methane has a lower specific impulse than liquid hydrogen, but is easier to store due to its higher boiling point and density, as well as its lack of hydrogen embrittlement. It also leaves less residue in the engines compared to kerosene, which is beneficial for reusability. In addition, it can be produced on Mars via the Sabatier reaction. In NASA's Mars Design Reference Mission 5.0 documents (between 2009 and 2012), liquid methane/LOX (methalox) was the chosen propellant mixture for the lander module. , no methane-fueled rocket has reached orbit, although several rockets are in development and Zhuque-2 had one failed orbital launch attempt. SpaceX developed the Raptor engine for its Starship super-heavy-lift launch vehicle. It has been used in test flights from 2019 to 2021. SpaceX had previously used only RP-1/LOX in their engines. Blue Origin and United Launch Alliance developed the BE-4 LOX/LNG engine for Vulcan Centaur and New Glenn. The BE-4 will provide of thrust. In July 2014, Firefly Space Systems announced their plans to use methane fuel for their small satellite launch vehicle, Firefly Alpha with an aerospike engine design. LandSpace developed the TQ-12 engine for its Zhuque-2 rocket. Relativity Space developed the Aeon 1 engine for its Terran 1 rocket. Monopropellants High-test peroxide High test peroxide is concentrated Hydrogen peroxide, with around 2% to 30% water. It decomposes to steam and oxygen when passed over a catalyst. This was historically used for reaction control systems, due to being easily storable. It is often used to drive Turbopumps, being used on the V2 rocket, and modern Soyuz. Hydrazine decomposes energetically to nitrogen, hydrogen, and ammonia (2N2H4 → N2+H2+2NH3) and is the most widely used in space vehicles. (Non-oxidized ammonia decomposition is endothermic and would decrease performance). Nitrous oxide decomposes to nitrogen and oxygen. Steam when externally heated gives a reasonably modest Isp of up to 190 seconds, depending on material corrosion and thermal limits. Present use , liquid fuel combinations in common use: Kerosene (RP-1) / liquid oxygen (LOX) Used for the lower stages of the Soyuz boosters, the first stages of Saturn V and the Atlas family, and both stages of Electron and Falcon 9. Very similar to Robert Goddard's first rocket. Liquid hydrogen (LH) / LOX Used in the stages of the Space Shuttle, Space Launch System, Ariane 5, Delta IV, New Shepard, H-IIB, GSLV and Centaur. Unsymmetrical dimethylhydrazine (UDMH) or monomethylhydrazine (MMH) / dinitrogen