Electric Propulsion Developments for Interplanetary Flight

With the advent of the Deep Space 1 (DS1) mission Electric Propulsion (EP) has moved from providing station keeping capability for spacecraft to being its primary propulsion system. In this paper the trends and expectations for the future development in EP for interplanetary flight is discussed. Three paths are explored. First the path opened by DS1 is treated, covering the relative near future between now and 2005. Three future developments based on the DS1 baseline design are presented: 1) Improved performance derivatives, i.e. engines with better efficiencies, lower dry mass, and greater service life capability; 2) The Multiple Mission EP system, a system that can be used for a range of deep-space missions; 3) Scaled-down DS1 systems, following the trend toward smaller scientific spacecrafts. Emphasis is put on the background for these developments and the how they will improve deep space exploration. The second path is the development of higher power EP systems, in particular Direct-drive TAL systems and Variable Isp Propulsion Systems (VIPS). These are developments that are expected to be available in the mid-term time frame, i.e. between 2005-2020. The paper discusses the fundamental aspects behind these systems and the possible gain that can be achieved. Finally, a general discussion on mass savings possibilities and the trend in the future EP development in Europe is given.