Abstract: A method and assembly for manufacturing and storing a cryogenic monopropellant, such as cryogenic mixtures of liquid methane and liquid oxygen, and the components thereof. A fuel, such as liquid methane, is manufactured and stored safely and effectively without venting any methane vapors. Liquid methane and liquid oxygen are manufactured such that these components are mixed at thermal equilibrium thereby preventing the formation of vapors in the liquid phase. In this manner, the mixture can be safely stored and used.