Propulsion for Interplanetary Journeys

Almost all spacecraft at present use propellant to produce a thrust to implement any change of velocity and the only propellantless propulsion envisaged is light or magnetic sails. Since the mass of the propellant which is carried on board is a large fraction of the initial mass to be carried in low Earth orbit (IMLEO) of any spacecraft and thus constitutes a large fraction of the cost of space missions.