[Type] Monopropellant rocket [Description] Propellant (such as hydrazine, hydrogen peroxide or nitrous oxide) flows over a catalyst and exothermically decomposes; hot gases are emitted through nozzle. [Advantages] Simple in concept, throttleable, low temperatures in combustion chamber [Disadvantages] 
catalysts can be easily contaminated, monopropellants can detonate if contaminated or provoked, Isp is perhaps 1/3 of best liquids