When writing history, it is tempting to identify thematic periods in the often continuous stream of events under review and label them as “eras,” or to point to certain achievements and call them “milestones.”Keeping in mind that such demarcations and designations inevitably entail some arbitrariness, we shall not resist this temptation. Indeed, the history of electric propulsion (EP), which now spans almost a full century, particularly lends itself to a subdivision that epitomizes the progress of the field from its start as the dream realm of a few visionaries, to its transformation into the concern of large corporations.We shall therefore idealize the continuous history of the field as a series of five essentially consecutive eras:
1) The Era of Visionaries: 1906–1945
2) The Era of Pioneers: 1946–1956
3) The Era of Diversification and Development: 1957–1979
4) The Era of Acceptance: 1980–1992
5) The Era of Application: 1993–present
This paper, represents a first installment in this historical study and focuses on the first two eras above.