Optimal Low-Thrust Escape Trajectories Using Gravity Assist

TLDR

Electric propulsion provides continuous steering, enabling approach to a planet with hyperbolic excess velocity that boosts gravity assist. The paper seeks the low‑thrust escape strategy that maximizes spacecraft energy for a given payload and engine operating time. The authors compute optimal trajectories using constant exhaust power with either constant or variable specific impulse, determining optimal power levels, engine on/off switching, and evaluating cases that exploit Jupiter or Venus gravity assists. The study presents optimal escape conditions for free‑height and minimum‑height cases, computes trajectories exploiting Jupiter or Venus, and shows that adding coast arcs and engine throttling improves system performance.

Abstract

Electric propulsion provides a spacecraft with continuous steering capabilities, which can be used to approach a planet with hyperbolic excess velocity that enhances the gravity assist. Low-thrust trajectories to escape from the solar system are considered in the present paper, which searches for the strategy that maximizes the spacecraft energy for assigned payload and engine operating time. The optimal conditions to escape using electric propulsion and gravity assist are presented for the cases of free-height and minimum-height  ybys. Optimal trajectories that exploit Jupiter or Venus  ybys have been computed for constant exhaust power with either constant or variable speciŽ c impulse; the procedure is also able to determine the optimal power level and to suggest when it is convenient to switch the engine on and off. The beneŽ t that system performance can receive by increasing the number of controls, i.e., by adding the possibility of coast arcs and engine throttling to the thrust direction control, is also noted.