How to Build a Liquid-Fuel Rocket Engine at Home: An Overview for Hobbyists

Introduction

Building a liquid-fuel rocket engine is a highly specialized task that requires a deep understanding of engineering principles and materials. This article provides an overview of the different types of liquid-fuel rocket engines, their construction, and the challenges associated with creating such a complex device in a home or garage setting.

Types of Liquid-Fuel Rocket Engines

There are several types of liquid-fuel rocket engines, each with its own design and complexity. The most advanced type, known as the Staged Combustion Engine, is currently used by SpaceX and the Soviet Union. These engines are characterized by high chamber pressures due to powerful turbopumps and better efficiency since all the fuel and oxidizer are consumed in the combustion chamber.

Full Flow Staged Combustion Engine

Sophisticated engines like the SpaceX Raptor, NK-33, and RD-180 use the full flow staged combustion cycle. This type of engine is highly efficient as all the fuel and oxidizer are eventually utilized. However, building such an engine requires specialized tools, including CNC machines and 3D metal printers, which are usually not found in home workshops.

Simpler Engine Designs

For those without access to such advanced tools, simpler open cycle turbopump engines are a more feasible option. These engines use the rocket's own fuel and oxidizer to power the turbopumps, which can be generated through the decomposition of hydrogen peroxide or by using electric engines.

Hydrogen Peroxide System

Hydrogen peroxide can be decomposed to generate steam, which can be used to spin a turbine and power the pumps. This method was used in the German Walter turbine to power submarines, but it comes with the added complexity of extra tanks and plumbing. Another option is using an electric engine to run the pumps, as employed by Rocket Lab's Electron rocket. While this method avoids the issues of using steam or other chemical energy sources, it does have limitations due to the size and weight of the batteries.

Pressure Fed Engines

The simplest liquid-fuel rocket engine is the pressure-fed engine, where pressurized gas forces fuel and oxidizer into the combustion chamber. This design was used in the Apollo mission's Lunar Module (LEM) ascent engine, which needed to be the simplest and most reliable engine possible to ensure the safety of the astronauts.

Scalability and Efficiency

Pressure-fed engines are easier to build, but they require careful handling due to the high energy released during combustion. Hypergolic fuels, used in the LEM ascent engine, are highly toxic and reactive, making their use in a garage risky. However, Bob Truax explored the scalability of pressure-fed engines, conceptually designing a large rocket capable of putting 500 tons into orbit, known as the "Sea Dragon." While this design never came to fruition, it highlights the potential for pressure-fed engines in extremely large spacecraft.

Conclusion

Building a liquid-fuel rocket engine is both an art and a science, requiring a deep understanding of materials, engineering principles, and safety protocols. While it is possible to build simpler engines like pressure-fed types, the more advanced designs like staged combustion engines are beyond the capabilities of most hobbyists. Nevertheless, the excitement and potential of space exploration make building a model rocket engine a worthwhile endeavor for enthusiasts with the requisite skills and knowledge.