Design of the first interplanetary solar electric propulsion mission

Deep Space 1 was the first interplanetary mission to be propelled by solar electric propulsion. The detailed design, development, and analysis of its trajectory have led to important new insights into the design of low-thrust trajectories. Tying the testing of solar electric propulsion technology to an operational mission has allowed the identification of trajectory design issues that were not considered in concept studies, such as constraints on the spacecraft attitude and periods of thrusting or coasting that are dictated by reasons other than trajectory considerations. Models of the spacecraft performance unimportant for trajectory analysis in missions using conventional chemical propulsion are intimately connected with the design of the trajectory when solar electric propulsion is employed. In addition, mass margin is not sufficient to assess a low-thrust mission. Unplanned thrust interruptions may result in a situation in which the propulsion system cannot provide sufficient impulse to compensate for the lost thrust in time to reach encounter targets. Mission margin (as distinct from mass margin) is a quantification of the mission's susceptibility to loss of thrust and is an important indicator of mission robustness for low-thrust trajectories.