ABSTRACT
The various types of electric propulsion which have been proposed operate by firing a rocket with a very small thrust but a high specific impulse over a long period of time, so building up a high velocity by small increments. The project was cancelled before a prototype rocket was ready and in the present climate of anti-nuclear feeling in the United States it is unlikely to be revived. The Ride report does not specify exactly how many of these big rockets would be needed for each of the sprint missions, but the sketches used to illustrate it imply that there would have to be a total of six launches per mission. In a paper presented at the International Astronautical Federation's Congress in Brighton in 1987, Michael B Duke of the Johnson Space Center gave some comparative figures for different types of missions.
