LM

Liquid methane (LM) is methane gas compressed and cooled to approximately 112 K (−161 °C) at atmospheric pressure, stored as a cryogenic liquid. In aerospace applications, it serves as a high-energy propellant for rocket engines, particularly in upper stages and lander descent systems. The substance is colorless, odorless in its pure form, and denser than liquid hydrogen but less dense than kerosene-based fuels.

Liquid methane has a specific impulse of roughly 370 seconds in vacuum when burned with liquid oxygen, sitting between kerosene (around 310 seconds) and liquid hydrogen (around 450 seconds). This middle ground, combined with its simpler handling compared to hydrogen, makes it attractive for both terrestrial and extraplanetary missions. It can be extracted from Martian atmospheric carbon dioxide and subsurface ice, which drives its use in long-term lunar and Mars exploration architectures.

Handling and Storage Requirements

Storage of liquid methane demands vacuum-jacketed tanks or insulated vessels to minimize boil-off during both ground operations and flight. Boiling losses are significant; tanks must be actively cooled or topped up frequently. Equipment handling LM must be compatible with cryogenic temperatures, meaning aluminum and stainless steel are standard; certain alloys become brittle at these temperatures. Fuel lines, regulators, and engine injectors require careful design to prevent thermal shock and cracking.

The combustion of liquid methane with liquid oxidizer produces water vapor and carbon dioxide as primary exhaust products, making it cleaner than kerosene engines in terms of particulate and soot emission. However, this water can condense on cold engine surfaces and cause corrosion or erosion problems in certain engine geometries. Ground support equipment must account for the extreme cold; personnel require specialized protective equipment and procedures to prevent frostbite and manage vapor clouds.

Liquid methane remains less established in operational flight hardware than kerosene or hydrogen, though development programs are active in both government and commercial sectors. Its intermediate properties and in-situ resource utilization potential position it as a bridge technology for deep space missions, even as hydrogen and traditional hypergolic propellants remain the current operational baseline in most launch and spacecraft systems.