Page "Dual mode propulsion rocket" Paragraph 0

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 / N < sub > 2 </ sub > O < sub > 4 </ sub >, or MMH / hydrogen 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 oxidizer, and conducts the remainder of its mission in a simple, predictable monopropellant