Interplanetary propulsion

Means of providing propulsive power for flight to the Moon or to a planet. A variety of different propulsion systems can be used. The space vehicles for these missions consist of a series of separate stages, each with its own set of propulsion systems. When the propellants of a given stage have been expended, the stage is jettisoned to prevent its mass from needlessly adding to the inertia of the vehicle. Although all propulsion systems actually used in interplanetary flight have been chemical rockets, several basically different propulsion systems have been studied. See also Ion propulsion; Rocket propulsion; Rocket staging; Spacecraft propulsion.