Fuel for rockets: liquid oxygen

Liquid oxygen is used in many ways in industry and medicine. In addition, liquid oxygen (LOX) is also used as an oxidizer for conventional rocket fuel. The fuel and the rocket's mode of operation must be designed in such a way that it reaches a minimum speed of 7.9 km/s at launch. That is 20 times the speed of sound.

Liquid oxygen is produced using the Linde process, a method developed by Carl von Linde for liquefying gases or gas mixtures.

When extracting it from air, the first step is to separate out water vapor, carbon dioxide, and dust. This is followed by compression to 200 bar and subsequent expansion. This cooled air is returned to the compressor via a counterflow heat exchanger and is thus used to cool further compressed air before it expands. This process results in gradual cooling until liquefaction occurs at 20 bar and -183 °C.