, the fuel is typically a solid material, while the oxidizer is a liquid or gaseous substance. Separate components within the engine house the fuel and oxidizer. During the combustion proces they are brought together to produce thrust. Hybrid rocket engines offer several advantages over other types of rocket engines, including greater safety, lower cost, and simpler design. While hybrid rocket engines are more environmentally friendly due to their ability to produce less harmful emissions than traditional liquid-fueled rocket engines, they also have some disadvantages. For instance, they offer lower thrust and less efficiency than liquid-fueled engines.


Rocket engines are an essential component of the technology that allows spaceflight. They provide the thrust needed to launch spacecraft into orbit and beyond. By understanding the basic principles behind rocket engines and the types of engines used in spaceflight, we can gain a greater appreciation for the incredible engineering feats involved in exploring the final frontier.