In recent times liquid oxygen-liquid methane (LO2/LCH4) has been considered as a potential “green” propellant alternative for future exploration missions. In addition, a fairly high Isp can be achieved using methane, and its density is desirable for easy storage in small tanks, compared to what would be required for liquid hydrogen. Methane is also abundant in the outer solar system. It can be harvested from Mars, Titan, Jupiter, and many other planets and moons. With fuel waiting at the destination, a rocket leaving Earth wouldn’t have to carry so much propellant, reducing the cost of a mission.
The thrust chamber consists of the volume between the injector faceplate and the throat where the combustion process takes place. In order to ensure that combustion stability is achieved, the thrust chamber must be designed such that the length is long enough to ensure proper mixing and combustion of the propellants. If the length is too short and the propellants exit the chamber without mixing and combusting, performance is lost. Combustion chamber volume is designed considering propellant mass flowrate, average specific volume, and the propellant stay time. Chamber length is often characterized as L*, which is referred to as the “characteristic length.” L* is defined as