Pseudostate theory based iterative preliminary design method for powered gravity-assist interplanetary trajectories

The patched conic method is usually used for preliminarily design of gravity-assist transfer trajectories. However, gravity assist is usually simplified as an instantaneous velocity impulse and the time of flight for gravity assist is ignored, which differs from actual scenarios. In this paper, gravity assist is considered as a continuous process and a novel method employing the pseudostate theory is proposed to design gravity-assist transfer trajectories. The mission trajectory is categorized as gravity-assist segments and interplanetary transfer segments. A powered gravity-assist model based on the pseudostate theory is used to solve the gravity-assist segments with the restricted three-body dynamics. Then, these gravity-assist segments thus solved are patched with the interplanetary transfer segments using an adaptive iterative patching technique, which adopts an adaptive parameter adjustment strategy to improve the efficiency and robustness. Thereafter, a consecutive interplanetary mission trajectory is finally obtained. In addition, a new estimation formula of the sweepback duration is derived according to the radius of gravity field and the excess velocity. The simulation results verify the effectiveness and accuracy of the proposed formula. The transfer trajectories to Jupiter with Venus, Earth and Mars gravity assists are respectively obtained by the proposed method. Compared with patched conic methods, the fuel optimal and more realistic trajectories are efficiently solved utilizing the proposed method for gravity-assist interplanetary mission.