Dual mode propulsion rocket

Dual mode propulsion systems combine the high efficiency of bipropellant rockets with the reliability and simplicity of monopropellant rockets. Dual mode systems are either hydrazine/N₂O₄, or MMH/peroxide (the former is much more common). Typically, this system works as follows: During the initial high-impulse orbit-raising maneuvers, the system operates in a bipropellant fashion, providing high thrust at high efficiency; when it arrives on orbit, it closes off either the fuel or oxidier, and conducts the remainder of its mission in a simple, predictable monopropellant fashion.

See also: spacecraft propulsion