They are a type of rockets where the elements of combustion (fuel and combustion) are in liquid state separated from each other in different tanks. These elements are mixed in the combustion chamber to generate the desired thrust. [2].

Among the liquid propellants we find:

• Mixtures of liquid hydrogen (fuel) and liquid oxygen (oxidant).

• Hydrazine (fuel) and nitrogen tetroxide (oxidant).• Hydrogen peroxide, as monopropellant [1].

Advantage:

1. The initially calculated thrust can be controlled during the flight.

2. The fuel itself can be used as a cooling medium.

3. It provides greater thrust for the same volume of propellant [1], [2].

Disadvantages:

1. More complex and expensive motor system

2. Greater maintenance of the engine.

3. Mmayor knowledge and care in the handling of substances is necessary.

4. Storage is very limited: the propellant must be introduced only a few hours before turning on the motors [1], [2].

The generated thrust will be as shown in [4].

(Sources for both concepts: [1] https://www.masscience.com/2015/12/18/solido-o-liquido-he-ahi-la-cuestion/; [2] https://es.wikipedia.org/wiki/Propelente_de_cohetes)[3] article “Theory of Rocket Engines of Solid Propellant” by Richard Nakka (] search in folder “Bibliographic Sources”)[4] https://www.grc.nasa.gov/www/k-12/airplane/lrockth.html).

 

Disadvantages:

1. Once the reaction has begun, it is not possible to regulate or stop it.
2. Initially calculated thrust can not be controlled after the engine is started.
3. They do not have refrigeration for their elements, so the duration of the ignition can not be prolonged [1], [2].