Mixed low thrust - Coast ARC model for interplanetary gravity assist trajectory optimization

International audienceTrajectory optimization has always been of great interest in space exploration, from orbital transfer to interplanetary trajectory. Optimization methods, direct or indirect, are often of major use, although for low thrust interplanetary transfer, the initialization of these methods usually lack of efficiency. Recent advances manage to solve this problem by proposing low thrust models. These allow computing a pseudo-optimal trajectory that can later be used as an initial guess for a direct approach solver. Consequently, the more the model will be close to the optimal solution, the best chance we have to get a good optimum. Some work on the reliability of the model toward the real low thrust trajectory should be done. The purpose of this paper is to extend the family of shape based model for low thrust trajectory. A new model is introduced and an investigation is done on a method which allows implementing both thrust and coast phases in the trajectory. An optimization problem is introduced to find the best coast duration and place. A decrease of the final braking manoeuvre cost is observed when increasing the number of coast periods. To solve multi gravity assist problems, an algorithm is introduced and allows easily computing many possible options for an interplanetary preliminary decision tool. Some examples are studied to emphasize the method