CHARACTERISTICS OF ELECTRIC PROPULSION SYSTEMS FOR OPTIMAL INTERPLANETARY TRAJECTORIES

The paper revisits the classical problem of optimal low-thrust trajectories, by searching not only the optimal steering law, but also the characteristics of the spacecraft propulsion system that maximize the payload. The analysis is applied to a simplified Earth-Mars mission and, in fact, considers the basic transfer between the planets’ orbits that are assumed circular and coplanar. Thus, attention can be paid to the general features of low-thrust interplanetary trajectories, neglecting the specific requirements of an actual mission opportunity. The analysis first investigates the structure of the optimal solutions, that is, the number of thrust arcs and their lengths, that depend on the thrust level and on the type (nuclear or solar) of electric propulsion system. The optimal values of the specific impulse are then found for different thrust levels and compared with the results of approximate analyses. The last step is the search for the optimal characteristics of the propulsion system that provide the maximum payload for assigned trip time.