Low-thrust trajectory optimization for multiple target bodies tour mission

Abstract

Spacecraft science missions to planets or asteroids have historically visited only one or several celestial bodies per mission. The research goal of this paper is to create a trajectory design algorithm that generates trajectory allowing a spacecraft to visit a significant number of asteroids during a single mission. For the problem of global trajectory optimization, even with recent advances in low-thrust trajectory optimization, a full enumeration of this problem is not possible. This work presents an algorithm to traverse the searching space in a practical fashion and generate solutions. The flight sequence is determined in ballistic scenario, and a differential evolution method is used with constructing a three-impulse transfer problem, then the local optimization is implemented with low-thrust propulsion on the basis of the solutions of impulsive trajectories. The proposed method enables trajectory design for multiple asteroids tour by using available low thrust propulsion technology within fuel and time duration constraints.With the recent launches of SMART-1, 1 Deep Space 1, 2 Dawn 3 and Hayabusa, 4 low-thrust electric propulsion has become a feasible option for solar system exploration. At the conceptual design level, exploring the full extent of the design space over a large range of potential launch dates, flight times, and target bodies, is important in order to select the best possible set of solutions, these choices are generally based on global trajectory optimization. Furthermore, solving a single low-thrust trajectory optimization for a given launch date and flight times is an inner-loop local optimization problem.However, due to the huge searching space, in particular, the designing space is multi-phase and even discontinuous when considering multiple targets, searching for the best trajectory is a difficult problem. To obtain this, many trajectory optimization algorithms have been developed for low-thrust trajectories, 5-10 but none of these methods can be globally optimized for spacecraft trajectory.In 2010, the 5th Global Trajectory Optimization Competition (GTOC5) posed a trajectory designing problem of "How to visit the greatest number of asteroids with revisiting". 11 This problem was chosen to be representative of challenge mission designers face when designing low-thrust trajectories to multiple bodies in the solar system. This paper presents a combined algorithm and attempts to produce the best possible trajectory, using low-thrust electric propulsion that would flyby and rendezvous the maximum number of asteroids from the pre-defined asteroids groups. The combined algorithm of trajectory optimization compasses a) ballistic scenario using differential evolution method for global optimization, as well as low-thrust scenario using direct shooting method for local optimization.The spacecraft starts from the Earth. The target asteroids are defined in the presented list. For the first time spacecraft should rendezvous with an asteroid, for the second time the velocity of flyby should not be l...