Optimal Control of Gravity-Tractor Spacecraft for Asteroid Deflection

Abstract

Near-Earth objects can pose a major threat to Earth. New ideas and concepts are continually proposed to mitigate possible impact. Among them, the gravity tractor is promising and has been the focus of many recent studies on asteroid deflection. The gravity-tractor concept is studied and trajectories are designed to lessen the risk of impact of a near-Earth object. By means of a mathematical model of the gravity tractor, a high-fidelity trajectory design method for deflection is proposed. The optimal deflection of an asteroid is computed by an indirect method, and the trajectory of the spacecraft is deduced by an inversion of dynamics and optimal control. When the deflection achieved is compared with results published to date, the better performance of the deflection is clear. This paper shows that current literature analyses of the gravity-tractor design may be nonoptimal because the assumption made about the control penalizes the concept. The use of optimal control actually improves the robustness of the designed trajectory while obtaining higher deflection.